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PacketStar
®
PSAX 4500 Multiservice Media Gateway User Guide
, Issue 2
Release 8.0.0
Chapter 3 System Features
User Interfaces
dual constituency, electing a PGL to represent it at the next highest level, up
to a maximum of 10 levels, in accordance with ATM Forum PNNI standard
af-pnni-0055.000 Annex F
,
Hierarchy Configuration
, and
Appendix G, Minimum
Subsets
(all border node capable switching systems features). Each switch in a
PNNI network has a unique 20-byte address that corresponds to the network
service access point (NSAP) schema. Much like IP subnet addresses, NSAP
identifiers have a network part and a user part. The user part is the last seven
bytes, and is reserved for end-system identification (insignificant to the
PNNI). The network part is the first 13 bytes, and is used to identify peer
groups.
Each level in the PNNI hierarchy is also assigned a scope number. Similar to
an IP subnet mask, the scope specifies how much of the 13-byte network part
is common to the switch addresses at a particular level in the hierarchy. For
example, a scope of 72 (bits) masks the first 9 bytes of the network part as
being common in all switches at that level. Higher levels have shorter scopes
because they do not look as far into the NSAP; a level with a scope of 64
(masking the first 8 bytes) resides above a level with a scope of 72.
To make the best use of PNNI’s capabilities, network architects must pay care-
ful attention to the ATM addressing structure, allocating correct addresses to
switches at each level of the hierarchy.