[e2e] TCP and Implementation Related Questions

Salman Abdul Baset salman at cs.columbia.edu
Fri Jul 21 22:48:07 PDT 2006

1) I want to confirm if Windows XP implements:
 a) RFC 2581 TCP Congestion Window (probably)
 b) RFC 2861 TCP Congestion Window Validation (not sure)
 c) RFC 3465 Appropriate Byte Counting (probably not)

Does anyone know if they will be supported in Windows Vista?

2) RFC 2861 specified two key points
 a) Congestion window should be reduced after a idle period.
 b) Congestion window should not be increased more than the application
    rate if application is rate-limited or, saying it differently, cwnd
    should not be increased if current cwnd was not fully utilized.

 This is an experimental RFC. Are there any updates to this? Is it
 recommended that all implementations should support it?

3) If an implementation only follows RFC 2581, then even for a
rate-limited application, the cwnd will keep increasing, beyond the rate
at which application is sending data. There are some interesting effects
of this phenomena for CBR traffic. To check that, RFC 2861 proposed to
limit cwnd increase if the cwnd was not fully utilized.

4) Does ns2 implement RFC 2861? I don't think so because if I rate limit
the application (use CBR over TCP), cwnd keeps increasing beyond the
application rate.

5) Finally, does anyone know how to get the cwnd variable in Windows? I
don't think this is possible using getsockopt() (Linux, TCP_INFO) but have
not been able to confirm the non-existence of such a method.


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