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Transport aspects 2

The GCC1 #1 to #n plus GCC2 #1 to #n overhead may be combined to provide one communication channel
as illustrated in Figure 15-25 with an approximated bandwidth of n × 27.525 Mbit/s.

Figure 15-25 – OTUCn GCC1, GCC2 and GCC1+2 transmission order

15.8.2.4 ODU automatic protection switching and protection communication channel (APS/PCC)
A four-byte ODU-APS/PCC signal is defined in row 4, columns 5 to 8 of the ODU overhead. Up to eight levels
of nested APS/PCC signals may be present in this field.
The ODUk and ODUCn contain one instance of ODU APS/PCC overhead.

For ODUk, the APS/PCC bytes in a given frame are assigned to a dedicated connection monitoring level
depending on the value of MFAS as follows:

Table 15-8  Multiframe to allow separate APS/PCC for each monitoring level

MFAS APS/PCC channel applies to Protection scheme using the
bits 6 7 8 connection monitoring level APS/PCC channel (Note 1)

0 0 0 ODUk Path ODUk SNC/Ne, ODUj CL-SNCG/I, Client SNC/I, ODU
SRP-p
0 0 1 ODUk TCM1 ODUk SNC/S, ODUk SNC/Ns
0 1 0 ODUk TCM2 ODUk SNC/S, ODUk SNC/Ns
0 1 1 ODUk TCM3 ODUk SNC/S, ODUk SNC/Ns

1 0 0 ODUk TCM4 ODUk SNC/S, ODUk SNC/Ns
1 0 1 ODUk TCM5 ODUk SNC/S, ODUk SNC/Ns
1 1 0 ODUk TCM6 ODUk SNC/S, ODUk SNC/Ns, ODU SRP-1
1 1 1 ODUk server layer trail (Note 2) ODUk SNC/I
NOTE 1 – An APS channel may be used by more than one protection scheme and/or protection scheme instance. In case of
nested protection schemes, care should be taken when an ODUk protection is to be set up in order not to interfere with the APS
channel usage of another ODUk protection on the same connection monitoring level, e.g., protection can only be activated if
that APS channel of the level is not already being used.
NOTE 2 – Examples of ODUk server layer trails are an OTUk or a server ODUk (e.g., an ODU3 transporting an ODU1).
For ODUCn, the APS/PCC signal is used to support coordination of the end points in linear (ODUk CL-
SNCG/I) and ring (ODUk SRP) protection applications.
For linear protection schemes, the bit assignments for these bytes and the bit-oriented protocol are given
in [ITU-T G.873.1]. Bit assignment and byte-oriented protocol for ring protection schemes are given in
[ITU-T G.873.2].

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