TCP SRTT


art@acc.arpa
21 Aug 87 11:09:00 PST


I implemented the SRTT algoritm posted by Van Jacobsen a while back.
This is the one that accumulates both a smoothed round trip time estimate
(SRTT) and also a smoothed variance estimate (which I call SRTV). The
retransmit timer is set to: (SRTT + 2*SRTV)*rxmt_backoff_factor.

This has greatly improved the behavior of TCP over low speed links
(4800-9600 baud), while showing no noticable effect over Ethernet.
Using the standard SRTT algorithm, I was seeing as low as 10% link
utilization because of spurious retransmissions. The new algorithm
is giving over 90% link utilization.

I would recommend others consider using this algoritm if there TCP
ever uses a path with large delay variance (such as low speed lines
or Arpa Internet).
                                        Art Berggreen
                                        art@acc.arpa

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