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ForeRunner
ATM Switch Network Configuration Manual
ForeThought PNNI
5.1 FT-PNNI Routing
The FT-PNNI routing protocol serves to distribute topology and address reachability informa-
tion between switches and groups of switches in a network. This topology and addressing
information is used by switches to compute paths through the network. The functions of the
FT-PNNI routing protocol include the following:
•
Hello Protocol
•
Topology Database Exchange
•
Flooding
•
Hierarchical Routing
5.1.1 Hello Protocol
FT-PNNI hello packets are exchanged between neighboring nodes. Each switch (node) trans-
mits a hello indication on each of its FT-PNNI routing channels at regular intervals. The time
between these hello indications is called the Hello Indication Interval. When a switch receives
a hello indication from one of its neighbors, it stores the logical link (loglink) from that neigh-
bor to itself in the topology database.
Based on the hello indications, loglinks are refreshed periodically. Since loglinks discovered as
a result of hello indications are unidirectional, each switch stores unidirectional loglinks with
its immediate neighbor as the source and itself as the destination.
5.1.2 Topology Database Exchange
Each switch sends to each of its neighbors a group of loglinks from its topology database at
regular intervals, called the NSAP map indication interval. This exchange of information
between neighboring switches ensures that the topology databases of the switches stays syn-
chronized.
5.1.3
Flooding
Flooding is a reliable hop-by-hop propagation of loglinks throughout a peer group. Whenever
a new loglink is discovered by a switch, the switch immediately broadcasts the existence of
this link to all of its neighbors. The neighboring switches then broadcast the existence of the
same link to all of their neighbors. Very quickly, the existence of the new loglink is flooded
throughout all of the switches in the network.
Similarly, when a link goes down, or when a significant change is seen in the metrics of a
loglink, the latest state of the loglink is propagated immediately throughout the network.
Summary of Contents for forerunner series
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Page 16: ...TOC 10 ForeRunner ATM Switch Network Configuration Manual Table of Contents ...
Page 20: ...LOF 4 ForeRunner ATM Switch Network Configuration Manual List of Figures ...
Page 22: ...LOT 2 ForeRunner ATM Switch Network Configuration Manual List of Tables ...
Page 30: ...viii ForeRunner ATM Switch Network Configuration Manual Preface ...
Page 144: ...3 58 ForeRunner ATM Switch Network Configuration Manual Configuring an Emulated LAN ...
Page 180: ...6 12 ForeRunner ATM Switch Network Configuration Manual ATM Forum PNNI ...
Page 220: ...9 6 ForeRunner ATM Switch Network Configuration Manual Configuring Timing ...
Page 300: ...D 24 ForeRunner ATM Switch Network Configuration Manual Configuring FramePlus Modules ...
Page 308: ...Acronyms 8 ForeRunner ATM Switch Network Configuration Manual Acronyms ...
Page 346: ...Glossary 38 ForeRunner ATM Switch Network Configuration Manual Glossary ...
Page 352: ...Index 6 ForeRunner ATM Switch Network Configuration Manual Index ...