What Is A Device That Enables A Computer To Transmit And Receive Data?

A communications device is any type of hardware capable of transmitting data, instructions, and information between a sending device and a receiving device. One type of communications device that connects a communications channel to a sending or receiving device such equally a com- puter is a modem. Computers process data as digital signals. Data, instructions, and information travel along a communications aqueduct in either analog or digital course, depending on the com- munications aqueduct. An analog signal consists of a continuous electrical wave. A digital signal consists of individual electrical pulses that correspond bits grouped together into bytes.

For communications channels that use digital signals (such equally cable television lines), the modem transfers the digital signals between the computer and the communications aqueduct. If a communications channel uses analog signals (such as some telephone lines), however, the modem first converts betwixt analog and digital signals.

The following pages describe the following types of communications devices: punch-up modems, ISDN and DSL modems, cable modems, wireless modems, network cards, wireless access points, and routers.

Dial-Upwardly Modems

As previously discussed, a computer'southward digital signals must be converted to analog signals before they are transmitted over standard telephone lines. The communications device that performs this conversion is a modem , sometimes called a dial-up modem. The word, modem, is derived from the combination of the words, attune, to change into an analog bespeak, and demodulate, to convert an analog point into a digital indicate.

A modem normally is in the course of an adapter carte that yous insert in an expansion slot on a com- puter'southward motherboard. One end of a standard telephone cord attaches to a port on the modem card and the other terminate plugs into a telephone outlet.

ISDN and DSL Modems

If you admission the Net using ISDN or DSL, you lot need a communications device to send and receive the digital ISDN or DSL signals. An ISDN modem sends digital information and data from a figurer to an ISDN line and receives digital data and information from an ISDN line. A DSL modem sends digital data and information from a computer to a DSL line and receives digital data and data from a DSL line. ISDN and DSL modems usually are external devices, in which ane finish connects to the telephone line and the other end connects to a port on the organization unit.

Cable Modems

A cable modem is a digital modem that sends and receives digital information over the cable television (CATV) network (Figure viii-18). With more than 110 million homes wired for cable television, cablevision modems provide a faster Net access alternative to dial-up for the home user and have speeds similar to DSL. Cable modems currently can transmit data at speeds that are much faster than either a dial-up modem or ISDN.

Wireless Modems

Some mobile users accept a wireless modem that uses the cell phone network to connect to the Internet wirelessly from a notebook computer, a smart telephone, or other mobile device (Figure 8-19). Wireless modems, which accept an external or congenital-in antenna, are available as PC Cards, ExpressCard modules, and wink cards.

Network Cards

A network card is an adapter card, PC Card, ExpressCard module, USB network adapter, or flash carte du jour that enables a reckoner or device that does not accept networking capability to access a network. The network card coordinates the manual and receipt of data, instructions, and information to and from the figurer or device containing the network card.

Network cards are available in a variety of styles (Effigy viii-xx). A network card for a desktop estimator is an adapter card that has a port to which a cable connects. A network card for mobile computers and devices is in the form of a PC Menu, ExpressCard module, USB network adapter, or a flash card. Network cards that provide wireless data transmission also are bachelor. This type of card, sometimes called a wireless network card, often has an antenna.

A network bill of fare follows the guidelines of a detail network communications standard, such as Ethernet or token ring. An Ethernet carte is the virtually common type of network card.

Wireless Access Points

A wireless access signal is a central communications device that allows com- puters and devices to transfer data wirelessly amid themselves or to transfer data wire- lessly to a wired network (Effigy 8-7 on page 303). Wireless admission points take high-quality antennas for optimal signals.

Routers

A router is a communications device that connects multiple computers or other routers together and transmits data to its correct desti- nation on the network. A router can be used on whatever size of network. On the largest scale, routers forth the Cyberspace backbone forward data packets to their destination using the fastest available path. For smaller business and abode networks, a router allows multiple computers to share a single high-speed Internet connectedness such every bit a cablevision modem or DSL modem (Figure viii-21). These routers connect from two to 250 computers.

To forestall unauthorized users from accessing files and computers, many routers are protected past a built-in firewall, called a hardware firewall. Some too have born antivirus protection. Today'south routers or combination wireless access point/routers are easy to configure and secure against unauthorized access.