The NHRP (Next Hop Resolution Protocol) comes from the Internet world and is described in RFC 1932. It allows to search the ATM corresponding to an IP address in an NBMA network of several DSL. Specifically, NHRP allows the resolution of an IP address of a workstation on a remote DSL NBMA address of a network (ATM address, frame relay, etc.).
Each LIS has a route server, called NHS (Next Hop Server), often located in a router. When a client requests a connection, it is for the NHS to which it belongs LIS to obtain routing information on the packet. If the local NHS can not solve the problem of location, it sends a request to related NHS, and so on until reaching the LIS to which the recipient belongs.
This solution allows you to find a more direct route that passes through the different NHS, as shown in Figure. Phase 1 is the address conversion request to the first DSL Router NHR, which turns with the Phase 2 NHR DSL Router which depends the remote user. Phases 3 and 4 correspond to the return of the address conversion. With ATM the customer address opens a virtual circuit to the remote: it is the phase 5. One can thus obtain a direct connection of two ATM stations belonging to remote DSL without having to go back to IP the router.