TCP/IP 详解卷1 ch24 TCP的未来和性能

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本文介绍了TCP/IP网络中路径最大传输单元发现(Path MTU Discovery)的重要性，并探讨了长肥管道(Long Fat Pipes)环境下如何提高网络效率。此外，还讨论了千兆网络的特点，以及TCP协议的几种扩展选项，如窗口扩大(Window Scale Option)、时间戳(Timestamp Option)和PAWS等，这些都旨在提升网络传输性能。

1. Path MTU Discovery

It is the minimum MTU on any network that is currently in the path between two hosts.

MTU(A, B) = min { MTU(a, b) | (a,b) is on the path between host A and B}

分组并不是越大越好

2. 长肥管道（Long Fat Pipes）

capacity(b) = bandwidth(b/s) * round-trip time(s)

1) 窗口大小 =>更大的吞吐量？

2) 分组丢失会使吞吐量急剧减少

3) 需要更好的RTT测量机制

4) 序号回绕

3. Gigabit Networks

At gigabit speeds we are latency limited, not bandwidth limited.

4. 窗口扩大选项 Window Scale Option

5. Timestamp Option

The timestamp option lets the sender place a timestamp value in every segment. The receiver reflects this value in the acknowledgment, allowing the sender to calculate an RTT for each received ACK.

6. PAWS: Protection Against Wrapped Sequence Numbers

7. T/TCP: A TCP Extension for Transactions

A transaction is a client request followed by a server response with the following characteristics:
1) The overhead of connection establishment and connection termination should be avoided. When possible, send one request packet and receive one reply packet.
2) The latency should be reduced to RTT plus SPT, where RTT is the round-trip time and SPT is the server processing time to handle the request.
3) The server should detect duplicate requests and not replay the transaction when a duplicate request arrives. (Avoiding the replay means the server does not process the request again. The server sends back the saved reply corresponding to that request.)