Huawei NE80 router 2.5G PoS port connect to Cisco 12416 router directly, PoS port physical layer and link protocol can't come up.
If NE80 PoS port make a loopback (Local or remote, physical or logical) , and link protocol using HDLC, PoS port don't have any problem. If we change two sides PoS port scramble encapsulation type CRC the phenomenon still the same.
We check Cisco router's PoS port packet format, and find that C2 byte are different with Huawei NE80 router. and Cisco router can't modify that C2 parameter, it's default is 16, so we just change our side C2 byte to 16 and ensure other parameter same, that phenomenon disappear.
Cisco router PoS port are adopt north American standardand, it isn't standard SDH formate. , but Huawei router PoS port adopt standard SDH formate, So there have some difference parameters between these two transmission standard.
There have many case about Huawei router Pos port connect to Cisco router PoS port , but still don't have any case introduce about C2 byte, because if Cisco router's IOS different it's PoS port also have some difference. so if you have this kind of problem, first try to check link protocol scramble encapsulation type CRC byte, if you can guarantee two sides PoS port parameters same, but PoS port link protocol still can't come up, you can use command "flag c2 16" to modify C2 byte.