2018 question paper

Computer Networks

3 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 layer20182m

   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

   (iv) Both session layer and presentation layer

   TCP/IP's Application layer merges the functionality of OSI's Session, Presentation, and Application layers into one. So Session and Presentation exist only as explicit, separate layers in the OSI model.

2. Q1b. Application layer is implemented on: (i) end systems (ii) NIC (iii) ethernet (iv) route20182m

   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

   Why: The application layer is implemented only on end systems (hosts) — protocols such as HTTP, SMTP, FTP, DNS and SNMP run directly in the communicating user processes/hosts. NIC is a network-layer-2 hardware device, Ethernet is a link/physical-layer standard, and routers/routes operate at the network layer (layer 3) — none of them implement application-layer protocols.

3. Q1c. Which of the following is not applicable for IP? (i) Error reporting (ii) Handle addressing conventions (iii) Datagram format (iv) Packet handling conventions20182m

   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

   Why: IP itself performs only best-effort delivery — it defines the datagram format, handles addressing conventions (classful/CIDR addressing) and packet handling conventions (fragmentation, TTL, options), but error reporting is not done by IP; it is the job of the companion protocol ICMP, which carries error and control messages (destination unreachable, time exceeded, echo, etc.) inside IP datagrams.