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Marco Di Felice

Network Modeling and Simulation with Network Simulator 2 ( ns2 ). Marco Di Felice. Department of Computer Science and Engineering University of Bologna. Italy difelice@cs.unibo.it. NS2 : Architecture and Design. NS2 : Use Cases and Features. NS2 : Building simple network models.

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Marco Di Felice

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  1. Network Modeling and Simulation with Network Simulator 2 (ns2) Marco Di Felice Department of Computer Science and Engineering University of Bologna. Italy difelice@cs.unibo.it

  2. NS2: Architecture and Design NS2: Use Cases and Features NS2: Building simple network models NS2: Demo & Analysis Outline

  3. Ns2: An Overview NS2: A (discrete event) networksimulatortool. Generallyspeaking, a network simulator is a dedicated softwarethatallows to: • Modelthe behaviour of network protocols/applications(e.g. TCP protocol). • Reproducethe behaviour of a computer networkas a whole(e.g. a wireless LAN). • Quantifythe network performance, throughwell-definednetwork metrics(e.g. systemthroughput).

  4. Ns2: WHAT Q.Whenmay I use a network simulator? Case 1: Network planning • Need to build a network infrastructure, with coverage and Quality of Service (QoS) issues. Q1. Where to place the network gateways? Q2. How many gateways do I really need?

  5. Ns2: WHAT Q.Whenmay I use a network simulator? Case 2: Network Evaluation An example: Early Collision Detection Systems In VANETs • Need to evaluate the performance of a (possibly large-scale) network infrastructure or network application. • Use an existing testbed  BUT … Q1. What is the cost of setting up the experiments? Q2. Are the experiments easily reproducible?

  6. Ns2: WHAT Q.Whenmay I use a network simulator? Case 3: Researchon NetworkingSystems • Need to evaluate the performance of a new network protocol, architecture, or application. An example: Proposing a new TCP variant for wireless LANs. 1. A real deployment might not be feasible, or might be too costly. 2. Analytical models might be too complex to model all the components of the scenario under study.

  7. Ns2: WHAT • Network simulators might be used to model several kinds of networkingsystems (wired, wireless, optical, etc). • In practice, simulationconstitutes the main evaluation technique for wirelesssystems. • Possibility to build reproducible experiments (hard to guarantee with wireless testbeds). • Possibility to reproduce wireless propagation phenomena in an accurate way through probabilistic models (e.g. fading) • Possibility to model large-scale wireless networks composed by several interacting nodes.

  8. Ns2: WHAT • Simulation is a meaningful evaluation approach only when it produces “trustable” results. • Validation is needed to certify that the simulation models reproduce correctly the characteristics and dynamics of the system under study. • HOW to VALIDATE a NETWORK MODEL? • Compare Simulation vs AnalyticalModel • Compare Simulation vs RealMeasurements SIM. THROUGPUT EXPERIMENTS ANALYTICAL

  9. Ns2: WHAT • NS2: A network simulation tool • Discrete Eventsimulator(details later …) • NS2 allows to model and evaluate several IP networking systems(LAN/WAN). It includes: • Network protocols model(e.g. MAC, routing, …) • Network applications model (e.g. CBR, FTP, …) • Queue management algorithms (e.g. FIFO, RED, …) • Network link models (e.g. lossy link) • …

  10. Ns2: WHERE • http://www.isi.edu/nsnam/ns • http://sourceforge.net/projects/nsnam • download ns-allinone • includes several tools (ns2, nam, awk, otcl, …) • mailing list: ns-users@isi.edu • documentation: • Referencemanual and Tutorials on the website • Other tutorials on the Web

  11. Ns2: WHEN • The project started from REAL project in 1989 • ns-1 by Floyd and McCanne at Lawrance Berkeley National Laboratory (LBNL). • ns-2 by Steve McCanne, within the VINT project involving a consortium of US universities (LBL, PARC,USC, ...) • currently maintained at USC/ISI (University of Southern California), but several forks available. • NS3 relased in 2008 (now NS3.15) • Deployed by a team lead by Tom Henderson and Sally Floyd (University of Washington) • A completely new tool, not a mere extension of Ns2 !

  12. Ns2: WHY • NS2: A network simulation tool • Discrete Eventsimulator(details later …) OTHER SIMULATION TOOLS • OMNET++ • OPNET • JiST • NS3 • GLOMOSIM • … Q. WHY should I use NS2 for my research?

