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Transport aspects 2

1 2 3 4 5 6 7 8
PSI[2] 00 00 0000 TS1

PSI[3] 00 00 0001 TS2
PSI[4] 00 00 0010 TS3

PSI[5] 00 00 0011 TS4

Figure 19-15 – OPU2-MSI coding – Payload type 20

19.4.1.2 OPU3 multiplex structure identifier (MSI) – Payload type 20

For the 16 OPU3 2.5G tributary slots 16 bytes of the PSI are used (PSI[2] .. PSI[17]) as MSI bytes as shown in
Figures 19-14A, 19-16A and 19-16B. The MSI indicates the ODTU content of each tributary slot of the OPU3.
One byte is used for each tributary slot.
– The ODTU type in bits 1 and 2 indicates if the OPU3 TS is carrying ODTU13 or ODTU23. The default
ODTU type is ODTU13; it is present when either a tributary slot carries an ODTU13, or is not
allocated to carry an ODTU. Refer to Appendix V for some examples.

– The tributary port # in bits 3 to 8 indicates the port number of the ODTU13/23 that is being
transported in this 2.5G TS; for the case of ODTU23, a flexible assignment of tributary ports to
tributary slots is possible, for the case of ODTU13, this assignment is fixed, the tributary port
number equals the tributary slot number. ODTU23 tributary ports are numbered 1 to 4.

1 2 3 4 5 6 7 8
PSI[2] ODTU type Tributary Port # TS1
PSI[3] ODTU type Tributary Port # TS2
PSI[4] ODTU type Tributary Port # TS3
PSI[5] ODTU type Tributary Port # TS4
PSI[6] ODTU type Tributary Port # TS5
PSI[7] ODTU type Tributary Port # TS6
PSI[8] ODTU type Tributary Port # TS7
PSI[9] ODTU type Tributary Port # TS8
PSI[10] ODTU type Tributary Port # TS9
PSI[11] ODTU type Tributary Port # TS10

PSI[12] ODTU type Tributary Port # TS11
PSI[13] ODTU type Tributary Port # TS12
PSI[14] ODTU type Tributary Port # TS13
PSI[15] ODTU type Tributary Port # TS14
PSI[16] ODTU type Tributary Port # TS15
PSI[17] ODTU type Tributary Port # TS16

Figure 19-16A – OPU3-MSI coding – Payload type 20

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