COMMUNICATIONS AND NETWORKS 9 CHAPTER COMMUNICATIONS AND NETWORKS The purpose of this book is to help the student become computer literate Competent in computer–related skills The goal is to be valuable immediately to a potential employer Chapter one gives an overview of an information system This system consists of the following: People Procedures Software Hardware Data

Competencies (Page 1 of 2) Discuss connectivity, the wireless revolution, and communication systems Describe physical and wireless communications channels Discuss connection devices, including modems, T1, DSL, cable modem, and satellite connections Describe data transmission factors, including bandwidths and protocols Discuss network and key network terminology Page 238

Competencies (Page 2 of 2) Describe different types of networks, including local area, metropolitan area, and wide area networks Describe network architectures, including configurations and strategies Describe organizational uses of Internet technologies, including intranets, extranets, and firewalls Page 238

Communications Ask students to give examples of communication devices that they use daily The process of sharing data, programs, and information between two or more computers Page 240

Communications Today Numerous applications depend on communication systems—E-mail, Instant messaging (IM), Internet telephone, and Electronic commerce Connectivity uses computer networks to link people and resources Going wireless has been the most dramatic change Connectivity is a concept related to using computer networks to link people and resources Microcomputers. minicomputers, and mainframes can all be connected Wireless revolution Use of mobile or wireless devices The revolution is the support of more than just the wireless telephone Many devices can and will connect to one another without any physical connection Page 240

Communication Systems Four basic elements Sending and receiving devices Communication channel Connection devices Data transmission specifications Electronic systems that transmit data from one location to another Communication systems can be wired or wireless Basic elements Sending and receiving devices – computer or a specialized communication device Communication channel – carries the message Connection devices – act as an interface between sending and receiving devices Data transmission specifications – rules and procedures that coordinate the sending and receiving devices Page 241

Communication Channels Channels carry data from one computer to another Two categories of communication channels Physical connection Wireless connection Channels are essential to a communication system They carry data Types of channels Telephone lines Coaxial cables Fiber-optic cable Infrared Broadcast radio Microwave Satellite Page 242

Physical Connections Telephone lines Coaxial cable Fiber-optic cable Telephone lines – consists of twisted pair cable; slowest; being phased out by more advanced and reliable media Coaxial cable – single solid copper core; 80 times transmission of twisted pair; television and computer networks Fiber optic – 26,000 times capacity of twisted pair cable; more secure and reliable; best over limited distances; lighter, more reliable, and less expensive than coaxial cable Return Page 242

Wireless Connections - Infrared, Broadcast Radio, Microwave Wi-FI (wireless fidelity)/802.11 Microwave Stations Bluetooth Wireless connections do not use a solid substance to connect; uses the air itself Types of wireless connections are: Infrared Light waves used over short distances Sometimes called line of sight communications Sending and receiving devices must be in clear view of one another Broadcast radio Uses towers called transceivers Web-enabled devices follow a standard known as Wi-FI (wireless fidelity) Microwave Uses high-frequency radio waves Also line of sight Used for short distances Bluetooth used for distances up to 33 feet (not line of sight) Microwave dish Page 242

Wireless Connections - Satellites Uplink/Downlink Global Positioning System Global positioning Network of 24 satellites Owned by the Defense Department Global positioning system (GPS) Devices used to determine location Provides navigational support Satellite – uses satellite orbiting 22,000 miles above the earth as microwave relay stations Uplink is sending information Downlink refers to receiving Bad weather can disrupt signals GPS are becoming popular in automobiles to provide navigation Return Page 242

Connection Device Signals Types of signals Analog Digital Signals Sent analog – telephone signals; continuous electronic wave Sent digital – computer signals; presence or absence of an electronic pulse; on/off Page 244

Connection Device Types Types of modems External Internal PC Card Wireless Modem – modulator-demodulator External – stands apart from the computer is typically connected with a cable Internal – built into the computer system unit already PC card – credit card-size expansion board that is inserted into portable computers; telephone cable connects the modem to the telephone wall jack Wireless modem may be external, internal, or a PC card Does not use cables Signals are sent through the air Page 244

