Subject: PIM-SM: Join latency when source registers first

From: Nair Venugopal <[email-masked]>
Date: Thu, 19 Aug 1999 10:29:41 -0700 (PDT)

Section 3.3.2.1.d in the PIM-SM rfc (PostScript version) states that ...

  "If there is no G or (*,*,RP) entry corresponding to G, the packet is
   dropped , and a Register Stop is triggered."

Now, if the RP receives a (*,G)-PIM/IGMP join during the period the
source's DR is Register-Suppressed, there would be a delay in the
receivers downstream to the RP getting traffic to this mcast group.

I guess, this "join-latency" could be reduced (at the expense of more
state) by creating (S,G)-Null OIF state on the RP when it receives a
PIM-Register for a previously unknown group, G. Now, when the RP receives
the first IGMP/(*,G)-PIM "join" for the group, it could immediately
trigger an (S,G) Join to the source.

I couldnt find a "blurb" in the PIM-spec which permits/forbids this
approach. 

1) Is there a (sub)section in the spec which addresses this?
2) If not, would this be a bad thing to add to one's
   implementation?

Thanks.
--Venu

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Nair Venugopal  --- [email-masked] --- 3Com WAP Engineering