Network Modeling and Simulation with Network Simulator …difelice/sm/slides/ns2.pdf · Marco Di Felice NS2: An Overview Marco Di Felice Network Modeling and Simulation with Network

Marco Di Felice NS2: An Overview

Marco Di Felice

Network Modeling and Simulation with Network Simulator 2 (ns2)

Department of Computer Science and Engineering

University of Bologna. Italy

[email protected]


Outline

NS2: Architecture and Design

NS2: Use Cases and Features

NS2: Building simple network models

NS2: Demo & Analysis


Ns2: An Overview

NS2: A (discrete event) network simulator tool.

Generally speaking, a network simulator is a dedicated software that allows to:

Ø  Model the behaviour of network protocols/applications (e.g. TCP protocol).

Ø  Reproduce the behaviour of a computer network as a whole (e.g. a wireless LAN).

Ø  Quantify the network performance, through well-defined network metrics (e.g. system throughput).


Ns2: WHAT

Q. When may I use a network simulator?

Case 1: Network planning

Ø  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?


Ns2: WHAT


Case 2: Network Evaluation

Ø  Need to evaluate the performance of a (possibly large-scale) network infrastructure or network application.

Ø  Use an existing testbed à BUT …

Q2. Are the experiments easily reproducible?

Q1. What is the cost of setting up the experiments?

An example: Early Collision Detection Systems In VANETs


Ns2: WHAT


Case 3: Research on Networking Systems

Ø  Need to evaluate the performance of a new network protocol, architecture, or application.

2. Analytical models might be too complex to model all the components of the scenario under study.

1. A real deployment might not be feasible, or might be too costly.

An example: Proposing a new TCP variant for wireless LANs.


Ns2: WHAT

Ø  Network simulators might be used to model several kinds of networking systems (wired, wireless, optical, etc).

Ø  In practice, simulation constitutes the main evaluation technique for wireless systems.

²  Possibility to build reproducible experiments (hard to guarantee with wireless testbeds).

²  Possibility to reproduce wireless propagation phenomena in an accurate way through probabilistic models (e.g. fading)

²  Possibility to model large-scale wireless networks composed by several interacting nodes.


Ns2: WHAT

Ø  Simulation is a meaningful evaluation approach only when it produces “trustable” results.

Ø  Validation is needed to certify that the simulation models reproduce correctly the characteristics and dynamics of the system under study.

Ø HOW to VALIDATE a NETWORK MODEL?

²  Compare Simulation vs Analytical Model

²  Compare Simulation vs Real Measurements

SIM. THROUGPUT

Θ(1 / n ⋅ logn)ANALYTICAL EXPERIMENTS


Ns2: WHAT

NS2: A network simulation tool

Ø  Discrete Event simulator (details later …)

NS2 allows to model and evaluate several IP networking systems (LAN/WAN). It includes:

²  Network protocols model (e.g. MAC, routing, …)

²  Network applications model (e.g. CBR, FTP, …)

²  Queue management algorithms (e.g. FIFO, RED, …)

²  Network link models (e.g. lossy link) ²  …


Ns2: WHERE

v  http://www.isi.edu/nsnam/ns

v  http://sourceforge.net/projects/nsnam

Ø  download ns-allinone

Ø  includes several tools (ns2, nam, awk, otcl, …)

v  mailing list: [email protected]

v  documentation:

Ø  Reference manual and Tutorials on the website

Ø  Other tutorials on the Web


Ns2: WHEN

v  The project started from REAL project in 1989 Ø  ns-1 by Floyd and McCanne at Lawrance Berkeley National Laboratory (LBNL).

Ø  ns-2 by Steve McCanne, within the VINT project involving a consortium of US universities (LBL, PARC,USC, ...)

Ø  currently maintained at USC/ISI (University of Southern California), but several forks available.

v  NS3 relased in 2008 (now NS3.25) Ø  Deployed by a team lead by Tom Henderson and Sally Floyd (University of Washington)

Ø  A completely new tool, not a mere extension of Ns2 !


