The Private Network-to-Network Interface (PNNI) is a link-state routing protocol used in Asynchronous Transfer Mode (ATM) networks.
The five common reasons for updating PTSEs are as follows: 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.
If the switch is unable to establish the RCC with the adjacent node, then PTSE information is not exchanged.
PNNI measures line capacities and delays in addition to simple cost metrics.