ATM Interfaces and Protocols

In an ATM network, switches and end systems (such as routers, personal computers and any other equipment with ATM network interface cards) are interconnected by transmission links. The UNI connects an end system to an access switch, whereas the NNI connects two switches belonging to the same network The UNI and the NNIs are specified by the ATM Forum and ITU-T for private and public ATM networks, respectively.

In particular, the PNNI protocol, ATM Forum’s standard VC routing protocol, is specified for use between private ATM switches. A link-state routing protocol is defined for distributing topology information between switches. This information is used to compute paths through the network by applying a hierarchy mechanism to ensure the scalability for large ATM networks. PNNI also specifies a protocol for signaling, that is, message flows used to establish point-to-point and point-to-multi-point ATM VC’s. This protocol is based on the ATM Forum UNI signaling, with mechanisms added to support source routing and alternate routing in case of connection setup failure. More detailed information is presented in the section covering IP over ATM techniques.