Multi-Protocol Label Switching (MPLS) encapsulation has the following characteristics:
LSPs (label switched paths) are used through the network, for example, primary, secondary, loose hop, and so on These paths define how traffic traverses the network from point A to B. If a path is down, depending on the configuration parameters, another path is substituted.
Paths can be manually defined or a constraint-based routing protocol (such as OSPF-TE or CSPF) can be used to determine the best path with specific constraints.
The 7450 ESS and 7750 SR OS support both signaled and non-signaled LSPs through the network.
Non-signaled paths are defined at each hop through the network.
Signaled paths are communicated via protocol from end to end using Resource Reservation Protocol (RSVP).
Because services are carried in encapsulation tunnels and an SDP is an entrance to the tunnel, an SDP has an implicit Maximum Transmission Unit (MTU) value. The MTU for the service tunnel can affect and interact with the MTU supported on the physical port where the SAP is defined.