slide 4-1 chapter 4 data communications and networking considerations introduction to information...

Slide 4-11

Chapter 4Chapter 4

Data Communications and Networking Considerations

Introduction to Information Systems

Judith C. Simon

Slide 4-22

"Copyright © 2001 John Wiley & Sons, Inc. All rights reserved. "Copyright © 2001 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted Reproduction or translation of this work beyond that permitted in Section 117 of the 1976 United States Copyright Act without in Section 117 of the 1976 United States Copyright Act without

the express written permission of the copyright owner is the express written permission of the copyright owner is unlawful. Request for further information should be addressed unlawful. Request for further information should be addressed to the Permissions Department, John Wiley & Sons, Inc. The to the Permissions Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publisher assumes no and not for distribution or resale. The Publisher assumes no

responsibility for errors, omissions, or damages, caused by the responsibility for errors, omissions, or damages, caused by the use of these programs or from the use of the information use of these programs or from the use of the information

contained herein."contained herein."

Slide 4-33

Chapter 4 Major TopicsChapter 4 Major Topics

General conceptsGeneral concepts Characteristics of communications channelsCharacteristics of communications channels Data communications mediaData communications media Communications carriersCommunications carriers Data communications hardwareData communications hardware Network topologiesNetwork topologies Network protocolsNetwork protocols LANs and WANsLANs and WANs Intranet and extranet communicationsIntranet and extranet communications Distributed systemsDistributed systems Strategic network issuesStrategic network issues Communications infrastructureCommunications infrastructure Ubiquitous networksUbiquitous networks

Slide 4-44

General Concepts of Data CommunicationsGeneral Concepts of Data Communications

Data communicationsData communications: computer-based electronic : computer-based electronic transmission of datatransmission of data Components: sender, receiver, medium (“channel”), Components: sender, receiver, medium (“channel”),

messagemessage

NetworkNetwork: collection of computers and other : collection of computers and other hardware connected through communications hardware connected through communications media, along with programs to provide capabilities media, along with programs to provide capabilities of sharing resourcesof sharing resources

Slide 4-55

Characteristics of Communications ChannelsCharacteristics of Communications Channels

Characteristics of communications channels Characteristics of communications channels (described on next slides) include(described on next slides) include type of servicetype of service direction of communicationdirection of communication number of data pathsnumber of data paths number of connectionsnumber of connections type of signaltype of signal speed of transmissionspeed of transmission mode of transmissionmode of transmission

Slide 4-66

Types of ServiceTypes of Service

Dedicated channelDedicated channel: assigned exclusively to a particular service, : assigned exclusively to a particular service, such as PC-to-printer, in which the channel is available full such as PC-to-printer, in which the channel is available full time for communication between the two devicestime for communication between the two devices

Circuit-switched channelCircuit-switched channel: communication circuit is established : communication circuit is established for a transmission, then released to be available to others, which for a transmission, then released to be available to others, which is less expensive than dedicated (e.g., telephone system)is less expensive than dedicated (e.g., telephone system)

Packet-switched channelPacket-switched channel: store-and-forward design widely : store-and-forward design widely used on networks, in which long messages are separated into used on networks, in which long messages are separated into smaller “packets” for transmission, often relayed through smaller “packets” for transmission, often relayed through intermediate computers on the way to the destination computerintermediate computers on the way to the destination computer

Slide 4-77

Types of Channel ConnectionsTypes of Channel Connections

Dedicated communications channel(point-to-point)

Slide 4-88


Circuit-switched communications channel

Slide 4-99


NetworkServer

Packet-switched communications channel (multipoint)

Slide 4-1010

Direction of CommunicationDirection of Communication

SimplexSimplex: data may be transmitted in only one : data may be transmitted in only one direction; e.g., radio and televisiondirection; e.g., radio and television

Half duplexHalf duplex: data may be transmitted in one : data may be transmitted in one direction or the other, but not in both directions at direction or the other, but not in both directions at the same time; e.g., CB radiothe same time; e.g., CB radio

Full duplex (or “duplex”)Full duplex (or “duplex”): data may be : data may be transmitted in both directions at the same time, transmitted in both directions at the same time, e.g., telephonee.g., telephone

Slide 4-1111

Simplex CommunicationSimplex Communication

Data is transmitted in one direction only

Slide 4-1212

Half-Duplex CommunicationHalf-Duplex Communication

Data can be transmitted in both directions,but not at the same time.

