What is Voice over Internet Protocol?

Voice over Internet Protocol

Before we begin our discussion on transporting voice over a data networks, it is important to understand the concept and terms associated with a traditional telephone network. One of the most common piece of telecommunication equipment used today is the telephone. When you plug an ordinary analog telephone into the wall jack installed by the local telephone company, you are connected to the telephone network and are able to place calls. 1), but how is this process performed?

In early telephone networks, call completion was dependent on an operator to complete the calls. When you wanted to place a call you would pick up the receiver and be connected to an operator at the Central Office (CO). The CO is the local telephone office which all local lines connect too and where circuit switching of subscriber lines occurs. The operator would determine which two lines need to be connected for the parties to talk and connect the lines. To connect the two lines the operator would plug a cord connecting the two ports on a cord board to bridge the two ports together. The cord board used by the operator to connect the two parties was the first example of an early switching system.

In today’s telephone networks a CO switch or a private branch exchange (PBX) provides the same service once performed by an operator. A PBX is a premise switching system, serving a commercial or government organization, and usually located on that organization's premise. PBX’s provide telecommunication services at the location and access to public and private telecommunications network services. The PBX switch is connected to a similar switch located at the CO.

Now we will discuss some of the key components of any telephone network. These components are loops, lines and trunks. “Loop transmission facilities connect switching systems to customer premises equipment throughout the serving area. A loop is a transmission path between a customer's premises and a local exchange carrier (LEC) central office” (Loop Transmission). A line is a communication connection between your telephone and the local phone company’s switch, such as a PBX or a CO switch. No that we know that a line connects a telephone to the switch, the next stage is the trunk. A trunk is a shared communication channel that connects multiple telephone switches together and has the ability to transfer a telephone call from one location to the next.