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  • TCP retransmission statistics from Google

    Abstract

    This article is an abstract from a paper which analyses TCP data from Google Web and vedio servers and

    present key statistics on the nature of retransmissions.

    Statistics

    (1)TCP and HTTP statistics

    TCP

        Total connections                                                     Billions

        Connections support SACK                                   96%

        Connections support Timestamp                         12%

        HTTP / 1.1 connections                                           94%

        Average requests per connection                         3.1

        Average retransmissions rate                               2.8%

    HTTP

        Average response size                                            7.5KB

        Responses with TCP retransmissions               6.1%

    Summary of Google TCP and HTTP statistics sampled for one week in May 2011.

    The data include both port 80 and 443 but exclude YouTube videos and bulk downloads.

    The majority of clients are Microsoft Windows which by default do not use TCP Timestamps.

    The average user network bandwidth as observed from Google is 1.9Mbps.

    (2)Breakdown of TCP retransmission types

                                                                                    Web pages                  video

    Fast retransmits                                                  24%                               54%

    Timeout retransmits                                           43%                               17%

        Timeout in Open                                              30%                                8%

        Timeout in Disorder                                         2%                                 3%

        Timeout in Recovery                                        1%                                  2%

        Timeout Exp. Backoff                                      10%                                 4%

    Slow start retransmits                                        17%                                29%

    Failed retransmits                                               15%                                 0%

    (3)Fast recovery related statistics

                                                                                   Web pages                   video

    Fast retransmits / FR                                         3.15                                2.93

    DSACKs / FR                                                       12%                                4%

    DSACKs / retransmit                                          3.8%                              1.4%

    Lost (fast) retransmits / FR                               6%                                  9%

    Lost retransmits / retransmit                            1.9%                               3.1%

    (4)other

    TCP recover losses in two ways

    Fast recovery (1RTT) need dupacks

    Timeout (often 5 ~ 10 RTTs)

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  • 原文地址:https://www.cnblogs.com/aiwz/p/6333358.html
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