GRAP 3175 Computer Applications for Drafting Unit VI Data Communication

1. GRAP 3175Computer Applications for DraftingUnit VIData 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. Networks0verview • When data-communication channels link several computers and other devices • Each computer usually has its own processing capabilities • WAN, MAN, LAN, & TAN

27. Network TopologiesOverview • 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 NetworkWAN • Two or more computers that are geographically dispersed but are linked by common communication carriers • NSFnet, INTERnet, BITnet • Compuserve, AOL, etc.

33. WANMethods 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 NetworksLAN • 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