Data Communication Systems

A typical data communication system includes sender and receiver devices, modems or routers, and a communication medium (channel). Before examining these components, you need to review some basic concepts in data communication.

Bandwidth is the amount of data that can be transferred from one point to another in a certain time period, usually one second. It is often expressed as bits per second (bps). Other measurements include kilobits per second (Kbps), megabits per second (Mbps), and gigabits per second (Gbps). Attenuation is the loss of power in a signal as it travels from the sending device to the receiving device.

Data transmission channels are generally divided into two types: broadband and narrowband. In broadband data transmission, multiple pieces of data are sent simultaneously to increase the transmission rate. As of January 2016, about 90 percent of all Americans had access to broadband communication. Narrowband is a voice-grade transmission channel capable of transmitting a maximum of 56,000 bps, so only a limited amount of information can be transferred in a specific period of time.

Before a communication link can be established between two devices, they must be synchronized, meaning that both devices must start and stop communicating at the same point. Synchronization is handled with protocols, rules that govern data communication, including error detection, message length, and transmission speed. Protocols also help ensure compatibility between different manufacturers’ devices.

A modem (short for “modulator-demodulator”) is a device that connects a user to the Internet. Not all Internet connections require a modem; for example, wireless users connect via access points, and satellite users use a satellite dish. However, dial-up, digital subscriber line (DSL), and cable access require modems to connect

A communication medium can be a point-to-point or a multipoint system. In a point-to-point system, only one device at a time uses the medium. In a multi-point system, several devices share the same medium, and a transmission from one device can be sent to all other devices sharing the link. The information box “Google Invests in Communication Media” highlights Google investment in communication media in particular satellite.