WorldCast Equinox - Release 3.1 - user manual
– 07/2011
Page 148
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Fig : frame of decoder media and FEC packets that presents a burst loss of packet information.
Running FEC limits the route latency in the Worldcast Meridian. SMPTE restricts the time
window in which the FEC packets must be transmitted once created. Column FEC packets must
be sent a minimum of L packets after the last media packet protected. This minimum latency
ensures that associated media and FEC packets are not lost in the same single burst loss. The
maximum latency is defined by the fact that column FEC packets must be sent up to a
maximum of L × D packets after the last media packet protected.
To ensure that the FEC stream does not add to IP traffic conjestion at routers and switches,
each FEC packet is transmitted on the maximum permissible interval in this SMPTE window.
The figure below shows that each FEC packet is transmitted onto the FEC port at the end of
each row of media packets to achieve an even spacing between each FEC transmission.
The
size of latency buffer required to recover a media in the FEC receiver software is then the dis-
tance between packets in position 5 of the scheme and FEC position c4, i.e. a minimum of 45
packets
M
M
M
M
M
M
M
M
M
M
LP
LP
LP
LP
M
M
c1
c2
c3
c4
M
M
LP
M
M
M
M
M
c5
M
L=5
D=5
Column FECs
