Call Rerouting for Virtual Tie Lines 341Placing Telephone CallsThe final step to verify a virtual tie line connection is to place telephonecalls in both directions between each pair of connected sites.Call Rerouting forVirtual Tie LinesTo enable the system to better deal with network problems, you canconfigure the system dial plan so that some virtual tie line (VTL) calls canbe rerouted if a VTL connection cannot be made.VTL calls can be rerouted if:■ The dial plan contains an invalid IP address■ The remote system is not responding■ All VTL channels on the remote system are currently busy■ All IP addresses in the IP On-the-Fly address pool are in useSome VTL calls are not rerouted. Example situations in which a call is notrerouted 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 trunksare busy on the other system■ Dialing an invalid telephone numberIf 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 routerfailure occurs, or if all VTL ports on the site A system are busy, VTL callsthat fail to reach site B are then dialed using the alternate route.If your VTL call is rerouted, you see additional routing information in thedisplay panel on your telephone.The system log file contains records of failed VTL calls that were rerouted.Example Dial PlanEntriesIf you normally dial a site code such as 72 to reach site B, and if thetelephones at the other site use four-digit extensions, the dial plan entriesto manage the initial call and the rerouting of the call might look like theexample shown in Figure 25.
