A service distribution path (SDP) acts as a logical way of directing traffic from one router to another through a unidirectional (one-way) service tunnel. The SDP terminates at the far-end router which directs packets to the correct service egress service access point (SAP) on that device. All services mapped to an SDP use the same transport encapsulation type defined for the SDP (either GRE or MPLS).
For information about service transport tunnels, see the Service Distribution Paths (SDPs) section in the 7450 ESS, 7750 SR, 7950 XRS, and VSR Services Overview Guide. They can support up to eight forwarding classes and can be used by multiple services. Multiple LSPs with the same destination can be used to load-balance traffic.