1. Difference between group functions and single row functions.
Group Function Single Row Function
A group function operates A single row function
on many rows returns one and result for one row.
returns single result.
Not allowed in Pl/sql procedural Allowed in Pl/Sql
Procedural statements
statements.
eg SUM(),AVG,MIN,MAX etc eg UPPER,LOWER,CHR...
2. Difference between DECODE and TRANSLATE
DECODE is value by value TRANSLATE is character by
character replacement. replacement.
Ex SELECT DECODE('ABC','A',1,'B',2,'ABC',3) eg SELECT
from dual; o/p 3 TRANSLATE('ABCGH',
'ABCDEFGHIJ', 1234567899)
FROM DUAL; o/p 12378
(DECODE command is used to bring IF,THEN,ELSE logic to SQL.It tests for the IF values(s) and then aplies THEN value(s) when true, the ELSE value(s) if not.)
3. Difference between TRUNCATE and DELETE
TRUNCATE deletes much faster than DELETE
Truncate Delete
It is a DDL statement It is a DML statement
It is a one way trip,cannot One can Rollback
ROLLBACK
Doesn't have selective features (where clause) Has
Doesn't fire database triggers Does
It requires disabling of referential Does not require
constraints.
4. What is a CO-RELATED SUBQUERY
A CO-RELATED SUBQUERY is one that has a correlation
name as table or view designator in the FROM clause of the outer
query and the same correlation name as a qualifier of a search
condition in the WHERE clause of the subquery.
eg
SELECT field1 from table1 X
WHERE field2>(select avg(field2) from table1 Y
where
field1=X.field1);
(The subquery in a correlated subquery is revaluated
for every row of the table or view named in the outer query.)
5. What are various joins used while writing SUBQUERIES
Self join-Its a join foreign key of a table references the same table.
Outer Join--Its a join condition used where One can query all the rows of one of the
tables in the join condition even though they don't satisfy the join condition.
Equi-join--Its a join condition that retrieves rows from one or more tables in which one
or more columns in one table are equal to one or more columns in the second table.
6. What are various constraints used in SQL
NULL
NOT NULL
CHECK
DEFAULT
7. What are different Oracle database objects
TABLES
VIEWS
INDEXES
SYNONYMS
SEQUENCES
TABLESPACES etc
8. What is difference between Rename and Alias
Rename is a permanent name given to a table or column whereas Alias is a temporary
name given to a table or column which do not exist once the SQL statement is
executed.
9. What is a view
A view is stored procedure based on one or more tables, it’s a virtual table.
What are various privileges that a user can grant to another user
SELECT
CONNECT
RESOURCES
10. What is difference between UNIQUE and PRIMARY KEY constraints
A table can have only one PRIMARY KEY whereas there can be any number of UNIQUE keys.
The columns that compose PK are automatically define NOT NULL, whereas a column that compose a UNIQUE is not automatically defined to be mandatory must also specify the column is NOT NULL.
11. Can a primary key contain more than one columns
Yes
12. How you will avoid duplicating records in a query
By using DISTINCT
13. What is difference between SQL and SQL*PLUS
SQL*PLUS is a command line tool where as SQL and PL/SQL language interface and
reporting tool. Its a command line tool that allows user to type SQL commands to be
executed directly against an Oracle database. SQL is a language used to query the
relational database(DML,DCL,DDL). SQL*PLUS commands are used to format query
result, Set options, Edit SQL commands and PL/SQL.
14. Which datatype is used for storing graphics and images
LONG RAW data type is used for storing BLOB's (binary large objects).
15. How will you delete duplicating rows from a base table
DELETE
FROM table_name A
WHERE rowid>(SELECT min(rowid) from table_name B where
B.table_no=A.table_no);
CREATE TABLE new_table AS SELECT DISTINCT * FROM old_table;
DROP old_table
RENAME new_table TO old_table
DELETE FROM table_name A
WHERE rowid NOT IN (SELECT MAX(ROWID) FROM table_name
GROUP BY column_name)
16. What is difference between SUBSTR and INSTR
SUBSTR returns a specified portion of a string
eg SUBSTR('BCDEF',4) output BCDE
INSTR provides character position in which a pattern
is found in a string.
eg INSTR('ABC-DC-F','-',2) output 7 (2nd occurence of '-')
17. There is a string '120000 12 0 .125' ,how you will find the
position of the decimal place
INSTR('120000 12 0 .125',1,'.')
output 13
18. There is a '%' sign in one field of a column. What will be
the query to find it.
'\' Should be used before '%'.
19. When you use WHERE clause and when you use HAVING clause
HAVING clause is used when you want to specify a condition for a group function and it
is written after GROUP BY clause
The WHERE clause is used when you want to specify a condition for columns, single
row functions except group functions and it is written before GROUP BY clause if it is
used.
20. Which is more faster - IN or EXISTS
EXISTS is more faster than IN because EXISTS returns
a Boolean value whereas IN returns a value.
21. What is a OUTER JOIN
Outer Join--Its a join condition used where you can query all the rows of one of the
tables in the join condition even though they don’t satisfy the join condition.
22. How you will avoid your query from using indexes
SELECT * FROM emp
Where emp_no+' '=12345;
i.e you have to concatenate the column name with
space within codes in the where condition.
SELECT /*+ FULL(a) */ ename, emp_no from emp
where emp_no=1234;
i.e using HINTS
23. What is a pseudo column. Give some examples
It is a column that is not an actual column in the
table.
eg USER, UID, SYSDATE, ROWNUM, ROWID, NULL, AND LEVEL.
24. Suppose customer table is there having different columns
like customer no, payments.What will be the query to select top three max payments.
SELECT customer_no, payments from customer C1
WHERE 3<=(SELECT COUNT(*) from customer C2
WHERE C1.payment <= C2.payment)
25. What is the purpose of a cluster.
Oracle does not allow a user to specifically locate tables, since that is a part of the
function of the RDBMS. However, for the purpose of increasing performance, oracle allows a developer to create a CLUSTER. A CLUSTER provides a means for storing
data from different tables together for faster retrieval than if the table placement were
left to the RDBMS.
26. What is a cursor.
Oracle uses work area to execute SQL statements and store processing information
PL/SQL construct called a cursor lets you name a work area and access its stored
information A cursor is a mechanism used to fetch more than one row in a Pl/SQl
block.
27. Difference between an implicit & an explicit cursor.
PL/SQL declares a cursor implicitly for all SQL data manipulation statements, including
quries that return only one row. However,queries that return more than one row you
must declare an explicit cursor or use a cursor FOR loop.
Explicit cursor is a cursor in which the cursor name is explicitly assigned to a SELECT
statement via the CURSOR...IS statement. An implicit cursor is used for all SQL statements Declare, Open, Fetch, Close. An explicit cursors are used to process multirow SELECT statements An implicit cursor is used to process INSERT, UPDATE,
DELETE and single row SELECT. .INTO statements.
28. What are cursor attributes
%ROWCOUNT
%NOTFOUND
%FOUND
%ISOPEN
29. What is a cursor for loop.
Cursor For Loop is a loop where oracle implicitly declares a loop variable, the loop index that of the same record type as the cursor's record.
30. Difference between NO DATA FOUND and %NOTFOUND
NO DATA FOUND is an exception raised only for the SELECT....INTO statements
when the where clause of the querydoes not match any rows. When the where clause
of the explicit cursor does not match any rows the %NOTFOUND attribute is set to
TRUE instead.
31. What a SELECT FOR UPDATE cursor represent.
SELECT......FROM......FOR......UPDATE[OF column-reference][NOWAIT] The
processing done in a fetch loop modifies the rows that have been retrieved by the
cursor.
A convenient way of modifying the rows is done by a method with two parts: the FOR
UPDATE clause in the cursor declaration, WHERE CURRENT OF CLAUSE in an
UPDATE or declaration statement.
32. What 'WHERE CURRENT OF ' clause does in a cursor.
LOOP
SELECT num_credits INTO v_numcredits FROM classes
WHERE dept=123 and course=101;
UPDATE students
SET current_credits=current_credits+v_numcredits
WHERE CURRENT OF X;
END LOOP
COMMIT;
END;
33. What is use of a cursor variable? How it is defined.
A cursor variable is associated with different statements at run time, which can hold
different values at run time. Static cursors can only be associated with one run time
query. A cursor variable is reference type(like a pointer in C).
Declaring a cursor variable:
TYPE type_name IS REF CURSOR RETURN return_type type_name is the name of
the reference type,return_type is a record type indicating the types of the select list
that will eventually be returned by the cursor variable.
34. What should be the return type for a cursor variable.Can we use a scalar data type as return type.
The return type for a cursor must be a record type.It can be declared explicitly as a
user-defined or %ROWTYPE can be used. eg TYPE t_studentsref IS REF
CURSOR RETURN students%ROWTYPE
35. How you open and close a cursor variable.Why it is required.
OPEN cursor variable FOR SELECT...Statement
CLOSE cursor variable In order to associate a cursor variable with a particular
SELECT statement OPEN syntax is used.In order to free the resources used
for the query CLOSE
statement is used.
36. How you were passing cursor variables in PL/SQL 2.2.
In PL/SQL 2.2 cursor variables cannot be declared in a package.This is because the storage for a cursor variable has to be allocated using Pro*C or OCI with version 2.2,the only means of passing a cursor variable to a PL/SQL block is via bind variable or a procedure parameter.
37. Can cursor variables be stored in PL/SQL tables.If yes how.If not why.
No, a cursor variable points a row which cannot be stored in a two-dimensional PL/SQL table.
38. Difference between procedure and function.
Functions are named PL/SQL blocks that return a value and can be called with arguments procedure a named block that can be called with parameter. A procedure all is a PL/SQL statement by itself, while a Function call is called as part of an expression.
39. What are different modes of parameters used in functions and procedures.
IN
OUT
INOUT
40. What is difference between a formal and an actual parameter
The variables declared in the procedure and which are passed, as arguments are called
actual, the parameters in the procedure declaration. Actual parameters contain the
values that are passed to a procedure and receive results. Formal parameters are the
placeholders for the values of actual parameters
41. Can the default values be assigned to actual parameters.
Yes
42. Can a function take OUT parameters.If not why.
No.A function has to return a value,an OUT parameter cannot return a value.
43. What is syntax for dropping a procedure and a function .Are these operations possible.
Drop Procedure procedure_name
Drop Function function_name
44. What are ORACLE PRECOMPILERS.
Using ORACLE PRECOMPILERS ,SQL statements and PL/SQL blocks can be contained
inside 3GL programs written in C,C++,COBOL,PASCAL, FORTRAN,PL/1 AND ADA.
The Precompilers are known as Pro*C,Pro*Cobol,...
This form of PL/SQL is known as embedded pl/sql,the language in which pl/sql is
embedded is known as the host language.
The prcompiler translates the embedded SQL and pl/sql ststements into calls to the
precompiler runtime library.The output must be compiled and linked with this library to
creater an executable.
45. What is OCI. What are its uses.
Oracle Call Interface is a method of accesing database
from a 3GL program. Uses--No precompiler is required,PL/SQL blocks are executed like
other DML
statements.
The OCI library provides
-functions to parse SQL statemets
-bind input variables
-bind output variables
-execute statements
-fetch the results
46. Difference between database triggers and form triggers.
a) Data base trigger(DBT) fires when a DML operation is performed on a data base table.Form trigger(FT) Fires when user presses a key or navigates between fields on the screen
b) Can be row level or statement level No distinction between row level and statement level.
c) Can manipulate data stored in Oracle tables via SQL Can manipulate data in Oracle tables as well as
variables in forms.
d) Can be fired from any session executing the triggering DML statements. Can be fired only from the form that define the trigger.
e) Can cause other database triggers to fire.Can cause other database triggers to fire,but not other form triggers.
47. What is an UTL_FILE.What are different procedures and functions associated with it.
UTL_FILE is a package that adds the ability to read and write to operating system files
Procedures associated with it are FCLOSE, FCLOSE_ALL and 5 procedures to output
data to a file PUT, PUT_LINE, NEW_LINE, PUTF, FFLUSH.PUT, FFLUSH.PUT_LINE,FFLUSH.NEW_LINE. Functions associated with it are FOPEN, ISOPEN.
48. Can you use a commit statement within a database trigger.
No
49. What is the maximum buffer size that can be specified using the DBMS_OUTPUT.ENABLE function?
1,000,000
Sunday, February 21, 2010
RDBMS Concepts
What is database?
A database is a logically coherent collection of data with some inherent meaning, representing some aspect of real world and which is designed, built and populated with data for a specific purpose.
What is DBMS?
It is a collection of programs that enables user to create and maintain a database. In other words it is general-purpose software that provides the users with the processes of defining, constructing and manipulating the database for various applications.
What is a Database system?
The database and DBMS software together is called as Database system.
Advantages of DBMS?
Redundancy is controlled.
Unauthorised access is restricted.
Providing multiple user interfaces.
Enforcing integrity constraints.
Providing backup and recovery.
Disadvantage in File Processing System?
Data redundancy & inconsistency.
Difficult in accessing data.
Data isolation.
Data integrity.
Concurrent access is not possible.
Security Problems.
Describe the three levels of data abstraction?
The are three levels of abstraction:
Physical level: The lowest level of abstraction describes how data are stored.
Logical level: The next higher level of abstraction, describes what data are stored in database and what relationship among those data.
View level: The highest level of abstraction describes only part of entire database.
Define the "integrity rules"
There are two Integrity rules.
Entity Integrity: States that “Primary key cannot have NULL value”
Referential Integrity: States that “Foreign Key can be either a NULL value or should be Primary Key value of other relation.
What is extension and intension?
Extension -
It is the number of tuples present in a table at any instance. This is time dependent.
Intension -
It is a constant value that gives the name, structure of table and the constraints laid on it.
What is System R? What are its two major subsystems?
System R was designed and developed over a period of 1974-79 at IBM San Jose Research Center. It is a prototype and its purpose was to demonstrate that it is possible to build a Relational System that can be used in a real life environment to solve real life problems, with performance at least comparable to that of existing system.
Its two subsystems are
Research Storage
System Relational Data System.
How is the data structure of System R different from the relational structure?
Unlike Relational systems in System R
Domains are not supported
Enforcement of candidate key uniqueness is optional
Enforcement of entity integrity is optional
Referential integrity is not enforced
What is Data Independence?
Data independence means that “the application is independent of the storage structure and access strategy of data”. In other words, The ability to modify the schema definition in one level should not affect the schema definition in the next higher level.
Two types of Data Independence:
Physical Data Independence: Modification in physical level should not affect the logical level.
Logical Data Independence: Modification in logical level should affect the view level.
NOTE: Logical Data Independence is more difficult to achieve
What is a view? How it is related to data independence?
A view may be thought of as a virtual table, that is, a table that does not really exist in its own right but is instead derived from one or more underlying base table. In other words, there is no stored file that direct represents the view instead a definition of view is stored in data dictionary.
Growth and restructuring of base tables is not reflected in views. Thus the view can insulate users from the effects of restructuring and growth in the database. Hence accounts for logical data independence.
What is Data Model?
A collection of conceptual tools for describing data, data relationships data semantics and constraints.
What is E-R model?
This data model is based on real world that consists of basic objects called entities and of relationship among these objects. Entities are described in a database by a set of attributes.
What is Object Oriented model?
This model is based on collection of objects. An object contains values stored in instance variables with in the object. An object also contains bodies of code that operate on the object. These bodies of code are called methods. Objects that contain same types of values and the same methods are grouped together into classes.
What is an Entity?
It is a 'thing' in the real world with an independent existence.
What is an Entity type?
It is a collection (set) of entities that have same attributes.
What is an Entity set?
It is a collection of all entities of particular entity type in the database.
What is an Extension of entity type?
The collections of entities of a particular entity type are grouped together into an entity set.
What is Weak Entity set?
An entity set may not have sufficient attributes to form a primary key, and its primary key compromises of its partial key and primary key of its parent entity, then it is said to be Weak Entity set.
What is an attribute?
It is a particular property, which describes the entity.
What is a Relation Schema and a Relation?
A relation Schema denoted by R(A1, A2, …, An) is made up of the relation name R and the list of attributes Ai that it contains. A relation is defined as a set of tuples. Let r be the relation which contains set tuples (t1, t2, t3, ..., tn). Each tuple is an ordered list of n-values t=(v1,v2, ..., vn).
What is degree of a Relation?
It is the number of attribute of its relation schema.
What is Relationship?
It is an association among two or more entities.
What is Relationship set?
The collection (or set) of similar relationships.
What is Relationship type?
Relationship type defines a set of associations or a relationship set among a given set of entity types.
What is degree of Relationship type?
It is the number of entity type participating.
What is DDL (Data Definition Language)?
A data base schema is specifies by a set of definitions expressed by a special language called DDL.
What is VDL (View Definition Language)?
It specifies user views and their mappings to the conceptual schema.
What is SDL (Storage Definition Language)?
This language is to specify the internal schema. This language may specify the mapping between two schemas.
What is Data Storage - Definition Language?
The storage structures and access methods used by database system are specified by a set of definition in a special type of DDL called data storage-definition language.
What is DML (Data Manipulation Language)?
This language that enable user to access or manipulate data as organised by appropriate data model.
Procedural DML or Low level: DML requires a user to specify what data are needed and how to get those data.
Non-Procedural DML or High level: DML requires a user to specify what data are needed without specifying how to get those data.
What is DML Compiler?
It translates DML statements in a query language into low-level instruction that the query evaluation engine can understand.
What is Query evaluation engine?
It executes low-level instruction generated by compiler.
What is DDL Interpreter?
It interprets DDL statements and record them in tables containing metadata.
What is Record-at-a-time?
The Low level or Procedural DML can specify and retrieve each record from a set of records. This retrieve of a record is said to be Record-at-a-time.
What is Set-at-a-time or Set-oriented?
The High level or Non-procedural DML can specify and retrieve many records in a single DML statement. This retrieve of a record is said to be Set-at-a-time or Set-oriented.
What is Relational Algebra?
It is procedural query language. It consists of a set of operations that take one or two relations as input and produce a new relation.
What is Relational Calculus?
It is an applied predicate calculus specifically tailored for relational databases proposed by E.F. Codd. E.g. of languages based on it are DSL ALPHA, QUEL.
How does Tuple-oriented relational calculus differ from domain-oriented relational calculus
The tuple-oriented calculus uses a tuple variables i.e., variable whose only permitted values are tuples of that relation. E.g. QUEL
The domain-oriented calculus has domain variables i.e., variables that range over the underlying domains instead of over relation. E.g. ILL, DEDUCE.
What is normalization?
It is a process of analysing the given relation schemas based on their Functional Dependencies (FDs) and primary key to achieve the properties
Minimizing redundancy
Minimizing insertion, deletion and update anomalies.
