Network Simulator – NS-2

1. Network Simulator – NS-2 JIA-HUI HUANG INSTITUTE OF COMPUTER SCIENCE AND INFORMATION ENGINEERING NATIONAL TAIPEI UNIVERSITY OF TECHNOLOGY 2007.10.15

2. Reference • http://140.116.72.80/~smallko/ns2/ns2.htm • http://www.isi.edu/nsnam/ns/ • Ns document

3. Outline • Introduction • Installation • TCL script • Related tools • New protocol for NS • Examples • Conclusion

4. Introduction • Methods for network research • Analytical • General expression or close form • Mathematical model • Emulation • Real code • Duplicates the functions of one system with a different system • Simulation • Abstract model • Behavior of system

5. Introduction (cont.) • Self-Developed • Without strong persuasion • Simulation frameworks • Commercial • OPNET • QualNet • OMNEST (commercial version of OMNetT++) • Free • NS-2 (network simulator version 2) • OMNetT++

6. Introduction (cont.) • Ns-2 is a discrete event simulator • Scheduler • Advance of time depends on the timing of events • Object-oriented simulator • C++ : fast to run, slower to change – protocol implementation • Otcl : slower to run, fast to change – simulation configuration • Components • Ns – simulator itself • Nam – network animator • Visualize ns (or other) output

7. Introduction (cont.) • Pre-processing • Traffic and topology model • Post-processing • Trace analysis, often in awk, perl, or tcl • Simulation procedure

8. Installation • Platform • Unix • Windows (cygwin) • Packages • Tcl/tk • Otcltclcl • Ns-2 • Nam • Xgraph • C++ compiler • Ns AllInOne package

9. Installation (cont.) • Cygwin, AllInOne installation (windows) • http://140.116.72.80/~smallko/ns2/setup_en.htm • Installation problems • http://www.isi.edu/nsnam/ns/ns-problems.html#general • Cygwin setup • gcc • Ns-2 setup • Path setting • Cygwin/home/user-name/.bashrc • Testing (startxwin.bat) - ~/ns-allinone-x.x/ns-x.x/ns-tutorial/examples

10. TCL script • TCL script for scenario setup • Scenario script format • Simulator object • Trace file • Finish procedure • Network setup (node, link, agent, parameter…) • Other procedure, if any • Event scheduling (run simulation, stop simulation …)

11. TCL script (cont.) • Example topology #Create a simulator object set ns [new Simulator] #Open the nam trace file set nf [open out.nam w] $ns namtrace-all $nf #Define a 'finish' procedure proc finish {} { global ns nf $ns flush-trace #Close the trace file close $nf #Execute nam on the trace file exec nam out.nam & exit 0 }

12. #Create two nodes set n0 [$ns node] set n1 [$ns node] #Create a duplex link between the nodes $ns duplex-link $n0 $n1 1Mb 10ms DropTail #Create a UDP agent and attach it to node n0 set udp0 [new Agent/UDP] $ns attach-agent $n0 $udp0 # Create a CBR traffic source and attach it to udp0 set cbr0 [new Application/Traffic/CBR] $cbr0 set packetSize_ 500 $cbr0 set interval_ 0.005 $cbr0 attach-agent $udp0 #Create a Null agent (a traffic sink) and attach it to node n1 set null0 [new Agent/Null] $ns attach-agent $n1 $null0 #Connect the traffic source with the traffic sink $ns connect $udp0 $null0 #Schedule events for the CBR agent $ns at 0.5 "$cbr0 start" $ns at 4.5 "$cbr0 stop" #Call the finish procedure after 5 seconds of simulation time $ns at 5.0 "finish" #Run the simulation $ns run

13. Related tools • nsBench • Graphical User Interface For NS • Language - java • Features • Nodes, simplex/duplex links and Lans • Agents: TCP, UDP, TCP/Reno, … • Application Traffic: FTP, Telnet, …. • …. • http://www.mnlab.cs.depaul.edu/projects/nsbench/

14. Related tools (cont.) • NSG • Java based ns2 scenario generator • For wireless ad-hoc scenario • Features • wireless node • Connection between nodes • Node movement • http://wushoupong.googlepages.com/ns2scenariosgeneratorchinese

15. Related tools (cont.) • Topology Generator • Georgia Tech Internetwork Topology Models (GT-ITM) • How closely model correlate with real network ? • Transit-Stub model • Transit domain • Interconnect stub domains • Example topology

16. New protocol for ns • Packet type • Structure declaration – packet header • Name binding • Bind packet header to TCL interface • Usage • Routing agent • MANET routing protocol • Agent object • Tcl hook • Important functions

