Re: [aqm] ECT(1)

[Mikael Abrahamsson <[e-mail]>]

On Tue, 4 Aug 2015, Bob Briscoe wrote:

> *Combining ECT(0) and CE with a globally assigned DSCP solely during initial 
> deployment of L4S seems the least worst choice.

Having the same bits in the header mean different things in combination 
with DSCP seems like a really hard to get deployed Internet-wide.

ECN is just now gaining traction and seems like it might actually see real 
deployment. Repurposing those bits just now would most likely just cause 
confusion.

I started using ECN when it first appeared in the Linux kernel around 2001 
or whenever it was. I had to immediately turn it off because some 
firewalls dropped those packets. Now almost 15 years later after this 
sitting in the operating systems for at least 10 years, we're now getting 
to a point where we're ready to start turning it on widely because things 
do not break when it's turned on.

So whatever you come up with now that requires host stack changes, expect 
5-10 years at least until it can be deployed. This means you have to be 
really sure this is what you actually want before you start to push for 
deployment. Also, deployment impacts should be taken a lot into account 
when deciding what to do.

So how sure are you that L4S as it currently stands is the way to go? If 
you think you're going to invent something new in 2-3 years, then please 
wait until then. Experimentation is all fine and dandy, but until we can 
actually get DSCP codepoints working on Internet-wide scale, this approach 
isn't feasable for that use-case (which for me is close to "the only" 
use-case).

My proposal has been before that we should try to get 7 DSCP codepoints 
deployed by using 000xxx, and nudge providers to incrementally just not 
bleach them and treat them as BE in their core networks, so we can use 
them on the edge to influence AQM there.

So, if we're going to invent new meaning of ECN bits in combination with 
DSCP, then that needs to be coupled with work of getting some DSCP working 
Internet-wide in a fashion that someone actually believes will work out, 
as in actually getting significant Internet-wide deployment.

-- 
Mikael Abrahamsson    email: [e-mail]