Voice Vs. Data

The basic differences between voice and data networks — in other words, between standard telephone service and the Internet — are rooted in the nature of traditional voice communication technology. To understand how voice and data networks differ — and the issues involved in integrating them — you'll want to understand a few key distinctions:

• analog versus digital
• circuit-switched versus packet-switched
• dedicated versus connectionless

Standard voice networks use analog technology.

The standard telephone system uses analog technology to convey voice signals electronically between sender and receiver. Starting with a carrier wave — an alternating electromagnetic current at a given frequency — the system adds electromagnetic signals of varying frequency or amplitude, modulating the carrier wave in a pattern analogous to the fluctuations of the voice itself.

Analog information is characterised by such fluctuations and by the waves that carry them. Digital information, on the other hand, is binary, meaning that a unit of data has two possible states: positive or negative, 1 or 0, on or off. Thus, digital data is transmitted and stored as a series of ones and zeroes. A modem is simply a device used to convert a computer's digital information to analog signals for transmission over a phone line, and to convert the analog data it receives back to the digital format a computer requires.

Standard voice networks use circuit-switched, dedicated connections.

In a circuit-switched network, two end-points in the network establish and maintain a single connection over a specific physical path for the duration of the connection. Ordinary voice phone service is circuit-switched and uses a dedicated connection. The telephone company reserves a specific physical path to the number you are calling for the duration of your call. During that time, no one else can use the physical lines involved.

In a packet-switched network, by contrast, relatively small units of data called packets are routed through a network based on the destination address contained within each packet. Breaking communication down into packets allows the same data path to be shared among many users in the network. This type of communication between sender and receiver is known as connectionless. Most traffic over the Internet uses packet switching; the Internet is basically a connectionless network.

Some packet-switched networks, such as the X.25 network, enable virtual circuit-switching. A virtual circuit-switched connection is a dedicated logical connection that allows sharing of the physical path among multiple virtual circuit connections.