Introduction Model Simulation Application Summary

A Peer-to-Peer Simulator

Uwe Schmidt

Bachelor Thesis

August 17, 2006

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Introduction Model Simulation Application Summary

Outline

1 Introduction

2 Model

3 Simulation

4 Application

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Introduction Model Simulation Application Summary

Outline

1 Introduction

2 Model

3 Simulation

4 Application

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Introduction Model Simulation Application Summary

Peer-to-Peer File-Sharing

Gaining Importance

Less expensive in comparison to dedicated file serversExploit bandwidth of usersResilient to flashcrowds

BitTorrentFiles are separated into chunksPopular (also for legal purposes)

Microsoft AvalancheUses network coding for chunk distribution

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Introduction Model Simulation Application Summary

Motivation

Freeriding

Common problem of all P2P systemsLarge fraction of peers are free-ridersBitTorrent tries to restrain it by enforcing a tit-for-tat strategy

Primary purpose of the simulator:

Research the impact of the amount of free-riders on ...Download timesPeer load

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Introduction Model Simulation Application Summary

Outline

1 Introduction

2 Model

3 Simulation

4 Application

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Introduction Model Simulation Application Summary

General

Similar to BitTorrent (chunk-based file-sharing)Global knowledge of all other peers in the systemNo incentives to upload are given (such as tit-for-tat)Peers wait random time between downloads

Download BehaviorMultiple DownloadsQueued RequestsChunk SelectionPeer Selection

File

Peer Lists for Chunks

Chunk#1 Chunk#2 ... Chunk#n

ListPeer#6

Peer#40List

Peer#13Peer#2

Peer#77Peer#19

ListPeer#11Peer#5Peer#8

Peer

Chunk Selection

Peer Selection

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Introduction Model Simulation Application Summary

General Configuration GUI

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Introduction Model Simulation Application Summary

Peers

Separated into peer groups:

Peer GroupNumber of membersNumber of free-ridersBandwidth (upstream & downstream)Maximum number of simultaneous uploads & downloadsDisconnect probability after successful file download

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Introduction Model Simulation Application Summary

Peers Configuration GUI

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Introduction Model Simulation Application Summary

Files

Separated into file types:

File TypeNumber of filesNumber of copies (per file)File size (determines number of chunks)File distribution to peer groupsPopularity distribution of files among type

Global Chunk SizeApplies to all file types

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Introduction Model Simulation Application Summary

Files Configuration GUI

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Introduction Model Simulation Application Summary

Requests

Mean request periodRequest distribution to file types

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Introduction Model Simulation Application Summary

Requests Configuration GUI

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Introduction Model Simulation Application Summary

Outline

1 Introduction

2 Model

3 Simulation

4 Application

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Introduction Model Simulation Application Summary

Preliminaries

FactoriesCreate peers and filesDeploy files to peers

File Request GeneratorUses request configuration and file popularity settingsCreates empirical distributions for file indexesReplays this distributions during the simulation

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Introduction Model Simulation Application Summary

Discrete Event Simulation Concept

Ordered Event List

Next Event

removes

Entities

changes state

New Events

schedule

Data Collection

append data

inserted

Simulation Executive

executes

appends data

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Introduction Model Simulation Application Summary

Simulation Cycle

Peer

Download Part Upload Part

More Downloadspossible?

Select Chunk

yes

Update Downloads

no

Last Chunkof File?

Maybego Offline

yes

Select Peer Download Chunk

Incoming Chunk RequestDownload File

Add Chunks toDownload Queue

Process Download Queue

Download Complete

Chunk Download started Chunk Request Queued

Maybe startnew Request

More Uploadspossible?

Upload Chunk

yes

Queue Chunk Request

no

Update Uploads

no

Upload Complete

Process Upload Queue

File Request Generator

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Introduction Model Simulation Application Summary

Control

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Introduction Model Simulation Application Summary

Collected Data

Before the SimulationPeer groupsFile typesList of files with chunk mappingList of peers with file mapping

During the Simulation

Completed chunk transfersCompleted file downloadsMiscellaneous (e.g. peer goes offline)

After the SimulationList of peers with file mapping

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Introduction Model Simulation Application Summary

Outline

1 Introduction

2 Model

3 Simulation

4 Application

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Introduction Model Simulation Application Summary

Overview

Written in Java SE 5Used Eclipse 358 classes in 8 packages≈ 8000 lines of code and comments (JavaDoc)

Used LibrariesJakarta Commons Math→ Random Number GeneratorsJakarta Commons Configuration→ XML ConfigurationJFreeChart→ Charts

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Introduction Model Simulation Application Summary

Structure

Graphical User Interface

Configuration

changes

Simulator

controls

Random Number Generators

uses

Config File

save

Next Event

executes

Log Files

writes

Factories

uses

Console Mode

controls

load

Event List

removes

Peers

controls

New Events

schedule write

Chunks

transfer

Strategies

use

inserted

use create

Files

create

use consist of

File Request Generator

uses

returns Filesto download

uses

User

starts starts

use

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Introduction Model Simulation Application Summary

Used Design Patterns

Observer PatternSimulator→ Simulation State & ProgressConfiguration→ Changes

Singleton Pattern

Implemented by frequently used componentsSingle point of access from everywhereNo need to pass references on to other components

Command PatternHashtable that maps an ActionString to a CommandAvoid code duplication

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Introduction Model Simulation Application Summary

Extensions

General modular designSelection strategies are easy to change and extend

Example (Chunk Selection)Select rarest chunk among 50 randomly selected ones toreflect that peers have no global knowledge in reality

Example (Peer Selection)Select peer with most upstream leftSelect peer with smallest upload queue (if all are busy)

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Introduction Model Simulation Application Summary

Demo

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Introduction Model Simulation Application Summary

Summary

Easy and flexible way to simulate P2P systems (similar toBitTorrent)Tool to research the impact of free-riders, and otherparameters, on a P2P systemModular designed and extendable

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Thank you for your attention

Questions?

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