VSC6134
Datasheet
Figure 1. OTU Row Structure Using RS(255,239) Codes
codeword #16
FEC sub -row #16
Information bytes
Parity check bytes
1
2
3
9
2
4
0
2
5
5
codeword #2
FEC sub -row #2
Information bytes
Parity check bytes
1
2
3
9
2
4
0
2
5
5
codeword #1
FEC sub -row #1
Information bytes
Parity check bytes
1
1
2
3
9
2
4
0
2
5
5
Information bytes
Parity check bytes
OTU row
2
1
6
3
8
2
4
3
8
2
5
3
8
2
6
3
8
4
0
4
0
8
0
...
...
In Standard FEC mode, the VSC6134 performs error correction and detection using only RS codes.
Figure 4, page 43 shows the bit-error ratio (BER) enhancement as a result of RS(255,239) coding.
The generator polynomial of the code is given by:
(EQ 1)
15
⎛
⎜
⎜
⎝
⎞
⎟
i
G(z) =
(z – α )
∏
⎟
⎠
i = 0
8
4
3
2
where α is a root of the binary primitive polynomial x + x + x + x + 1. The FEC code word consists
of information bytes and parity bytes (FEC redundancy) and is represented by the polynomial:
C(z) = I(z) + R(z)
(EQ 2)
(EQ 3)
(EQ 4)
Information bytes are represented by:
254
253
16
I(z) = D × z + D × z + ... + D × z
254
253
16
Where D (j = 16 to 254) is the information byte represented by an element out of GF(256) and
j
D = d × α 7 + d × α 6 + ... + d × α 1 + d
j
7j
6j
1j
0j
Bit d is the MSB and d the LSB of the information byte. D corresponds to the byte 1 in the
7j
0j
254
RS codeword and D to byte 239.
16
39 of 438
VMDS-10185 Revision 4.0
July 2006
VITESSE [ VITESSE SEMICONDUCTOR CORPORATION ]