What is Functional Dependency?
A Functional dependency is denoted by X Y between two sets of attributes X and Y that are subsets of R specifies a constraint on the possible tuple that can form a relation state r of R. The constraint is for any two tuples t1 and t2 in r if t1[X] = t2[X] then they have t1[Y] = t2[Y]. This means the value of X component of a tuple uniquely determines the value of component Y.
When is a functional dependency F said to be minimal?
Every dependency in F has a single attribute for its right hand side.
We cannot replace any dependency X A in F with a dependency Y A where Y is a proper subset of X and still have a set of dependency that is equivalent to F.
We cannot remove any dependency from F and still have set of dependency that is equivalent to F.
What is Multivalued dependency?
Multivalued dependency denoted by X Y specified on relation schema R, where X and Y are both subsets of R, specifies the following constraint on any relation r of R: if two tuples t1 and t2 exist in r such that t1[X] = t2[X] then t3 and t4 should also exist in r with the following properties
t3[x] = t4[X] = t1[X] = t2[X]
t3[Y] = t1[Y] and t4[Y] = t2[Y]
t3[Z] = t2[Z] and t4[Z] = t1[Z]
where [Z = (R-(X U Y)) ]
What is Lossless join property?
It guarantees that the spurious tuple generation does not occur with respect to relation schemas after decomposition.
What is 1 NF (Normal Form)?
The domain of attribute must include only atomic (simple, indivisible) values.
What is Fully Functional dependency?
It is based on concept of full functional dependency. A functional dependency X Y is full functional dependency if removal of any attribute A from X means that the dependency does not hold any more.
What is 2NF?
A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully functionally dependent on primary key.
What is 3NF?
A relation schema R is in 3NF if it is in 2NF and for every FD X A either of the following is true
X is a Super-key of R.
A is a prime attribute of R.
In other words, if every non prime attribute is non-transitively dependent on primary key.
What is BCNF (Boyce-Codd Normal Form)?
A relation schema R is in BCNF if it is in 3NF and satisfies an additional constraint that for every FD X A, X must be a candidate key.
What is 4NF?
A relation schema R is said to be in 4NF if for every Multivalued dependency X Y that holds over R, one of following is true
X is subset or equal to (or) XY = R.
X is a super key.
What is 5NF?
A Relation schema R is said to be 5NF if for every join dependency {R1, R2, ..., Rn} that holds R, one the following is true
Ri = R for some i.
The join dependency is implied by the set of FD, over R in which the left side is key of R.
What is Domain-Key Normal Form?
A relation is said to be in DKNF if all constraints and dependencies that should hold on the the constraint can be enforced by simply enforcing the domain constraint and key constraint on the relation.
What are partial, alternate,, artificial, compound and natural key?
Partial Key:
It is a set of attributes that can uniquely identify weak entities and that are related to same owner entity. It is sometime called as Discriminator.
Alternate Key:
All Candidate Keys excluding the Primary Key are known as Alternate Keys.
Artificial Key:
If no obvious key, either stand alone or compound is available, then the last resort is to simply create a key, by assigning a unique number to each record or occurrence. Then this is known as developing an artificial key.
Compound Key:
If no single data element uniquely identifies occurrences within a construct, then combining multiple elements to create a unique identifier for the construct is known as creating a compound key.
Natural Key:
When one of the data elements stored within a construct is utilized as the primary key, then it is called the natural key.
What is indexing and what are the different kinds of indexing?
Indexing is a technique for determining how quickly specific data can be found.
Types:
Binary search style indexing
B-Tree indexing
Inverted list indexing
Memory resident table
Table indexing
What is system catalog or catalog relation? How is better known as?
A RDBMS maintains a description of all the data that it contains, information about every relation and index that it contains. This information is stored in a collection of relations maintained by the system called metadata. It is also called data dictionary.
What is meant by query optimization?
The phase that identifies an efficient execution plan for evaluating a query that has the least estimated cost is referred to as query optimization.
What is join dependency and inclusion dependency?
Join Dependency:
A Join dependency is generalization of Multivalued dependency.A JD {R1, R2, ..., Rn} is said to hold over a relation R if R1, R2, R3, ..., Rn is a lossless-join decomposition of R . There is no set of sound and complete inference rules for JD.
Inclusion Dependency:
An Inclusion Dependency is a statement of the form that some columns of a relation are contained in other columns. A foreign key constraint is an example of inclusion dependency.
What is durability in DBMS?
Once the DBMS informs the user that a transaction has successfully completed, its effects should persist even if the system crashes before all its changes are reflected on disk. This property is called durability.
What do you mean by atomicity and aggregation?
Atomicity:
Either all actions are carried out or none are. Users should not have to worry about the effect of incomplete transactions. DBMS ensures this by undoing the actions of incomplete transactions.
Aggregation:
A concept which is used to model a relationship between a collection of entities and relationships. It is used when we need to express a relationship among relationships.
What is a Phantom Deadlock?
In distributed deadlock detection, the delay in propagating local information might cause the deadlock detection algorithms to identify deadlocks that do not really exist. Such situations are called phantom deadlocks and they lead to unnecessary aborts.
What is a checkpoint and When does it occur?
A Checkpoint is like a snapshot of the DBMS state. By taking checkpoints, the DBMS can reduce the amount of work to be done during restart in the event of subsequent crashes.
What are the different phases of transaction?
Different phases are
Analysis phase
Redo Phase
Undo phase
What do you mean by flat file database?
It is a database in which there are no programs or user access languages. It has no cross-file capabilities but is user-friendly and provides user-interface management.
What is "transparent DBMS"?
It is one, which keeps its Physical Structure hidden from user.
Brief theory of Network, Hierarchical schemas and their properties
Network schema uses a graph data structure to organize records example for such a database management system is CTCG while a hierarchical schema uses a tree data structure example for such a system is IMS.
What is a query?
A query with respect to DBMS relates to user commands that are used to interact with a data base. The query language can be classified into data definition language and data manipulation language.
What do you mean by Correlated subquery?
Subqueries, or nested queries, are used to bring back a set of rows to be used by the parent query. Depending on how the subquery is written, it can be executed once for the parent query or it can be executed once for each row returned by the parent query. If the subquery is executed for each row of the parent, this is called a correlated subquery.
A correlated subquery can be easily identified if it contains any references to the parent subquery columns in its WHERE clause. Columns from the subquery cannot be referenced anywhere else in the parent query. The following example demonstrates a non-correlated subquery.
E.g. Select * From CUST Where '10/03/1990' IN (Select ODATE From ORDER Where CUST.CNUM = ORDER.CNUM)
What are the primitive operations common to all record management systems?
Addition, deletion and modification.
Name the buffer in which all the commands that are typed in are stored
‘Edit’ Buffer
What are the unary operations in Relational Algebra?
PROJECTION and SELECTION.
Are the resulting relations of PRODUCT and JOIN operation the same?
No.
PRODUCT: Concatenation of every row in one relation with every row in another.
JOIN: Concatenation of rows from one relation and related rows from another.
What is RDBMS KERNEL?
Two important pieces of RDBMS architecture are the kernel, which is the software, and the data dictionary, which consists of the system-level data structures used by the kernel to manage the database
You might think of an RDBMS as an operating system (or set of subsystems), designed specifically for controlling data access; its primary functions are storing, retrieving, and securing data. An RDBMS maintains its own list of authorized users and their associated privileges; manages memory caches and paging; controls locking for concurrent resource usage; dispatches and schedules user requests; and manages space usage within its table-space structures
.
Name the sub-systems of a RDBMS
I/O, Security, Language Processing, Process Control, Storage Management, Logging and Recovery, Distribution Control, Transaction Control, Memory Management, Lock Management
Which part of the RDBMS takes care of the data dictionary? How
Data dictionary is a set of tables and database objects that is stored in a special area of the database and maintained exclusively by the kernel.
What is the job of the information stored in data-dictionary?
The information in the data dictionary validates the existence of the objects, provides access to them, and maps the actual physical storage location.
Not only RDBMS takes care of locating data it also
determines an optimal access path to store or retrieve the data
How do you communicate with an RDBMS?
You communicate with an RDBMS using Structured Query Language (SQL)
Define SQL and state the differences between SQL and other conventional programming Languages
SQL is a nonprocedural language that is designed specifically for data access operations on normalized relational database structures. The primary difference between SQL and other conventional programming languages is that SQL statements specify what data operations should be performed rather than how to perform them.
Name the three major set of files on disk that compose a database in Oracle
There are three major sets of files on disk that compose a database. All the files are binary. These are
Database files
Control files
Redo logs
The most important of these are the database files where the actual data resides. The control files and the redo logs support the functioning of the architecture itself.
All three sets of files must be present, open, and available to Oracle for any data on the database to be useable. Without these files, you cannot access the database, and the database administrator might have to recover some or all of the database using a backup, if there is one.
What is an Oracle Instance?
The Oracle system processes, also known as Oracle background processes, provide functions for the user processes—functions that would otherwise be done by the user processes themselves
Oracle database-wide system memory is known as the SGA, the system global area or shared global area. The data and control structures in the SGA are shareable, and all the Oracle background processes and user processes can use them.
The combination of the SGA and the Oracle background processes is known as an Oracle instance
What are the four Oracle system processes that must always be up and running for the database to be useable
The four Oracle system processes that must always be up and running for the database to be useable include DBWR (Database Writer), LGWR (Log Writer), SMON (System Monitor), and PMON (Process Monitor).
What are database files, control files and log files. How many of these files should a database have at least? Why?
Database Files
The database files hold the actual data and are typically the largest in size. Depending on their sizes, the tables (and other objects) for all the user accounts can go in one database file—but that's not an ideal situation because it does not make the database structure very flexible for controlling access to storage for different users, putting the database on different disk drives, or backing up and restoring just part of the database.
You must have at least one database file but usually, more than one files are used. In terms of accessing and using the data in the tables and other objects, the number (or location) of the files is immaterial.
The database files are fixed in size and never grow bigger than the size at which they were created
Control Files
The control files and redo logs support the rest of the architecture. Any database must have at least one control file, although you typically have more than one to guard against loss. The control file records the name of the database, the date and time it was created, the location of the database and redo logs, and the synchronization information to ensure that all three sets of files are always in step. Every time you add a new database or redo log file to the database, the information is recorded in the control files.
Redo Logs
Any database must have at least two redo logs. These are the journals for the database; the redo logs record all changes to the user objects or system objects. If any type of failure occurs, the changes recorded in the redo logs can be used to bring the database to a consistent state without losing any committed transactions. In the case of non-data loss failure, Oracle can apply the information in the redo logs automatically without intervention from the DBA.
The redo log files are fixed in size and never grow dynamically from the size at which they were created.
What is ROWID?
The ROWID is a unique database-wide physical address for every row on every table. Once assigned (when the row is first inserted into the database), it never changes until the row is deleted or the table is dropped.
The ROWID consists of the following three components, the combination of which uniquely identifies the physical storage location of the row.
Oracle database file number, which contains the block with the rows
Oracle block address, which contains the row
The row within the block (because each block can hold many rows)
The ROWID is used internally in indexes as a quick means of retrieving rows with a particular key value. Application developers also use it in SQL statements as a quick way to access a row once they know the ROWID
What is Oracle Block? Can two Oracle Blocks have the same address?
Oracle "formats" the database files into a number of Oracle blocks when they are first created—making it easier for the RDBMS software to manage the files and easier to read data into the memory areas.
The block size should be a multiple of the operating system block size. Regardless of the block size, the entire block is not available for holding data; Oracle takes up some space to manage the contents of the block. This block header has a minimum size, but it can grow.
These Oracle blocks are the smallest unit of storage. Increasing the Oracle block size can improve performance, but it should be done only when the database is first created.
Each Oracle block is numbered sequentially for each database file starting at 1. Two blocks can have the same block address if they are in different database files.
What is database Trigger?
A database trigger is a PL/SQL block that can defined to automatically execute for insert, update, and delete statements against a table. The trigger can e defined to execute once for the entire statement or once for every row that is inserted, updated, or deleted. For any one table, there are twelve events for which you can define database triggers. A database trigger can call database procedures that are also written in PL/SQL.
Name two utilities that Oracle provides, which are use for backup and recovery.
Along with the RDBMS software, Oracle provides two utilities that you can use to back up and restore the database. These utilities are Export and Import.
The Export utility dumps the definitions and data for the specified part of the database to an operating system binary file. The Import utility reads the file produced by an export, recreates the definitions of objects, and inserts the data
If Export and Import are used as a means of backing up and recovering the database, all the changes made to the database cannot be recovered since the export was performed. The best you can do is recover the database to the time when the export was last performed.
What are stored-procedures? And what are the advantages of using them.
Stored procedures are database objects that perform a user defined operation. A stored procedure can have a set of compound SQL statements. A stored procedure executes the SQL commands and returns the result to the client. Stored procedures are used to reduce network traffic.
How are exceptions handled in PL/SQL? Give some of the internal exceptions' name
PL/SQL exception handling is a mechanism for dealing with run-time errors encountered during procedure execution. Use of this mechanism enables execution to continue if the error is not severe enough to cause procedure termination.
The exception handler must be defined within a subprogram specification. Errors cause the program to raise an exception with a transfer of control to the exception-handler block. After the exception handler executes, control returns to the block in which the handler was defined. If there are no more executable statements in the block, control returns to the caller.
User-Defined Exceptions
PL/SQL enables the user to define exception handlers in the declarations area of subprogram specifications. User accomplishes this by naming an exception as in the following example:
ot_failure EXCEPTION;
In this case, the exception name is ot_failure. Code associated with this handler is written in the EXCEPTION specification area as follows:
EXCEPTION
when OT_FAILURE then
out_status_code := g_out_status_code;
out_msg := g_out_msg;
The following is an example of a subprogram exception:
EXCEPTION
when NO_DATA_FOUND then
g_out_status_code := 'FAIL';
RAISE ot_failure;
Within this exception is the RAISE statement that transfers control back to the ot_failure exception handler. This technique of raising the exception is used to invoke all user-defined exceptions.
System-Defined Exceptions
Exceptions internal to PL/SQL are raised automatically upon error. NO_DATA_FOUND is a system-defined exception. Table below gives a complete list of internal exceptions.
PL/SQL internal exceptions.
Exception Name Oracle Error
CURSOR_ALREADY_OPEN ORA-06511
DUP_VAL_ON_INDEX ORA-00001
INVALID_CURSOR ORA-01001
INVALID_NUMBER ORA-01722
LOGIN_DENIED ORA-01017
NO_DATA_FOUND ORA-01403
NOT_LOGGED_ON ORA-01012
PROGRAM_ERROR ORA-06501
STORAGE_ERROR ORA-06500
TIMEOUT_ON_RESOURCE ORA-00051
TOO_MANY_ROWS ORA-01422
TRANSACTION_BACKED_OUT ORA-00061
VALUE_ERROR ORA-06502
ZERO_DIVIDE ORA-01476
In addition to this list of exceptions, there is a catch-all exception named OTHERS that traps all errors for which specific error handling has not been established.
Does PL/SQL support "overloading"? Explain
The concept of overloading in PL/SQL relates to the idea that you can define procedures and functions with the same name. PL/SQL does not look only at the referenced name, however, to resolve a procedure or function call. The count and data types of formal parameters are also considered.
PL/SQL also attempts to resolve any procedure or function calls in locally defined packages before looking at globally defined packages or internal functions. To further ensure calling the proper procedure, you can use the dot notation. Prefacing a procedure or function name with the package name fully qualifies any procedure or function reference.
Tables derived from the ERD
a) Are totally unnormalised
b) Are always in 1NF
c) Can be further denormalised
d) May have multi-valued attributes
(b) Are always in 1NF
Spurious tuples may occur due to
i. Bad normalization
ii. Theta joins
iii. Updating tables from join
a) i & ii b) ii & iii
c) i & iii d) ii & iii
(a) i & iii because theta joins are joins made on keys that are not primary keys.
A B C is a set of attributes. The functional dependency is as follows
AB -> B
AC -> C
C -> B
a) is in 1NF
b) is in 2NF
c) is in 3NF
d) is in BCNF
(a) is in 1NF since (AC)+ = { A, B, C} hence AC is the primary key. Since C B is a FD given, where neither C is a Key nor B is a prime attribute, this it is not in 3NF. Further B is not functionally dependent on key AC thus it is not in 2NF. Thus the given FDs is in 1NF.
In mapping of ERD to DFD
a) entities in ERD should correspond to an existing entity/store in DFD
b) entity in DFD is converted to attributes of an entity in ERD
c) relations in ERD has 1 to 1 correspondence to processes in DFD
d) relationships in ERD has 1 to 1 correspondence to flows in DFD
(a) entities in ERD should correspond to an existing entity/store in DFD
A dominant entity is the entity
a) on the N side in a 1 : N relationship
b) on the 1 side in a 1 : N relationship
c) on either side in a 1 : 1 relationship
d) nothing to do with 1 : 1 or 1 : N relationship
(b) on the 1 side in a 1 : N relationship
Select 'NORTH', CUSTOMER From CUST_DTLS Where REGION = 'N' Order By
CUSTOMER Union Select 'EAST', CUSTOMER From CUST_DTLS Where REGION = 'E' Order By CUSTOMER
The above is
a) Not an error
b) Error - the string in single quotes 'NORTH' and 'SOUTH'
c) Error - the string should be in double quotes
d) Error - ORDER BY clause
(d) Error - the ORDER BY clause. Since ORDER BY clause cannot be used in UNIONS
What is Storage Manager?
It is a program module that provides the interface between the low-level data stored in database, application programs and queries submitted to the system.
What is Buffer Manager?
It is a program module, which is responsible for fetching data from disk storage into main memory and deciding what data to be cache in memory.
What is Transaction Manager?
It is a program module, which ensures that database, remains in a consistent state despite system failures and concurrent transaction execution proceeds without conflicting.
What is File Manager?
It is a program module, which manages the allocation of space on disk storage and data structure used to represent information stored on a disk.
What is Authorization and Integrity manager?
It is the program module, which tests for the satisfaction of integrity constraint and checks the authority of user to access data.
What are stand-alone procedures?
Procedures that are not part of a package are known as stand-alone because they independently defined. A good example of a stand-alone procedure is one written in a SQL*Forms application. These types of procedures are not available for reference from other Oracle tools. Another limitation of stand-alone procedures is that they are compiled at run time, which slows execution.
What are cursors give different types of cursors.
PL/SQL uses cursors for all database information accesses statements. The language supports the use two types of cursors
Implicit
Explicit
What is cold backup and hot backup (in case of Oracle)?
Cold Backup:
It is copying the three sets of files (database files, redo logs, and control file) when the instance is shut down. This is a straight file copy, usually from the disk directly to tape. You must shut down the instance to guarantee a consistent copy.
