Page 1104 - 5G Basics - Core Network Aspects

2 Transport aspects

Interleaved versions of the OTU, ODU and OPU overhead may be present on OTUCn interfaces. This
interleaving is interface specific and specified for OTN interfaces with standardized application codes in the
interface specific Recommendations (ITU-T G.709.x series). Within the other clauses of this
Recommendation an OTUCn, ODUCn and OPUCn are presented in an interface independent manner, by
means of n OTUC, ODUC and OPUC instances that are marked #1 to #n.

Column #
. . . . . .
1 7 8 14 15 16
1 Frame alignment area OTU specific overhead area
Row # 2 3 ODU specific overhead area OPU specific overhead area

4
G.709-Y.1331(12)_F5-1

Figure 5-1  OTU, ODU and OPU overhead

6 Optical transport network interface structure
The optical transport network as specified in [ITU-T G.872] defines two interface types, each with two sub-
types:
– Single optical transport unit interfaces:
• without optical layer overhead (SOTU);
• with optical layer overhead (SOTUm).

– Multi optical transport unit interfaces:
• without optical layer overhead (MOTU);
• with optical layer overhead (MOTUm).
The OTN interfaces without optical layer overhead are defined with 3R processing at each end of the
interface.
The interfaces consist of digital and management information defined in this Recommendation as carried
by a physical interface, the specifications of which are outside the scope of this Recommendation.

Each interface may be associated with one or more application identifiers. Each application identifier
represents either a standardized application code or a vendor specific identifier. An interface with an
application code may be used to interconnect (OTN) equipment from different vendors. An interface with a
vendor specific identifier is to be used to interconnect (OTN) equipment from the same vendor. When
considering interconnection over an interface between user and provider administrations or provider to
provider administrations, 3R termination shall be used on either side of the interface, unless mutually
agreed otherwise.

6.1 Basic signal structure
The basic structure is shown in Figures 6-1 and 6-2 and consists of a digital and an optical structure.

6.1.1 OTN digital structure
The OTN digital structure (see Figure 6-1) consists of two classes of optical transport units (OTU); the OTUk
and OTUCn. The OTUk signal consists of a 4080 column by 4 row frame, which includes 256 columns
allocated to contain a forward error correction code (FEC) and is operated at various bit rates that are
represented by the value of k. The OTUCn signal consists of n interleaved 3824 column by 4 row frames,
which do not include a FEC area and is operated at n times a basic rate that is represented by OTUC. FEC for
the OTUCn signal is interface specific and not included in the OTUCn definition.

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