C/IL 102 Computer and Information Literacy
CHAPTER 6
COMMUNICATIONS AND NETWORKS
WHAT IS COMMUNICATIONS?
 Transmission of data and information between two or more computers
EXAMPLES OF HOW COMMUNICATIONS IS USED
 Electronic mail (e-mail)
 Voice mail
 Facsimile (fax)
 Telecommuting
 Videoconferencing
 Groupware
 Electronic data interchange (EDI)
 Global positioning systems (GPSs)
 Bulletin board systems (BBSs)
 Online services
 The Internet
A COMMUNICATIONS SYSTEM MODEL
 A computer or a terminal
 Communications equipment that sends data
 Communications channel
 Communications equipment that receives data
 Another computer
 Communications software
TRANSMISSION MEDIA
 Twisted-pair cable
 Shielded twisted-pair (STP)
 Unshielded twisted-pair (UTP) or 10baseT
 Coaxial cable (coax)
 Cable TV
 Thinnet - 10base2
 Fiber-optic cable
 Low weight
 High speed
 Microwave transmission
 Terrestrial microwave
 Communications satellites
 Uplink
 Downlink
 Geosynchronous orbit
 Wireless transmission: radio and light waves
 Infrared light
 Portable radio data terminal
 Cellular telephone
 Communications Channels
LINE CONFIGURATIONS
 Point-to-point lines
 Switched line -- Handshake
 Dedicated line (leased or private line)
 Multidrop (multipoint) lines
Spring 1998
C/IL 102 Computer and Information Literacy
 Multiple devices (terminals) along a single line
CHARACTERISTICS OF COMMUNICATIONS CHANNELS
 Types of signals: digital and analog
 Digital signals are electrical pulses – T1(1.5Mbps), T3(45Mbps)
 Analog signals are continuous wave -- voice
 ISDN
 Transmission modes: asynchronous and synchronous
 Asynchronous - irregular intervals
 Synchronous - regular intervals
 Direction of transmission: simplex, half-duplex, and full-duplex
 Simplex - one direction only
 Half-duplex - either direction, but only one direction at a time
 Full-duplex - both directions at the same time
 Transmission rate
 Bandwidth
 Measured in bits per second (bps)
COMMUNICATIONS SOFTWARE
 Dialing
 File transfer
 Terminal emulation
 Internet access
COMMUNICATIONS EQUIPMENT
 Modems: External & internal modem
 Multiplexers (MUX): combines multiple data streams into one
 Front-end processors: dedicated to handling the communications
 Network interface cards (NIC)
 Wiring hubs (concentrator or multistation access unit (MAU))
 Gateways: Connect different types of networks
 Bridges: Connect similar types of networks
 Routers: Connect several networks together
COMMUNICATIONS NETWORKS
 Local area networks (LANs)
 LAN Applications
 HW, SW, and information resource sharing
 File-server and client-server networks
 Peer-to-peer networks
 Network operating systems
 Wide area networks (WANs)
 Metropolitan area network (MAN)
 Common carriers
 Value-added carriers
 Value-added networks
 Packet-switching
NETWORK CONFIGURATIONS
 Star network
 Bus network
 Ring network
COMMUNICATIONS PROTOCOLS
 A set of rules and procedures for exchanging information between computers
 Ethernet
Spring 1998
C/IL 102 Computer and Information Literacy
 Most widely used (10Mbps)
 Fast-Ethernet (100Mbps)
 Token ring
 Second most widely used
 Token
Spring 1998