Subject: [magma] IGMP and link propagation delay

From: Thomas Morin <[email-masked]>
Date: Fri, 17 Mar 2006 15:44:21 +0100

Hi,

I'm wondering if IGMP (v2/v3) has something equivalent or similar to the
link propagation delay that was introduced in PIMv2.

On reception of a membership query a terminal will start a timer with a
random delay d in the [0:max-response-time], before sending a report for
the query.  It might be that d is very close to max-response-time, thus
(max-response-time - d) might be very small; consequently it could
occur, depending on the link, that (max-response-time - d) is lower than
round-time trip between terminal and IGMP querier.  In that case, it
appears to me like the response to the query may in some rare cases
arrive "too late" on the querier, which may thus interrupt the
forwarding of the multicast flow for a short period of time.

PIMv2 has introduced an additional delay to handle this case (section
4.3.3 of draft-ietf-pim-sm-v2-new), but I found nothing similar in
IGMPv2 and v3 specs. 

Is this something that has been already discussed ?

Cheers,

-Thomas

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