TEXT 15. Working with Communications

Connecting computers allows computer communications. Two approaches are the most common for microcomputer users networking and telecommunications.

Telecommunications uses existing telephone lines and modems to send and receive data, making it possible for computers to share and exchange data with other computers almost anywhere in the world.

Telecommunications allows sending and receiving electronic mail (E-mail) and facsimiles (faxes), participating in bulletin boards, and accessing databases. On-line services provide one or more of these services to their subscribers, including access to stock and bond data, encyclopedic information, news, sports, and even airline schedules. Some of the more popular information services include: the Source, Dow Jones News Service, CompuServe, and Prodigy.

Data communication is either synchronous or asynchronous. Synchronous communication is faster, but it requires more expensive and specialized equipment and is therefore most commonly used in mainframe communications and networks. Asynchronous communication is slower but less expensive and easier to implement; it is the common choice for microcomputer telecommunications.

Telecommunications software controls the speed at which data are transferred (the baud rate, roughly equal to bits-per-second); whether the data II in one direction (half-duplex) or both (full-duplex); whether you see what type or only what the other computer sends you (echo); file transfer protocols (XMODEM, YMODEM, etc.) that help ensure error-free transmission; and emulation choices that make your computer act like a specific terminal attached to a mainframe computer.

Networking – the other major type of computer communications – involves physically connecting two or more computers with specifically designed cables. Computers can then share information from one central computer, and access the same printers, and users can send messages to one another. Networking makes it possible for one computer to house all the application software for all computers in an office.

A client-server network includes the host, or file server, and the workstation. The host computer is the central computer that maintains and controls access to the files and programs used by all other computers – the workstations – on the network. On peer-to-peer networks, however, all stations have the same status and share information directly; such networks are simpler and less secure than client-server networks.

Two types of networks are commonly used with microcomputers. A local area network connects computers within a limited physical area. Computers in a wide area network can be several to hundreds of miles apart.

Local area networks commonly use three types of topology. A bus network connects all workstations to the host with a single cable; data travels from one computer directly to another. In a star network (the most common), each workstation is connected to the host by a separate cable. A ring network connects all computers in a large loop, with data flowing around the loop from one computer to another.

Distributed processing is a decentralized approach to networking in which processing requirements are shared among several smaller computer systems, each with a different processing role.