This enumerated value indicates whether the APS group switches uni-directionally (only the affected end switches) or bi-directionally (both ends switch together) when a protection event occurs. Admins need to know this mode because it determines whether both ends of a SONET link move to protection together or independently, which affects how a switchover is diagnosed and coordinated with the far-end device. For example, a group configured as bi-directional(2) means that if the local end switches to protection, the admin should also expect the far-end switch to report a matching switchover, whereas a uni-directional(1) group would not.