If a cold backup is performed, the only option available in the event of data file loss is restoring all the files from the latest backup. All work performed on the database since the last backup is lost.
Hot Backup:
Some sites (such as worldwide airline reservations systems) cannot shut down the database while making a backup copy of the files. The cold backup is not an available option.
So different means of backing up database must be used — the hot backup. Issue a SQL command to indicate to Oracle, on a tablespace-by-tablespace basis, that the files of the tablespace are to backed up. The users can continue to make full use of the files, including making changes to the data. Once the user has indicated that he/she wants to back up the tablespace files, he/she can use the operating system to copy those files to the desired backup destination.
The database must be running in ARCHIVELOG mode for the hot backup option.
If a data loss failure does occur, the lost database files can be restored using the hot backup and the online and offline redo logs created since the backup was done. The database is restored to the most consistent state without any loss of committed transactions.
What are Armstrong rules? How do we say that they are complete and/or sound
The well-known inference rules for FDs
Reflexive rule :
If Y is subset or equal to X then X Y.
Augmentation rule:
If X Y then XZ YZ.
Transitive rule:
If {X Y, Y Z} then X Z.
Decomposition rule :
If X YZ then X Y.
Union or Additive rule:
If {X Y, X Z} then X YZ.
Pseudo Transitive rule :
If {X Y, WY Z} then WX Z.
Of these the first three are known as Amstrong Rules. They are sound because it is enough if a set of FDs satisfy these three. They are called complete because using these three rules we can generate the rest all inference rules.
How can you find the minimal key of relational schema?
Minimal key is one which can identify each tuple of the given relation schema uniquely. For finding the minimal key it is required to find the closure that is the set of all attributes that are dependent on any given set of attributes under the given set of functional dependency.
Algo. I Determining X+, closure for X, given set of FDs F
1. Set X+ = X
2. Set Old X+ = X+
3. For each FD Y Z in F and if Y belongs to X+ then add Z to X+
4. Repeat steps 2 and 3 until Old X+ = X+
Algo.II Determining minimal K for relation schema R, given set of FDs F
1. Set K to R that is make K a set of all attributes in R
2. For each attribute A in K
a. Compute (K – A)+ with respect to F
b. If (K – A)+ = R then set K = (K – A)+
What do you understand by dependency preservation?
Given a relation R and a set of FDs F, dependency preservation states that the closure of the union of the projection of F on each decomposed relation Ri is equal to the closure of F. i.e.,
((PR1(F)) U … U (PRn(F)))+ = F+
if decomposition is not dependency preserving, then some dependency is lost in the decomposition.
What is meant by Proactive, Retroactive and Simultaneous Update.
Proactive Update:
The updates that are applied to database before it becomes effective in real world .
Retroactive Update:
The updates that are applied to database after it becomes effective in real world .
Simulatneous Update:
The updates that are applied to database at the same time when it becomes effective in real world .
What are the different types of JOIN operations?
Equi Join: This is the most common type of join which involves only equality comparisions. The disadvantage in this type of join is that there
A database is a logically coherent collection of data with some inherent meaning, representing some aspect of real world and which is designed, built and populated with data for a specific purpose.
What is DBMS?
It is a collection of programs that enables user to create and maintain a database. In other words it is general-purpose software that provides the users with the processes of defining, constructing and manipulating the database for various applications.
What is a Database system?
The database and DBMS software together is called as Database system.
Advantages of DBMS?
Redundancy is controlled.
Unauthorised access is restricted.
Providing multiple user interfaces.
Enforcing integrity constraints.
Providing backup and recovery.
Disadvantage in File Processing System?
Data redundancy & inconsistency.
Difficult in accessing data.
Data isolation.
Data integrity.
Concurrent access is not possible.
Security Problems.
Describe the three levels of data abstraction?
The are three levels of abstraction:
Physical level: The lowest level of abstraction describes how data are stored.
Logical level: The next higher level of abstraction, describes what data are stored in database and what relationship among those data.
View level: The highest level of abstraction describes only part of entire database.
Define the "integrity rules"
There are two Integrity rules.
Entity Integrity: States that “Primary key cannot have NULL value”
Referential Integrity: States that “Foreign Key can be either a NULL value or should be Primary Key value of other relation.
What is extension and intension?
Extension -
It is the number of tuples present in a table at any instance. This is time dependent.
Intension -
It is a constant value that gives the name, structure of table and the constraints laid on it.
What is System R? What are its two major subsystems?
System R was designed and developed over a period of 1974-79 at IBM San Jose Research Center. It is a prototype and its purpose was to demonstrate that it is possible to build a Relational System that can be used in a real life environment to solve real life problems, with performance at least comparable to that of existing system.
Its two subsystems are
Research Storage
System Relational Data System.
How is the data structure of System R different from the relational structure?
Unlike Relational systems in System R
Domains are not supported
Enforcement of candidate key uniqueness is optional
Enforcement of entity integrity is optional
Referential integrity is not enforced
What is Data Independence?
Data independence means that “the application is independent of the storage structure and access strategy of data”. In other words, The ability to modify the schema definition in one level should not affect the schema definition in the next higher level.
Two types of Data Independence:
Physical Data Independence: Modification in physical level should not affect the logical level.
Logical Data Independence: Modification in logical level should affect the view level.
NOTE: Logical Data Independence is more difficult to achieve
What is a view? How it is related to data independence?
A view may be thought of as a virtual table, that is, a table that does not really exist in its own right but is instead derived from one or more underlying base table. In other words, there is no stored file that direct represents the view instead a definition of view is stored in data dictionary.
Growth and restructuring of base tables is not reflected in views. Thus the view can insulate users from the effects of restructuring and growth in the database. Hence accounts for logical data independence.
What is Data Model?
A collection of conceptual tools for describing data, data relationships data semantics and constraints.
What is E-R model?
This data model is based on real world that consists of basic objects called entities and of relationship among these objects. Entities are described in a database by a set of attributes.
What is Object Oriented model?
This model is based on collection of objects. An object contains values stored in instance variables with in the object. An object also contains bodies of code that operate on the object. These bodies of code are called methods. Objects that contain same types of values and the same methods are grouped together into classes.
What is an Entity?
It is a 'thing' in the real world with an independent existence.
What is an Entity type?
It is a collection (set) of entities that have same attributes.
What is an Entity set?
It is a collection of all entities of particular entity type in the database.
What is an Extension of entity type?
The collections of entities of a particular entity type are grouped together into an entity set.
What is Weak Entity set?
An entity set may not have sufficient attributes to form a primary key, and its primary key compromises of its partial key and primary key of its parent entity, then it is said to be Weak Entity set.
What is an attribute?
It is a particular property, which describes the entity.
What is a Relation Schema and a Relation?
A relation Schema denoted by R(A1, A2, …, An) is made up of the relation name R and the list of attributes Ai that it contains. A relation is defined as a set of tuples. Let r be the relation which contains set tuples (t1, t2, t3, ..., tn). Each tuple is an ordered list of n-values t=(v1,v2, ..., vn).
What is degree of a Relation?
It is the number of attribute of its relation schema.
What is Relationship?
It is an association among two or more entities.
What is Relationship set?
The collection (or set) of similar relationships.
What is Relationship type?
Relationship type defines a set of associations or a relationship set among a given set of entity types.
What is degree of Relationship type?
It is the number of entity type participating.
What is DDL (Data Definition Language)?
A data base schema is specifies by a set of definitions expressed by a special language called DDL.
What is VDL (View Definition Language)?
It specifies user views and their mappings to the conceptual schema.
What is SDL (Storage Definition Language)?
This language is to specify the internal schema. This language may specify the mapping between two schemas.
What is Data Storage - Definition Language?
The storage structures and access methods used by database system are specified by a set of definition in a special type of DDL called data storage-definition language.
What is DML (Data Manipulation Language)?
This language that enable user to access or manipulate data as organised by appropriate data model.
Procedural DML or Low level: DML requires a user to specify what data are needed and how to get those data.
Non-Procedural DML or High level: DML requires a user to specify what data are needed without specifying how to get those data.
What is DML Compiler?
It translates DML statements in a query language into low-level instruction that the query evaluation engine can understand.
What is Query evaluation engine?
It executes low-level instruction generated by compiler.
What is DDL Interpreter?
It interprets DDL statements and record them in tables containing metadata.
What is Record-at-a-time?
The Low level or Procedural DML can specify and retrieve each record from a set of records. This retrieve of a record is said to be Record-at-a-time.
What is Set-at-a-time or Set-oriented?
The High level or Non-procedural DML can specify and retrieve many records in a single DML statement. This retrieve of a record is said to be Set-at-a-time or Set-oriented.
What is Relational Algebra?
It is procedural query language. It consists of a set of operations that take one or two relations as input and produce a new relation.
What is Relational Calculus?
It is an applied predicate calculus specifically tailored for relational databases proposed by E.F. Codd. E.g. of languages based on it are DSL ALPHA, QUEL.
How does Tuple-oriented relational calculus differ from domain-oriented relational calculus
The tuple-oriented calculus uses a tuple variables i.e., variable whose only permitted values are tuples of that relation. E.g. QUEL
The domain-oriented calculus has domain variables i.e., variables that range over the underlying domains instead of over relation. E.g. ILL, DEDUCE.
What is normalization?
It is a process of analysing the given relation schemas based on their Functional Dependencies (FDs) and primary key to achieve the properties
Minimizing redundancy
Minimizing insertion, deletion and update anomalies.
What is Functional Dependency?
A Functional dependency is denoted by X Y between two sets of attributes X and Y that are subsets of R specifies a constraint on the possible tuple that can form a relation state r of R. The constraint is for any two tuples t1 and t2 in r if t1[X] = t2[X] then they have t1[Y] = t2[Y]. This means the value of X component of a tuple uniquely determines the value of component Y.
When is a functional dependency F said to be minimal?
Every dependency in F has a single attribute for its right hand side.
We cannot replace any dependency X A in F with a dependency Y A where Y is a proper subset of X and still have a set of dependency that is equivalent to F.
We cannot remove any dependency from F and still have set of dependency that is equivalent to F.
What is Multivalued dependency?
Multivalued dependency denoted by X Y specified on relation schema R, where X and Y are both subsets of R, specifies the following constraint on any relation r of R: if two tuples t1 and t2 exist in r such that t1[X] = t2[X] then t3 and t4 should also exist in r with the following properties
t3[x] = t4[X] = t1[X] = t2[X]
t3[Y] = t1[Y] and t4[Y] = t2[Y]
t3[Z] = t2[Z] and t4[Z] = t1[Z]
where [Z = (R-(X U Y)) ]
What is Lossless join property?
It guarantees that the spurious tuple generation does not occur with respect to relation schemas after decomposition.
What is 1 NF (Normal Form)?
The domain of attribute must include only atomic (simple, indivisible) values.
What is Fully Functional dependency?
It is based on concept of full functional dependency. A functional dependency X Y is full functional dependency if removal of any attribute A from X means that the dependency does not hold any more.
What is 2NF?
A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully functionally dependent on primary key.
What is 3NF?
A relation schema R is in 3NF if it is in 2NF and for every FD X A either of the following is true
X is a Super-key of R.
A is a prime attribute of R.
In other words, if every non prime attribute is non-transitively dependent on primary key.
What is BCNF (Boyce-Codd Normal Form)?
A relation schema R is in BCNF if it is in 3NF and satisfies an additional constraint that for every FD X A, X must be a candidate key.
What is 4NF?
A relation schema R is said to be in 4NF if for every Multivalued dependency X Y that holds over R, one of following is true
X is subset or equal to (or) XY = R.
X is a super key.
What is 5NF?
A Relation schema R is said to be 5NF if for every join dependency {R1, R2, ..., Rn} that holds R, one the following is true
Ri = R for some i.
The join dependency is implied by the set of FD, over R in which the left side is key of R.
What is Domain-Key Normal Form?
A relation is said to be in DKNF if all constraints and dependencies that should hold on the the constraint can be enforced by simply enforcing the domain constraint and key constraint on the relation.
What are partial, alternate,, artificial, compound and natural key?
Partial Key:
It is a set of attributes that can uniquely identify weak entities and that are related to same owner entity. It is sometime called as Discriminator.
Alternate Key:
All Candidate Keys excluding the Primary Key are known as Alternate Keys.
Artificial Key:
If no obvious key, either stand alone or compound is available, then the last resort is to simply create a key, by assigning a unique number to each record or occurrence. Then this is known as developing an artificial key.
Compound Key:
If no single data element uniquely identifies occurrences within a construct, then combining multiple elements to create a unique identifier for the construct is known as creating a compound key.
Natural Key:
When one of the data elements stored within a construct is utilized as the primary key, then it is called the natural key.
What is indexing and what are the different kinds of indexing?
Indexing is a technique for determining how quickly specific data can be found.
Types:
Binary search style indexing
B-Tree indexing
Inverted list indexing
Memory resident table
Table indexing
What is system catalog or catalog relation? How is better known as?
A RDBMS maintains a description of all the data that it contains, information about every relation and index that it contains. This information is stored in a collection of relations maintained by the system called metadata. It is also called data dictionary.
What is meant by query optimization?
The phase that identifies an efficient execution plan for evaluating a query that has the least estimated cost is referred to as query optimization.
What is join dependency and inclusion dependency?
Join Dependency:
A Join dependency is generalization of Multivalued dependency.A JD {R1, R2, ..., Rn} is said to hold over a relation R if R1, R2, R3, ..., Rn is a lossless-join decomposition of R . There is no set of sound and complete inference rules for JD.
Inclusion Dependency:
An Inclusion Dependency is a statement of the form that some columns of a relation are contained in other columns. A foreign key constraint is an example of inclusion dependency.
What is durability in DBMS?
Once the DBMS informs the user that a transaction has successfully completed, its effects should persist even if the system crashes before all its changes are reflected on disk. This property is called durability.
What do you mean by atomicity and aggregation?
Atomicity:
Either all actions are carried out or none are. Users should not have to worry about the effect of incomplete transactions. DBMS ensures this by undoing the actions of incomplete transactions.
Aggregation:
A concept which is used to model a relationship between a collection of entities and relationships. It is used when we need to express a relationship among relationships.
What is a Phantom Deadlock?
In distributed deadlock detection, the delay in propagating local information might cause the deadlock detection algorithms to identify deadlocks that do not really exist. Such situations are called phantom deadlocks and they lead to unnecessary aborts.
What is a checkpoint and When does it occur?
A Checkpoint is like a snapshot of the DBMS state. By taking checkpoints, the DBMS can reduce the amount of work to be done during restart in the event of subsequent crashes.
What are the different phases of transaction?
Different phases are
Analysis phase
Redo Phase
Undo phase
What do you mean by flat file database?
It is a database in which there are no programs or user access languages. It has no cross-file capabilities but is user-friendly and provides user-interface management.
What is "transparent DBMS"?
It is one, which keeps its Physical Structure hidden from user.
Brief theory of Network, Hierarchical schemas and their properties
Network schema uses a graph data structure to organize records example for such a database management system is CTCG while a hierarchical schema uses a tree data structure example for such a system is IMS.
What is a query?
A query with respect to DBMS relates to user commands that are used to interact with a data base. The query language can be classified into data definition language and data manipulation language.
What do you mean by Correlated subquery?
Subqueries, or nested queries, are used to bring back a set of rows to be used by the parent query. Depending on how the subquery is written, it can be executed once for the parent query or it can be executed once for each row returned by the parent query. If the subquery is executed for each row of the parent, this is called a correlated subquery.
A correlated subquery can be easily identified if it contains any references to the parent subquery columns in its WHERE clause. Columns from the subquery cannot be referenced anywhere else in the parent query. The following example demonstrates a non-correlated subquery.
E.g. Select * From CUST Where '10/03/1990' IN (Select ODATE From ORDER Where CUST.CNUM = ORDER.CNUM)
What are the primitive operations common to all record management systems?
Addition, deletion and modification.
Name the buffer in which all the commands that are typed in are stored
‘Edit’ Buffer
What are the unary operations in Relational Algebra?
PROJECTION and SELECTION.
Are the resulting relations of PRODUCT and JOIN operation the same?
No.
PRODUCT: Concatenation of every row in one relation with every row in another.
JOIN: Concatenation of rows from one relation and related rows from another.
What is RDBMS KERNEL?
Two important pieces of RDBMS architecture are the kernel, which is the software, and the data dictionary, which consists of the system-level data structures used by the kernel to manage the database
You might think of an RDBMS as an operating system (or set of subsystems), designed specifically for controlling data access; its primary functions are storing, retrieving, and securing data. An RDBMS maintains its own list of authorized users and their associated privileges; manages memory caches and paging; controls locking for concurrent resource usage; dispatches and schedules user requests; and manages space usage within its table-space structures
.
Name the sub-systems of a RDBMS
I/O, Security, Language Processing, Process Control, Storage Management, Logging and Recovery, Distribution Control, Transaction Control, Memory Management, Lock Management
Which part of the RDBMS takes care of the data dictionary? How
Data dictionary is a set of tables and database objects that is stored in a special area of the database and maintained exclusively by the kernel.
What is the job of the information stored in data-dictionary?
The information in the data dictionary validates the existence of the objects, provides access to them, and maps the actual physical storage location.
Not only RDBMS takes care of locating data it also
determines an optimal access path to store or retrieve the data
How do you communicate with an RDBMS?
You communicate with an RDBMS using Structured Query Language (SQL)
Define SQL and state the differences between SQL and other conventional programming Languages
SQL is a nonprocedural language that is designed specifically for data access operations on normalized relational database structures. The primary difference between SQL and other conventional programming languages is that SQL statements specify what data operations should be performed rather than how to perform them.
Name the three major set of files on disk that compose a database in Oracle
There are three major sets of files on disk that compose a database. All the files are binary. These are
Database files
Control files
Redo logs
The most important of these are the database files where the actual data resides. The control files and the redo logs support the functioning of the architecture itself.
All three sets of files must be present, open, and available to Oracle for any data on the database to be useable. Without these files, you cannot access the database, and the database administrator might have to recover some or all of the database using a backup, if there is one.
What is an Oracle Instance?
The Oracle system processes, also known as Oracle background processes, provide functions for the user processes—functions that would otherwise be done by the user processes themselves
Oracle database-wide system memory is known as the SGA, the system global area or shared global area. The data and control structures in the SGA are shareable, and all the Oracle background processes and user processes can use them.
The combination of the SGA and the Oracle background processes is known as an Oracle instance
What are the four Oracle system processes that must always be up and running for the database to be useable
The four Oracle system processes that must always be up and running for the database to be useable include DBWR (Database Writer), LGWR (Log Writer), SMON (System Monitor), and PMON (Process Monitor).
