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P1 P2 P3
P4
F
R
1 If packet P6 is lost or corrupted (x), the loss
can be corrected by using the F
R
2 FEC packet.
However, corrupt packets P14, P15, and P16
cannot be corrected using the row FEC packet
(F
R
4) because too much data is missing.
To correct these packets, the column FEC data is
used. Packets 15 and 16 can be corrected using
F
C
3 and F
C
4 column FEC packets. Before
P5 x P7
P8
F
R
2
P9 P10 P11
P12
F
R
3
P13 x x x F
R
4
P17 P18 P19
P20
F
R
5
F
C
1 F
C
2 F
C
3 F
C
4
correcting packet 14, packet 6 must rst be corrected using the row FEC. After this,
the column FEC can be used to correct packet 14.
Ö Fec Rows and FEC Columns — Extron recommends a setting of 5 for rows and 5 for
columns, which should be the starting point for the error correction for the audio
transport and provides rugged operation on uncorrected IP networks.
The values that you set in the FEC row and column drop down lists depend on the
quality of the network link that is in use. The diagrams above show that the FEC data
can add large overhead to the overall bit rate transported over the network. Therefore
certain settings, while they may provide a high level of reliability, are inefficient.
Alternatively, settings that add little overhead may not provide a sufficient level of
protection on networks with a poor quality of service.
ñ Error Injection Rate — This setting should be left at 0. It used for test purposes only,
to drop packets artificially in order to test the effectiveness of the FEC scheme.
Streams panel
The audio encoder configuration page streams panel (see figure 29) provides details of any
active audio encoder streams. The data transport method, TCP or RTP, is defined on the
decoder configuration page (see “Configure Encoders or Decoders”). Audio multicasting
is selected in this panel (see “Enable multicast streaming“ to select the multicast and
“Data Transport Methods“ for definitions of the methods).
Figure 29. Audio Encoder Streams Panel
NOTE: This setting does NOT track the same setting applied in other (video, anc,
colfec, and rowfec) encoder configuration pages. For most applications, you
should set the same transport for all stream elements, but this is not mandatory.
The
New Export Stream function is not supported.
Configuration Page — Colfec and Rowfec Encoders
The colfec and row encoder configuration pages (see figure 30, on the next page)
provide the same basic function, enabling of multicasting. The encoder that you may
need to configure depends on whether you have selected column only (colfec encoder) or
and Row + column (rowfec encoder) as the FEC mode (see “Forward error correction
(FEC) panel“). The streams panel provides details of any active FEC encoder streams.
The data transport method, TCP or RTP, is defined on the decoder configuration page
(see “Configure Encoders or Decoders”). FEC multicasting is selected on this page
(see “Enable multicast streaming“ to select the multicast and “Data Transport
Methods“ for definitions of the methods).
VN-Matrix 325 Serial Digital Over IP CODEC • Operation 41