Re:[pim] PIM RP register mechanism

Here is my guess on it...just some ideas.

SwitchToSptDesired(S,G) as the draft says is an
implementation defined policy function to decide when
to initiate an (S,G) tree. 

On the RP, it could be based on the rate at which it
receives PIM Register Packets. Taking this assumption,
the RP could decide that the current Register packet
rate for the (S,G) is large enough to initiate
building the (S,G) source tree (to get the packets
natively) but finds that there are no receivers
(inherited_olist(S,G) == NULL) yet and hence decided
to send a Register Stop. This would prevent the
unnecessary 'substantial' (after all
SwitchToSptDesired(S,G) is True)Register traffic for
which there are no receivers.

If the Register traffic rate is 'low'
(SwitchToSptDesired(S,G) == False), it might not send
Register Stop even if (inherited_olist(S,G) == NULL).
This may be because the traffic rate is 'low' enough
to pay for faster covergence achieved when the
receiver does appear.

Hope it helps.

saurabh

>Dear all: I have a question on PIM-SM RP register
>mechanism: Why there
>needs this term "( SwitchToSptDesired(S,G) AND (
>inherited_olist(S,G) ==
>NULL ))" in pseudocode describing action when RP
>receiving following a
>Register message in PIM-SM protocol (v2-new-12)? 
>
>The text is as the following:
> 
>
>"draft-ietf-pim-sm-v2-new-12.txt", Part 4.4.2----
>Receiving Register
>Messages at the RP:  
>
>When an RP receives a Register message, the course of
>action is decided
>according to the following pseudocode:
>
>packet_arrives_on_rp_tunnel( pkt ) 
>{ 
>   
>   if( I_am_RP(G) AND outer.dst == RP(G) ) {
>
>       ..... 
>       if ( SPTbit(S,G) OR
>           ( SwitchToSptDesired(S,G) AND (
>inherited_olist(S,G) == NULL
>))) {
>            send Register-Stop(S,G) to outer.src
>            sentRegisterStop = TRUE;
>          }
>       ......
>   }  else {.....
>           }
>}
>
>
>many thanks!
>
>           Chunyan
>

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