CprE 543x – ns-2 Tutorial Zak Abichar, Dept of Electrical and Computer Engineering Iowa State University Ames, IA Based on a presentation by Polly Huang (2 nd European ns-2 Workshop, April 2001)

2 Tutorial Goals overview/intro/essentials/getting started tcl/otcl/ns-2 fundamentals designing a simulation examples

3 Outline Introduction –The project, the software, the philosophy –Software architecture –Installation and getting started –About extending ns-2 tcl/otcl/ns-2 fundamentals –Programming tcl/otcl Running a ns-2 simulation –Simulation design –Example scripts

4 The VINT Project Virtual InterNet Testbed –a common platform for network research –focus on multi-protocol interactions and scale – Follow-up projects –SAMAN: scenario and performance –CONSER: educational use

5 Multi-state collaboration AT&T Research Lawrence Berkeley National Laboratory UC Berkeley USC/ISI Xerox PARC ETH TIK (Swiss Federal Institute of Technology)

6 Project Goal To support collaborative simulation effort –promote sharing incorporate recent simulation models –increase confidence in results establish regression test suite –establish common reference current and periodic availability of source code Base software is ns-2

7 ns-2 Discrete event simulator Packet level Link layer and up Wired and wireless

8 Development Status Columbia NEST UCB REAL ns-1 ns-2 –100K lines of C++ code –70K lines of otcl support code –30K lines of test suites –20K lines of documentation

9 Usage and Releases Users from approximately –600 institutes –50 countries Releases –periodic official releases –nightly snapshots (probably compiles and works, but buyers beware) –available from USC/ISI or UK mirror

10 Platforms Most UNIX and UNIX-like systems  FreeBSD or *BSD  Linux  Sun Solaris  HP, SGI Window 95/98/NT... Emulation only for FreeBSD for now

11 Words of Caution While we have considerable confidence in ns, ns is not a polished and finished product, but the result of an ongoing effort of research and development. In particular, bugs in the software are still being discovered and corrected. Users of ns are responsible for verifying for themselves that their simulations are not invalidated by bugs.

12 Preliminary for NS-2 Ability to write correct programs Familiarity with object-oriented programming Patience to debug NS source code when needed –Simple usage will not need NS source code debugging –More complex simulations may need modification to NS source code Debugging skills –NS uses C++ and Otcl –User scripts are in Otcl

13 What you can do using NS-2 Simulate different scenarios with existing protocols (TCP/UDP) Wired Routing protocols - Distance Vector and Link State (with the link state patch) Ad-Hoc Routing protocols - DSR, AODV, TORA MAC protocols , (Wireless MAC) Scheduling disciplines - DropTail, RED, WFQ, DRR, LQD etc. Different traffic characterizations - Poisson, Exponential, Pareto etc.

14 What you can do using NS-2 Modify NS-2 to implement your own versions of the above protocols or even code totally new protocols Measurement of Statistics: –Throughput, Delay, Jitter etc. –Queue Monitoring, Drops at Queues. –Literally all that you will need to know with your simulations. Graphic visualization - using “nam” (Network Animator)

15 The downside Cannot capture all the nuances of the real world networks. Very large scale simulations take a lot of time – they may not be feasible Still in the research phase, and there may be many more bugs lurking out there Documentation not adequate No fancy user interface – often perceived as “unfriendly” (at least by people who are new to ns-2)

16 Outline Introduction –The project, the software, the philosophy –Software architecture –Installation and getting started –About extending ns-2 tcl/otcl/ns-2 fundamentals –Programming tcl/otcl Running a ns-2 simulation –Simulation design –Example scripts

17 Object-Oriented +Reusability +Maintainability –Careful planning ahead –Performance

18 C++ and otcl Separation C++ for data –per packet action otcl for control –periodic or triggered action +Compromize between composibility and speed –Learning & debugging

19 otcl and C++: The Duality C++ otcl

20 tcl Interpreter With Extents otcl: Object-oriented support tclcl: C++ and otcl linkage Discrete event scheduler Data network components tcl8.0 otcl tclcl ns-2 Event Scheduler Network Component

21 Installation Getting the code: – Installing ns-2 –

22 About extending ns-2 Implement new functionalities not covered in ns-2 –Essential for researchers –Implementing and evaluating new protocols and schemes Requires the understanding of the internal architecture –Not that hard Need more information?

