important computer networking 2 marks

                                                                           UNIT I

Data communications

1. Explain ISO/OSI reference model.

_ Physical layer

_ Data link layer

_ Network layer

_ Transport layer

_ Session layer

_ Presentation layer

_ Application layer

2. Explain the topologies of the network.

_ Mesh topology

_ Star topology

_ Tree topology

_ Bus topology

_ Ring topology

3. Explain the categories of networks.

_ Local Area Network(LAN)

_ Metropolitan Area Network(MAN)

_ Wide Area Network(WAN)

4. Explain coaxial cable & fiber optics.

_ Coaxial cable

_ Coaxial cable standards

_ Coaxial cable connectors

_ Fiber optics

_ Propagation modes

_ Fiber sizes

_ Cable composition

_ Light sources for optical cable

_ Fiber optic connectors

_ Advantages & disadvantages of optical fiber

5. Explain line coding (digital to digital conversion).

_ Unipolar

_ DC component

_ Synchronization

_ Polar

_ Non return to zero(NRZ)

_ NRZ-L

_ NRZ-I

_ Return to zero

_ Biphase

_ Manchester

_ Differential Manchester

_ Bipolar

_ Alternate Mark Inversion(AMI)

_ Bipolar 8-zero substitution(B8ZS)

_ High-Density Bipolar 3(HDB3)

                                                          UNIT II

Data link layer

1. Explain error detection and error correction techniques.

_ Types of errors

_ Single bit error

_ Burst error

_ Error detection

_ Vertical redundancy check(VRC)

_ Longitudinal redundancy check(LRC)

_ Cyclic redundancy check(CRC)

_ Checksum

_ Error correction

_ Single-bit error correction

_ Hamming code

_ Burst error correction

2. Explain error control mechanism.

_ Stop and wait ARQ

_ Sliding window ARQ

_ Go back-n

_ Selective-reject

3. Explain the flow control mechanism

_ Stop and wait

_ Sliding window.

4. Explain the timers and time registers in FDDI.

Time registers

_ Synchronous allocation(SA)

_ Target token rotation time(TTRT)

_ Absolute maximum time(AMT)

_ Timers

_ Token rotation timer(TRT)

_ Token holding timer(THT)

5. Explain about Ethernet.

_ Access method :CSMA/CD

_ Addressing

_ Electrical specification

_ Frame format

_ Implementation:

_ 10 base 5 :Thick Ethernet

_ 10 base 2 :Thin Ethernet

_ 10 base T :Twisted-pair Ethernet

_ 1 base 5 :Star LAN

6. Explain the frame format for token ring and token bus.

_ Access method: Token passing

_ Priority and reservation

_ Time limits

_ Monitor stations

7. Explain about HDLC.

_ Station types:

_ Primary station

_ Secondary station

_ Configurations:

_ Unbalanced configuration

_ Symmetrical configuration

_ Balanced configuration

_ Modes of communication:

_ Normal Response Mode(NRM)

_ Asynchronous Response Mode(ARM)

_ Asynchronous Balanced Mode(ABM)

_ Frames :

_ Flag field

_ Address field

_ Control field

_ Information field

_ FCS field

UNIT III

Network layer

1. Explain the two approaches of packet switching techniques.

_ Datagram approach

_ Virtual circuit approach

_ Switched virtual circuit(SVC)

_ Permanent virtual circuit(PVC)

_ Circuit – switched connection versus virtual – circuit connection

_ Path versus route

_ Dedicated versus shared

2. Explain IP addressing method.

_ Internetwork protocol (IP)