Ns2: WHY

NS2: A network simulation tool

Ø  Discrete Event simulator (details later …)

²  OMNET++ ²  OPNET ²  JiST ²  NS3 ²  GLOMOSIM ² …

OTHER SIMULATION TOOLS

Q. WHY should I use NS2 for my research?


Ns2: WHY

MAC Layer

Network Layer

Transport Layer

Application Layer

Ethernet, 802.11 (WIFI), 802.15.4, Bluetooth, 802.16 (WIMAX), …

Wired routing (RIP), Ad Hoc Routing (AODV, OLSR, DSR), …

UDP, TCP (Reno, NewReno, Vegas, SACK), …

FTP, Telnet, HTTP, Multimedia, Exponential traffic, …

Link Models:

Ø  Wired Links, Ø  Wireless Links, Ø  Satellite Links, …

Ø NS2 includes a vast model library of network components.


Ns2: WHY

v  Collaborative deployment environment

Ø  possibility to freely modify the existing NS2 code based on each user’s needs.

Ø  possibility to share network models for research/education purposes (e.g. a new implementation of TCP).

Ø  possibility to compare his/her own model with models implemented by other research teams.

v  Multi-platform support Ø  GNU/Linux, MAC OSX, Solaris, Windows, …

Ø NS2 is distributed with GNU General Public Licence (GPL)


Ns2: WHY

MOBIHOC Conference: Statistics on tools used to produce a simulation study within the papers submitted at the ACM MOBIHOC conference (2000-2006).

Number of Users: 10K

Institutes: 1K

% Papers: 44.4%

Ø NS2 is a popular tool, widely adopted by researchers working on the field of computer networks.


Ns2: WHY

Q. WHY NOT to use NS2 for my research?

Ø  Performance issues ²  Monolithic (basic) scheduler,

scalability constitutes a big issue. Ø  Architectural issues

²  Not really a modular architecture, difficult to share the code of network models.

Ø  Evaluation issues

²  No support for the trace analysis.

#nodes

CP

U ti

me

?

NS2 TRACE


NS2: HOW

Ø  OTCL for simulation setup and execution Ø  Quickly define the simulation environment

Ø  C++ for model deployment Ø  Implement the behaviour of a network component

Ø  Two programming languages: C++ and OTCL.


NS2: HOW

Ø  The core of the NS2 simulator is the Scheduler

² Discrete-event scheduler. ² Basic implementation, few optimization.

Event in NS2 ID TYPE TIME HANDLER

Timer Events

Packet Events

NS2 Object + function name

that should be invoked once the

event is fired.

Simulation time of the event

Packet sent

Packet received

Packet dropped


NS2: HOW

Ø  The Scheduler manages the simulation event list.

² The elements are the events of the simulation. ² The list is ordered on the basis of the time field.

E1 E2 E3 E4 E5 E6 SIMULATION

TIME: t

At each simulation step: 1.  The head element of the list is removed 2.  The simulation time is set to E1.time 3.  The event handler (E1.handler) is executed.

1 TYPE TIME HANDLER

SIMULATION TIME: E1.time


NS2: HOW

Ø  The Scheduler manages the simulation event list.

² The elements are the events of the simulation. ² The list is ordered on the basis of the time field.

E2 E3 E4 E5 E6 E7 SIMULATION

TIME: t

At each simulation step:

Ø  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)

SIMULATION TIME: E1.time

E1.HANDLER


NS2: HOW

Ø  Let’s make an example on a network scenario …

NODE A NODE B

APPLICATION

MAC

APPLICATION

MAC ETHERNET LINK

SIMULATION TIME: 0

EVENT LIST

Ø  At t=0, the Application module of node A is invoked


NS2: HOW


NODE A NODE B

APPLICATION

MAC

APPLICATION

MAC ETHERNET LINK

SIMULATION TIME: 0

EVENT LIST

Ø  A timer event is scheduled at time 4 by node A

1 Send 4 A.APPLICATION

E1


NS2: HOW


NODE A NODE B

APPLICATION

MAC

APPLICATION

MAC ETHERNET LINK

SIMULATION TIME: 4

EVENT LIST 2 Recv 4.5 A.MAC

E2 E3



NS2: HOW


NODE A NODE B

APPLICATION

MAC

APPLICATION

MAC ETHERNET LINK

SIMULATION TIME: 4.5

EVENT LIST 4 Recv 5.0 B.MAC

E4 E3



NS2: HOW


NODE A NODE B

APPLICATION

MAC

APPLICATION

MAC ETHERNET LINK

SIMULATION TIME: 5

EVENT LIST 5 Recv 5.2 B.APPLICATION

E5 E3



NS2: HOW


NODE A NODE B

APPLICATION

MAC

APPLICATION

MAC ETHERNET LINK

SIMULATION TIME: 5.2

EVENT LIST

E3


Ø  The message is processed by Node B at time 5.2


Ns2: HOW

v  Two ways of interactions: Ø  Modify/Create a new network model

-  Network models: network protocols, applications, queue policies, network architecture models, etc.

