Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain Chapter 4 TCP/IP Network Simulation.

Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain

Chapter 4

TCP/IP Network Simulation


Objectives

Appreciate the role of simulation in performance evaluation of TCP/IP networks

Acquire the knowledge needed to conduct steady state simulation

Master basic skills for analyzing confidence level Describe types of simulation tools available Familiarize with the capabilities of popular

simulation tools


Contents

Why use simulation Systematic simulation study Types of simulations Simulation validation and verification Confidence level of simulation results Simulation with self similar traffic Simulation tools


Why Use

Simulation


Why Use Simulation

Predict performance for proposed network Allow performance evaluation under a wide

variety of network conditions Compare alternative architectures under

identical and repeatable conditions Produce results closer to reality Validate analytical results


Systematic

Simulation

Study


Systematic Simulation Study

Pre-software stage Define problem/objective Design network model and select fixed parameters Select performance metrics Select variable parameters


Systematic Simulation Study (Cont.)

Software stageModel constructionSimulation configurationSimulation execution/Data collectionResult presentation


Types of

Simulation


Types of simulations

Continuos vs. discrete event Terminating vs. steady state Synthetic vs. trace-driven


Steady State

If we are interested in asymptotic behavior of a network system, we cannot use terminating simulations

Must continue until it reaches steady state


Trace-Driven Simulations

Actual network traces can be used as simulation input

Results can be more convincing


Validation and Verification


Simulation Validation and Verification

Validation: Make sure that the assumptions are realistic

Verification: Make sure that the model implements assumptions correctly

Guidelines to followLook for “surprise” in outputEmploy analytical modelingCompare with real network data


Confidence Level Analysis


Confidence Level

Relative precision formula for 95% confidence (see Eq. 4.8, pp. 84)

Confidence level in terminating simulation

Repeat the entire simulation many times with different random numbers (or seeds)

p105, Fig. 4.4


Confidence Level (cont.)

Confidence level in steady-state simulation

Fixed length simulation

Adaptive length simulation


Self Similar Traffic


Self Similar Traffic

Poisson model does not capture the burstiness of TCP/IP traffic TCP/IP traffic usually exhibits self similar property Generated by superimposing many ON/OFF sources with Pareto

distribution


Simulation Tools


Classification of Simulation Tools GPPL: General Purpose Programming Language PSL: “Plain” Simulation Language SP: Simulation Package p110, Fig. 4.7


NS Simulator

Developed by UC Berkeley Public domain SP Object-oriented Written in C++ and object-oriented tcl

(Otcl) Network components are represented by

classes


Ns class hierarchy


Reference network for TCP simulation with background traffic


Sequence No. vs. time


Average throughput vs buffer size


Single FTP with trace-driven “star wars movie” internet traffic


TCP throughput vs time


TCP packet delay vs time


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


Modeling hierarchy in OPNET


Screen shot of a network-level modeling in OPNET


Screen shot of a node-level modeling in OPNET


Screen shot of a process-level modeling in OPNET


Editing pad of state executives for process modeling in OPNET


Link editor dialog box to set parameters of a point to point link object


Packet editor to specify or edit details of TCP header fields


Packet Editor to specify or edit details of TCP header


Probe Editor to collect seven different types of statistics


Simulation Tool showing two different simulation sequences


Main menu of Analysis Tool


Network model for RED gateway


Evolution of buffer occupancy under FIFO and RED


Network model for fairness evolution


Average TCP/UDP throughput under FIFO


Average TCP/UDP throughput under RED


Average TCP/UDP throughput under WFQ


Selecting the Right Tool

Built-in libraries Credibility User-Friendliness Technical support Level of Details Resource consumption Cost


NS vs. OPNET

Both have emerged as de facto “standard” for simulating TCP/IP networks

P143, Table 4.6


Packet delay vs link capacity

Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain Chapter 4 TCP/IP Network Simulation.

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