Page 1197 - 5G Basics - Core Network Aspects

Transport aspects 2

This ODUj into OPUk multiplexing is performed in two steps:

1) asynchronous mapping of ODUj into optical data tributary unit (ODTU) using either AMP or GMP;
2) byte-synchronous mapping of ODTU into one or more OPUk tributary slots.

19.1 OPUk tributary slot definition
The OPUk is divided into a number of tributary slots (TS) and these tributary slots are interleaved within the
OPUk. A tributary slot includes a part of the OPUk OH area and a part of the OPUk payload area. The bytes
of the ODUj frame are mapped into the ODTU payload area and the ODTU bytes are mapped into the OPUk
tributary slot or slots. The bytes of the ODTU justification overhead are mapped into the OPUk OH area.

There are two types of tributary slots:
1) Tributary slot with a bandwidth of approximately 2.5 Gbit/s; an OPUk is divided into n tributary
slots, numbered 1 to n.
2) Tributary slot with a bandwidth of approximately 1.25 Gbit/s; an OPUk is divided into 2n tributary
slots, numbered 1 to 2n.

OPU2 and OPU3 interface ports supporting 1.25 Gbit/s tributary slots must also support the 2.5 Gbit/s
tributary slot mode for interworking with interface ports supporting only the 2.5G tributary slot mode (i.e.,
interface ports compliant with issues of this Recommendation: prior to the definition of 1.25G tributary
slots). When operated in 2.5G tributary slot mode, 1.25G tributary slots "i" and "i+n" (i = 1 to n, n = 4
(OPU2) and n = 16 (OPU3)) function as one 2.5G tributary slot.
19.1.1 OPU2 tributary slot allocation

Figure 19-1 presents the OPU2 2.5G tributary slot allocation and the OPU2 1.25G tributary slot allocation.
An OPU2 is divided into four 2.5G tributary slots numbered 1 to 4, or in eight 1.25G tributary slots
numbered 1 to 8.
– An OPU2 2.5G tributary slot occupies 25% of the OPU2 payload area. It is a structure with 952
columns by 16 (4  4) rows (see Figures 19-1 and 19-7) plus a tributary slot overhead (TSOH). The
four OPU2 TSs are byte interleaved in the OPU2 payload area and the four OPU2 TSOHs are frame
interleaved in the OPU2 overhead area.

– An OPU2 1.25G tributary slot occupies 12.5% of the OPU2 payload area. It is a structure with 476
columns by 32 (8  4) rows (see Figures 19-1 and 19-7) plus a tributary slot overhead (TSOH). The
eight OPU2 TSs are byte interleaved in the OPU2 payload area and the eight OPU2 TSOHs are
frame interleaved in the OPU2 overhead area.
An OPU2 2.5G tributary slot "i" (i = 1,2,3,4) is provided by two OPU2 1.25G tributary slots "i" and "i+4" as
illustrated in Figure 19-1.
The tributary slot overhead (TSOH) of OPU2 tributary slots is located in column 16 plus column 15, rows 1,
2 and 3 of the OPU2 frame.
The TSOH for a 2.5G tributary slot is available once every 4 frames. A 4-frame multiframe structure is used
for this assignment. This multiframe structure is locked to bits 7 and 8 of the MFAS byte as shown in
Table 19-1 and Figure 19-1.
The TSOH for a 1.25G tributary slot is available once every 8 frames. An 8-frame multiframe structure is
used for this assignment. This multiframe structure is locked to bits 6, 7 and 8 of the MFAS byte as shown in
Table 19-1 and Figure 19-1.

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