(SEM VI) THEORY EXAMINATION 2018-19 COMPUTER NETWORK

Computer Network (RCS-601)

B.Tech Semester VI – Section-Wise Exam Notes

SECTION A – Short Answer Notes (2 Marks Each)

1. Headers and Trailers

Headers and trailers are control information added to data during transmission.
The header is added at the beginning of the data and contains addressing, sequencing, and control information.
The trailer is added at the end and mainly contains error detection bits like CRC.
At the receiver side, headers and trailers are removed layer by layer.

2. Maximum Efficiency of FDDI Ring

Efficiency depends on token rotation time and token holding time.
If token holding time is high compared to rotation time, efficiency increases.
Efficiency = Token holding time / (Token holding time + Rotation time).

3. Network Layer vs Transport Layer Delivery

Network layer ensures host-to-host delivery using IP addresses.
Transport layer ensures process-to-process delivery using port numbers and provides reliability, flow control, and error control.

4. Hosts per Subnet (Class B)

Subnet mask: 255.255.248.0                      Remaining host bits = 11
Maximum hosts = 2¹¹ − 2 = 2046 hosts

5. Count-to-Infinity Problem

A routing problem in distance vector routing where routers continuously increase metric values due to incorrect routing updates after a link failure.

6. UA vs MTA

User Agent (UA): Used by end users to compose and read emails.

Mail Transfer Agent (MTA): Transfers emails between mail servers.

7. Time To Live (TTL)

TTL is a field in IP header that limits packet lifetime.
Each router decreases TTL by 1 to prevent infinite looping.

SECTION B – Descriptive Answers (7 Marks)

1. Network Topologies

Bus Topology:
All devices share a single cable. Cheap but prone to collisions.

Star Topology:
All devices connect to a central hub/switch. Easy fault detection.

Ring Topology:
Devices form a closed loop. Data travels in one direction.

2. Stop-and-Wait Protocol Efficiency

Efficiency depends on frame transmission time, propagation delay, and acknowledgment delay.
Faults increase waiting time and reduce efficiency significantly.

3. Unicast Routing

Unicast routing delivers packets from one source to one destination.
Protocols include RIP, OSPF, and BGP.

4. TCP Header and TCP vs UDP

TCP provides reliable, connection-oriented service with flow control and error control.
UDP is faster, connectionless, and does not guarantee delivery.

5. FTP vs TFTP & SNMP Functions

FTP: Uses TCP, reliable, secure.                   TFTP: Uses UDP, simple, faster.

SNMP Functions:

Monitoring                                                  Configuration

Fault management

SECTION C – Long Answer Notes (7 Marks)

1. OSI Model

OSI model has 7 layers:
Physical, Data Link, Network, Transport, Session, Presentation, Application.
Each layer has defined responsibilities ensuring standard communication.

2. Line Coding Techniques

Unipolar, Bipolar NRZ-L, NRZ-I, RZ, Manchester, Differential Manchester, and AMI convert digital data into digital signals for transmission.

3. Slotted ALOHA

Throughput depends on frame rate.   Maximum throughput occurs at G = 1 and equals 1/e ≈ 36.8%.

4. ARQ Error Control

Automatic Repeat reQuest uses acknowledgments and retransmissions.
Types include Stop-and-Wait ARQ, Go-Back-N, and Selective Repeat.

5. IPv6 Advantages                             Larger address space

Better security                                    Simplified header

Improved routing efficiency

6. TCP Header Analysis

Hexadecimal fields represent sequence number, acknowledgment number, window size, and ports which control reliable transmission.

7. DNS and BOOTP vs DHCP

DNS translates domain names to IP addresses.
DHCP dynamically assigns IP addresses, whereas BOOTP is static.