In the 7705 SAR, adjacency management is done through the establishment of a Service Destination Point (SDP) object, which is a service entity in the Nokia service model.
The service model uses logical entities that interact to provide a service. The service model requires the service provider to create and configure four main entities:
customers
services
Service Access Points (SAPs) on local 7705 SAR routers
SDPs that connect to one or more remote 7705 SAR routers or 77x0 SR routers
An SDP is the network-side termination point for a tunnel to a remote 7705 SAR or 77x0 SR router. An SDP defines a local entity that includes the system IP address of the remote 7705 SAR routers and 77x0 SR routers, and a path type.
Each SDP comprises:
the SDP ID
the transport encapsulation type, MPLS
the far-end system IP address
If the SDP is identified as using LDP signaling, then an LDP extended hello adjacency is attempted.
If another SDP is created to the same remote destination and if LDP signaling is enabled, no further action is taken, because only one adjacency and one LDP session exists between the pair of nodes.
An SDP is a unidirectional object, so a pair of SDPs pointing at each other must be configured in order for an LDP adjacency to be established. After an adjacency is established, it is maintained through periodic hello messages.