Subject: RE: [Diffserv] RE: Two new Internet-Drafts submitted

From: Nabil Bitar <[email-masked]>
Date: Fri, 12 Nov 1999 16:08:25 -0500

Hi,
I have a question about LBE. Is LBE supposed to have less share of 
bandwidth (whether excess or available) than BE and higher drop precedence 
than BE? Or is it different. If this the case, one can argue that BE  and 
LBE can possibly be implemented using two different instances of AF with 
the appropriate parameter settings.

Regarding the current number of AF classes and how they are perceived to be 
used, all that there is to the AF PHB is that it allows up 3 drop 
precedence levels for each class (preferably 3 and possibly 2). The number 
of 4 classes allows reservation of 12 DSCPs for AF. Thus, there is nothing 
that limits the configuration of more or less AF classes. So, if 4 AF 
classes are needed to run better than LBE and BE services, a 5th AF class 
can be configured to run an LBE service. I guess that the question is if 
there is need to grab DSCP(s) out of the non-experimental space for this AF 
class to provide LBE service (as done for the existing 4 AF classes). In 
addition, for this LBE service, do you need 3 drop precedence levels? That 
is, do you need to use three DSCPs? I am not sure what the this PHB is 
supposed to provide. If you need one drop precedence, then it can be 
configured as an AF class with one drop precedence level (i.e. possibly 
drop whenever you exceed a certain buffer size). In that case, do we still 
call it AF? That brings me to another point. It seems that anything can be 
configured using AF. Even EF, as some people claim, can be implemented 
using the AF PHB ! (although one may dispute that).  Is AF a universal PHB 
so that any PHB can be mapped to an appropriately configured instance of 
AF? Is it the way that is intended to be?

Nabil.
On Thursday, November 11, 1999 12:45 PM, Nabil Seddigh 
[SMTP:[email-masked]] wrote:
> Juha Heinanen writes:
>
>
> >i don't see any mythical in definition of background SERVICE.  it is a
> >service to which no promises nor even expectations are made.  it can be
> >IMPLEMENTED as an af class that has been allocated some buffering
> >resources, but no scheduling resources,
>
> LBE can certainly be implemented as an AF class. However, I have seen a
> number of different service proposals for Diffserv. In many of these,
> the AF classes are already spoken for by services that require better
> than LBE. So, while in principle, AF can be used, if there are  enough
> people who want to use all the AF classes for other services, we may
> want to consider a different solution.
>
> -
> Regards,
> Nabil Seddigh
> [email-masked]
>
>
>
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---

From: Juha Heinanen <[email-masked]>
Date: Wed, 17 Nov 1999 02:34:46 +0200 (EET)

Nabil Bitar writes:

 > Is AF a universal PHB 

i don't claim that af is universial, but it fits very well to cases
where cbwfq with a possible ceiling can be used for packet forwarding
and where dropping of packets can be based on red.  background service
definitely fits very well to that.

-- juha