Ericsson AVP 1000 1RU, Reference Manual, Page: 313 / 508

Web GUI Control
EN/LZT 790 0023/1 R16A
5-137
Background
Forward Error Correction or FEC, enables packets lost during transmission over IP
networks to be recovered by adding extra information to the transmitted data. The
particular type of FEC used on the unit is that specified by (SMPTE 2012-1, 2).
The key features of ProMPEG FEC (SMPTE 2012-1, 2) are:
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Open standard FEC scheme.
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Increased robustness of transmission.
•
Increases network reach through FEC on high loss links.
•
Highly configurable depending on bandwidth vs. robustness.
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FEC transmitted separately to media stream.
•
Independent of video compression standard (MPEG-2, MPEG-4).
ProMPEG FEC (SMPTE 2012-1, 2) can help to solve the problems caused by
missing packets. It is an open standard for protection of contribution broadcast real-
time transmissions over IP networks by facilitating real-time lost packet recovery at
the receive units. It permits flexible configurations for optimization requirements.
The scheme uses an RTP layer which adds timing information for sequence
correction. FEC packets are transmitted in separate IP packets. The FEC packets
are calculated by arranging the media packets into a matrix. The matrix size defined
by columns (L) and rows (D).FEC packets are calculated along columns and rows
using the XOR function. FEC can be 1D (Column Only) or 2D (Column and Row).
Media and FEC packets are transmitted on separate IP streams with the Column
FEC stream offset from media stream and have a UDP port number which is the
media port 2. The Row FEC stream is offset from Media stream and has
UDP port number which is the media port 4. This arrangement means that
non-enabled FEC receivers can simply ignore FEC streams and decode the media
packets.
The FEC data stream is off-set from the media stream to protect against burst error
loss and jitter. At the receiver, lost packets recovered using the FEC data packets.
The Column FEC protects against burst errors and the Row FEC protects against
random errors. ProMPEG FEC recovers lost packets using column and (optionally)
row FEC packets using the XOR function on the remaining packets. Depending on
the distribution and severity of the pack loss not all errors are recoverable.
Overhead
The overhead which results from ProMPEG FEC transmitting extra packets depends
on whether column or column and row FEC is selected and how many columns and
rows there are. (Note that L = number of columns, D = number of rows.)