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2015 question paper

Computer Networks

25 questions

  1. Q1a. Network layer of OSI model does not establish any relationship among different packets of same message. (Write True or False)20152m

    Module 3: Network Layer & Routing

    Network layer of OSI model does not establish any relationship among different packets of same message. (Write True or False)

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    Answer

    True

    Explanation

    The Network layer is responsible primarily for logical addressing, routing, and forwarding packets from source to destination.

    When a message is divided into multiple packets, the Network layer can treat those packets independently, particularly in a connectionless datagram network. Different packets may take different routes and may arrive out of order.

    The Network layer does not provide the end-to-end relationship, sequencing, acknowledgements, or retransmissions required for reliable delivery. Those functions are normally provided by the Transport layer when a reliable transport protocol such as TCP is used.

    Therefore, the statement that the Network layer does not establish a relationship among different packets of the same message is True.

    Final answer: True.

  2. Q1b. What is repeater?20152m

    Module 1: Physical Layer & Data Communication

    What is repeater?

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    Answer

    A repeater is a Physical-layer networking device that receives a weakened or distorted signal, regenerates it, and retransmits it.

    Purpose

    Signals become weaker as they travel over long distances due to attenuation. A repeater restores the signal so the network can cover a greater physical distance.

    Key point

    A repeater does not make routing decisions or inspect IP/MAC addresses. Its primary function is signal regeneration at the Physical layer.

    Exam-ready: A repeater regenerates and retransmits signals to extend the transmission distance of a network.

  3. Q1c. What is baud rate?20152m

    Module 1: Physical Layer & Data Communication

    What is baud rate?

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    Answer

    Baud rate is the number of signal symbols transmitted per second over a communication channel. Its unit is baud (symbols/second).

    Important distinction

    Baud rate is not always the same as bit rate. If each symbol carries more than one bit, then:

    Bit rate=Baud rate×bits per symbol\text{Bit rate} = \text{Baud rate} \times \text{bits per symbol}

    For example, if one symbol represents 2 bits and the baud rate is 1000 baud, the bit rate is 2000 bits/s.

    Exam-ready: Baud rate = number of signal symbols transmitted per second.

  4. Q1d. What is switch?20152m

    Module 2: Data Link Layer & MAC Sublayer

    What is switch?

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    Answer

    A network switch is a Data Link-layer device that connects devices within a LAN and forwards Ethernet frames based on MAC addresses.

    Working

    A switch learns the source MAC address of incoming frames and associates it with the receiving port in its MAC/forwarding table. When a frame arrives, it checks the destination MAC address:

    • If the destination is known, it forwards the frame only through the appropriate port.
    • If unknown, it floods the frame within the relevant LAN/VLAN.

    Advantages

    Switches reduce unnecessary traffic and allow multiple devices to communicate simultaneously using separate switch ports.

    Exam-ready: A switch is a multiport Data Link-layer device that forwards frames using MAC addresses.

  5. Q1e. What is flooding in routing?20152m

    Module 3: Network Layer & Routing

    What is flooding in routing?

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    Flooding is a routing technique in which a router forwards an incoming packet on all outgoing links except the link on which it arrived, subject to rules that prevent indefinite circulation.

    Key idea

    Instead of calculating one best route, the packet is propagated throughout the network. A packet can reach the destination through multiple paths.

    Advantages

    • Very simple routing method.
    • Does not require complete routing information.
    • Can be highly robust because multiple copies may reach the destination.

    Disadvantages

    • Creates many duplicate packets and wastes bandwidth.
    • Can cause congestion unless controlled.

    Common controls include a hop count/TTL and packet sequence numbers to discard duplicates.

    Exam-ready definition: Flooding forwards packets over all possible outgoing paths, with mechanisms such as hop limits used to control duplicates and loops.

  6. Q1f. What is TCP?20152m

    Module 4: Transport Layer & Congestion Control

    What is TCP?

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  7. Q1g. What is the role of a bridge?20152m

    Module 2: Data Link Layer & MAC Sublayer

    What is the role of a bridge?

