From: DWINKWORTH@wi.rr.com
Date: Wed May 09 2007 - 12:43:45 ART
An answer to your question is found on page 156 of Beau Williamson's
book "Developing IP Multicast Networks." Here are some relevant quotes:
"By joining the SPT, multicast traffic is routed directly to the
receivers without having to go through the RP, thereby reducing network
latency and possible congestion at the RP."
"...the overall amount of (S,G) information maintained by the routers
in a PIM-SM network that uses SPTs is generally much less than is
necessary for dense mode protocols."
"By joining SPTs in PIM-SM, we gain the advantage of an optimal
distribution tree without suffering from the overhead and
inefficiencies associated with other dense mode protocols."
"...without the shared tree to deliver the first few multicast packets
from a source, routers have no way of knowing that a source is active."
You should really buy the book. This is one of the only books I read
from cover-to-cover when I was studying.
Derick Winkworth, CCIE #15672
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