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CHAPTER 6 PHY FUNCTION
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(4) Creation of SONET/SDH frame
The SONET STS-3c/SDH STM-1 frame format is created by multiplexing the overhead information of the
SONET/SDH frame with subsequent ATM cells. The
μ
PD98405 creates the H1, H2, H3, K2, Z2, G1, A1,
and A2 bytes as frame overhead information and links these bytes to the payload.
The frame format is shown in
Figure 6-2
.
*
Creating AU pointer and byte information
The position of POH (path overhead) of the transmit frame sent by the
μ
PD98405 is always fixed, and
the address value of the J1 byte at the beginning of POH is 20AH = "1000001010". Because the ATM
cell is always stored into the payload starting from the end of the H4 byte, "00000000" is stored as the
contents of the H3 byte used as a destuff byte, which is used to adjust the frequency. The
μ
PD98405
does not support Frequency Justification when creating a transmit frame.
The
μ
PD98405 can change the SS bits, which are the fifth and sixth bits of the H1 byte in the overhead
of the transmit frame, by setting it in the SS bit table of the MDR1 register.
Figure 6-4. Overhead H1 through H3 Bytes of Transmit Frame
H1 byte
H2 byte
H3 byte
1st
0110 SS10
0000 1010
0000 0000
2nd
1001 SS11
1111 1111
0000 0000
3rd
1001 SS11
1111 1111
0000 0000
Remark
SS bit: Inserts the bit stored into the SS table of MDR1. The default value is "00."
Of the byte information in the overhead, an insert register is provided for the C1, F1, K1, K2, F2, C2, and H4
bytes. The
μ
PD98405 transmits data according to the register contents, sending the default value until the
register contents are changed.
*
Creating a transmit BIP
The
μ
PD98405 executes BIP (Bit Interleaved Parity) calculation in respect to the transmit data, and
inserts the result of the calculation into the positions corresponding to the B1, B2, and B3 bytes of the
next transmit overhead data.
BIP calculation for each byte is as follows:
B1: BIP-8 (even parity, 8 bits wide)
BIP-8 calculation is performed for all the bits (including the A1, A2, and C1 bytes after frame scrambling)
of the transmit data. The result of the calculation is stored into the overhead B1 byte of the next frame.