1 9 9 TELECOMMUNICATIONS AND NETWORKS

2 Telecommunications Communicating information via electronic means over some distance Information SuperHighway High-speed digital telecommunications networks that are national or worldwide in scope and accessible by the general public

3 Components of a Telecommunications System Computers I/O devices Communications channels – cables, telephone lines Communications Processors – modems, multiplexors Communications Software Uses Protocols

4 Types of Signals Analog signal –Continuous waveform –Voice communications Digital signal –Discrete waveform –Two states: 0 and 1 –On-off electrical pulses –Data communications Modem –Translates b/t digital and analog

5 Communications Channels The links by which data or voice are transmitted Twisted wire Coaxial cable Fiber-optic cable Wireless –microwave –Satellite and other wireless channels –Pagers –Cellular phones –PCS –PDAs

6 Transmission Speed Transmission –Bits per second (bps) Bandwidth –Range of frequencies that can be accommodated on a channel –Greater range  Greater bandwidth  Greater capacity

7 Speeds and Costs MediumSpeedCost Twisted wire300 bps – 10 MbpsLow Microwave256 Kbps – 100 Mbps Satellite256 Kbps – 100 Mbps Coaxial cable56 Kbps – 200 Mbps Fibre optic cable500 Kbps – 6+ TbpsHigh Bps=bits per second; Kbps=kilobits per second; Mbps=megabits per second; Tbps=terabits per second

8 Communications Processors Front- end processor –Special purpose computer that manages communication for host computer in a network Concentrator –Computer that collects & temporarily stores messages from terminals for batch transmission to host computer Multiplexer –allows channel to carry data from multiple sources simultaneously

9 Network Topologies: Star All computers and devices connected to a central host computer

10 Network Topologies: Bus All computers are linked by a single circuit

11 Network Topologies: Ring All computers are linked by a closed loop Data is passed in one direction

12 Local Networks Private branch exchange (PBX) –Firm’s central switching system –Handles digital and voice Local area network (LAN) –Dedicated channels –Limited distance (less than 700 metre radius) –Higher capacity than PBX

13 Typical LAN

14 LAN Technology Gateway –A communications processor that connects dissimilar networks Router –A device that forwards packets of data between similar networks Bridge –A device that connects segments of the same or similar networks Network operating system (NOS) –Coordinates resources

15 Wide Area Networks (WAN) A telecommunications network that spans a large geographical distance Switched lines –Telephone lines used by a computer to send data Dedicated lines –Continuously available –Conditioned to transmit data at high speeds MAN and GAN –Metropolitan and global area networks

16 Network Technologies Packet Switching –Data broken into small packets –Packets are then routed in the most economical way Frame Relay –A shared network service technology that packages data into bundles –Does not use error-correction –Cheaper and faster than packet-switching Asynchronous Transfer Mode (ATM) –Information parceled into 8-byte cells –Data transmitted between computers of any vendor

17 Network Technologies Integrated Services Digital Network (ISDN) –Dialup: voice, data, image, video on single line Digital Subscriber Lines (DSL) –Operate over existing telephone lines –High speed transmissions Cable Modems –Operates over cable lines to provide access to networks T1 Line –Dedicated telephone line, rate of Mbps

18 Electronic Data Interchange (EDI) Computer-to-computer exchange of standard business transaction documents