2007:257 civ master's thesis mobile peer-to-peer ...1024904/fulltext01.pdfthe opportunity to...

2007:257 CIV

M A S T E R ' S T H E S I S

Mobile Peer-to-Peer Applicationsin Cellular Networks

Simon Persson

Luleå University of Technology

MSc Programmes in Engineering Media Technology

Department of Computer Science and Electrical EngineeringDivision of Media Technology

2007:257 CIV - ISSN: 1402-1617 - ISRN: LTU-EX--07/257--SE

Abstract

Since the introduction of Napster in 1999, Peer-to-peer applications has generatedcontroversy through providing users with tools for sharingfiles, which has resultedin a large increase of traffic in fixed networks while raising piracy issues. In re-cent years, other application areas for legal commercial services based on peer-to-peer technology have started to appear. Advancements in capabilities for mobilephones, combined with significant improvements in mobile networks introducedthe opportunity to provide mobile peer-to-peer services.

This thesis explores possible application areas for peer-to-peer in cellular net-works and for mobile phones. Through brainstorming and studying existing peer-to-peer applications in fixed and mobile networks, potential application areas areidentified. By combining analysis of identified applications combined with in-terviews of service providers and operators, the study provides an insight to thepossible benefits and drawbacks of peer-to-peer in cellularnetworks.

Data pricing, battery limitations and difficulties of adapting services to the mul-titude of different available mobile phones are identified as major obstacles formobile peer-to-peer service deployment. While these challenges are not unique topeer-to-peer architectures, the effects of pricing and battery consumption have aneven larger impact on applications built upon peer-to-peer, as they are relying oncontribution of resources from its users. Current characteristics of mobile indus-try, mobile phones and cellular networks do not provide an ideal entry point forpeer-to-peer architectures. However, the future is uncertain. If mobile data pricingapproaches flat-rate and services are light on mobile terminals, peer-to-peer couldoffer service providers a way to deploy services quickly with minimal investmentsin infrastructure. A first step toward mobile peer-to-peer could be to take advantageof peer-to-peer architectures in fixed networks to provide mobile services.

Preface

This is a master thesis report, presented at Luleå University of Technology as thefinal part of a Master of Science degree in Media Engineering.The work has beencarried out on the initiative of Ericsson Research in Luleå.

I would like to thank the employees at Ericsson Research, especially my super-visor Tommy Arngren. I would also like to thank Johan Kristiansson, for valuablefeedback, and Pontus, Daniel, Patrik, Andreas and Sarker for participating in abrainstorming session around mobile peer-to-peer applications. Finally I wouldlike to thank all respondents to the interviews carried out during the project and mysupervisor at LTU, Kåre Synnes.

Contents

1 Introduction 71.1 Objectives and Delimitations . . . . . . . . . . . . . . . . . . . . 71.2 Thesis Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2 Method 92.1 Literature Studies . . . . . . . . . . . . . . . . . . . . . . . . . . 92.2 Identifying Application Areas . . . . . . . . . . . . . . . . . . . 9

2.2.1 Studies of Existing Peer-to-Peer Applications . . . . .. . 92.2.2 Brainstorming . . . . . . . . . . . . . . . . . . . . . . . 10

2.3 Application Analysis . . . . . . . . . . . . . . . . . . . . . . . . 102.4 Mobile Business Survey . . . . . . . . . . . . . . . . . . . . . . 10

2.4.1 Respondent Selection . . . . . . . . . . . . . . . . . . . . 112.5 Method Review . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3 Background 133.1 Communication Models . . . . . . . . . . . . . . . . . . . . . . . 13

3.1.1 Client/Server . . . . . . . . . . . . . . . . . . . . . . . . 133.1.2 Peer-to-Peer . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.2 Peer-to-Peer and IMS . . . . . . . . . . . . . . . . . . . . . . . . 173.3 Mobile Phones . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.3.1 Device Capacity . . . . . . . . . . . . . . . . . . . . . . 183.3.2 Input/Output Capabilities . . . . . . . . . . . . . . . . . . 193.3.3 Platforms and languages . . . . . . . . . . . . . . . . . . 19

3.4 Cellular Networks . . . . . . . . . . . . . . . . . . . . . . . . . . 203.4.1 Addressing . . . . . . . . . . . . . . . . . . . . . . . . . 203.4.2 Network Capacity . . . . . . . . . . . . . . . . . . . . . 20

4 Applications for Mobile Peer-to-Peer 234.1 Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

4.1.1 Applications . . . . . . . . . . . . . . . . . . . . . . . . 234.1.2 Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . 25

4.2 Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274.2.1 Applications . . . . . . . . . . . . . . . . . . . . . . . . 27

3

4.2.2 Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . 284.3 Sharing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

