Subject: Re: [MMUSIC] ICE keepalive potential issues

From: Flemming Andreasen <[email-masked]>
Date: Sat, 02 Dec 2006 16:53:17 -0500

Jean-Francois Mule wrote:

>   This is a follow-up on one of the issues presented at the meeting
>today (the slide 18 of
>http://www3.ietf.org/proceedings/06nov/slides/mmusic-2.pdf).
>There was rough consensus to go with the slide proposal to loosen up the
>requirements for keepalives and for using binding indications of 3489bis
>which is still a worthwhile optimization. 
>
>That said, the slide presents a potential issue with some layer-2 access
>networks like DOCSIS cable networks that may provide media streams QoS
>at layer 2 using unsolicited grant services. 
>After reviewing some DOCSIS specs and discussing the use case with Kevin
>Johns, this should be a non-issue for DOCSIS:
>  
>
I disagree. The extra occasional grant is largely to deal with clock 
skew issues and you're now cutting into that. Also, the CMTS would only 
give you more UGS grants. Are the messages going to fit within the 
grants? If not, they are most likely going to be dropped (this is 
dependent on the request/transmission policy). Also, in DOCSIS, it's 
only a SHOULD that the CMTS responds to the QI bit anyway, so you can't 
rely on it.

>	- if the agent has to send an ICE keepalive, or keepalive ack on
>top scheduled media, it just sends it,
>	- at layer 2, the cable modem can request an extra grant to sent
>it. The CMTS QoS scheduler will respond by issuing an extra grant (not
>to exceed 1% of the provisioned bandwidth). This can be asserted
>continuously or only as needed. For folks who want a reference, it is
>described in more details in
>http://www.cablemodem.com/downloads/specs/CM-SP-RFI2.0-I11-060602.pdf,
>in section VI.1.
>
>I write this mostly to provide more background info and close the loop.
>I also want to state that the wg should probably not do special things
>for special layer-2 nets...
>  
>
Conversely, ignoring reality doesn't help either, and cable-based DOCSIS 
networks aren't the only ones operating along these lines.

-- Flemming

>Jean-Francois.
>
>
>
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>  
>

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