1. Chapter 7 Networking: Computer Connections

2. 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

3. Data Transmission Methods n digital signal - data is sent as distinct pulses (on or off) (0 or 1) n analog signal - data is sent as a continuous electrical signal in the form of a wave n most in place communications media are analog –phone lines, coaxial cable, microwave circuits n 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

4. 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

5. More alternatives n Cable modems –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 n Cellular modems –convenient for mobile users

6. Asynchronous and Synchronous Transmission n Methods for keeping sending and receiving systems “on the same page” n 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

7. 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

8. Protocols n protocol - a set of rules for the exchange of data n 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

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

10. 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

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

12. 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

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