大一计算机导论第九章.doc

Communications (242) The process of sharing data, programs, and information between two or more computers. Connectivity - using computer networks to link people and resources. The Wireless Revolution - the widespread use of mobile or wireless telephones. The single most dramatic change in connectivity and communications in the past five years Communications systems (243) - electronic systems that transmit data from one location to another Sending and receiving devices - originate (send) as well as accept (receive) messages in the form of data, information, and/or instructions Communication channel – transmission medium that carries the message. Connection devices - convert outgoing messages into packets that can travel across the communication channel and reverse the process for incoming messages. Data transmission specifications - rules and procedures that coordinate the sending and receiving devices Communications Channels (244) Actually carry the data from one computer to another Physical (wired) - a solid medium to connect sending and receiving devices. Twisted pair - hundreds of copper wires. Coaxial cable - a high-frequency transmission cable Fiber-optic cable - transmits data as pulses of light through tiny tubes of glass. Wireless (245) Infrared - uses infrared light waves to communicate over short distances (line-of-sight) Broadcast radio - uses special sending and receiving towers called transceivers, which send and receive radio signals from wireless devices Microwave - communication through high-frequency radio waves and provides line-of-sight communication but over short distances. Bluetooth is a form of microwave transmission Satellite - amplified microwaves that use point-to-point communication to relay devices (satellites) orbiting the earth. Communication interferences can occur in bad weather. Connection Devices (247) Modems - connection computers over analog phone lines. The convert the computer’s digital signal to an analog transmission t