3com SuperStack 3 NBX Manual De Usuario

C

HAPTER

 2: D

IAL

 P

LAN

The final step when verifying a virtual tie line connection is to place 
telephone calls in both directions between each pair of connected sites.

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.

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 

.