Powered by DeSiaMore4 Our Agenda (cont’d.) Network Concepts Local Area Networks Wide Area Networks Internetworks The Internet Electronic Commerce
Powered by DeSiaMore5 Learning Objectives Summarize the communications hardware and software needed for computers to communicate with other computers. Describe the main characteristics of communications channels.
Powered by DeSiaMore6 Learning Objectives (cont’d.) Describe the main types of communications processors and give several examples. Describe the main functions of communications software. Explain how local area networks are organized and list the special hardware and software used in them.
Powered by DeSiaMore7 Learning Objectives (cont’d.) Describe the structure of wide area networks. Explain how and why networks are interconnected. Explain what the Internet, intranets, and extranets are. Describe the special hardware and software needed for E-Commerce.
Powered by DeSiaMore8 Communications Concepts Information System Networks and the Internet
Powered by DeSiaMore9 Communications Concepts Two main types of communications hardware Communications channel – the link over which data is sent Communications processors – provide processing capabilities between the computer and the communications channel A modem is a communication processor
Powered by DeSiaMore10 Communications Hardware Information System Networks and the Internet
Powered by DeSiaMore11 Communications Hardware Communications channel characteristics Data is transmitted over the channel as bits. Each bit is sent one after the other. Bits are grouped to form bytes that represent characters using ASCII, EBCDIC, Unicode or some other code.
Powered by DeSiaMore12 Communications Hardware (cont’d.) The way in which bits are sent determines two main characteristics of the channel Signal type Data rate
Powered by DeSiaMore13 Signal Type Bits can be sent either as An Analog signal – data is transmitted by a wave pattern that varies continuously A Digital signal – data is transmitted as a series of high and low pulses The human voice is analog Telephones are analog Computers are digital
Powered by DeSiaMore14 Data Rate Data rate is measured as bits per second (bps). Each type of channel has a maximum data rate. Baud rate is used to express data rate 9,600 baud = 9,600 bps. Bandwidth describes how much data can be transmitted over a channel.
Powered by DeSiaMore15 Communications Channel Media Wire cables – sometimes called “copper” have been used since the 1800s. Two main forms Twisted-pair wiring Coaxial cable
Powered by DeSiaMore16 Communications Channel Media (cont’d.) Twisted-pair wiring Two wires twisted together Most telephone lines are twisted-pair Can also be used for data Data transmission rate is slow compared to other media
Powered by DeSiaMore17 Communications Channel Media (cont’d.) Coaxial cable Copper wire insulated with rubber and plastic. Used with cable television systems. Data transmission rate is faster than twisted-pair, and more expensive, but slower than other media.
Powered by DeSiaMore18 Communications Channel Media (cont’d.) Fiber-optic cables Bundles of glass or plastic fibers. Each fiber is 1/2000 inch thick – about the size of a human hair. Data is transmitted by a laser that pulses light through the fiber. Data transmission rate is very fast.
Powered by DeSiaMore19 Communications Channel Media (cont’d.) Microwave Special types of radio signals sent from one microwave antenna to another. Transmission is line-of-sight, i.e, one antenna must be able to “see” the other. Two types Land based – antenna approximately 30 miles apart. Satellite – positioned 22,300 miles in space – geosynchronous orbit.
Powered by DeSiaMore20 Communications Channel Media (cont’d.) Other media Infrared spectrum Very short distances Relatively slow Wireless systems Used for mobile computing Usually in small areas or hard to wire areas
Powered by DeSiaMore21 Communications Processors Channel interface devices Communications control units Communications protocols Communications security
Powered by DeSiaMore22 Channel Interface Devices Modems – convert digital signals to analog signals at the origin and reverse the process at the destination of the signal. Digital to analog is modulation. Analog to digital is demodulation. Modems may be either internal or external to the computer.
Powered by DeSiaMore23 Channel Interface Devices (cont’d.) Modem data rates are typically 33 Kbps to 56 Kbps. Cable modems – are devices to provide the interface between a computer and a cable system’s data transmission capability. For ISDN or DSL a terminal adapter is required.
Powered by DeSiaMore24 Communication Control Units Multiplexer – combines signals from several slow-speed devices to transmit over a faster device. Controller – stores and forwards signals to improve the throughput of the channel. Front-End Processor – operates between the channel and the main computer.