OROR

Slide 4-1313

Full-Duplex CommunicationFull-Duplex Communication

Data can be transmitted in both directions,at the same time.

Slide 4-1414

Number of Data PathsNumber of Data Paths

SerialSerial: one data-carrying path in a channel: one data-carrying path in a channel ParallelParallel: several data paths in a channel: several data paths in a channel

Slide 4-1515

Serial CommunicationsSerial Communications

SerialSerialChannelChannel

0 1 0 0 0 0 1 1 1 0 0 0 0 01 10 1 0 0 0 0 1 1 1 0 0 0 0 01 1

EBCDIC “B”EBCDIC “B” EBCDIC “A”EBCDIC “A”

One data-carrying path in communications channel

Slide 4-1616

Parallel CommunicationsParallel Communications

ParallelParallelChannelChannel

Data Carrying PathsData Carrying PathsEBCDIC “B”EBCDIC “B” EBCDIC “A”EBCDIC “A”

11 110000

000011

00

11110000000000

11

Multiple data paths in communications channel,e.g., 8 data-carrying paths

Slide 4-1717

Number of ConnectionsNumber of Connections

Point-to-pointPoint-to-point: only two devices connected to the : only two devices connected to the channel, e.g., one computer and one printerchannel, e.g., one computer and one printer

MultipointMultipoint: more than two devices connected to : more than two devices connected to the channelthe channel

Slide 4-1818

Number of ConnectionsNumber of Connections

Multipoint LinesMultipoint Lines Point-to-Point LinesPoint-to-Point Lines

Slide 4-1919

Type of Signal - and Related TermsType of Signal - and Related Terms

Digital signalDigital signal: discrete: discrete Analog signalAnalog signal: continuous: continuous ModulationModulation: altering an analog (“carrier”) signal to represent : altering an analog (“carrier”) signal to represent

digital datadigital data DemodulationDemodulation: changing a digital signal back to analog after : changing a digital signal back to analog after

transmissiontransmission ModemModem: device that performs modulation/demodulation: device that performs modulation/demodulation CodecCodec: device that converts analog video and audio data into : device that converts analog video and audio data into

digital signals, such as for storage on a CDdigital signals, such as for storage on a CD DSLDSL: digital subscriber line, which provides higher-speed : digital subscriber line, which provides higher-speed

transmission of data than traditional telephone linestransmission of data than traditional telephone lines

Slide 4-2020

Digital and Analog SignalsDigital and Analog Signals

amplitudeamplitude

timetime

Continuous (Analog)Continuous (Analog)

amplitudeamplitude

timetime

Discrete (Digital)Discrete (Digital)

Slide 4-2121

Speed of TransmissionSpeed of Transmission

Bits per second (bps)Bits per second (bps): how fast : how fast datadata may be sent over may be sent over a communications channel; bps is the way that speed of a communications channel; bps is the way that speed of transmission is typically measuredtransmission is typically measured

Baud rateBaud rate: how fast : how fast signalssignals may be sent over a may be sent over a communications channel; more than one bit may be communications channel; more than one bit may be sent per signal, so bps may be higher than baudsent per signal, so bps may be higher than baud

BandwidthBandwidth: difference between highest and lowest : difference between highest and lowest frequencies that may be transmitted over the frequencies that may be transmitted over the communications channel; bandwidth affects speed of communications channel; bandwidth affects speed of signal transmission, which affects speed of data signal transmission, which affects speed of data transmissiontransmission

Slide 4-2222

Mode of TransmissionMode of Transmission

Synchronous (same-time) transmissionSynchronous (same-time) transmission: block-at-a-: block-at-a-time transmission, performed by transmitting a timing time transmission, performed by transmitting a timing signal with the data signal so that both sender and signal with the data signal so that both sender and receiver use the same timing signal (prevents timing receiver use the same timing signal (prevents timing problems that could cause data loss)problems that could cause data loss)

