Bypass tunnel—A label-switched path (LSP) that is used to protect multiple LSPs in many-to-one (facility) backup.
CSPF—Constrained Shortest Path First. An MPLS algorithm that has been modified to take into account specific restrictions when calculating the shortest path across the network.
Detour LSP—The LSP that is used to reroute traffic around a failure in one-to-one backup.
DMP—Detour Merge Point. In the case of one-to-one backup, this is an LSR where multiple detours converge. Only one detour is signaled beyond that LSR.
Facility backup—A local repair method in which a bypass tunnel is used to protect one or more protected LSPs that traverse the point of local repair, the resource being protected, and the merge point, in that order.
Local repair—Techniques used to repair LSP tunnels quickly when a node or link along the LSP fails.
LSP—An MPLS label-switched path (LSP). In this document, an LSP is always explicitly routed.
LSR—Label-switching router. A router on which MPLS is enabled and that can process label-switched packets.
Merge point— The LSR where one or more backup tunnels rejoin the path of the protected LSP downstream of the potential failure. The same LSR may simultaneously be a merge point and a point of local repair.
Next-hop bypass tunnel—A backup tunnel that bypasses a single link for different LSPs.
Next-next-hop bypass tunnel—A backup tunnel that bypasses a single node of the protected LSP.
One-to-one backup—A local repair method in which a detour LSP is separately created for each protected LSP at a point of local repair.
Point of local repair—The ingress (head-end) LSR of a backup tunnel or a detour LSP.
Protected LSP—An LSP is protected at a given hop if it has one or multiple detours or bypass paths.