Cabletron Systems MMAC-Plus SFCS-1000, Руководство по настройке

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F-4
ForeThought PNNI
F.1.4.1.2 Switch Summary Prefix
Each switch is configured with a switch mask (swmask) which gives the length
of the switch summary prefix within the switch prefix. The swmask gives the
number of most significant bits of the switch prefix that constitute the switch
summary prefix. Since all end system addresses attached to a switch have the
same switch summary prefix, their reachability information can be summa-
rized by this prefix (i.e., by the switch summary prefix).
F.1.4.1.3 Peer Group ID
Each switch is configured with a peer group mask (pgmask) which gives the
length of the peer group ID within the switch summary prefix. The pgmask
gives the number of most significant bits of the switch summary prefix that
constitute the peer group ID.
The peer group ID is a unique identifier for every node (switch or end system)
in a particular peer group. Every switch and host in peer group A, for exam-
ple, will have the same peer group ID.
A simple example of summarizing by peer group ID can be seen in Figure F.3,
where every switch (and end system, although not shown) in peer group A is
identified starting with “A.”
F.1.4.2 Path Computation
Path computation is performed on demand whenever FT-PNNI signalling
requests a path to a given destination. The Bellman-Ford Shortest Path algo-
rithm is used to compute the shortest path tree of all nodes in the topology
with the local node as the source. The administrative weight metric in the
loglinks is used as the minimizing criterion in computing the shortest path
route. In the case of finding multiple equal-cost paths to a given destination,
available cell rate is used to break ties.