Subject: [Diffserv] forwarding & aggregating of AF classes (RFC2597)

From: Mudassir Tufail <[email-masked]>
Date: Thu, 3 Feb 2000 18:14:12 -0800

Hello

Some questions raised in my mind while reading the second paragraph in
section 2.0 of RFC2597 which says:

"A DS node SHOULD implement all four general use AF classes. Packets in one
AF class MUST be forwarded independently from packets in another AF class,
i.e., a DS node MUST NOT aggregate two or more AF classes together."

1) Does it exclude the possibility of having AF classes being "relatively"
forwarded? 
For example AF1x class being forwarded with two times lesser delay than
class AF2x. In this case, packets of AF1x class are not being forwarded
independently from packets of AF2x class. Does it not violate the
requirement (of independent forwarding) quoted above?

2) If I remember correct, there have been a discussion on the list for
mapping many DSCPs to a single PHB (in case if a node imlpements fewer
PHBs). This behavior of node does not make it DS non-compliant (correct me
if it is wrong). Is it not the case of aggregating two or more AF classes
together (i.e. a possible violation of the above quote)?

Thank you,  

Mudassir Tufail

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From: Juha Heinanen <[email-masked]>
Date: Fri, 4 Feb 2000 15:57:14 +0200 (EET)

> 1) Does it exclude the possibility of having AF classes being "relatively"

i don't read it that way.  the "i.e." part tries to interpret what the
earlier part of the sentence says and that doesn't prevent relative
allocation of resources.  the only requirement regarding resource
allocation is

   A DS node MUST allocate a configurable, minimum amount of forwarding
   resources (buffer space and bandwidth) to each implemented AF class.
   Each class SHOULD be serviced in a manner to achieve the configured
   service rate (bandwidth) over both small and large time scales.

and a minimun amount of forwarding resources can be calculated from a
relative weight.

 > together (i.e. a possible violation of the above quote)?

a node SHOULD implement all four classes, but if it doesn't, it still is
not allowed to aggregate two classes together.

-- juha