2019 question paper

Computer Networks

22 questions

1. Q1a. This layer is an addition to OSI model when compared with TCP/IP model: (i) Application layer (ii) Presentation layer (iii) Session layer (iv) Both session layer and presentation layer20192m

   Module 1: Physical Layer & Data Communication

   This layer is an addition to OSI model when compared with TCP/IP model:
   (i) Application layer
   (ii) Presentation layer
   (iii) Session layer
   (iv) Both session layer and presentation layer

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   Worked Solution

   Answer

   (iv) Both Session layer and Presentation layer

   Explanation

   The OSI model has 7 layers:

   1. Physical
   2. Data Link
   3. Network
   4. Transport
   5. Session
   6. Presentation
   7. Application

   The traditional TCP/IP model has fewer layers. Its Application layer combines the responsibilities of the OSI Application, Presentation, and Session layers.

   Therefore, when comparing the two models, the Session and Presentation layers are separate layers in OSI but are not separate layers in the traditional TCP/IP model.

   Option analysis

   • (i) Application: Exists in both models, although its scope differs.
   • (ii) Presentation: Separate in OSI; its functions are incorporated into TCP/IP's Application layer.
   • (iii) Session: Separate in OSI; its functions are incorporated into TCP/IP's Application layer.
   • (iv) Both session layer and presentation layer: Correct.

   Final answer: (iv) Both session layer and presentation layer.

2. Q1b. Application layer is implemented on: (i) end systems (ii) NIC (iii) ethernet (iv) route20192m

   Module 5: Application Layer & Security

   Application layer is implemented on:
   (i) end systems
   (ii) NIC
   (iii) ethernet
   (iv) route

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   Worked Solution

   Answer

   (i) End systems

   Explanation

   The Application layer contains protocols and services used directly by network applications such as HTTP, SMTP, DNS, and FTP. These application processes run on end systems (hosts) rather than on intermediate forwarding devices such as routers or switches.

   Final answer: (i) end systems.

3. Q1c. Which of the following is not applicable for IP? (i) Error reporting (ii) Handle addressing conventions (iii) Datagram format (iv) Packet handling conventions20192m

   Module 3: Network Layer & Routing

   Which of the following is not applicable for IP?
   (i) Error reporting
   (ii) Handle addressing conventions
   (iii) Datagram format
   (iv) Packet handling conventions

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   Worked Solution

   Answer

   (i) Error reporting

   Explanation

   IP is responsible for logical addressing, packet/datagram format, and packet handling/routing conventions. However, IP itself is a connectionless best-effort delivery protocol and does not provide error reporting as a core IP function.

   Error reporting for IP-related delivery problems is provided by ICMP (Internet Control Message Protocol), which works alongside IP.

   Therefore, among the given choices, error reporting is not directly an IP function.

   Final answer: (i) Error reporting.

4. Q1d. Which one of the following is not a function of network layer? (i) Routing (ii) Inter-networking (iii) Congestion control (iv) None of the above20192m

   Module 3: Network Layer & Routing

   Which one of the following is not a function of network layer?
   (i) Routing
   (ii) Inter-networking
   (iii) Congestion control
   (iv) None of the above

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   Worked Solution

   Answer

   (iv) None of the above

   Explanation

   All three listed functions can be associated with the Network layer:

   1. Routing: Determines suitable paths for packets through an internetwork.
   2. Internetworking: IP provides communication across interconnected networks.
   3. Congestion control: Network-layer mechanisms and protocols can participate in congestion management, although congestion control is also handled at the Transport layer in systems such as TCP.

   Therefore, none of options (i), (ii), or (iii) is the intended answer as a non-function.

   Final answer: (iv) None of the above.

5. Q1e. For a 10 Mbps Ethernet link, if the length of the packet is 32 bits, the transmission delay is (in milliseconds): (i) 3.2 (ii) 32 (iii) 0.32 (iv) None of the above20192m

   Module 1: Physical Layer & Data Communication

   For a 10 Mbps Ethernet link, if the length of the packet is 32 bits, the transmission delay is (in milliseconds):
   (i) 3.2
   (ii) 32
   (iii) 0.32
   (iv) None of the above

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   Worked Solution

   Answer

   (iv) None of the above

   Calculation

   Transmission delay is:
   $T_t = \frac{L}{R}$

   where $L$ is packet length and $R$ is transmission rate.

   Given:

   • $L=32$ bits
   • $R=10$ Mbps $=10\times10^6$ bits/s

   Therefore:
   $T_t=\frac{32}{10\times10^6}=3.2\times10^{-6}$ s.

   Convert to milliseconds:
   $3.2\times10^{-6}\times1000=0.0032$ ms.

   None of the listed numerical options equals 0.0032 ms.

   Final answer: (iv) None of the above.

6. Q1f. Transmission delay does not depend on: (i) packet length (ii) distance between the routers (iii) transmission rate (iv) None of the above20192m

   Module 1: Physical Layer & Data Communication

   Transmission delay does not depend on:
   (i) packet length
   (ii) distance between the routers
   (iii) transmission rate
   (iv) None of the above

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   Worked Solution

   Answer

   (ii) Distance between the routers

   Explanation

   Transmission delay is the time required to push all packet bits onto the link:
   $T_t=\frac{L}{R}$.

