A service is a globally unique entity that refers to a type of connectivity service for either Internet or VPN connectivity. Each service is uniquely identified by a service ID and an optional service name within a service area. The Nokia service router model uses logical service entities to construct a service. In the service model, logical service entities provide a uniform, service-centric configuration, management, and billing model for service provisioning.
In the Nokia router services can provide Layer 2 bridged service or Layer 3 IP-routed connectivity between a service access point (SAP) on one router and another service access point (a SAP is where traffic enters and exits the service) on the same (local) router or another router (distributed). A distributed service spans more than one router.
Distributed services use service distribution points (SDPs) to direct traffic to another Nokia router through a service tunnel. SDPs are created on each participating router, specifying the origination address (the router participating in the service communication) and the destination address of another router. SDPs are then bound to a specific customer service. Without the binding process, far-end router is not able to participate in the service (there is no service without associating an SDP with a service).