For packets arriving on all interfaces that need to be transmitted over APS protected interfaces, the next hop associated with all these interfaces are programmed in all Flexible Fast-Path complexes in each MDA with a logical next-hop index. This next hop-index identifies the actual next-hop information used to direct traffic to the APS working circuit on IOM-1/MDA-1.
All Flexible Fast-Path complexes in each MDA are also programmed with next hop information used to direct traffic to the APS protect circuit on IOM-2/MDA-1. When the transmitted data needs to be switched from the working to the protect circuit, only the relevant next hop indexes need to be changed to the pre-programmed next-hop information for the protect circuit on IOM-2/MDA-1.
Although the control CPM on the SF/CPM blade initiates the changeover between the working to protect circuit, the changeover is transparent to the upper layer protocols and service layers that the switchover occurs.
Physical link monitoring of the link is performed by the CPU on the relevant IOM for both working and protect circuits.