We looked at three protocols for providing reliable transport: Alternating Bit, Go-Back-N and Selective-Repeat. Given a window size, W , what is the minimum sequence space required for each of these protocols?
Try an answer before revealing the guidance below.
Key Concepts
- Sequence number wrap-around
- W + 1 for GBN
- 2W for SR
- 1 bit for Alternating Bit
Answer Approach
- Alternating Bit has a window of 1: how many numbers distinguish new from duplicate?
- For GBN, consider a full window sent and all ACKs lost.
- For SR, the sender and receiver windows must not overlap.
Full Answer
Answer status: Draft answer (unofficial). Revision notes, not an official marking scheme.
Alternating Bit: 2 sequence numbers (0 and 1). Go-Back-N: W + 1. Selective Repeat: 2W (the window can be at most half the sequence space).
AB: 2GBN: ≥ W + 1SR: ≥ 2WShortcuts: K concepts · A approach · F answer · R reviewed · B bookmark · ← / → previous / next