4.3.1 Applications . . . . . . . . . . . . . . . . . . . . . . . . 304.3.2 Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . 31

4.4 Gaming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344.4.1 Applications . . . . . . . . . . . . . . . . . . . . . . . . 344.4.2 Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . 34

4.5 Indirect Peer-to-Peer Services . . . . . . . . . . . . . . . . . . . 364.5.1 Applications . . . . . . . . . . . . . . . . . . . . . . . . 364.5.2 Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . 37

4.6 Evaluation Summary . . . . . . . . . . . . . . . . . . . . . . . . 384.6.1 Peer-to-Peer . . . . . . . . . . . . . . . . . . . . . . . . . 384.6.2 Business Opportunity . . . . . . . . . . . . . . . . . . . . 384.6.3 Device Feasibility . . . . . . . . . . . . . . . . . . . . . 394.6.4 Network Feasibility . . . . . . . . . . . . . . . . . . . . . 394.6.5 User Value . . . . . . . . . . . . . . . . . . . . . . . . . 40

5 Operators and Service Providers 415.1 Operator Pricing Strategies . . . . . . . . . . . . . . . . . . . . . 41

5.1.1 Volume based . . . . . . . . . . . . . . . . . . . . . . . . 425.1.2 Flat-rate . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

5.2 Revenue Sharing . . . . . . . . . . . . . . . . . . . . . . . . . . 445.3 Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

6 Discussion 496.1 Difficulty of Defining Peer-to-Peer . . . . . . . . . . . . . . . . . 496.2 Service Deployment . . . . . . . . . . . . . . . . . . . . . . . . . 506.3 Designing a Mobile Peer-to-Peer Application . . . . . . . . .. . 506.4 User Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

7 Conclusions 55

8 Recommendations 57

References 57

A Interview notes 63A.1 Respondent 1 - Service Provider Perspective . . . . . . . . . .. . 63A.2 Respondent 2 - Operator Perspective . . . . . . . . . . . . . . . . 63A.3 Respondent 3 - Operator Perspective . . . . . . . . . . . . . . . . 63A.4 Respondent 4 - Academic Perspective . . . . . . . . . . . . . . . 64A.5 Respondent 5 - Service Provider Perspective . . . . . . . . . .. . 64A.6 Respondent 6 - Service Provider Perspective . . . . . . . . . .. . 64

5

Abbreviations

3GPP 3rd Generation Partnership ProgramAMR Adaptive Multi-RateAPI Application Programming InterfaceCDMA Wideband Code Division Multiple AccessCPU Central Processing UnitDHT Distributed Hash TableDRM Digital Rights ManagementEDGE Enhanced Data-rates for GSM EvolutionEVDO Evolution-Data OptimizedGPRS General Packet Radio ServiceGSM Global System for Mobile communicationsHSDPA High-Speed Downlink Packet AccessHSPA High-Speed Packet AccessIM Instant MessengerIMS IP Multimedia SubsystemIP Internet ProtocolJava ME Java Micro EditionLTE Long Term EvolutionMIDP Mobile Information Device ProfileMSN Microsoft NetworkNAT Network Adress TranslatorNFC Near Field CommunicationP2P Peer-to-PeerPDA Personal Digital AssistantSIP Session Initiation ProtocolSIM Subscriber Identity ModuleQoS Quality of ServiceRIAA Recording Industry Association of AmericaUMTS Universial Mobile Telecommunications SystemVoIP Voice over Internet ProtocolWCDMA Wideband Code Division Multiple Access

Chapter 1

Introduction

When Shawn Fanning founded Napster in 1999, he probably did not know thattoday, almost 10 years later, peer-to-peer related traffic would account for over 70percent of Internet bandwidth consumption [1]. He probablycould not imaginethat we would today have mobile phones with vivid color displays, built in highresolution cameras, combined with high speed mobile Internet access.

With Napster, peer-to-peer became strongly affiliated withpiracy, but peer-to-peer networking can offer more services than just file-sharing. Voice over IP, In-stant Messaging and Internet television are a few examples of what can be and hasbeen implemented using peer-to-peer technology. Peer-to-peer networks have re-ceived attention in current research due to the interestingproperty that it is providedwith additional resources as new peers join the network. This indicates potential forproviding scalable services with low deployment costs. Canthese technical charac-teristics be exploited in a mobile environment? Which services could be developedwhen combining mobile phones with the concept of peer-to-peer networking?

1.1 Objectives and Delimitations

This master thesis aims to explore the area of mobile peer-to-peer in cellular net-works. Characteristics of peer-to-peer, mobile networks and cellular devices willbe investigated. Peer-to-peer applications in fixed and mobile networks will bestudied and analyzed. The thesis main objectives are:

• To identify business opportunities and future possible mobile peer-to-peerapplications.

