Page 1158 - 5G Basics - Core Network Aspects

2 Transport aspects

15.8.2.2.7 Blank clause

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15.8.2.2.8 ODU TCM delay measurement (DMti, i=1 to 6)
For ODU tandem connection monitoring, a one-bit tandem connection delay measurement (DMti) signal is
defined to convey the start of the delay measurement test.

The ODUk and ODUCn contain one instance of ODU TCM DMti overhead.
The DMti signal consists of a constant value (0 or 1) that is inverted at the beginning of a two-way delay
measurement test. The transition from 01 in the sequence …0000011111…, or the transition from 10
in the sequence …1111100000… represents the path delay measurement start point. The new value of the
DMti signal is maintained until the start of the next delay measurement test.
This DMti signal is inserted by the DMti originating TC-CMEP and sent to the far-end TC-CMEP. This far-end
TC-CMEP loops back the DMti signal towards the originating TC-CMEP. The originating TC-CMEP measures
the number of frame periods between the moment the DMti signal value is inverted and the moment this
inverted DMti signal value is received back from the far-end TC-CMEP. The receiver should apply a
persistency check on the received DMti 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 TC-CMEP should loop back each received DMti bit within
approximately 100 µs.

Refer to [ITU-T G.798] for the specific tandem connection delay measurement process specifications.
NOTE 1 – Tandem connection 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 tandem connection delay monitoring. For such equipment, the DMti bit is a bit reserved for future
international standardization.
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 ODUk tandem connection are of unequal lengths (e.g., in
networks deploying unidirectional protection switching).

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

15.8.2.3 ODU general communication channels (GCC1, GCC2)
Two fields of two bytes are allocated in the ODU overhead to support two general communications
channels or two discovery channels as specified in [ITU-T G.7714.1] between any two network elements
with access to the ODU frame structure (i.e., at 3R regeneration points).

These general communication channels are clear channels and any format specification is outside of the
scope of this Recommendation. The bytes for GCC1 are located in row 4, columns 1 and 2, and the bytes for
GCC2 are located in row 4, columns 3 and 4 of the ODU overhead.

The ODUk contains one instance of ODU GCC1, GCC2 overhead. The ODUCn contains n instances of the
ODU GCC1, GCC2 overhead, numbered 1 to n (GCC1 #1 to GCC1 #n, GCC2 #1 to GCC2 #n).

The GCC1 #1 to #n overhead are combined to provide one communication channel as illustrated in Figure
15-25 with an approximated bandwidth of n × 13.768 Mbit/s.

The GCC2 #1 to #n overhead are combined to provide another communication channel as illustrated in
Figure 15-25 with an approximated bandwidth of n × 13.768 Mbit/s.

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