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3.1 SONET Overhead Processing
3.1.1 Transmission Function
(1) Generation of SONET frame
The cell/packet stream is mapped onto the payload area of STS-12c SPE of SONET, and the µPD98413 creates
a SONET STS-12c frame by adding the path overhead (POH) and transport overhead (TOH) information. For
details of the format of the frame to be created, see Figure 3-4.
36 bytes
1
2
3
4
STS TOH (324
5
bytes)
6
7
8
9
The overhead generated by the µPD98413 and the selection of a mode is described below.
(a) Selecting contents of unused OH byte
All 00H is inserted into the following areas of TOH (hatched area in Figure 3-5). The inserted value can be
changed to FFH by using the UUBM bit of the MDSOHT and MDLOHT registers.
<1> Unused byte area (area marked
<2> H3 byte (Negative Stuff byte)
<3> Z1 and Z2 bytes (except the 1st Z2 byte)
40
CHAPTER 3 FUNCTIONAL OUTLINE
Figure 3-4. STS-12c SPE
STS-12c SPE (Synchronous Payload Envelope)
3
1
STS-12c Payload
(9,360 bytes)
1,044 bytes
in Figure 3-5)
PRELIMINARY
NEC confidential and Proprietary
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