We looked at three protocols for providing reliable transport: Alternating Bit, Go-Back-N and Selective-Repeat. Assume we have a delay-bandwidth product of 1MByte and a maximum segment size (MSS) of 1KByte. Assume the local memory available for buffering is not a limiting factor. Give one advantage for each of the three protocols
Try an answer before revealing the guidance below.
Key Concepts
- Stop-and-wait simplicity
- Pipelining
- Cumulative ACK
- Individual retransmission
Answer Approach
- Compare how many segments each protocol keeps in flight.
- Compare receiver complexity and buffering.
- Compare what each retransmits after a loss.
- Pick one strength per protocol that the others lack or do worse.
Full Answer
Answer status: Draft answer (unofficial). Revision notes, not an official marking scheme.
Alternating Bit: simplest to implement, with only one segment outstanding, one timer, a 1-bit sequence number and minimal buffering. Go-Back-N: pipelined, so it fills the link, while the receiver stays simple (no out-of-order buffering, cumulative ACKs, one timer). Selective Repeat: retransmits only the lost or corrupted segments, so it wastes the least bandwidth when errors occur.
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