We looked at three protocols for providing reliable transport: Alternating Bit, Go-Back-N and Selective-Repeat. What is the optimal size for the sending and receiving window for each of these protocols?
Try an answer before revealing the guidance below.
Key Concepts
- Bandwidth-delay product
- Send window
- Receive window
- Stop-and-wait
Answer Approach
- Alternating Bit is stop-and-wait: how many segments can be outstanding?
- For pipelined protocols, what send window keeps the link busy?
- How many segments must each receiver be able to hold?
Full Answer
Answer status: Draft answer (unofficial). Revision notes, not an official marking scheme.
Alternating Bit: send window 1, receive window 1 (stop-and-wait). Go-Back-N: send window ≈ the bandwidth-delay product (enough segments to fill the pipe for one RTT); receive window 1, since only the next in-order segment is accepted. Selective Repeat: send window ≈ bandwidth-delay product and receive window equal to the send window, so every out-of-order segment in flight can be buffered.
Optimal send window ≈ bandwidth × RTTShortcuts: K concepts · A approach · F answer · R reviewed · B bookmark · ← / → previous / next