Subject: [DiffServ] A question on draft-ietf-diffserv-model-05

From: Banu Mohan <[email-masked]>
Date: Tue, 27 Feb 2001 11:32:13 -0600

I understand that the draft-ietf-diffserv-mib-06 is designed based on
the Differentiated Services Informal Management Model documented in
[MODEL].

In Section 8 of [MODEL] decribes the Traffic Conditioning Blocks (TCB)
which describes the configuration and management of a DiffServ interface
as follows:

TCB that contains, by definition, zero or more
Classifier, Meter, Action, Algorithmic Dropper, Queue and Scheduler
elements.  These elements are arranged arbitrarily according to the
policy being expressed, but always in the order here. Traffic may be
classified; classified traffic may be metered; each stream of traffic
identified by a combination of classifiers and meters may have some set
of actions performed on it, followed by drop algorithms; packets of the
traffic stream may ultimately be stored into a queue and then be
scheduled out to the next TCB or physical interface.  It is permissible
to omit elements or include null elements of any type, or to concatenate

multiple functional datapath elements of the same type.

And the section 2.1 of the DIFFSERV-MIB explains Relationship to the
Diffserv Informal Management Model as follows:

This MIB is designed according to the Differentiated Services Informal
Management Model documented in [MODEL]. The model describes the way that

ingress and egress interfaces of an 'n'-port router are modelled. It
describes the configuration and management of a Diffserv interface in
terms of a Traffic Conditioning Block (TCB) which contains, by
definition, zero or more classifiers, meters, actions, algorithmic
droppers, queues and schedulers. These elements are arranged according
to the QoS policy being expressed, always in that order. Traffic may be
classified; classified traffic may be metered; each stream of traffic
identified by a combination of classifiers and meters may have some set
of actions performed on it; it may have dropping algorithms applied and
it may ultimately be stored into a queue before being scheduled out to
its next destination, either onto a link or to another TCB. When the
treatment for a given packet must have any of those elements repeated in

a way that breaks the permitted sequence {classifier, meter, action,
algorithmic dropper, queue, scheduler}, this must be modelled by
cascading multiple TCBs.

The MIB represents this cascade by following the "Next" attributes of
the various elements. They indicate what the next step in Diffserv
processing will be, whether it be a classifier, meter, action,
algorithmic dropper, queue, scheduler or a decision to now forward a
packet.

For example, let me take a diffServActionNext Mib Object,
diffServActionNext OBJECT-TYPE
    SYNTAX       RowPointer
    MAX-ACCESS   read-create
    STATUS       current
    DESCRIPTION
       "This selects the next diffserv  functional  datapath
       element  to  handle traffic for this data path.  This
       RowPointer should point to an instance of one of:
         diffServClfrEntry
         diffServMeterEntry
         diffServActionEntry
         diffServAlgDropEntry
         diffServQEntry

       A value of zeroDotZero in this attribute indicates no
       further Diffserv treatment is performed on traffic of
       this datapath.  The use of zeroDotZero is the  normal
       usage for the last functional datapath element of the
       current data path.

       If the row pointed to does not exist,  the  treatment
       is  as  if  this  attribute contains a value of zero-
       DotZero."
    DEFVAL      { zeroDotZero }
    ::= { diffServActionEntry 2 }

Based on [MODEL] and DIFFSERV-MIB description, my question is that
1. Wouldn't this diffServActionNext Rowpointer ONLY points to an
instance of :
diffServActionEntry, diffServAlgDropEntry, diffServQEntry INSTEAD OF all
the groups?
2. Please let me know whether the decription column in this Mib object
is right. If so , please explain.

Sorry for the long mail. Thanks in Advance.

Thank you.
Banu Mohan.

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From: Brian E Carpenter <[email-masked]>
Date: Tue, 27 Feb 2001 15:03:46 -0600

Well, you are behind the version numbers. The model is at version 6
and the MIB is at version 8. I suspect that your question has been
answered, or at least transformed, in the current drafts.

   Brian

Banu Mohan wrote:
...