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Paging and Intercom

On legacy phone systems you can find the following kinds of paging;
  • Dial a code to connect to a separate overhead paging and announcement system (like in an airport)
  • Dial a code and connect directly to a built-in one-way announcement speaker on one or more phones
  • Dial a code and connect directly to a built-in two-way announcement and talkback function on one or more phones
Some overhead paging systems also provide a talkback system so that the person being paged can just speak to respond. Background noise issues limit where this feature can be used. The talkback function is usually setup to be hands free. That means that the person responding to the page does not need to take any action other then speaking.

If a phone is in use when a page arrives, some systems can do a "whisper page" so that only the person being paged can hear the page.

SIP phones for the most part don't support any of these phone based paging functions. If a SIP phone offers an Auto Answer function, you can approximate limited paging intercom functionality. The phones most often mentioned supporting this are:
Intercom DOES work with the Snom 200 as the mailing list link above shows. Tested on 12/20/04 with firmware 2.04g on Snom 200. One change for that posting is that the variable called in the dialplan must read "_VXML_URL" instead of "VXML_URL".

Some analog phones have an Auto Answer function. These phone are often used in door phone systems.

For overhead paging, you can make an Asterisk Extension go to the sound card, and wire its output to a traditional external paging system. You can also get boxes to interface an phone FXO or FXS port directly to a sound system. Examles:
  • Viking CPA-7B Paging/Loud Ringing Amplifier
    • Has both FXS and FXO ports.
    • Can connect to a normal ATA FXS port in place of a phone
    • Example: Ethernet SIP ATA Viking CPA-7B Paging speakers
    • Other models available with multi-zone paging, etc.
  • Radio Design Labs ST-TC1 Telephone System Coupler
    • Also sold as: Smarthome Product
    • connects to an FXO port, so more suitable for interface with PBX or other phone system
  • Valcom V-2001A
    • connects to an FXO port, so more suitable for interface with PBX or other phone system

Another method for overhead paging is to solder a cable, with an RCA jack(or whatever you need), directly to the speaker of a phone that provides auto-answer. This cable can be connected directly to your amp or sound sytem used for paging. You can use the Grandstream Budgetone phone mentioned above, it even has a round punch-out that can be used to run your cable through.


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