For a bearer network, 2*GE are bound between two NE80s for more bandwidth and security. The optical links between two ERs are in the same channel, so the customer provides cable and MSTP transmission link to avoid complete failure of physical links. In actual test, if the cable is disconnected, 1-2 packets will be discarded over TRUNK link; when MSTP link disrupts, TRUNK link fails.
For the functionalities of current equipment, it'd better to use cable to replace the MSTP link, and the route of two cables should not be the same physically (with the help of third ER for transfer). To avoid that the TRUNK link disrupts because of failure in a single cable, it needs to set the interconnected GE to auto-negotiation.
For the existence of MSTP transmission equipment, two NE80s at both sides cannot acknowledge that the interface is down at the same time, and asol that the link fais, so if only the interface is up, they will transmit packets to it. NE80 does not have the functionality to detect the physical status of TRUNK link and the statistics over receiving and transmiting packets over the interface, and it cannot realize auto-negotiation and adjust the TRUNK link between both sides.
It is suggested to add the policy for TRUNK port member changing, which is triggerred by the change to port status and statistics over receiving and transmitting packets.