Subject: Re: NetBSD SACK, Rate-Halving and ECN
To: None <>
From: Rui Paulo <>
List: tech-net
Date: 10/30/2004 17:53:18
On 2004.10.30 12:04:08 +0000, Matt Mathis wrote:
> Be aware that our SACK code predates NewReno, ECN and other improvements to 
> TCP congestion control.  It is not too hard to get our patch to go into 
> current kernels, but as a consequence of dueling algorithms, the resulting 
> code is definitely not correct.  (or so we have been told).

Either way, I'm intrested in your project.

> Also Rate-Halving has proven to have some problematic corner cases, which 
> is why the work was never finished....  Although I still believe that it is 
> the correct (probably even optimal) algorithm if the network it the 
> bottleneck, it does the wrong thing if the window is limited by something 
> else, such as disks.

Is there any known paper describing Rate-Halving problems ? 

> It pains me greatly that NetBSD is now a non-starter for a number of key 
> applications, because the TCP implementation does not support SACK.

In a previous email, someone said that rate-halving was more
interesting to implement than SACK, IIRC.
> We have not worked on NetBSD for more than 5 years now, and can not take up 
> a serious new development project. It would be a good thing for somebody in 
> the NetBSD community to take this up.   I would be happy to offer advice 
> and help any way I can, short of hacking the code myself.


Rui Paulo                          "Simplicity is the ultimate sophistication."
                                      -- Leonardo da Vinci