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TCP拥塞控制
TCP拥塞控制让每个源通过维护一个与通告窗口并行的拥塞窗口来探测网络提供多少容量：当确认及时到达时加法增大该窗口，丢包时乘法减小；慢启动阶段从冷启动开始呈指数增长；当三个重复确认揭示丢包时，通过快速重传和快速恢复迅速恢复；现代变体如CUBIC则优化对可用带宽的搜索。
1. The congestion window and self-clocking
The congestion window and self-clocking
2. Additive increase and multiplicative decrease
Additive increase and multiplicative decrease
3. Slow start and fast retransmit
Slow start and fast retransmit
4. From Reno to CUBIC
From Reno to CUBIC
5. The effective window
A TCP connection has CongestionWindow equal to 8000 bytes and AdvertisedWindow equal to 12000 bytes, with 2000 bytes currently unacknowledged. How many more bytes may the source send right now?
6. Reading the sawtooth
A TCP flow in steady state loses a packet every time its congestion window reaches 16 segments. Assuming the classic algorithm with halving on loss and additive increase afterward, what does the window do next?
7. Why three duplicate ACKs
Why does TCP's fast retransmit wait for three duplicate acknowledgments before resending the missing packet, instead of retransmitting on the very first duplicate?
8. Slow start's growth
A new TCP connection starts slow start with a congestion window of one segment and loses nothing for four round trip times. How many segments does the window allow in transit at the end of the fourth round trip?
9. Self-clocking
TCP is often described as self-clocking. What does that description refer to?
10. The state variable
TCP congestion control adds one state variable per connection to limit how much data the source may have in transit, the counterpart of flow control's advertised window. Give its name in camel case as used in the protocol literature.
11. The threshold that ends slow start
During slow start the congestion window doubles each round trip until it crosses a remembered value, after which additive increase takes over. Give the usual name for this threshold, in camel case or as plain words.
12. The signal for fast retransmit
Fast retransmit fires without waiting for a timer when the sender has seen a specific count of identical acknowledgments for the same sequence number. How many duplicate acknowledgments trigger it?
13. The two flavors of loss
A TCP sender detects congestion once through a coarse timeout and once through three duplicate ACKs. How do the two responses differ?
14. The acronym for the strategy
Classic TCP grows its window by one segment per round trip when things go well and halves it on loss. Networking texts name this strategy with a four letter acronym. Give it.