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2                                                 Transport aspects


            16.5.1  ODU alarm indication signal (ODU-AIS)

            ODUk-AIS is specified as all "1"s in the entire ODU signal, excluding the frame alignment overhead (FA OH),
            OTU overhead (OTU OH) (see Figure 16-3).
            The ODUk contains one instance of ODU AIS. The ODUCn contains n instances of ODU AIS, numbered 1 to n
            (ODU AIS #1 to #n).



















                                                  Figure 16-3  ODU-AIS


            In  addition,  the  ODU-AIS  signal  may  be  extended  with  one  or  more  levels  of  ODU  tandem  connection,
            GCC1, GCC2, EXP and/or APS/PCC overhead before it is presented at the OTN interface. This is dependent
            on the functionality between the ODU-AIS insertion point and the OTN interface.
            The presence of the ODU-AIS is detected by monitoring the ODU STAT bits in the PM and TCMi overhead
            fields.
            16.5.2  ODUk open connection indication (ODUk-OCI)

            ODUk-OCI is specified as a repeating "0110 0110" pattern in the entire ODUk signal, excluding the frame
            alignment overhead (FA OH) and OTUk overhead (OTUk OH) (see Figure 16-4).

            NOTE – ODUCn OCI is not defined.



















                                                  Figure 16-4  ODUk-OCI

            NOTE – The repeating "0110 0110" pattern is the default pattern; other patterns are also allowed as long as the STAT
            bits in the PM and TCMi overhead fields are set to "110".

            In addition, the ODUk-OCI signal may be extended with one or more levels of ODUk tandem connection,
            GCC1, GCC2, EXP and/or APS/PCC overhead before it is presented at the OTM interface. This is dependent
            on the functionality between the ODUk-OCI insertion point and the OTM interface.
            The presence of ODUk-OCI is detected by monitoring the ODUk STAT bits in the PM and TCMi overhead
            fields.



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