COMPUTER NETWORK: MODELING AND SIMULATION

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COMPUTER NETWORKMODELING AND SIMULATION

• -Abhaykumar Kumbhar
• Computer Science Department

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Motivation

• Bridge between Real life application and
  Theoretical world.

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Contents

• Introduction.
• Modeling.
• Simulation.
• How to develop a Model.
• Classification .
• NS simulator.
• OPNET.
• An Ethernet Case Study.
• Requirements of a good Network Simulating Tool
• Evolution.
• Conclusion and Future Work

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Introduction

• Performance analysis of computer networks
  increase in size and geographical extent.
• The size of the networks and the inherent
  complexity of network protocols complicate this
  analysis.
• Analysis techniques such as queuing models have
  difficulty modeling dynamic behavior
  retransmission timeouts and congestion.
• Simulation offers a better method of studying
  computer networks, since one can simulate the
  details of actual protocols.

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• Simulation is an analysis and evaluation tool.
• Every simulation is tight to a model that
  represents the real world.
• Inconsistent modeling
• Modeling itself is a crucial step towards
  meaningful results.
• Aim systematic modeling techniques -increase the
  quality and validity of results

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Modeling

• Constructing a conceptual framework that
  describes a system.

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Modeling Taxonomy
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Simulation
system boundary
system under study (has deterministic rules
governing its behavior)
exogenous inputs to system (the environment)
real life
observer
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Why Simulation?

• study system performance, operation
• real-system not available, is complex/costly or
  dangerous (eg space simulations, flight
  simulations)
• quickly evaluate design alternatives (eg
  different system configurations)
• evaluate complex functions for which closed form
  formulas or numerical techniques not available

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When to Use Simulation?

• Whenever Mathematical Analysis Is Difficult or
  Impossible.
• For Validating Analytic Models.
• For Experimentation Without Disturbing an
  Operational System

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How to develop a model

• Determine the goals and objectives
• Build a conceptual model
• Convert into a specification model
• Convert into a computational model
• Verify
• Validate

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Simulation Model Development Methodology
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Simulation Model Verification and Validation
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Classification of Simulation Tools

• GPPL General Purpose Programming Language
• PSL Plain Simulation Language
• SP Simulation Package

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NS Simulator

• Began as REAL in 1989
• Developed by UC Berkeley
• Public domain SP
• Object-oriented
• Written in C and object-oriented tcl (Otcl)
• Network components are represented by classes

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Ns class hierarchy
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OPNET

• Developed by OPNET Technologies Inc.
• Commercial SP
• Object-oriented
• Totally menu-driven package
• Built-in model libraries contain most popular
  protocols and applications
• Simulation task made easy

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Modeling hierarchy in OPNET
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An Ethernet Case Study

• Bridging the Gap Between Reality and Simulations
• We set up our test-bed using two nodes connected
  by a 3 meter cross-over Ethernet cable.
• a simple test-bed experiment and attempt to
  replicate the obtained results by simulation in
  ns-2,QualNet and OPNET.

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• Network details
• set packet size of the application to 1472 bytes.
  This was to ensure that the maximum Ethernet
  frame of 1500 bytes would be transmitted

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Delay experienced by packets in saturated case
with non-blocking sockets

• particularly interested in the saturation
  performance of the system and we chose multiple
  rates near the maximum link bandwidth

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• The maximum delay of the system is experienced
  when the source bufferis full.
• This delay is given as max delay tx delay
  buffer size in packets.
• The transmission delay for one packet is the
  minimum delay.
• The buffer size is then calculated as max
  delay/min delay. Hence a buffer size of 78
  packets was arrived at 94/1.2 78packets
  128KB.

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• Setting up simulations in QualNet
• --the link propagation delay being negligible,
  set it to 25 µs to model test-bed network
  characteristics.
• --queue size from its default value of 50 KB to
  117 KB, which corresponds to 78 packets of 1500
  bytes each.

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• Setting up simulations in OPNET
• Ethernet Station Advanced (ESA).
• The ESA has a traffic generator built over the
  Ethernet MAC.
• the queue length to infinity.
• OPNET models queues as a set of sub-queues,
  allowing the possibility of different
  application traffic to map on to different
  queues. By default only one sub-queue is created
  in the Ethernet MAC process model and this is a
  hidden parameter. This sub queue is accessed as a
  process interface of the Ethernet MAC process
  model. The sub-queue packet capacity was set to
  78 packets.

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• Setting up simulations in NS-2
• configurable parameters node objects, link
  bandwidth, maximum length and type of the
  interface queue and delay.
• queue length to 78.
• maximum propagation delay is 25 µs for 10 Mbps.

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• Results

• Figure Throughput

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• Figure Packet Delivery Fraction

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• Figure Average End-to-End Delay

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Requirements for Network Simulation tools

• Model development simplicity
• Modeling flexibility
• Fast modeling
• Animation
• Different kinds of implemented components
• Component adaptability
• Creating new components
• Static capabilities of a simulator
• Graphs

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Evolution of Network Simulation Tools

• Zeroth Generation General Purpose Languages
• - Fortran, C/C, Pascal, Basic
• First Generation General Purpose Queueing
  System Simulations
• -GPSS, SLAM, SIMSCRIPT
• Second Generation Application Specific
  Computer Systems and Wide-Area Communication
  Networks
• Third Generation Integration of Second
  Generation Languages
• -With a Graphics-Oriented Analysis and Modeling
  Environment
• -SES/Workbench
• -OPNET

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Conclusion and Future work

• Best way to learn Protocols.

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References

• 1Advanced Modelling and Simulation Methods
• for Communication Networks Jože Mohorko, Fras
  Matjaž, Klampfer Saša.
• 2www.sciencedirect.com
• 3www.ieeexplore.org

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• THANK YOU
• QUESTIONS??