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Communications Technology

Communications Technology. Chapter 7 Starting Along the Information Superhighway. © The McGraw-Hill Companies, Inc., 2000. Overview. Technology basics Channels Factors among devices Communication networks Local networks Networking options. Computers to Communicate: Technological Basics.

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Communications Technology

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  1. Communications Technology Chapter 7 Starting Along the Information Superhighway © The McGraw-Hill Companies, Inc., 2000

  2. Overview • Technology basics • Channels • Factors among devices • Communication networks • Local networks • Networking options © The McGraw-Hill Companies, Inc., 2000

  3. Computers to Communicate: Technological Basics • Communications or telecommunications • transfer of data from a transmitter or source to a receiver or sink • may have intermediate devices to set up a path or maintain adequate signal strength © The McGraw-Hill Companies, Inc., 2000

  4. Analog Signals • Analog • called a carrier wave • frequency • amplitude • telephones, radios, televisions • digital telephones and television broadcasts are increasing © The McGraw-Hill Companies, Inc., 2000

  5. Digital Signals • Uses on/off or present/absent electrical or optical pulses in discontinuous or discrete bursts © The McGraw-Hill Companies, Inc., 2000

  6. Modem • Analog modem • modulator/demodulator • analog modems convert digital signals into an analog form for telephone lines • does not actually change digital signals • rather changes form of the wave to represent 1s and 0s © The McGraw-Hill Companies, Inc., 2000

  7. Modem • Digital modems • cable • ASDL • DSL • G. Lite • ISDN © The McGraw-Hill Companies, Inc., 2000

  8. Internal Modems • Internal • separate • ISA or PCI © The McGraw-Hill Companies, Inc., 2000

  9. External Modems • External • does not occupy additional IRQ • generally has volume control • shows communication lights • easily moved to a new computer © The McGraw-Hill Companies, Inc., 2000

  10. Additionally • PCMCIA cards for laptops • some even have combo modem and network cards, so that workers who have to use the network in the office and yet have access while out of town on business may do so © The McGraw-Hill Companies, Inc., 2000

  11. Transmission Speeds • Faster transmission speeds mean faster downloads of graphics, video, sound, and data or program files • Expressed in bits per second (bps) • Speeds obtained can be affected by • line quality, distance from communications center, line traffic, modem speed at the ISP © The McGraw-Hill Companies, Inc., 2000

  12. v.90 standard • By the middle of 2000, most ISPs will have their modem racks filled with the 56K v.90 standard • Slower modems can still communicate, but at a speed slower than v.90 © The McGraw-Hill Companies, Inc., 2000

  13. Communications Software • Often incorporated into an operating system • Establishes communication • Error correction • Data compression • Remote control of another system • Terminal emulation © The McGraw-Hill Companies, Inc., 2000

  14. ISDN • Integrated Services Digital Network • Uses POT (plan old telephone system) • Capable of transmitting five times faster than conventional modems • Need special ISDN connection box or adapter card © The McGraw-Hill Companies, Inc., 2000

  15. ASDL • Asymmetric Digital Subscriber Line • Often good return on costs compare to ISDN in the United States • Runs on POTS © The McGraw-Hill Companies, Inc., 2000

  16. Cable Modems • Up to 1000 times faster than POTS • Two-way transmission • Shared cable line with community • Security questions • Can get bogged down, if many subscribers in the same building or neighborhood, for instance © The McGraw-Hill Companies, Inc., 2000

  17. Dishes • 15 times faster than standard cable • Upload currently through ISP phone modem • With more low-level satellites, there is the potential to directly upload © The McGraw-Hill Companies, Inc., 2000

  18. Channels • Twisted-pair • Coaxial cable • Fiber-optic cable • Microwave systems • Satellite systems • Other wireless systems © The McGraw-Hill Companies, Inc., 2000

  19. Twisted-Pair • Copper wire • Most telephone connections • UTP • unshielded twisted pair • STP • shielded twisted pair • Most common connection worldwide • 16 to 100 Mbps © The McGraw-Hill Companies, Inc., 2000

  20. Coaxial Cable • “Co-ax” • Insulation resists noise, or electronic interference • Up to 200 Mbps • Often many or bundled together © The McGraw-Hill Companies, Inc., 2000

  21. Fiber-Optic • Strands of glass transmitting light farther and with fewer errors • No effected by electromagnetic interference • Addition of plastic fiber allows the last 100 feet to install for curb-to-home wiring • 1 trillion bps per fiber • Being laid worldwide © The McGraw-Hill Companies, Inc., 2000

  22. Microwave • Voice and data as high-frequency radio waves • Line-of-sight • More than half of telephones system use microwave © The McGraw-Hill Companies, Inc., 2000

  23. Satellite • Computer communications satellites are microwave relay stations • Normal orbit 22,300 miles above earth • geo-stationary orbit (GEO) • Medium-earth orbits • 5,000 to 10,000 require less power to transmit • Low-earth orbits • 400 to 800 miles up © The McGraw-Hill Companies, Inc., 2000

  24. Other Wireless • Two-way radio • Mobile telephones • Global Positioning system • GPS • high accuracy to a few feet • Local Position Systems (LPS) • uses radio frequency for tracking © The McGraw-Hill Companies, Inc., 2000

  25. More Communications • Pagers • “beepers” • radio receivers • becoming two-way with voice or prerecorded messages • Analog cellular phones • 824 to 894 MHz using ground-area cells • direct calls through Mobile Telephone Switching Office © The McGraw-Hill Companies, Inc., 2000

  26. Other Phones and Radios • Digital cellular phones • higher promise of more accurate transmission • not universal standard • World Trade Organization (WTO) • hoping to standardize telecommunications systems • Packet radio • useful for mobile workers who need to communicate frequently with a corporate database © The McGraw-Hill Companies, Inc., 2000

