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Peer-to-Peer Simulators
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Peer-to-Peer Simulators
Mark Baker and Rahim Lakhoo
ACET
University of Reading
{Mark.Baker@computer.org, r.n.lakhoo@rdg.ac.uk}
Date: 1
st
May 2007
Abstract
In this technical report, we present our findings on network simulators, which can be
used to help test and design a P2P system. The Portal-based P2P system under
development uses portals to provide a user interface and P2P volunteers to provide
resources to the network. The aim is to create an infrastructure that can be used by the
scientific community, based on existing social networks, to help download and
maintain large datasets. Network simulators provide a virtual network environment,
which can potentially provide assurance for software developers, when making design
decisions. This report outlines the architecture of the Portal-based P2P system and
defines a set of criteria for a suitable simulator, to aid the development of the P2P
system. A number of network simulators are reviewed and briefly tested for their
suitability based on criteria. The experience gained from reviewing network
simulators is presented in this report.
2
1. INTRODUCTION.....................................................................................................................................3
1.1 P2P SYSTEMS........................................................................................................................................3
1.2 PORTAL-BASED P2P SYSTEM ...............................................................................................................3
1.3 NETWORK SIMULATORS .......................................................................................................................5
2. REVIEW.....................................................................................................................................................5
2.1 CRITERIA ...............................................................................................................................................6
2.2 SIMULATORS .........................................................................................................................................6
2.2.1 NS-2 and NAM .............................................................................................................................6
2.2.2 PeerSim.........................................................................................................................................8
2.2.3 PlanetSim......................................................................................................................................8
2.2.4 OMNeT++....................................................................................................................................8
2.2.5 OverSim ........................................................................................................................................9
2.2.6 GPS ...............................................................................................................................................9
2.2.7 AgentJ .........................................................................................................................................10
2.2.8 P2PSim .......................................................................................................................................10
3. INSTALLATIONS AND TESTS..........................................................................................................11
3.1 NS-2 AND NAM .................................................................................................................................11
3.2 PEERSIM..............................................................................................................................................12
3.3 PLANETSIM .........................................................................................................................................13
3.4 OMNET++..........................................................................................................................................13
3.5 OVERSIM.............................................................................................................................................15
3.6 GPS .....................................................................................................................................................16
3.7 AGENTJ ...............................................................................................................................................17
3.8 P2PSIM................................................................................................................................................17
4. SUMMARY AND CONCLUSIONS ....................................................................................................18
4.1 SUMMARY ...........................................................................................................................................18
4.2 CONCLUSION.......................................................................................................................................20
REFERENCES ............................................................................................................................................22
3
1. Introduction
In recent years, Peer-to-Peer (P2P) technologies have become increasingly popular. A
P2P system can be defined as a distributed network architecture, whereby participants
share a part of their own hardware resources, such as processing power, storage
capacity, or network bandwidth. The shared resources are necessary to provide the
service and content offered by the network, such as file-sharing. The service or
content provided by the P2P network is accessible by other peers directly, without
passing intermediary entities [1].
1.1 P2P Systems
P2P systems are commonly used to distribute content as part of a Content Distribution
Network (CDN). One of the main reasons for the success of P2P networks is
providing users with the ability to distribute content by contributing bandwidth back
to the network. This concept is the social aspect of a P2P network, whereby users
freely give bandwidth to other users. Most, if not all, members of a P2P network
contribute resources to the network; essentially users are helping each other download
files. Popular examples of P2P networks/applications used are Gnutella [1],
BitTorrent [3], Kazaa [4], eDonkey [5], Limewire [6] and Freenet [7].
P2P technologies are mainly used for file sharing and are becoming the normal
method for the distribution of Linux operating systems. The P2P method of file
distribution is superseding the older mechanisms, such as the File Transfer Protocol
(FTP). When using traditional FTP servers, the bandwidth for all users downloading
from the server is split between the numbers of users. This can lead to a server’s
bandwidth being completely depleted, leaving users with a less than optimal transfer
rate. The centralised architecture of the traditional FTP server is known not to scale
well. However, P2P systems such as BitTorrent have been seen to scale to over
100,000 users for a single file/data set. P2P applications like BitTorrent, which have
made efficient use of bandwidth have forced Internet Service Providers (ISP) to
reassess their price plans [8], due to the increased flow of traffic from broadband
users. Even though broadband users do not have much bandwidth, when compared to
enterprise Internet connections, they still manage to accumulate enough bandwidth to
transfer many Gbytes of data. A study monitored over 90 thousand BitTorrent users,
downloading a file of approximately 2Gbytes, over a period of 8 months. During June
2004, BitTorrent was 53 per cent of all P2P traffic on the Internet backbone [9].
