[e2e] Question on ssthresh setting in RFC 2581

rick jones perfgeek at mac.com
Tue May 16 08:30:22 PDT 2006

On May 15, 2006, at 8:47 AM, Detlef Bosau wrote:

> Mark Allman wrote:
>>> can anybody explain why equation (3) in RFC 2581 is
>>>  ssthresh = max (FlightSize / 2, 2*SMSS)
>>> and why this has changed from RFC 2001 where min(rwnd, cwnd)/2 was 
>>> used.
>>> In some postings, I found that FlightSize is usually equal to
>>> min(rwnd, cwnd) - but not always. According to the RFC, flightsize is
>>> "the amount of data that has been sent but not yet acknowledged".
>> One hopes that FlightSize == cwnd.  However, we introduced the
>> FlightSize notion in RFC2581 because this is not always the case.  
>> Some
>> stacks let cwnd be changed regardless of how much of the window is
>                                    ^^^^^^^^^ changed or unchanged? ;
> Are there actually stacks who change, i.e. decrease, cwnd when cwnd is 
> not fully used?

If you mean say after idle or whatnot, the Linux stack in 
"contemporary" 2.6 kernels is doing ABC.  It goes so far as to have a 
packet-based cwnd, only increasing it by one packet for every MSS of 
data exchanged.

rick jones
Wisdom teeth are impacted, people are affected by the effects of events

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