From: Ivan Dementiev (ivan@xxxxxxx)
Date: Sat Oct 28 2000 - 09:07:59 GMT-3
Hello!
Jansen wrote:
> hi,everybody:
>
> Can anybody explain these for me?
>
> When hosts join a multicast group, the directly connected routers send PIM jo
in messages to the RP.
> The RP keeps track of multicast groups. Hosts that send multicast packets are
registered with the
> RP by that host's first-hop router.
> The RP then sends joins toward the source(Question 1: what does
> the source mean? mulitcast sender or receiver? ).
It sends joins only when source == sender becomes active. When there are no sen
ders,
RP knows only about receivers of multicast group and does not send any joins
to sources.
> At this point, packets are forwarded on
> shared distribution tree. If the multicast traffic from a specific source is
sufficient,
> (Question 2: what does the "specific source" mean? sender of receiver?) the r
eciver's first-hop router
> may send joins toward the source to build a souce-based distribution tree.
Specific source menas (S,G) = (Sender,Group) , not (*,G) entry in first-hop ro
uter's
m-cast routing table.
> Question 3: If all these sources are refer to the sender, then how does the r
eciver know the multicast
> traffic from a specific source is sufficient?
Not receiver, the first-hop router near receiver decides when to swith to SPT.
As far as I remember router maintains something like 'packet per time-interval
'
value for (*,G) entry in routing table. When it reaches threshold, router marks
that entry and starts switching from shared path to shorted path tree procedure
for next (S,G) packet that arrives. Then switching procedure may be repeted for
other (S1,G) ... (SN,G) pairs.
-- Best regards, Ivan Dementiev, CCIE #5967ABAK, Network and telecommunications division Tel: +7-8432-642393, Fax: +7-8432-769559 E-mail: ivan@abak.ru
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