Mike Lowery
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 Posted:
Tue Nov 29, 2005 9:30 pm Post subject:
Multicast log anamoly |
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We've got a multicast publishing point streaming video at ~450kbs. Multicast
logging back to an IIS server is enabled and appears to be working normally.
Unicast retransmission/failback is disabled. Our clients are using wireless
802.11 which always results in lost packets. However, I occasionally get
entries back from clients that don't make sense. Here is such an entry from the
logs:
x-duration: 3213 (seconds watched)
c-bytes: 169802335 (total bytes received)
c-pkts-received: 118312 (total packets received)
c-pkts-lost-client: 0 (no packet loss, which can't be true)
c-pkts-lost-net: 716 (so there were losses, but...)
c-pkts-lost-cont-net: 289 (that's a large chunk to lose at once)
c-pkts-recovered-ECC: 716 (...huh? How did WMP recover all these packets
especially if 289 were lost at one time?)
Again, there is no packet retransmission going on here, so if a client loses a
packet it can't get it back, with one exception. If I understand Windows Media
ECC correctly, it's able to recover 1 packet out of every 11. Specifically, if
you send 10 packets WMS adds an 11th forward error correction (FEC) packet which
allows you to recover one of those 10 packets if it is lost. But if you lost
two or more consecutively, there's no way WMS FEC could recover them (2 out of
10 lost and we can only recover 1 out of 10.)
Can someone explain these numbers or am I correct in assuming that they must be
wrong, which would indicate a bug?
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