Subject: (S,G) join message direction

From: "Matthew Koivisto" <[email-masked]>
Date: Tue, 10 Apr 2001 15:05:09 -0400

Hi, I've been having this conversation with some other people and it has
been brought to my attention that i should bring it to the mailing list.

Say there is already a spt tree established between S and R, so no packets
are getting recieved by R from the RP. (we're in phase 3). Now say another
node (R2), who is topolgocially close to R1, wishes to join that spt
directly (he does not wat to go through all the phases), his DR sends a
(S,G) join message. Now does that (S,G) join message travel towards the RP?
or does it travel towards S? The draft is not clear as to where that (S,G)
join travels too. (see page 10, 3rd paragraph). Now it makes perfect sence
to me that the message will go towards S, but this isn't the case is it?

Additionally, it just occured to me that durring phase 3 of PIM-SM no
packets are being recieved form the RP, so if a new source starts to send
packets on the group, the RP tree has been removed and R will not recieve
those new packets right? Hence the reason to not goto phase 3.

Thanks,
Matt

---

From: Mark Handley <[email-masked]>
Date: Tue, 10 Apr 2001 13:11:51 -0700

>to me that the message will go towards S, but this isn't the case is it?

To answer detailed questions, you need to read the spec, not just the
brief introductory overview section.

(S,G) Joins/Prunes are always sent towards S.  (*,G) Joins/Prunes and
(S,G,rpt) Joins/Prunes are always sent towards RP(G).  Join/Prune
messages are generated from the upstream state machines.  See Section
4.4.7 - (S,G) Joins/Prunes are sent to RPF'(S,G).

>those new packets right? Hence the reason to not goto phase 3.

No.  The RP tree hasn't been removed - just the old source has been
pruned off it.

Cheers,
	Mark