Connection Services Dial-Up services Leased lines – T1, T2, T3 and T4 Digital subscriber line (DSL) Uses existing phone lines One type widely used is ADSL Cable modems Uses existing TV cable Provides speeds as fast as DSL at a lower cost Satellite/air connection services Seven times faster than dial-up Slower than DSL & cable modem Standard telephone lines and conventional modems use a dial-up service Slow Still popular, but many are using other types of connections T1, T2, T3, and T4 leased lines – do not require conventional modems and provide very high capacity and is expensive—mainly used by corporations not typical end user; T1 lines provide a speed of 1.5 mbps (mega bits per second) which is over 26 times as fast as a conventional modem DSL – uses existing telephone lines to provide high-speed connections; uses DSL modems Cable modems – Cable connections reach 90% of homes in America but not all cable companies support cable modems presently Satellite/air connection services – Uses just what it says—satellite and air connections; older satellites couldn’t upload and dial up was still used for the process; but newer satellites are two-way satellites capable of handling both uploading and downloading; available almost anywhere but slower than DSL Page 245

Typical User Connection Costs & Speeds Type Fee Speed Seconds to Get Images Dial-up $16 56 kbps 45.0 DSL 50 1.5 mbps 1.7 Cable Modem 40 Satellite 60 900 kbps 2.8 Page 245

Bandwidth Measurement of the capacity of the channel Categories Low bandwidths or Voiceband Medium band Broadband Used for high capacity transmission Used by DSL, cable, and satellite Several technical matters affect data communications One is bandwidth – bits-per-second (bps) transmission capability of a channel Three types: Voiceband – also known as voice grade or low bandwidth; standard phone line; too slow for many types of transmissions – especially high-quality video; typical speeds are 56 to 96 kbps Medium band – with special leased lines to connect minicomputers and mainframes as well as to transmit data over long distances (for larger computer systems); not typically used by individuals Broadband – used for high-capacity transmissions (DSL, cable, satellite connections); specialized high-speed devices; effectively transmits high-quality video and other communication needs; typically 1.5 mbps; higher speeds possible Page 246

Protocols Set of communication rules Standard for Internet: TCP/IP (Transmission control protocol/Internet protocol) Identifies devices Reformats information Rules for exchanging data between computers Essential features of protocol Identifying sending and receiving devices (IP address); Internet unique number address Reformatting – allows message to be broken into packets so easier to transmit over Internet through various interconnected networks; allows message to be reassembled at destination Page 247

Networks A computer network is a communication system Connects two or more computers Allows information exchange A computer network is a communication system that connects two or more computers so that they can exchange information and share resources Page 247

Computer Networks Connect Computers Network Terms Computer Networks Connect Computers Node Client Server Hub Network interface cards (NIC) Network operating system (NOS) Distributed processing Host computer Network manager Node – any device connected to a network Client – a node that requests and uses resources available from other nodes Server – a node that shares resources with other nodes; dedicated servers specialize in performing specific tasks—could be an application server, communication server, database server, file server, printer server, or Web server Hub – the center or central node for other nodes Network interface cards (NIC) – connects the computer to a network Network operating system (NOS) – software to control and coordinate activities between computers on a network Distributed processing - computing power located and shared at different locations Host computer – large centralized computer Network manager – a computer specialist; network administrator Page 248

