Subject: Re: [PATCH] TCP Veno module for kernel 2.6.16.13

From: Stephen Hemminger <[email-masked]>
Date: Thu, 25 May 2006 13:50:11 -0700

On Thu, 25 May 2006 13:23:50 -0700 (PDT)
David Miller <[email-masked]> wrote:

> From: "#ZHOU BIN#" <[email-masked]>
> Date: Thu, 25 May 2006 16:30:48 +0800
> 
> > Yes, I agree. Actually the main contribution of TCP Veno is not in
> > this AI phase. No matter the ABC is added or not, TCP Veno can
> > always improve the performance over wireless networks, according to
> > our tests.
> 
> It seems to me that the wireless issue is seperate from congestion
> control.
> 
> The key is to identify "true loss" due to overflow of intermediate
> router queues, vs. "false loss" which is due to temporary radio
> signal interference.

Is it really possible to tell the two apart.  Also, a lot of times when
an access point is overloaded, performance is killed because of congestion
overload. 

> This determination is a job for the loss detection in the generic ACK
> processing code in tcp_input.c, not for a congestion control algorithm.
> The congestion control algorithm uses the "true loss" information to
> make congestion control decisions.
> 
> We already have code that tries to make this differentiation, in the
> form of FRTO, and your techniques can likely be placed there as well.

The general idea of resetting cwnd to an estimate of capacity seems to
be a general feature of Westwood, Veno, Compound and Africa. Also FreeBSD
does the same thing, but they don't have a cool name.