Hello, FRR is an MPLS-TE application. It is made to protect an MPLS link (tunnel), path or node. It can not be used to protect a normal link, because it works with the reaction time of Sonet combined with label swapping.
A POS interface will detect the failure and the specific node will do the normal label swapping + and extra label for the backup tunnel. When this backup tunnel reach its destination the last node of the backup path will pop the extra label and the receiving node will only see the normal labels which are used in a normal condition. Node and path protection are still under development, there are no configuration possible yet.
I hope this is a bit clear???
