Anirban Chakrabarti

1
Introduction to NS-2

• Presented by
• Anirban Chakrabarti
• Dependable Computing Networking Laboratory
• Department of Electrical and Computer Engineering
• Iowa State University
• Ames, IA 50011

2
Overview

• Introduction to NS architecture
• Example of a typical NS script
• Some useful NS classes
• Documentation Information

3
Introduction

• Event Driven Simulator
• Implemented in UC Berkeley
• Official web-site
• http//www.isi.edu/nsnam/ns/
• Documentations available in
• http//titan.cs.uni-bonn.de/greis/ns/ns.html

4
Implementation

• NS-2 is implemented in C and Otcl (Object Tcl)
• C is used for the detailed simulations of large
  data sets
• C compiler is used
• Otcl is used for data tweaking
• Otcl Interpreter is used

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Abstraction
User Script
OTCL
C
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Class Tcl

• Encapsulates the Otcl interpreter
• Obtain a reference to the Tcl instance
• Invokes Otcl procedures
• Report results back to the interpreter

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Class TclObject

• Base classes for most classes in compiled and
  interpreted hierarchies
• Calls the constructors of all the classes
• Maintains the interpreted object in the hash
  tables
• Takes care of variable binding

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Class TclClass

• Pure Virtual class
• User is required to derive the class from the
  TclClass
• Provide the constructor and the create function
• Constructor passes the name of the class in the
  interpreted hierarchy

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Problem ...
TCP Source (FTP)
0
1
3
2
Sink
UDP Source
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Script File

• An example shown
• Ns is instantiated
• Open the trace file
• Set the nodes
• Attach agents
• Run the simulation

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UDP Flows Attached
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TCP Flow Attached ...
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Queue buildup ...
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Nodes

• Implemented in Tcl
• Nodes are instantiated by ns node
• Nodes are assigned default addresses
• Can be made to support multicasting by the macro
  multicast on at the simulator instantiation

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Links

• Simplex or Duplex
• Facility for link up/down option
• Links can have different bandwidths assigned
• Different Packet Schedulers can be attached to
  the link

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Queues currently available

• DropTail
• FQ
• RED
• CBQ
• WFQ (downloaded version available)

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Agents

• Class Agent is responsible for packet allocation
  and generation
• One has to attach agents to the nodes for packet
  transmission and reception
• The different agents are
• TCP and its variants
• UDP
• Loss Monitor

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Analysis

• Through Network Animator (nam)
• Trace files are generated
• Nam shows the trace file by animation
• Through user created trace files
• User can have their own trace files

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Multicast support in ns

• Different types of multicast trees
• Centralized, Shared tree and bi-directional
  shared tree
• Facilities for joining and leaving groups
• ltiifgt and ltoiflistgt specifies the multicast tree

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Special ns support

• Random number generator
• Uniform, exponential, pareto, constant and Hyper
  exponential
• Mathematical support
• Integrals

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Where to find...

• Logon to linux.ee.iastate.edu
• NS source code available in
• /remote/cpre541/ns-allinone.1b6/ns-2.1b6
• Examples in
• /remote/cpre541/ns-allinone.1b6/ns2.1b6/tcl/ex