Audio conferencing using Voice over IP (VoIP) works very similarly to a traditional conference call using analog telephones. In a conference call, callers connect to a conference bridge, a server that allows multiple people to talk to one another. VoIP audio conferences use the same principle -- callers connect to a conference bridge via their telephones or computers.

The main difference involves how the data moves from one point to another. Traditional telephones use circuit switching. For circuit-switched conferencing, the telephone system routes calls through a series of interconnected switches until it reaches the conference bridge. The conference bridge then connects multiple calls to one another. If all of the callers are located in the same office building, their calls connect to the bridge through the private branch exchange (PBX), which is a miniature phone network within the office. Either way, all the connections stay open as long as the call continues. Usually, only one person talks at a time, so only parts of the connection are actually in use at any given time.

VoIP networks do not use circuit switching. Instead, they use packet switching. While circuit switching keeps the connection open and constant, packet switching opens a brief connection -- just long enough to send a small chunk of data, called a packet, from one system to another. Instead of traveling from switch to switch, the data travels across the Internet, usually following the most efficient path.

Conference calling capabilities are often built into VoIP networks or available as a service upgrade. If a business uses a VoIP network for its telephones, calls from outside of the company can still typically connect the conference bridges. External lines may connect directly to the bridge server, or external calls may reach the server through the VoIP network.

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