  13. Ns2: WHY • NS2 includes a vast modellibraryof network components. • Link Models: • Wired Links, • Wireless Links, • Satellite Links, … ApplicationLayer FTP, Telnet, HTTP, Multimedia, Exponential traffic, … TransportLayer UDP, TCP (Reno, NewReno, Vegas, SACK), … NetworkLayer Wired routing (RIP), Ad Hoc Routing (AODV, OLSR, DSR), … MACLayer Ethernet, 802.11 (WIFI), 802.15.4, Bluetooth, 802.16 (WIMAX), …

  14. Ns2: WHY • NS2 is distributed with GNU General Public Licence (GPL) • Collaborative deployment environment • possibility to freely modify the existing NS2 code based on each user’s needs. • possibility to share network models for research/education purposes (e.g. a new implementation of TCP). • possibility to compare his/her own model with models implemented by other research teams. • Multi-platform support • GNU/Linux, MAC OSX, Solaris, Windows, …

  15. Ns2: WHY • NS2 is a popular tool, widely adopted by researchers working on the field of computer networks. NumberofUsers: 10K Institutes: 1K % Papers: 44.4% MOBIHOC Conference: Statistics on toolsused to produce a simulationstudywithin the paperssubmittedat the ACM MOBIHOC conference (2000-2006).

  16. Ns2: WHY Q. WHYNOT to use NS2 for my research? • Performanceissues • Monolithic (basic) scheduler, scalability constitutes a big issue. • Architecturalissues • Not really a modular architecture, difficult to share the code of network models. • Evaluationissues • No support for the trace analysis. CPU time ? #nodes NS2 TRACE

  17. NS2: HOW • Two programming languages: C++ and OTCL. • OTCL for simulation setup and execution • Quickly define the simulation environment • C++ for model deployment • Implement the behaviour of a network component

  18. NS2: HOW • The core of the NS2 simulator is the Scheduler • Discrete-event scheduler. • Basic implementation, few optimization. Event in NS2 ID TYPE TIME HANDLER Packet sent NS2 Object + function name that should be invoked once the event is fired. Packet Events Timer Events Packet received Packet dropped Simulation time of the event

  19. NS2: HOW • The Scheduler manages the simulation event list. • The elements are the events of the simulation. • The list is ordered on the basis of the time field. E1 E2 E3 E4 E5 E6 SIMULATION TIME: t SIMULATION TIME: E1.time • At each simulation step: • The head element of the list is removed • The simulation time is set to E1.time • The eventhandler (E1.handler) is executed. 1 TYPE TIME HANDLER

  20. NS2: HOW • The Scheduler manages the simulation event list. • The elements are the events of the simulation. • The list is ordered on the basis of the time field. E2 E3 E4 E5 E6 E7 SIMULATION TIME: t SIMULATION TIME: E1.time • At each simulation step: • E1.handler is executed, and it might generate new events (e.g. E7), that are inserted into the event list (at a position denoted by E7.time) E1.HANDLER

  21. NS2: HOW • Let’s make an example on a network scenario … NODE A NODE B APPLICATION APPLICATION MAC MAC ETHERNET LINK SIMULATION TIME: 0 EVENT LIST • At t=0, the Application module of node A is invoked

  22. NS2: HOW • Let’s make an example on a network scenario … NODE A NODE B APPLICATION APPLICATION MAC MAC ETHERNET LINK SIMULATION TIME: 0 E1 EVENT LIST 1 Send 4 A.APPLICATION • A timer event is scheduled at time 4 by node A

  23. NS2: HOW • Let’s make an example on a network scenario … NODE A NODE B APPLICATION APPLICATION MAC MAC ETHERNET LINK SIMULATION TIME: 4 E2 E3 EVENT LIST 2 Recv 4.5 A.MAC 3 Send 8 A.APPLICATION

  24. NS2: HOW • Let’s make an example on a network scenario … NODE A NODE B APPLICATION APPLICATION MAC MAC ETHERNET LINK SIMULATION TIME: 4.5 E4 E3 EVENT LIST 4 Recv 5.0 B.MAC 3 Send 8 A.APPLICATION

  25. NS2: HOW • Let’s make an example on a network scenario … NODE A NODE B APPLICATION APPLICATION MAC MAC ETHERNET LINK SIMULATION TIME: 5 E5 E3 EVENT LIST 5 Recv 5.2 B.APPLICATION 3 Send 8 A.APPLICATION

  26. NS2: HOW • Let’s make an example on a network scenario … NODE A NODE B APPLICATION APPLICATION MAC MAC ETHERNET LINK SIMULATION TIME: 5.2 E3 EVENT LIST 3 Send 8 A.APPLICATION • The message is processed by Node B at time 5.2

  27. Ns2: HOW • Two ways of interactions: • Modify/Create a new network model • Network models: network protocols, applications, queue policies, network architecture models, etc. • Coding in C++ • Recompile at the end. • Configure/Run a network simulation • Coding in OTCL • Executed by an interpreter, no need to recompile. NOT EASY QUITE EASY