_ Datagram

_ Addressing

_ Classes

_ Dotted decimal notation

_ A sample internet

3. Define routing & explain distance vector routing and link state routing.

_ Distance vector routing

_ Sharing information

_ Routing table

_ Creating the table

_ Updating the table

_ Updating algorithm

_ Link state routing

_ Information sharing

_ Packet cost

_ Link state packet

_ Getting information about neighbors

_ Initialization

_ Link state database

4. Define bridge and explain the type of bridges.

_ Bridges

_ Types of bridges

_ Simple bridge

_ Multiport bridge

_ Transparent bridge

5. Explain subnetting

_ Subnetting

_ Three levels of hierarchy

_ Masking

_ Masks without subnetting

_ Masks with subnetting

_ Finding the subnetwork address

_ Boundary level masking

_ Non-boundary level masking

6. Write short notes about repeaters, routers and gateways.

_ Repeaters

_ Routers

_ Routing concepts

_ Least-cost routing

_ Non adaptive routing

_ Adaptive routing

_ Packet lifetime

_ Gateways

                                                                       UNIT IV

Transport layer

1. Explain the duties of transport layer.

End to end delivery

Addressing

Reliable delivery

• Error control

• Sequence control

• Loss control

• Duplication control

Flow control

Multiplexing

2. Explain socket in detail.

• Introduction

• Explanation

• program

3. Explain UDP & TCP.

_ User Datagram Protocol(UDP)

_ Source port address

_ Destination port address

_ Total length

_ Checksum

_ Transmission Control Protocol(TCP)

_ Source port address

_ Destination port address

_ Sequence number

_ Acknowledgement number

_ Header length

_ Reserved

_ Control

_ Window size

_ Check sum

_ Urgent pointer

_ Options and padding

4. Explain about congestion control.

_ Congestion avoidance

_ BECN

_ FECN

_ Four situations

_ Discarding

5. Explain leaky bucket and token bucket algorithm

_ Leaky bucket algorithm

_ Leaky bucket

_ Switch controlling the output rate

_ Flowchart

                                                                  UNIT V

Application Layer

1. Explain the functions of SMTP.

• System for sending messages to other computer users based on e-mail

addresses. SMTP provides mail exchange between users on the same

or different computers.

• User Agent

• Mail Transfer Agent

• Multipurpose Internet Mail Extensions

• Post Office Protocol

2. Write short notes on FTP.

• Transfer a file from one system to another.

• TCP connections

• Basic model of FTP

3. Explain about HTTP.

• HTTP transactions

• HTTP messages

• URL

4. Explain the WWW in detail.

• Hypertext & Hypermedia

• Browser Architecture

• Categories of Web Documents

• HTML

• CGI

• Java

5. Explain the type of encryption/decryption method.

Conventional Methods:

• Character-Level Encryption: Substitutional & Transpositional

• Bit-Level Encryption: Encoding/Decoding, Permutation, Substitution,

Product, Exclusive-Or & Rotation

Public key Methods

6. Explain about RSA algorithm.

• Public key Encryption technique.

• Encryption algorithm

• Decryption algorithm

• Security in RSA

7. Explain about secret key encryption algorithm.

• Data Encryption Standard

• Algorithm

• Sub key generation

UNIT – V APPLICATION LAYER

1. What is the purpose of Domain Name System?

Domain Name System can map a name to an address and conversely an address to

name.

2. Discuss the three main division of the domain name space.

Domain name space is divided into three different sections: generic domains,

country domains & inverse domain.

Generic domain: Define registered hosts according to their generic behavior, uses

generic suffixes.

Country domain: Uses two characters to identify a country as the last suffix.

Inverse domain: Finds the domain name given the IP address.

3. Discuss the TCP connections needed in FTP.

FTP establishes two connections between the hosts. One connection is used for

data transfer, the other for control information. The control connection uses very

simple rules of communication. The data connection needs more complex rules due to

the variety of data types transferred.

4. Discuss the basic model of FTP.

The client has three components: the user interface, the client control process, and

the client data transfer process. The server has two components: the server control

process and the server data transfer process. The control connection is made between

the control processes. The data connection is made between the data transfer

processes.

5. What is the function of SMTP?

The TCP/IP protocol supports electronic mail on the Internet is called Simple

Mail Transfer (SMTP). It is a system for sending messages to other computer users

based on e-mail addresses. SMTP provides mail exchange between users on the same

or different computers.

