Business Data Communications, Fourth Edition Chapter 3: Communications Media, Servers, and Clients

Learning Objectives Describe the difference between guided media and unguided media Define twisted pair wire, coaxial cable, and fiber optic cable Describe how different types of cables are used in networks List five forms of transmission that use unguided media Describe the difference between microwave and broadcast radio Chapter 5: Communications Media, Servers, and Clients2

Learning Objectives Identify the advantages of one medium over another in terms of cost, speed, and data reliability Describe the use of various types of computers in a communications system Explain the differences among servers and various types of clients Describe the line configurations used to connect terminals in a network Chapter 5: Communications Media, Servers, and Clients3

Learning Objectives Explain how computers and modems communicate using RS-232 connectors List applications of the RS-449, Universal Serial Bus, and FireWire standards Chapter 5: Communications Media, Servers, and Clients4

Introduction Devices on a network are connected using a medium Physical wire – guided medium Wireless – unguided medium Cost and performance differ among the types of media Chapter 5: Communications Media, Servers, and Clients5

Guided Media Twisted Pair Wire –Insulated copper wire, twisted to prevent interference –Unshielded twisted pair (UTP) No extra insulation Prone to interference Used for residential telephones –Shielded twisted pair (STP) Each pair of wires is in a metallic shield Good insulation qualities –UTP Categories 1 through 6 Chapter 5: Communications Media, Servers, and Clients6

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Guided Media Coaxial Cable (Coax) –Better insulation than UTP or STP –Broadband Many channels on one physical cable Cable TV –Baseband One channel (or signal) on one cable Used in computer networks Chapter 5: Communications Media, Servers, and Clients8

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Guided Media Fiber Optic Cable –Construction of fiber Very pure glass or plastic Outer sheathing to bundle the fibers –How data is transmitted Uses a light source Light-emitting diode (LED) Laser Chapter 5: Communications Media, Servers, and Clients11

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Guided Media Fiber Optic Cable –Multimode step index Light bounces off the walls of the sheathing –Multimode graded index Cable core varies in density, light bent at more shallow angles –Single-mode cable Light travels in a straight line, due to very thin core Chapter 5: Communications Media, Servers, and Clients13

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Guided Media Fiber Optic Cable –Problems with transmission of light Attenuation – loss of signal Dispersion – spreading of signal –Interference Better protection than copper wires No crosstalk occurs Chapter 5: Communications Media, Servers, and Clients15

Unguided Media Wireless media Broadcast radio –Omnidirectional transmission –Signals send over range of frequencies –Radio broadcast Shortwave, citizen band Ultrahigh frequency, very high frequency High definition television (HDTV) Digital Television Technology (DTV) Digital Radio Chapter 5: Communications Media, Servers, and Clients16

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Unguided Media Microwave –Unidirectional transmission –Terrestrial microwave –Satellite microwave Geosynchronous Earth orbiting satellite (GEOS) –Satellite footprint –Transponder (uplinks, downlinks) –Propagation delay Low Earth orbiting satellite (LEOS) Medium Earth orbiting satellite (MEOS) Chapter 5: Communications Media, Servers, and Clients18

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Radiated Media Microwave –Satellite microwave Mobile satellite service (MSS) –Two-way voice and data communication Global Mobile Personal Communications by Satellite (GMPCS) –Early warning for emergencies Direct broadcast satellites –DirectTV Global positioning system (GPS) –Triangulation method to determine spot on earth –Used in autos, boats, planes, golf carts Chapter 5: Communications Media, Servers, and Clients22

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Unguided Media Cellular Radio –Cellular telephones –Broadcast area Cells Antenna in each cell –Used for voice and data –Transmissions can be picked up by scanners –Cloning occurs less frequently now Chapter 5: Communications Media, Servers, and Clients24

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Unguided Media Spread Spectrum Radio –Spreads radio transmission over a range rather over a narrow frequency –Any device in the area can pick up the signal –Frequency-hopping spread spectrum Signal hops over a series of frequencies Devices must be synchronized –Direct sequence spread spectrum Signal is broadcast on several frequencies simultaneously Chip is added to identify the transmission to devices Several users can use the same frequency LANs use DSSS Chapter 5: Communications Media, Servers, and Clients26

Unguided Media Infrared Transmission –Light signals sent at a frequency that cannot be seen –Used in remote controls –IrDA ports used with printers, keyboards, mouse –LANs use this for wireless transmission Chapter 5: Communications Media, Servers, and Clients27

