Page 1098 - 5G Basics - Core Network Aspects

2 Transport aspects

– ODU path CMEP (P_CMEP), which represents the end-points of the ODUkP/ODUCnP trail. The PM
overhead field contains the related CMOH.

3.2.7 non-associated overhead: Supervisory information transported in an optical supervisory signal,
overhead communication channel or other means.

3.2.8 optical data unit (ODU): The ODU is an information structure consisting of the information
payload (OPU) and ODU related overhead, either as ODUk or ODUCn.

3.2.9 optical payload unit (OPU): The OPU is the information structure used to adapt client information
for transport over the OTN, either as an OPUk or an OPUCn. It comprises client information together with
any overhead needed to perform rate adaptation between the client signal rate and the OPU payload rate,
and other OPU overheads supporting the client signal transport. The index k or Cn (see clause 5) is used to
identify the approximate bit rate and different versions.

3.2.9 optical transport unit (OTU): The OTU is the information structure used for transport of an ODU
over an optical layer trail, either as an OTUk or an OTUCn.

When the optical layer trail does not support a complete set of overhead (i.e., in case of OCh, OPS), the
OTU overhead is used as overhead for such optical layer trail, and the OTU must terminate where the
optical layer trail is terminated. Otherwise (i.e., in case of OTSiA), the OTU overhead may or may not be
terminated where the optical layer trail is terminated.
Three versions of the OTUk are defined: completely standardized OTUk (OTUk), functionally standardized
OTUk (OTUkV) and an OTUk with completely standardized overhead and functionally standardized FEC
(OTUk-v). The completely standardized OTUk is used on OTN IrDIs and may be used on OTN IaDIs. The other
two are used on OTN IaDIs.

3.2.10 OCh: The OCh is the information structure used to support the OCh trail. The OCh is an
information structure consisting of the information payload (OCh_PLD) with a certain bandwidth and
non-associated overhead (OCh_OH) for management of the OCh.

3.2.11 optical physical section (OPS): A layer network that provides functionality for transmission of a
multi-wavelength optical signal on optical media of various types (e.g., [ITU-T G.652], [ITU-T G.653] and
[ITU-T G.655] fibre). Note that a "multi-wavelength" signal includes the case of just one OTU signal.
3.2.12 optical transport network: An optical transport network (OTN) is composed of a set of optical
network elements connected by optical fibres, that provide functionality to encapsulate, transport,
multiplex, route, manage, supervise and provide survivability of client signals. The information of the client
signals is processed in the digital domain and carried across the media, according to the requirements given
in [ITU-T G.872].
3.2.13 optical transport network node interface (ONNI): The interface at an optical transport network
node which is used to interconnect with another optical transport network node.

4 Abbreviations and acronyms

This Recommendation uses the following abbreviations and acronyms:
16FS 16 columns with Fixed Stuff

3R Reamplification, Reshaping and Retiming
AI Adapted Information
AIS Alarm Indication Signal

AMP Asynchronous Mapping Procedure
API Access Point Identifier

APS Automatic Protection Switching
ASI Asynchronous Serial Interface for DVB

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