TCP/IP 详解卷1 ch24 TCP的未来和性能-优快云博客

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)对网络性能的影响。同时，文章还讨论了千兆网络下的延迟限制问题，以及TCP选项如窗口扩大(Window Scale Option)、时间戳(Timestamp Option)和PAWS(Protection Against Wrapped Sequence Numbers)等技术如何改善网络性能。

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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.)