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Transport aspects 2

Figure 15-26  OPU overhead
15.9.2 OPU OH definition

15.9.2.1 OPU payload structure identifier (PSI)

One byte is allocated in the OPU overhead to transport a 256-byte payload structure identifier (PSI) signal.
The byte is located in row 4, column 15 of the OPU overhead.

The OPUk contains one instance of OPU PSI overhead. The OPUCn contains n instances of the OPU PSI
overhead, numbered 1 to n (PSI #1 to PSI #n).

The 256-byte PSI signal is aligned with the ODU multiframe (i.e., PSI[0] is present at ODU multiframe
position 0000 0000, PSI[1] at position 0000 0001, PSI[2] at position 0000 0010, etc.).
PSI[0] contains a one-byte payload type or is reserved for future international standardization. PSI[1] to
PSI[255] are mapping and concatenation specific, except for PT 0x01 (experimental mapping) and PTs 80-
0x8F (for proprietary use).

15.9.2.1.1 OPU payload type (PT)
A one-byte payload type signal is defined in the PSI[0] byte of the payload structure identifier to indicate
the composition of the OPU signal. The code points are defined in Table 15-9.
The OPUk and OPUCn contain one instance of OPU PT overhead.

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