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Transport aspects 2

MFAS Multi- Column
bits frame Frame
8 row row 1 ..... 15 16 17 18 19 20 ..... 3823 3824
1 1
2 2
0 TSOH TS1 .....
3 3
4 4
5 1
6 2
1 TSOH TS2 .....
7 3
8 4 1 2 1 2 1 2 1.25G TS#
G.709-Y.1331(12)_F19-3

Figure 19-3 – OPU1 tributary slot allocation

Table 19-3 – OPU1 tributary slot OH allocation

MFAS TSOH 1.25G TS
bit 8
0 1
1 2

19.1.4 OPU4 tributary slot allocation

Figures 19-4A and 19-4B present the OPU4 1.25G tributary slot allocation. An OPU4 is divided into eighty
1.25G tributary slots (numbered 1 to 80), which are located in columns 17 to 3816, and 8 columns of fixed
stuff located in columns 3817 to 3824. The OPU4 frame may be represented in a 320 row by 3810 column
format (Figure 19-4A) and in a 160 row by 7620 column format (Figure 19-4B).
– An OPU4 1.25G tributary slot occupies 1.247% of the OPU4 payload area. It is a structure with 95
columns by 160 (80  4/2) rows (see Figure 19-4B) plus a tributary slot overhead (TSOH). The
eighty OPU4 1.25G TSs are byte interleaved in the OPU4 payload area and the eighty OPU4 TSOHs
are frame interleaved in the OPU4 overhead area.

The tributary slot overhead (TSOH) of OPU4 tributary slots is located in rows 1 to 3, columns 15 and 16 of
the OPU4 frame.

The TSOH for a 1.25G tributary slot is available once every 80 frames. An 80-frame multiframe structure is
used for this assignment. This multiframe structure is locked to bits 2, 3, 4, 5, 6, 7 and 8 of the OMFI byte as
shown in Table 19-4.

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