private network to network interface (ATM) (PNNI)
The Private Network to Network Interface (PNNI) is a specification created by the ATM Forum with which ATM switching nodes in private networks can communicate with each other. PNNI is a routing protocol that enables heterogeneous ATM networks to be set up and communication between different ATM nodes. In addition, PNNI supports the exchange of management data and the establishment of virtual dial-up connections.
The ATM Forum has specified PNNI as a link state protocol( LSP) for routing in large ATM networks, relying on three different Hello protocols, the Neighboring Peer Protocol or the PGL Election Protocol, for which the organization has defined two protocols. One protocol distributes information about the network topology to subscribers, and the other is a signaling protocol for establishing connections between ATM switching units. The signaling protocol is based on UNI signaling and has some additional routing mechanisms. In 1996, version 1.0 of PNNI was adopted as a standard.
A special feature of PNNI is the "crankback". This mode of operation allows blocked connections within an ATM network to be bypassed by selecting a new route at a previous connection point.