Asynchronous (not-same-time) transmissionAsynchronous (not-same-time) transmission: : character-at-a-time transmission; start and stop bits character-at-a-time transmission; start and stop bits are used (instead of a timing signal) to identify the are used (instead of a timing signal) to identify the beginning and ending of each characterbeginning and ending of each character

Slide 4-2323

Data Communications Media(Media = Channels or Means of Transmission)

Data Communications Media(Media = Channels or Means of Transmission)

Wire pairsWire pairs: most common medium, widely used by local phone : most common medium, widely used by local phone companies; usually twisted-pair wires; relatively inexpensive but companies; usually twisted-pair wires; relatively inexpensive but low-speed mediumlow-speed medium

Coaxial cableCoaxial cable: widely used for long-distance connections and in : widely used for long-distance connections and in local area networks (LANs); faster data transmission than wire local area networks (LANs); faster data transmission than wire pairs because of greater bandwidthpairs because of greater bandwidth

Optical fiberOptical fiber: considered the most secure medium because : considered the most secure medium because tapping into its signals is more difficult; preferred in locations tapping into its signals is more difficult; preferred in locations such as hospital operating rooms with extensive electrical such as hospital operating rooms with extensive electrical equipment as well as a critical need for accurate data, because its equipment as well as a critical need for accurate data, because its laser light signals are not affected by electrical or magnetic laser light signals are not affected by electrical or magnetic interferenceinterference

Slide 4-2424

Data Communications Media(continued)

Data Communications Media(continued)

Broadcast radioBroadcast radio: wireless method used for cellular phone : wireless method used for cellular phone and handheld computer transmissionsand handheld computer transmissions

MicrowaveMicrowave: both terrestrial and satellite systems use line-: both terrestrial and satellite systems use line-of-sight signals (transmitter and receiver must be in a of-sight signals (transmitter and receiver must be in a straight line with no barriers between them); signals are straight line with no barriers between them); signals are subject to distortion by weather; many satellite systems subject to distortion by weather; many satellite systems are in geosynchronous orbit 22,000+ miles above the are in geosynchronous orbit 22,000+ miles above the equator, although low- and medium-orbit satellite systems equator, although low- and medium-orbit satellite systems are increasing in useare increasing in use

InfraredInfrared: line-of-sight signals being used in some : line-of-sight signals being used in some wireless local area networks; security of transmission is wireless local area networks; security of transmission is an issue unless data is encrypted (scrambled)an issue unless data is encrypted (scrambled)

Slide 4-2525

Communications CarriersCommunications Carriers

Communications carriersCommunications carriers: companies that provide : companies that provide a common type of communications service to a common type of communications service to many customersmany customers

POTSPOTS: plain old telephone service, available from : plain old telephone service, available from companies such as ATT, Bell systems (BellSouth, companies such as ATT, Bell systems (BellSouth, etc.), MCI, and Sprintetc.), MCI, and Sprint

Value-added carrierValue-added carrier: typically leases POTS-type : typically leases POTS-type services, enhances them, and resells the use of the services, enhances them, and resells the use of the facilities to someone elsefacilities to someone else

Slide 4-2626

Data Communications HardwareData Communications Hardware

ModemModem: described earlier; allows users to transmit digital : described earlier; allows users to transmit digital data over analog facilitiesdata over analog facilities

BridgeBridge: device (usually a computer) used to connect two : device (usually a computer) used to connect two homogeneous networks, i.e., with the same protocols and homogeneous networks, i.e., with the same protocols and topologies (described later)topologies (described later)

GatewayGateway: device used to connect two heterogeneous : device used to connect two heterogeneous networks, i.e., with different protocols and topologiesnetworks, i.e., with different protocols and topologies

RouterRouter: device that makes decisions as to channel (route) : device that makes decisions as to channel (route) that a message will take to its destinationthat a message will take to its destination

Multiplexer & concentratorMultiplexer & concentrator: devices that provide line-: devices that provide line-sharing capabilities, i.e., multiple computer transmissions sharing capabilities, i.e., multiple computer transmissions over shared communications channels at the same timeover shared communications channels at the same time

