Optical Channel Transport Unit (OTUk, OTUkV)

With the introduction of an overhead into each client signal as is representative of that signal only, it becomes necessary to introduce a further OH that will provide information to equipment handling regeneration. The information the equipment uses to perform this task is inserted into the OTU overhead (OTU OH). This information relates to the maintenance and operation functions to support the optical channel section. 

These functions include:  

•Functionalities of section monitoring 

•General communication channel 

•Reserved bits 

This unit also contains information that defines the use of a FEC (forward error control) as a way to improve signal quality and reliability. This unit is represented as follows: 

ODUk	OTUk
ODU1	OTU1
ODU2	OTU2
ODU3	OTU3
ODU4	OTU4

The OTU terminates at the point of assembly/disassembly and this is identical to the regeneration overhead in SDH. Note: The standard defines that the use of several types of FEC is possible though the only one standardized at the time was RS (255,239) the type of FEC used now though is based on Reed-Solomon and it is used to define the OTUk. Other possibilities of FEC are inserted into the OTUkV.