Subject: Re: Congestion window problem

From: David Borman <[email-masked]>
Date: Thu, 21 Oct 1999 11:40:25 -0500 (CDT)

Zoran,

> From [email-masked] Thu Oct 21 10:56:03 1999
> Date: Thu, 21 Oct 1999 10:37:41 -0400
> From: Zoran Kostic <[email-masked]>
> To: [email-masked]
> Subject: Congestion window problem
>
>   Is the following scenario a legitimate problem:

No.

> * Receive window is fully open
> * Congestion window is 5 wide, all five segments (1,2,3,4,5) got
> transmitted,
>    waiting for ACQs
> * Segment 2 is being timed
> * Channel is poor
> * Timeout happens
> * Congestion window collapses to 1
> * Segment 1 which is the first unacked segment gets transmitted
> * Segment 1 is timed
> * Segments1,2,3 get acqs but 4 and 5 are not ACQed
> * Retransmit timer has stopped since 1 was acked

This is the problem.  The retransmit timer continues to run
as long as there is outstanding, un-acked data, so getting
segment 1 acked does not turn of the retransmit timer, since
4 and 5 are still outstanding.

> * Congestion window became of size 2, but no new segments can be
> accepted
>    into the window since 4 and 5 occupy the space in the window
> * Channel is still poor, no Acqs are comming and Nothing is being timed
> now so
>    the timeout can not occur -> therefore no segment will get
> retransmitted,
>    the window can not grow .... we are stuck
>
> If this is not a problem, could you comment on where the error in
> thinking is,
> or which mechanism pulls us out of trouble.
>
> Zoran Kostic, AT&T

		-David Borman, [email-masked]