Panasonic KX-TDA50 Features Manual page 185

Example Network 5
Four PBXs connected to each other by four TIE lines.
Each PBX is connected to the public network via CO lines.
It is possible for any PBX extension to call an outside party by routing a call via TIE line to another PBX,
then to the public network.
Telephone
Company
Telephone
Company
4.
Identifying PBXs and their Extensions
When PBXs are connected to each other to form a private network, there must be some way to
distinguish the PBXs from each other so that calls can be sent to the intended destination of the desired
PBX. This can be done either by identifying each PBX specifically, or by making each extension number
in the private network unique. Each PBX on a private network must be programmed to use the same
method to identify itself, explained below.
a)
PBX Code Method (Access with PBX Code)
PBXs can be distinguished from each other on a private network by assigning a PBX code to
each one. These codes are used by the PBXs to determine how to route calls to other PBXs,
and also let a PBX know when it receives a call that it should handle itself. If a call does not
contain a PBX code, the call will not be handled correctly.
PBX codes also allow the same extension numbers to be used on different PBXs. (→ 1.25.1.2
PBX Code Method (Access with PBX Code))
b)
Extension Number Method (Access without PBX Code)
PBXs can also be distinguished by the extension numbers they use. With this method, the
extension number is all that is needed for a PBX to determine how to route calls to other PBXs;
no PBX code is necessary.
While this method allows extensions in other PBXs to be called easily—there are fewer
numbers to dial—the number of extension numbers which can be used throughout the private
network will be limited. (→ 1.25.1.3 Extension Number Method (Access without PBX Code))
Private Network
PBX-1
PBX-4
PBX-2
Telephone
Company
Telephone
Company
PBX-3
1.25 Networking Features
Feature Guide 185