Re: [Bloat] First draft of complete "Bufferbloat And You" enclosed.

[d@taht.net (Dave Täht)]

Jim Gettys <jg@freedesktop.org> writes:

> Several reactions:
> [elided]
> But memory is sooo cheap we've paved Texas over with extra road, just
> in case.

Why pick on Texas? The maximum latency yet reported was 40 seconds,
which is like 31 lunar distances (40/1.28), or half that if you are
measuring latency as RTT. 

It's one of those mind-bogglingly big numbers that douglas adams warned
us about. I wouldn't be surprised if someone reported RTT times as large
as between here and Venus.

Texas has enough problems.

> (QOS isn't universal, much less your complicated rules). Fix the
> bloat: then classify.

For years a very simple classification scheme has existed by
default. Most UDP packets actually used the TOS field sanely and the
 OS would prioritize those packets appropriately.

It worked, mostly. It's been devilish with SIP, however. 

A few other classification schemes have worked well in the field - the
wondershaper started a trend to prioritize interactive ack packets,
which helps interactive traffic (ssh, x11, stuff like that) a lot,
improving latency under load for latency dependent tcp streams.

Most of the others... Not so much. Interesting edge cases. Maybe a
diamond in the rough here and there.

Lastly, I make a distinction between QoS and AQM - one that's kind of
hard to define. To me AQM is about trying to ensure overall fairness and
goodput (techniques like RED and SFB) by managing queues sanely, and QoS
is about providing high speed lanes with special properties for certain
kinds of traffic.

Both ARE useful, but can be addressed in order of reducing unmanaged
buffers, applying AQM, and then QoS. 

> Many people will need to replace their routers, and will believe that
> is expensive; and to them, buying a $100 router *is*
> expensive. Remember your audience. And various ISP's aren't going to
> like the bottom line cost of replacing/upgrading all the broken
> equipment.

A lot of them can just get new firmware. Although it's likely that
dd-wrt and openwrt are worse, out of the box, at present.

My concern is after observing several reviews of new wireless kit in the
press that the most modern gear is exhibiting bufferbloat problems, as
yet undiagnosed. 

Possibly here:

http://online.wsj.com/article/SB10001424052748704774604576035691589888786.html

Certainly here:

http://www.dd-wrt.com/phpBB2/viewtopic.php?p=416640&sid=635145ce6d7ee3bb695b39ace6b9c101


-- 
Dave Taht
http://nex-6.taht.net