Subject: [Diffserv-interest] How to use AF PHB?

From: ÀÖ´ºêÍ <[email-masked]>
Date: Wed, 27 Mar 2002 16:35:26 +0800

Hi, all!
   I've read some paper and RFC on diffserv. But I'm not clear about the use of AF. Will it be used for some realtime services such as video and audio, or just for better than best effort service? If it's for the latter one, will the realtime services be beared by EF? 

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From: Le Chunhui <[email-masked]>
Date: Thu, 28 Mar 2002 17:7:18 +0800

Hi,Michael E. Flannagan!
   Thank you very much for your explanation. However, I'm still not quite clear about some questions. I think some CBR applications, such as audio is fit for EF PHB. But how about VBR realtime applications, such as video or large static images, for instance, pictures compressed via JPEG 2000? Those applications can adapt their quality image and amount of data according to the state of the network, and only relative small bit rates are required to ensured. Is AF more fit for them than EF? A new PHB, delay bounded PHB, is proposed in the newly passed RFC 3248, will it be even more fit for those VBR?
   Thanks a lot in advance!

>EF PHB should be used for real time UDP traffic.  AF PHB is used to
>deliver multiple levels of drop preference, which corresponds to the {1
>or 2}-rate 3-color marker.  Example:  Traffic of a given type from 0-1Mb
>gets marked AF11, 1-2Mb gets marked AF12, Above 2Mb gets marked AF13.
>Per the RFC, if you then enable a WRED mechanism on an egress interface
>(assuming that mechanism is DiffServ compliant), AF13 traffic will be
>dropped with a probability greater than (or equal to) AF12, which will in
>turn be dropped with a probability greater than (or equal to) AF11.
>
>The accomplishes the task of dropping "out of profile" packets with a
>higher probablity than "in profile" packets, and adds the benefit of
>never re-ordering packets within the entire AF1x class.
>
>
>
>Hope that helps,
>
>Mike Flannagan, CCIE #7651
>Network Consulting Engineer
>Cisco Systems, Inc.
>
>
>> -----Original Message-----
>> From: [email-masked]
>> [mailto:[email-masked]]On Behalf Of 乐春晖
>> Sent: Wednesday, March 27, 2002 3:35 AM
>> To: Diffserv-interest
>> Subject: [Diffserv-interest] How to use AF PHB?
>>
>>
>> Hi, all!
>>    I've read some paper and RFC on diffserv. But I'm not clear
>> about the use of AF. Will it be used for some realtime
>> services such as video and audio, or just for better than best
>> effort service? If it's for the latter one, will the realtime
>> services be beared by EF?
>>
>>

            Le Chunhui
            [email-masked]

---

From: Jiang Yuming <[email-masked]>
Date: Mon, 1 Apr 2002 09:01:53 +0800

Chunhui,

As mentioned by Michael, AF provids multiple levels of drop. This can be
utilized by VBR realtime applications. For example, in the case you
mentioned, JPEG 2000 image or video may be marked as AF. The user can select
among the three drop levels. It is true that with wavelet coding, JPEG 2000
can adapt to the network situation (mainly drop) and hence with relatively
small ensured rate, the quality retrieved is still acceptable. However, less
drop will produce better quality. 

BTW, RFC 3248 is a revision of RFC 2598 (by loosing "leased-line" with some
delay bound) where EF was originally defined.

Regards,
Yuming Jiang

-----Original Message-----
From: Le Chunhui
To: Michael E.Flannagan
Cc: Diffserv-interest
Sent: 3/28/02 1:00 AM
Subject: Re: RE: [Diffserv-interest] How to use AF PHB?

Hi,Michael E. Flannagan!
   Thank you very much for your explanation. However, I'm still not
quite clear about some questions. I think some CBR applications, such as
audio is fit for EF PHB. But how about VBR realtime applications, such
as video or large static images, for instance, pictures compressed via
JPEG 2000? Those applications can adapt their quality image and amount
of data according to the state of the network, and only relative small
bit rates are required to ensured. Is AF more fit for them than EF? A
new PHB, delay bounded PHB, is proposed in the newly passed RFC 3248,
will it be even more fit for those VBR?
   Thanks a lot in advance!

>> [mailto:[email-masked]]On Behalf Of ???

            Le Chunhui
            [email-masked]