Question

Consider the following statements about flow and error control :
A. Go-Back-N retransmits only the frame that is lost

B. Selective Repeat improves the bandwidth utilization over Go-Back-N

C. Parity bits can detect all single-bit errors

D. Stop and wait protocol achieves high channel utilization on long-delay networks

E. Cyclic Redundancy check provides stronger error detection than single parity

Choose the correct answer from the options given below :

• A. A, B, E only
• B. A, C, D only
• C. B, C, D only
• D. B, C, E only

Hint:

Go-Back-N = Retransmit $N$ frames. Selective Repeat = Retransmit only the 1 lost frame. CRC is the "gold standard" for error detection in networking.

Answer 1

The Correct Option is D

Let's analyze the mechanisms of data link layer protocols and error detection techniques. 1. Evaluating Statements A, B, and C:
• A (Go-Back-N): False. In Go-Back-N, if a frame is lost, the sender retransmits the lost frame and all subsequent frames in the window.
• B (Selective Repeat): True. It retransmits only the lost frame, which reduces unnecessary retransmissions and improves bandwidth efficiency.
• C (Parity Bits): True. A single parity bit is specifically designed to detect any single-bit flip within a data unit. 2. Evaluating Statements D and E:
• D (Stop-and-Wait): False. It is highly inefficient on long-delay networks because the sender must wait for an ACK for every single packet, leaving the channel idle most of the time.
• E (CRC): True. CRC uses polynomial division and is significantly more robust than simple parity, as it can detect burst errors and multiple-bit errors. 3. Final Logic: Statements B, C, and E are correct. Statement A describes Selective Repeat, and Statement D is the opposite of the truth regarding efficiency.