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可靠传输
帧可能损坏或丢失，因此可靠交付建立在 ARQ 一族的确认与超时机制之上；停等协议是其中最简单的成员，却会浪费长肥链路的大部分容量；滑动窗口通过发送窗口和接收窗口限制未确认帧、并以累积确认进行管理，从而保持管道满载；有限的序号迫使窗口必须保持在序号空间的一半以下；而 ARPANET 的并发逻辑信道表明，停等协议在多路复用时也能填满一条链路。
1. Acknowledgments and timeouts
Acknowledgments and timeouts
2. Stop-and-wait and the price of waiting
Stop-and-wait and the price of waiting
3. Sliding window
Sliding window
4. Another way to fill the pipe
Another way to fill the pipe
5. The acknowledgment ambiguity
In stop-and-wait, a frame arrives intact but its acknowledgment is lost. What failure follows without sequence numbers?
6. Pricing stop-and-wait
On a 1.5 megabit per second link with a 45 millisecond RTT, stop-and-wait sends one 1 kilobyte frame per round trip. What sending rate results?
7. The sender's invariant
Which invariant must the sliding window sender always maintain?
8. Cumulative acknowledgments
A receiver with window 4 has last acknowledged frame 5. Frames 7 and 8 arrive, then frame 6. What happens?
9. The half-space rule
With RWS equal to SWS, why must the window be strictly less than half the sequence number space?
10. Concurrent logical channels
How did the ARPANET link protocol keep a link full while using only stop-and-wait?
11. The timeout's partner
ARQ combines timeouts with small control frames the receiver sends back to confirm arrival. What are these control frames called?
12. The one-bit fix
Stop-and-wait distinguishes a retransmitted frame from the next new frame using a sequence number field. How many bits wide is that field?
13. The cumulative rule
In sliding window, what kind of acknowledgment covers every frame up to the acknowledged number, even if some higher frames arrived earlier?
14. The window bound
With the receive window equal to the send window, the send window must stay strictly below half of what quantity, raised by one?