-  Coding in C++

-  Recompile at the end.

Ø  Configure/Run a network simulation

-  Coding in OTCL

-  Executed by an interpreter, no need to recompile.

QUITE EASY

NOT EASY


Ns2: HOW

v  Running an OTCL script:

ns script-‐file.tcl [parameters]

Ø  Initialize the scheduler

Ø  Define the simulation parameters (e.g. start time)

Ø  Build the network topology

Ø  Generate the traffic load

Ø  Define the protocol stack used by each node

v  OTCL à scripting language, OO-extension of TCL à


Ns2: OTCL inside

v  Assign a value to a variable set x 0

v  Keyword $ returns the value of a variable set y $x

v  Selection Statements if (if < expr > ... else ...) if {$x == $y } { puts “Hello world” }

v  Iterative Statements

for {set i 0; $i < $x ; incr i}{puts “Hello world” }

v  Function Declaration proc name_FUNCTION {par1, ...parn} {... return $x}

OTCL Overview


Ns2: HOW










Ns2: Initialize the Scheduler v  Creating the Event Scheduler

set ns [new Simulator]

v  Starting the simulation $ns run

v  Initializing the random number generator

$ns-‐random SEED

v  Scheduling the events $ns at <time> <event>

v  Stopping the simulation at time 300 $ns at 300 "finish“

SEED=0 à current timestamp

All the random variable used by the current simulation are initialized with this SEED.


Ns2: HOW










Ns2: Building the network (WIRED)

v  Define the nodes of the network

set n0 [$ns node] set n1 [$ns node]

v  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

CASE 1. Modeling a wired network.



v  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.

CASE 1. Modeling a wired network.



v  Define the nodes of the network

set n0 [$ns node] set n1 [$ns node]

v  Define the position set topograpy [new Topography]

$topography load_flatgrid 400 400

v  Define the position

$n0 set X_ 300 $n0 set Y_ 400 $n0 set Z_ 0

CASE 1. Modeling a wireless network.

Set node 0 at position <300,400,0>

Set simulation area to 400mx400m



v  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)

v  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)



v  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”


v  Any mobility simulator can be used for trace generation.

MOB. TRACE

MOBILITY SIMULATOR

OTCL SCRIPT

NS2

e.g. SUMO SOURCE


Ns2: HOW










Ns2: Creating connections (UDP/TCP)

v  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]

v  Connect sender and receiver $ns attach-‐agent $n0 $src $ns attach-‐agent $n1 $dst $ns connect $src $dst

Several TCP variants:

Ø  TCP Tahoe Ø  TCP Reno Ø  TCP NewReno Ø  TCP Vegas Ø  TCP SACK …


Ns2: Attaching Applications

v  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]


Ns2: HOW










Ns2: HOW

v  A wireless 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_ PHY LAYER

ANTENNA PROPAGATION

MAC LAYER

NET LAYER QUEUE

LL LAYER


Ns2: HOW





ANTENNA PROPAGATION

MAC LAYER

NET LAYER QUEUE

LL LAYER


Ns2: HOW

v  Configuring the PHY Layer set val(netif) Phy/WirelessPhy[Ext]

² 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

² Functionalities offered by the PHY Layers Ø  Signal capture Ø  Modulation & Bit-rate setting Ø  Modeling of collision/transmission errors Ø  …


Ns2: HOW





ANTENNA PROPAGATION

MAC LAYER

NET LAYER QUEUE

LL LAYER


Ns2: HOW

v  Configuring the Propagation model set val(prop) Propagation/TwoRayGround set val(prop) Propagation/FreeSpace

FREE SPACE

TWORAY

SENDER RECEIVER

v  Configuring the Antenna model set val(antType) Antenna/OmniAntenna set val(antType) Antenna/Directional

DIRECTIONAL OMNIDIRECTIONAL





-‐ifqLen $val(ifqlen) -‐adhocRouting $val(rp) -‐topoInstance $topo -‐channel $chan

