data communications eighth edition by william stallings chapter 1 – data communications, data...
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Data CommunicationsData Communications
Eighth EditionEighth Edition
by William Stallingsby William Stallings
Chapter 1 – Chapter 1 – Data Communications, Data Communications, Data Networks, and the InternetData Networks, and the Internet
Data Communications, Data Data Communications, Data Networks, and the InternetNetworks, and the Internet
The fundamental problem of The fundamental problem of communication is that of communication is that of reproducing at reproducing at one point either exactly or approximately a one point either exactly or approximately a message selected at another point message selected at another point - - The The Mathematical Theory of CommunicationMathematical Theory of Communication, , Claude ShannonClaude Shannon
Contemporary Data CommsContemporary Data Comms
Trends influenced by:Trends influenced by: traffic growth traffic growth at a high & steady rateat a high & steady rate Requirement / development of Requirement / development of new servicesnew services advances in technologyadvances in technology
significant change in requirements led to:significant change in requirements led to: emergence of high-speed LANsemergence of high-speed LANs corporate WAN needscorporate WAN needs Use of digital electronicsUse of digital electronics
Key Communications TasksKey Communications Tasks
Transmission system utilization Addressing
Interfacing Routing
Signal generation Recovery
Synchronization Message formatting
Exchange management Security
Error detection and correction Network management
Flow control
Transmission MediumTransmission Medium selection is a basic choiceselection is a basic choice
internal use entirely up to businessinternal use entirely up to business long-distance links made by carrierlong-distance links made by carrier
rapid technology advances affects choicerapid technology advances affects choice fiber optic – high capacity, getting cheaperfiber optic – high capacity, getting cheaper Wireless - mobilityWireless - mobility
transmission cost is still transmission cost is still highhigh hence interest in efficiency improvements hence interest in efficiency improvements
– – multiplexingmultiplexing and and compressioncompression
NetworkingNetworking
growth of number & power of computers is growth of number & power of computers is driving need for interconnectiondriving need for interconnection
also seeing rapid integration of voice, also seeing rapid integration of voice, data, image & video technologiesdata, image & video technologies
two broad categories of communications two broad categories of communications networks:networks: Local Area Network (LAN)Local Area Network (LAN) Wide Area Network (WAN)Wide Area Network (WAN)
Wide Area NetworksWide Area Networks span a large geographical areaspan a large geographical area rely in part on common carrier circuitsrely in part on common carrier circuits alternative WAN technologies used alternative WAN technologies used
include:include: circuit switchingcircuit switching packet switchingpacket switching frame relayframe relay Asynchronous Transfer Mode (ATM)Asynchronous Transfer Mode (ATM)
Circuit SwitchingCircuit Switching
uses a dedicated communications path uses a dedicated communications path established for duration of communicationestablished for duration of communication
comprising a sequence of physical linkscomprising a sequence of physical links with a dedicated logical channelwith a dedicated logical channel eg. telephone networkeg. telephone network
Packet SwitchingPacket Switching
data sent out in sequencedata sent out in sequence small chunks (packets) of data at a timesmall chunks (packets) of data at a time packets passed from node to node packets passed from node to node
between source and destinationbetween source and destination used for terminal to computer and used for terminal to computer and
computer to computer communicationscomputer to computer communications
Frame RelayFrame Relay
packet switching systems have large packet switching systems have large overheads to compensate for errorsoverheads to compensate for errors
modern systems are more modern systems are more reliablereliable errors can be caught in end systemerrors can be caught in end system Frame Relay provides higher speedsFrame Relay provides higher speeds with most error control overhead removedwith most error control overhead removed
Asynchronous Transfer ModeAsynchronous Transfer Mode
ATM - evolution of frame relayATM - evolution of frame relay fixed packet (called cell) lengthfixed packet (called cell) length with little overhead for error controlwith little overhead for error control anything from 10Mbps to Gbpsanything from 10Mbps to Gbps constant data rate using packet switching constant data rate using packet switching
technique with multiple virtual circuitstechnique with multiple virtual circuits
Local Area NetworksLocal Area Networks
smaller scopesmaller scope Building or small campusBuilding or small campus
usually owned by same organization as usually owned by same organization as the attached devicesthe attached devices
data rates much higher withindata rates much higher within switched LANs, eg Ethernetswitched LANs, eg Ethernet wireless LANswireless LANs
Metropolitan Area NetworksMetropolitan Area Networks
MANMAN middle ground between LAN and WANmiddle ground between LAN and WAN private or public networkprivate or public network high speedhigh speed large area – city or metrolarge area – city or metro
## In a network with 25 computers, which In a network with 25 computers, which topology would require the least extensive topology would require the least extensive cabling?cabling? MeshMesh StarStar BusBus RingRing## For six devices connected in mesh, how many For six devices connected in mesh, how many
cables are needed? How many ports are cables are needed? How many ports are needed for each device?needed for each device?
## What is the consequence if a connection fails What is the consequence if a connection fails for five devices arranged in:for five devices arranged in:
a) Mesh b) Star (excluding hub) c) Bus d) Ringa) Mesh b) Star (excluding hub) c) Bus d) Ring
The InternetThe Internet
Internet evolved from ARPANETInternet evolved from ARPANET first operational packet networkfirst operational packet network applied to tactical radio & satellite nets alsoapplied to tactical radio & satellite nets also had a need for interoperabilityhad a need for interoperability led to standardized TCP/IP protocolsled to standardized TCP/IP protocols
MCQMCQ The The protocol/medium/signal/all the above protocol/medium/signal/all the above is is
the physical path over which message travels.the physical path over which message travels. The information to be communicated in a data The information to be communicated in a data
communications system is the communications system is the medium/protocol/message/transmission.medium/protocol/message/transmission.
Frequency of failure and network recovery Frequency of failure and network recovery time after a failure are measures of the time after a failure are measures of the performance/reliability/security/feasibilityperformance/reliability/security/feasibility of a of a network.network.