Bidirectional 1+1 switchover operation example

Table 1 describes the steps that a bidirectional protection switching process goes through during a typical automatic switchover.

Table 1. Actions for the bidirectional protection switching process
Status	APS commands sent in K1 and K2 bytes on protection line		Action
	B -> A	A -> B	At site B	At site A
No failure (Protection line is not in use).	No request	No request	No action	No action
Working line Degraded in direction A->B.	SD on working channel 1	No request	Failure detected, notify A and switch to protection line	No action
Site A receives SD failure condition.	Same	Reverse request	No action	Remote failure detected, acknowledge and switch to protection line
Site B receives Reverse request.	Same	Same	No action	No action