• To identify technical and business oriented challenges that are to be facedwhen developing and deploying mobile peer-to-peer services.

Limiting the scope of the study is important. This since mobile peer-to-peercan include a wide range of networks, devices and technologies. To cover all pos-sible combinations would require far more time and effort than a master thesis.

7

8 CHAPTER 1. INTRODUCTION

The study will focus on cellular networks and will not look into short-range tech-nologies as Bluetooth, Near Field Communication (NFC) and WiFi, despite thepossibility that peer-to-peer could be well suited for short-range ad-hoc networks.Applications will be identified and analyzed with cell-phones as a starting point.The motivation is that by selecting cell phones and cellularnetworks, the studywill have to take business relations between operators and service providers intoconsideration much more than with non-operator controllednetworks.

Focus of the thesis will be on business and technological issues. Consumerattitudes and values toward mobile peer-to-peer will only be of secondary impor-tance. Some technical challenges that will be investigated, most notably devicelimitations as battery performance, will however translate directly into consumerlevels of satisfaction of mobile peer-to-peer services. Thus, the study will coveruser aspects indirectly.

1.2 Thesis Outline

The report is structured as follows: The first chapter will provide a brief introduc-tion to the master thesis and its objectives. The second chapter will describe theresearch approach and methodology used throughout the project. Chapter threewill provide a theoretical overview of mobile devices and peer-to-peer networking.The fourth chapter will explore potential application areas for mobile peer-to-peerand chapter five will cover business relations, pricing, revenue sharing and operatorcontrol. Chapter six discusses results and the seventh chapter concludes the thesiswork.

Chapter 2

Method

According to Cooper et. al [2] exploratory studies mainly rely on qualitative tech-niques and can be particularly useful if the area of investigation is new, vague orif important variables are not known or thoroughly defined. Peer-to-peer can havemultiple definitions and meanings, which will be discussed in section 3.1.2, and thepotential usage of peer-to-peer networking in cellular networks is not clear. Thusan exploratory approach can be motivated. This chapter willdescribe the methodsused.

2.1 Literature Studies

Exploration typically starts with searches of published data [2]. At an initial stageof this thesis, literature studies included academic literature and technical reportson mobile and fixed peer-to-peer in order to gain a first insight into the researcharea. Computer-aided mind mapping provided a tool for structuring gathered data.

2.2 Identifying Application Areas

After establishing technical background through initial literature studies, the nextstep was to identify possible applications for mobile peer-to-peer in cellular net-works. At this stage, studies of existing peer-to-peer applications and brainstorm-ing were the two main methods used.

2.2.1 Studies of Existing Peer-to-Peer Applications

Existing fixed and mobile peer-to-peer applications were studied throughout theproject. At first, the purpose was to identify application areas and find what waspossible to implement. At a later stage, implementation details provided a basefor further analysis. Information about respective applications was gathered fromacademic literature and commercial web sites.

9

10 CHAPTER 2. METHOD

2.2.2 Brainstorming

In addition to studying existing peer-to-peer applications, a brainstorming sessionwas performed in an attempt to gather new and original ideas for possible mobilepeer-to-peer applications.

Participants

Participants consisted of five master thesis students at Ericsson research in Luleå,with educational backgrounds in computer science or telecommunication. The se-lection of participants in the brainstorming session is likely to have affected therange of ideas generated.

2.3 Application Analysis

After identifying application areas, each area was analyzed in an attempt to asses itsmarket potential and applicability to mobile peer-to-peer. The analysis was basedon inspection of peer-to-peer architectures and through literature studies. Identifiedapplication areas were analyzed with respect to the following aspects:

1. Peer-to-peer:How does a peer-to-peer implementation compare to alterna-tive solutions? What technical advantages or disadvantages can be identi-fied?

2. Business opportunities: Is there a business opportunity in providing theservice? How will this be affected by a peer-to-peer implementation?

3. Device feasibility: Is this service possible to implement on mobile plat-forms? How will the implementation be affected by platformsand devicecapacities?

4. Network feasibility: How will mobile networking conditions affect the ap-plication area?

5. User value: What effects would a peer-to-peer implementation have onusers? What would be drivers and barriers for user adoption?

2.4 Mobile Business Survey

Apart from literature studies and application explorations, interviews were madeto explore different viewpoints on peer-to-peer and mobilebusiness. Six inter-views were made in total, of which three were in person, one over telephone andtwo through email. The in-person and telephone interviews where unstructured,only guided by a list of subjects to be covered. The email interview required pre-determined questions due to its written format. In this casethe questions where

2.4. MOBILE BUSINESS SURVEY 11

open ended and follow up questions where posted on replies, mimicking a semi-structured interview format. Recording equipment was not used for the interviews,but notes were taken during the session and reviewed immediately after the inter-view. Brief interview summaries can be found in Appendix A.

