Subject: Re: FW: ssthressh

From: Randall Stewart <[email-masked]>
Date: Thu, 30 Jun 2005 05:18:08 -0400

Brian F. G. Bidulock wrote:

>>Once the shared bottleneck detection algorithms are fully
>>worked out ... then we can actuall do it as a standard thing :-D
> 
> 
> Works fine with or without a shared bottleneck.
> 
> What problems do you envisage?
> 
The problem is NOT for the SCTP sender.. its for
the rest of the internet. The basic goal of CC is to
make sure a particular sender does on harm to the network
and yet gets its fair share of the bandwidth... with
a design goal of 1/Nth of the bandwidth where
N is the number of competing users.

So in this situation:

          ----IP-a<------Inet-a-Path------> IP-x
         /                                       \
sender                                             receiver
        \                                        /
         ----IP-b<-------Inet-b-Path------> IP-y

which is a typical sigtran for example.. CMT (conncurent
multipath transfer) does no harm.. providing that you do
fix the problem with Fast Retransmits (with similar algorithms
to what Jana is working on at the U-of-Deleware)... No problem.

However if you have this:

          ----IP-a<--           -----> IP-x
         /          \          /      \
sender               -bottle-          receiver
        \           /         \        /
         ----IP-b<--           -------> IP-y

You now have sender getting 2/Nths of the bandwidth of
the bottleneck.. which gives the sender more bandwidth
of the bottleneck then it is entitled to.

If you can detect the shared bottleneck (which I know
there is several research studies going on in this
area.. then you can compensate for this).

I add Mark on... he might want to comment futher :-D

Mark? any thoughts :-D

R

-- 
Randall Stewart
ITD - Cisco Systems Inc.
803-345-0369 <or> 815-342-5222 (cell)