GRAP 3175 Computer Applications for Drafting Unit VI Data Communication.

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GRAP 3175 Computer Applications for Drafting Unit VI Data Communication

Transcript of GRAP 3175 Computer Applications for Drafting Unit VI Data Communication.

GRAP 3175Computer Applications for

Drafting

Unit VI

Data Communication

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)

The effects of Data Communication

• Our link to the world

• Necessary for CAD labs

Data Transmission

• Two forms of data transmission– Analog– Digital

Analog Data Transmission

• The transmission of data in a continuous wave form

• Telephone system

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

Wireless Transceiver

• Between computers

• Between buildings

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.

Networks

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

Star Topology

• Several devices connected to one centralized computer

Ring Topology

• Consists of several devices connected to each other in a closed loop

• IBM Token-ring

Tree Topology

• Links computers in a hierarchical fashion and requires data to flow through branches

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

LAN Disadvantages

• Training

• Cost

• Security