ATM PNNI: ATM Private Network-to-Network Interface 

The ATM Private Network-Node Interface (PNNI), an ATM network-to-network signaling protocol, provides mechanisms to support scalable, QoS-based ATM routing and switch-to-switch switched virtual connection (SVC) interoperability.

The PNNI (Private Network-to-Network Interface), is a hierarchical, dynamic link-state routing protocol. It is designed to support large-scale ATM networks. The PNNI protocol uses VPI/VCI 0,18 for its messages. In addition, it uses signalling messages to support connection establishment across multiple networks. PNNI is based on UNI 4.0 and Q.2931. Specific information elements were added to UNI 4.0 in order to support the routing process of PNNI. PNNI Signalling contains the procedure to dynamically establish, maintain and clear ATM connections at the private network to network interface or network node interface between 2 ATM networks or 2 ATM network nodes. The PNNI signalling protocol is based on the ATM forum UNI specification and on Q.2931 .

PNNI Messages include:ALERTING, CALL PROCEEDING, CONNECT, SETUP, RELEASE, RELEASE COMPLETE, NOTIFY, STATUS, STATUS ENQUIRY, RESTART, RESTART ACKNOWLEDGE, STATUS, ADD PARTY, ADD PARTY ACKNOWLEDGE, PARTY ALERTING, ADD PARTY REJECT, DROP PARTY, DROP PARTY ACKNOWLED

• Packet type: The following packet types are defined:
1. Hello - Sent by each node to identify neighbor nodes belonging to the same peer group.
2. PTSP - PNNI Topology State Packet. Passes topology information between groups.
3. PTSE - PNNI Topology State Element (Request and Ack). Conveys topology parameters such as active links, their available bandwidth, etc.
4. Database Summary - Used during the original database exchange between two neighboring peers.
• Packet length- The length of the packet.
• Prot ver - Protocol Version. The version according to which this packet was formatted.
• Newest ver / Oldest ver - Newest version supported / oldest version supported. The newest version supported and the oldest version supported fields are included in order for nodes to negotiate the most recent protocol version that can be understood by both nodes exchanging a particular type of packet

The ATM protocols are based on standards developed by the ITU.
http://www-comm.itsi.disa.mil/atmf/sig.html#af10.1 : UNI 4.0 Specification
http://www.atmforum.com/standards/approved.html : ATM Forum approved specifications