Chapter 7 Networking Computer Connections Networks n Network

Chapter 7 Networking: Computer Connections

Networks n Network - a computer system that uses communications equipment to connect two or more computers and their resources – share hardware, software, and data n Local Area Network (LAN) - a computer network that spans a relatively small geographic area – often connects users in an office or building n Wide Area Network (WAN) - a computer network that spans a large geographic area

Data Transmission Methods n n digital signal - data is sent as distinct pulses (on or off) (0 or 1) analog signal - data is sent as a continuous electrical signal in the form of a wave most in place communications media are analog – phone lines, coaxial cable, microwave circuits modem - device to convert digital signals to analog (modulation) and analog signals to digital (demodulation) – may be internal or external – transmission rates of 56, 000 bps

Alternatives to modems n ISDN - Integrated Services Digital Network – transmission rates of 128, 000 bps – requires an adapter and phone service, possibly a new phone line n DSL - Digital Subscriber Line – even slower services several times faster than standard modems – uses modulation/demodulation, but acts like many modems working simultaneously

More alternatives n Cable modems – – – n uses coaxial television cables speeds up to 10 million bps always “on”, does not require dialing users share capacity, decreasing performance security can be an issue Cellular modems – convenient for mobile users

Asynchronous and Synchronous Transmission n n Methods for keeping sending and receiving systems “on the same page” asynchronous - start signal is sent, then a character, then a stop signal – receiving system sets up a timing mechanism when start signal is received – slow transmission rates n synchronous - sending and receiving systems are synchronized by a bit pattern at the beginning of the message – large blocks transmitted – more complex and expensive, faster

Communications Media n communications medium - physical means of data transmission – most networks use a combination of media • twisted pair wire - traditional telephone lines • coaxial cable - cable television lines • fiber-optic cable - bundles of fine glass or plastic fibers, guide light beams, very high transmission speeds • microwave transmission - line-of-sight transmission from station to station, susceptible to weather conditions • satellite transmission - microwave transmission using satellite as relay station n bandwidth - measure of the capacity of the link

Protocols n n protocol - a set of rules for the exchange of data communicating systems must agree on – transmission method, speed, duplex setting, etc. n TCP/IP - Transmission Control Protocol/Internet Protocol - standard set of rules for Internet communication

Topology n n topology - physical layout of a network node - any physical device in the network star bus ring

Wide Area Networks n communications services provided by common carriers – dedicated service permanently connects 2 or more locations (may be leased) – switched (dial-up) service provides a temporary connection n WAN hardware and software – host - mainframe to control network – multiplexer - combines transmissions from many sources into a single stream, decomposes stream when received – terminal emulation software - allows a mainframe to view PC as a terminal

Local Area Networks n n n components connected by some type of network cable each computer has a network interface card bridge - hardware/software that connects similar networks gateway - hardware/software that connects dissimilar networks (protocol conversion) router - computer that directs communications traffic, selects best path – strategy used in e-mail transmission

Types of LAN’s n client/server – server - computer that controls the network – client - other computers that request service from the server n peer-to-peer – all computers have equal status – users share resources – may be slow with heavy use

Uses and Advantages of Networking n n n n electronic mail fax technology groupware - sharing software teleconferencing - bring people together despite geographical differences telecommuting - working from home via computer electronic data interchange (EDI) - electronic transfer of “paperwork” sharing of hardware resources