Overhead paging is a concept which is very popular with Analog / Digital Telephony systems. One could just dial an extension from an analog/ digital phone and speak over the handset to make an announcement over a group of overhead speakers. There are paging controllers that interface with EPABX systems to provide zoning control of paging speakers (dividing all the speakers in to various groups – based on the floor, for example and sending messages over a particular group). It is very much possible to provide the same functionality with IP PBX/ IP Telephony systems.
Most of the IP Phones/ SIP Phones have built-in speakers. These speakers can be configured as a paging group and they can be simultaneously accessed by an operator (for example) to make an announcement. Once an operator dials the paging extension meant for this group, all the speaker phones in the group go off-hook and their speakers are automatically enabled. So, what ever is announced by the operator can be heard in the entire area around these speaker phones. Multiple such speaker phones in a paging group can make a building announcement system.
One advantage of using IP Phone speakers as paging speakers is the fact that the person to whom the page was messaged (announcement was made) can dial a code from any IP phone he is near to, and talk-back to the operator. This can also be done with certain systems other than IP Phones, but it is easier to implement talk-back with IP Phones provided that the IP PBX/ IP Telephony software supports this feature.
If IP Phones support multicasting , network bandwidth can be saved as single stream of the voice message can be sent to multiple phones simultaneously, without requiring to send one voice stream for each IP phone.
Certain IP Telephony / VOIP Systems support Auto-answer functionality. This is like paging, but the message goes to a single extension which is configured for auto-answer. So, the phone goes off-hook automatically after certain rings and the operator/anyone else can speak over the loud-speakers. This is used as a mini-paging system in elevators, etc.
Some IP Phones have a 3.5 mm headset jack/ audio out port that can be directly connected to speakers/ amplifiers. These can be used to create a loudspeaker based paging system using IP Telephony system/ IP Phones.
It is possible to interface analog paging systems (both speakers and paging controllers) to IP Telephony/ VOIP system in order to use the existing paging infrastructure with IP Phones. It may require an external adapter (like an FXS device that converts IP voice into analog voice) for this operation.
The best part about IP Telephony / VOIP Paging systems – There are (SIP based) Speakers and Paging Controllers that can now connect directly to an IP Network (See products from the following vendors: Valcom & Cyberdata).
So, one can use a POE switch to connect directly to a SIP based Overhead paging speaker/ Amplifier using Cat6 network cables (without having to connect a power source) and control it from an IP PBX (for example). There are Wi-Fi based Overhead paging speakers that are available in the market which can be connected to a wireless network, but power line might be required to be connected directly to these systems.
There are SIP based Paging controllers that connect to the network and can provide multi-zone paging operations for these SIP based overhead speakers. The only downside is, they are a bit on the expensive side right now. But as with other IP based systems, we can expect the cost to come down rapidly with mass adoption.
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