Nortel Remote Gateway 50 Configuration Manual page 131

Alternative Call Routing for Network Bandwidth Management
How Alternative Call Routing for NBWM works
When a user dials a station-to-station call between two different zones (that
is, the calling and called telephones are not located in the same geographic
area) and the bandwidth limit has been reached, then the Alternative Call
Routing feature is invoked.
The following steps occur in Alternative Call Routing scenarios.
Call from branch office telephone in Normal Mode
1 The interzone station-to-station call is attempted. There is insufficient
bandwidth available to make the call.
2 The main office inserts the ALTPrefix associated with the originator's
zone (the branch office in this case) before the dialed digits.
3 The main office uses Coordinated Dialing Plan (CDP) or Vacant Number
Routing (VNR) to route the call to a virtual trunk.
4 A request is made to the NRS in order to determine the endpoint. The
NRS returns the branch office address as the endpoint.
5 The call is routed on the virtual trunk to the branch office.
6 The branch office treats the ALTPrefix as a steering code. The branch
office determines the Route List Index (RLI) and uses a Digit
Manipulation Index (DMI) to change the dialed number into a PSTN/
MCDN format number.
7 The call is routed over the PSTN/MCDN trunks to the telephone at the
main office or other branch office.
Call from main office telephone to branch office telephone
1 The interzone station-to-station call is attempted. There is insufficient
bandwidth available to make the call.
2 The main office inserts the ALTPrefix associated with the originator's
zone (the main office in this case) before the dialed digits.
3 The main office uses CDP and recognizes the ALTPrefix as a steering
code.
Main Office Configuration for Survivable Remote Gateway 50
Page 131 of 258
Configuration Guide