Subject: mboned: Multicast sources discovery issues and SIP

From: Hoerdt Mickael <[email-masked]>
Date: Wed, 09 Mar 2005 13:44:50 +0100

Hello,

I listened to Marshall talk about using SIP for source discovery
yesterday, and I have
a couple of things to say about what I think about the problem.
Marshall distinguished
network multicast source discovery from application multicast source
discovery. I think
that there is another complementary possible classification,
regarding the current state of the art of multicast applications :

Extra-group-session discovery, session announce, or multicast group
discovery

. Using an protocols like SAP, web or mail, DNS or Internet Media
guides it
~  is possible to discover IP-SSM or IP-ASM sessions.

Intra-group-session source discovery : you first find the group with
extra-group-session
discovery mechanism, and if they are multicast source dynamics inside
this group,
it should be coped :

. In the network/in-band, with ASM model architectures
~  like MSDP, PIM-RP-embedded.
. over the IP layer with SSM model architectures with
~  session layer solutions. (see draft-lehtonen-mboned-multissm-01 or   
~  draft-beck-mboned-ssm-source-discovery-protocol or the reference at
the end of this mail)

One question that arise from this classification is : Could the
existing extra-group-session
source discovery mechanisms be used for intra-group-session source
discovery ?

. I think that it depends mainly on the session dynamics, the more the
session is dynamic
regarding the departure/arrival of new sources, the more the mechanism
have to be efficient in term of delay to announce new multicast
sources inside the session. for example. In-band inter-domain scalable
solutions
like PIM-RP-embedded may have the most interesting delay today as with
ASM "sender just send", but there is still a delay to join the RP for
receivers.
In an application use SAP, web or mail to discover new multicast
groups belonging used by the application itself the rendez-vous
is in higher layers compared to RP-embedded and thus introduce higher
delays

My conclusions about this are that :

. Using IP-ASM for sessions without multicast sources dynamics should
be depreciated and IP-SSM should the recommended solutions for these
types of sessions, unless they are protocol version deployment issues to
solve (IGMP versioning or IGMP snooping for example).

. Using IP-SSM for sessions with multicast source dynamics should
be considered at the session layer to enhance compatibility between
applications needing such a session layer .

. Using IP-ASM for sessions with multicast source dynamics propose should
be recommenced for embedded-like applications, needing an very efficient
source discovery mechanism to solve problems like the bursty source one.

For further information about using SIP for SSM multicast source
discovery,
I think that this document  is very interesting to read :

http://www.tik.ee.ethz.ch/%7Eetl/Docu/MSource-SSM-TechReport.pdf

This work is part of the "Easy teach and learn" project in Zurich,
switzerland :

http://www.tik.ee.ethz.ch/%7Eetl/index.php3

Best regards,

Hoerdt Mickaël

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