Subject: Re: [Tsvwg] Congestion window init

From: Randall Stewart <[email-masked]>
Date: Mon, 01 Apr 2002 05:18:54 -0600

"Iain.Thomson" wrote:
> 
> Randall,
> small comment below
> Iain
> =========================
>   Iain Thomson
>   Thales Research Ltd
>   [email-masked]
> =========================
> 
> -----Original Message-----
> From: Randall Stewart [mailto:[email-masked]]
> Sent: Wednesday, March 27, 2002 2:32 PM
> To: Arun Prasad
> Cc: [email-masked]; [email-masked]
> Subject: Re: [Tsvwg] Congestion window init
> 
> Randall wrote:
> >A couple of observations:
> >
> >1) If your peer is limiting you to 1500 bytes no matter if
> >   you are in slow-start or CA you are stuck sending only one
> >   segment at a time.
> >
> >2) You can never grow your cwnd if your peer limits the rwnd
> >   below the value of cwnd.
> 
> With TCP the cwnd grows according to the received ACKs and so may grow very large but the number of bytes that can be sent will still be limited by the size of rwnd. Is SCTP different? I think its RFC 2861 (TCP Congestion Window Validation) that has a useful discussion on this.

Yes, SCTP is a tiny bit  different:

1) You can never grow your cwnd unless you are using all of it.
2) You only are allowed to increase the cwnd by either the
   number of bytes actually ack'd <OR> one P-MTU which ever
   is smaller.

So what will end up happening is that the last ACK that grows the
cwnd may put you slightly over the rwnd (up to P-MTU-1) but after
that it will never grow anymore... since you are never using
the full cwnd....

R
-- 
Randall R. Stewart
[email-masked] 815-342-5222 (cell phone)

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