[e2e] Why do we need congestion control?

LOCHIN Emmanuel Emmanuel.LOCHIN at isae.fr
Fri Apr 5 23:56:06 PDT 2013

Le 05.04.2013 23:29, Detlef Bosau a écrit :
> Am 04.04.2013 14:22, schrieb Emmanuel Lochin:
>> On 04/04/2013 13:31, Detlef Bosau wrote:
>>> Simple question. Where is "fair dropping" that different from
>>> "fair queueing"?
>> The FairDrop queue we have implemented to drive our tests with DCTP
>> simply drops packet of the most opportunistic flows in the queue.
>> Meaning that if you have 3 flows and a full queue of 30 packets, you
>> should have 10 packets of each flow enqueued.
>  Three flows.
>  Manu, how do you want to implement fair queueing on a backbone 
> router

First, I've never claimed that I wanted to implement such mechanism 
inside the core router.

> with actually 200.000 flows? 150.000 of them being "mice"?

You talk on average not instantaneously. You only maintain a state for 
flows currently enqueued.
It means that if you have a queue size of 30 packets, you can't have 
more than 30 states in your table.

>  At least this question should be discussed for both kind of
> approaches, VJCC and DTCP.

It has been already discussed for TCP, just google FairDrop and TCP.

>  So to my understanding, neither VJCC nor DTCP separates the problem
> of resource allocation from the problem of congestion control, nor do
> they eventually _solve_ the problem of (fair) resource allocation.

Anyway, my ISP with CAC or DiffServ does?

>  To my understanding, many of us recognize the problem of a missing
> (convincing) resource allocation scheme here and replacing VJCC by a
> scheme which runs into the same difficulties as VJCC is a bit beating
> about the bush.

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