Subject: [Diffserv-interest] Re: streaming/QoS

From: Fred Baker <[email-masked]>
Date: Mon, 08 Apr 2002 16:25:05 -0700

At 03:26 PM 4/8/2002, Ayyasamy, Senthilkumar (UMKC-Student) wrote:
>1.Of all the existing applications,video and audio streaming demands more 
>QoS mechanisms.
>Is their is any study relating these streaming applications with diffserv.

well google seems to have some pointers to various papers. Is that what 
you're asking?

I'm not certain, BTW, that these are the principal applications. VoIP has 
certainly driven a certain class of interest. But my observation since 
~1984 has been that one cannot sell a routing or switching product in an 
enterprise environment if it lacks features that enable the manager to 
apply policies to his traffic. The policy may be that a certain application 
needs sub-second response time and should get priority or a certain 
bandwidth, or needs to be limited to some bandwidth on some manner. But QoS 
technology is the technology that allows him to select a subset of his 
traffic and make something be true of it.

>2.This question is more or less related to the first.Please refer to some
>research work which discusses relation between Audio& video qulaity and 
>network
>performance.Some thoughts about this topic is also appreciated.

I didn't see a question mark. What was the question?

>3.Is expedited forwarding only way to give guaranteed treatment to 
>audio/video
>streaming applications

no, it's just the only one that works :^)

A little more seriously, there are basically three queuing policies that 
diffserv generally applies to a class. It can give it priority, which it 
publicly only does using EF. It can give it a rate or a percentage of the 
line, and use the rate of the queue, augmented in the worst case active 
marking or dropping, to slow down traffic when the aggregate exceeds the 
available bandwidth. It can do the second and additionally use specialized 
marking to ensure that the subset of the aggregate most affected is the 
part that is over-using some contract. This third, of course, is AF.

I generally think that EF is a good thing for interactive VoIP. If the 
queue for a set of video streams is provisioned for the sum of their peak 
rates, AF4 is probably a good choice for RTP video; this does imply knowing 
what microflows are going through the class, and what their peak rates are, 
which in my mind implies some form of signalling. I honestly don't see the 
difference between Real Networks or Microsoft Media Player and a file 
transfer, other than that they might start doing something with the file 
before they have received the whole thing.

>4.E-model of ITU-T estimates MOS by mapping voice quality with impairments 
>like delay, signaling and user expection.Can we related these impairments 
>with diffserv drop precedence for mapping streaming application with QoS.

Could you forward a pointer to that which doesn't require membership in a 
closed user group to review it?

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