Subject: RE: [Diffserv] Re: Mapping IP QoS Info to ATM QoS

From: "Manfredi, Albert E" <[email-masked]>
Date: Fri, 16 Jun 2000 16:19:48 -0400

> -----Original Message-----
> From: Grenville Armitage [mailto:[email-masked]]
> 
> John Schnizlein wrote:
>
>  [ ... ]
>
> > Dan's "by whatever name" refers to the linguistic debate spawned
> > by the attempt to move a litte closer to service specification
> > named "behavior aggregate" and renamed "per domain behavior" (PDB).
> 
> That part I understand, but I still dont see why DiffServ needs
> to define services before anyone can figure out what ATM
> level services can usefully support particular DS PHBs.
> 
> > While we are out here in the weeds, note that the tidy lawn view of
> > this is as Brian said - ATM virtual circuits connect router hops
> > through a virtual link. And the link behavior is part of the per-hop
> > behavior.
> 
> Well, that's pretty much what I said in different words. IP PHB
> is DS PHB + link service class. So what's the question that cannot
> be answered by this approach?

I'm going to assume that ATM is used in part or all of the diffserv domain
and that the approach used is to map diffserv PHBs to ATM CoSs, or vice
versa.

What can be said, at this stage? As far as I can tell, not much more than:

1. For EF, use CBR.

2. For AFxy, use VBR or ABR, or GFR.

3. For so-called best effort, use UBR.

Does that tell you anything. For that matter, is it even correct? I think
there is a lot more quantifying of services that needs to be done before
anything meaningful can be said about mapping. It's possible that the
diffserv wg will never go to that level of definition.

In my view, once (or if) diffserv determines what EF means in terms of
packet drop probabilities, latency, and jitter, and what the different AF
classes mean in terms of peak, avergage, and min bit rates, drop
probabilties, and latency, then once can start working out real
equivalencies in terms of the kind of QoS an ATM setup message must demand
when serving a diffserv domain.

Or vice versa.

Or am I missing something?

Bert
[email-masked]

_______________________________________________
diffserv mailing list
[email-masked]
http://www1.ietf.org/mailman/listinfo/diffserv
Archive: http://www-nrg.ee.lbl.gov/diff-serv-arch/

---

From: "Mohammed Atiquzzaman" <[email-masked]>
Date: Fri, 16 Jun 2000 16:47:01 -0400

An issue related to DiffServ-ATM mapping (in addition to
the mapping of the services) is the mapping of the drop precedences from
DiffServ to ATM.  The question is, even if can map AF to VBR or ABR, how do
we map multiple drop precedences from the Assured Service to only two drop
precedence of ATM (ATM has only one CLP bit to indicate the drop
precedence).

Anyone has any thoughts or pointers to literature?

Regards

Mohammed Atiquzzaman       | Email: [email-masked]
Department of Electrical & |        [email-masked]
  Computer Engineering     | Voice: (937) 229 3183,
University of Dayton,      |  (937) 229 3191 (sec), (937) 229 4974 (lab)
Dayton, Ohio 45469-0226.   | Fax:   (520) 962 8422 or (937) 229 4529
                           | http://www.engr.udayton.edu/faculty/matiquzz/

> From: [email-masked] [mailto:[email-masked]]On Behalf
> Of Manfredi, Albert E
> Sent: Friday, June 16, 2000 4:20 PM
> To: 'Grenville Armitage'
> Cc: [email-masked]
> Subject: RE: [Diffserv] Re: Mapping IP QoS Info to ATM QoS
>
>

---

From: Brian E Carpenter <[email-masked]>
Date: Fri, 16 Jun 2000 16:02:44 -0500

"Manfredi, Albert E" wrote:
...
> Does that tell you anything. For that matter, is it even correct?

As I said earlier, I would just use either one CBR VC for everything,
or a separate CBR VC for each diffserv PDB. We know that works. What
is the advantage in complicating things with VBR etc.? We will already
have schedulers for each PHB at the IP level, why do the work
again at cell level?

  Brian

---

From: Scott W Brim <[email-masked]>
Date: Fri, 16 Jun 2000 17:28:40 -0400

>precedence of ATM (ATM has only one CLP bit to indicate the drop

AF already says

    If a DS node only implements two different levels of loss probability
    for an AF class x, the codepoint AFx1 MUST yield the lower loss
    probability and the codepoints AFx2 and AFx3 MUST yield the higher
    loss probability.

which easily implies AFx1 -> CLP0, AFx{2,3} -> CLP1.

By the way, just for fun, CLP is defined as ignored in ABR. :-)

---

From: Hung <[email-masked]>
Date: Fri, 16 Jun 2000 17:40:42 -0400

Certainly it will work, but why bother to have ATM if everything is CBR. Why not
just put them over sonet directly? Mapping AF to CBR could be very inefficient.
-- Keith.

---

From: Dan Grossman <[email-masked]>
Date: Tue, 20 Jun 2000 09:51:15 -0400

> is the advantage in complicating things with VBR etc.?

For the same reason you probably don't want to map a best effort end-to-end 
service onto EF. Yes, it can be done, but it is a gross waste of resources.

>We will already
Because scheduling is an integral part of the ATM traffic management system.  
I doubt very much that anybody will strip out the scheduler on an ATM switch 
on the premise that scheduling will be done (never mind done better) at the IP 
level.  One could argue the opposite, though.

---

From: Dan Grossman <[email-masked]>
Date: Tue, 20 Jun 2000 09:38:39 -0400

> What can be said, at this stage? As far as I can tell, not much more than:
Or maybe rt-VBR.
> when serving a diffserv domain.
That's the core of the problem.  PHBs define local forwarding behavior, not 
edge-to-edge system behavior.  The argument (which I still agree with, 
although not as strongly as before this thread started) is that the ATM LIS 
contributes to edge-to-edge system behavior in a way that is not reduceable to 
local forwarding behavior.