While Communication media means of sending or receiving information or data. A communication device is a hardware component that enables a computer to send transmit and receive data, instructions, and information to and from one or more computers or mobile devices. A widely used communication device is a modem. Communication occur over cables, telephone lines, cellular radio networks, satellites, and other transmission media.
Some transmission media , such as satellites and cellular radio networks, are wireless, which means they have no physical lines or wires. Communication media means of sending or receiving information or data. And in telecommunication, Communication media refers to the channel or tool or device through which data will be transmitted. More readily used now as costs declines. Some cellular phones offer facilities for browsing the internet and sending and receiving faxes and electronic mail.
The geographical area that is served by a transmitter is called a CELL. Unique frequencies are assigned to each cell. Each cell phone transmits and receives a signal.
When you place a call, the cell in which the caller is located detects the signal from your cell phone. The cell then assigns a specific frequency to that call and the call is transmitted to the receiving unit.
As you move away from the transmitter, the signal weakens. If the signal falls to a preset level, the computer recognizes that you have left the cell and scans the surrounding cells to determine the new area into which you have moved. The transmitter in the new cell takes over the call and a new frequency is assigned to your phone. This happens so quickly that you do not detect the transfer. If you move too far away from any network transmitter, the connection breaks. It is a worldwide collection of networks that links together millions of computers by means of modems, telephone lines and other communication devices and media.
It is used by more that million people. It can be accessed either through a file server or through an Internet service provider ISP or online service. A file server is a computer that is permanently connected to the Internet. An ISP is an organisation that supplies connections to the Internet for a monthly fee. An online service provides access to the Internet but also provides other services such as financial information, entertainment, hardware and software guides, news and weather, and direct messaging.
Fees for online service are usually higher than for an ISP. The internet enables users to send and receive mail electronically. It has also made Ecommerce possible. Discussions boards allow participants to type messages about a given topic. Responses are usually linked to each other to allow the reader to easily follow the discussion.
These functions include: and newsgroups They do not allow access via the internet and has security features to prevent unauthorised access. Extranet — an internal company network that has a connection to the public internet and allows users to gain access via the internet. It provides access to people in the organisation who are working away from the office. Web page — a file that is saved on the computer on the internet.
Web site — a collection of web pages. It is a group conference call in which all participants are able to speak with each other. Online meetings allow computer users to access the Internet to create a chat room in which they can exchange typed messages instantaneously. Video conferencing — allows users in distant locations to see each other. Networking: Computer Connections Chapter 7 Data Communications Send and receive information over communications lines. The Network System A network links components electronically.
Each component is a NODE. The word, modem, is derived from the combination of the words, modulate, to change into an analog signal, and demodulate, to convert an analog signal into a digital signal. One end of a standard telephone cord attaches to a port on the modem card and the other end plugs into a telephone outlet.
ISDN and DSL modems usually are external devices, in which one end connects to the telephone line and the other end connects to a port on the system unit. Cable Modems. A cable modem is a digital modem that sends and receives digital data over the cable television CATV network Figure With more than million homes wired for cable television, cable modems provide a faster Internet 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. Some mobile users have a wireless modem that uses the cell phone network to connect to the Internet wirelessly from a notebook computer, a smart phone, or other mobile device Figure Wireless modems, which have an external or built-in antenna, are available as PC Cards, ExpressCard modules, and flash cards.
Network Cards. A network card is an adapter card, PC Card, ExpressCard module, USB network adapter, or flash card that enables a computer or device that does not have networking capability to access a network. The network card coordinates the transmission and receipt of data, instructions, and information to and from the computer or device containing the network card.
Network cards are available in a variety of styles Figure A network card for a desktop computer is an adapter card that has a port to which a cable connects.
Network cards that provide wireless data transmission also are available. This type of card, sometimes called a wireless network card, often has an antenna.
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