概述

Each end-to-end path is characterized by its own minimum possible RTT, given by the sum of link
propagation latencies and transmssion and processing delays on all nodes in the forward and reverse
direction. This quantity represents the fixed component of RTT experienced by each segment of a
connection. Segment RTTs may have additional variable components due to queuing and processing
delays at overloaded routers and end-hosts.

数据分析

（一）Per-segment RTT Distribution

The observed RTTs range from 1ms to more than 200ms.
A little over 40% of RTT samples are 100ms or less, but 50% of the samples have values between
100ms and 1s. Less than 3% of RTT samples have values smaller than 10ms while 5% of RTT
samples have values between 1s and 10s.

5%的RTT小于10ms。
15%的RTT介于10~50ms。
25%的RTT介于50~100ms。
20%的RTT介于100~200ms。
25%的RTT介于200~1000ms。
5%的RTT介于1~10s。

（二）Per-connection RTTs

Distributions of the minimum, maximum, mean, median and 90th percentile RTTs observed for each
connection.

对于min RTTs：
20%连接的最小RTT小于20ms。
20%连接的最小RTT介于20~50ms。
20%连接的最小RTT介于50~100ms。
20%连接的最小RTT介于100~200ms。
20%连接的最小RTT大于200ms。

（三）Standard Deviation of Per-connection RTTs

Variable components of RTT are estimated by the standard deviation.

Approximately 50% connections have a standard deviation greater than 50ms and about 25% are
greater than 100ms.

25%的连接的标准方差小于10ms。
25%的连接的标准方差介于10~50ms。
25%的连接的标准方差介于50~100ms。
25%的连接的标准方差大于100ms。

How variability is related to the fixed components (estimated by the minimum) ?

RTT variability increases only slightly as the fixed (minimum) delay increases up to about 100ms.
From 100 to 1000ms, RTT variability increases linearly with increasing minimum RTT but then
increases only slightly with minimums from 1sec to 10sec.

（四）SYN RTT

For almost 72% of connections, the min RTT is equal to the SYN RTT. This suggests that the
SYN RTT may be used as a reasonable approximation of the min RTT. However, for 14% of the
connections, the SYN RTT exceeds the min RTT by more than 10%.

Reference

《Variability in TCP Round-trip Times》