E-Iisp Hierarchical Routing Algorithm - 3Com CoreBuilder 7000 Operation Manual

60 C 3: E-IISP P
HAPTER
E-IISP Hierarchical
Routing Algorithm
ROTOCOL
Figure 13 Hierarchical Switch Addressing in Tree Topology
After you have set up the addressing scheme in this manner, the routing
algorithm ensures that any switch in this network can find every tree in it
(and therefore the location of every other switch) by first accessing the
root node of its own tree. From there it can approach the destination
switch of any other tree in the network in descending order of levels. For
details about the routing algorithm, see "E-IISP Hierarchic Routing
Algorithm" on page 125.
The CoreBuilder 7000 family ATM switch E-IISP protocol features a
proprietary hierarchical routing algorithm by which calls are routed
efficiently through a network with a hierarchical topology. The routing
algorithm determines the optimum output port of the switch on which to
transmit the call onwards towards its destination.
The efficiency of the algorithm is based on the hierarchical ATM
addressing system (see "Hierarchical ATM Addressing" on page 55) and
on the fact that each switch knows the net prefix of the ATM address of
each of its NNI neighbors, as well as the full ATM address of each UNI
neighbor. In principle, the algorithm will always be successful; a route will
always be found to the destination. This is because, in a hierarchical
network topology, every node can be reached by every other node.
The following description of the routing method assumes that an external
link of a virtual channel has already been established to an input port of
the switch. In addition, the call's destination address, which was
embedded in the signaling SETUP message, is available to the switch. The
routing method now seeks to establish an internal link from the input
port to an optimum output port.
The routing method consists of the following steps:
1 The CoreBuilder 7000 family ATM switch receives the ATM address of the
destination ATM user, the ATM destination address, from the signaling
SETUP message that establishes the external link to the input port. The
ATM destination address is comprised of two parts:


The network prefix part corresponding to the network prefix of the
CoreBuilder 7000 family ATM switch connected to the receiving ATM
user