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Transport aspects 2

19.5 Mapping ODUj into ODTUjk

The mapping of ODUj signals (with up to 20 ppm bit-rate tolerance) into the ODTUjk signal ((j,k) = {(0,1),
(1,2); (1,3), (2,3)}) is performed as an asynchronous mapping.
NOTE 1 – The maximum bit-rate tolerance between OPUk and the ODUj signal clock, which can be accommodated by
this mapping scheme is –130 to +65 ppm (ODU0 into OPU1), –113 to +83 ppm (ODU1 into OPU2), –96 to +101 ppm
(ODU1 into OPU3) and –95 to +101 ppm (ODU2 into OPU3).
The ODUj signal is extended with a frame alignment overhead as specified in clauses 15.6.2.1 and 15.6.2.2
and an all-0s pattern in the OTUj overhead field (see Figure 19-22).

Column #
1 ... 7 8 ... 14 15 ... 3824
FA overhead Fixed stuff
1
area (all-0s)
2 OPUj area
ODUj overhead (4  3810 bytes)
3 area
Row # 4

Figure 19-22 – Extended ODUj frame structure
(FA OH included, OTUj OH area contains fixed stuff)

The OPUk signal and therefore the ODTUjk (k = 1,2,3) signals are created from a locally generated clock
(within the limits specified in Table 7-3), which is independent of the ODUj (j = 0,1,2) client signals.

The extended ODUj (j = 0,1,2) signal is mapped into the ODTUjk (k = 1,2,3) using an asynchronous mapping
with –1/0/+1/+2 positive/negative/zero (pnz) justification scheme.

An extended ODUj byte is mapped into an ODTUjk byte.
The asynchronous mapping process generates the JC, NJO, PJO1 and PJO2 according to Table 19-7. The de-
mapping process interprets JC, NJO, PJO1 and PJO2 according to Table 19-7. Majority vote (two out of
three) shall be used to make the justification decision in the de-mapping process to protect against an error
in one of the three JC signals.

Table 19-7 – JC, NJO, PJO1 and PJO2 generation and interpretation

JC
NJO PJO1 PJO2 Interpretation
7 8
0 0 justification byte data byte data byte no justification (0)
0 1 data byte data byte data byte negative justification (–1)
1 0 justification byte justification byte justification byte double positive justification (+2)
(Note)
1 1 justification byte justification byte data byte positive justification (+1)
NOTE – Note that this code is not used for the case of ODU0 into OPU1.
The value contained in NJO, PJO1 and PJO2 when they are used as justification bytes is all-0s. The receiver
is required to ignore the value contained in these bytes whenever they are used as justification bytes.
During a signal fail condition of the incoming ODUj client signal (e.g., OTUj-LOF), this failed incoming signal
will contain the ODUj-AIS signal as specified in clause 16.5.1. This ODUj-AIS is then mapped into the
ODTUjk.

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