What are database files, control files and log files. How many of these files should a database have at least? Why?
Database Files
The database files hold the actual data and are typically the largest in size. Depending on their sizes, the tables (and other objects) for all the user accounts can go in one database file—but that's not an ideal situation because it does not make the database structure very flexible for controlling access to storage for different users, putting the database on different disk drives, or backing up and restoring just part of the database.
You must have at least one database file but usually, more than one files are used. In terms of accessing and using the data in the tables and other objects, the number (or location) of the files is immaterial.
The database files are fixed in size and never grow bigger than the size at which they were created
Control Files
The control files and redo logs support the rest of the architecture. Any database must have at least one control file, although you typically have more than one to guard against loss. The control file records the name of the database, the date and time it was created, the location of the database and redo logs, and the synchronization information to ensure that all three sets of files are always in step. Every time you add a new database or redo log file to the database, the information is recorded in the control files.
Redo Logs
Any database must have at least two redo logs. These are the journals for the database; the redo logs record all changes to the user objects or system objects. If any type of failure occurs, the changes recorded in the redo logs can be used to bring the database to a consistent state without losing any committed transactions. In the case of non-data loss failure, Oracle can apply the information in the redo logs automatically without intervention from the DBA.
The redo log files are fixed in size and never grow dynamically from the size at which they were created.
What is ROWID?
The ROWID is a unique database-wide physical address for every row on every table. Once assigned (when the row is first inserted into the database), it never changes until the row is deleted or the table is dropped.
The ROWID consists of the following three components, the combination of which uniquely identifies the physical storage location of the row.
Oracle database file number, which contains the block with the rows
Oracle block address, which contains the row
The row within the block (because each block can hold many rows)
The ROWID is used internally in indexes as a quick means of retrieving rows with a particular key value. Application developers also use it in SQL statements as a quick way to access a row once they know the ROWID
What is Oracle Block? Can two Oracle Blocks have the same address?
Oracle "formats" the database files into a number of Oracle blocks when they are first created—making it easier for the RDBMS software to manage the files and easier to read data into the memory areas.
The block size should be a multiple of the operating system block size. Regardless of the block size, the entire block is not available for holding data; Oracle takes up some space to manage the contents of the block. This block header has a minimum size, but it can grow.
These Oracle blocks are the smallest unit of storage. Increasing the Oracle block size can improve performance, but it should be done only when the database is first created.
Each Oracle block is numbered sequentially for each database file starting at 1. Two blocks can have the same block address if they are in different database files.
What is database Trigger?
A database trigger is a PL/SQL block that can defined to automatically execute for insert, update, and delete statements against a table. The trigger can e defined to execute once for the entire statement or once for every row that is inserted, updated, or deleted. For any one table, there are twelve events for which you can define database triggers. A database trigger can call database procedures that are also written in PL/SQL.
Name two utilities that Oracle provides, which are use for backup and recovery.
Along with the RDBMS software, Oracle provides two utilities that you can use to back up and restore the database. These utilities are Export and Import.
The Export utility dumps the definitions and data for the specified part of the database to an operating system binary file. The Import utility reads the file produced by an export, recreates the definitions of objects, and inserts the data
If Export and Import are used as a means of backing up and recovering the database, all the changes made to the database cannot be recovered since the export was performed. The best you can do is recover the database to the time when the export was last performed.
What are stored-procedures? And what are the advantages of using them.
Stored procedures are database objects that perform a user defined operation. A stored procedure can have a set of compound SQL statements. A stored procedure executes the SQL commands and returns the result to the client. Stored procedures are used to reduce network traffic.
How are exceptions handled in PL/SQL? Give some of the internal exceptions' name
PL/SQL exception handling is a mechanism for dealing with run-time errors encountered during procedure execution. Use of this mechanism enables execution to continue if the error is not severe enough to cause procedure termination.
The exception handler must be defined within a subprogram specification. Errors cause the program to raise an exception with a transfer of control to the exception-handler block. After the exception handler executes, control returns to the block in which the handler was defined. If there are no more executable statements in the block, control returns to the caller.
User-Defined Exceptions
PL/SQL enables the user to define exception handlers in the declarations area of subprogram specifications. User accomplishes this by naming an exception as in the following example:
ot_failure EXCEPTION;
In this case, the exception name is ot_failure. Code associated with this handler is written in the EXCEPTION specification area as follows:
EXCEPTION
when OT_FAILURE then
out_status_code := g_out_status_code;
out_msg := g_out_msg;
The following is an example of a subprogram exception:
EXCEPTION
when NO_DATA_FOUND then
g_out_status_code := 'FAIL';
RAISE ot_failure;
Within this exception is the RAISE statement that transfers control back to the ot_failure exception handler. This technique of raising the exception is used to invoke all user-defined exceptions.
System-Defined Exceptions
Exceptions internal to PL/SQL are raised automatically upon error. NO_DATA_FOUND is a system-defined exception. Table below gives a complete list of internal exceptions.
PL/SQL internal exceptions.
Exception Name Oracle Error
CURSOR_ALREADY_OPEN ORA-06511
DUP_VAL_ON_INDEX ORA-00001
INVALID_CURSOR ORA-01001
INVALID_NUMBER ORA-01722
LOGIN_DENIED ORA-01017
NO_DATA_FOUND ORA-01403
NOT_LOGGED_ON ORA-01012
PROGRAM_ERROR ORA-06501
STORAGE_ERROR ORA-06500
TIMEOUT_ON_RESOURCE ORA-00051
TOO_MANY_ROWS ORA-01422
TRANSACTION_BACKED_OUT ORA-00061
VALUE_ERROR ORA-06502
ZERO_DIVIDE ORA-01476
In addition to this list of exceptions, there is a catch-all exception named OTHERS that traps all errors for which specific error handling has not been established.
Does PL/SQL support "overloading"? Explain
The concept of overloading in PL/SQL relates to the idea that you can define procedures and functions with the same name. PL/SQL does not look only at the referenced name, however, to resolve a procedure or function call. The count and data types of formal parameters are also considered.
PL/SQL also attempts to resolve any procedure or function calls in locally defined packages before looking at globally defined packages or internal functions. To further ensure calling the proper procedure, you can use the dot notation. Prefacing a procedure or function name with the package name fully qualifies any procedure or function reference.
Tables derived from the ERD
a) Are totally unnormalised
b) Are always in 1NF
c) Can be further denormalised
d) May have multi-valued attributes
(b) Are always in 1NF
Spurious tuples may occur due to
i. Bad normalization
ii. Theta joins
iii. Updating tables from join
a) i & ii b) ii & iii
c) i & iii d) ii & iii
(a) i & iii because theta joins are joins made on keys that are not primary keys.
A B C is a set of attributes. The functional dependency is as follows
AB -> B
AC -> C
C -> B
a) is in 1NF
b) is in 2NF
c) is in 3NF
d) is in BCNF
(a) is in 1NF since (AC)+ = { A, B, C} hence AC is the primary key. Since C B is a FD given, where neither C is a Key nor B is a prime attribute, this it is not in 3NF. Further B is not functionally dependent on key AC thus it is not in 2NF. Thus the given FDs is in 1NF.
In mapping of ERD to DFD
a) entities in ERD should correspond to an existing entity/store in DFD
b) entity in DFD is converted to attributes of an entity in ERD
c) relations in ERD has 1 to 1 correspondence to processes in DFD
d) relationships in ERD has 1 to 1 correspondence to flows in DFD
(a) entities in ERD should correspond to an existing entity/store in DFD
A dominant entity is the entity
a) on the N side in a 1 : N relationship
b) on the 1 side in a 1 : N relationship
c) on either side in a 1 : 1 relationship
d) nothing to do with 1 : 1 or 1 : N relationship
(b) on the 1 side in a 1 : N relationship
Select 'NORTH', CUSTOMER From CUST_DTLS Where REGION = 'N' Order By
CUSTOMER Union Select 'EAST', CUSTOMER From CUST_DTLS Where REGION = 'E' Order By CUSTOMER
The above is
a) Not an error
b) Error - the string in single quotes 'NORTH' and 'SOUTH'
c) Error - the string should be in double quotes
d) Error - ORDER BY clause
(d) Error - the ORDER BY clause. Since ORDER BY clause cannot be used in UNIONS
What is Storage Manager?
It is a program module that provides the interface between the low-level data stored in database, application programs and queries submitted to the system.
What is Buffer Manager?
It is a program module, which is responsible for fetching data from disk storage into main memory and deciding what data to be cache in memory.
What is Transaction Manager?
It is a program module, which ensures that database, remains in a consistent state despite system failures and concurrent transaction execution proceeds without conflicting.
What is File Manager?
It is a program module, which manages the allocation of space on disk storage and data structure used to represent information stored on a disk.
What is Authorization and Integrity manager?
It is the program module, which tests for the satisfaction of integrity constraint and checks the authority of user to access data.
What are stand-alone procedures?
Procedures that are not part of a package are known as stand-alone because they independently defined. A good example of a stand-alone procedure is one written in a SQL*Forms application. These types of procedures are not available for reference from other Oracle tools. Another limitation of stand-alone procedures is that they are compiled at run time, which slows execution.
What are cursors give different types of cursors.
PL/SQL uses cursors for all database information accesses statements. The language supports the use two types of cursors
Implicit
Explicit
What is cold backup and hot backup (in case of Oracle)?
Cold Backup:
It is copying the three sets of files (database files, redo logs, and control file) when the instance is shut down. This is a straight file copy, usually from the disk directly to tape. You must shut down the instance to guarantee a consistent copy.
If a cold backup is performed, the only option available in the event of data file loss is restoring all the files from the latest backup. All work performed on the database since the last backup is lost.
Hot Backup:
Some sites (such as worldwide airline reservations systems) cannot shut down the database while making a backup copy of the files. The cold backup is not an available option.
So different means of backing up database must be used — the hot backup. Issue a SQL command to indicate to Oracle, on a tablespace-by-tablespace basis, that the files of the tablespace are to backed up. The users can continue to make full use of the files, including making changes to the data. Once the user has indicated that he/she wants to back up the tablespace files, he/she can use the operating system to copy those files to the desired backup destination.
The database must be running in ARCHIVELOG mode for the hot backup option.
If a data loss failure does occur, the lost database files can be restored using the hot backup and the online and offline redo logs created since the backup was done. The database is restored to the most consistent state without any loss of committed transactions.
What are Armstrong rules? How do we say that they are complete and/or sound
The well-known inference rules for FDs
Reflexive rule :
If Y is subset or equal to X then X Y.
Augmentation rule:
If X Y then XZ YZ.
Transitive rule:
If {X Y, Y Z} then X Z.
Decomposition rule :
If X YZ then X Y.
Union or Additive rule:
If {X Y, X Z} then X YZ.
Pseudo Transitive rule :
If {X Y, WY Z} then WX Z.
Of these the first three are known as Amstrong Rules. They are sound because it is enough if a set of FDs satisfy these three. They are called complete because using these three rules we can generate the rest all inference rules.
How can you find the minimal key of relational schema?
Minimal key is one which can identify each tuple of the given relation schema uniquely. For finding the minimal key it is required to find the closure that is the set of all attributes that are dependent on any given set of attributes under the given set of functional dependency.
Algo. I Determining X+, closure for X, given set of FDs F
1. Set X+ = X
2. Set Old X+ = X+
3. For each FD Y Z in F and if Y belongs to X+ then add Z to X+
4. Repeat steps 2 and 3 until Old X+ = X+
Algo.II Determining minimal K for relation schema R, given set of FDs F
1. Set K to R that is make K a set of all attributes in R
2. For each attribute A in K
a. Compute (K – A)+ with respect to F
b. If (K – A)+ = R then set K = (K – A)+
What do you understand by dependency preservation?
Given a relation R and a set of FDs F, dependency preservation states that the closure of the union of the projection of F on each decomposed relation Ri is equal to the closure of F. i.e.,
((PR1(F)) U … U (PRn(F)))+ = F+
if decomposition is not dependency preserving, then some dependency is lost in the decomposition.
What is meant by Proactive, Retroactive and Simultaneous Update.
Proactive Update:
The updates that are applied to database before it becomes effective in real world .
Retroactive Update:
The updates that are applied to database after it becomes effective in real world .
Simulatneous Update:
The updates that are applied to database at the same time when it becomes effective in real world .
What are the different types of JOIN operations?
Equi Join: This is the most common type of join which involves only equality comparisions. The disadvantage in this type of join is that there
Networking concepts
What are the two types of transmission technology available?
(i) Broadcast and (ii) point-to-point
What is subnet?
A generic term for section of a large networks usually separated by a bridge or router.
Difference between the communication and transmission.
Transmission is a physical movement of information and concern issues like bit polarity, synchronisation, clock etc.
Communication means the meaning full exchange of information between two communication media.
What are the possible ways of data exchange?
(i) Simplex (ii) Half-duplex (iii) Full-duplex.
What is SAP?
Series of interface points that allow other computers to communicate with the other layers of network protocol stack.
What do you meant by "triple X" in Networks?
The function of PAD (Packet Assembler Disassembler) is described in a document known as X.3. The standard protocol has been defined between the terminal and the PAD, called X.28; another standard protocol exists between hte PAD and the network, called X.29. Together, these three recommendations are often called "triple X"
What is frame relay, in which layer it comes?
Frame relay is a packet switching technology. It will operate in the data link layer.
What is terminal emulation, in which layer it comes?
Telnet is also called as terminal emulation. It belongs to application layer.
What is Beaconing?
The process that allows a network to self-repair networks problems. The stations on the network notify the other stations on the ring when they are not receiving the transmissions. Beaconing is used in Token ring and FDDI networks.
What is redirector?
Redirector is software that intercepts file or prints I/O requests and translates them into network requests. This comes under presentation layer.
What is NETBIOS and NETBEUI?
NETBIOS is a programming interface that allows I/O requests to be sent to and received from a remote computer and it hides the networking hardware from applications.
NETBEUI is NetBIOS extended user interface. A transport protocol designed by microsoft and IBM for the use on small subnets.
What is RAID?
A method for providing fault tolerance by using multiple hard disk drives.
What is passive topology?
When the computers on the network simply listen and receive the signal, they are referred to as passive because they don’t amplify the signal in any way. Example for passive topology - linear bus.
What is Brouter?
Hybrid devices that combine the features of both bridges and routers.
What is cladding?
A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.
What is point-to-point protocol
A communications protocol used to connect computers to remote networking services including Internet service providers.
How Gateway is different from Routers?
A gateway operates at the upper levels of the OSI model and translates information between two completely different network architectures or data formats
What is attenuation?
The degeneration of a signal over distance on a network cable is called attenuation.
What is MAC address?
The address for a device as it is identified at the Media Access Control (MAC) layer in the network architecture. MAC address is usually stored in ROM on the network adapter card and is unique.
Difference between bit rate and baud rate.
Bit rate is the number of bits transmitted during one second whereas baud rate refers to the number of signal units per second that are required to represent those bits.
baud rate = bit rate / N
where N is no-of-bits represented by each signal shift.
What is Bandwidth?
Every line has an upper limit and a lower limit on the frequency of signals it can carry. This limited range is called the bandwidth.
What are the types of Transmission media?
Signals are usually transmitted over some transmission media that are broadly classified in to two categories.
Guided Media:
These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that accept and transport signals in the form of electrical current. Optical fiber is a glass or plastic cable that accepts and transports signals in the form of light.
b) Unguided Media:
This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are broadcast either through air. This is done through radio communication, satellite communication and cellular telephony.
What is Project 802?
It is a project started by IEEE to set standards to enable intercommunication between equipment from a variety of manufacturers. It is a way for specifying functions of the physical layer, the data link layer and to some extent the network layer to allow for interconnectivity of major LAN
protocols.
It consists of the following:
802.1 is an internetworking standard for compatibility of different LANs and MANs across protocols.
802.2 Logical link control (LLC) is the upper sublayer of the data link layer which is non-architecture-specific, that is remains the same for all IEEE-defined LANs.
Media access control (MAC) is the lower sublayer of the data link layer that contains some distinct modules each carrying proprietary information specific to the LAN product being used. The modules are Ethernet LAN (802.3), Token ring LAN (802.4), Token bus LAN (802.5).
802.6 is distributed queue dual bus (DQDB) designed to be used in MANs.
What is Protocol Data Unit?
The data unit in the LLC level is called the protocol data unit (PDU). The PDU contains of four fields a destination service access point (DSAP), a source service access point (SSAP), a control field and an information field. DSAP, SSAP are addresses used by the LLC to identify the protocol stacks on the receiving and sending machines that are generating and using the data. The control field specifies whether the PDU frame is a information frame (I - frame) or a supervisory frame (S - frame) or a unnumbered frame (U - frame).
What are the different type of networking / internetworking devices?
Repeater:
Also called a regenerator, it is an electronic device that operates only at physical layer. It receives the signal in the network before it becomes weak, regenerates the original bit pattern and puts the refreshed copy back in to the link.
Bridges:
These operate both in the physical and data link layers of LANs of same type. They divide a larger network in to smaller segments. They contain logic that allow them to keep the traffic for each segment separate and thus are repeaters that relay a frame only the side of the segment containing the intended recipent and control congestion.
Routers:
They relay packets among multiple interconnected networks (i.e. LANs of different type). They operate in the physical, data link and network layers. They contain software that enable them to determine which of the several possible paths is the best for a particular transmission.
Gateways:
They relay packets among networks that have different protocols (e.g. between a LAN and a WAN). They accept a packet formatted for one protocol and convert it to a packet formatted for another protocol before forwarding it. They operate in all seven layers of the OSI model.
What is ICMP?
ICMP is Internet Control Message Protocol, a network layer protocol of the TCP/IP suite used by hosts and gateways to send notification of datagram problems back to the sender. It uses the echo test / reply to test whether a destination is reachable and responding. It also handles both control and error messages.
What are the data units at different layers of the TCP / IP protocol suite?
The data unit created at the application layer is called a message, at the transport layer the data unit created is called either a segment or an user datagram, at the network layer the data unit created is called the datagram, at the data link layer the datagram is encapsulated in to a frame and finally transmitted as signals along the transmission media.
What is difference between ARP and RARP?
The address resolution protocol (ARP) is used to associate the 32 bit IP address with the 48 bit physical address, used by a host or a router to find the physical address of another host on its network by sending a ARP query packet that includes the IP address of the receiver.
The reverse address resolution protocol (RARP) allows a host to discover its Internet address when it knows only its physical address.
What is the minimum and maximum length of the header in the TCP segment and IP datagram?
The header should have a minimum length of 20 bytes and can have a maximum length of 60 bytes.
What is the range of addresses in the classes of internet addresses?