  27. Factors Affecting Channel Speed • Transmission rate • Line configurations • Serial vs. parallel transmission • Simplex, half-duplex, full-duplex • Asynchronous vs. synchronous • Packet switching • Multiplexing • Protocols © The McGraw-Hill Companies, Inc., 2000

  28. Frequency • Frequency • amount of data that can be transmitted on a channel depends on the wave frequency • the cycles of waves per second in hertz • 400 hertz twisted-pair may send 1 kilobyte of data a second • 100 megahertz coax may send 10 megabytes • 200 trillion hertz fiber-optic may send 1 gigabyte © The McGraw-Hill Companies, Inc., 2000

  29. Bandwidth • The difference between the highest and lowest frequencies transmitted • There maybe several frequencies within a bandwidth • Rate of speed expressed in bits per second (bps), kilobits per second (Kbps), megabits per second (Mbps) © The McGraw-Hill Companies, Inc., 2000

  30. Point-to-Point • Point-to-point line directly connects the sending and receiving devices • terminal to central computer • private (leased) line use • T1 lines can carry 24 signals on a single set of copper wires © The McGraw-Hill Companies, Inc., 2000

  31. Multipoint • A multipoint line is a single line that connects several communications devices to one computer • often only one communications device, but can transmit at any time © The McGraw-Hill Companies, Inc., 2000

  32. Serial and Parallel Transmission • In serial transmission, bits are transmitted sequentially • twisted-pair • communications lines, modems, many mice • In parallel transmission, bits are transmitted through separate lines simultaneously • faster than serial, but not as efficient after 15 feet • printer and some scanners © The McGraw-Hill Companies, Inc., 2000

  33. Asynchronous vs. Synchronous • Asynchronous • sent one byte or character in a line • sent whenever its is convenient for the sender • Synchronous • sync bytes transmitted at start and stop of blocks of data • best for large amounts of data on large systems © The McGraw-Hill Companies, Inc., 2000

  34. Packet Switching • Maximum-fixed-length block of data for transmission • Contains instructions about destination • Packets arrive at destination, reassembled • Used in large networks © The McGraw-Hill Companies, Inc., 2000

  35. Circuit Switching • Transmitter has full use of the circuit until all the data has been transmitted • Used by telephone company for voice network © The McGraw-Hill Companies, Inc., 2000

  36. Asynchronous Transfer Mode • ATM • Combines efficiency of packet switching with some of circuit switching features • Handles both data and real-time voice and video • Designed to operate on fiber-optic cables © The McGraw-Hill Companies, Inc., 2000

  37. Multiplexing • Transmission of multiple signals over a signal communications channel • Multiplexer • merges several low-speed transmissions into one high-speed transmission • Concentrator • similar to multiplexer, but collects data in a temporary storage area, then sends to a receiving computer © The McGraw-Hill Companies, Inc., 2000

  38. Multiplexing • Front-end processors • a smaller computer for mainframes and midframes assists in communication functions • corrects errors and relieves larger computer of routing computational tasks • Sometimes used synonymously with communications controller • but this is usually less sophisticated • in LAN, an adapter does this task © The McGraw-Hill Companies, Inc., 2000

  39. Protocols • Rules of data transmission • A set of conventions governing the exchanging of data between hardware and/or software • OSI, Open Systems Interconnection, provides a seven-layer look at software responsibilities • hope for more universal usage © The McGraw-Hill Companies, Inc., 2000

  40. Communications Network • A system of interconnected computers, telephones, and other communications devices that can communicate and share data and applications • Run through a NOS or Network Operating System • NetWare • Windows NT © The McGraw-Hill Companies, Inc., 2000

  41. NOS • May require operating system to function © The McGraw-Hill Companies, Inc., 2000

  42. Hosts and Nodes • Host computer • main computer in a system using communications link • Node • device attached to a network © The McGraw-Hill Companies, Inc., 2000

  43. Advantages of Networks • Sharing of peripheral devices • Sharing of programs and data • Better communications • Security of information • Access to databases © The McGraw-Hill Companies, Inc., 2000

  44. Local Area Network • Private branch exchange (PBX) • private or leased switching system connecting to outside telephone systems • Newer PBXs can handle not only analog telephones but also digital equipment • Local Area Network (LAN) • “lans” usually require installation of own communications channels © The McGraw-Hill Companies, Inc., 2000

  45. Types of LANs • Client-server • microcomputer clients using devices that provide a service, called servers • Microcomputers connection to AOL © The McGraw-Hill Companies, Inc., 2000

  46. LAN • File server • Print server • Application server • Database server © The McGraw-Hill Companies, Inc., 2000

  47. Peer-to-Peer • No reliance on server • Can be less expensive than client-server • Backups and recovery more difficult • Systems slow down under heavy use • Can be a mix of peer-to-peer and client-server © The McGraw-Hill Companies, Inc., 2000

  48. Components • Connection or cabling system • Microcomputer or workstations with network interface cards (NICs) • Network operating system • Other shared devices • printers, fax machines, scanners, storage devices © The McGraw-Hill Companies, Inc., 2000

  49. Bridges, Routers, Gateways • Bridge is interface to same type of network • protocol independent • Router is intelligent device supporting like and unlike LANs, and LANs and WANs • protocol reading • Gateway performs all functions of bridges and routers, including protocol conversion • slowest of three © The McGraw-Hill Companies, Inc., 2000

  50. Topology of LANs • Star • central hub • Ring • continuous loop • Bus • on a network backbone using coax, STP, or UTP • Hybrid • combination © The McGraw-Hill Companies, Inc., 2000

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