The Private Network-to-Network Interface (PNNI) is a link-state

routing protocol A routing protocol specifies how routers communicate with each other to distribute information that enables them to select routes between nodes on a computer network. Routers perform the traffic directing functions on the Internet; data packets ...

used in

Asynchronous Transfer Mode Asynchronous Transfer Mode (ATM) is a telecommunications standard defined by American National Standards Institute (ANSI) and ITU-T (formerly CCITT) for digital transmission of multiple types of traffic. ATM was developed to meet the needs of ...

(ATM) networks. PNNI is similar to the

open shortest path first Open Shortest Path First (OSPF) is a routing protocol for Internet Protocol (IP) networks. It uses a link state routing (LSR) algorithm and falls into the group of interior gateway protocols (IGPs), operating within a single autonomous sys ...

(OSPF) used for IP routing. PNNI is a suite of network protocols that can be used to discover an ATM network topology, create a database of topology information, and route calls over the discovered topology. PNNI is a

link-state routing protocol Link-state routing protocols are one of the two main classes of routing protocols used in packet switching networks for computer communications, the others being distance-vector routing protocols. Examples of link-state routing protocols include ...

, which means that the protocol collects information about the current state of links and nodes in the network to build a network database. The PNNI network database can be used to determine the network structure and the current state of network components. To build the PNNI network database, each PNNI node must receive topology information from all the other devices in the network. To keep the database current, the node must receive regular updates from other nodes. The PNNI protocol communicates the state of a PNNI network in PNNI Topology State Elements (PTSEs). PTSEs are discrete messages that contain information about one of the following types of network components: * PNNI nodes * Reachable addresses * PNNI links between nodes To enable communications with other nodes, each switch needs to have all the PTSE information for each switch in the network. Each node is responsible for flooding out its own PTSE information to all the other switches in the network. Since up-to-date PTSE information is required for optimal routing decisions to be made, there are several different mechanisms in place to help ensure that all nodes have reasonably accurate PTSE information. The five common reasons for updating PTSEs are as follows: * Resources administratively added, removed or altered on a node. * Resource failure such as a loss of signal (LOS) on a link. * A significant change in link resources due to

virtual circuit A virtual circuit (VC) is a means of transporting data over a data network, based on packet switching and in which a connection is established within the network between two endpoints. The network, rather than having a fixed data rate reservation ...

s (VCs) routing or . * Periodic updates defined by the PTSE refresh and PTSE lifetime interval timers. * A processor switch module (PXM) switchover. PTSE information is passed between nodes using PNNI topology state packets (PTSPs). These packets utilize the routing control channel (RCC; VPI = 0 and VCI = 18) between adjacent nodes. The RCC is also used for Hello packets and other PNNI messages. If the switch is unable to establish the RCC with the adjacent node, then PTSE information is not exchanged. Once a node receives PTSE information, the node stores the contents, or element information, in the database. This information is used to generate precomputed routing tables that identify routes to other network devices. PNNI uses the

Dijkstra's algorithm Dijkstra's algorithm ( ) is an algorithm for finding the shortest paths between nodes in a graph, which may represent, for example, road networks. It was conceived by computer scientist Edsger W. Dijkstra in 1956 and published three years ...

for

shortest path first Dijkstra's algorithm ( ) is an algorithm for finding the shortest paths between nodes in a graph, which may represent, for example, road networks. It was conceived by computer scientist Edsger W. Dijkstra in 1956 and published three years ...

(SPF) calculation. The PNNI database is also used to perform on-demand routing when the appropriate routing table does not contain a viable path. PNNI measures line capacities and delays in addition to simple cost metrics.

References

External links

*{{cite web , url=https://www.cisco.com/c/en/us/td/docs/switches/wan/mgx/mgx_8850/software/mgx_r5-2/data/pnni/network/planning/guide/ppg/pintro.html , title=Cisco PNNI Network Planning Guide for MGX and SES Products, Release 5.2; Chapter: Introduction to PNNI , author= , website=Cisco.com , publisher=

Cisco Systems Cisco Systems, Inc., commonly known as Cisco, is an American-based multinational corporation, multinational digital communications technology conglomerate (company), conglomerate corporation headquartered in San Jose, California. Cisco develo ...

, access-date=August 7, 2017 ITU-T recommendations Networking standards Routing protocols