Page 1219 - 5G Basics - Core Network Aspects

Transport aspects 2

1 2 3 4 5 6 7 8 1.25G TS

PSI[2] TS occupied Tributary Port # TS1
PSI[3] TS occupied Tributary Port # TS2
PSI[4] TS occupied Tributary Port # TS3
PSI[5] TS occupied Tributary Port # TS4
PSI[6] TS occupied Tributary Port # TS5
PSI[7] TS occupied Tributary Port # TS6
PSI[8] TS occupied Tributary Port # TS7
PSI[9] TS occupied Tributary Port # TS8
: : : :
: : : :
PSI[81] TS occupied Tributary Port # TS80

Figure 19-18A – OPU4 1.25G TS MSI coding – Payload type 21

1 2 3 4 5 6 7 8
PSI[1+ i] Occupation Tributary Port # TS #i

Figure 19-18B – OPU4 MSI coding – Payload type 21

19.4.1.5 OPU2 multiplex structure identifier (MSI) – Payload type 21
For the eight OPU2 1.25G tributary slots 8 bytes of the PSI (PSI[2] to PSI[9]) are used as MSI bytes as show
in Figures 19-14B, 19-19A and 19-19B. The MSI indicates the ODTU content of each tributary slot of an
OPU. One byte is used for each tributary slot.

– The ODTU type in bits 1 and 2 indicates if the OPU2 1.25G TS is carrying an ODTU12 or ODTU2.ts.
The default ODTU type is 11 (unallocated); it is present when a tributary slot is not allocated to
carry an ODTU.
– The tributary port # in bits 3 to 8 indicates the port number of the ODTU that is being transported
in this TS; a flexible assignment of tributary ports to tributary slots is possible, ODTU12 tributary
ports are numbered 1 to 4, and ODTU2.ts tributary ports are numbered 1 to 8. The value is set to
all-0s when the ODTU type has the value 11 (tributary slot is unallocated).

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