A user can activate Dual Homing to dial a telephone number and have the system route the call to its destination over alternate facilities if the initial route is unavailable. This operation is transparent to the user, and no special dialing is required.
Dual Homing uses the Precedence Routing feature to provide alternate routing to nodes on a DSN. If a call fails to complete over the first trunk access line, the call is rerouted over a different trunk access line. This process can continue for any number of alternate routes.
If the call fails to complete by the time the call gets to the last trunk access line, the system routes the call to either:
Busy tone, or
The Blocked precedence call recorded announcement, see Announcements for Precedence Calling.
For example, a user dials a DSN number, such as 345-8854. Using Precedence Routing, you administer the system to route all calls that begin with the digits 345:
First over trunk group 20
Then over trunk group 21
Finally over trunk group 22
If all trunks in trunk group 20 are busy, the system next checks for idle trunks in trunk group 21, and finally in trunk group 22. If all trunks in all three trunk groups are busy, the system routes the call to fast busy tone or to a recorded announcement.
For a more detailed description of the available routing options, see Precedence Routing.