Slide 4-2727

Network TopologiesNetwork Topologies

TopologyTopology: interconnection of devices and channels; many : interconnection of devices and channels; many ways exist for connecting computers, including:ways exist for connecting computers, including:

Fully interconnected (plex)Fully interconnected (plex): uses point-to-point channels to : uses point-to-point channels to connect each computer to each other computer on the connect each computer to each other computer on the network; expensive method but provides good backup in network; expensive method but provides good backup in case of a failure of any linkscase of a failure of any links

ChainChain: first computer has a point-to-point link to the : first computer has a point-to-point link to the second, second is linked to third, etc.; failure of one link second, second is linked to third, etc.; failure of one link can cease communications from that point oncan cease communications from that point on

LoopLoop: similar to chain, except that last computer is linked : similar to chain, except that last computer is linked back to first computer through point-to-point channel; back to first computer through point-to-point channel; failure of one link will not cease communicationsfailure of one link will not cease communications

Slide 4-2828

Network TopologiesNetwork Topologies

StarStar: one central computer is connected by point-: one central computer is connected by point-to-point channel to each of the other computers; to-point channel to each of the other computers; failure of the central computer would shut down failure of the central computer would shut down the entire network, although failure of one link the entire network, although failure of one link affects only the one computer connected to the affects only the one computer connected to the central computercentral computer

RingRing: uses point-to-point channels to connect ring : uses point-to-point channels to connect ring repeaters in a configuration similar to a loop; repeaters in a configuration similar to a loop; computers are connected to the ring repeaterscomputers are connected to the ring repeaters

BusBus: all the computers are connected to a : all the computers are connected to a common communications channelcommon communications channel

Slide 4-2929

Fully Interconnected TopologyFully Interconnected Topology

Slide 4-3030

Chain, Loop & Star TopologiesChain, Loop & Star Topologies

ChainChainLoopLoop

StarStar

Slide 4-3131

Ring & Bus TopologiesRing & Bus Topologies

RingRingTopologyTopology

BusBusTopologyTopology

Slide 4-3232

Network Protocols(Rules for Network Communications)

Network Protocols(Rules for Network Communications)

ISO-OSI Reference ModelISO-OSI Reference Model: guidelines for development of : guidelines for development of protocols so different vendors’ hardware will work protocols so different vendors’ hardware will work togethertogether

ContentionContention: early protocol used on point-to-point channels : early protocol used on point-to-point channels for determining when a computer can send information for determining when a computer can send information over the channel; each computer “contends” for channel over the channel; each computer “contends” for channel control by sending a set of characters that requests control by sending a set of characters that requests permission to transmitpermission to transmit

PollingPolling: early protocol used on multipoint channels which : early protocol used on multipoint channels which involved a master computer checking with subordinate involved a master computer checking with subordinate computers to see if they had something to transmitcomputers to see if they had something to transmit

Slide 4-3333

Network Protocols (continued)Network Protocols (continued)

X.25X.25: protocol widely used today for connecting : protocol widely used today for connecting computers to public and private networks with packet-computers to public and private networks with packet-switching servicesswitching services

ISDNISDN: protocol that describes how a communications : protocol that describes how a communications channel can be shared to have various services channel can be shared to have various services simultaneously on one communications channelsimultaneously on one communications channel

CSMA/CDCSMA/CD: widely used in LANs, using a bus topology; a : widely used in LANs, using a bus topology; a computer wanting to transmit data checks the channel to computer wanting to transmit data checks the channel to see if another computer is transmitting (looks for a carrier see if another computer is transmitting (looks for a carrier signal); if none is found, it transmits but still checks to be signal); if none is found, it transmits but still checks to be sure no other computer starts transmitting at the same time sure no other computer starts transmitting at the same time (a potential collision)(a potential collision)

Slide 4-3434

Network Protocols (continued)Network Protocols (continued)

Token passingToken passing: widely used in LANs, usually : widely used in LANs, usually with a ring topology; a token (string of characters) with a ring topology; a token (string of characters) circulates among the computers, and any computer circulates among the computers, and any computer can take control of it as it passes so that it can can take control of it as it passes so that it can transmit and then release the tokentransmit and then release the token

TCP/IPTCP/IP: used for Internet communications : used for Internet communications because it allows computers to communicate because it allows computers to communicate regardless of their operating systems and hardwareregardless of their operating systems and hardware

ATMATM: allows one high-speed channel to : allows one high-speed channel to simultaneously carry different types of services, simultaneously carry different types of services, such as voice, TV, data, etc.such as voice, TV, data, etc.