   It depends on:

   • $L$ = packet length
   • $R$ = transmission rate

   It does not depend on physical distance between routers. Distance affects propagation delay, which is approximately:
   $T_p=\frac{d}{v}$.

   Therefore, the correct answer is (ii) Distance between the routers.

   Remember

   Transmission delay → packet size + link rate

   Propagation delay → distance + propagation speed

7. Q1g. In TCP, sending and receiving data is done as: (i) stream of bytes (ii) sequence of characters (iii) lines of data (iv) packets20192m

   Module 4: Transport Layer & Congestion Control

   In TCP, sending and receiving data is done as:
   (i) stream of bytes
   (ii) sequence of characters
   (iii) lines of data
   (iv) packets

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8. Q1h. Suppose a TCP connection is transferring a file of 1000 bytes. The first byte is numbered 10001. What is the sequence number of the segment if all data is sent in only one segment? (i) 10000 (ii) 10001 (iii) 12001 (iv) 1100120192m

   Module 4: Transport Layer & Congestion Control

   Suppose a TCP connection is transferring a file of 1000 bytes. The first byte is numbered 10001. What is the sequence number of the segment if all data is sent in only one segment?
   (i) 10000
   (ii) 10001
   (iii) 12001
   (iv) 11001

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9. Q1i. The protocol on which DNS application run is: (i) Telnet (ii) UDP (iii) HTTP (iv) None of the above20192m

   Module 5: Application Layer & Security

   The protocol on which DNS application run is:
   (i) Telnet
   (ii) UDP
   (iii) HTTP
   (iv) None of the above

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10. Q1j. __________ allows you to connect and login to a remote computer. (i) Telnet (ii) FTP (iii) HTTP (iv) None of the above20192m

    Module 5: Application Layer & Security

    __________ allows you to connect and login to a remote computer.
    (i) Telnet
    (ii) FTP
    (iii) HTTP
    (iv) None of the above

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12. Q2a. Draw a neat diagram of TCP/IP protocol stack with the protocols and functionality implemented on each layer. Also explain, why there is a need for having a layered architecture (like OSI and TCP/IP) in networks.201914m

    Module 1: Physical Layer & Data Communication

    Draw a neat diagram of TCP/IP protocol stack with the protocols and functionality implemented on each layer. Also explain, why there is a need for having a layered architecture (like OSI and TCP/IP) in networks.

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13. Q3a. We know that there are 2 types of address schemes (i.e. IP address and MAC address) in computer networks. Explain what the need of having two types of addresses. What will happen if we use only IP address in computer networks?201914m

    Module 3: Network Layer & Routing

    We know that there are 2 types of address schemes (i.e. IP address and MAC address) in computer networks. Explain what the need of having two types of addresses. What will happen if we use only IP address in computer networks?

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14. Q4a. What do you mean by Random Access Protocols? Explain the limitations of using ALOHA as random access protocol.201914m

    Module 2: Data Link Layer & MAC Sublayer

    What do you mean by Random Access Protocols? Explain the limitations of using ALOHA as random access protocol.

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15. Q5a. In the context of Transmission Control Protocol (TCP), explain the statement, "TCP help us to establish a reliable connection over an unreliable network".20197m

    Module 4: Transport Layer & Congestion Control

    In the context of Transmission Control Protocol (TCP), explain the statement, "TCP help us to establish a reliable connection over an unreliable network".

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16. Q5b. Outline the difference between TCP and UDP.20197m

    Module 4: Transport Layer & Congestion Control

    Outline the difference between TCP and UDP.

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17. Q6a. Why there is a need of doing error control at transport layer despite of the fact that we are doing the same thing at the data link layer? Why we are doing this error correction multiple times?201914m

    Module 2: Data Link Layer & MAC Sublayer

    Why there is a need of doing error control at transport layer despite of the fact that we are doing the same thing at the data link layer? Why we are doing this error correction multiple times?

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18. Q7a. Explain type of delays in computer networks. Suppose a node A wants to send data of 200 mb to node B. The bandwidth of the channel is 1 Gbps. There are three routers in between node A to node B. Assume other delays equal to 0. Calculate the total delay involved.201914m

    Module 1: Physical Layer & Data Communication

    Explain type of delays in computer networks. Suppose a node A wants to send data of 200 mb to node B. The bandwidth of the channel is 1 Gbps. There are three routers in between node A to node B. Assume other delays equal to 0. Calculate the total delay involved.

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19. Q8a. With the help of neat figures, explain sliding window mechanism.201914m

    Module 2: Data Link Layer & MAC Sublayer

    With the help of neat figures, explain sliding window mechanism.

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20. Q9a. Compare the following terms: (a) ARP vs RARP201914m

    Module 3: Network Layer & Routing

    Compare the following terms: (a) ARP vs RARP

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21. Q9b. Compare the following terms: (b) Unicast vs Multicast201914m

    Module 5: Application Layer & Security

    Compare the following terms: (b) Unicast vs Multicast

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23. Q9c. Compare the following terms: (c) Flooding vs Broadcasting201914m

    Module 2: Data Link Layer & MAC Sublayer

    Compare the following terms: (c) Flooding vs Broadcasting

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24. Q9d. Compare the following terms: (d) Amplifiers vs Repeaters201914m

    Module 1: Physical Layer & Data Communication

    Compare the following terms: (d) Amplifiers vs Repeaters

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