1. UNIT-V TRAFFIC ANALYSIS

2. Traffic Analysis
Method for determining the cost effectiveness of various sizes and configurations of networks.
Helps us to decide how many telephone trunks we should use to service organizations.
Formulas were used; now, computer modeling is almost exclusively used.

3. Uses of Traffic Engineering
Utilizing the correct number of links at the best price point.
Cost versus effectiveness
What do you engineer to?
The busiest hour?
The average amount of traffic?
The minimum required that will still retain customers?
How are our road systems engineered?

4. Grade of Service GOS – How many callers will be refused service.
This could be a busy tone or a redirection to voice mail.
Telephone companies have designed their networks so that the probability that a circuit will be blocked must be between 1 and 5 percent.
To get a lower blocking percentage than 1 percent gets exponentially more difficult.

5. Traffic Analysis Erlang’s ideas are used extensively in: Data networks
Voice networks
Busy hour traffic on interstates
Banking/Supermarket queuing theory.
General max/min optimization problems

6. Holding Time:
Cellularsystemsuseoneormoreoffourdifferenttechniquesofaccess(TDMA,FDMA,CDMA,SDMA).SeeCellularconcepts.LetacaseofCodeDivisionMultipleAccessbeconsideredfortherelationshipbetweentrafficcapacityandcoverage(areacoveredbycells).CDMAcellularsystemscanallowanincreaseintrafficcapacityattheexpenseofthequalityofservice.
•InTDMA/FDMAcellularradiosystems,FixedChannelAllocation(FCA)isusedtoallocatechannelstocustomers.InFCAthenumberofchannelsinthecellremainsconstantirrespectiveofthenumberofcustomersinthatcell.Thisresultsintrafficcongestionandsomecallsbeinglostwhentrafficgetsheavy.
•AbetterwayofchannelallocationincellularsystemsisDynamicChannelAllocation(DCA)whichissupportedbytheGSM,DCSandothersystems.DCAisabetterwaynotonlyforhandlingburstycelltrafficbutalsoinefficientlyutilisingthecellularradioresources.DCAallowsthenumberofchannelsinacelltovarywiththetrafficload,henceincreasingchannelcapacitywithlittlecosts.Sinceacellisallocatedagroupoffrequencycarriesforeachuser,thisrangeoffrequenciesisthebandwidthofthatcell,BW.IfthatcellcoversanareaAc,andeachuserhasbandwidthBthenthenumberofchannelswillbeBW/B.Thedensityofchannelswillbe.ThisformulashowsthatasthecoverageareaAcisincreased,thechanneldensity

7. Importantparameterslikethecarriertointerference(C/I)ratio,spectralefficiencyandreusedistancedeterminethequalityofserviceofacellularnetwork.ChannelHoldingTimeisanotherparameterthatcanaffectthequalityofserviceinacellularnetwork,henceitisconsideredwhenplanningthenetwork.Itmustbementionedthatitisnotaneasytasktocalculatethechannelholdingtime.(ThisisthetimeaMobileStation(MS)remainsinthesamecellduringacall).ChannelholdingtimeisthereforelessthancallholdingtimeiftheMStravelsmorethanonecellashandoverwilltakeplaceandtheMSrelinquishesthechannel.Practically,itisnotpossibletodetermineexactlythechannelholdingtime.Asaresult,differentmodelsexistsformodellingthechannelholdingtimedistribution.Inindustry,agoodapproximationofthechannelholdingtimeisusuallysufficienttodeterminethenetworktrafficcapability.OneofthepapersinKeyandSmithdefineschannelholdingtimeasbeingequaltotheaverageholdingtimedividedbytheaveragenumberofhandoverspercallplusone.Usuallyanexponentialmodelispreferredtocalculatethechannelholdingtimeforsimplicityinsimulations.Thismodelgivesthedistributionfunctionofchannelholdingtimeanditisanapproximationthatcanbeusedtoobtainestimateschannelholdingtime.Theexponentialmodelmaynotbecorrectlymodellingthechannelholdingtimedistributionasotherpapersmaytrytoprove,butitgivesanapproximation.Channelholdingtimeisnoteasilydeterminedexplicitly,callholdingtimeanduser'smovementshavetobedeterminedinordertoimplicitlygivechannelholdingtime.Themobilityoftheuserandthecellshapeandsizecausethechannelholdingtimetohaveadifferentdistributionfunctiontothatofcallduration(callholdingtime).Thisdifferenceislargeforhighlymobileusersandsmallcellsizes.Sincethechannelholdingtimeandcalldurationrelationshipsareaffectedbymobilityandcellsize,forastationaryMSandlargecellsizes,channelholdingtimeandcalldurationarethesame.

8. Traffic load and cell size
Semakin banyak trafik dibangkitkan, semakin banyak diperlukan base station untuk melayani pelanggan. Jumlah dari base station sederhananya sama dengan jumlah sel,
Bagaimana menambah jumlah pengguna yang dapat dilayani ?
–cel splitting
This simply works by dividing the cells already present into smaller sizes hence increasing the traffic capacity
–Sektorisasi
The cost of equipment can also be cut down by reducing the number of base stations through setting up three neighbouring cells, with the cells serving three 120°sectors with different channel groups.

17. End-to-End principle
Easier to replace and update routers inside the network since fewer requirements to satisfy.
Limiting code to simple tasks reduces likelihood of software/ hardware bugs or algorithmic flaws that bring the network down.
Extending the network is easier.
But inadequate at protecting the networks from attacks

18. What Is Congestion? -1 Data network is a network of queues
Congestion occurs when the number of packets being transmitted through the network approaches the packet handling capacity of the network
Input and Output Queues at a Network Node

19. What Is Congestion? - 2
If the arrival rate is larger than the transmission rate, queues grow to infinity  unresolvable congestion
If the arrival rate is smaller than the transmission rate
queues grow and congestion starts as the arrival rate approaches to the transmission rate (i.e. number of packets being transmitted through the network approaches the packet handling capacity of the network)
Generally 80% utilization is critical
growth in queue = more delay
queues may overflow since it is of finite capacity
Congestion control aims to keep the number of packets below the level at which performance starts to degrade dramatically

20. Effects of Congestion Arriving packets are stored at input buffers
Routing decision made
Packet moves to appropriate output buffer
Packets queued for output are transmitted as fast as possible
If packets
arrive too fast to be processed/ routed, input buffers will fill up
arrive faster than that can be transmitted, output buffers will fill up
Precautions
discard packets
flow control over neighbors