Subject: [Diffserv] basic doubts about PHBs

From: "Grace Kou" <[email-masked]>
Date: Wed, 20 Dec 2000 22:29:28

Hi,

I am studying Diffserv (from a service provider's perspective)
and have some basic questions.  I would like to know what are the
typical services (or any real-world examples) to be supported by EF
and AF PHBs?  If EF is targeted for typically low-delay and low
jitter, real-time, applications, then what kind of services are
the "better-than-best-effort" AF PHBs targeting? With these PHBs,
in particular AF PHBs, as loosely defined as they are now, how is a
service provider supposed to construct services with QoS over a
heterogeneous network that supports these "building blocks", which
may come from different vendors and look and implemented very differently?  
Suppose my SLS is defined by a 3-tuple:
<bandwidth, loss_ratio, end-to-end_delay>. How am I supposed to
create a service based on this 3-tuple using Diffserv "building
blocks" if I don't even know what AF1, AF2, AF3, and AF4 are?
If I have to individually tune the parameters of meters, the schedulers
and the like on a per-hop basis along the path to ensure my SLS is met,
then what is the need for all these PHB's any way? As far as I am
concerned, AF PHBs are only useful intra domain for, perhaps, creating
a PDB.

Thank you.

- G. Kou
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From: Brian E Carpenter <[email-masked]>
Date: Wed, 20 Dec 2000 17:31:52 -0600

Grace,

The AF proponents have not yet attempted to publish PDB (per-domain
behavior) definitions based on AF, so I don't think we have an answer
to your question for AF. For EF, despite all the recent debate,
we do have a generic view that something like Virtual Wire is the right
type of PDB, and that is work in progress. 

For purely practical discussion on this I'd suggest the diffserv
implementation list. But if anyone wants to draft a PDB based on AF,
now is the time to do so. 

   Brian

-- 
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Brian E Carpenter 
Program Director, Internet Standards & Technology, IBM 
On assignment for IBM at http://www.iCAIR.org 
Board Chairman, Internet Society http://www.isoc.org
Non-IBM email: [email-masked]

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From: Kathleen Nichols <[email-masked]>
Date: Wed, 20 Dec 2000 17:29:28 -0800

Actually, there WAS an unsubmitted draft from Nabil Seddigh, Biswajit
Nandy,
and Juha Heinanen on something called an AR PDB. (Assured Rate, I
think). They sent us a url for it after the I-D deadline and we 
encouraged them to submit it, but said it was too late for
the San Diego IETF.

	Kathie

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From: demir <[email-masked]>
Date: Wed, 20 Dec 2000 17:42:14 -0800 (PST)

Grace,
I think "do nothing PDB", "do whatever you want PDB" and "do everything
you can PDB" will give you a vast amount of services for AF. Like Brian
said, "do whatever needed PDB" is not yet attempted. To me, "do nothing
PDB" is enough for some applications and they will be happy about it. I
don't agree with your statement on "better-than-best-effort" service
attempt of AF PHB. To me in a multi-class-service environment, it is not
possible to compare services unless there is a relation with compared
services or one defines what comparision means (this option might
mislead). I don't agree with your referring "loosely defined" for AF PHB
or EF PHB (RFC-2598). I guess what you mean is "based on
coarse-grained" mechanisms for diffserv services. To me, it is not
possible to compare "coarse-grained" mechanisms without above assumptions
I made in a general way. However, market decides the "pricing" and this is
not only based on PHBs, I assume.

Alper K. Demir