[Codel] [RFC PATCH] codel: ecn mark at target

Richard Scheffenegger rscheff at gmx.at
Sat Aug 4 09:38:48 EDT 2012


My 0.02 EUR:

mark every packet with a sojourn time above target is OK.

The reaction of the congestion controller to ECN marks need to be more 
differentiated; ECN can deliver much more fine-grained information about the 
current state of the network. If a congestion controller (e.g. legacy 3168 
ECN TCP) chooses to overshoot in it's reaction, thats a problem for that 
particular controller... But even if every packet of a window is marked, a 
legacy TCP will only reduce cwnd once per window, reacting the same as is a 
non-ECN had a single drop in that window...

DCTCP (ECN alpha/beta) does things more fine-grained, and would push legacy 
(non ECN) out of the way, while maintainig full bandwidth and very low 
sojourn time (queue occupancy).

Fixing the reaction of congestion controllers to ECN signals (deliberate 
plural) will be the next step in that area...

Best regards,

----- Original Message ----- 
From: "Roger Jørgensen" <rogerj at gmail.com>
To: "Dave Täht" <dave.taht at bufferbloat.net>
Cc: <codel at lists.bufferbloat.net>
Sent: Saturday, August 04, 2012 9:00 AM
Subject: Re: [Codel] [RFC PATCH] codel: ecn mark at target

On Sat, Aug 4, 2012 at 4:44 AM, Dave Täht <dave.taht at bufferbloat.net> wrote:
> From: Dave Taht <dave.taht at bufferbloat.net>
> The consensus at ietf was that ecn marking should start at
> target, and then the results fed into the codel drop scheduler.
> While I agree with the latter, I feel that waiting an interval
> before starting to mark will be more in-tune with the concept
> of a sojourn time, and lead to better utilization.
> As I am outnumbered and outgunned, do it at target.

Well, what do you think is The Best way of doing it? Prove'em wrong if
you really think they are wrong;)


Roger Jorgensen           | ROJO9-RIPE
rogerj at gmail.com          | - IPv6 is The Key!
http://www.jorgensen.no   | roger at jorgensen.no
Codel mailing list
Codel at lists.bufferbloat.net

More information about the Codel mailing list