In MSTP+ product (Optix OSN). The protection of Packet services when we use MPLS tunnel APS with PW has a limitation in link networks. For example, if we have a link of 3 sites (A, B and C) and there is one E-line service between A and C carried by one PW and one Tunnel between A and C (picture 1/ case 1). in the case of working fiber cut between B and C, the tunnel will switch to the protecting one but the switching occurs in Ingress and Egress Node (A and C) (picture 1/ case2). So, if we have other fiber cut in the protection fiber between A and B, the service will be interrupted (picture 1/ case 3).
1. Create working and protecting tunnels between A and B
2. Create working and protecting tunnels between B and C
3. Create PW between A and C and configure it the change tunnel in site B (switch node)
This problem occurs because the tunnel switches from end to end and we have one APS protection group. But if we configure two tunnels between A and B, one is working and the other is protecting. And two others tunnels between B and C. in this case, we will have two independent APS protection groups (picture 2/ case 2)). We can create one PW carried by the first protection group in A-B section and configure it to change to the second protection group in B-C section. We have to use MS-PW and the service will be protected (picture2/ case 3).
for MSTP+ project, it's better to use MS-PW in link networks.