17. Packet type • Packet header #include <packet.h> #define HDR_PROTONAME_PKT(p) hdr_protoname_pkt::access(p) struct hdr_protoname_pkt { …. (define some fields of packet) static int offset_; inline static int& offset() { return offset_ ; } inline static hdr_protoname_pkt* access(const Packet* p) { return (hdr_protoname_pkt*)p->access(offset_); }

18. Packet type (cont.) • Name binding int protoname_pkt::offset_; static class ProtonameHeaderClass : public PacketHeaderClass { public: ProtonameHeaderClass() PacketHeaderClass("PacketHeader/Protoname", sizeof(hdr_protoname_pkt)) { bind_offset(&hdr_protoname_pkt::offset_); } }

19. Packet type (cont.) • Usage Packet* p = allocpkt(); struct hdr_cmn* ch = HDR_CMN(p); struct hdr_ip* ih = HDR_IP(p); struct hdr_protoname_pkt* ph = HDR_PROTONAME_PKT(p); ph->…. ih->…. ch->…

20. Routing agent • Agent object #include <agent.h> …. class NewProtocol : public Agent { protected : … public : NewProtocol(nsaddr_t); int command (int, const char*const*); void recv(Packet*, Handler*); …. }

21. Routing agent (cont.) • Tcl hook • Let NewProtocl to be instantiated from Tcl. static class ProtonameClass : public TclClass { public: ProtonameClass() : TclClass("Agent/Protoname") {} TclObject* create(int argc, const char*const* argv) { assert(argc == 5); return (new Protoname((nsaddr_t)Address::instance().str2addr(argv[4]))); } }

22. Routing agent (cont.) • Important functions • Command() • Operations that we went to make accessible from TCL • maodv-join-group • maodv-leave-group • Example - maodv.cc, MAODV_SimScript.tcl, cbr-5-3-2 • Recv () • Invoked whenever the routing agent receives a packet

23. Needed changes • Needed changes • Packet type declaration - \ns-x.xx\common\packet.h • Tracing support - \ns-x.xx\cmu-trace.h • Tcl library • Tcl\lib\ns-packet.tcl • Tcl\lib\ns-default.tcl • Priority queue - \queue\priqueue.cc • Make file

24. Example1 - TCP slow start • Transport layer protocol • UDP – user datagram protocol (connectionless, unreliable service) • TCP – transmission control protocol (connect-oriented, reliable, with flow and congestion control service) • Connection-oriented – three-way handshaking • Reliable – acknowledgment, retransmission • Flow control – sender won’t buffers by transmitting to much and too fast • Congestion control – to limit the total amount of data entering the internet

25. Example1 - TCP slow start (cont.) • Important variables for congestion control – slow start • cwnd – congestion window • ssthresh – defines threshold between two slow start phase and congestion control phase • Operations – slow start • When connection begins, increase rate exponentially fast until first loss event (slow start phase) • Set ssthresh = cwnd/2 • Set cwnd = 1 and perform slow start process • For cwnd >= ssthresh, increase cwnd linearly (congestion avoidance)

26. Example1 - TCP slow start (cont.) • TCP standards • TCP Tahoe – slow start & congestion avoidance • RFC 2581 • TCP Vegas • TCP Reno • RFC 2581 • TCP NewReno • RFC 2582 • FACK (forward acknowledgement) • SACK (selective acknowledgement) • RFC 2018

27. Example1 - TCP slow start (cont.) • TCP experiment – congestion window • TCP Tahoe • Slow-start • Congestion avoidance Simulation topology Source1 (TCP) n0 Receiver n2 n3 n1 Source2(UDP)

28. Example2 – queuing system • Queuing systems • M/M/1 • M/D/1 • … • Notation • Arrival process/Service time/Servers • M = exponential, D = Deterministic, ….

29. Queuing system – M/M/1 (cont.) • Arrival & departure model • Poisson arrival • Exponential distribution • single server • Parameters • Arrival rate λ • Departure rate (service time) μ • load (stability condition : ρ < 1) • (# of packets in system)

30. Queuing system – M/M/1 (cont.) • queue.tcl • Arrival rate : 30 • Departure rate : 33 • E[Q] = 10

31. Tips • Ns document is not easy to understand • Error message is not very useful • Understand and Implementation • Implementation issues • Iterative design

32. Conclusion • Basic concept of NS2 • Two levels of simulation • Exist modules for NS beginner

33. Internet domain structure Example of Internet domain structure