Class A 0.0.0.0 - 127.255.255.255
Class B 128.0.0.0 - 191.255.255.255
Class C 192.0.0.0 - 223.255.255.255
Class D 224.0.0.0 - 239.255.255.255
Class E 240.0.0.0 - 247.255.255.255
What is the difference between TFTP and FTP application layer protocols?
The Trivial File Transfer Protocol (TFTP) allows a local host to obtain files from a remote host but does not provide reliability or security. It uses the fundamental packet delivery services offered by UDP.
The File Transfer Protocol (FTP) is the standard mechanism provided by TCP / IP for copying a file from one host to another. It uses the services offer by TCP and so is reliable and secure. It establishes two connections (virtual circuits) between the hosts, one for data transfer and another for control information.
What are major types of networks and explain?
Server-based network
Peer-to-peer network
Peer-to-peer network, computers can act as both servers sharing resources and as clients using the resources.
Server-based networks provide centralized control of network resources and rely on server computers to provide security and network administration
What are the important topologies for networks?
BUS topology:
In this each computer is directly connected to primary network cable in a single line.
Advantages:
Inexpensive, easy to install, simple to understand, easy to extend.
STAR topology:
In this all computers are connected using a central hub.
Advantages:
Can be inexpensive, easy to install and reconfigure and easy to trouble shoot physical problems.
RING topology:
In this all computers are connected in loop.
Advantages:
All computers have equal access to network media, installation can be simple, and signal does not degrade as much as in other topologies because each computer regenerates it.
What is mesh network?
A network in which there are multiple network links between computers to provide multiple paths for data to travel.
What is difference between baseband and broadband transmission?
In a baseband transmission, the entire bandwidth of the cable is consumed by a single signal. In broadband transmission, signals are sent on multiple frequencies, allowing multiple signals to be sent simultaneously.
Explain 5-4-3 rule?
In a Ethernet network, between any two points on the network ,there can be no more than five network segments or four repeaters, and of those five segments only three of segments can be populated.
What MAU?
In token Ring , hub is called Multistation Access Unit(MAU).
What is the difference between routable and non- routable protocols?
Routable protocols can work with a router and can be used to build large networks. Non-Routable protocols are designed to work on small, local networks and cannot be used with a router
Why should you care about the OSI Reference Model?
It provides a framework for discussing network operations and design.
What is logical link control?
One of two sublayers of the data link layer of OSI reference model, as defined by the IEEE 802 standard. This sublayer is responsible for maintaining the link between computers when they are sending data across the physical network connection.
What is virtual channel?
Virtual channel is normally a connection from one source to one destination, although multicast connections are also permitted. The other name for virtual channel is virtual circuit.
What is virtual path?
Along any transmission path from a given source to a given destination, a group of virtual circuits can be grouped together into what is called path.
What is packet filter?
Packet filter is a standard router equipped with some extra functionality. The extra functionality allows every incoming or outgoing packet to be inspected. Packets meeting some criterion are forwarded normally. Those that fail the test are dropped.
What is traffic shaping?
One of the main causes of congestion is that traffic is often busy. If hosts could be made to transmit at a uniform rate, congestion would be less common. Another open loop method to help manage congestion is forcing the packet to be transmitted at a more predictable rate. This is called traffic shaping.
What is multicast routing?
Sending a message to a group is called multicasting, and its routing algorithm is called multicast routing.
What is region?
When hierarchical routing is used, the routers are divided into what we will call regions, with each router knowing all the details about how to route packets to destinations within its own region, but knowing nothing about the internal structure of other regions.
What is silly window syndrome?
It is a problem that can ruin TCP performance. This problem occurs when data are passed to the sending TCP entity in large blocks, but an interactive application on the receiving side reads 1 byte at a time.
What are Digrams and Trigrams?
The most common two letter combinations are called as digrams. e.g. th, in, er, re and an. The most common three letter combinations are called as trigrams. e.g. the, ing, and, and ion.
Expand IDEA.
IDEA stands for International Data Encryption Algorithm.
What is wide-mouth frog?
Wide-mouth frog is the simplest known key distribution center (KDC) authentication protocol.
What is Mail Gateway?
It is a system that performs a protocol translation between different electronic mail delivery protocols.
What is IGP (Interior Gateway Protocol)?
It is any routing protocol used within an autonomous system.
What is EGP (Exterior Gateway Protocol)?
It is the protocol the routers in neighboring autonomous systems use to identify the set of networks that can be reached within or via each autonomous system.
What is autonomous system?
It is a collection of routers under the control of a single administrative authority and that uses a common Interior Gateway Protocol.
What is BGP (Border Gateway Protocol)?
It is a protocol used to advertise the set of networks that can be reached with in an autonomous system. BGP enables this information to be shared with the autonomous system. This is newer than EGP (Exterior Gateway Protocol).
What is Gateway-to-Gateway protocol?
It is a protocol formerly used to exchange routing information between Internet core routers.
What is NVT (Network Virtual Terminal)?
It is a set of rules defining a very simple virtual terminal interaction. The NVT is used in the start of a Telnet session.
What is a Multi-homed Host?
It is a host that has a multiple network interfaces and that requires multiple IP addresses is called as a Multi-homed Host.
What is Kerberos?
It is an authentication service developed at the Massachusetts Institute of Technology. Kerberos uses encryption to prevent intruders from discovering passwords and gaining unauthorized access to files.
What is OSPF?
It is an Internet routing protocol that scales well, can route traffic along multiple paths, and uses knowledge of an Internet's topology to make accurate routing decisions.
What is Proxy ARP?
It is using a router to answer ARP requests. This will be done when the originating host believes that a destination is local, when in fact is lies beyond router.
What is SLIP (Serial Line Interface Protocol)?
It is a very simple protocol used for transmission of IP datagrams across a serial line.
What is RIP (Routing Information Protocol)?
It is a simple protocol used to exchange information between the routers.
What is source route?
It is a sequence of IP addresses identifying the route a datagram must follow. A source route may optionally be included in an IP datagram header.
(i) Broadcast and (ii) point-to-point
What is subnet?
A generic term for section of a large networks usually separated by a bridge or router.
Difference between the communication and transmission.
Transmission is a physical movement of information and concern issues like bit polarity, synchronisation, clock etc.
Communication means the meaning full exchange of information between two communication media.
What are the possible ways of data exchange?
(i) Simplex (ii) Half-duplex (iii) Full-duplex.
What is SAP?
Series of interface points that allow other computers to communicate with the other layers of network protocol stack.
What do you meant by "triple X" in Networks?
The function of PAD (Packet Assembler Disassembler) is described in a document known as X.3. The standard protocol has been defined between the terminal and the PAD, called X.28; another standard protocol exists between hte PAD and the network, called X.29. Together, these three recommendations are often called "triple X"
What is frame relay, in which layer it comes?
Frame relay is a packet switching technology. It will operate in the data link layer.
What is terminal emulation, in which layer it comes?
Telnet is also called as terminal emulation. It belongs to application layer.
What is Beaconing?
The process that allows a network to self-repair networks problems. The stations on the network notify the other stations on the ring when they are not receiving the transmissions. Beaconing is used in Token ring and FDDI networks.
What is redirector?
Redirector is software that intercepts file or prints I/O requests and translates them into network requests. This comes under presentation layer.
What is NETBIOS and NETBEUI?
NETBIOS is a programming interface that allows I/O requests to be sent to and received from a remote computer and it hides the networking hardware from applications.
NETBEUI is NetBIOS extended user interface. A transport protocol designed by microsoft and IBM for the use on small subnets.
What is RAID?
A method for providing fault tolerance by using multiple hard disk drives.
What is passive topology?
When the computers on the network simply listen and receive the signal, they are referred to as passive because they don’t amplify the signal in any way. Example for passive topology - linear bus.
What is Brouter?
Hybrid devices that combine the features of both bridges and routers.
What is cladding?
A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.
What is point-to-point protocol
A communications protocol used to connect computers to remote networking services including Internet service providers.
How Gateway is different from Routers?
A gateway operates at the upper levels of the OSI model and translates information between two completely different network architectures or data formats
What is attenuation?
The degeneration of a signal over distance on a network cable is called attenuation.
What is MAC address?
The address for a device as it is identified at the Media Access Control (MAC) layer in the network architecture. MAC address is usually stored in ROM on the network adapter card and is unique.
Difference between bit rate and baud rate.
Bit rate is the number of bits transmitted during one second whereas baud rate refers to the number of signal units per second that are required to represent those bits.
baud rate = bit rate / N
where N is no-of-bits represented by each signal shift.
What is Bandwidth?
Every line has an upper limit and a lower limit on the frequency of signals it can carry. This limited range is called the bandwidth.
What are the types of Transmission media?
Signals are usually transmitted over some transmission media that are broadly classified in to two categories.
Guided Media:
These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that accept and transport signals in the form of electrical current. Optical fiber is a glass or plastic cable that accepts and transports signals in the form of light.
b) Unguided Media:
This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are broadcast either through air. This is done through radio communication, satellite communication and cellular telephony.
What is Project 802?
It is a project started by IEEE to set standards to enable intercommunication between equipment from a variety of manufacturers. It is a way for specifying functions of the physical layer, the data link layer and to some extent the network layer to allow for interconnectivity of major LAN
protocols.
It consists of the following:
802.1 is an internetworking standard for compatibility of different LANs and MANs across protocols.
802.2 Logical link control (LLC) is the upper sublayer of the data link layer which is non-architecture-specific, that is remains the same for all IEEE-defined LANs.
Media access control (MAC) is the lower sublayer of the data link layer that contains some distinct modules each carrying proprietary information specific to the LAN product being used. The modules are Ethernet LAN (802.3), Token ring LAN (802.4), Token bus LAN (802.5).
802.6 is distributed queue dual bus (DQDB) designed to be used in MANs.
What is Protocol Data Unit?
The data unit in the LLC level is called the protocol data unit (PDU). The PDU contains of four fields a destination service access point (DSAP), a source service access point (SSAP), a control field and an information field. DSAP, SSAP are addresses used by the LLC to identify the protocol stacks on the receiving and sending machines that are generating and using the data. The control field specifies whether the PDU frame is a information frame (I - frame) or a supervisory frame (S - frame) or a unnumbered frame (U - frame).
What are the different type of networking / internetworking devices?
Repeater:
Also called a regenerator, it is an electronic device that operates only at physical layer. It receives the signal in the network before it becomes weak, regenerates the original bit pattern and puts the refreshed copy back in to the link.
Bridges:
These operate both in the physical and data link layers of LANs of same type. They divide a larger network in to smaller segments. They contain logic that allow them to keep the traffic for each segment separate and thus are repeaters that relay a frame only the side of the segment containing the intended recipent and control congestion.
Routers:
They relay packets among multiple interconnected networks (i.e. LANs of different type). They operate in the physical, data link and network layers. They contain software that enable them to determine which of the several possible paths is the best for a particular transmission.
Gateways:
They relay packets among networks that have different protocols (e.g. between a LAN and a WAN). They accept a packet formatted for one protocol and convert it to a packet formatted for another protocol before forwarding it. They operate in all seven layers of the OSI model.
What is ICMP?
ICMP is Internet Control Message Protocol, a network layer protocol of the TCP/IP suite used by hosts and gateways to send notification of datagram problems back to the sender. It uses the echo test / reply to test whether a destination is reachable and responding. It also handles both control and error messages.
What are the data units at different layers of the TCP / IP protocol suite?
The data unit created at the application layer is called a message, at the transport layer the data unit created is called either a segment or an user datagram, at the network layer the data unit created is called the datagram, at the data link layer the datagram is encapsulated in to a frame and finally transmitted as signals along the transmission media.
What is difference between ARP and RARP?
The address resolution protocol (ARP) is used to associate the 32 bit IP address with the 48 bit physical address, used by a host or a router to find the physical address of another host on its network by sending a ARP query packet that includes the IP address of the receiver.
The reverse address resolution protocol (RARP) allows a host to discover its Internet address when it knows only its physical address.
What is the minimum and maximum length of the header in the TCP segment and IP datagram?
The header should have a minimum length of 20 bytes and can have a maximum length of 60 bytes.
What is the range of addresses in the classes of internet addresses?
Class A 0.0.0.0 - 127.255.255.255
Class B 128.0.0.0 - 191.255.255.255
Class C 192.0.0.0 - 223.255.255.255
Class D 224.0.0.0 - 239.255.255.255
Class E 240.0.0.0 - 247.255.255.255
What is the difference between TFTP and FTP application layer protocols?
The Trivial File Transfer Protocol (TFTP) allows a local host to obtain files from a remote host but does not provide reliability or security. It uses the fundamental packet delivery services offered by UDP.
The File Transfer Protocol (FTP) is the standard mechanism provided by TCP / IP for copying a file from one host to another. It uses the services offer by TCP and so is reliable and secure. It establishes two connections (virtual circuits) between the hosts, one for data transfer and another for control information.
What are major types of networks and explain?
Server-based network
Peer-to-peer network
Peer-to-peer network, computers can act as both servers sharing resources and as clients using the resources.
Server-based networks provide centralized control of network resources and rely on server computers to provide security and network administration
What are the important topologies for networks?
BUS topology:
In this each computer is directly connected to primary network cable in a single line.
Advantages:
Inexpensive, easy to install, simple to understand, easy to extend.
STAR topology:
In this all computers are connected using a central hub.
Advantages:
Can be inexpensive, easy to install and reconfigure and easy to trouble shoot physical problems.
RING topology:
In this all computers are connected in loop.
Advantages:
All computers have equal access to network media, installation can be simple, and signal does not degrade as much as in other topologies because each computer regenerates it.
What is mesh network?
A network in which there are multiple network links between computers to provide multiple paths for data to travel.
What is difference between baseband and broadband transmission?
In a baseband transmission, the entire bandwidth of the cable is consumed by a single signal. In broadband transmission, signals are sent on multiple frequencies, allowing multiple signals to be sent simultaneously.
Explain 5-4-3 rule?
In a Ethernet network, between any two points on the network ,there can be no more than five network segments or four repeaters, and of those five segments only three of segments can be populated.
What MAU?
In token Ring , hub is called Multistation Access Unit(MAU).
What is the difference between routable and non- routable protocols?
Routable protocols can work with a router and can be used to build large networks. Non-Routable protocols are designed to work on small, local networks and cannot be used with a router
Why should you care about the OSI Reference Model?
It provides a framework for discussing network operations and design.
What is logical link control?
One of two sublayers of the data link layer of OSI reference model, as defined by the IEEE 802 standard. This sublayer is responsible for maintaining the link between computers when they are sending data across the physical network connection.
What is virtual channel?
Virtual channel is normally a connection from one source to one destination, although multicast connections are also permitted. The other name for virtual channel is virtual circuit.
What is virtual path?
Along any transmission path from a given source to a given destination, a group of virtual circuits can be grouped together into what is called path.
What is packet filter?
Packet filter is a standard router equipped with some extra functionality. The extra functionality allows every incoming or outgoing packet to be inspected. Packets meeting some criterion are forwarded normally. Those that fail the test are dropped.
What is traffic shaping?
One of the main causes of congestion is that traffic is often busy. If hosts could be made to transmit at a uniform rate, congestion would be less common. Another open loop method to help manage congestion is forcing the packet to be transmitted at a more predictable rate. This is called traffic shaping.
What is multicast routing?
Sending a message to a group is called multicasting, and its routing algorithm is called multicast routing.
What is region?
When hierarchical routing is used, the routers are divided into what we will call regions, with each router knowing all the details about how to route packets to destinations within its own region, but knowing nothing about the internal structure of other regions.
What is silly window syndrome?
It is a problem that can ruin TCP performance. This problem occurs when data are passed to the sending TCP entity in large blocks, but an interactive application on the receiving side reads 1 byte at a time.
What are Digrams and Trigrams?
The most common two letter combinations are called as digrams. e.g. th, in, er, re and an. The most common three letter combinations are called as trigrams. e.g. the, ing, and, and ion.
Expand IDEA.
IDEA stands for International Data Encryption Algorithm.
What is wide-mouth frog?
Wide-mouth frog is the simplest known key distribution center (KDC) authentication protocol.
What is Mail Gateway?
It is a system that performs a protocol translation between different electronic mail delivery protocols.
What is IGP (Interior Gateway Protocol)?
It is any routing protocol used within an autonomous system.
What is EGP (Exterior Gateway Protocol)?
It is the protocol the routers in neighboring autonomous systems use to identify the set of networks that can be reached within or via each autonomous system.
What is autonomous system?
It is a collection of routers under the control of a single administrative authority and that uses a common Interior Gateway Protocol.
What is BGP (Border Gateway Protocol)?
It is a protocol used to advertise the set of networks that can be reached with in an autonomous system. BGP enables this information to be shared with the autonomous system. This is newer than EGP (Exterior Gateway Protocol).
What is Gateway-to-Gateway protocol?
It is a protocol formerly used to exchange routing information between Internet core routers.
What is NVT (Network Virtual Terminal)?
It is a set of rules defining a very simple virtual terminal interaction. The NVT is used in the start of a Telnet session.
What is a Multi-homed Host?
It is a host that has a multiple network interfaces and that requires multiple IP addresses is called as a Multi-homed Host.
What is Kerberos?
It is an authentication service developed at the Massachusetts Institute of Technology. Kerberos uses encryption to prevent intruders from discovering passwords and gaining unauthorized access to files.
What is OSPF?
It is an Internet routing protocol that scales well, can route traffic along multiple paths, and uses knowledge of an Internet's topology to make accurate routing decisions.
What is Proxy ARP?
It is using a router to answer ARP requests. This will be done when the originating host believes that a destination is local, when in fact is lies beyond router.
What is SLIP (Serial Line Interface Protocol)?
It is a very simple protocol used for transmission of IP datagrams across a serial line.
What is RIP (Routing Information Protocol)?
It is a simple protocol used to exchange information between the routers.
What is source route?
It is a sequence of IP addresses identifying the route a datagram must follow. A source route may optionally be included in an IP datagram header.
Computer Networks Interview Questions
Computer Networks Interview
1. What are 10Base2, 10Base5 and 10BaseT Ethernet LANs
10Base2—An Ethernet term meaning a maximum transfer rate of 10 Megabits per second that uses baseband
signaling, with a contiguous cable segment length of 100
meters and a maximum of 2 segments.
10Base5—An Ethernet term meaning a maximum transfer rate of 10 Megabits per second that uses baseband
signaling, with 5 continuous segments not exceeding 100
meters per segment.
10BaseT—An Ethernet term meaning a maximum transfer rate of 10 Megabits per second that uses baseband
signaling and twisted pair cabling.
2. What is the difference between an unspecified passive open and a fully specified passive open
An unspecified passive open has the server waiting for a connection request from a client. A fully specified passive
open has the server waiting for a connection from a
specific client.
