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
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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
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Learning Objectives
• Explain how computers and modems
communicate using RS-232 connectors
• List applications of the RS-449, Universal
Serial Bus, and FireWire standards
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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
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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
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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
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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
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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
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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
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Unguided Media
• Wireless media
• Broadcast radio
– Omnidirectional transmission
– Signals send over range of frequencies
– Radio broadcast
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•
•
•
•
Shortwave, citizen band
Ultrahigh frequency, very high frequency
High definition television (HDTV)
Digital Television Technology (DTV)
Digital Radio
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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)
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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
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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
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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
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•
•
•
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
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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
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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
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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
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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
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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
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Computers and Terminals in a
Communications Network
• Clients (Terminals)
– Device for input/output
– Dumb terminals
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•
•
•
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
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Computers and Terminals in a
Communications Network
• Clients (Terminals)
– Intelligent Terminals
• Memory
• Contains firmware
• Operate in controlled mode
– Programmable Terminals
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•
•
•
Limited memory and processing capability
Can act as stand-alone devices
Less flexible than a PC
Popular before PCs
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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
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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
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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
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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
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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
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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
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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
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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 Clients
• Mainframes,
supercomputers,
minicomputers, personal
computers can be part of a
network
• Terminals are generalpurpose or special-purpose
• Point-to-point configurations
• Multipoint configurations
• Terminals connections - RS232F or RS-449
• USB and FireWire are new
interface standards
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