How OTN can carry synchronous signal while it is Asynchronous ?
- The OTN does not require any synchronization functionality. But the OTN specifically the mapping/demapping/multiplexing/demultiplexing processes and justification granularity information were designed to transport synchronous client signals, like synchronous STM-N and synchronous Ethernet signals. (ITU G.798.1)
- OTN layer itself does not need to transport network synchronization like SDH . but the OTN optical channel data rate is derived from client rate clock recovery , then the frequency difference is taken up via stuffing bytes.
The maximum frequency difference that can be accommodated between optical channel frame and client is +/- 65 ppm
- The OTN uses 3 mapping ways to insert client signal into the ODUK , one synchronous and 2 asynchronous they are :-
1- BMP (Bit-Synchronous Mapping Procedure)
2- AMP (Asynchronous Mapping Procedure)
3- GMP (Generic Mapping Procedure)
OTN can use the 3 mapping modes to send synchronous signals but with different quality and jitter values .
The best way is BMP(Bit-Synchronous Mapping Procedure) , In this mode the server (ODUK) Clock signal must be phase-locked to the client clock signal and it adds some Fixed Stuffing.
The other two Asynchronous mapping modes AMP (Asynchronous Mapping Procedure) or GMP (Generic Mapping Procedure) Also can send synchronous signals but with frequency offset of ±20 ppm . The OTN terminal can accommodate these timing differences by performing variable negative or positive-justification.
I hope to be useful to you
