Subject: [mpls] MPLS/DiffServOA and BA

From: Andreas Hess <[email-masked]>
Date: Thu, 16 Sep 2004 18:14:37 +0200

Hi,
I am not sure if I really understood the concept of OAs and BAs.
To my understanding a DSCP value consists of a PHB scheduling class part and a 
drop precedence part. Furthermore, a BA is identified via the DSCP value.
So far, things are fine.
But I am not sure about  the definition of an ordered aggregate (OA), which is 
said to be a set of BAs that share an ordering constraint. Does this mean 
that an OA specifies the interaction of multiple PHBs on a diffserv node such 
that no reordering --- on microflow basis --- of packets occurs?
Is this correct?
Thanks for helping!

Regards Andreas

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From: Eric Gray <[email-masked]>
Date: Sat, 18 Sep 2004 08:34:30 -0400

Andreas,

    As I understand it, you are close but not exactly right.

    In the simplest terms, the thing that makes it so that a group of 
(two or more)
Behavior Aggregates cannot be part of the same Ordered Aggregate is when we
either cannot define, or cannot agree on a definition, for a 
deterministic decision
process for handling a near simultaneous arrival of packets from two or 
more BA
within the same (hypothetical) OA - for every possible combination.

    There are two things to note here. The first is that this difficulty 
should have no
effect on ordering within a BA unless the decision making rules are 
pathological.
The second is that this does not mean that clever people have not 
already thought
of ways to make such a decision.

--
Eric