Subject: RE: [pim] Update_SPTbit(S,G)

From: "James Huang" <[email-masked]>
Date: Thu, 27 Jun 2002 14:24:29 -0700

SPTbit(S,G) will be set to FALSE when JoinDesired(S,G) becomes FALSE.
This will allow the switch back from the SPT tree to RPT tree.

James Huang

> -----Original Message-----
> From: Ju, Yu [mailto:[email-masked]]
> Sent: Thursday, June 27, 2002 2:15 PM
> To: [email-masked]
> Subject: [pim] Update_SPTbit(S,G)
> 
> 
> Hi,
> 
> When a packet arrives, the (S,G) SPTbit is updated as follows:
> 
>      void
>      Update_SPTbit(S,G,iif) {
>        if ( iif == RPF_interface(S)
>              AND JoinDesired(S,G) == TRUE
>              AND ( DirectlyConnected(S) == TRUE
>                    OR RPF_interface(S) != RPF_interface(RP)
>                    OR inherited_olist(S,G,rpt) == NULL
>                    OR RPF'(S,G) == RPF'(*,G) ) ) {
>           Set SPTbit(S,G) to TRUE
>        }
>      }
> 
> So if the condition is not satisfied, the SPTbit(S,G) is not 
> set to TRUE and
> keep its previous value which could be TRUE. 
> So once SPTbit(S,G) is set to TRUE, it will never be set back 
> to FALSE until
> (S,G) state times out.  Am I right? Is this why PIM-SM does 
> not provide a
> mechanism to switch back from SPT tree to RPT tree?
> 
> 
> Thanks,
> 
> Yu
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> 
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