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The traffic for the group G from any source S is measured
once each second. If the threshold is exceeded, then set a flag for
(*,G) to remember that the threshold was exceeded. When the next
packet for G arrives from any source, if the threshold exceeded flag
is set, then clear the flag in (*,G), set the flag in (S,G), and
switch to the source tree for that particular source. Again, every
second the state of the flag is in (S,G) will be checked and if the
traffic rate is less than the threshold, then switch back to the
shared tree. The advantages of switching to the source tree is that
traffic is being received on the shortest path tree. The shortest
path tree will generally have a lower latency than the shared tree.
The disadvantage is that (S,G) state will have to be maintained in
the router. In other words, there is more detail that has to be
maintained. |
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