1. RS, MS, AND Path Overheads
Difference among POH, MSOH, & RSOH
Repeater
Repeater
Add-Drop Mux
Term Mux
Term Mux
POH
MSOH
RSOH
Path OH – end to end circuit
Multiplex Section OH – multiplexer to multiplexer
Regenerator Section OH – repeater to adjacent node or vice versa

2. Section Overhead (SOH)
Multiplex Section Overhead (MSOH)
-MSOH– supervises each STM-1 of STM-N frame
Regenerator Section Overhead (RSOH)
RSOH– supervises the whole STM-N frame

3. Path Overhead (POH) Lower order POH (LPOH) Higher order (HPOH)
---HPOH and LPOH are used for VC4, VC3, and VC12 monitoring
POH monitors individual low-rate signals within STM-N frame, while SOH monitors the whole package i.e., STM-N frame

4. STM – Performance Monitoring And Management
RSOH, MSOH and POH provide monitoring and management function for different layers/levels of STM-N frame
For STM-64 frame:
RSOH monitors the overall transmission performance of STM-64 signal
MSOH monitors the performance of individual STM-1s
POH monitors each low-rate signal (e.g., 2 Mbps)

5. SDH Overhead Summary RSOH SOH MSOH Overhead High Order POH POH
Low Order POH