Re: TCP congestion control and large router buffers

[Mikael Abrahamsson <swmike () swm pp se>]

On Mon, 13 Dec 2010, Sam Stickland wrote:

> Ironically though, wouldn't smaller buffers cost less thus making the CPEs

1 megabyte of buffer (regular RAM) isn't really expensive.

> cheaper still? I believe the argument made in the blog post is that 
> cheaper RAM been causing the CPE manufacturers to mistakenly provision 
> too much buffer space, which in turn apparently means that TCP can't 
> stabilize at a rate less than available bandwidth (I.e. It's the old 
> 1980's congestion collapse problem all over again). Of course, you'll 
> only see this if a single TCP stream is actually capable of saturating 
> the link. Sam

I would guess they're running standard OSes and haven't tuned the buffers 
at all. Implementing WRED or fair-queue (even if it just means turning it 
on) requires validation which the CPE manufacturers want to minimize.

Also it's our fault as a business, how many ISPs have included AQM in 
their RFPs for CPEs and actually would pay USD5 more per device for this 
feature? I'm not very surprised at the lack of this though, it's hard to 
explain to the end customer with some kind of marketing, both for the ISP 
and the CPE vendor if they're selling to end customers.

It's one of those "in the black box" things that should just work, but 
there is little upside in having it because it's hard to charge for.

--
Mikael Abrahamsson    email: swmike () swm pp se