Subject: RE: [Diffserv] Why to obligates the field diffServQShaper?

From: Yossi Bar Sheshet <[email-masked]>
Date: Tue, 27 Mar 2001 10:49:34 +0200

I will sharpen my question,

In an implementation that doesn't use a shaper to shape or to limit the data
rate, the maximum data rate will be limited by the physical interface itself
(for example, UTOPIA interface for ATM, POS-PHY for packets over sonet,
etc.).

In absence of shaper, the configuration parameters for the shaper are not
needed.
The MIB mentions that a ZeroDotZero is an illegal configuration.
What should be configured in such scenario to fulfill the diffServQShaper
MIB ?
Why the MIB obligate diffServQShaper ?

> Hi,
> 
> Let's assume an implementation that uses the physical layer 
> for shaping
> and no shaping parameters configuration is actually needed.
> 
> The MIB mentions that a ZeroDotZero is an illegal configuration.
> Why does the MIB obligate the diffServQShaper?

If you're using the physical layer to take care of QoS issues, such as
jitter control or what have you, then why do you need Diffserv or its MIB?
For example, you could use an ATM backbone with ATM techniques to achieve
your QoS requirements, in which case the diffserv queues would not be an
issue.

To go a bit beyond that, ATM is, or certainly was, looking at implementing
diffserv over UBR, in which case the diffserv shapers would certainly be
required there as well.

That would be my answer. (Brian will suggest this be moved over to
diffserv-interest.)

Bert

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---

From: Brian E Carpenter <[email-masked]>
Date: Tue, 27 Mar 2001 10:03:36 -0600

For the case you describe, I suppose you would configure a shaper with 
diffServShapingRateAbs set to zero. This effectively amounts to a
null shaper, but without inserting a null pointer in the MIB.

diffServShapingRateAbs OBJECT-TYPE                                        |
    SYNTAX       Unsigned32                                               |
    UNITS        "kilobits per second"
    MAX-ACCESS   read-create
    STATUS       current
    DESCRIPTION
       "The maximum rate in kilobits/sec that a downstream scheduler
       element should allocate to this queue. If the value is zero, then
       there is effectively no maximum rate limit and that the scheduler
       should attempt to be work-conserving for this queue...."

   Brian

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Brian E Carpenter 
Program Director, Internet Standards & Technology, IBM 
On assignment for IBM at http://www.iCAIR.org 
Board Chairman, Internet Society http://www.isoc.org
Non-IBM email: [email-masked]