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  8. Q1h. What do you mean by connectionless service?20152m

    Module 5: Application Layer & Security

    What do you mean by connectionless service?

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  9. Q1i. List two protocols in channelization category.20152m

    Module 1: Physical Layer & Data Communication

    List two protocols in channelization category.

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  10. Q1j. What is byte-oriented protocol?20152m

    Module 2: Data Link Layer & MAC Sublayer

    What is byte-oriented protocol?

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  12. Q2a. Explain the responsibilities of first four layers of OSI model.20158m

    Module 1: Physical Layer & Data Communication

    Explain the responsibilities of first four layers of OSI model.

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  13. Q2b. Compare between TCP/IP and OSI models.20156m

    Module 1: Physical Layer & Data Communication

    Compare between TCP/IP and OSI models.

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  14. Q3a. Explain the transmission characteristics of twisted pair.20157m

    Module 1: Physical Layer & Data Communication

    Explain the transmission characteristics of twisted pair.

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  15. Q3b. Compare and contrast between byte-oriented and bit-oriented protocols. Also compare between byte-stuffing and bit-stuffing.20157m

    Module 2: Data Link Layer & MAC Sublayer

    Compare and contrast between byte-oriented and bit-oriented protocols. Also compare between byte-stuffing and bit-stuffing.

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  16. Q4a. Explain the reasons for moving from stop-and-wait ARQ protocol to Go-back-N ARQ protocol.20157m

    Module 2: Data Link Layer & MAC Sublayer

    Explain the reasons for moving from stop-and-wait ARQ protocol to Go-back-N ARQ protocol.

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  17. Q4b. Define framing and discuss the reasons for its need. What are fixed-size and variable-size framings?20157m

    Module 2: Data Link Layer & MAC Sublayer

    Define framing and discuss the reasons for its need. What are fixed-size and variable-size framings?

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  18. Q5a. Draw the flow diagram for the CSMA/CD and explain. Also compare CSMA/CD with ALOHA.201514m

    Module 2: Data Link Layer & MAC Sublayer

    Draw the flow diagram for the CSMA/CD and explain. Also compare CSMA/CD with ALOHA.

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  19. Q6a. What is bridge? Explain about spanning tree.20158m

    Module 2: Data Link Layer & MAC Sublayer

    What is bridge? Explain about spanning tree.

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  20. Q6b. What are the common Gigabit Ethernet implementations?20156m

    Module 1: Physical Layer & Data Communication

    What are the common Gigabit Ethernet implementations?

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  21. Q7a. Explain the procedure for checksum and verification in the IPv4 protocol. What part of an IPv4 packet is covered in the checksum calculation and why? Are options, if present, included in the calculation?20158m

    Module 3: Network Layer & Routing

    Explain the procedure for checksum and verification in the IPv4 protocol. What part of an IPv4 packet is covered in the checksum calculation and why? Are options, if present, included in the calculation?

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  23. Q7b. Discuss the types of ICMP messages.20156m

    Module 3: Network Layer & Routing

    Discuss the types of ICMP messages.

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  24. Q8a. Discuss four types of link defined by OSPF. What is the basis of classification for the four types of link defined by OSPF?20158m

    Module 3: Network Layer & Routing

    Discuss four types of link defined by OSPF. What is the basis of classification for the four types of link defined by OSPF?

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  25. Q8b. List RIP shortcomings and their corresponding fixes.20156m

    Module 3: Network Layer & Routing

    List RIP shortcomings and their corresponding fixes.

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  26. Q9a. TCP is sending data at 2 Mbytes/sec. If the sequence number starts with 7000, how long does it take before the sequence number goes back to zero?20157m

    Module 4: Transport Layer & Congestion Control

    TCP is sending data at 2 Mbytes/sec. If the sequence number starts with 7000, how long does it take before the sequence number goes back to zero?

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  27. Q9b. Explain connection establishment in TCP using three-way handshaking.20157m

    Module 4: Transport Layer & Congestion Control

    Explain connection establishment in TCP using three-way handshaking.

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