3Com NBX 100 Administrator's Manual - page 85
Overview of Virtual Tie Lines
85
3 In the Primary DNS, Secondary DNS, and Tertiary DNS text boxes, type the
IP addresses of three Domain Name Servers. If you have the IP address of
only one server, type it in the Primary DNS text box. If you have the IP
address of only two servers, type them in the Primary and Secondary DNS
text boxes. Click OK.
Overview of
Virtual Tie Lines
A Virtual Tie Line (VTL) provides a way to make calls between NBX system
sites that are separated geographically but tied together by a Wide Area
Network (WAN). VTLs are a licensed feature of the NBX systems.
■
NBX V3000 — support for 48 simultaneous VTL connections
■
SuperStack 3 NBX — support for 48 simultaneous VTL connections
■
NBX 100 — support for 8 simultaneous VTL connections
On any NBX system, a VTL connection can be used either for an incoming
VTL call from any site or for an outgoing VTL call to any site. A VTL
connection is not dedicated in the same way as a physical tie line, which
always connects the same pair of sites. In the example in
Figure 10
, the
VTLs on the Chicago NBX system can be used for any combination of
incoming and outgoing VTL calls to either Atlanta or Dallas.
The NBX system can reroute VTL calls that fail to reach their destination
on the first attempt. For details, see
“Call Rerouting for Virtual Tie Lines”
on
page 99
.
■
You must configure the system for either IP On-the-Fly or Standard IP
in order to use VTL connections to other NBX systems.
■
VTL connections cannot be configured to run through firewalls or NAT
routers.
■
When you calculate the number of devices on an NBX system, do not
include the number of VTLs.
There are two implementation techniques you can use: unique extension
ranges, as described next, or site codes, which begins on
page 86
.
VTL Connections
Using Unique
Extension Ranges
If you can restrict the extension ranges on each of the NBX systems so
that they do not overlap, you can configure the dial plans to route calls
based only on the extension that is being dialed. The caller does not have
to dial any digits to specify the site.