(SEM VI) THEORY EXAMINATION 2022-23 DATA COMMUNICATION NETWORKS

DATA COMMUNICATION NETWORKS – KEC-063

Section-wise Important Questions & Ready Answers

SECTION A

(Attempt all questions in brief – 2 marks each)

(a) Difference between TDMA and FDMA

TDMA (Time Division Multiple Access) divides the available bandwidth into time slots and allocates each user a specific time slot to transmit data. FDMA (Frequency Division Multiple Access) divides the bandwidth into frequency bands and assigns each user a separate frequency channel for continuous transmission.

(b) Network Goals

The main goals of a computer network are resource sharing, high reliability, cost reduction, improved communication, scalability, and efficient data transfer between users and devices.

(c) Piggybacking

Piggybacking is a technique in which acknowledgment frames are combined with outgoing data frames in the reverse direction. This reduces overhead and improves channel utilization.

(d) Protocol

A protocol is a set of rules and conventions that govern data communication between devices. It defines how data is formatted, transmitted, received, and acknowledged.

(e) Expansion Cryptography

Expansion cryptography increases the size of the plaintext by adding redundancy before encryption. This helps in strengthening security and is commonly used in block cipher algorithms.
(In exam, a simple block diagram is expected.)

(f) Advantages of Byte Stuffing

Byte stuffing prevents confusion between data and control characters. It also ensures data transparency, allowing any data pattern to be transmitted safely.

(g) UDP (User Datagram Protocol)

UDP is a connectionless transport layer protocol that provides fast data transmission without error recovery or flow control. It is used in applications like video streaming, DNS, and online gaming.

(h) Fast Ethernet vs Gigabit Ethernet

Fast Ethernet supports data rates up to 100 Mbps, while Gigabit Ethernet supports up to 1000 Mbps. Gigabit Ethernet provides higher speed, better performance, and supports modern high-bandwidth applications.

(i) IP Datagram

An IP datagram consists of a header and data section. The header includes source address, destination address, version, TTL, protocol, and checksum fields.

(j) IPv4 Address Conversion to Binary

(i) 111.63.35.58
111 → 01101111
63 → 00111111
35 → 00100011
58 → 00111010

(ii) 221.54.9.92
221 → 11011101
54 → 00110110
9 → 00001001
92 → 01011100

SECTION B

(Attempt any three – 10 marks each)

2(a) Binary Exponential Back-Off Strategy

Binary exponential back-off is used in Ethernet to handle collisions. After each collision, the sender waits for a random time before retransmission. The waiting time doubles with each collision, reducing the chance of repeated collisions and improving network efficiency.

2(b) CSMA/CD (Carrier Sense Multiple Access with Collision Detection)

In CSMA/CD, a station senses the channel before transmitting. If the channel is idle, it transmits data. If a collision is detected, the station sends a jam signal, stops transmission, and waits for a random back-off time before retrying.
(Neat labeled diagram is expected in exam.)

2(c) OSI Model – Layers and Functions

The OSI model consists of seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application. Each layer performs specific functions such as transmission, error control, routing, end-to-end delivery, data formatting, and user interaction.
(Diagram compulsory in exam.)

2(d) DES Algorithm

DES (Data Encryption Standard) is a symmetric block cipher that encrypts 64-bit plaintext using a 56-bit key through 16 rounds of permutation, substitution, and XOR operations. It uses Feistel structure for encryption and decryption.

2(e) Distance Vector Routing Algorithm

Distance vector routing uses routing tables that store distance and next-hop information. Routers periodically exchange tables with neighbors and update routes using algorithms like Bellman-Ford.

SECTION C

3(a) Short Notes

(i) Email
Email is an electronic messaging system that allows users to send and receive messages over a network using protocols like SMTP, POP, and IMAP.

(ii) FTP
FTP (File Transfer Protocol) is used for transferring files between computers over a network. It supports uploading and downloading of files.

(iii) Selective Repeat ARQ
Selective Repeat ARQ retransmits only the frames that are lost or damaged, improving efficiency compared to Go-Back-N.

(iv) Bluetooth Technology
Bluetooth is a short-range wireless communication technology used for connecting devices like smartphones, headsets, and IoT devices.

3(b) IPv6 Datagram Format and Comparison with IPv4

IPv6 uses 128-bit addresses, simplified headers, improved security, and better support for mobility compared to IPv4. IPv4 uses 32-bit addresses and has limited address space.