  28. Ns2: HOW • Running an OTCL script: • ns script-file.tcl [parameters] • Initialize the scheduler • Define the simulation parameters (e.g. start time) • Build the network topology • Generate the traffic load • Define the protocol stack used by each node • OTCL scripting language, OO-extension of TCL 

  29. Ns2: OTCL inside • Assign a value to a variable • set x 0 • Keyword $ returns the value of a variable • set y $x • Selection Statements if (if < expr > ... else ...) • if {$x == $y } { puts “Hello world” } • Iterative Statements • for {set i 0; $i < $x ; incr i}{puts “Hello world” } • Function Declaration • proc name_FUNCTION {par1, ...parn} {... return $x} OTCL Overview

  30. Ns2: HOW • Running an OTCL script: • ns script-file.tcl [parameters] • Initialize the scheduler • Define the simulation parameters (e.g. start time) • Build the network topology • Generate the traffic load • Define the protocol stack used by each node • OTCL scripting language, OO-extension of TCL 

  31. Ns2: Initialize the Scheduler • Creating the Event Scheduler • set ns [new Simulator] • Starting the simulation • $ns run • Initializing the random number generator • $ns-random SEED • Scheduling the events • $ns at <time> <event> • Stopping the simulation at time 300 • $ns at 300 "finish“ SEED=0  current timestamp All the random variable used by the current simulation are initialized with this SEED.

  32. Ns2: HOW • Running an OTCL script: • ns script-file.tcl [parameters] • Initialize the scheduler • Define the simulation parameters (e.g. start time) • Build the network topology • Generate the traffic load • Define the protocol stack used by each node • OTCL scripting language, OO-extension of TCL 

  33. Ns2: Building the network (WIRED) CASE 1. Modeling a wired network. • Define the nodes of the network • set n0 [$ns node] • set n1 [$ns node] • Define the Links among nodes • #Nodes connected with an Ethernet cable, 10 Mb/s • $ns duplex-link $n0 $n1 10Mb 100ms DropTail Specifies bandwidth, delay, and queue policy: DropTail, RED, CBQ, FQ, SFQ, DRR

  34. Ns2: Building the network (WIRED) CASE 1. Modeling a wired network. • Define the error model on wired links • set loss_module [new ErrorModel] • $loss_module set rate_ 0.1 • $loss_module ranvar [new RandomVariable/Uniform] • $loss_module drop-target [new Agent/Null] • $ns lossmodel $loss_module $n0 $n1 Lossy link between node 0 and node 1, with error rate equal to 0.1. Packets with errors are sent to Agent/Null, i.e. they are discarded.

  35. Ns2: Building the network (WIRED) CASE 1. Modeling a wireless network. • Define the nodes of the network • set n0 [$ns node] • set n1 [$ns node] • Define the position • set topograpy [new Topography] • $topography load_flatgrid 400 400 • Define the position • $n0 set X_ 300 • $n0 set Y_ 400 • $n0 set Z_ 0 Set simulation area to 400mx400m Set node 0 at position <300,400,0>

  36. Ns2: Building the network (WIRED) CASE 1. Modeling a wireless network. • Define the mobility of wireless nodes • NS_OBJ at TIME “NODE setdest X_COOR Y_COOR SPEED” • $ns at 10.5 “$node(0) setdest 100 100 5.0” At time 10.5, node 0 will move toward position (100,100) with speed equal to 5 m/s (constant speed) • Utilize the General Object Director (GOD) • set $god [new God] Object that stores global information about the state of the environment (e.g. the matrix of connectivity among nodes)

  37. Ns2: Building the network (WIRED) CASE 1. Modeling a wireless network. • The mobility traces of wireless nodes can be pre-generated by using the setdest tool (random waypoint model) • ./setdest [-n num_of_nodes] [-p pausetime] [-maxspeed] • [-t simtime] [-x][-y] > [fileOutput] • In the TCL script: source “fileOutput” • Any mobility simulator can be used for trace generation. MOBILITY SIMULATOR MOB. TRACE OTCL SCRIPT NS2 e.g. SUMO SOURCE

  38. Ns2: HOW • Running an OTCL script: • ns script-file.tcl [parameters] • Initialize the scheduler • Define the simulation parameters (e.g. start time) • Build the network topology • Generate the traffic load • Define the protocol stack used by each node • OTCL scripting language, OO-extension of TCL 

  39. Ns2: Creating connections (UDP/TCP) • Define the end-points of the communication • TCP Connections: • set src [new Agent/TCP] • set dst [new Agent/TCPSink] • UDP Connections: • set src [new Agent/UDP] • set dst [new Agent/Null] • Connect sender and receiver • $ns attach-agent $n0 $src • $ns attach-agent $n1 $dst • $ns connect $src $dst • Several TCP variants: • TCP Tahoe • TCP Reno • TCP NewReno • TCP Vegas • TCP SACK • …

