Page 1152 - 5G Basics - Core Network Aspects

2 Transport aspects

This DMp signal is inserted by the DMp originating P-CMEP and sent to the far-end P-CMEP. This far-end P-
CMEP loops back the DMp signal towards the originating P-CMEP. The originating P-CMEP measures the
number of frame periods between the moment the DMp signal value is inverted and the moment this
inverted DMp signal value is received back from the far-end P-CMEP. The receiver should apply a
persistency check on the received DMp signal to be tolerant for bit errors emulating the start of delay
measurement indication. The additional frames that are used for such persistency checking should not be
added to the delay frame count. The looping P-CMEP should loop back each received DMp bit within
approximately 100 µs.

Refer to [ITU-T G.798] for the specific path delay measurement process specifications.
NOTE 1 – Path delay measurements can be performed on-demand, to provide the momentary two-way transfer delay
status, and pro-active, to provide 15-minute and 24-hour two-way transfer delay performance management
snapshots.
NOTE 2 – Equipment designed according to the 2008 or earlier versions of this Recommendation may not be capable
of supporting this path delay monitoring. For such equipment, the DMp bit is a bit reserved for future international
standardization and set to zero.
NOTE 3 – This process measures a round trip delay. The one way delay may not be half of the round trip delay in the
case where the transmit and receive directions of the ODU network connection are of unequal lengths (e.g., in
networks deploying unidirectional protection switching).

15.8.2.1.7 ODU PM reserved overhead (RES)
For path monitoring of the OTUCn, 12 bits in the PM overhead in the ODU OH #2 to #n are reserved for
future international standardization. The value of these bits is set to "0".
The ODUk contains no ODU PM RES overhead. The ODUCn contains n-1 instances of the ODU PM RES
overhead.
15.8.2.2 ODU tandem connection monitoring (TCM) overhead

Six fields of an ODU tandem connection monitoring (TCM) overhead are defined in row 2, columns 5 to 13
and row 3, columns 1 to 9 of the ODU overhead; and six additional bits of tandem connection monitoring
are defined in row 2, column 3, bits 1 to 6.
TCM supports monitoring of ODUk connections for one or more of the following network applications
(refer to [ITU-T G.805], [ITU-T G.872], [ITU-T G.873.2] and [ITU-T G.7714.1]):
 optical UNI-to-UNI tandem connection monitoring; monitoring the ODU connection through the
public transport network (from public network ingress network termination to egress network
termination);
 optical NNI-to-NNI tandem connection monitoring; monitoring the ODU connection through the
network of a network operator (from operator network ingress network termination to egress
network termination);
 sublayer monitoring for linear 1+1, 1:1 and 1:n ODUk subnetwork connection protection switching,
to determine the signal fail and signal degrade conditions;

 sublayer monitoring for ODUk shared ring protection (SRP-1) protection switching as specified in
[ITU-T G.873.2], to determine the signal fail and signal degrade conditions;

 sublayer monitoring for ODUk connection passing through two or more concatenated ODUk link
connections (supported by back-to-back OTU trails), to provide a discovery message channel as
specified in [ITU-T G.7714.1];
 monitoring an ODUk tandem connection for the purpose of detecting a signal fail or signal degrade
condition in a switched ODUk connection, to initiate automatic restoration of the connection
during fault and error conditions in the network;

 monitoring an ODUk tandem connection for, e.g., fault localization or verification of delivered
quality of service.

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