Network Simulator - ns2

1. ECE 6610 Sandeep Kakumanu GNAN research Lab Network Simulator - ns2

2. Announcements • T-Square wiki is up: Go to https://t-square.gatech.edu/portal Login with your prism ID. Select ECE6610 tab. Use wiki to post questions on class/assignments/ns2/others. • Groups have been formed. • Assignment 1 has been posted.

3. Outline • Discrete event Simulations • ns-2 architecture • Working with Tcl • Working with C++ • Important files • Trace analysis • Miscellaneous • Assignment 1 overview

4. Classification of simulation paradigms Computer simulation Discrete models Continuous time models event driven time-stepped

5. Discrete event simulations: • As-fast-as-possible execution of simulation as opposed to scaled real-time simulation. • Event based scheduling. • A single queue of events. • Each event has a time stamp. Chronological execution of events. • An event might create more events. These new events are inserted into the queue.

6. Ns-2: Introduction • NS-2: network simulator version 2 • Discrete event simulator • Packet level simulation • Features • Open source • Scheduling, routing and congestion control • Wired networks: P2P links, LAN • Wireless networks: terrestrial (ad-hoc, cellular; GPRS, UMTS, WLAN, Bluetooth), satellite • Emulation and trace

7. Ns-2 Paradigm • Object-oriented programming • Protocol layering • Modularity and extensibility • Large scale simulation • Maintenance and reusability • Split-language programming • Scripting language (Tcl) • System programming language (C++)

8. Ns-2: Split Languages • Tcl scripts (Tcl/OTcl) • Interpreted (interactive) • Setup and configuration • C codes (C/C++) • Compiled (efficient) • Algorithms and protocols • TclCL (OTcl/C++) • Link Tcl/OTcl scripts and C/C++ codes • Provide a layer of C++ glue over OTcl

9. NS-2: Split Objects OTcl/C++ split objects Pure C++ objects Pure OTcl objects TclCL linkage OTcl C++ NS-2

10. NS-2: Directory Structure ns-allinone ... Tcl8 TK8 OTcl TclCL ns-2 nam-1 C++ code ... tcl ex test mcast lib ... examples validation tests OTcl code

11. Structure of a wired node

12. Structure of a wired simplex link

13. A wired LAN

14. A wireless node

15. Setting up ns-2 • Requirements: Linux box with at least 500 MB free space. • Download the latest ns-allinone-2.33.tar.gz from the ns-2 website (google ns-2). • Untar the archive: > tar –xvfz ns-allinone-2.33.tar.gz • Install: > cd ns-allinone-2.33 > ./install • Setup the environment variables in the bash or csh script. • Close xterm and open again. • ns-2 should work now.

16. Setting the environment variables • Bash: $ vi .bashrc export PATH=$PATH:/path_to_ns-allinone-2.33/bin:/path_to_ns-allinone-etc/ export LD_LIBRARY_PATH=$PATH:/path_to_ns-allinone…etc/ export TCL_LIBRARY=$PATH:/path_to_ns-allinone…etc/ • Csh: > vi .cshrc setenv PATH /path_to_ns-allinone-2.33/bin:/path_to_ns-allinone-etc/:$PATH

17. Working with tcl • Tcl is the front-end in ns-2. • Define node configurations, node topology, agents etc. • Agents can be UDP/TCP, CBR/FTP/VBR/Webtraffic/... • For wired nodes: setup links, define link delays, link errors, define LAN configurations, buffer sizes... • For wireless nodes: node positions, node mobility, chose from different MAC, routing protocols. • Simple procedures for printing aggregated results like total throughput, total simulation time etc.

18. Working with tcl (cont'd) • A command consists of words cmdName arg1 arg2 … • cmdName: core command or procedure • set, puts, expr, open, if, for, … • All words are considered as strings • White space (space/tab) separates arguments • Newline or semicolon (;) terminates a command • Command evaluation: parsing and execution • The interpreter does “substitution” and “grouping” (parsing) before running a command • Every command returns a result string after execution

19. Basic Tcl commands: • puts - tcl equivalent of printf • Ex – puts $a; #will print the value of a • set – set value to variable • Ex – set a 3; #set value of a=3 • expr – evaluate a mathematical expression • Ex – expr $a+2 ; #add 2 to a. • Complex groupings: • set rate [expr 5*$a]; #compute a*5 and set to rate

20. Tcl: procedures • Procedures are like functions in C. • Variables defined outside a procedure are invisible inside it. Global variables are visible everywhere. • Variable length of arguments using args. • Examples proc add args { set s 0 foreach i $args {incr s $i} return $s } proc inc {var {dv 1}} { set a [expr $var+$dv] return $a }

