IT-502 Computer Networks - Jun 2025 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aWhat is the purpose of the physical layer? Discuss various physical media for data transmission?
   How to answer

   • Define physical layer as lowest OSI layer for bit transmission over medium
   • List functions: bit encoding, data rate, synchronization, interface, topology, transmission mode
   • Discuss guided media: twisted pair, coaxial, fiber optic with characteristics
   • Discuss unguided media: radio, microwave, infrared, satellite
2. 7 Marks
   bWhen RARP is required? Explain how it works. What is the limitation of RARP?
   How to answer

   • Define RARP and when diskless host needs IP from MAC
   • Explain RARP request broadcast and RARP server reply process
   • Describe packet format and server mapping table
   • List limitations: broadcast only, no subnet, needs dedicated server, replaced by BOOTP/DHCP
3. 7 Marks
   aTwo neighboring nodes (A and B) use a sliding-window protocol with a 3-bit sequence number. As the ARQ mechanism, go-back-N is used with a window size of 4. Assuming A is transmitting and B is receiving, show the window positions for the following succession of events:

   1. i)Before A sends any frames
   2. ii)After A sends frames 0, 1, 2 and receives acknowledgement from B for 0 and 1.
   3. iii)After A sends frames 3, 4 and 5 acknowledges 4 and the ACK is received by A.
   How to answer

   • State 3-bit means sequence 0-7, window size 4 for Go-Back-N
   • Show sender window before sending: [0,1,2,3]
   • Show window after sending 0,1,2 and ACK 0,1: slide to [2,3,4,5]
   • Show window after sending 3,4,5 and ACK 4: slide to [5,6,7,0] with wrap
4. 7 Marks
   bWhat is CSMA/CD? How does it work? Distinguish between 1-Persistent and Non-Persistent CSMA.
   How to answer

   • Define CSMA/CD and its use in Ethernet
   • Explain listen-before-talk, collision detection and backoff steps
   • Define 1-persistent: transmit immediately when idle with pros/cons
   • Contrast non-persistent: wait random time, lower collision vs delay
5. 7 Marks
   aOne of the addresses in a block is $167.199.170.82/77$. Find the number of addresses in the network, the first address, and the last address.
   How to answer

   • Calculate total addresses as $2^{32-27}=32$
   • Find network mask and first address by keeping 27 prefix bits
   • Compute last address by setting host bits to 1
   • State first address 167.199.170.64/27 and last 167.199.170.95
6. 7 Marks
   bWhat is bit stuffing and why is it needed in HDLC?
   How to answer

   • Define bit stuffing and HDLC flag $01111110$
   • Explain need to avoid flag imitation in data for transparency
   • Describe stuffing rule: insert 0 after five consecutive 1s and removal at receiver
7. 7 Marks
   aWhat are the duties of transport layer? Explain in brief.
   How to answer

   • Define transport layer as end-to-end delivery layer
   • List duties: segmentation, connection control, flow and error control
   • Briefly explain addressing, multiplexing and congestion aspects
8. 7 Marks
   bExplain the UDP Encapsulation and protocol layering.
   How to answer

   • Define UDP encapsulation with headers at each layer
   • Show data to UDP datagram to IP datagram to frame
   • Explain protocol layering and port addressing concept
9. 7 Marks
   aExplain the message transfer using simple mail transfer protocol.
   How to answer

   • Define SMTP as TCP-based mail transfer protocol
   • Explain roles of UA, MTA, MAA and commands
   • Describe connection establishment, mail transfer and closing phases with example
10. 7 Marks
    bWhy is an application such as POP needed for electronic messaging?
    How to answer

    • State SMTP limitation: only transfer, no retrieval
    • Explain need for mailbox access protocol like POP3
    • Describe POP modes, commands and download-delete operation
11. 7 Marks
    aCompare Open loop Congestion Control and Closed loop congestion control.
    How to answer

    • Define congestion control and open-loop vs closed-loop concept
    • List open-loop policies: retransmission, window, ACK, discard
    • List closed-loop: feedback, backpressure, choke packet, RED
    • Compare in table on timing, feedback and examples
12. 7 Marks
    bExplain why gateway is called protocol converter and also explain its working in detail.
    How to answer

    • Define gateway operating on all layers for dissimilar networks
    • Explain protocol conversion need across formats and addresses
    • Describe working: receive, translate, forward with example
13. 7 Marks
    aExplain the architecture of IEEE 802.11. Differentiate IEEE 802.11 A and IEEE 802.11 B.
    How to answer

    • Describe IEEE 802.11 components: BSS, ESS, AP, STA, DS
    • Explain MAC and PHY architecture with services
    • Compare 802.11a (5 GHz, OFDM, 54 Mbps) vs 802.11b (2.4 GHz, DSSS, 11 Mbps) in table
14. 7 Marks
    bState the major differences between Distance Vector Routing and Link State Routing. Discuss how these routing techniques work.
    How to answer

    • Define distance vector (Bellman-Ford) vs link state (Dijkstra) principles
    • Explain working: neighbor exchange vs flooding LSP and SPF tree
    • Compare on convergence, overhead, count-to-infinity, examples RIP vs OSPF
15. 14 Marks
    Write short note on (Any Three):

    1. i)IPv6
    2. ii)BOOTP
    3. iii)Bridges
    4. iv)TCP Timers
    How to answer

    • Select any three topics for short notes
    • Give definition, key features and purpose for each
    • Add header format, example or diagram where relevant
    • Conclude with use-case or limitation