scope:

The optical transport hierarchy (OTH) supports the operation and management aspects of optical networks of various architectures, e.g., point-to-point, ring and mesh architectures.

This Recommendation defines the interfaces of the optical transport network to be used within and between subnetworks of the optical network, in terms of:

- optical transport hierarchy (OTH);

- functionality of the overhead in support of multi-wavelength optical networks;

- frame structures;

- bit rates;

- formats for mapping client signals.

The interfaces defined in this Recommendation can be applied at user-to-network interfaces (UNI) and network node interfaces (NNI) of the optical transport network. It is recognized, for interfaces used within optical subnetworks, that aspects of the interface are optical technology dependent and subject to change as technology progresses. Therefore, optical technology dependent aspects (for transverse compatibility) are not defined for these interfaces to allow for technology changes. The overhead functionality necessary for operations and management of optical subnetworks is defined.

The second revision of this Recommendation introduces:

- support for an extended (unlimited) set of constant bit rate client signals;

- a flexible ODUk, which can have any bit rate and a bit rate tolerance up to ±100 ppm;

- a client/server independent generic mapping procedure to map a client signal into the payload of an OPUk, or to map an ODUj signal into the payload of one or more tributary slots in an OPUk;

- ODUk delay measurement capability.