3Com CoreBuilder 7000, Operation Manual

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PNNI vs. E-IISP 69
Advantages of
Implementing a PNNI
Network
There are many advantages of implementing a network with PNNI. First, it
creates a more stable network. Since the nodes are aware of every
network problem (low bandwidth, no connection, etc.) less time is spent
in finding the best route to the destination. Furthermore, since the nodes
do not have to crankback every time there is a problem with the network,
there is less traffic on the network, which ensures faster delivery of all
network transmissions. Finally, PNNI is easy to configure, is scalable to very
large networks and automatically responds to all changes in the network.
In essence, PNNI is the next step after E-IISP.
When to Use PNNI It is recommended to use PNNI when your network has more than 15
switches, there is a need for scalability and interoperability and you feel
that QoS-based routing is important. PNNI is also recommended when
you want to use a multi-vendor environment. The CoreBuilder 7000
extended software version 4.0 is PNNI 1.0 standard-compliant.
PNNI vs. E-IISP
Enhanced Interim Interswitch Protocol (e-IISP) is a hop-by-hop dynamic
pre-standard routing protocol in which each node only knows about its
adjacent neighbors. This protocol is a proprietary protocol, developed by
3Com and is very similar to IISP (Interim Interswitch Protocol). IISP was
developed by the ATM forum as a predecessor to PNNI phase 1, and is
also known as PNNI phase 0.
As opposed to PNNI, with E-IISP, the network nodes do not have a global
view. Therefore, using E-IISP topology,
loops can occur which prevent
reliable cell delivery, as shown in Figure 15.