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Simulation of GPRS MS-BS Interface Using ns -Network Simulator. Dual Degree Presentation by Richa Jain (96D07007) Department of Electrical Engineering, Indian Institute of Technolgy, Mumbai, India. Outline. Introduction to GPRS About ns -Network Simulator Scope of the Project
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Simulation of GPRS MS-BS Interface Using ns-Network Simulator Dual Degree Presentation by Richa Jain (96D07007) Department of Electrical Engineering, Indian Institute of Technolgy, Mumbai, India.
Outline • Introduction to GPRS • About ns-Network Simulator • Scope of the Project • Implementation details • Experiments • Concluding remarks..
The General Packet Radio Service • Packet switched radio transmission • Suited for bursty applications (eg Internet) • Data rates upto 170 kbps • Re-uses GSM resources • Lower call set-up times; cheaper
About ns • Public domain • Event driven simulator • Split language – OTcl and C++ • Nodes and links; routing algorithms; queuing schemes • Protocols – TCP, UDP, IP • Traffic generators – CBR, Exponential, Pareto • Basic mobility support.
A simple ns script set ns [new Simulator] #Creating two nodes set n0 [$ns node]; set n1 [$ns node] #Creating a link btwn the nodes; prop delay=10ms; Drop tail. $ns duplex-link $n0 $n1 1Mb 10ms DropTail #Nodes themselves don't send/rx data. Create an agent to do so set cbr0 [new Agent/CBR] $ns attach-agent $n0 $cbr0 #create sink set 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" $ns at 4.5 "$cbr0 stop“ $ns run
Wireless Features • Mobile node (ad-hoc node) • Air interface • Radio propagation model • Adhoc routing protocols • Mobile IP
Sample script for a wireless simulation # Set up hierarchical routing. # Specify topology. # Create ‘God’ # Create a Base Station $ns_ node-config -adhocRouting 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 $chan_
Sample script for a wireless simulation set BS(0) [$ns_ 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 OFF set 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(0) setdest 200.0 150.0 15.0 : : :
Scope of the project We simulate the network stack for the MS-BS interaction and focus on the handling of radio resources.
GPRS Air interface • TDMA • Uplink-downlink skew of 3 slots • Physical channel = a slot on a frequency. • Logical channels – Broadcast/Control/Data. • Multiplexing logical channels onto physical channels • Transmission bursts
0 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 Transmission over the air interface (in GPRS) 200bytes A radio block (RLC PDU) TDMA frames 0 1 2 3
Features of our GPRS simulator • The Set-up • A single cell • The wireless node now has LL, RLC, MAC for GPRS. • Supports traffic in either direction : MS to BS or BS to MS • BS can transmit/receive on multiple frequencies GPRS sim
Air Interface / Channels • Separate 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 frame • Signaling channel – slot0, on uplink/downlink frequency 0. GPRS sim
Transmission and reception over the air-interface • RLC 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 sim
Signaling for Call Set-Up and Handling • Resource Request Message • from MS to BS • on the Random Access channel (slot0, freq0) • lock IFQ • wait only one TDMA frame for reply • Resource Reply Message • from BS to MS on allotted channel • update vlr_ tables • wait till MS receives reply before transmitting GPRS sim
Signaling…. • Resource Release Message • from MS to BS • on the dedicated slot • clear entries • later requests will be treated on par with fresh requests GPRS sim
Resource Handling • Slot Allocation • first free slot is alloted. • allocation symmetric on uplink and downlink. • Slot Release • MS initiates message on expiry of slot_release_timer. • BS deletes vlr_ entries on receipt of message. • timer value based on experiments. GPRS sim
Dealing with Exceptions • Collisions • happen only on the Random Access channel. • BS drops all colliding requests. • each MS waits one TDMA frame, then backs off for a random interval. • Slot level errors • error model introduced. • users may include/not; user defined rate. • Multiple ARP requests • secondary requests dropped. GPRS sim
Experiments • Studying the average packet delay • Scenario • Observations • Inferences GPRS sim
Simulations … • Resource release timer • Scenario • Observations • Inferences • Interaction of LL/RLC and TCP’s ARQ • GPRS vs GSM capacity analysis GPRS sim
Summarizing …. • 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.