1. GRAP 3175 Computer Applications for Drafting Unit VI Data Communication

2. Data Communication Overview The process of sending data electronically from one point to another. Linking one computer to another. Direct-cable link or telecommunication (telephone / microwave)

3. The effects of Data Communication Our link to the world Necessary for CAD labs

4. Data Transmission Two forms of data transmission –Analog –Digital

5. Analog Data Transmission The transmission of data in a continuous wave form Telephone system

6. Digital Data Transmission The transmission of data using distinct on and off electrical states Computers Digital is faster and more efficient than analog communication Using the existing telephone systems to send digital transmission by modulation- demodulation

7. Modulation, Demodulation, and Modems Modulation -- process of converting a digital signal to analog Demodulation -- process of converting analog signal back to digital Modem -- modulation-demodulation

9. Three Types of Modems Acoustic modem (acoustic coupler) –Uses the telephone headset –Not used anymore

10. Three Types of Modems External direct-connect modem –External to the computer and connects directly to the telephone –Less distorted and faster data transfer –Hayes Smartmodem - the standard (Hayes compatible) –Connects to a serial interface on the computer –Allows phone to use line when modem is not connected

11. Three Types of Modems Internal direct-connect modem –Board that fits into an empty slot –Convenient PCMCA Cards -- used in notebooks

13. Communication Channels Overview -- the medium, or pathway, through which data are transmitted between devices. Three basic types: –Wire cable –Microwave –Fiber optics

14. Wire Cable Twisted-pair –POTS -- Analog, up to 56k bps –ISDN -- Digital, up to 128k bps –ADSL -- Digital, up to 1.5 to 9M bps –Disadvantages -- analog, electrical interferences Coaxial -- Digital, up to 10M bps –Minimal interference

15. Fiber Optics Digital -- light impulses through clear flexible tubing 2.5 Billion bps Very high speeds and very reliable Optic backbone

16. Microwave or Radio Signals Signals transmitted through the atmosphere Line-of-sight -- Straight lines between transmitter towers and/or satellite 48M bps Reliable Expensive

18. Wireless Transceiver Between computers Between buildings

19. Channel Configurations Point-to-point -- computer or terminal is connected directly to another device Multipoint -- three or more devices are connected to one line.

20. Rate of Data Transmission Baud rate -- the number of times per second that a signal being transmitted changes. Often thought of as bits per second. Sometimes a signal carries more than one bit Modems speeds -- 300, 1200, 2400, 9600, 14.4, 28.8, 33.6, and 56k bps Direct connections between computer and output devices -- 9600+

21. Communication Channel Bandwidths Bandwith -- determines the rate or speed that data can be transmitted Three bandwiths: –Narrow-band -- 40 bps to 100 bps –Voice-band (POTS) -- 110 bps to 56k bps –Broad-band -- up to several million bps 57KB - 622M, T1, T3

23. Asynchronous & Synchronous Transmissions Asynchronous -- method that sends one character at a time Synchronous -- block of characters are transmitted at a time Protocol -- traffic rules and procedures. Must be the same on each end of the transmission.

24. Modes of Transmission Simplex -- data transmitted in only one direction. (Burglar alarm) Half-duplex -- allows a device to send and receive data, but not at the same time Full-duplex -- allows a device to receive and send data simultaneously.

25. Networks

26. Networks 0verview When data-communication channels link several computers and other devices Each computer usually has its own processing capabilities WAN, MAN, LAN, & TAN

27. Network Topologies Overview Each computer is called a node The arrangement is called the topology Star, Ring, Tree, Bus

28. Star Topology Several devices connected to one centralized computer

29. Ring Topology Consists of several devices connected to each other in a closed loop IBM Token-ring

30. Tree Topology Links computers in a hierarchical fashion and requires data to flow through branches

31. Bus Topology Each computer is connected to a single communication cable via an interface Every computer can communicate directly other computers or devices on the network

32. Wide Area Network WAN Two or more computers that are geographically dispersed but are linked by common communication carriers NSFnet, INTERnet, BITnet Compuserve, AOL, etc.

33. WAN Methods to Move Data Circuit switching -- dedicated link. Real- time communication can take place. TELNET Message switching -- messages usually temporarily stored & then relayed to next node

34. Methods to Move Data Packet switching -- one of the most complicated methods. Messages (data) are divided into standard size packets or blocks. Used for large data transmission. FTP WWW -- world wide web, hypertext, links

35. Local Area Networks LAN Two or more computers directly linked within a small area: room, building, cluster of buildings Stand-alone computers Gateway -- LANs to LANs or LANs to WANs Bridge -- connects rings or zones

36. LAN Components Two or more computers Server(s) Peripheral devices Cabling Interface card LAN software

37. LAN Servers Computer shared by network Types: file, print, communications LAN operating system Security

38. LAN Access Methods Token (Ring) –A token (string of bits) passed around network Ethernet (Bus) –Carrier Sense Multiple Access/Collision Detection (CMSA/CD) –Device listens for clear channel

39. LAN Advantages Ability to share hardware, software, and data files Electronic mail Different computer architectures Internet/Intranet access

40. LAN Disadvantages Training Cost Security