Intercom

Digital intercom stations can be connected using Cat 5 cable and can even use existing computer networks as a means of interfacing distant parties.

Performing arts venues such as theaters and concert halls often have a combination of permanently mounted and portable intercom elements.

Multiple channels of simultaneous conversations can be carried over additional conductors within a cable or by frequency- or time-division multiplexing in the analogue domain.

Portable intercoms are connected primarily using common shielded, twisted pair microphone cabling terminated with 3-pin XLR connectors.

Digital intercoms use Category 5 cable and relay information back and forth in data packets using the Internet protocol suite.

Intercom systems are widely used in TV stations and outside broadcast vehicles such as those seen at sporting events or entertainment venues.

There are essentially two different types of intercoms used in the television world: two-wire party line or four-wire matrix systems.

This type of format allowed the two channels to operate in standard microphone cable, a feature highly desired by the broadcasters.

This reconfiguration was usually handled at a central location, but because voltage is used on the circuit to power the external user stations as well as communicate, there would usually be a pop when the channels were switched.

So while one could change the system on-the-fly, it was usually not desirable to do so in the middle of a production, as the popping noise would distract the rest of the television crew.

There may be concerns about privacy since conversations may be picked up on a scanner, baby monitor, cordless phone, or a similar device on the same frequency.

Power line communication units that send signal over house wiring have been referred to as "wireless" intercoms.

Some telephones include intercom functions that enable paging and conversation between instruments of similar make and model.

A single device can add intercom functionality to multiple standard telephones on a common phone line, even of different makes and models.

This standard is now used globally, though in the United States, primarily AT&T, T-Mobile, and a few other providers use GSM, while Sprint and Verizon used CDMA (Code Division Multiple Access) technology.