3. Explain the function of Transmission Control Block
A TCB is a complex data structure that contains a considerable amount of information about each connection.
4. What is a Management Information Base (MIB)
A Management Information Base is part of every SNMP-managed device. Each SNMP agent has the MIB database that
contains information about the device's status, its
performance, connections, and configuration. The MIB is queried by SNMP.
5. What is anonymous FTP and why would you use it
Anonymous FTP enables users to connect to a host without using a valid login and password. Usually, anonymous FTP
uses a login called anonymous or guest, with the
password usually requesting the user's ID for tracking purposes only. Anonymous FTP is used to enable a large number
of users to access files on the host without having
to go to the trouble of setting up logins for them all. Anonymous FTP systems usually have strict controls over the areas
an anonymous user can access.
6. What is a pseudo tty
A pseudo tty or false terminal enables external machines to connect through Telnet or rlogin. Without a pseudo tty, no
connection can take place.
7. What is REX
What advantage does REX offer other similar utilities
8. What does the Mount protocol do
The Mount protocol returns a file handle and the name of the file system in which a requested file resides. The message
is sent to the client from the server after reception
of a client's request.
9. What is External Data Representation
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External Data Representation is a method of encoding data within an RPC message, used to ensure that the data is not
system-dependent.
10. What is the Network Time Protocol ?
11. BOOTP helps a diskless workstation boot. How does it get a message to the network looking for its IP
address and the location of its operating system boot files
BOOTP sends a UDP message with a subnetwork broadcast address and waits for a reply from a server that gives it
the IP address. The same message might contain the
name of the machine that has the boot files on it. If the boot image location is not specified, the workstation sends
another UDP message to query the server.
12. What is a DNS resource record
A resource record is an entry in a name server's database. There are several types of resource records used, including
name-to-address resolution information. Resource
records are maintained as ASCII files.
13. What protocol is used by DNS name servers
DNS uses UDP for communication between servers. It is a better choice than TCP because of the improved speed a
connectionless protocol offers. Of course,
transmission reliability suffers with UDP.
14. What is the difference between interior and exterior neighbor gateways
Interior gateways connect LANs of one organization, whereas exterior gateways connect the organization to the outside
world.
15. What is the HELLO protocol used for
The HELLO protocol uses time instead of distance to determine optimal routing. It is an alternative to the Routing
Information Protocol.
16. What are the advantages and disadvantages of the three types of routing tables
The three types of routing tables are fixed, dynamic, and fixed central. The fixed table must be manually modified every
time there is a change. A dynamic table changes its
information based on network traffic, reducing the amount of manual maintenance. A fixed central table lets a manager
modify only one table, which is then read by other
devices. The fixed central table reduces the need to update each machine's table, as with the fixed table. Usually a
dynamic table causes the fewest problems for a network
administrator, although the table's contents can change without the administrator being aware of the change.
17. What is a TCP connection table
18. What is source route
It is a sequence of IP addresses identifying the route a datagram must follow. A source route may
optionally be included in an IP datagram header.
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19. What is RIP (Routing Information Protocol)
It is a simple protocol used to exchange information between the routers.
20. What is SLIP (Serial Line Interface Protocol)
It is a very simple protocol used for transmission of IP datagrams across a serial line.
21. What is Proxy ARP
It is using a router to answer ARP requests. This will be done when the originating host believes that a destination is
local, when in fact is lies beyond router.
22. What is OSPF
It is an Internet routing protocol that scales well, can route traffic along multiple paths, and uses knowledge of an
Internet's topology to make accurate routing decisions.
23. What is Kerberos
It is an authentication service developed at the Massachusetts Institute of Technology. Kerberos uses encryption to
prevent intruders from discovering passwords and
gaining unauthorized access to files.
24. What is a Multi-homed Host
It is a host that has a multiple network interfaces and that requires multiple IP addresses is called as a Multi-homed
Host.
25. What is NVT (Network Virtual Terminal)
It is a set of rules defining a very simple virtual terminal interaction. The NVT is used in the start of a Telnet session.
26. What is Gateway-to-Gateway protocol
It is a protocol formerly used to exchange routing information between Internet core routers.
27. What is BGP (Border Gateway Protocol)
It is a protocol used to advertise the set of networks that can be reached with in an autonomous system. BGP enables
this information to be shared with the autonomous
system. This is newer than EGP (Exterior Gateway Protocol).
28. What is autonomous system
It is a collection of routers under the control of a single administrative authority and that uses a common Interior
Gateway Protocol.
29. What is EGP (Exterior Gateway Protocol)
It is the protocol the routers in neighboring autonomous systems use to identify the set of networks that can be reached
within or via each autonomous system.
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30. What is IGP (Interior Gateway Protocol)
It is any routing protocol used within an autonomous system.
31. What is Mail Gateway
It is a system that performs a protocol translation between different electronic mail delivery protocols.
32. What is wide-mouth frog
Wide-mouth frog is the simplest known key distribution center (KDC) authentication protocol.
33. What are Digrams and Trigrams
The most common two letter combinations are called as digrams. e.g. th, in, er, re and an. The most common three
letter combinations are called as trigrams. e.g. the, ing,
and, and ion.
34. What is silly window syndrome
It is a problem that can ruin TCP performance. This problem occurs when data are passed to the sending TCP entity in
large blocks, but an interactive application on the
receiving side reads 1 byte at a time.
35. What is region
When hierarchical routing is used, the routers are divided into what we call regions, with each router knowing all the
details about how to route packets to destinations
within its own region, but knowing nothing about the internal structure of other regions.
36. What is multicast routing
Sending a message to a group is called multicasting, and its routing algorithm is called multicast routing.
37. What is traffic shaping
One of the main causes of congestion is that traffic is often busy. If hosts could be made to transmit at a uniform rate,
congestion would be less common. Another open loop
method to help manage congestion is forcing the packet to be transmitted at a more predictable rate. This is called
traffic shaping.
38. What is packet filter
Packet filter is a standard router equipped with some extra functionality. The extra functionality allows every incoming or
outgoing packet to be inspected. Packets meeting
some criterion are forwarded normally. Those that fail the test are dropped.
39. What is virtual path
Along any transmission path from a given source to a given destination, a group of virtual circuits can be grouped
together into what is called path.
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40. What is virtual channel
Virtual channel is normally a connection from one source to one destination, although multicast connections are also
permitted. The other name for virtual channel is virtual
circuit.
41. What is logical link control
One of two sublayers of the data link layer of OSI reference model, as defined by the IEEE 802 standard. This sublayer
is responsible for maintaining the link between
computers when they are sending data across the physical network connection.
42. Why should you care about the OSI Reference Model
It provides a framework for discussing network operations and design.
43. What is the difference between routable and non- routable protocols
Routable protocols can work with a router and can be used to build large networks. Non-Routable protocols are
designed to work on small, local networks and cannot be
used with a router
44. What is MAU
In token Ring , hub is called Multistation Access Unit(MAU).
45. Explain 5-4-3 rule
In a Ethernet network, between any two points on the network, there can be no more than five network segments or four
repeaters, and of those five segments only three of
segments can be populated.
46. What is the difference between TFTP and FTP application layer protocols
The Trivial File Transfer Protocol (TFTP) allows a local host to obtain files from a remote host but does not provide
reliability or security. It uses the fundamental packet
delivery services offered by UDP.
The File Transfer Protocol (FTP) is the standard mechanism provided by TCP / IP for copying a file from one host to
another. It uses the services offered by TCP and so is
reliable and secure. It establishes two connections (virtual circuits) between the hosts, one for data transfer and another
for control information.
47. What is the range of addresses in the classes of internet addresses
Class A 0.0.0.0 - 127.255.255.255
Class B 128.0.0.0 - 191.255.255.255
Class C 192.0.0.0 - 223.255.255.255
Class D 224.0.0.0 - 239.255.255.255
Class E 240.0.0.0 - 247.255.255.255
48. What is the minimum and maximum length of the header in the TCP segment and IP datagram
The header should have a minimum length of 20 bytes and can have a maximum length of 60 bytes.
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49. What is difference between ARP and RARP
The address resolution protocol (ARP) is used to associate the 32 bit IP address with the 48 bit physical address, used
by a host or a router to find the physical address of
another host on its network by sending a ARP query packet that includes the IP address of the receiver.
The reverse address resolution protocol (RARP) allows a host to discover its Internet address when it knows only its
physical address.
50. What is ICMP
ICMP is Internet Control Message Protocol, a network layer protocol of the TCP/IP suite used by hosts and gateways to
send notification of datagram problems back to the
sender. It uses the echo test / reply to test whether a destination is reachable and responding. It also handles both
control and error messages.
51. What are the data units at different layers of the TCP / IP protocol suite
The data unit created at the application layer is called a message, at the transport layer the data unit created is called
either a segment or an user datagram, at the network
layer the data unit created is called the datagram, at the data link layer the datagram is encapsulated in to a frame and
finally transmitted as signals along the transmission
media.
52. What is Project 802
It is a project started by IEEE to set standards that enable intercommunication between equipment from a variety of
manufacturers. It is a way for specifying functions of the
physical layer, the data link layer and to some extent the network layer to allow for interconnectivity of major LAN
protocols.
It consists of the following:
802.1 is an internetworking standard for compatibility of different LANs and MANs across protocols.
802.2 Logical link control (LLC) is the upper sublayer of the data link layer which is non-architecture-specific, that is
remains the same for all IEEE-defined LANs.
Media access control (MAC) is the lower sublayer of the data link layer that contains some distinct modules each
carrying proprietary information specific to the LAN product
being used. The modules are Ethernet LAN (802.3), Token ring LAN (802.4), Token bus LAN (802.5).
802.6 is distributed queue dual bus (DQDB) designed to be used in MANs.
53. What is Bandwidth
Every line has an upper limit and a lower limit on the frequency of signals it can carry. This limited range is called the
bandwidth.
54. Difference between bit rate and baud rate.
Bit rate is the number of bits transmitted during one second whereas baud rate refers to the number of signal units per
second that are required to represent
those bits.
baud rate = bit rate / N
where N is no-of-bits represented by each signal shift.
55. What is MAC address
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The address for a device as it is identified at the Media Access Control (MAC) layer in the network architecture. MAC
address is usually stored in ROM on the network
adapter card and is unique.
56. What is attenuation
The degeneration of a signal over distance on a network cable is called attenuation.
57. What is cladding
A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.
58. What is RAID
A method for providing fault tolerance by using multiple hard disk drives.
59. What is NETBIOS and NETBEUI
NETBIOS is a programming interface that allows I/O requests to be sent to and received from a remote computer and it
hides the networking hardware from applications.
NETBEUI is NetBIOS extended user interface. A transport protocol designed by microsoft and IBM for the use on small
subnets.
60. What is redirector
Redirector is software that intercepts file or prints I/O requests and translates them into network requests. This comes
under presentation layer.
61. What is Beaconing
The process that allows a network to self-repair networks problems. The stations on the network notify the other
stations on the ring when they are not receiving the
transmissions. Beaconing is used in Token ring and FDDI networks.
62. What is terminal emulation, in which layer it comes
Telnet is also called as terminal emulation. It belongs to application layer.
63. What is frame relay, in which layer it comes
Frame relay is a packet switching technology. It will operate in the data link layer.
64. What do you meant by "triple X" in Networks
The function of PAD (Packet Assembler Disassembler) is described in a document known as X.3. The standard protocol
has been defined between the terminal and the
PAD, called X.28; another standard protocol exists between hte PAD and the network, called X.29. Together, these
three recommendations are often called "triple X"
65. What is SAP
Series of interface points that allow other computers to communicate with the other layers of network protocol stack.
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66. What is subnet
A generic term for section of a large networks usually separated by a bridge or router.
67. What is Brouter
Hybrid devices that combine the features of both bridges and routers.
68. How Gateway is different from Routers
A gateway operates at the upper levels of the OSI model and translates information between two completely different
network architectures or data formats.
69. What are the different type of networking / internetworking devices
Repeater:
Also called a regenerator, it is an electronic device that operates only at physical layer. It receives the signal in the
network before it becomes weak, regenerates the original
bit pattern and puts the refreshed copy back in to the link.
Bridges:
These operate both in the physical and data link layers of LANs of same type. They divide a larger network in to smaller
segments. They contain logic that allow them to
keep the traffic for each segment separate and thus are repeaters that relay a frame only the side of the segment
containing the intended recipent and control congestion.
Routers:
They relay packets among multiple interconnected networks (i.e. LANs of different type). They operate in the physical,
data link and network layers. They contain software
that enable them to determine which of the several possible paths is the best for a particular transmission.
Gateways:
They relay packets among networks that have different protocols (e.g. between a LAN and a WAN). They accept a
packet formatted for one protocol and convert it to a
packet formatted for another protocol before forwarding it. They operate in all seven layers of the OSI model.
70. What is mesh network
A network in which there are multiple network links between computers to provide multiple paths for data to travel.
71. What is passive topology
When the computers on the network simply listen and receive the signal, they are referred to as passive because they
don’t amplify the signal in any way. Example for
passive topology - linear bus.
72. What are the important topologies for networks
BUS topology:
In this each computer is directly connected to primary network cable in a single line.
Advantages:
Inexpensive, easy to install, simple to understand, easy to extend.
STAR topology:
In this all computers are connected using a central hub.
Advantages:
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Can be inexpensive, easy to install and reconfigure and easy to trouble shoot physical problems.
RING topology:
In this all computers are connected in loop.
Advantages:
All computers have equal access to network media, installation can be simple, and signal does not degrade as much as
in other topologies because each computer
regenerates it.
73. What are major types of networks and explain
Server-based network
Peer-to-peer network
Peer-to-peer network, computers can act as both servers sharing resources and as clients using the resources.
Server-based networks provide centralized control of network resources and rely on server computers to provide
security and network administration
74. What is Protocol Data Unit
The data unit in the LLC level is called the protocol data unit (PDU). The PDU contains of four fields a destination
service access point (DSAP), a source service access
point (SSAP), a control field and an information field. DSAP, SSAP are addresses used by the LLC to identify the
protocol stacks on the receiving and sending machines
that are generating and using the data. The control field specifies whether the PDU frame is a information frame (I -
frame) or a supervisory frame (S - frame) or a
unnumbered frame (U - frame).
75. What is difference between baseband and broadband transmission
In a baseband transmission, the entire bandwidth of the cable is consumed by a single signal. In broadband
transmission, signals are sent on multiple frequencies, allowing
multiple signals to be sent simultaneously.
76. What are the possible ways of data exchange
(i) Simplex (ii) Half-duplex (iii) Full-duplex.
77. What are the types of Transmission media
Signals are usually transmitted over some transmission media that are broadly classified in to two categories.
Guided Media:
These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic
cable. A signal traveling along any of these media
is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that accept
and transport signals in the form of electrical
current. Optical fiber is a glass or plastic cable that accepts and transports signals in the form of light.
Unguided Media:
This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are
broadcast either through air. This is done through radio
communication, satellite communication and cellular telephony.
78. What is point-to-point protocol
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A communications protocol used to connect computers to remote networking services including Internet service
providers.
79. What are the two types of transmission technology available
(i) Broadcast and (ii) point-to-point
80. Difference between the communication and transmission.
Transmission is a physical movement of information and concern issues like bit polarity, synchronization, clock etc.
Communication means the meaning full exchange of information between two communication media.
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1. What are 10Base2, 10Base5 and 10BaseT Ethernet LANs
10Base2—An Ethernet term meaning a maximum transfer rate of 10 Megabits per second that uses baseband
signaling, with a contiguous cable segment length of 100
meters and a maximum of 2 segments.
10Base5—An Ethernet term meaning a maximum transfer rate of 10 Megabits per second that uses baseband
signaling, with 5 continuous segments not exceeding 100
meters per segment.
10BaseT—An Ethernet term meaning a maximum transfer rate of 10 Megabits per second that uses baseband
signaling and twisted pair cabling.
2. What is the difference between an unspecified passive open and a fully specified passive open
An unspecified passive open has the server waiting for a connection request from a client. A fully specified passive
open has the server waiting for a connection from a
specific client.
3. Explain the function of Transmission Control Block
A TCB is a complex data structure that contains a considerable amount of information about each connection.
4. What is a Management Information Base (MIB)
A Management Information Base is part of every SNMP-managed device. Each SNMP agent has the MIB database that
contains information about the device's status, its
performance, connections, and configuration. The MIB is queried by SNMP.
5. What is anonymous FTP and why would you use it
Anonymous FTP enables users to connect to a host without using a valid login and password. Usually, anonymous FTP
uses a login called anonymous or guest, with the
password usually requesting the user's ID for tracking purposes only. Anonymous FTP is used to enable a large number
of users to access files on the host without having
to go to the trouble of setting up logins for them all. Anonymous FTP systems usually have strict controls over the areas
an anonymous user can access.
6. What is a pseudo tty
A pseudo tty or false terminal enables external machines to connect through Telnet or rlogin. Without a pseudo tty, no
connection can take place.
7. What is REX
What advantage does REX offer other similar utilities
8. What does the Mount protocol do
The Mount protocol returns a file handle and the name of the file system in which a requested file resides. The message
is sent to the client from the server after reception
of a client's request.
9. What is External Data Representation
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External Data Representation is a method of encoding data within an RPC message, used to ensure that the data is not
system-dependent.
10. What is the Network Time Protocol ?
11. BOOTP helps a diskless workstation boot. How does it get a message to the network looking for its IP
address and the location of its operating system boot files
BOOTP sends a UDP message with a subnetwork broadcast address and waits for a reply from a server that gives it
the IP address. The same message might contain the
name of the machine that has the boot files on it. If the boot image location is not specified, the workstation sends
another UDP message to query the server.
12. What is a DNS resource record
A resource record is an entry in a name server's database. There are several types of resource records used, including
name-to-address resolution information. Resource
records are maintained as ASCII files.
13. What protocol is used by DNS name servers
DNS uses UDP for communication between servers. It is a better choice than TCP because of the improved speed a
connectionless protocol offers. Of course,
transmission reliability suffers with UDP.
14. What is the difference between interior and exterior neighbor gateways
Interior gateways connect LANs of one organization, whereas exterior gateways connect the organization to the outside
world.
15. What is the HELLO protocol used for
The HELLO protocol uses time instead of distance to determine optimal routing. It is an alternative to the Routing
Information Protocol.
16. What are the advantages and disadvantages of the three types of routing tables
The three types of routing tables are fixed, dynamic, and fixed central. The fixed table must be manually modified every
time there is a change. A dynamic table changes its
information based on network traffic, reducing the amount of manual maintenance. A fixed central table lets a manager
modify only one table, which is then read by other
devices. The fixed central table reduces the need to update each machine's table, as with the fixed table. Usually a
dynamic table causes the fewest problems for a network
administrator, although the table's contents can change without the administrator being aware of the change.