Slide 4-3535

LANs and WANsLANs and WANs

Local area network (LAN)Local area network (LAN): operates within a restricted : operates within a restricted geographic area such as within one building; usually geographic area such as within one building; usually owned by a single organizationowned by a single organization

Wide area network (WAN)Wide area network (WAN): operates over a large : operates over a large geographic area; usually includes computers owned by geographic area; usually includes computers owned by the network user and communications channels owned the network user and communications channels owned by someone else, such as a telephone companyby someone else, such as a telephone company

LAN vs. WAN ComparisonLAN vs. WAN Comparison: LAN transmission speed is : LAN transmission speed is usually greater than WAN, and LAN usually has lower usually greater than WAN, and LAN usually has lower error rates than WANs, due to LAN’s shorter travel error rates than WANs, due to LAN’s shorter travel distance; LANs share more than data, e.g., peripherals, distance; LANs share more than data, e.g., peripherals, programs, processing powerprograms, processing power

Slide 4-3636

Intranet and Extranet CommunicationsIntranet and Extranet Communications

IntranetIntranet: uses Internet technology for private : uses Internet technology for private (internal) business operations; cost of developing (internal) business operations; cost of developing and maintaining these systems is often lower than and maintaining these systems is often lower than for LANsfor LANs

ExtranetExtranet: uses Internet technology for business-: uses Internet technology for business-to-business operations, in which one business has to-business operations, in which one business has access to data located within another business’ access to data located within another business’ intranet; parts of two business’ intranets may be intranet; parts of two business’ intranets may be linkedlinked

Slide 4-3737

Distributed SystemsDistributed Systems

DistributedDistributed: data and programs are spread out : data and programs are spread out over several locations, and computers share the over several locations, and computers share the workloadworkload

Client/server systemClient/server system: distributed system in which : distributed system in which a server (usually a combination of special a server (usually a combination of special hardware and software) provides services to other hardware and software) provides services to other computer(s) called clients; server and client may computer(s) called clients; server and client may both be PCs, and one computer may be a server both be PCs, and one computer may be a server for some activities and a client for other activitiesfor some activities and a client for other activities

Slide 4-3838

Strategic Network IssuesStrategic Network Issues

Planning and implementation issues include:Planning and implementation issues include: ThroughputThroughput, i.e., how much data can be sent in a , i.e., how much data can be sent in a

time periodtime period Response timeResponse time from user request to receipt of from user request to receipt of

responseresponse ConsistencyConsistency in speed and quality of service in speed and quality of service ReliabilityReliability of network system to keep functioning of network system to keep functioning AvailabilityAvailability of network when needed of network when needed

Slide 4-3939

Strategic Network Issues, continuedStrategic Network Issues, continued

SecuritySecurity of data of data FlexibilityFlexibility when changes in network are needed when changes in network are needed Backup/recoveryBackup/recovery provisions in case any computers provisions in case any computers

quit workingquit working EfficiencyEfficiency in use of resources without unnecessary in use of resources without unnecessary

waste, such as in transmission time and storage waste, such as in transmission time and storage spacespace

Slide 4-4040

Communications InfrastructureCommunications Infrastructure

Communications infrastructureCommunications infrastructure refers to the refers to the underlying base of facilities, equipment, software, underlying base of facilities, equipment, software, and services needed to support applications that and services needed to support applications that are dependent on communicationsare dependent on communications

Slide 4-4141

Ubiquitous NetworksUbiquitous Networks

UbiquitousUbiquitous: very widespread: very widespread Data communications networks are found Data communications networks are found

worldwide (“ubiquitous”)worldwide (“ubiquitous”)

Slide 4-4242

slide 4-1 chapter 4 data communications and networking considerations introduction to information...

Documents