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MPLS-TP tunnels provide the transport network service layer over which IP and MPLS traffic traverse. MPLS-TP tunnels help transition from SONET/SDH TDM technologies to packet switching to support services with high bandwidth utilization and lower cost. Transport networks are connection oriented, statically provisioned, and have long-lived connections. Transport networks usually avoid control protocols that change identifiers (like labels). MPLS-TP tunnels provide this functionality through statically provisioned bidirectional label switched paths (LSPs)
MPLS-TP LSPs are bidirectional and co-routed and are comprised of two unidirectional LSPs that are supported by the MPLS forwarding infrastructure. A TP tunnel consists of a pair of unidirectional tunnels providing a bidirectional LSP. Each unidirectional tunnel can optionally be protected with a protect LSP that activates automatically upon failure conditions.
MPLS-TP (MPLS Transport Profile) extends IP/MPLS to facilitate the evolution to packet transport. Compared with IP/MPLS, the MPLS-based MPLS-TP simplifies transport requirements at data forwarding layer and enhances OAM and protection.
MPLS-TP is a variant of the traditional MPLS that is based in the unified principles of transport technologies such as SONET, SDH and OTN, it is considerably much simpler than the traditional MPLS due to the reduced complexity and extensive standardization. One of the key differences is that in traditional MPLS the path traffic takes is very often asymmetric, whereas in MPLS-TP return traffic must always take the path of the original traffic (but in opposite direction). Another difference is that MPLS-TP nodes are able to switch packets without IP in the forwarding plane while MPLS nodes do need IP on the interfaces that encapsulates and switch the packets. The ability to run without a dedicated control plane adjust MPLS-TP to the new trends of the industry such as SDN, meaning that clouds of MPLS-TP nodes can be made entirely of switches instead of high CPU capable routers.