17. What is a TCP connection table
18. What is source route
It is a sequence of IP addresses identifying the route a datagram must follow. A source route may
optionally be included in an IP datagram header.
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19. What is RIP (Routing Information Protocol)
It is a simple protocol used to exchange information between the routers.
20. What is SLIP (Serial Line Interface Protocol)
It is a very simple protocol used for transmission of IP datagrams across a serial line.
21. What is Proxy ARP
It is using a router to answer ARP requests. This will be done when the originating host believes that a destination is
local, when in fact is lies beyond router.
22. What is OSPF
It is an Internet routing protocol that scales well, can route traffic along multiple paths, and uses knowledge of an
Internet's topology to make accurate routing decisions.
23. What is Kerberos
It is an authentication service developed at the Massachusetts Institute of Technology. Kerberos uses encryption to
prevent intruders from discovering passwords and
gaining unauthorized access to files.
24. What is a Multi-homed Host
It is a host that has a multiple network interfaces and that requires multiple IP addresses is called as a Multi-homed
Host.
25. What is NVT (Network Virtual Terminal)
It is a set of rules defining a very simple virtual terminal interaction. The NVT is used in the start of a Telnet session.
26. What is Gateway-to-Gateway protocol
It is a protocol formerly used to exchange routing information between Internet core routers.
27. What is BGP (Border Gateway Protocol)
It is a protocol used to advertise the set of networks that can be reached with in an autonomous system. BGP enables
this information to be shared with the autonomous
system. This is newer than EGP (Exterior Gateway Protocol).
28. What is autonomous system
It is a collection of routers under the control of a single administrative authority and that uses a common Interior
Gateway Protocol.
29. What is EGP (Exterior Gateway Protocol)
It is the protocol the routers in neighboring autonomous systems use to identify the set of networks that can be reached
within or via each autonomous system.
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30. What is IGP (Interior Gateway Protocol)
It is any routing protocol used within an autonomous system.
31. What is Mail Gateway
It is a system that performs a protocol translation between different electronic mail delivery protocols.
32. What is wide-mouth frog
Wide-mouth frog is the simplest known key distribution center (KDC) authentication protocol.
33. What are Digrams and Trigrams
The most common two letter combinations are called as digrams. e.g. th, in, er, re and an. The most common three
letter combinations are called as trigrams. e.g. the, ing,
and, and ion.
34. What is silly window syndrome
It is a problem that can ruin TCP performance. This problem occurs when data are passed to the sending TCP entity in
large blocks, but an interactive application on the
receiving side reads 1 byte at a time.
35. What is region
When hierarchical routing is used, the routers are divided into what we call regions, with each router knowing all the
details about how to route packets to destinations
within its own region, but knowing nothing about the internal structure of other regions.
36. What is multicast routing
Sending a message to a group is called multicasting, and its routing algorithm is called multicast routing.
37. What is traffic shaping
One of the main causes of congestion is that traffic is often busy. If hosts could be made to transmit at a uniform rate,
congestion would be less common. Another open loop
method to help manage congestion is forcing the packet to be transmitted at a more predictable rate. This is called
traffic shaping.
38. What is packet filter
Packet filter is a standard router equipped with some extra functionality. The extra functionality allows every incoming or
outgoing packet to be inspected. Packets meeting
some criterion are forwarded normally. Those that fail the test are dropped.
39. What is virtual path
Along any transmission path from a given source to a given destination, a group of virtual circuits can be grouped
together into what is called path.
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40. What is virtual channel
Virtual channel is normally a connection from one source to one destination, although multicast connections are also
permitted. The other name for virtual channel is virtual
circuit.
41. What is logical link control
One of two sublayers of the data link layer of OSI reference model, as defined by the IEEE 802 standard. This sublayer
is responsible for maintaining the link between
computers when they are sending data across the physical network connection.
42. Why should you care about the OSI Reference Model
It provides a framework for discussing network operations and design.
43. What is the difference between routable and non- routable protocols
Routable protocols can work with a router and can be used to build large networks. Non-Routable protocols are
designed to work on small, local networks and cannot be
used with a router
44. What is MAU
In token Ring , hub is called Multistation Access Unit(MAU).
45. Explain 5-4-3 rule
In a Ethernet network, between any two points on the network, there can be no more than five network segments or four
repeaters, and of those five segments only three of
segments can be populated.
46. What is the difference between TFTP and FTP application layer protocols
The Trivial File Transfer Protocol (TFTP) allows a local host to obtain files from a remote host but does not provide
reliability or security. It uses the fundamental packet
delivery services offered by UDP.
The File Transfer Protocol (FTP) is the standard mechanism provided by TCP / IP for copying a file from one host to
another. It uses the services offered by TCP and so is
reliable and secure. It establishes two connections (virtual circuits) between the hosts, one for data transfer and another
for control information.
47. What is the range of addresses in the classes of internet addresses
Class A 0.0.0.0 - 127.255.255.255
Class B 128.0.0.0 - 191.255.255.255
Class C 192.0.0.0 - 223.255.255.255
Class D 224.0.0.0 - 239.255.255.255
Class E 240.0.0.0 - 247.255.255.255
48. What is the minimum and maximum length of the header in the TCP segment and IP datagram
The header should have a minimum length of 20 bytes and can have a maximum length of 60 bytes.
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49. What is difference between ARP and RARP
The address resolution protocol (ARP) is used to associate the 32 bit IP address with the 48 bit physical address, used
by a host or a router to find the physical address of
another host on its network by sending a ARP query packet that includes the IP address of the receiver.
The reverse address resolution protocol (RARP) allows a host to discover its Internet address when it knows only its
physical address.
50. What is ICMP
ICMP is Internet Control Message Protocol, a network layer protocol of the TCP/IP suite used by hosts and gateways to
send notification of datagram problems back to the
sender. It uses the echo test / reply to test whether a destination is reachable and responding. It also handles both
control and error messages.
51. What are the data units at different layers of the TCP / IP protocol suite
The data unit created at the application layer is called a message, at the transport layer the data unit created is called
either a segment or an user datagram, at the network
layer the data unit created is called the datagram, at the data link layer the datagram is encapsulated in to a frame and
finally transmitted as signals along the transmission
media.
52. What is Project 802
It is a project started by IEEE to set standards that enable intercommunication between equipment from a variety of
manufacturers. It is a way for specifying functions of the
physical layer, the data link layer and to some extent the network layer to allow for interconnectivity of major LAN
protocols.
It consists of the following:
802.1 is an internetworking standard for compatibility of different LANs and MANs across protocols.
802.2 Logical link control (LLC) is the upper sublayer of the data link layer which is non-architecture-specific, that is
remains the same for all IEEE-defined LANs.
Media access control (MAC) is the lower sublayer of the data link layer that contains some distinct modules each
carrying proprietary information specific to the LAN product
being used. The modules are Ethernet LAN (802.3), Token ring LAN (802.4), Token bus LAN (802.5).
802.6 is distributed queue dual bus (DQDB) designed to be used in MANs.
53. What is Bandwidth
Every line has an upper limit and a lower limit on the frequency of signals it can carry. This limited range is called the
bandwidth.
54. Difference between bit rate and baud rate.
Bit rate is the number of bits transmitted during one second whereas baud rate refers to the number of signal units per
second that are required to represent
those bits.
baud rate = bit rate / N
where N is no-of-bits represented by each signal shift.
55. What is MAC address
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The address for a device as it is identified at the Media Access Control (MAC) layer in the network architecture. MAC
address is usually stored in ROM on the network
adapter card and is unique.
56. What is attenuation
The degeneration of a signal over distance on a network cable is called attenuation.
57. What is cladding
A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.
58. What is RAID
A method for providing fault tolerance by using multiple hard disk drives.
59. What is NETBIOS and NETBEUI
NETBIOS is a programming interface that allows I/O requests to be sent to and received from a remote computer and it
hides the networking hardware from applications.
NETBEUI is NetBIOS extended user interface. A transport protocol designed by microsoft and IBM for the use on small
subnets.
60. What is redirector
Redirector is software that intercepts file or prints I/O requests and translates them into network requests. This comes
under presentation layer.
61. What is Beaconing
The process that allows a network to self-repair networks problems. The stations on the network notify the other
stations on the ring when they are not receiving the
transmissions. Beaconing is used in Token ring and FDDI networks.
62. What is terminal emulation, in which layer it comes
Telnet is also called as terminal emulation. It belongs to application layer.
63. What is frame relay, in which layer it comes
Frame relay is a packet switching technology. It will operate in the data link layer.
64. What do you meant by "triple X" in Networks
The function of PAD (Packet Assembler Disassembler) is described in a document known as X.3. The standard protocol
has been defined between the terminal and the
PAD, called X.28; another standard protocol exists between hte PAD and the network, called X.29. Together, these
three recommendations are often called "triple X"
65. What is SAP
Series of interface points that allow other computers to communicate with the other layers of network protocol stack.
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66. What is subnet
A generic term for section of a large networks usually separated by a bridge or router.
67. What is Brouter
Hybrid devices that combine the features of both bridges and routers.
68. How Gateway is different from Routers
A gateway operates at the upper levels of the OSI model and translates information between two completely different
network architectures or data formats.
69. What are the different type of networking / internetworking devices
Repeater:
Also called a regenerator, it is an electronic device that operates only at physical layer. It receives the signal in the
network before it becomes weak, regenerates the original
bit pattern and puts the refreshed copy back in to the link.
Bridges:
These operate both in the physical and data link layers of LANs of same type. They divide a larger network in to smaller
segments. They contain logic that allow them to
keep the traffic for each segment separate and thus are repeaters that relay a frame only the side of the segment
containing the intended recipent and control congestion.
Routers:
They relay packets among multiple interconnected networks (i.e. LANs of different type). They operate in the physical,
data link and network layers. They contain software
that enable them to determine which of the several possible paths is the best for a particular transmission.
Gateways:
They relay packets among networks that have different protocols (e.g. between a LAN and a WAN). They accept a
packet formatted for one protocol and convert it to a
packet formatted for another protocol before forwarding it. They operate in all seven layers of the OSI model.
70. What is mesh network
A network in which there are multiple network links between computers to provide multiple paths for data to travel.
71. What is passive topology
When the computers on the network simply listen and receive the signal, they are referred to as passive because they
don’t amplify the signal in any way. Example for
passive topology - linear bus.
72. What are the important topologies for networks
BUS topology:
In this each computer is directly connected to primary network cable in a single line.
Advantages:
Inexpensive, easy to install, simple to understand, easy to extend.
STAR topology:
In this all computers are connected using a central hub.
Advantages:
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Can be inexpensive, easy to install and reconfigure and easy to trouble shoot physical problems.
RING topology:
In this all computers are connected in loop.
Advantages:
All computers have equal access to network media, installation can be simple, and signal does not degrade as much as
in other topologies because each computer
regenerates it.
73. What are major types of networks and explain
Server-based network
Peer-to-peer network
Peer-to-peer network, computers can act as both servers sharing resources and as clients using the resources.
Server-based networks provide centralized control of network resources and rely on server computers to provide
security and network administration
74. What is Protocol Data Unit
The data unit in the LLC level is called the protocol data unit (PDU). The PDU contains of four fields a destination
service access point (DSAP), a source service access
point (SSAP), a control field and an information field. DSAP, SSAP are addresses used by the LLC to identify the
protocol stacks on the receiving and sending machines
that are generating and using the data. The control field specifies whether the PDU frame is a information frame (I -
frame) or a supervisory frame (S - frame) or a
unnumbered frame (U - frame).
75. What is difference between baseband and broadband transmission
In a baseband transmission, the entire bandwidth of the cable is consumed by a single signal. In broadband
transmission, signals are sent on multiple frequencies, allowing
multiple signals to be sent simultaneously.
76. What are the possible ways of data exchange
(i) Simplex (ii) Half-duplex (iii) Full-duplex.
77. What are the types of Transmission media
Signals are usually transmitted over some transmission media that are broadly classified in to two categories.
Guided Media:
These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic
cable. A signal traveling along any of these media
is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that accept
and transport signals in the form of electrical
current. Optical fiber is a glass or plastic cable that accepts and transports signals in the form of light.
Unguided Media:
This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are
broadcast either through air. This is done through radio
communication, satellite communication and cellular telephony.
78. What is point-to-point protocol
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A communications protocol used to connect computers to remote networking services including Internet service
providers.
79. What are the two types of transmission technology available
(i) Broadcast and (ii) point-to-point
80. Difference between the communication and transmission.
Transmission is a physical movement of information and concern issues like bit polarity, synchronization, clock etc.
Communication means the meaning full exchange of information between two communication media.
Computer Networks Interview Questions
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FREE Bonus #1 – 500+ Technical Interview Questions with Answers
There are 175 Pages in this eBook which contains the questions on the following streams
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• Data Structures
• C
• C++/OOPS
• Quantitative Aptitude
• UNIX
• RDBMS
• SQL
• Computer Networks
• Operating Systems.
Download URL : www.bestebooksworld.com/digital/
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Password : t@ch@b00k
This is a limited time access to download the eBook, so make sure you
download the eBook before the password gets expired.
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Password : vyom
Networking concepts
What are the two types of transmission technology available?
(i) Broadcast and (ii) point-to-point
What is subnet?
A generic term for section of a large networks usually separated by a bridge or router.
Difference between the communication and transmission.
Transmission is a physical movement of information and concern issues like bit polarity, synchronisation, clock etc.
Communication means the meaning full exchange of information between two communication media.
What are the possible ways of data exchange?
(i) Simplex (ii) Half-duplex (iii) Full-duplex.
What is SAP?
Series of interface points that allow other computers to communicate with the other layers of network protocol stack.
What do you meant by "triple X" in Networks?
The function of PAD (Packet Assembler Disassembler) is described in a document known as X.3. The standard protocol has been defined between the terminal and the PAD, called X.28; another standard protocol exists between hte PAD and the network, called X.29. Together, these three recommendations are often called "triple X"
What is frame relay, in which layer it comes?
Frame relay is a packet switching technology. It will operate in the data link layer.
What is terminal emulation, in which layer it comes?
Telnet is also called as terminal emulation. It belongs to application layer.
What is Beaconing?
The process that allows a network to self-repair networks problems. The stations on the network notify the other stations on the ring when they are not receiving the transmissions. Beaconing is used in Token ring and FDDI networks.
What is redirector?
Redirector is software that intercepts file or prints I/O requests and translates them into network requests. This comes under presentation layer.
What is NETBIOS and NETBEUI?
NETBIOS is a programming interface that allows I/O requests to be sent to and received from a remote computer and it hides the networking hardware from applications.
NETBEUI is NetBIOS extended user interface. A transport protocol designed by microsoft and IBM for the use on small subnets.
What is RAID?
A method for providing fault tolerance by using multiple hard disk drives.
What is passive topology?
When the computers on the network simply listen and receive the signal, they are referred to as passive because they don’t amplify the signal in any way. Example for passive topology - linear bus.
What is Brouter?
Hybrid devices that combine the features of both bridges and routers.
What is cladding?
A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.
What is point-to-point protocol
A communications protocol used to connect computers to remote networking services including Internet service providers.
How Gateway is different from Routers?
A gateway operates at the upper levels of the OSI model and translates information between two completely different network architectures or data formats
What is attenuation?
The degeneration of a signal over distance on a network cable is called attenuation.
What is MAC address?
The address for a device as it is identified at the Media Access Control (MAC) layer in the network architecture. MAC address is usually stored in ROM on the network adapter card and is unique.
Difference between bit rate and baud rate.
Bit rate is the number of bits transmitted during one second whereas baud rate refers to the number of signal units per second that are required to represent those bits.
baud rate = bit rate / N
where N is no-of-bits represented by each signal shift.
What is Bandwidth?
Every line has an upper limit and a lower limit on the frequency of signals it can carry. This limited range is called the bandwidth.
What are the types of Transmission media?
Signals are usually transmitted over some transmission media that are broadly classified in to two categories.
Guided Media:
These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that accept and transport signals in the form of electrical current. Optical fiber is a glass or plastic cable that accepts and transports signals in the form of light.
b) Unguided Media:
This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are broadcast either through air. This is done through radio communication, satellite communication and cellular telephony.
What is Project 802?
It is a project started by IEEE to set standards to enable intercommunication between equipment from a variety of manufacturers. It is a way for specifying functions of the physical layer, the data link layer and to some extent the network layer to allow for interconnectivity of major LAN
protocols.
It consists of the following:
802.1 is an internetworking standard for compatibility of different LANs and MANs across protocols.
802.2 Logical link control (LLC) is the upper sublayer of the data link layer which is non-architecture-specific, that is remains the same for all IEEE-defined LANs.
Media access control (MAC) is the lower sublayer of the data link layer that contains some distinct modules each carrying proprietary information specific to the LAN product being used. The modules are Ethernet LAN (802.3), Token ring LAN (802.4), Token bus LAN (802.5).
802.6 is distributed queue dual bus (DQDB) designed to be used in MANs.
What is Protocol Data Unit?
The data unit in the LLC level is called the protocol data unit (PDU). The PDU contains of four fields a destination service access point (DSAP), a source service access point (SSAP), a control field and an information field. DSAP, SSAP are addresses used by the LLC to identify the protocol stacks on the receiving and sending machines that are generating and using the data. The control field specifies whether the PDU frame is a information frame (I - frame) or a supervisory frame (S - frame) or a unnumbered frame (U - frame).
What are the different type of networking / internetworking devices?
Repeater:
Also called a regenerator, it is an electronic device that operates only at physical layer. It receives the signal in the network before it becomes weak, regenerates the original bit pattern and puts the refreshed copy back in to the link.
Bridges:
These operate both in the physical and data link layers of LANs of same type. They divide a larger network in to smaller segments. They contain logic that allow them to keep the traffic for each segment separate and thus are repeaters that relay a frame only the side of the segment containing the intended recipent and control congestion.
Routers:
They relay packets among multiple interconnected networks (i.e. LANs of different type). They operate in the physical, data link and network layers. They contain software that enable them to determine which of the several possible paths is the best for a particular transmission.
Gateways:
They relay packets among networks that have different protocols (e.g. between a LAN and a WAN). They accept a packet formatted for one protocol and convert it to a packet formatted for another protocol before forwarding it. They operate in all seven layers of the OSI model.
What is ICMP?
ICMP is Internet Control Message Protocol, a network layer protocol of the TCP/IP suite used by hosts and gateways to send notification of datagram problems back to the sender. It uses the echo test / reply to test whether a destination is reachable and responding. It also handles both control and error messages.
What are the data units at different layers of the TCP / IP protocol suite?