  40. Ns2: Attaching Applications • Define the application and attach it to the sender • FTP Agent • set ftp [new Application/FTP] • $ftp attach-agent $src • $ns at TIME “$ftp start” • CBR Agent • set cbr [new Application/Traffic/CBR] • $cbr attach-agent $src • $ns at TIME “$cbr start” • Exponential Traffic Generator • set exp [new Application/Traffic/Exponential]

  41. Ns2: HOW • Running an OTCL script: • ns script-file.tcl [parameters] • Initialize the scheduler • Define the simulation parameters (e.g. start time) • Build the network topology • Generate the traffic load • Define the protocol stack used by each node • OTCL scripting language, OO-extension of TCL 

  42. Ns2: HOW • Awireless environment can be modeled by configuring the protocol stack of each node. • $ns_ node-config –phyType $val(netif) • -propType $val(prop) • -antType $val(type) • -llType $val(ll) • -macType $val(mac) • -ifqType $val(ifq) • -ifqLen $val(ifqlen) • -adhocRouting $val(rp) • -topoInstance $topo • -channel $chan_ NET LAYER QUEUE LL LAYER MAC LAYER ANTENNA PROPAGATION PHY LAYER

  43. Ns2: HOW • Awireless environment can be modeled by configuring the protocol stack of each node. • $ns_ node-config –phyType $val(netif) • -propType $val(prop) • -antType $val(type) • -llType $val(ll) • -macType $val(mac) • -ifqType $val(ifq) • -ifqLen $val(ifqlen) • -adhocRouting $val(rp) • -topoInstance $topo • -channel $chan_ NET LAYER QUEUE LL LAYER MAC LAYER ANTENNA PROPAGATION PHY LAYER

  44. Ns2: HOW • Configuring the PHY Layer • set val(netif) Phy/WirelessPhy[Ext] • Some parameters to be tuned: • Phy/WirelessPhy set Pt 2.07983391e-01 • Phy/WirelessPhy set RXThresh 2.591168e-08 • Phy/WirelessPhy set CSThresh 3.497734e-09 • Functionalities offered by the PHY Layers • Signal capture • Modulation & Bit-rate setting • Modeling of collision/transmission errors • …

  45. Ns2: HOW • Awireless environment can be modeled by configuring the protocol stack of each node. • $ns_ node-config –phyType $val(netif) • -propType $val(prop) • -antType $val(type) • -llType $val(ll) • -macType $val(mac) • -ifqType $val(ifq) • -ifqLen $val(ifqlen) • -adhocRouting $val(rp) • -topoInstance $topo • -channel $chan_ NET LAYER QUEUE LL LAYER MAC LAYER ANTENNA PROPAGATION PHY LAYER

  46. Ns2: HOW • Configuring the Propagation model • set val(prop) Propagation/TwoRayGround • set val(prop) Propagation/FreeSpace FREE SPACE TWORAY RECEIVER SENDER • Configuring the Antenna model • set val(antType) Antenna/OmniAntenna • set val(antType) Antenna/Directional OMNIDIRECTIONAL DIRECTIONAL

  47. Ns2: HOW • Awireless environment can be modeled by configuring the protocol stack of each node. • $ns_ node-config –phyType $val(netif) • -propType $val(prop) • -antType $val(type) • -llType $val(ll) • -macType $val(mac) • -ifqType $val(ifq) • -ifqLen $val(ifqlen) • -adhocRouting $val(rp) • -topoInstance $topo • -channel $chan NET LAYER QUEUE LL LAYER MAC LAYER ANTENNA PROPAGATION PHY LAYER

  48. Ns2: HOW • Configuring the LL layer • set val(ll) LL Include ARP protocol • Configuring the MAC model • set val(mac) Mac/802_11 • Select a MAC protocol: • 802.11 (Wifi) • 802.15.4 (Sensors) • CSMA/CA • … • Configuring the Queue Layer • set val(ifq) Queue/DropTail/PrimaryQueue • set val(ifqlen) 50 • Define the queue policy: • PrimaryQueue • RED Queue • … Set the queue length

  49. Ns2: HOW • Awireless environment can be modeled by configuring the protocol stack of each node. • $ns_ node-config –phyType $val(netif) • -propType $val(prop) • -antType $val(type) • -llType $val(ll) • -macType $val(mac) • -ifqType $val(ifq) • -ifqLen $val(ifqlen) • -adhocRouting $val(rp) • -topoInstance $topo • -channel $chan NET LAYER QUEUE LL LAYER MAC LAYER ANTENNA PROPAGATION PHY LAYER

  50. Ns2: HOW • Configuring the routing protocol • set val(adhocrouting) AODV • Select a routing protocol for multi-hop networks: • AODV, DSDV, DSR, TORA, …. SOURCE ROUTING PATH DESTINATION

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