1、Simulation of GPRS MS-BS Interface Using ns-Network SimulatorDual Degree PresentationbyRicha Jain(96D07007)Department of Electrical Engineering,Indian Institute of Technolgy,Mumbai,India.Outline Introduction to GPRSAbout ns-Network SimulatorScope of the ProjectImplementation detailsExperimentsConclu
2、ding remarks.The General Packet Radio ServicePacket switched radio transmission Suited for bursty applications(eg Internet)Data rates upto 170 kbpsRe-uses GSM resourcesLower call set-up times;cheaperGPRS ArchitectureGPRS Protocol StackAbout nsPublic domainEvent driven simulatorSplit language OTcl an
3、d C+Nodes and links;routing algorithms;queuing schemesProtocols TCP,UDP,IPTraffic generators CBR,Exponential,ParetoBasic mobility support.A simple ns scriptset ns new Simulator#Creating two nodesset n0$ns node;set n1$ns node#Creating a link btwn the nodes;prop delay=10ms;Drop tail.$ns duplex-link$n0
4、$n1 1Mb 10ms DropTail#Nodes themselves dont send/rx data.Create an agent to do soset cbr0 new Agent/CBR$ns attach-agent$n0$cbr0#create sinkset null0 new Agent/Null$ns attach-agent$n1$null0#connect the two agents$ns connect$cbr0$null0#Tell cbr0 when to start and stop$ns at 0.5$cbr0 start$ns at 4.5$cb
5、r0 stop“$ns run Wireless FeaturesMobile node(ad-hoc node)Air interfaceRadio propagation modelAdhoc routing protocolsMobile IPStructure of a wireless node in nsSample script for a wireless simulation#Set up hierarchical routing.#Specify topology.#Create God#Create a Base Station$ns_ node-config-adhoc
6、Routing DSR -llType LL -macType 802.11 -ifqType DropTail -ifqLen 100 -antType OmniAntenna -propType TwoRayGround -phyType WirelessPhy -topoInstance$topo -wiredRouting ON -agentTrace ON -routerTrace ON -macTrace ON -movementTrace OFF -channel$chan_ Sample script for a wireless simulationset BS(0)$ns_
7、 node 1.0.0$BS(0)random-motion 0$BS(0)set X_ 1.0$BS(0)set Y_ 2.0#create mobilenodes in the same domain as BS(0)$ns_ node-config-wiredRouting OFFset node_(0)$ns_ node 1.0.1$node_(0)base-station AddrParams addr2id$BS(0)node-addr#create and attach Agents TCP/UDP/CBR :#include movement.$ns_at 10.0“$node
8、(0)setdest 200.0 150.0 15.0 :Scope of the projectWe simulate the network stack for the MS-BS interaction and focus on the handling of radio resources.GPRS Air interfaceTDMAUplink-downlink skew of 3 slotsPhysical channel=a slot on a frequency.Logical channels Broadcast/Control/Data.Multiplexing logic
9、al channels onto physical channelsTransmission burstsA radio block(RLC PDU)01234567012345670123200bytesTDMAframesTransmission over the air interface(in GPRS)Features of our GPRS simulatorThe Set-upA single cellThe wireless node now has LL,RLC,MAC for GPRS.Supports traffic in either direction:MS to B
10、S or BS to MSBS can transmit/receive on multiple frequenciesGPRS simAir Interface/ChannelsSeparate uplink/downlink frequencies.TDMA structure with 8 slots per frame.Uplink-downlink skew of 3 slots.User defined options:-number of frequencies-number of GPRS slots per frameSignaling channel slot0,on up
11、link/downlink frequency 0.GPRS simTransmission and reception over the air-interfaceRLC PDU size set to 50 bytes=50 bytes transmitted per slot.Propagation delay set to 0.Timers model transmission and reception.A radio:switched ON during transmission/reception,OFF otherwise.GPRS simSignaling for Call
12、Set-Up and Handling Resource Request Messagefrom MS to BSon the Random Access channel(slot0,freq0)lock IFQwait only one TDMA frame for reply Resource Reply Messagefrom BS to MS on allotted channelupdate vlr_ tableswait till MS receives reply before transmittingGPRS simSignaling.Resource Release Mess
13、agefrom MS to BSon the dedicated slotclear entrieslater requests will be treated on par with fresh requestsGPRS simResource HandlingSlot Allocation first free slot is alloted.allocation symmetric on uplink and downlink.Slot ReleaseMS initiates message on expiry of slot_release_timer.BS deletes vlr_
14、entries on receipt of message.timer value based on experiments.GPRS simDealing with Exceptions1.Collisions1.happen only on the Random Access channel.2.BS drops all colliding requests.3.each MS waits one TDMA frame,then backs off for a random interval.2.Slot level errors1.error model introduced.2.use
15、rs may include/not;user defined rate.3.Multiple ARP requests1.secondary requests dropped.GPRS simExperimentsStudying the average packet delayScenarioObservationsInferencesGPRS simAverage packet delay for various data ratesGPRS simAverage packet delay for various data ratesGPRS simAverage packet dela
16、y vs data generation ratesGPRS simSimulations Resource release timerScenarioObservationsInferencesInteraction of LL/RLC and TCPs ARQGPRS vs GSM capacity analysisGPRS simSummarizing.A simulator for the GPRS MS-BS interface was developed.Features of the simulator were tested.Experiments on the average packet delay,slot release timer etc were performed.
