art@ACC.ARPA (08/21/87)
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 ------