The data unit created at the application layer is called a message, at the transport layer the data unit created is called either a segment or an user datagram, at the network layer the data unit created is called the datagram, at the data link layer the datagram is encapsulated in to a frame and finally transmitted as signals along the transmission media.
What is difference between ARP and RARP?
The address resolution protocol (ARP) is used to associate the 32 bit IP address with the 48 bit physical address, used by a host or a router to find the physical address of another host on its network by sending a ARP query packet that includes the IP address of the receiver.
The reverse address resolution protocol (RARP) allows a host to discover its Internet address when it knows only its physical address.
What is the minimum and maximum length of the header in the TCP segment and IP datagram?
The header should have a minimum length of 20 bytes and can have a maximum length of 60 bytes.
What is the range of addresses in the classes of internet addresses?
Class A 0.0.0.0 - 127.255.255.255
Class B 128.0.0.0 - 191.255.255.255
Class C 192.0.0.0 - 223.255.255.255
Class D 224.0.0.0 - 239.255.255.255
Class E 240.0.0.0 - 247.255.255.255
What is the difference between TFTP and FTP application layer protocols?
The Trivial File Transfer Protocol (TFTP) allows a local host to obtain files from a remote host but does not provide reliability or security. It uses the fundamental packet delivery services offered by UDP.
The File Transfer Protocol (FTP) is the standard mechanism provided by TCP / IP for copying a file from one host to another. It uses the services offer by TCP and so is reliable and secure. It establishes two connections (virtual circuits) between the hosts, one for data transfer and another for control information.
What are major types of networks and explain?
Server-based network
Peer-to-peer network
Peer-to-peer network, computers can act as both servers sharing resources and as clients using the resources.
Server-based networks provide centralized control of network resources and rely on server computers to provide security and network administration
What are the important topologies for networks?
BUS topology:
In this each computer is directly connected to primary network cable in a single line.
Advantages:
Inexpensive, easy to install, simple to understand, easy to extend.
STAR topology:
In this all computers are connected using a central hub.
Advantages:
Can be inexpensive, easy to install and reconfigure and easy to trouble shoot physical problems.
RING topology:
In this all computers are connected in loop.
Advantages:
All computers have equal access to network media, installation can be simple, and signal does not degrade as much as in other topologies because each computer regenerates it.
What is mesh network?
A network in which there are multiple network links between computers to provide multiple paths for data to travel.
What is difference between baseband and broadband transmission?
In a baseband transmission, the entire bandwidth of the cable is consumed by a single signal. In broadband transmission, signals are sent on multiple frequencies, allowing multiple signals to be sent simultaneously.
Explain 5-4-3 rule?
In a Ethernet network, between any two points on the network ,there can be no more than five network segments or four repeaters, and of those five segments only three of segments can be populated.
What MAU?
In token Ring , hub is called Multistation Access Unit(MAU).
What is the difference between routable and non- routable protocols?
Routable protocols can work with a router and can be used to build large networks. Non-Routable protocols are designed to work on small, local networks and cannot be used with a router
Why should you care about the OSI Reference Model?
It provides a framework for discussing network operations and design.
What is logical link control?
One of two sublayers of the data link layer of OSI reference model, as defined by the IEEE 802 standard. This sublayer is responsible for maintaining the link between computers when they are sending data across the physical network connection.
What is virtual channel?
Virtual channel is normally a connection from one source to one destination, although multicast connections are also permitted. The other name for virtual channel is virtual circuit.
What is virtual path?
Along any transmission path from a given source to a given destination, a group of virtual circuits can be grouped together into what is called path.
What is packet filter?
Packet filter is a standard router equipped with some extra functionality. The extra functionality allows every incoming or outgoing packet to be inspected. Packets meeting some criterion are forwarded normally. Those that fail the test are dropped.
What is traffic shaping?
One of the main causes of congestion is that traffic is often busy. If hosts could be made to transmit at a uniform rate, congestion would be less common. Another open loop method to help manage congestion is forcing the packet to be transmitted at a more predictable rate. This is called traffic shaping.
What is multicast routing?
Sending a message to a group is called multicasting, and its routing algorithm is called multicast routing.
What is region?
When hierarchical routing is used, the routers are divided into what we will call regions, with each router knowing all the details about how to route packets to destinations within its own region, but knowing nothing about the internal structure of other regions.
What is silly window syndrome?
It is a problem that can ruin TCP performance. This problem occurs when data are passed to the sending TCP entity in large blocks, but an interactive application on the receiving side reads 1 byte at a time.
What are Digrams and Trigrams?
The most common two letter combinations are called as digrams. e.g. th, in, er, re and an. The most common three letter combinations are called as trigrams. e.g. the, ing, and, and ion.
Expand IDEA.
IDEA stands for International Data Encryption Algorithm.
What is wide-mouth frog?
Wide-mouth frog is the simplest known key distribution center (KDC) authentication protocol.
What is Mail Gateway?
It is a system that performs a protocol translation between different electronic mail delivery protocols.
What is IGP (Interior Gateway Protocol)?
It is any routing protocol used within an autonomous system.
What is EGP (Exterior Gateway Protocol)?
It is the protocol the routers in neighboring autonomous systems use to identify the set of networks that can be reached within or via each autonomous system.
What is autonomous system?
It is a collection of routers under the control of a single administrative authority and that uses a common Interior Gateway Protocol.
What is BGP (Border Gateway Protocol)?
It is a protocol used to advertise the set of networks that can be reached with in an autonomous system. BGP enables this information to be shared with the autonomous system. This is newer than EGP (Exterior Gateway Protocol).
What is Gateway-to-Gateway protocol?
It is a protocol formerly used to exchange routing information between Internet core routers.
What is NVT (Network Virtual Terminal)?
It is a set of rules defining a very simple virtual terminal interaction. The NVT is used in the start of a Telnet session.
What is a Multi-homed Host?
It is a host that has a multiple network interfaces and that requires multiple IP addresses is called as a Multi-homed Host.
What is Kerberos?
It is an authentication service developed at the Massachusetts Institute of Technology. Kerberos uses encryption to prevent intruders from discovering passwords and gaining unauthorized access to files.
What is OSPF?
It is an Internet routing protocol that scales well, can route traffic along multiple paths, and uses knowledge of an Internet's topology to make accurate routing decisions.
What is Proxy ARP?
It is using a router to answer ARP requests. This will be done when the originating host believes that a destination is local, when in fact is lies beyond router.
What is SLIP (Serial Line Interface Protocol)?
It is a very simple protocol used for transmission of IP datagrams across a serial line.
What is RIP (Routing Information Protocol)?
It is a simple protocol used to exchange information between the routers.
What is source route?
It is a sequence of IP addresses identifying the route a datagram must follow. A source route may optionally be included in an IP datagram header.
(i) Broadcast and (ii) point-to-point
What is subnet?
A generic term for section of a large networks usually separated by a bridge or router.
Difference between the communication and transmission.
Transmission is a physical movement of information and concern issues like bit polarity, synchronisation, clock etc.
Communication means the meaning full exchange of information between two communication media.
What are the possible ways of data exchange?
(i) Simplex (ii) Half-duplex (iii) Full-duplex.
What is SAP?
Series of interface points that allow other computers to communicate with the other layers of network protocol stack.
What do you meant by "triple X" in Networks?
The function of PAD (Packet Assembler Disassembler) is described in a document known as X.3. The standard protocol has been defined between the terminal and the PAD, called X.28; another standard protocol exists between hte PAD and the network, called X.29. Together, these three recommendations are often called "triple X"
What is frame relay, in which layer it comes?
Frame relay is a packet switching technology. It will operate in the data link layer.
What is terminal emulation, in which layer it comes?
Telnet is also called as terminal emulation. It belongs to application layer.
What is Beaconing?
The process that allows a network to self-repair networks problems. The stations on the network notify the other stations on the ring when they are not receiving the transmissions. Beaconing is used in Token ring and FDDI networks.
What is redirector?
Redirector is software that intercepts file or prints I/O requests and translates them into network requests. This comes under presentation layer.
What is NETBIOS and NETBEUI?
NETBIOS is a programming interface that allows I/O requests to be sent to and received from a remote computer and it hides the networking hardware from applications.
NETBEUI is NetBIOS extended user interface. A transport protocol designed by microsoft and IBM for the use on small subnets.
What is RAID?
A method for providing fault tolerance by using multiple hard disk drives.
What is passive topology?
When the computers on the network simply listen and receive the signal, they are referred to as passive because they don’t amplify the signal in any way. Example for passive topology - linear bus.
What is Brouter?
Hybrid devices that combine the features of both bridges and routers.
What is cladding?
A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.
What is point-to-point protocol
A communications protocol used to connect computers to remote networking services including Internet service providers.
How Gateway is different from Routers?
A gateway operates at the upper levels of the OSI model and translates information between two completely different network architectures or data formats
What is attenuation?
The degeneration of a signal over distance on a network cable is called attenuation.
What is MAC address?
The address for a device as it is identified at the Media Access Control (MAC) layer in the network architecture. MAC address is usually stored in ROM on the network adapter card and is unique.
Difference between bit rate and baud rate.
Bit rate is the number of bits transmitted during one second whereas baud rate refers to the number of signal units per second that are required to represent those bits.
baud rate = bit rate / N
where N is no-of-bits represented by each signal shift.
What is Bandwidth?
Every line has an upper limit and a lower limit on the frequency of signals it can carry. This limited range is called the bandwidth.
What are the types of Transmission media?
Signals are usually transmitted over some transmission media that are broadly classified in to two categories.
Guided Media:
These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that accept and transport signals in the form of electrical current. Optical fiber is a glass or plastic cable that accepts and transports signals in the form of light.
b) Unguided Media:
This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are broadcast either through air. This is done through radio communication, satellite communication and cellular telephony.
What is Project 802?
It is a project started by IEEE to set standards to enable intercommunication between equipment from a variety of manufacturers. It is a way for specifying functions of the physical layer, the data link layer and to some extent the network layer to allow for interconnectivity of major LAN
protocols.
It consists of the following:
802.1 is an internetworking standard for compatibility of different LANs and MANs across protocols.
802.2 Logical link control (LLC) is the upper sublayer of the data link layer which is non-architecture-specific, that is remains the same for all IEEE-defined LANs.
Media access control (MAC) is the lower sublayer of the data link layer that contains some distinct modules each carrying proprietary information specific to the LAN product being used. The modules are Ethernet LAN (802.3), Token ring LAN (802.4), Token bus LAN (802.5).
802.6 is distributed queue dual bus (DQDB) designed to be used in MANs.
What is Protocol Data Unit?
The data unit in the LLC level is called the protocol data unit (PDU). The PDU contains of four fields a destination service access point (DSAP), a source service access point (SSAP), a control field and an information field. DSAP, SSAP are addresses used by the LLC to identify the protocol stacks on the receiving and sending machines that are generating and using the data. The control field specifies whether the PDU frame is a information frame (I - frame) or a supervisory frame (S - frame) or a unnumbered frame (U - frame).
What are the different type of networking / internetworking devices?
Repeater:
Also called a regenerator, it is an electronic device that operates only at physical layer. It receives the signal in the network before it becomes weak, regenerates the original bit pattern and puts the refreshed copy back in to the link.
Bridges:
These operate both in the physical and data link layers of LANs of same type. They divide a larger network in to smaller segments. They contain logic that allow them to keep the traffic for each segment separate and thus are repeaters that relay a frame only the side of the segment containing the intended recipent and control congestion.
Routers:
They relay packets among multiple interconnected networks (i.e. LANs of different type). They operate in the physical, data link and network layers. They contain software that enable them to determine which of the several possible paths is the best for a particular transmission.
Gateways:
They relay packets among networks that have different protocols (e.g. between a LAN and a WAN). They accept a packet formatted for one protocol and convert it to a packet formatted for another protocol before forwarding it. They operate in all seven layers of the OSI model.
What is ICMP?
ICMP is Internet Control Message Protocol, a network layer protocol of the TCP/IP suite used by hosts and gateways to send notification of datagram problems back to the sender. It uses the echo test / reply to test whether a destination is reachable and responding. It also handles both control and error messages.
What are the data units at different layers of the TCP / IP protocol suite?
The data unit created at the application layer is called a message, at the transport layer the data unit created is called either a segment or an user datagram, at the network layer the data unit created is called the datagram, at the data link layer the datagram is encapsulated in to a frame and finally transmitted as signals along the transmission media.
What is difference between ARP and RARP?
The address resolution protocol (ARP) is used to associate the 32 bit IP address with the 48 bit physical address, used by a host or a router to find the physical address of another host on its network by sending a ARP query packet that includes the IP address of the receiver.
The reverse address resolution protocol (RARP) allows a host to discover its Internet address when it knows only its physical address.
What is the minimum and maximum length of the header in the TCP segment and IP datagram?
The header should have a minimum length of 20 bytes and can have a maximum length of 60 bytes.
What is the range of addresses in the classes of internet addresses?
Class A 0.0.0.0 - 127.255.255.255
Class B 128.0.0.0 - 191.255.255.255
Class C 192.0.0.0 - 223.255.255.255
Class D 224.0.0.0 - 239.255.255.255
Class E 240.0.0.0 - 247.255.255.255
What is the difference between TFTP and FTP application layer protocols?
The Trivial File Transfer Protocol (TFTP) allows a local host to obtain files from a remote host but does not provide reliability or security. It uses the fundamental packet delivery services offered by UDP.
The File Transfer Protocol (FTP) is the standard mechanism provided by TCP / IP for copying a file from one host to another. It uses the services offer by TCP and so is reliable and secure. It establishes two connections (virtual circuits) between the hosts, one for data transfer and another for control information.
What are major types of networks and explain?
Server-based network
Peer-to-peer network
Peer-to-peer network, computers can act as both servers sharing resources and as clients using the resources.
Server-based networks provide centralized control of network resources and rely on server computers to provide security and network administration
What are the important topologies for networks?
BUS topology:
In this each computer is directly connected to primary network cable in a single line.
Advantages:
Inexpensive, easy to install, simple to understand, easy to extend.
STAR topology:
In this all computers are connected using a central hub.
Advantages:
Can be inexpensive, easy to install and reconfigure and easy to trouble shoot physical problems.
RING topology:
In this all computers are connected in loop.
Advantages:
All computers have equal access to network media, installation can be simple, and signal does not degrade as much as in other topologies because each computer regenerates it.
What is mesh network?
A network in which there are multiple network links between computers to provide multiple paths for data to travel.
What is difference between baseband and broadband transmission?
In a baseband transmission, the entire bandwidth of the cable is consumed by a single signal. In broadband transmission, signals are sent on multiple frequencies, allowing multiple signals to be sent simultaneously.
Explain 5-4-3 rule?
In a Ethernet network, between any two points on the network ,there can be no more than five network segments or four repeaters, and of those five segments only three of segments can be populated.
What MAU?
In token Ring , hub is called Multistation Access Unit(MAU).
What is the difference between routable and non- routable protocols?
Routable protocols can work with a router and can be used to build large networks. Non-Routable protocols are designed to work on small, local networks and cannot be used with a router
Why should you care about the OSI Reference Model?
It provides a framework for discussing network operations and design.
What is logical link control?
One of two sublayers of the data link layer of OSI reference model, as defined by the IEEE 802 standard. This sublayer is responsible for maintaining the link between computers when they are sending data across the physical network connection.
What is virtual channel?
Virtual channel is normally a connection from one source to one destination, although multicast connections are also permitted. The other name for virtual channel is virtual circuit.
What is virtual path?
Along any transmission path from a given source to a given destination, a group of virtual circuits can be grouped together into what is called path.
What is packet filter?
Packet filter is a standard router equipped with some extra functionality. The extra functionality allows every incoming or outgoing packet to be inspected. Packets meeting some criterion are forwarded normally. Those that fail the test are dropped.
What is traffic shaping?
One of the main causes of congestion is that traffic is often busy. If hosts could be made to transmit at a uniform rate, congestion would be less common. Another open loop method to help manage congestion is forcing the packet to be transmitted at a more predictable rate. This is called traffic shaping.
What is multicast routing?
Sending a message to a group is called multicasting, and its routing algorithm is called multicast routing.
What is region?
When hierarchical routing is used, the routers are divided into what we will call regions, with each router knowing all the details about how to route packets to destinations within its own region, but knowing nothing about the internal structure of other regions.
What is silly window syndrome?
It is a problem that can ruin TCP performance. This problem occurs when data are passed to the sending TCP entity in large blocks, but an interactive application on the receiving side reads 1 byte at a time.
What are Digrams and Trigrams?
The most common two letter combinations are called as digrams. e.g. th, in, er, re and an. The most common three letter combinations are called as trigrams. e.g. the, ing, and, and ion.
Expand IDEA.
IDEA stands for International Data Encryption Algorithm.
What is wide-mouth frog?
Wide-mouth frog is the simplest known key distribution center (KDC) authentication protocol.
What is Mail Gateway?
It is a system that performs a protocol translation between different electronic mail delivery protocols.
What is IGP (Interior Gateway Protocol)?
It is any routing protocol used within an autonomous system.
What is EGP (Exterior Gateway Protocol)?
It is the protocol the routers in neighboring autonomous systems use to identify the set of networks that can be reached within or via each autonomous system.
What is autonomous system?
It is a collection of routers under the control of a single administrative authority and that uses a common Interior Gateway Protocol.
What is BGP (Border Gateway Protocol)?
It is a protocol used to advertise the set of networks that can be reached with in an autonomous system. BGP enables this information to be shared with the autonomous system. This is newer than EGP (Exterior Gateway Protocol).
What is Gateway-to-Gateway protocol?
It is a protocol formerly used to exchange routing information between Internet core routers.
What is NVT (Network Virtual Terminal)?
It is a set of rules defining a very simple virtual terminal interaction. The NVT is used in the start of a Telnet session.
What is a Multi-homed Host?
It is a host that has a multiple network interfaces and that requires multiple IP addresses is called as a Multi-homed Host.
What is Kerberos?
It is an authentication service developed at the Massachusetts Institute of Technology. Kerberos uses encryption to prevent intruders from discovering passwords and gaining unauthorized access to files.
What is OSPF?
It is an Internet routing protocol that scales well, can route traffic along multiple paths, and uses knowledge of an Internet's topology to make accurate routing decisions.
What is Proxy ARP?
It is using a router to answer ARP requests. This will be done when the originating host believes that a destination is local, when in fact is lies beyond router.
What is SLIP (Serial Line Interface Protocol)?
It is a very simple protocol used for transmission of IP datagrams across a serial line.
What is RIP (Routing Information Protocol)?
It is a simple protocol used to exchange information between the routers.
What is source route?
It is a sequence of IP addresses identifying the route a datagram must follow. A source route may optionally be included in an IP datagram header.
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