VOIP (Voice over Internet Protocol) is a technology that transmits traditional telephone signals over a data IP network; these IP networks could be internet, wireless networks and local area network. In simple terms, you can make telephone calls via the internet instead of through your normal telephone lines.

How does VOIP work?

A traditional business environment typically operate on two networks; voice network (a network of telephone handsets located throughout the office(s)) and data network (a network of computers located throughout the office(s)). These two networks are separate and run in parallel with each other (refer to Figure 1)

Figure 1. Traditional Network (Click on picture for larger view)

VOIP merges the voice and data networks together; this is often referred to as convergence. Convergence can be achieved by one of two ways; using a VOIP gateway or replacing the telephone system with a VOIP telephone system.

Convergence with VOIP Gateway

A VOIP gateway brings convergence to the business networks by being physically connected to both the voice network and to the data network. The VOIP Gateway has a three way connection to the PABX, IP network (usually to a network data switch) and telephone line (these lines can be analogue, ISDN or E1 type connections). Refer to Figure 2.

Figure 2. Converged Network with Gateway (Click on picture for larger view)

All outbound phone calls are sent to the VOIP gateway and depending on the call type; the VOIP Gateway determines whether to send the calls to the internet or to the standard telephone line.

All inbound calls from either the internet or standard telephone line are sent to the VOIP Gateway and it determines whether to send the incoming call to the PABX, IP Phone or to another VOIP Gateway.

Using IP PBX

An IP PBX is a telephone system that communicates to both the standard telephone line and to the internet.

The IP PBX is connected directly to the same IP network (typically a data switch) where the computers and file servers are connected. The IP telephone handset is also connected to the same data switch; this means that all data and voice devices are join to one network. Refer to Figure 3.

Figure 3. Converged Network with IPPBX (Click on picture for larger view)

A phone call is initiated by the IP telephone handset or the computer (using a software phone), the call request is sent to the IP PBX where it determines where to direct the phone call. The calls could either be sent to the IP network (internet or private network) or to the standard telephone line.