Subject: Clarification for the need for SPT tree bet. Source & RP.

From: "L.N.Subramanian" <[email-masked]>
Date: Tue, 21 Mar 2000 10:08:10 +0530

Hi,
        I have a small question. When the source sends Packets to the RP, it encapsulates in Register Messages and Unicasts.
        It stops sending Encapsulated Messages whwn receives a Register-Stop Msg frm RP. But I think the path taken by
        Register Packets and Normal Multicat Forwarding bet  RP and DR of Source is the same. So even after switching to
        SPT tree by RP, the data rate  remains the same. So I dont understand the condition on which the RP switches 
        to SPT tree.
                         Help me in this regard.

Subramanian.L.N

---

From: Renu Agarwal <[email-masked]>
Date: Tue, 21 Mar 2000 10:42:54 +0530

Hello Subramanian,

The data rate shall be increased slightly due to saving of the
encapsulation effort at DR and decapsulation effort at the RP. The data
path shall remain same in both the cases.
Also, after switching to SPT, the data packets shall be forwarded
directly by the kernel while in previous case the data forwarding had to
be done by the user process at least at the DR. (taking a reference to
Pimd implementation on unix kind of environment).

Hope it answers your question,

Regards,
Renu

---

From: "Wilbert de Graaf" <[email-masked]>
Date: Mon, 20 Mar 2000 22:12:52 -0800

Hi Subramanian,

I think it's not the source encapsulating the multicast traffic in
pim-register but it's designated router (DR) does. So if multiple routers
are connected to the source, and a path exists between a non-DR and the RP
which is shorter/better than the path between DR and RP, the SPT will not be
from DR to RP. After all, the DR was mereley based on the ip-address, right
?

But about the treshold and the decision for the RP start to build a SPT
towards the source (and send the join), I think the point is not that
traffic will be more or less between both situations (#1
data-in-register-messages, #2 SPT-between-RP-and-source). I think the point
is that encapsulated multicast data will consume way more resources (cpu
time for all intermediate routers), and the path might less optimal than the
SPT from RP to the source. At some point, it's simply worth investing
efforts to switch to the more optimal situation: the SPT from the source to
RP.

- Wilbert

----- Original Message -----
From: L.N.Subramanian <[email-masked]>
To: <[email-masked]>
Sent: Monday, March 20, 2000 8:38 PM
Subject: Clarification for the need for SPT tree bet. Source & RP.

> Hi,
>         I have a small question. When the source sends Packets to the RP,
it encapsulates in Register Messages and Unicasts.
>         It stops sending Encapsulated Messages whwn receives a
Register-Stop Msg frm RP. But I think the path taken by
>         Register Packets and Normal Multicat Forwarding bet  RP and DR of
Source is the same. So even after switching to
>         SPT tree by RP, the data rate  remains the same. So I dont
understand the condition on which the RP switches