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Chapter 6 Configuration Basics
ISG50 User’s Guide
88
• FXS (Foreign Exchange Subscriber) Extension - This is an extension assigned to an analog
phone directly connected to an FXS port on the ISG50 (See Figure 62 on page 88). The FXS
ports on the ISG50 work the same way as the phone sockets in your home. In your home you
are a subscriber to the telephone services of your local telephone company and when you
connect an analog phone to the ISG50 you subscribe to the telephone services of the ISG50.
• Authority Group - This is a set of extensions. Each extension can only belong to one authority
group. Authority groups manage extensions by allowing them to make only certain types of calls.
For example, if you create two authority groups, you can allow one group to make local calls and
long distance calls and the second authority group to make local calls only.
• Outbound Line Group - This is a set of connections or lines going to the outside world.
• SIP Trunk - This is a connection to your ITSP (Internet Telephony Service Provider).
• ISDN BRI Trunk - This is a connection to your ISDN Service Provider.
• Trusted Peer - This is a connection to another IP PBX or SIP server. The trusted peer device
must also specify your ISG50 as a trusted peer.
• FXO (Foreign Exchange Office) Trunk - This type of outbound line group consists of
telephone cables connected to FXO ports on the ISG50. The telephone cables lead to the PSTN
(Public Switched Telephone Network), or in other words your traditional (non-VoIP) telephone
company. FXO ports always point in the direction of the telephone services.
The figure below shows the relationship between FXS and FXO ports.
Figure 62 FXS and FXO Ports
• LCR (Least Cost Routing) - This is a rule which specifies which outbound line group is used
when making an outbound call. It consists of a dialing condition, for example dial 0 to make a call
via a specific FXO trunk or dial 1 for calls via a SIP trunk. LCRs also set priority to which
outbound line group should be tried first, second, third and so on when making outbound calls
with the same dialing condition.
FXO
FXO
FXS
FXS
PSTN
ISG