21. Tcl Core commands • Control flow • if, switch, while, for, foreach • File access • open, close, flush, puts, gets • String manipulation • glob-style and regular expression • List manipulation • llength, lindex, linsert, lreplace • lappend

22. A simple tcl script set ns [new Simulator] set nf [open out.tr w];$ns trace-all $nf for {set i 0} {$i<2} {incr i} { ;# create the nodes set n($i) [$ns node]} $ns duplex-link $n(0) $n(1) 1Mb 10ms DropTail set udp(0) [new Agent/UDP] # Create a UDP agent $ns attach-agent $n(0) $udp(0)set null0 [new Agent/LossMonitor]$ns attach-agent $n(1) $null0set cbr(0) [new Application/Traffic/CBR]$cbr(0) set packetSize_500$cbr(0) set rate_ 100kb$cbr(0) attach-agent $udp(0)$ns connect $udp(0) $null0$ns at 0.0 "$cbr(0) start"$ns at 10.0 "$cbr(0) stop" proc finish {} { global ns nf $ns flush-trace; close $nf } $ns at 10.0 "finish" $ns run

23. Working with C++ • All protocols are written in C++. • Everything is an object. Otcl will attach the necessary C++ objects. • All objects are inherited from tclclass. • Every object has atleast one header (.h) file and one .cc file. • Different objects talk to each other using packets. • Every object has a recv() function which receives a packet, and has pointers to all the other attached objects known as targets (uptarget_, downtarget_ etc).

24. Packet • Packets are events • Can be scheduled to “arrive” • Packets contain header section and data • Header section is a cascade of all in-use headers • Each packet contains a common header • packet size (used to compute transmission time) • packet type • timestamp, uid, … • All in-use headers are included when simulation starts • Change packet size to reflect header cascading

25. Important files • packet.h – defines all the headers for packets. • scheduler.h,.cc – the C++ scheduler class. • agent.h,.cc – the base class for all agents. • tcp.h,.cc – TCP, udp.h,.cc – UDP, cbr_traffic.cc – cbr traffic, mac-802_11.h,.cc – 802.11 MAC. • tcl/lib/ns-defaults.tcl – All the default parameters for configurations of the various protocols. • tcl/lib/ns-lib.tcl – Otcl script connecting the various layers of the network stack in a single node.

26. Modifying C++ files • Modify existing C++ files. • C++ files are inside /path/ns-allinone-2.33/ns-2.33 directory. • The directory also has a Makefile. • When you edit only a .cc file: $ make • When you edit a .h file: $ make clean $ make

27. Traces • Ns-2 simulations provide a number of traces. • A trace file is used for post-processing of the simulation and find out what events happened at different times of the simulation. • Traces for wired and wireless simulations have different format. • Traces are text files. • Trace formats at: http://nsnam.isi.edu/nsnam/index.php/NS-2_Trace_Formats • Different ways to parse the traces – C, awk, perl... Use anyone in which you are comfortable.

28. Sample trace + 0.0008 0 1 cbr 1000 ------- 0 0.0 2.0 1 1- 0.0008 0 1 cbr 1000 ------- 0 0.0 2.0 1 1+ 0.0016 0 1 cbr 1000 ------- 0 0.0 2.0 2 2- 0.0016 0 1 cbr 1000 ------- 0 0.0 2.0 2 2+ 0.0024 0 1 cbr 1000 ------- 0 0.0 2.0 3 3- 0.0024 0 1 cbr 1000 ------- 0 0.0 2.0 3 3r 0.0028 0 1 cbr 1000 ------- 0 0.0 2.0 0 0+ 0.0028 1 2 cbr 1000 ------- 0 0.0 2.0 0 0- 0.0028 1 2 cbr 1000 ------- 0 0.0 2.0 0 0+ 0.0032 0 1 cbr 1000 ------- 0 0.0 2.0 4 4- 0.0032 0 1 cbr 1000 ------- 0 0.0 2.0 4 4r 0.0036 0 1 cbr 1000 ------- 0 0.0 2.0 1 1+ 0.0036 1 2 cbr 1000 ------- 0 0.0 2.0 1 1- 0.0036 1 2 cbr 1000 ------- 0 0.0 2.0 1 1+ 0.004 0 1 cbr 1000 ------- 0 0.0 2.0 5 5

29. Miscellaneous utlities • nam – Network animator: Used to animate the network events after the simulation has finished. nam will parse a name trace and show the animation. • cbrgen – create traffic patterns. • setdest – generate wireless topologies and set up mobility patterns using random waypoint model.

30. More help • Marc Greis tutorial (Chapters I-VI & VIII-XI). • ns-2 manual. • ns-2 mailing list. • T-square wiki.

31. Puzzle • Are there two dogs in world with the same number of hairs ? (Make reasonable assumptions)