GATE Networks 3 — Questions and Answers
Question 1: In CSMA/CD, after the k-th collision, a station waits a random number of slot times chosen from [0, 2^k - 1]. This is called:
- Exponential backoff
- Binary exponential backoff (Correct answer)
- Linear backoff
- Fibonacci backoff
Correct answer: Binary exponential backoff
Binary exponential backoff doubles the contention window after each successive collision, reducing the probability of repeated collisions.
Question 2: Which layer of the OSI model is responsible for end-to-end error detection and flow control between hosts?
- Network layer
- Data link layer
- Transport layer (Correct answer)
- Session layer
Correct answer: Transport layer
The transport layer (Layer 4) provides end-to-end reliable delivery, error detection, and flow control between communicating hosts.
Question 3: A network uses Go-Back-N ARQ with a window size of 4. If frame 3 is lost, which frames must be retransmitted?
- Only frame 3
- Frames 3 and 4
- Frames 3, 4, 5, and 6 (Correct answer)
- All frames from 3 onward up to window
Correct answer: Frames 3, 4, 5, and 6
In Go-Back-N, when frame 3 is lost, the receiver discards all subsequent frames; the sender must retransmit frame 3 and all frames sent after it within the window.
Question 4: Which protocol resolves an IP address to the corresponding MAC address on a local network?
- RARP
- ICMP
- ARP (Correct answer)
- DNS
Correct answer: ARP
ARP (Address Resolution Protocol) broadcasts an IP address query and receives the corresponding MAC address from the owning host.
Question 5: The OSPF routing protocol is based on which algorithm?
- Distance vector
- Link state (Correct answer)
- Path vector
- Diffusing update
Correct answer: Link state
OSPF (Open Shortest Path First) is a link-state protocol where each router maintains a complete topology map and runs Dijkstra's algorithm locally.
Question 6: In a slotted ALOHA system, the maximum throughput is approximately:
- 18.4%
- 36.8% (Correct answer)
- 50%
- 100%
Correct answer: 36.8%
Slotted ALOHA achieves maximum throughput of 1/e ≈ 36.8% when each station transmits with probability 1/N where N is the number of active stations.
Question 7: Which field in the TCP header identifies the application-layer protocol on the receiving end?
- Sequence number
- Acknowledgment number
- Destination port (Correct answer)
- Window size
Correct answer: Destination port
The destination port number in the TCP header identifies which application (e.g., HTTP on port 80) should receive the segment.
GATE Networks 3
In CSMA/CD, after the k-th collision, a station waits a random number of slot times chosen from [0, 2^k - 1].
This is called: