The functions of the PathOverhead (POH) in the STM data frame, Synchronous Transport Module (STM), primarily include quality monitoring and marking of the container.
Specifically, the Path Overhead performs the following functions: Sender description, error detection, container content composition, path status, path replacement information, and monitoring of a carrier section.
The functions are executed during the transmission of the payload (container) within an SDH network. The Path Overhead accompanies the container throughout the transmission path and is only removed at the destination node.
Path OverheadOrder Path Overhead and the Lower Order Path Overhead with a somewhat limited functionality. The Higher Order Path Overheads are characterized by the virtual containers VC-3 and VC-4 and are used for the transport of 140 Mbit/s, 34 Mbit/s and ATM signals. The Lower Order Path Overheads of the virtual containers VC-2, VC-11 and VC-12 are used to transport 1.544 Mbit/s, 2.048 Mbit/s and ATM signals.