Considerthetransferofalargedatafileof1MBytes(1million8-bitcharacters)from stationAtostationBusingpacketswitchingtechnique.
Generating a Policy Proposal
August 7, 2017Lesson plan
August 7, 2017Considerthetransferofalargedatafileof1MBytes(1million8-bitcharacters)from stationAtostationBusingpacketswitchingtechnique.
Question1
(a) Considerthetransferofalargedatafileof1MBytes(1million8-bitcharacters)from stationAtostationBusingpacketswitchingtechnique.ThetwostationsAandBare connectedbyacopperwireof500kmlong.Thedatarateofthelineis1Gbps.The propagationspeedis2x108m/s.Thefileisdividedintoframes,eachofwhichhasa framesizeof2000bitsincluding160 bitsoverhead,before transmitting.StationA
sendsablockof20framesandwaitsforanacknowledgement(100-bit frame)from
StationBbeforesending anotherblock of20frames. Assume error-freetransmission.
(i) Computetheone-waypropagationdelay,thetransmissiontimeforonedata frameandthe transmission time for oneacknowledgement frame.
(5 marks)
(ii) Compute the total elapsed time for sending 20 frames and getting the acknowledgement frame.
(6 marks)
(iii) Computethe totaltime to transmit the entire data file.
(6 marks)
(iv) Compute the effectivethroughputofthesystem.
(3 marks)
(b) Explain TWO situations where datagram packet switching gives a better delay performanceas compared to virtual circuitpacketswitching.
Question2
(a) AnalysethemechanismsprovidedinX.25thathelpstopreventlossandimprovethe throughput of thesendingof data packets.
(5 marks)
(b) Implement a LAN for a company that has 100employees, each has a desktop computerattachedtotheLAN.Recommendasuitabledatarateforthe LANifthe typicaluseoftheLANisasshownbelow.Justifyyouranswersbyworkingoutthe load for each requirement. State any assumption(s) that you have made in your answers.
• Eachemployeeneedstoretrieveafileofaveragesizeof1000,000 bytesper second.Anemployeemaydothisonaverage5timesduringthe8 hours workingtime.
• Eachemployeeneedstoaccesstheinternetat250Kbps.Thiscanhappenfor
10employees simultaneously.
• Each employee may receive 10emails per hour with an average size of
100KB.Half oftheemployees mayreceive emailsimultaneously.
(12 marks)
(c) Discussthedifferencesbetweenastore-and-forwardswitchandacut-throughswitch in terms ofits operations and throughput.
(8 marks)
Question3
(a) IEEE 802.3 and Ethernetuse atechnique known as binaryexponential back-off.
(i) Discuss what binaryexponential back-offis.
(5 marks)
(ii) Assumethatthedatarateis10Mbps. Computeallthepossibledelayvalues after 2ndattempt.
(6 marks)
(b) FigureQ3(b)showsabridgednetworkconsistingoftransparentbridges,BltoB5, interconnecting4EthernetLANs.
FigureQ3(b)
(i) Applythestandardspanningtreealgorithm(STA)toconstructthespanning treeforthenetwork.Inyouranswer,indicateclearlytherootbridge,root ports,designatedbridgesanddesignatedports.Identify thebridges/portsthat shouldbedisabled?AssumethatthebridgenumberindicatesthebridgeID (Blhasa lowerID thanB2andB2lower thanB3etc.) andbridges’priorities areignored forsimplicity.
(l2marks)
(ii) Illustrate the resulted spanningtree.
(2 marks)
Question4
(a) AnorganizationisgrantedtheblockofClassBaddressl78.45.0.0.Theadministrator wants to create 30subnets.
(i) Analyse and designan appropriate subnet addressingscheme.
(5 marks)
(ii) Stateasuitablesubnet mask.
(2 marks)
(iii) Computethenumberofhostsineachsubnet.Excludenetwork(all0s)and broadcast (allls)addresses.
(2 marks)
(iv) Computethe rangeof subnet addresses.Exclude all0s and alllssubnet addresses.
(2 marks)
(iv) Findthefirst(networkaddress)andthelastaddress(broadcastaddress)inthe last subnet.
(4 marks)
(b) ReviewTWOreasons thatIPv6 has overIPv4, besides havingmoreIPaddresses.
(6 marks)
(c) Suppose a TCP sender transmits four TCP segments with respective sequence numbersl000, 2000,3000,and4000.Thesenderreceivesfouracknowledgements with thefollowingsequencenumbers, 2000,2000,2000,and5000.CompleteFigure Q4(c)toshowthesequenceofTCPsegmentsthatare exchangedbetweensenderand receiver.
(4 marks)
FigureQ4(c)
