ATM WAN Interfaces

ATM WANs can support any of the following five interface types:

• ATM UNI Defines the interaction between the following:

  - ATM endpoint device and a private network switch

  - ATM endpoint device and a public network switch

  - A private network switch and a public network switch

  The UNI specifications also include physical layer specifications, Integrated Local Management Interface (ILMI), and parameters to control quality of service elements of the ATM connection; for example, to govern traffic management.

• ATM NNI Signaling used between ATM switches across NNI links.

• ATM Data Exchange Interface (DXI) Enables communication with a DXI-enabled router via the router's serial interface. ATM DXI requires an ATM data service unit (ADSU), which receives data from the router in ATM DXI format over a High-Speed Serial Interface (HSSI) from the ATM switch/router. The ADSU converts the data into ATM cells and transfers them to the ATM network over a DS-3/E3 line.

• ATM Private Network Node Interface or Private Network-to-Network Interface (PNNI) Enables different switch vendors to interoperate across an ATM WAN. Vendors can implement proprietary ATM signaling between their own switches, and often do, using PNNI to manage the inter-vendor connections. PNNI lets the switches inform each other about network topology so that appropriate forwarding decisions can be made. PNNI is based on the OSPF (Open Shortest Path First) protocol, but also measures line capacities and delays rather than just the cost metrics measured by OSPF. It is this PNNI operation that enables ATM switches to reroute packets dynamically, based on current line conditions.

  NOTE

  Cisco Systems, Inc. implements PNNI 1.0.

• ATM B-ICI Describes PNNI interface points enabling the interconnection of public ATM networks.