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

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

---

From: [email-masked] (Billy Ng)
Date: Thu, 19 Aug 1999 14:48:41 -0400

> From [email-masked] Thu Aug 19 14:37:08 1999
> 

Venu,

This would force the RP switching to SPT.  What if the user does not
want the RP to switch?  then we have to wait for the Register suppression
to time out.  You could always adjust the suppression timer to a lower
value to reduce the latency.

--Billy