[e2e] TCP and Implementation Related Questions
jsj at ieee.org
Tue Jul 25 19:28:10 PDT 2006
A reasonably detailed explanation of MS' Server 2003 stack is here:
This is in Word format. It is also available online (readable in a
Based on Lloyd Wood's IET link, I believe the server 2003 implementation
will be employed inVista too.
Lloyd Wood wrote:
> For an overview of Vista TCP features (and testing against Windows
> Server 2003 for a geo satellite delay environment -- they didn't test
> against anything else...), see slides and video at
> 26 Jun 2006 Technology - Communications
> IP over Satcom for Military Users
> David Race and Paul Thomas
> Event: Military SatComs 2006
> (search on Microsoft)
> This describes Microsoft's "Compound TCP" implementation. They made a
> big deal about having a 64K window improving the Vista stack
> performance in that environment, as if that wasn't the obvious thing
> to do with a 16-bit pointer on a machine with a gig of memory. See also
> A Compound TCP Approach for High-speed and Long Distance Networks
> Technical paper on an experimental variant of TCP optimised for
> high-speed, long-distance networks.
> Compound TCP: A Scalable and TCP-Friendly Congestion Control for High
> Speed Networks
> I expect from this that Microsoft's cwnd implementation will be
> somewhat outside RFC specs - more aggressive? Can't find any internet
> drafts describing it either; it seems they've not bothered with the
> IETF. (Does the IETF still do bakeoffs, anyway?)
> I believe that as TCP is an ever-decreasing amount of internet
> traffic, non-RFC changes to deployed congestion control really don't
> matter as a threat to The State of Internet Congestion That Must Be
> Preserved At All Costs and the Illusion that TCP Friendliness Matters.
> But as an endhost upgrade, Windows Vista deployment will have a
> significant effect on network performance for its userbase.
> hey, faster spam from 0wnd machines!
> At Saturday 22/07/2006 01:48 -0400, Salman Abdul Baset wrote:
>> 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
>> not been able to confirm the non-existence of such a method.
jsj at ieee.org
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