3Com CoreBuilder 7000 Operation Manual page 126

126 C 5: E
HAPTER STABLISHING
ATM C
HANNELS
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


The user part corresponding to the user part of the ATM destination
address of the receiving ATM user.
2 The CoreBuilder 7000 family ATM 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 7000
family ATM 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