[e2e] admission control vs congestion control

Fred Baker fred at cisco.com
Fri Apr 21 12:58:24 PDT 2006

For the record, there are products out there that are indeed  
delivering video on IP. My company has a couple, so do many others.  
You are correct that it requires steps to be taken to ensure that  
delivery is consistent.

One of our ISP friends on this list commented that the right solution  
is to make sure that the problem is swamped with bandwidth. That  
would be my preferred solution as well if infinite bandwidth were  
available for free regardless of location. Where cheap bandwidth is  
in fact available, it is my recommendation. My observation, however,  
is that many places that worry about QoS do so because bandwidth is  
not cheap nor necessarily readily available (fiber to the airplane,  
fiber to the ship at sea, fiber to the atoll..., fiber to the Congo),  
and even in well-engineered service networks published papers say  
that there are measurable service bumps that may be correlated with  
competing data streams that synchronize.

On Apr 21, 2006, at 9:20 AM, Detlef Bosau wrote:

> Fred Baker wrote:
>> On Apr 17, 2006, at 6:18 PM, Detlef Bosau wrote:
>>> Excuse me: What´s the very difference between these mechanisms  
>>> and  good ol´ TDM as it is used in line switched networks with  
>>> excellent  results for decacdes now?
>> simple. TDM is not statistical; these are.
>> In other words, if you allocate mumble percent of a link for  
>> video,  and have several video streams using the capacity, in a  
>> TDM world the  bits arrive in an orderly fashion and get clocked  
>> out the other side.  The only "congestion" is that you might use  
>> up the capacity you have  allocated. In the Internet, each video  
>> stream might, under certain  circumstances, have the first packet  
>> of its frame arrive  simultaneously, building up a queue.
> O.k., this is the particular story with speech compression etc.
> There _are_ scenarios where this approach makes sense (and is thus  
> conducted for some years now.)
> In addition, media streams will typically remain quite time  
> sensitive and you will have to provide appropriate switching  
> mechanims.
> What I´ve seen als "multimedia over the Internet" so far is not  
> convincing. And this is not surprising as I do not see a real  
> chance to have multimedia work in a best effort network.
> You talk about decent video.
> Is this "decent"? You surely don´t talk about these funny webcam  
> pictures and this stuff. This is not "decent". This is ridiculous.
> There was a certain multimedia over IP hype in the 90s.
> Thank´s god, it´s over now.
> Detlef
> -- 
> Detlef Bosau
> Galileistrasse 30
> 70565 Stuttgart
> Mail: detlef.bosau at web.de
> Web: http://www.detlef-bosau.de
> Mobile: +49 172 681 9937

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