(SEM VI) THEORY EXAMINATION 2022-23 COMPUTER NETWORKS

COMPUTER NETWORKS – KCS-603

Section-wise Important Questions & Ready Answers

SECTION A

(Attempt all questions – 2 marks each)

(a) Point-to-Point vs Point-to-Multipoint

In point-to-point communication, a dedicated link exists between two devices, ensuring exclusive use of the channel, such as a direct cable between two computers. In point-to-multipoint communication, a single channel is shared among multiple devices, where data sent by one device is received by all, as seen in wireless broadcasting systems.

(b) Bit Rate and Baud Rate

Bit rate is the number of bits transmitted per second, whereas baud rate is the number of signal units transmitted per second. Bit rate depends on both baud rate and number of bits per signal element.

(c) OSI Model vs TCP/IP Model

The OSI model has seven layers and is a theoretical reference model, while the TCP/IP model has four layers and is practically implemented on the internet. OSI separates services, interfaces, and protocols clearly, whereas TCP/IP combines some layers for efficiency.

(d) Polar NRZ-L and NRZ-I for Data 01001110

In NRZ-L, binary 0 is represented by positive voltage and binary 1 by negative voltage (or vice versa).
In NRZ-I, a transition at the beginning of the bit interval represents binary 1, and no transition represents binary 0.
(In exam, neat waveform diagrams must be drawn.)

(e) Piggybacking

Piggybacking is a technique in which an acknowledgment is attached to a data frame traveling in the reverse direction, reducing overhead and improving channel utilization.

(f) ICMP and BGP Protocols with Applications

ICMP is used for error reporting and network diagnostics, such as the ping command.
BGP (Border Gateway Protocol) is used to exchange routing information between autonomous systems on the internet, ensuring efficient global routing.

(g) Hamming Code Error Detection and Correction

Given received code: 1110101, parity bits are checked to locate the error position. The syndrome value indicates an error, which is corrected by flipping the erroneous bit to obtain the correct codeword.

(h) Quality of Service (QoS)

QoS refers to the ability of a network to provide guaranteed performance in terms of bandwidth, delay, jitter, and packet loss, especially for real-time applications like video conferencing.

(i) HTTP vs HTTPS

HTTP transmits data in plain text, making it insecure. HTTPS uses SSL/TLS encryption, ensuring confidentiality, integrity, and authentication of data exchanged over the web.

(j) Count-to-Infinity Problem

The count-to-infinity problem occurs in distance vector routing when routers continuously increase metric values due to incorrect routing updates after a link failure, leading to slow convergence.

SECTION B

(Attempt any three – 10 marks each)

2(a) Network Devices and Transmission Impairments

Common network devices include hub, switch, router, and gateway. Transmission impairments include attenuation (signal loss), distortion (signal shape change), and noise (unwanted interference), which degrade communication quality.

2(b) CSMA/CD vs CSMA/CA

CSMA/CD is used in wired Ethernet, where devices detect collisions and retransmit data after a random delay.
CSMA/CA is used in wireless networks, where collisions are avoided using acknowledgments and RTS/CTS mechanisms.
(Well-labeled diagrams are required in exam.)

2(c) Congestion Control Mechanism

Congestion control prevents network overload by regulating data transmission rates. TCP uses mechanisms like slow start, congestion avoidance, fast retransmit, and fast recovery to manage congestion efficiently.
(Neat diagram expected.)

2(d) Go-Back-N and Selective Repeat ARQ

In Go-Back-N, if a frame is lost, all subsequent frames are retransmitted.
In Selective Repeat, only the erroneous frames are retransmitted, improving efficiency but requiring more buffering.

2(e) Asymmetric Cryptography and RSA Algorithm

Asymmetric cryptography uses a public and private key pair. RSA involves key generation, encryption, and decryption steps. The character “F” is converted into numeric form, encrypted using the public key, and decrypted using the private key to demonstrate secure transmission.

SECTION C

3(a) OSI Model Layers

The OSI model consists of Physical, Data Link, Network, Transport, Session, Presentation, and Application layers, each responsible for specific network functions.
(Neat, labeled diagram is mandatory in exam.)

3(b) Network Topologies

Common topologies include bus, star, ring, mesh, and hybrid. Each topology differs in cost, reliability, scalability, and performance.
(Well-labeled diagrams required.)