Ns2: HOW

PHY LAYER ANTENNA PROPAGATION

MAC LAYER

NET LAYER QUEUE

LL LAYER


Ns2: HOW

v  Configuring the LL layer set val(ll) LL

v  Configuring the MAC model set val(mac) Mac/802_11

Include ARP protocol

Select a MAC protocol: Ø  802.11 (Wifi) Ø  802.15.4 (Sensors) Ø  802.16 (WiMax) Ø  …

v  Configuring the Queue Layer set val(ifq) Queue/DropTail/PrimaryQueue set val(ifqlen) 50

Define the queue policy: Ø  PrimaryQueue Ø  RED Queue …

Set the queue length


Ns2: HOW




-‐ifqLen $val(ifqlen) -‐adhocRouting $val(rp) -‐topoInstance $topo -‐channel $chan PHY LAYER

ANTENNA PROPAGATION

MAC LAYER

NET LAYER QUEUE

LL LAYER


Ns2: HOW

v  Configuring the routing protocol set val(adhocrouting) AODV

Select a routing protocol for multi-hop networks: Ø  AODV, DSDV, DSR, TORA, ….

SOURCE

DESTINATION ROUTING PATH


Ns2: HOW

v  Two ways of interactions: Ø  Modify/Create a new network model

-  Network models: network protocols, applications, queue policies, network architecture models, etc.

-  Coding in C++

-  Recompile at the end.

Ø  Configure/Run a network simulation

-  Coding in OTCL

-  Executed by an interpreter, no need to recompile.

QUITE EASY

NOT EASY


Ns2: HOW

v  In C++, each model extends the class NSObject.

v  Each NSObject has a correspective in OTCL.


Ns2: HOW

v When creating a new model in C++:

Ø  Extend the NSObject class

Ø  Create the corresponding OTCL class

Ø  Implement these methods

recv(Packet* p, Handler* h) à Callback once a packet is received from the upper layer.

command(int argc, const char*const* argv) à Binding between C++ and OTCL for the parameter passing from the TCL script.


Ns2: Simulation Output (TRACE)

v  The output of the simulation is a trace file, containing the description of the events occurred during the simulation. s 10.00000 0 MAC --- 0 RTS 44 [253e 1 0 0] r 10.00041 1 MAC --- 0 RTS 44 [253e 1 0 0] s 10.00042 1 MAC --- 0 CTS 38 [2404 0 0 0] r 10.00075 0 MAC --- 0 CTS 38 [2404 0 0 0] s 10.00076 0 MAC --- 100 cbr 1112 [13a 1 0 800] r 10.00982 1 MAC --- 100 cbr 1112 [13a 1 0 800]

Simulation Time

Event Type

Node Packet

ID

Traffic type

Packet size

MAC Header


Ns2: Simulation Output (TRACE)

v  Depending on the length of the simulation, the trace file might occupy lots of bytes on the disk.

$ns_ node-‐config –agentTrace ON/OFF -‐routerTrace ON/OFF -‐macTrace ON/OFF -‐mobilityTrace ON/OFF

Configure the granularity of the tracing process …

s 10.00078 1 AGT --- 100 cbr 1112 [13a 1 0 800] s 10.00078 1 MAC --- 100 cbr 1112 [13a 1 0 800] r 10.00078 0 MAC --- 100 cbr 1112 [13a 1 0 800] r 10.00078 0 AGT --- 100 cbr 1112 [13a 1 0 800]


Ns2: Simulation Output (NAM)

v  The output of the simulation can be visualized by using the Network Animator (NAM) tool.


Ns2: Analysis of Simulation Results

v  NS2 does NOT provide any specific support for the data analysis/validation and for the computation of performance metrics (e.g. throughput, delay).

v  Run multiple simulations with different seeds

v  Remove the transient phase from the trace file

v  Extract the performance metrics from the trace file

v  Compute the average and confidence intervals

v  Plot the results

v  External data processing tools must be used.

AWK, PERL, … GNUPLOT


Ns2: Analysis of Simulation Results

v Example: Computing the system throughput in AWK.

BEGIN { recvByte=sim_time=transient=0.0

} ($1==‘r’) && ($4==‘AGT’) && ($2>transient) {

recvByte+=$8 sim_time=$2

} END {

print recvByte/(sime_time-‐transient) }

Network Modeling and Simulation with Network Simulator …difelice/sm/slides/ns2.pdf · Marco Di Felice NS2: An Overview Marco Di Felice Network Modeling and Simulation with Network

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