GRAP 3175 Computer Applications for Drafting Unit VI Data Communication.
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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)
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
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
Three Types of Modems
• Acoustic modem (acoustic coupler)– Uses the telephone headset– Not used anymore
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
Three Types of Modems
• Internal direct-connect modem– Board that fits into an empty slot– Convenient
• PCMCA Cards -- used in notebooks
Communication Channels
• Overview -- the medium, or pathway, through which data are transmitted between devices.
• Three basic types:– Wire cable– Microwave– Fiber optics
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
Fiber Optics
• Digital -- light impulses through clear flexible tubing
• 2.5 Billion bps
• Very high speeds and very reliable
• Optic backbone
Microwave or Radio Signals
• Signals transmitted through the atmosphere
• Line-of-sight -- Straight lines between transmitter towers and/or satellite
• 48M bps
• Reliable
• Expensive
Channel Configurations
• Point-to-point -- computer or terminal is connected directly to another device
• Multipoint -- three or more devices are connected to one line.
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+
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
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.
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.
Networks0verview
• When data-communication channels link several computers and other devices
• Each computer usually has its own processing capabilities
• WAN, MAN, LAN, & TAN
Network TopologiesOverview
• Each computer is called a node
• The arrangement is called the topology
• Star, Ring, Tree, Bus
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
Wide Area NetworkWAN
• Two or more computers that are geographically dispersed but are linked by common communication carriers
• NSFnet, INTERnet, BITnet
• Compuserve, AOL, etc.
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
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
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
LAN Components
• Two or more computers
• Server(s)
• Peripheral devices
• Cabling
• Interface card
• LAN software
LAN Servers
• Computer shared by network
• Types: file, print, communications
• LAN operating system
• Security
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
LAN Advantages
• Ability to share hardware, software, and data files
• Electronic mail
• Different computer architectures
• Internet/Intranet access
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