Subject: AW: [Diffserv] about the concern of a rate loss in the definitio n ofdraft-charny-ef-definition-00

From: [email-masked]
Date: Thu, 10 Aug 2000 11:19:36 +0200

Shahram,

>In a router with more than 2 inputs, potentially an EF packet could have a
>jitter of > 2MTU. It follows from your definition of EF (B=2MTU) that we
>can't have a router which has more than 2 inputs. Which is a significant
>restriction.
Do you want to say that you can not find ANY scheduler which lets
the EF packet jitter less than T = 2MTU/R if your Router has > 2 inputs?

If I understand correctly, the VW PDB draft by Van et. proved the opposite.

Note that the spirit of the DS suggests to define PHB only with respect to
the traffic AGGREGATE, not to each flow within the Aggregate.  

Regards,
-Xiaoning

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From: Brian E Carpenter <[email-masked]>
Date: Thu, 10 Aug 2000 08:39:53 -0500

[email-masked] wrote:
..
> the traffic AGGREGATE, not to each flow within the Aggregate.

It's not just the spirit, it is the formal definition of a PHB. A PHB 
specification describes the behavior of a node for a BA, i.e. the outbound
stream of packets carrying  the corresponding DSCP, regardless of their 
origin, of merging within the node, or of their attribution to different 
microflows.

Which tells you that any assertions about rate, latency, or jitter
should refer to the BA, not to the individual flows within the BA.

I'm glad you brought this up, because I was wondering last night whether
people had lost sight of it.

  Brian

P.S. this doesn't stop vendors trying to do better, but it does
limit what goes in PHB definitions.