[tcpm] [Iccrg] Re: ECN feedback discussion

[Michael Welzl]

On Nov 9, 2012, at 4:06 PM, Yuchung Cheng wrote:

> 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.

Chicken-egg, I suppose: why support something that noone uses?

Cheers,
Michael