Network Types Local area networks Home networks WLAN Metropolitan area networks Wide area networks Communications networks differ in geographical size. Three important types are: 1)LANs Computers and devices linked in close proximity to each other Linked by cable Typically use a bus form of organization With gateways, LANs can be connected to other LANs or any other type of network Home Networks – LANs are now being commonly used by individuals in home/apartments; allow different computers to share resources including a common Internet connection; can be connected by various means including a wireless LAN (WLAN) that uses radio frequencies to connect computers Home networking includes the following: Radio frequency, telephone lines, electric wiring, cables, NIC/adapter cards 2)MANs (metropolitan area network)– also known as a regional network; span distances up to 100 miles Network linking nodes and resources within the geographical bounds of a city Cellular phones can extend the reach of a MAN 3)WANs (wide area networks) Countrywide and worldwide networks Use microwave relays and satellites to reach users Internet is the widest WAN Page 249

Network Architecture Architecture describes how a network is arranged Arrangement is called topology Types of network topology Star Bus Ring Hierarchical Networks are connections of two or more computers that work together to exchange information and share resources The network architecture describes how the network is arranged and how the resources are coordinated and shared Network architecture also describes how a computer network is configured and what strategies are used  Topology – network arrangement or configuration Page 251

Star Network Smaller computers linked to a central unit Central unit is called the network hub Control is maintained by polling Host computer – large centralized computer, usually a mainframe Star – nodes are connected to a single computer called a network hub All communications pass through the hub/host computer; each connecting device is asked (“polled”) whether it has a message to send and then each device is in turn allowed to send its message Can be used as a time-sharing system Return Page 251

Bus Network Each device handles its own communication control There is no host computer Has a common connecting cable called a backbone Bus network – each device handles its own communications control No host computer Common connecting cable called a bus or backbone Not as efficient as star, but it is low cost and widely used Return Page 254

Ring Network Each device is connected to two other devices No central file server or computer Useful in a decentralized environment Ring network Each device connected to two others forming a ring No central files server or computer Messages passed around ring until reach correct destination Often used to link mainframes—especially over wide geographical areas Useful in decentralized organization Makes possible distributed data processing system Computers can perform processing tasks on own Can also share programs, data, and other resources Return Page 254

Hierarchical Network Several computers linked to a central host Computers are hosts to other computers Useful in centralized organizations Sometime called hybrid network Consists of several computers linked to central host computer All computers can server as hosts to other computers (unlike star network) Host at top could be mainframe; computers below could be minis; then “down” to micros Useful in centralized organization Return Page 254

Strategies Strategy is a way of coordinating the sharing of information and resources Common network strategies Terminal Client/server Peer-to-peer Strategy: ways of coordinating the sharing of information and resources in a network Terminal network system Centralized host, usually a mainframe Nodes are usually terminals with little or no processing capabilities Reservation systems Client/server network systems Powerful computer coordinates services This server provides access to centralized resources Widely used on the Internet Peer-to-peer network system -Bus topology Nodes have equal authority and act as both servers and clients A node could obtain files from another node and provide files to another node Gnutella is a widely used peer-to-peer network system for sharing all kinds of files including music files Page 255

Internets and Extranets Intranets Private network within an organization Provides information to employees Extranets Private network that connects organizations Used to allow suppliers and others access Firewalls Security system Protects against external threats Intranet – Intranets use browsers, Web sites, and Web pages like the public Internet; typically include e-mail, mailing lists, newsgroups, and FTP services Extranet – Purpose is to increase efficiency and reduce costs Firewalls – Organizational firewalls include a proxy server that is a gatekeeper; all communications between the outside world and an organization must pass through the proxy server where the source and content of each communication is evaluated; end users have many of the same concerns regarding security as organizations and can use firewalls as well Page 257

A Look to the Future Wireless Robotic Car Pod car (Personalization on Demand) Predicts and responds Designed to learn and adapt to an individual's driving needs and habits Toyota and Sony are collaborating on a "smart" car Page 259

Discussion Questions Define and discuss connectivity, the wireless revolution, and communications. Identify and describe the various physical and wireless communication channels. Identify the standard Internet protocol and discuss its essential features. Define and discuss the four principal network topologies. Define and discuss the three most common network strategies. Have students turn to the end of Chapter 9 in their textbooks to view the same “Open-Ended” questions/statements Page 266