3Com NBX 100, Administrator'S Manual

Page: 101 / 496

Call Rerouting for Virtual Tie Lines 101
Call Rerouting for
Virtual Tie Lines
To enable the NBX system to better deal with network problems, you can
configure the system dial plan so that some virtual tie line (VTL) calls can
be rerouted if a VTL connection cannot be made.
VTL calls can be rerouted if:
■
The dial plan contains an invalid IP address
■
The remote NBX system is not responding
■
All VTL channels on the remote NBX system are currently busy
■
All IP addresses in the IP On-the-Fly address pool are in use
Some VTL calls are not rerouted. Example situations in which a call is not
rerouted include:
■
Placing a VTL call to another system with the intention of hopping off
(dialing a telephone number local to the other system) when all trunks
are busy on the other system
■
Dialing an invalid telephone number
If you normally connect calls from site A to site B using VTL connections,
you can define an alternate route to site B using Analog Line Card ports,
Digital Line Card channels, etc. If a network problem such as a router
failure occurs, or if all VTL ports on the site A NBX system are busy, VTL
calls that fail to reach site B are then dialed using the alternate route.
If your VTL call is rerouted, you see additional routing information in the
display panel on your NBX telephone.
The NBX system log file contains records of failed VTL calls that were
rerouted.
Example Dial Plan
Entries
If you normally dial a site code such as 72 to reach site B, and if the
telephones at the other site use four-digit extensions, the dial plan entries
to handle the initial call and the rerouting of the call might look like the
example shown in Figure 35.