Go Back N Window Sizes Explained | Generated by AI
Question: In the Go-Back-N sliding window protocol, what are the sizes of the sending window and receiving window?
Answer:
Go-Back-N (GBN) Protocol — Window Sizes
The correct answer is B: Sending Window > 1, Receiving Window = 1
Explanation of All Three Sliding Window Protocols
| Protocol | Sending Window | Receiving Window |
|---|---|---|
| Stop-and-Wait | = 1 | = 1 |
| Go-Back-N (GBN) | > 1 | = 1 |
| Selective Repeat (SR) | > 1 | > 1 |
Why Go-Back-N Has Receiving Window = 1?
Go-Back-N allows the sender to transmit multiple frames without waiting for acknowledgment (sending window > 1), but the receiver only accepts frames in strict sequential order.
- If a frame is received out of order, the receiver discards it and does not buffer it.
- Because the receiver only needs to track the next expected frame (no buffering of out-of-order frames), the receiving window size is 1.
- When an error occurs at frame n, the sender must go back and retransmit frame n and all subsequent frames — hence the name “Go-Back-N.”
Why NOT Option C (both > 1)?
Option C describes the Selective Repeat (SR) protocol, not Go-Back-N. In SR:
- The receiver buffers out-of-order frames, so receiving window > 1.
- Only the specific erroneous frame needs to be retransmitted (not all subsequent ones).
Summary
Go-Back-N trades off receiver buffer simplicity (window = 1, no buffering needed) against retransmission efficiency (must resend multiple frames on error). This is the key distinction from Selective Repeat.