3Com CoreBuilder 9000 User Manual page 369

2 The CoreBuilder 9000 ATM Enterprise Switch compares the ATM
destination address with the full ATM address of each of its UNI
neighbors. If a match is found, the SETUP message is sent on to the
appropriate UNI port, finishing the process successfully with a route
established.
3 If no match is found among its UNI neighbors, the CoreBuilder 9000 ATM
Enterprise Switch compares the network prefix of the ATM destination
address with the network prefix of the ATM address of each of its NNI
neighbors. A full match, a partial match, or no match are possible.


A full match means that a neighbor's network prefix is found that is
included in the destination address. For example, a neighbor's prefix of
A11 fully matches the destination address A113 because it is included
in it. In terms of the network topology, a full match means that the
neighbor is on the same tree and branch as the destination. In case
more than one neighbor's address fully matches, the longest address is
chosen. If no full match is found, a partial match is sought.


A partial match means that a neighbor's network prefix is found that is
identical to the destination address for at least one digit starting from
the left but does not fully match. For example, a neighbor's prefix of
A11 partially matches the destination address A123 because the first
two digits A1 are identical. In terms of the network topology, a partial
match means that the neighbor is on the same tree as the destination
but on a different branch. In case more than one neighbor's address
partially matches, the shortest address is chosen.


If neither a full or partial match is found, the algorithm seeks a
neighbor's network prefix whose significant length is shorter than that
of the switch itself. For example, a neighbor's prefix of A is shorter
than a switch address of A1. In terms of the network topology, this
means that the neighbor is on the same tree as the switch but closer
to the root. This is also called the default routing. If no such address is
found, a RELEASE message is sent back to the switch that sent the
SETUP message.
4 After an NNI neighbor is identified according to the procedure of the
previous step, an internal link is established to the output port to which
that neighbor is attached, and the VPI/VCI identifier and the neighbor's
address are recorded. This completes the virtual channel up to the output
port.
5 To continue the virtual channel, a SETUP message is forwarded to the NNI
neighbor to establish an external link (connection) to it.
Routing — Internal Links 369