1.2 Portal-based P2P System
The aim of the Portal-based P2P system is to allow users to store large datasets across
many peers, instead of a dataset being hosted centrally. Each peer in the network
contributes resources back to the network. Resources contributed, are network
bandwidth and file storage space. Portals within the P2P system provide users a way
to manage the dataset hosted by the P2P network. Our Portal-based P2P system is
designed to manage and update large scientific datasets. Projects such as the Sloan
Digital Sky Survey (SDSS) [10] are set to produce over 15 TBytes of data by the end
4
of the project lifetime [11]. Such projects have datasets, which are growing, and
subsequently the costs and logistics of transferring the datasets is becoming
increasingly difficult.
Our P2P system consists of a two-layered peer hierarchy, see Figure 1 for an
overview. The peers are arranged in a hierarchy of portal, and volunteer peers. Portal
peers host a portal that provides an interface for users of the P2P system to manage
the data stored, along with the contribution of resources. Volunteer peers are users
who contribute a user-defined amount of resources to the network. The backbone tier
(portal peers) consists of a portal service hosted, potentially by, academic institutes or
research laboratories, which are part of a particular project. The volunteer peers
consist of individuals and/or organisations that are either involved or interested in a
particular project or dataset. Volunteers will run a mini-peer within their Web browser
that contributes to the distribution of content. All peers in the Portal-based P2P
system will provide a distributed service for the network, so that peers can find each
other and data to download, this is commonly known as a tracker. The tracker will be
implemented using Tycho [12], which provides a virtual registry and an asynchronous
messaging framework. Tycho allows consumer/producer network end-points to
discover and communicate with each other over a wide-area network.
Portal Peers
Volunteer Peers
Portal Portal Portal
Web
User
Tycho Virtual Registry
Web
User
Web
User
Web
User
Web
User
Web
User
Web
User
Tracker Communication - HTTP Protocol
File Transfer - Socket Connection
Figure 1, Portal-based P2P Network Overview.
In order to provide greater assurance to the development and testing of the Portal-
based P2P system a simulator is needed.
It was decided that before implementing the P2P system, a P2P simulator should be
used, to model the Portal-based P2P system. This was to expose unaccounted
anomalies with the performance of the algorithms in use to store and distribute the
data. A simulator should allow us to experiment with different set-ups and
configuration scenarios. In theory, a simulator should help us to test and develop our
solution off-line and potentially with greater assurance. Network simulators can
reduce the development time for a P2P system. Therefore, it is important to review
the various simulator implementations, which provide support for P2P systems.
5
1.3 Network Simulators
Network simulators are typically used to simulate network communications in
particular scenarios or situations, without configuring ‘real’ machines or networks.
Simulators can help with the development and testing of a network application. There
are two main types of network simulators, packet-based and flow-based. Packet-based
network simulators, attempt to simulate data packets, such as NS-2 [13]. Other
simulators are flow-based, and work at the application level, which means they
disregard parts of the TCP/network stack. Several flow-based simulators, such as GPS
[14] have a mechanism to introduce packet delay, to provide realistic communication
characteristics, while others do not. Typically, packet-based simulators take longer to
complete a simulation than flow-based simulators. This is because of the calculations
made for each packet in the simulated network. Network simulators normally allow a
developer to produce a network topology and define delay, bandwidth and
connection/traffic characteristics for the nodes and links.
Lately, network simulators have evolved to allow the simulation of P2P systems.
Network simulators such as NS-2 have been used for testing P2P protocols, while
other network simulators, like OMNeT++ [15] have been forked to produce a
simulator specifically designed for P2P systems, namely OverSim [16].
P2P system development has many common issues found with programming other
distributed systems, such as difficulty when debugging. P2P systems add further
complications, especially when testing different topologies and setting–up scenarios
across multiple machines. Finding stable wide-area network connections and suitable
machines on these links is also a problem and can be impractical. Because the
environment is not fully controlled and results gathered may not be consistent. The
time taken to develop a P2P system can be longer, due to these issues. P2P network
simulators try to address the increased difficulty when designing or testing P2P
systems, by providing a virtual network environment.
This report will discuss the various network simulators suitable for P2P networks and
their features. We outline our experiences using the simulators and their ability to
model the Portal-based P2P system. Section 2 will review the network simulators and
provide the criteria for their suitability for our system. Section 3, discusses issues and
configurations with the simulators. Finally, Section 4 summarises and concludes.
2. Review
Simulators can be classified into two categories, packet-based and application-level.
Packet-based simulators calculate delay, bandwidth and routing for each packet
generated or used by the simulation. Application-level simulators do not account for
each packet instead they calculate bandwidth and delay to/from network end-points.
Application-level simulators usually use the terms ‘flow-based’ or ‘message-based’ to
describe how they evaluate communications between nodes in the simulation.
This section will review several network simulators suitable or specifically designed
for P2P systems. We define the criteria for the simulators, which lists our needs from
a simulator. Following this, we move on to detail the simulators, which includes NS-
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