Date : 2010/11/23Speaker : Chia-Wen Lu

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Network SimulationIntroduction to NS2Simple Simulation Example

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Network SimulationIntroduction to NS2Simple Simulation Example

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Suppose you devise a great protocol. How do you show that it’s great?

- Experiment

- Mathematical model - graph theory

- Simulation - programming (e.g., C++ or NS2)

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advantage disadvantageExperiment •realistic •expensive

•sometime not possible

Mathematical model

•insight •assumptions

Simulation •easy (cheap)•verification

•not much insight•assumptions

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Platform: - hardware , software, or hybrid Developer: - commercial or in-house Source code: - open or close Paradigm: - time-dependent/non-time-dependent; time-driven/event-driven

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simulation performance

- execution speed

- scalability

- fidelity

- cost Network Layer

- free: NS2, GloMoSim

- commercial: Opnet , QualNet7

Network SimulationIntroduction to NS2Simple Simulation Example

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Network Simulator (Version 2)

- widely known as NS2

- event driven simulation tool

- wired / wireless network, protocols

(e.g. routing algorithms, TCP, UDP)

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Events a, b, and c are executed in order

- example program 1 initialize {system states} 2 initialize {list of events} 3 while {state != finalState} % or while {this.event != Null} 4 expunge the previous event from list of events; 5 set SimClock := time of current event; 6 execute this.event 7 end while

Run by a set of events (schedule list)

Time gap between two events is not fixed

Simulation advance from one event to another

Event may induce one or more events

new event is usually inserted into the list

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Gathering information right after every event execution Simulation finishes

- at a pre-specified time

- when there is no more event

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Point-to-point wired communication link

- a one-way communication

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Arrival: - a packet arrival eventComplete: - a successful packet transmission event

Packet Servicetime

Arrivaltime

Completetime

P1 3 0 3

P2 2 2 5

P3 1 4 6

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P1 0

P2 2

P3 4

P1 3

P2 5

P3 6

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two key languages C++

- defines the internal mechanism of the simulation Objects

Otcl (Object-oriented Tool Command Language ) - sets up simulation scenarios

Linked together using TclCL

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Two language architecture: C++ and OTcl C++

- compiler - fast to run (run on machine codes) - slow to change (need compilation)

OTcl - interpreter - slow to run; fast to change

Why two languages? C++ coding styles

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Compile and create “prog.exe” - recompile for every minor changes (e.g., number of nodes, link speed)

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C++ coding with input arguments - use parameters input argument - e.g., “prog <num_node> <link_speed>” - what if there are too many parameters?

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C++ coding with input files - put input parameters in a configuration file - no need to change C++ code - one input argument—the filename - NS2 style!! - configuration file is called “Tcl Simulation script”

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Start from Tcl simulation script For each line: - execution path: Tcl -> Otcl -> C++ - returning path: C++ -> OTcl -> Tcl (next line)

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Network SimulationIntroduction to NS2Simple Simulation Example

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4 nodes : n0, n1, n2, n3

n0 and n2 =>2 Mbps 頻寬 ,10 ms 傳遞延遲時間 n1 and n2 =>2 Mbps 頻寬 ,10 ms 傳遞延遲時間

n2 and n3 =>1.7 Mbps 頻寬 ,20 ms 傳遞延遲時間

FTP session is based on TCP

CBR session is based on UDP

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# 產生一個模擬的物件set ns [new Simulator]#產生傳輸節點 (n0,n1)set n0 [$ns node]set n1 [$ns node]#產生路由器節點 (n2)set n2 [$ns node]#產生資料接收節點 (n3)set n3 [$ns node]

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#n0-n2 ,2Mbps 頻寬 ,10ms 傳遞延遲時間$ns duplex-link $n0 $n2 2Mb 10ms DropTail

#n1-n2,2Mbps 頻寬 ,10ms 傳遞延遲時間$ns duplex-link $n1 $n2 2Mb 10ms DropTail

#n2-n3, 1.7Mbps 頻寬 ,20ms 傳遞延遲時間$ns duplex-link $n2 $n3 1.7Mb 20ms DropTail

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# 建立 UDP 連線 (n1 到 n3)

set udp [new Agent/mUDP]$ns attach-agent $n1 $udpset null [new Agent/mUdpSink]$ns attach-agent $n3 $null$ns connect $udp $null

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# 在 UDP 連線之上建立 CBR 應用程式

set cbr [new Application/Traffic/CBR]$cbr attach-agent $udp$cbr set type_ CBR

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# 設定 FTP 和 CBR 資料傳送開始和結束時間

$ns at 0.1 "$cbr start"$ns at 1.0 "$ftp start"$ns at 4.0 "$ftp stop"$ns at 4.5 "$cbr stop"

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# 執行模擬$ns run

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Introduction to Network Simulator NS2 by T. Issariyakul and E. Hossain.

http://www.ns2ultimate.com/ http://www.ece.ubc.ca/~teerawat/NS2.htm

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Q & A

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