Powered by DeSiaMore25 Communications Protocols Protocols are the rules computers must follow when they communicate with one another. Computers that wish to communicate and have different protocols must use a protocol converter to standardize their communication.
Powered by DeSiaMore26 Communications Security A problem with data communications is the lack of security over a communications channel. One way of solving this problem is to use data encryption to convert the data to an unintelligible form for transmission and to return it to an intelligible form at the destination. Encryption requires a key.
Powered by DeSiaMore27 Communications Software Information System Networks and the Internet
Powered by DeSiaMore28 Communications Software Communications software is required to control communications between computers. It receives data from communications processors connected to the channel and passes the data to other software in the computer for processing.
Powered by DeSiaMore29 Communications Software (cont’d.) Types of communications software Terminal emulators Client software – as used in client/server computing File transfer protocol (FTP) – software Network Operating System software (NOS)
Powered by DeSiaMore30 Network Concepts Information System Networks and the Internet
Powered by DeSiaMore31 Network Topologies Star network – each node is connected to each other node. Hierarchical network – organized like a family tree. Bus network – each node is connected to a single, common communications channel. Ring network – each node is connected to a common channel forming a loop.
Powered by DeSiaMore32 Types of Networks Local Area Network (LAN) Wide Area Network (WAN) Metropolitan Area Network (MAN) Internetwork – connected networks
Powered by DeSiaMore33 Local Area Networks Information System Networks and the Internet
Powered by DeSiaMore34 Local Area Networks Local Area Network Structure Connection Topology. Media for communications channel. Usually either Ethernet or Token Ring. Require Network Interface Cards (NIC) in each device on the network. Permits sharing of resources.
Powered by DeSiaMore35 Wide Area Networks Information System Networks and the Internet
Powered by DeSiaMore36 Wide Area Networks Connection Topology. Media for communications channel. Permits sharing of resources. Can include a Virtual Private Network. Often a combination or resources.
Powered by DeSiaMore37 Internetworks Information System Networks and the Internet
Powered by DeSiaMore38 Internetworks Connecting two or more networks using Bridges Gateways Routers
Powered by DeSiaMore39 The Internet Information System Networks and the Internet
Powered by DeSiaMore40 Internet Origins in ARPANET in 1969. Grew slowly at first and “exploded” in 1993 with the adoption of the HTML standards for the World Wide Web. Two protocols Transmission Control Protocol (TCP) Internet Protocol (IP) Most users require a relationship with an Internet Service Provider (ISP).
Powered by DeSiaMore41 Internet Services Electronic Mail – E-Mail World Wide Web (WWW) Telnet File Transfer Protocol (FTP) Gopher Usenet or NetNews Chat
Powered by DeSiaMore42 Intranets and Extranets An Intranet is an Internet like network but access is restricted to within a business or organization. Firewalls are used to control access to an Intranet. An Extranet permits controlled outside access to an Intranet like network.
Powered by DeSiaMore43 Electronic Commerce Information System Networks and the Internet
Powered by DeSiaMore44 Hardware and Software Requires the business have a web site. The web software runs on a web server which has special e-commerce software.
Powered by DeSiaMore45 Information System Networks and the Internet Key Terms
Powered by DeSiaMore46 Key Terms Analog Signal Bandwidth Baud Rate Bus Network Cable Modem Channel Interface Device Client Software Communications Channel Communications Control Unit Communications Processor Database Server Data Encryption Digital Signal
Powered by DeSiaMore47 Key Terms (cont’d.) Downloading DSL Electronic Commerce (E-commerce) Electronic Mail (E-mail) Extranet File Server File Transfer Firewall Hierarchical Network Hybrid Network Information Superhighway Internet Internet Service Provider (ISP) Internetwork Intranet
Powered by DeSiaMore48 Key Terms (cont’d.) ISDN Local Area Network (LAN) Modem Network Computer Network Interface Card (NIC) Print Server Protocol Protocol Converter Ring Network Star Network Terminal Adapter Terminal Emulation Software Uniform Resource Locator (URL) Uploading
Powered by DeSiaMore49 Key Terms (cont’d.) Value Added Network (VAN) Virtual Private Network (VPN) Web Server Web Site Wide Area Network (WAN) Wireless LAN World Wide Web (WWW)