Subject: Question about SPT Join by receivers in MSDP/BGMP package

From: "Maciej Goraj" <[email-masked]>
Date: Thu, 4 Oct 2001 15:42:59 +0200

Hello Tarik,

I would like to know if in your MSDP/BGMP simulation package
is possible to send Join(S, G) not only by RP but also by a 
receiver (or by DR if we consider all nodes as routers).

PIM-SM allows both CBT and SPT. In your simulation package
RP of a domain can switch to SPT tree but inside a single domain
receivers will still get packets through the RP. Is it possible to switch
for SPT in case of intradomain routing ? How can I do it ?

I have done this using a rp-join-src function for a receveir,
however I'm not sure whether it is correct.
In the attached simulation scenario there is one source (node 11)
and five receivers (nodes 1, 4, 9 ,10, 13). Two of the receivers
has joined the source using rp-join-src, these are nodes 4 and 10.
Node 10 get data through intradomain routing and node 4 get data 
through intradomain routing.

I put these lines:

$ns at 0.2 "$n(4) rp-join-src $group1 _o147"
$ns at 0.2 "$n(10) rp-join-src $group1 _o147"

I didn't know how to refer to the source $cbr1 which is node 11
during debugging I've found that the correspondent Tcl object is
_o147. I know that this is not an elegant way. 

What I intend to achieve is to be able to use at the same time 
MSDP/RP and direct SPT joins for receivers that have the 
knowledge of multicast sources (also sources that are in other domains).
It would be similar to SSM (Source Specific Multicast), which is an
extension to standard IP multicast and allows only SPT Joins. 
In SSM there's no need for MSDP because all host have to know 
about multicast sources. It can be done by announcement of sessions, 
for example with SDR tool.

Thank you for any suggestions,
Cheers Maciej