Page 1153 - 5G Basics - Core Network Aspects

Transport aspects 2

TCM supports monitoring of segments of ODUCn connections which span multiple OTSiA subnetworks. The
ODUCn TC-CMEP are located on OTUCn SOTU and MOTU interface ports at the edge of OTSiA subnetworks
and/or on OTUCn SOTUm and MOTUm interface ports in ODUCn terminating nodes (e.g., in ODUk cross
connects).

The six TCM fields are numbered TCM1, TCM2, ..., TCM6.
The ODUk contains one instance of ODU TCM1 to TCM6 overhead. The ODUCn contains n instances of the
ODU TCM1 to TCM6 overhead, numbered 1 to n (TCMi #1 to TCMi #n).
Each TCMi and TCMi #1 field contains the following subfields (see Figure 15-19):

 trail trace identifier (TTI);
 bit interleaved parity 8 (BIP-8);
 backward defect indication (BDI);
 backward error indication and backward incoming alignment error (BEI/BIAE);

 status bits indicating the presence of a TCM overhead, incoming alignment error, or a
maintenance signal (STAT).

Each TCMi #2 to #n field contains the following subfields (see Figure 15-19):
 bit interleaved parity 8 (BIP-8);
 backward error indication and backward incoming alignment error (BEI/BIAE);

 reserved (RES).
The PMandTCM field contains the following TCM subfields (see Figure 15-19):
 tandem connection delay measurement (DMti, i=1 to 6).

For the case of ODUk, the content of the TCM fields, except the STAT subfield, will be undefined (pattern
will be all-1s, 0110 0110 or 0101 0101 repeating) during the presence of a maintenance signal (e.g., ODUk-
AIS, ODUk-OCI, ODUk-LCK). The content of the PM&TCM field will be undefined (pattern will be all-1s, 0110
0110 or 0101 0101 repeating) during the presence of a maintenance signal. Refer to clause 16.5.
For the case of ODUCn, the content of the TCM field groups, except the STAT subfield, will be undefined
(pattern will be all-1s or 0101 0101 repeating) during the presence of a maintenance signal (e.g., ODUCn-
AIS, ODUCn-LCK). The content of the PMand TCM field will be undefined (pattern will be all-1s or 0101 0101
repeating) during the presence of a maintenance signal. Refer to clause 6.5.

A TCM field and PM&TCM bit is assigned to a monitored connection as described in clause 15.8.2.2.6. The
number of monitored connections along an ODU trail may vary between 0 and 6. These monitored
connections may be nested, cascaded or both. Nesting and cascading are the default operational
configurations. Overlapping is an additional configuration for testing purposes only. Overlapped monitored
connections must be operated in a non-intrusive mode in which the maintenance signals ODU-AIS and
ODU-LCK are not generated. For the case where one of the endpoints in an overlapping monitored
connection is located inside an SNC protected domain while the other endpoint is located outside the
protected domain, the SNC protection should be forced to working when the endpoint of the overlapping
monitored connection is located on the working connection, and forced to protection when the endpoint is
located on the protection connection.
Nesting and cascading configurations are shown in Figure 15-21. Monitored connections A1-A2/B1-B2/C1-
C2 and A1-A2/B3-B4 are nested, while B1-B2/B3-B4 are cascaded. Overlapping is shown in Figure 15-22
(B1-B2 and C1-C2).

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