Subject: SPT switch initiation

From: Pavlin Ivanov Radoslavov <[email-masked]>
Date: Mon, 15 Jan 2001 18:02:37 -0800

Bill, Mark, Hugh and Isidor,

From the new PIM-SM spec:
=======================
3.  PIM-SM Protocol Overview

Phase Two: Register Stop

Although Register-encapsulation may continue indefinitely, for these
reasons, the RP will normally choose to switch to native forwarding.  To |
do this, when the RP receives a register-encapsulated data packet from   |
source S on group G, it will normally initiate an (S,G) source-specific  |
Join towards S.  This join message travels hop-by-hop towards S,         |
instantiating (S,G) multicast tree state in the routers along the path.  |
====================

In the original spec, the (S,G) switch by the RP was rate-based
(i.e. after the data rate of a source exceeds some limit). Here it
seems that the normal procedure is for the RP to originate the (S,G)
Join right after the first pkt.
In the new document I didn't see the rate-limit based switch
mentioned at all. Is it intentionally, and if "yes", what is the
reason behind it?

Further, there isn't any mentioning that the last-hop router may
initiate of a (S,G) Join if the data rate is too high. Is this
feature deprecated?

Thanks,
Pavlin

---

From: Isidor Kouvelas <[email-masked]>
Date: Mon, 15 Jan 2001 18:16:50 -0800

In message <[email-masked]>,
>From the new PIM-SM spec:

Both these issues have either been addressed in the last varsion of the
spec or are in the process of being covered...

thanks
I

---

From: Hitoshi Asaeda <[email-masked]>
Date: Tue, 16 Jan 2001 15:40:40 +0900 (JST)

> Further, there isn't any mentioning that the last-hop router may
                                               ^^^^^^^^^^^^^^^
should be "DR", if you mean the last-hop router is the forwarder?

--
Hitoshi Asaeda

---

From: Pavlin Ivanov Radoslavov <[email-masked]>
Date: Mon, 15 Jan 2001 23:32:08 -0800

> > Further, there isn't any mentioning that the last-hop router may

Good observation. "Last-hop router" may be the DR, but not
necessarily. From the RFC 2362 spec:

"Note that (S,G) state must be maintained in each last-hop router that is
 responsible for initiating and maintaining an SP-tree."

Also in the old spec:

"One proposed example is to do so based on data rate.  For example,
 when a (*,G), or corresponding (*,*,RP), entry is created, a data
 rate counter may be initiated at the last-hop routers."

Section 2.4 of the old spec clarifies that "last-hop router" is not
necessarily the DR. Indeed, the DR may lose a (*,G) Assert and
remove the LAN with local members from its (*,G) oifs.
Such DR may not be in position of receiving the (*,G) data on the
iif toward the RP, and therefore it cannot initiate the (S,G) SPT
switch.

XXX: note to the new spec authors:

The new spec however (Phase 3 in Section 3) defines that the DR
can initiate a SPT switch, and does not contain any reference to the
term "last-hop router" (i.e. the last-hop router does not have any
special function anymore). Having the DR only being able to initiate
the SPT switch may not always work. Hence, I think that the new spec
needs the "last-hop router" term from the old spec and should use it
to explain the SPT switch.

Pavlin