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Voice over IP explained

IP telephony, also known as Voice-over IP (VoIP), is the transmission of telephone calls over a data network. While you have probably heard of VoIP, you may not fully understand what it is and you may be surprised to know that many businesses are already using it in the connections between their regional offices. Getting to grips with the issues relating to IP telephony can take a while, especially as voice technologies are traditionally dealt with independently of data networking. However, a comparison of traditional style and IP based solutions should help clarify the key points.

Traditional Telephony (Circuit Switching)

Using a traditional telephone system (PBX) a call between two parties is maintained using technology known as Time Division Multiplexing (TDM). As you are connecting two points in both directions for the duration of the call, the connection is called a circuit. If you talk for 10 minutes the circuit is continuously open between the two phones for this period of time. During a typical phone conversation, much of this transmitted data is wasted eg. while you are talking, the other party is listening. This means that only half of the connection is in use at any given time.

Data networks do not use circuit switching. Your Internet connection would be inadequately slow if it maintained a constant connection to a Web page you were viewing. The two computers involved in the connection would be passing data back and forth the whole time, whether it was useful or not, instead of sending and retrieving data as you required it. Rather than using circuit switching, data networks use a method called packet switching.

Voice over Internet Protocol (VoIP)

While circuit switching keeps the connection open and constant, packet switching opens the connection just long enough to send a small chunk of data, called a packet, from one system to another. The sending computer chops data into these small packets, with an address on each one telling the network where to send them. When the receiving computer gets the packets, it reassembles them into the original data. Packet switching is very efficient. It minimizes the time that a connection is maintained between two systems, which reduces the load on the network.

Benefits of VoIP

Several telephone calls occupy the same amount of space occupied by only one in a circuit-switched network
Only half the amount of cabling required
Home workers can be economically connected to main site
Cheaper inter-site communications

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