[PPT] - Introduction to NS-3 Konstantinos Katsaros k.katsaros @ PowerPoint Presentation

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Introduction to NS-3

Konstantinos Katsaros

k.katsaros @ surrey.ac.uk

Centre for Communications System Research University of Surrey

System Level Simulations - Technical Club

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Outline

1

Introduction

2

NS-3 Modules

3

LTE Module

4

WiFi Example

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Introduction

ns-3 is written in C++, with bindings available for Python

simulation programs are C++ executables or Python programs ∼300,000 lines of mostly C++ (estimate based on cloc source code analysis)

ns-3 is a GNU GPLv2-licensed project ns-3 is mainly supported for Linux, OS X, and FreeBSD ns-3 is not backwards-compatible with ns-2

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Where to get it

Where do I get ns-3?

http://www.nsnam.org

Where do I get today’s code?

Download the latest release:

wget

http://www.nsnam.org/releases/ns-allinone-3.17.tar.bz2

tar xjf ns-allinone-3.17.tar.bz2

Clone the latest development code1:

hg clone http://code.nsnam.org/ns-3-allinone

1Mercurial is used as source code control tool

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Current Modules in main NS-3 tree

Network: Node, Sockets, Queues, Packet, etc Core: Smart Pointers, Callbacks, Event, Scheduler, Logging, Tracing, etc

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Module Organization

model/ ← contains source code for main part of module helper/ ← contains code for helper classes examples/ tests/ bindings/ ← files related to python doc/ wscript ← the “Makefile" equivalent

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Helper API

The ns-3 “helper API" provides a set of classes and methods that make common operations easier than using the low-level API Consists of:

container objects
helper classes

The helper API is implemented using the low-level API Users are encouraged to contribute or propose improvements to the ns-3 helper API

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Building NS-3

Waf is a Python-based framework for configuring, compiling and installing applications.

It is a replacement for other tools such as Autotools, CMake or Ant http://code.google.com/p/waf/

For those familiar with autotools: configure → ./waf configure make →./waf build

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Discrete-event simulations

Simulation time moves in discrete jumps from event to event C++ functions schedule events to occur at specific simulation times A simulation scheduler orders the event execution Simulator::Run() gets it all started Simulation stops at specific time or when events end

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Time in NS-3

Time is stored as a large integer in ns-3

Avoid floating point discrepancies across platforms

Special Time classes are provided to manipulate time (such as standard operators) Default time resolution is nanoseconds, but can be set to other resolutions Time objects can be set by floating-point values and can export floating-point: double timeDouble = t.GetSeconds();

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NS-3 API

Most of the ns-3 API is documented with Doxygen (http://www.doxygen.org/)

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Scalability

Distributed simulation in ns-3 allows a user to run a single simulation in parallel on multiple processors By assigning a different rank to nodes and connecting these nodes with point-to-point links, simulator boundaries are created Simulator boundaries divide Logical Processes (LPs), and each LP can be executed by a different processor Distributed simulation in ns-3 offers solid performance gains in time

f execution for large topologies

Simulation on a HPC cluster at the U.S. Mobile Network Modeling Institute (2011)2

176 cores, 3 TB of memory
360,448,000 simulated nodes
413,704.52 packet receive events per second [wall-clock]
2K. Renard et al, “A Performance and Scalability Evaluation of the NS-3

Distributed Scheduler. Proceedings of WNS3 2012

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Attribute System

Problem: Researchers want to identify all of the values affecting the results of their simulations and configure them easily ns-3 solution: Each ns-3 object has a set of attributes:

A name, help text
A type
An initial value

Control all simulation parameters for static objects Dump and read them all in configuration files Visualize them in a GUI Makes it easy to verify the parameters of a simulation List of all attributes in the API: http://www.nsnam.org/docs/release/3.17/doxygen/group___ attribute_list.html

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Tracing System

Simulator provides a set of pre-configured trace sources

Users may edit the core to add their own

Users provide trace sinks and attach to the trace source

Simulator core provides a few examples for common cases

Multiple trace sources can connect to a trace sink List of all trace sources in the API: http://www.nsnam.org/docs/release/3.17/doxygen/group_ __trace_source_list.html

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FlowMonitor

Network monitoring framework found in src/flow-monitor/ Goals:

detect all flows passing through network
stores metrics for analysis such as throughput, duration, delays, packet

sizes, packet loss ratios Currently works ONLY on IPv4 packets.

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NetAnim

Animate packets over wired-links and wireless- links

limited support for LTE traces

Packet timeline with regex filter on packet meta-data. Node position statistics with node trajectory plotting (path of a mobile node). Print brief packet meta-data on packets

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LTE module - Design

FemtoForum LTE MAC Scheduler API Radio signal model granularity: Resource Block

Symbol-level model not affordable
Simplified Channel PHY model

Realistic Data Plane Protocol stack model

Realistic RLC, PDCP, S1-U, X2-U
Allow proper interaction with IP networking
Allow end-to-end QoE evaluations

Hybrid Control Plane model:

Realistic RRC model
Simplified S1-C, X2-C and S11 models

Simplified EPC

One MME and one SGW
SGW and PGW in the same node (no S5/S8 interface)

Focus on connected mode

RRC connected, EMM Registered, ECM connected
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Model Overview

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Propagation Models

Buildings model

Add buildings to network topology

Path loss model

Okumura Hata (outdoor)
ITU-R P1411 LOS & NLOS (outdoor)
ITU-R P1238 (indoor)
External & internal wall losses
Log-normal shadowing
Pathloss logic chooses correct model depending on node position

