Specifications

Reference Guide
2-31
Applications ISDN Primary Rate Interface (PRI) Server
Figure 2-19. Bi-Directional Default Routing
2.6.7.4 Alternate routing
Alternate routing is provided for calls to take an alternate path in the event of a congested or
failed primary trunk. When there are more than two Primary Rate D channels, phone numbers
can be assigned to more than one D channel. Calls placed or routed through the PRI server
will now have an alternate route if no bandwidth is available on the first specified path.
Alternate routing will also take place in the event of a failure of the first Primary Rate circuit.
In the example shown in Figure 2-20, the call from D1 is usually routed to D2, as the D
channel numbering is more specific. However, should the D2 trunk become congested or go
out of service, the call will be routed to D3.
Figure 2-20. Alternate Routing
D ch 1
D ch 2
HSU/FXS
Default
IAD
PBX
ISDN
Switch
Dial 415 - 6xxx
415-6xxx
415-xxxx
D1
D2
D3
IAD
PBX
ISDN
Switch
ISDN
Switch