6. What is the difference between a user agent (UA) and a mail transfer agent

(MTA)?

The UA prepares the message, creates the envelope, and puts the message in the

envelope. The MTA transfers the mail across the Internet.

7. How does MIME enhance SMTP?

MIME is a supplementary protocol that allows non-ASCII data to be sent through

SMTP. MIME transforms non-ASCII data at the sender site to NVT ASCII data and

deliverers it to the client SMTP to be sent through the Internet. The server SMTP at

the receiving side receives the NVT ASCII data and delivers it to MIME to be

transformed back to the original data.

8. Why is an application such as POP needed for electronic messaging?

Workstations interact with the SMTP host which receives the mail on behalf of

every host in the organization, to retrieve messages by using a client-server protocol

such as Post Office Protocol , version 3(POP3). Although POP3 is used to download

messages from the server, the SMTP client still needed on the desktop to forward

messages from the workstation user to its SMTP mail server.

10. Give the format of HTTP response message.

Status Line

Headers

A Blank Line

Body

(present only in

some messages)

Request Line

Headers

A Blank Line

Body

(present only in

some messages)

11. Write down the three types of WWW documents.

The documents in the WWW can be grouped into three broad categories: static,

dynamic and active.

Static: Fixed-content documents that are created and stored in a server.

Dynamic: Created by web server whenever a browser requests the document.

Active: A program to be run at the client side.

12. What is the purpose of HTML?

HTML is a computer language for specifying the contents and format of a web

document. It allows additional text to include codes that define fonts, layouts,

embedded graphics and hypertext links.

13. Define CGI.

CGI is a standard for communication between HTTP servers and executable

programs. It is used in crating dynamic documents.

14. Name four factors needed for a secure network.

Privacy: The sender and the receiver expect confidentiality.

Authentication: The receiver is sure of the sender’s identity and that an imposter has

not sent the message.

Integrity: The data must arrive at the receiver exactly as it was sent.

Non-Reputation: The receiver must able to prove that a received message came from

a specific sender.

15. How is a secret key different from public key?

In secret key, the same key is used by both parties. The sender uses this key and

an encryption algorithm to encrypt data; the receiver uses the same key and the

corresponding decryption algorithm to decrypt the data.

In public key, there are two keys: a private key and a public key. The private key

is kept by the receiver. The public key is announced to the public.

16. What is a digital signature?

Digital signature is a method to authenticate the sender of a message. It is similar

to that of signing transactions documents when you do business with a bank. In

network transactions, you can create an equivalent of an electronic or digital signature

by the way you send data.

17. What are the advantages & disadvantages of public key encryption?

Advantages:

a) Remove the restriction of a shared secret key between two entities. Here each

entity can create a pair of keys, keep the private one, and publicly distribute the

other one.

b) The no. of keys needed is reduced tremendously. For one million users to

communicate, only two million keys are needed.

Disadvantage:

If you use large numbers the method to be effective. Calculating the cipher text using

the long keys takes a lot of time. So it is not recommended for large amounts of text.

18. What are the advantages & disadvantages of secret key encryption?

Advantage:

Secret Key algorithms are efficient: it takes less time to encrypt a message. The

reason is that the key is usually smaller. So it is used to encrypt or decrypt long

messages.

Disadvantages:

a) Each pair of users must have a secret key. If N people in world want to use this

method, there needs to be N (N-1)/2 secret keys. For one million people to

communicate, a half-billion secret keys are needed.

b) The distribution of the keys between two parties can be difficult.

19. Define permutation.

Permutation is transposition in bit level.

Straight permutation: The no. of bits in the input and output are preserved.

Compressed permutation: The no. of bits is reduced (some of the bits are dropped).

Expanded permutation: The no. of bits is increased (some bits are repeated).

20. Define substitutional & transpositional encryption.

Substitutional: A character level encryption in which each character is replaced by

another character in the set.

Transpositional: A Character level encryption in which the characters retain their

plaintext but the position of the character changes.