MT9072 Zarlink Semiconductor, Inc., MT9072 Datasheet - Page 50

• Manufacturer Part Number: MT9072
• Description: Octal T1-E1-J1 Framer
• Manufacturer: Zarlink Semiconductor, Inc.

MT9072
The CRC-4 frame alignment verification functions as follows. Initially, the CRC-4 operation must be activated
and CRC-4 multiframe alignment must be achieved at both ends of the link. At the local end of a link, all the bits
of every transmit submultiframe are passed through a CRC-4 polynomial (multiplied by X
X + 1), which generates a four bit remainder. This remainder is inserted in bit position one of the four FASs of
the following submultiframe before it is transmitted (see Table 12).
The submultiframe is then transmitted and, at the far end, the same process occurs. That is, a CRC-4
remainder is generated for each received submultiframe. These bits are compared with the bits received in
position one of the four FASs of the next received submultiframe. This process takes place in both directions of
transmission.
When more than 914 CRC-4 errors (out of a possible 1000) are counted in a one second interval, the framing
algorithm will force a search for a new basic frame alignment if automatic CRC-4 interworking is not invoked.
The result of the comparison of the received CRC-4 remainder with the locally generated remainder will be
transported to the far end by the E-bits. Therefore, if E
1 received at the far end; and if E
end. No submultiframe sequence numbers or re-transmission capabilities are supported with layer 1 PCM30
protocol. See ITU-T G.704 and G.706 for more details on the operation of CRC-4 and E-bits.
50
CRC-4
multiframe alignment signal.
indicates position of CRC-4
Frame/Type
11/NFAS
13/NFAS
15/NFAS
1/NFAS
3/NFAS
5/NFAS
7/NFAS
9/NFAS
10/FAS
12/FAS
14/FAS
CRC-4
0/FAS
2/FAS
4/FAS
6/FAS
8/FAS
Table 12 - CRC-4 FAS and NFAS Structure (E1)
2
= 0, a CRC-4 error was discovered in a submultiframe 2 received at the far
C
C
C
C
C
C
C
E
C
E
1
0
0
1
0
1
1
1
2
1
2
3
4
1
2
3
4
2
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
1
= 0, a CRC-4 error was discovered in a submultiframe
A
A
A
A
A
A
A
A
3
0
0
0
0
0
0
0
0
S
S
S
S
S
S
S
S
PCM30 Channel Zero
4
1
1
1
1
1
1
1
1
a4
a4
a4
a4
a4
a4
a4
a4
S
S
S
S
S
S
S
S
5
1
1
1
1
1
1
1
1
a5
a5
a5
a5
a5
a5
a5
a5
Advance Information
S
S
S
S
S
S
S
S
6
0
0
0
0
0
0
0
0
a6
a6
a6
a6
a6
a6
a6
a6
4
then divided by X
S
S
S
S
S
S
S
S
7
1
1
1
1
1
1
1
1
a7
a7
a7
a7
a7
a7
a7
a7
S
S
S
S
S
S
S
S
8
1
1
1
1
1
1
1
1
a8
a8
a8
a8
a8
a8
a8
a8
4
+