simulation of gprs ms-bs interface using ns-network simulator dual degree presentation by richa jain...
TRANSCRIPT
Simulation of GPRS MS-BS Interface
Using ns-Network Simulator
Dual Degree Presentationby
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 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 $n1 1Mb 10ms DropTail
#Nodes themselves don't send/rx data. Create an agent to do soset cbr0 [new Agent/CBR]$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 "$cbr0 stop“$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 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(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
A radio block(RLC PDU)
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3
200bytes
TDMAframes
Transmission over the air interface (in GPRS)
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
Simulations …
• Resource release timer• Scenario• Observations• Inferences
• Interaction of LL/RLC and TCP’s ARQ• GPRS vs GSM capacity analysis
GPRS sim