[Iccrg] Re: [tcpm] ECN feedback discussion

[Mikael Abrahamsson]

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?

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