23 Outline Introduction –The project, the software, the philosophy –Software architecture –Installation and getting started –About extending ns-2 tcl/otcl/ns-2 fundamentals –Programming tcl/otcl Running a ns-2 simulation –Simulation design –Example scripts

24 Hello World simple.tcl set ns [new Simulator] $ns at 1 “puts \“Hello World!\”” $ns at 1.5 “exit” $ns run % ns simple.tcl Hello World! %

25 Fundamentals tcl otcl –ftp://ftp.tns.lcs.mit.edu/pub/otcl/doc/tutorial.html ns-2 – – –

26 Basic tcl proc test {} { set a 43 set b 27 set c [expr $a + $b] set d [expr [expr $a - $b] * $c] for {set k 0} {$k < 10} {incr k} { if {$k < 5} { puts “k < 5, pow= [expr pow($d, $k)]” } else { puts “k >= 5, mod= [expr $d % $k]” } } } test k < 5, pow = 1.0 k < 5, pow = k < 5, pow = k < 5, pow = k < 5, pow = k > 5, mod = 0 k > 5, mod = 4 k > 5, mod = 0 k > 5, mod = 4

27 Basic otcl Class mom mom instproc init {age} { $self instvar age_ set age_ $age } mom instproc greet {} { $self instvar age_ puts “$age_ years old mom: How are you doing?” } Class kid -superclass mom kid instproc greet {} { $self instvar age_ puts “$age_ years old kid: What’s up, dude?” } set a [new mom 34] set b [new kid 6] $a greet $b greet 34 years old mom: How are you doing? 6 years old kid: What's up?

28 Outline Introduction –The project, the software, the philosophy –Software architecture –Installation and getting started –About extending ns-2 tcl/otcl/ns-2 fundamentals –Programming tcl/otcl Running a ns-2 simulation –Simulation design –Example scripts

29 NS input & output

30 Running a Simulation Design your simulation Build NS-2 scripts Run simulation program Analyze trace files Visualize your simulation (Animation)

31 Design your simulation Goal and expected results Network topology –Node –Link Specify Agents –Protocol Traffic Simulation Scenario

32 A simulation example

33 A TCL script example set ns [new Simulator] set n0 [$ns node] set n1 [$ns node] n0n1 set ftp [new Application/FTP] $ftp attach-agent $tcp $ns at 0.2 "$ftp start" $ns at 1.2 ”exit" $ns run $ns duplex-link $n0 $n1 1.5Mb 10ms DropTail set tcp [$ns create-connection TCP $n0 TCPSink $n1 0] Network Topology Transport Protocol Traffic Generation

34 Run simulation program Usage: ns file.tcl If the C++ source codes are modified, re-compilation is required What ns-2 does: –Read the tcl file –Run the simulation program –Create trace files –NAM (network animator) input files –Statistics (you may need to write post processing scripts)

35 Analyze trace file Use some scripts like awk or Perl, to filter the trace file Use Excel, xplot or xgraph to plot the results

36 Raw trace file tcp tcp r tcp tcp tcp r tcp ack ack r ack ack ack r ack tcp tcp

37 Open trace.out in Excel

38 Plot results in Excel

39 Outline Introduction –The project, the software, the philosophy –Software architecture –Installation and getting started –About extending ns-2 tcl/otcl/ns-2 fundamentals –Programming tcl/otcl Running a ns-2 simulation –Simulation design –Example scripts

40 A Simulation Example

41 TCL Script Step 1 #Create a simulator object set ns [new Simulator] #Open the NAM trace file set nf [open out.nam w] $ns namtrace-all $nf #Open the general trace file Set f [open out.tr w] $ns trace-all $f # has denotes a one line comment ns holds the name of the new simulation

42 TCL Script Step 2 #Create four nodes set n0 [$ns node] set n1 [$ns node] set n2 [$ns node] set n3 [$ns node] #Create links between the nodes $ns duplex-link $n0 $n2 2Mb 10ms DropTail $ns duplex-link $n1 $n2 2Mb 10ms DropTail $ns duplex-link $n2 $n3 1.7Mb 20ms DropTail

43 TCL Script Step 3 # Set Queue Size of link (n2-n3) to 10 $ns queue-limit $n2 $n3 10 #Setup a TCP connection set tcp [new Agent/TCP] $ns attach-agent $n0 $tcp set sink [new Agent/TCPSink] $ns attach-agent $n3 $sink $ns connect $tcp $sink #Setup a FTP over TCP connection set ftp [new Application/FTP] $ftp attach-agent $tcp

44 TCL Script Step 4 #Setup a UDP connection set udp [new Agent/UDP] $ns attach-agent $n1 $udp set null [new Agent/Null] $ns attach-agent $n3 $null $ns connect $udp $null #Setup a CBR over UDP connection set cbr [new Application/Traffic/CBR] $cbr attach-agent $udp $cbr set packet_size_ 1000 $cbr set rate_ 1mb

45 TCL Script Step 5 #Schedule events for the CBR and FTP agents $ns at 0.1 "$cbr start" $ns at 1.0 "$ftp start" $ns at 4.0 "$ftp stop" $ns at 4.5 "$cbr stop" #Call the finish procedure after 5 seconds of simulation time $ns at 5.0 "finish"

46 TCL Script Step 6 #Define a 'finish' procedure proc finish {} { global ns nf $ns flush-trace #Close the NAM trace file close $nf #Execute NAM on the trace file exec nam out.nam & exit 0 } #Run the simulation $ns run