[e2e] Why do we need congestion control?

Detlef Bosau detlef.bosau at web.de
Sat Apr 6 03:35:02 PDT 2013

Am 06.04.2013 08:56, schrieb LOCHIN Emmanuel:
> 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.

I see. Howver: To my understanding, fair queueing must be available on 
any router in this approach?
>> 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?

Do we talk about fair queueing in the sense of best effort? The problem 
to find the right trade off between a more or less uncontrolled system 
and a QoS system here. CAC and DiffServ are clearly on the QoS side.

Detlef Bosau
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