[altq:1656] Re: Shaping an ADSL pipe

[Nicolas Christin <nicolas@cs.virginia.edu>]

On 2 Oct 2002, Kirk Strauser wrote:

> I'm rather new to ALTQ, so I would appreciate any constructive criticism of
> my setup.  Does it seem reasonable?  Have I done anything plainly incorrect?
> Does this scheme seem like it would expand well for future use (i.e., adding
> *_colo2, *_colo3, ...)?  Is there anything I could improve on?

Kirk,

This is just my opinion, but the file looks just fine, and could be used
as a basis for a more complicated setup. (Do you want to reserve 64K at
all times for colo, even when it's not used?)

I'm not sure you want to use a RED dropper, though. RED has been shown
to cause more problems than anything else when it's not properly
configured, and configuring it is a mess. (There's a paper by Firoiu and
Borden at Infocom 2000 which dealt with the issue.) I would recommend
you use RED *with* ECN. That way, you don't drop packets unnecessarily.
True, ECN is not supported everywhere, far from that, but RED+ECN
seems like the best of both worlds: if the path your traffic uses is
ECN compliant, it shows better performance than DropTail. If not, you
reduce to DropTail. (RED w/o ECN, again, can drop a lot of packets
unnecessarily if not properly configured.)

That's just my thoughts about RED, but I'm not the only person to follow
this line of thoughts - RED is almost 10 years old, a lot of commercial
routers support it, yet, no one deploys it...

Best,
--
Nicolas Christin
Ph.D. Candidate, University of Virginia, Computer Science
http://www.cs.virginia.edu/~nicolas