[Iccrg] Is ECN too complicated?

[Bob Briscoe]

Mike,

The guys proposing ECN in RTP say their limited tests have found that 
ECN-capable packets get cleared to 00 on some paths.

This may be a case of firewalls with the rule "deny all, unless known 
to be safe," rather than "allow all, unless known to be unsafe". I 
think they used UDP packets and ECN on TCP is known to be safe, 
whereas ECN on UDP is not known to be unsafe.

Perhaps they should take advice from Bob Dylan, who said 
(paraphrasing) "Don't drop packets, that you don't understand; For 
the times they are a-changing."



Bob

At 14:10 31/07/2009, Mikael Abrahamsson wrote:
>On Fri, 31 Jul 2009, John Leslie wrote:
>
>>We do need them to leave ECN marking alone. (Has someone documented
>>which core router do and don't?)
>
>I don't know of any core router that will zero the ECN marking, all 
>I have seen either have ECN support (used in their WRED schemes) or 
>they don't know anything about ECN and just ignores the bits and 
>just passes the packet unchanged (ECN-wise).
>
>>   I don't feel the need for more detail of why intelligence in 
>> core routers is expensive. What we do need is an upper bound on 
>> packet drop (without ECN marking coming first) in actual core routers.
>
> From what I have seen in recent major vendors, the new platforms 
> seem to have around 50-200ms of buffers, coming down from the 
> common 600ms 5+ years back.
>
>This is for 10G and 40G interfaces.
>
>--
>Mikael Abrahamsson    email: swmike at swm.pp.se
>
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________________________________________________________________
Bob Briscoe,               Networks Research Centre, BT Research