Selection of Media Cost –UTP is least expensive –Fiber optic cable most expensive Speed –UTP slowest –Fiber Optic cable is fastest Rate of Errors Security Chapter 5: Communications Media, Servers, and Clients28

Computers and Terminals in a Communications Network Computers in a Network –Wide Area Network (WAN) Covers large geographic area –Local Area Network (LAN) Limited geographic area –Computers are nodes on a network –Server – controlling computer –Client – many types of devices that use information on the server Chapter 5: Communications Media, Servers, and Clients29

Computers and Terminals in a Communications Network Mainframe Computers and Supercomputers –Host Computers Accessed by many terminals Acts as a server in a network Used in WANs and LANs –Supercomputers Weather forecasting, space travel Universities and the government generally own them Chapter 5: Communications Media, Servers, and Clients30

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Computers and Terminals in a Communications Network Midrange computers –Smaller and slower than mainframe –May be used as a server –Used in WANs and LANs –Departmental computing Personal Computers –May be a server or a client –Extremely versatile Chapter 5: Communications Media, Servers, and Clients32

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Computers and Terminals in a Communications Network Clients (Terminals) –Device for input/output –Dumb terminals No processing or storage capability No buffers Operates in uncontrolled mode Asynchronous transmission –Smart terminals Has memory and buffer Operates in controlled mode Synchronous transmission Chapter 5: Communications Media, Servers, and Clients34

Computers and Terminals in a Communications Network Clients (Terminals) –Intelligent Terminals Memory Contains firmware Operate in controlled mode –Programmable Terminals Limited memory and processing capability Can act as stand-alone devices Less flexible than a PC Popular before PCs Chapter 5: Communications Media, Servers, and Clients35

Computers and Terminals in a Communications Network Clients (Terminals) –X Terminal Uses X Windows Graphical client used with TCP/IP or UNIX Can access many servers simultaneously –Terminal Emulation –Thin-Client (Network) Computer Used only to connect to a network –Network Personal Computer Has some memory and storage Chapter 5: Communications Media, Servers, and Clients36

Computers and Terminals in a Network Special-Purpose Terminals –Point-of-Sale Terminals Uses bar code reader to read UPC –Credit Card Authorization Devices –Smart Card –Automated Teller Machines –Airline Reservation Systems Chapter 5: Communications Media, Servers, and Clients37

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Computers and Terminals in a Communications Network Special-Purpose Terminals –Network Printers –Facsimile Machines –Telephone –Remote Input Clients Utility use Rental car agencies –Engineering Industry Clients CAD/CAM Chapter 5: Communications Media, Servers, and Clients39

Network Configurations Configuration is the way servers and clients are connected in a network Point-to-Point –Direct line between sending and receiving device –Point-to-Point Protocol Multipoint –Many clients on a shared circuit –Response time is how long a client waits for a response from the server Chapter 5: Communications Media, Servers, and Clients40

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Terminal Interfaces Interface –How devices are connected to a network Data Communication Equipment (DCE) –Modems, media, switching equipment Data Terminal Equipment (DTE) –Clients, servers, concentrators, multiplexers EIA RS-232F –Interface that connects DCE to DTE –25-pin electrical connection –Used on a serial port Compare to parallel port Chapter 5: Communications Media, Servers, and Clients43

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Terminal Interfaces RS-449 –37-pin connector –Allows expanded functions Universal Serial Bus (USB) –Used for low-volume I/O devices FireWire –High-speed video and audio connections Handshaking Chapter 5: Communications Media, Servers, and Clients46

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Summary Three types of guided media –Twisted pair –Coaxial cable –Fiber optic cable Unguided media use no wires –Radio –Microwave –Infrared Chapter 5: Communications Media, Servers, and Clients48

Summary Least expensive is twisted pair Most expensive is fiber optic cable Fiber optic transmits at fastest speed Error rate is lowest on fiber optic cable Fiber optic cable is the most secure medium Chapter 5: Communications Media, Servers, and Clients49

Summary Mainframes, supercomputers, minicomputers, personal computers can be part of a network Terminals are general-purpose or special- purpose Point-to-point configurations Multipoint configurations Terminals connections - RS-232F or RS-449 USB and FireWire are new interface standards Chapter 5: Communications Media, Servers, and Clients50

Chapter 3 Complete