Fast fading model

Trace-based
Freq. and time dependent

Antenna models

Isotropic
Sectorial (cosine & parabolic shape)
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PHY model

Only FDD is modelled Freq domain granularity: RB Time domain granularity: 1 TTI, further divided into

DL: ctrl, data - UL: ctrl+data, SRS

Gaussian Interference model CQI feedback Signal processing not modelled accurately → use error model SISO propagation model MIMO modeled as SINR gain over SISO

different gains for different TX modes

Supports different freqs and bandwidths per eNB

leveraging on the ns-3 Spectrum module
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MAC Scheduler model

Resource allocation model:

allocation type 0
RBs grouped into RBGs
localized mapping approach

Adaptive Modulation and Coding

two algorithms working on reported CQI feedback
“Piro" model: based on analytical BER (very conservative)
“Vienna" model: aim at max 10% BLER based on error model

curves

Dynamic TX mode selection supported

but no adaptive algorithm currently implemented Transport Block model

Mimics 3GPP structure

mux RLC PDU onto MAC PDU

Virtual MAC Headers and CEs (no real bits)

MAC overhead not modeled Consistent with requirements (scheduler neglects MAC OH)

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MAC Scheduler

Round Robin (RR) Proportional Fair (PF) Maximum Throughput (MT) Throughput to Average (TTA) Blind Average Throughput (BET) Token Bank Fair Queue (TBFQ) Priority Set Scheduler (PSS) All implementations based on the FemtoForum API The above algorithms are for downlink only For uplink, all current implementations use the same Round Robin algorithm

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Simulation Output

Lots of KPIs available at different levels: Channel

SINR maps
pathloss matrices

PHY

TB tx / rx traces
RSRP/RSRQ traces

MAC

UL/DL scheduling traces

RLC and PDCP

Time-averaged PDU tx / rx stats

IP and application stats

Can be obtained with usual ns-3 means
FlowMonitor, PCAP traces, get stats directly from app, etc.
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Features Highlighted

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Simulation Time

5s sim time, 1 UE per eNB, full traffic

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Walkthrough of WiFi Internet example

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NS-3 Implementation of WiFi Example

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Structure of NS-3 program

int main (int argc, char *argv[]) { // Set default attribute values // Parse command-line arguments // Configure the topology; nodes, channels, devices, mobility // Add (Internet) stack to nodes // Configure IP addressing and routing // Add and configure applications // Configure tracing // Run simulation }

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Source Code for P2P example

Starting your script with this line ensures that emacs editor will be able to indent your code correctly. The following lines ensure that your code is licensed under the GPLv2. /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil;

*- */

// GPLv2 Licence Include the proper header files. For simulation scripts, you can aggregate them with modules, but when developing your module, you have to include the specific header file (not the aggregated) include “ns3/core-module.h" include “ns3/network-module.h" include “ns3/internet-module.h" include “ns3/point-to-point-module.h" include “ns3/applications-module.h" ... Use the ns3 project namespace using namespace ns3;

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example cont.

Enable and disable console message logging by reference to the name

NS_LOG_COMPONENT_DEFINE (“FirstScriptExample"); int main (int argc, char *argv[]) LogComponentEnable (“UdpEchoClientApplication", LOG_LEVEL_INFO); LogComponentEnable (“UdpEchoServerApplication", LOG_LEVEL_INFO);

Topology Configuration

NodeContainer nodes; nodes.Create (2); PointToPointHelper pointToPoint; pointToPoint.SetDeviceAttribute ("DataRate", StringValue ("5Mbps")); pointToPoint.SetChannelAttribute ("Delay", StringValue ("2ms")); NetDeviceContainer devices; devices = pointToPoint.Install (nodes);

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example cont.

Set up Internet Stack

InternetStackHelper stack; stack.Install (nodes); Ipv4AddressHelper address; address.SetBase ("10.1.1.0", "255.255.255.0"); Ipv4InterfaceContainer interfaces = address.Assign (devices);

Set up applications

UdpEchoServerHelper echoServer (9); ApplicationContainer serverApps = echoServer.Install (nodes.Get (1)); serverApps.Start (Seconds (1.0)); serverApps.Stop (Seconds (10.0)); UdpEchoClientHelper echoClient (interfaces.GetAddress (1), 9); echoClient.SetAttribute ("MaxPackets", UintegerValue (1)); echoClient.SetAttribute ("Interval", TimeValue (Seconds (1.0))); echoClient.SetAttribute ("PacketSize", UintegerValue (1024)); ApplicationContainer clientApps = echoClient.Install (nodes.Get (0)); clientApps.Start (Seconds (2.0)); clientApps.Stop (Seconds (10.0));

Run your scenario

Simulator::Run (); Simulator::Destroy ();

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Resources

Web site: http://www.nsnam.org Mailing list: https://groups.google.com/forum/?fromgroups#!forum/ ns-3-users IRC: ns-3 at freenode.net Tutorial: http://www.nsnam.org/docs/tutorial/tutorial.html Code server: http://code.nsnam.org Wiki: http://www.nsnam.org/wiki/index.php/Main_Page For LENA project: http: //iptechwiki.cttc.es/LTE-EPC_Network_Simulator_(LENA)

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Acknowledgments

Special Thanks to: Tom Henderson Mathieu Lacage Nicola Baldo for borrowing material from their presenations

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