Subject: Re: [Diffserv] Dscp and DscpOrAny TCs

From: John Schnizlein <[email-masked]>
Date: Wed, 05 Mar 2003 12:29:07 -0500

Good catch, Bert.
The idea of a mask for the DSCP was killed some time ago in Policy Framework based on its incompatibility with the following explicit prohibition in the definition of the Differentiated Services Field:

RFC 2474 Section 3, page 7
   Implementors should note that the DSCP field is six bits wide.  DS-
   compliant nodes MUST select PHBs by matching against the entire 6-bit
   DSCP field, e.g., by treating the value of the field as a table index
   which is used to select a particular packet handling mechanism which
   has been implemented in that device.  The value of the CU field MUST
   be ignored by PHB selection.  The DSCP field is defined as an
   unstructured field to facilitate the definition of future per-hop
   behaviors.

John

At 11:36 AM 3/5/2003, Wijnen, Bert (Bert) wrote:
>Do Diffservers think that the following is wise and makes sense?
>
>   docsSubMgtPktFilterDscpValue OBJECT-TYPE
>       SYNTAX      Dscp
>       MAX-ACCESS  read-create
>       STATUS      current
>       DESCRIPTION
>           "The Differentiated Services Code Point (DSCP) value to match
>            in the IP packet."
>       DEFVAL { 0 }
>       ::= { docsSubMgtPktFilterEntry 9 }
>
>   docsSubMgtPktFilterDscpMask OBJECT-TYPE
>       SYNTAX      Dscp
>       MAX-ACCESS  read-create
>       STATUS      current
>       DESCRIPTION
>           "The mask to apply against the DSCP value to be matched in
>       the IP packet.  The default for both these objects taken together
>       matches all DSCP values. A packet matches this filter if the
>       following is true:
>           AND (FilterDscpValue, FilterDscpMask) ==
>           AND (Packet DSCP Value, FilterDscpMask)."
>       DEFVAL { 0 }
>       ::= { docsSubMgtPktFilterEntry 10 }
>
>It is defined in draft-ietf-ipcdn-subscriber-mib-10.txt and I'd like
>to hear comments from Diffserv experts.
>
>Thanks,
>Bert 

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---

From: "Andrew Smith" <[email-masked]>
Date: Wed, 5 Mar 2003 12:42:11 -0800

I've not been following the DOCSIS MIB work closely and don't know the
context in which this MIB was developed. That said, shouldn't IETF be
promoting the use of generic, already-standards-track solutions, instead
of trying to police each new reincarnation of the same thing? It would
have been nice if, given that this MIB is a work item of an IETF WG, the
IESG had put in some provision in the WG charter about re-use of
existing IETF work where appropriate, rather than reinventing the wheel
(which this looks like - see my first sentence above though). Granted,
there is a choice of almost-equivalent wheels for packet
matching/filtering in the IETF standards-track repertoire but that's not
an argument for creating yet another one.

This is one aspect of the general IETF process issue of how to ensure
that appropriate "subject matter experts" are available to a WG that
needs them, even when that subject matter's own WG is no longer
existent: the more generic the solutions that IESG steers us to, the
less this maintenance problem will be.

Reuse of already-defined MIB ojects/tables is also one of the issues
that an SMIng should try to make easier (and people have been looking at
doing this, I believe).

Andrew Smith

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf
Of John Schnizlein
Sent: Wednesday, March 05, 2003 9:29 AM
To: Wijnen, Bert (Bert)
Cc: [email-masked]
Subject: Re: [Diffserv] Dscp and DscpOrAny TCs

Good catch, Bert.
The idea of a mask for the DSCP was killed some time ago in Policy
Framework based on its incompatibility with the following explicit
prohibition in the definition of the Differentiated Services Field:

John

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---

From: Brian E Carpenter <[email-masked]>
Date: Fri, 07 Mar 2003 11:04:11 +0100

Andrew,

That is a valid point (we have the same issue for the IPv6 Flow Label).

However, in answer to Bert's question, John Schnizlein is correct.

It's a violation of the diffserv architecture to mask bits in a DSCP.
There are no encoded bit fields in a DSCP; it's an opaque 6 bit
quantity.

docsSubMgtPktFilterDscpMask needs to be deleted.

   Brian

---

From: Sapna Isotupa <[email-masked]>
Date: Sat, 8 Mar 2003 10:14:48 -0500 (EST)

Hello All:

Is there a simulator available for testing various scheduling policies for
diffserv?  If yes, could you tell me whom to contact to obtain one.  If
there is no simulator available, will others be interested if a simulator
for testing various scheduling policies is built?

Thanks.

Sapna

---

From: Martin Westhead <[email-masked]>
Date: Sun, 09 Mar 2003 02:20:36 +0000

>for testing various scheduling policies is built?

Hi Sapna,

This is off-topic for the diffserv list. I have cross posted to 
diffserv-interest and if there is any follow-up discussion it should go there.

Intersim is a simulation platform that models very precisely the behaviour 
of Cisco diffserv algorithms. It is currently under development by Internet 
Design Tools, funded by Cisco Systems. We have access to the IOS source 
code and have taken a lot of trouble to ensure, and have lab tests to 
demonstrate, that the simulator's performance is indeed very close to that 
of the real router. We have plans to extend the simulator to generic 
diffserv models, and models of other vendor's platforms, however we do not 
a timescale for that development. There is more information available at 
www.internetdesigntools.com.

Intersim is not commercially available at this point, but we have a small 
group of users, if you are interested in using it please contact me directly.

Other simulators that also have (less specialised) models of diffserv 
behaviour include:

Opnet: www.opnet.com
Qualnet: www.qualnet.com
ns-2: http://www.isi.edu/nsnam/ns/

The last one is open source and free, the others are commercial.

Cheers,

Martin

----------------------Internet-Design-Tools-Ltd.--------------------

  Dr. Martin Westhead            Phone: +44 77 189 189 64
                                 Email: [email-masked]