[Iccrg] Re: [tcpm] ECN feedback discussion

[Yuchung Cheng]

On Thu, Nov 8, 2012 at 11:49 PM, Mikael Abrahamsson <swmike at swm.pp.se> wrote:
> On Thu, 8 Nov 2012, Yuchung Cheng wrote:
>
>> My worries are that we can design fancier stuff, in the end if it does not
>> matter for applications, it does not matter. Is today's basic ECN not being
>> used b/c it's too basic?
>
>
> I'd imagine ECN isn't used today because nobody knows what it is and why
> it's good to use. It's like IPv6, it doesn't really solve anything for the
> individual entitiy (ISP|user|equipment vendor), but as a whole, it would be
> good if we had it.
>
> I would also venture to say that congestion used to happen in the core and
> distribution. This is not really the case anymore, now congestion happens
> much closer to the edge, which is also the place where there is least
> homogenous control and thus harder to coordinate any technology.
>
> I have been running with ECN on, on most my machines for years now, just to
> make sure it doesn't break anything. When it was first implemented in the
> Linux kernel, ECN broke a lot of things. PIX firewalls for instance, dropped
> ECN packets. This is not the case anymore as far as I can tell, I haven't
> noticed any ECN related problem at all since I re-enabled it, hm, 3-4 years
> ago perhaps.
>
> To get ECN (and other more advanced tech) into production networks, we need
> to be able to explain to users and manufacturers (and ISPs) what good it
> does, and how it can make their life metter. From the bufferbloat
> discussion, I'd say this is quite hard, since most don't even know how TCP
> works in conjunction with large buffers, much less the difference between
> different TCP algorithms. So teaching about benefits of ECN is quite hard.
>
> ECN is a good idea. IPv6 is a good idea. IPv6 is now happening (slowly)
> because IPv4 ran out. Nothing happened really for 5-10 years because IPv6
> didn't really solve any problem people thought they had. ECN is the same
> thing. ECN makes the network more efficient, in that it doesn't drop the
> packet if there is congestion. But how does that help the individual end
> user? That's harder to explain.
>
> Sorry for not being able to give any constructive suggestions on how to
> solve the problem of lack of ECN support, but if we can get some consensus
> about why ECN hasn't been implemented, perhaps that helps us making future
> decisions?
+1

ECN has many good things but it's not used. If we are going to develop
a "useful" ECN+ maybe we should ask why the operators don't use ECN.
And I know many ops guy that know extremely well about TCP so maybe
they have valid reasons.

Thanks.

>
> --
> Mikael Abrahamsson    email: swmike at swm.pp.se