A network node server (NNS) is a network node that provides resource location and route selection services to the LUs it serves. These LUs can be on the network node itself, or on end nodes that have established CP-CP sessions with this network node as their network node server.

To support the LUs on served end nodes, a network node server uses the CP-CP session to provide network information for session setup. Network node servers perform searches for partner LUs and calculate the best route to the partner LU.

Any network node can be a network node server for end nodes that are attached to it. The served end nodes are defined as being in that network node server domain.