2.4.1 Respondent Selection

Respondents were selected based on professional background and attempted tocover the area of peer-to-peer and mobile services from a wide range of perspec-tives. Representatives for mobile operators and service providers were questioned.

Respondent 1

Lead software engineer at a company that uses peer-to-peer technology to distributemedia. While the respondent is not involved in the mobile services, he has a deepunderstanding of peer-to-peer and its business implications.

Respondent 2

Has a high position at a mobile operator, responsible for information and publicrelations.

Respondent 3

Works as a senior consultant for a large mobile operator and has many years ofexperience working with business aspects of mobile services.

Respondent 4

Employed at a university research center focused on future anytime-anywhere mo-bile services. His focus is not on commercial interests, butrather trying out newconcepts with the aid of high-fidelity prototyping.

Respondent 5

CEO of a small company developing a wide range of mobile services. As suchhe has gained information first hand about launching mobile services and whatobstacles that needs to be overcome.

Respondent 6

CEO of a small company that is developing a mobile peer-to-peer application thatis soon to be released on the market. Has first hand experienceof aspects of mobilepeer-to-peer application development.

12 CHAPTER 2. METHOD

2.5 Method Review

Saunders et al. [3] states that it would not be possible to produce reliable resultsfrom qualitative studies without undermining its ability to explore the complexityof the topic. Reliability of this thesis can be difficult to asses due to the qualitativemethods used.

Brainstorming sessions are by definition not repeatable as they are intended togenerate new ideas. A possible limitation of the performed session is that, whileit might take some technical knowledge to grasp the concept of peer-to-peer, thesimilar technical background of the selected participantsis likely to have affectedthe range of ideas generated. It is perfectly understandable that categories of appli-cations might have been overlooked.

The in-depth interviews have been unstructured, i.e. not relying on predefinedquestions, making it difficult to provide reliable results.Involving external actors inassessing business relations can arguably be said to have increased validity. How-ever, the interviews only reflect the viewpoints of the selected respondents and thesmall number of interviews can be a limiting factor. Not using recording equip-ment, could introduce possible artifacts when re-telling exact words and phrasesfrom interviews. The choice of making interview respondents anonymous mayhave resulted in a greater freedom of speech, at the expense of making it difficultto assess reliability and validity.

This thesis has been based on characteristics, challenges and limitations of cur-rent conditions and trends pointing toward a possible future. As conditions change,the study will loose relevancy. However, as noted by Saunders [3] “findings fromusing non standardized methods are not necessarily intended to be repeatable asthey reflect reality at the time they were collected, in a situation which may be asubject of change ”.

Chapter 3

Background

This chapter aims to provide an introduction to peer-to-peer technology and how itcan be applied to cellular networks. Characteristics of cellular networks, peer-to-peer and mobile devices will be covered.

3.1 Communication Models

This section describes client/server and peer-to-peer communication models.

3.1.1 Client/Server

In a client/server distribution system, content is stored on a centralized resource, aserver, from which clients can request data. Each new clientputs an additional loadon the server, which could be a potential bottleneck in the system. If a server isincapable of handling all requests it is common to add additional servers forming acluster of hosts to increase capacity [4]. Client/server architectures provide contentaccess through known public addresses, minimizing signaling overhead.

3.1.2 Peer-to-Peer

“Ask ten different computer scientists what peer-to-peer is, and youmay get ten different answers. And chances are, all will be correct.That’s the trouble with grand terms such as peer-to-peer - they mayinclude so many different ideas that they could simultaneously meaneverything and nothing[5].”

The above quote by Fattah [5] illustrates the difficulties faced when trying to definewhat peer-to-peer actually is. Goodman et. al [1] refers to peer-to-peer as a networkof equals, where two or more individuals can spontaneously collaborate withoutnecessarily needing central coordination. The concept of equality is recurrent inother definitions. Fattah [5] simply defines peer-to-peer computing as the directcommunication between individual computers, or people, that operates as equal

13

14 CHAPTER 3. BACKGROUND

peers. Common for both definitions is that they leave room forinterpretation. Anuncertainty of whether the authors refer to peer-to-peer asend-to-end applicationsor as an architectural concept is reoccurring in many definitions.

In this thesis the definition of peer-to-peer will be separated into two levels,content level and resource level.

• Content level: On the content level, is defined as services where users ex-change content. If either party can initiate the content transfer on equalterms, the application can be said to be a peer-to-peer application on the con-tent level. This would include IM applications, VoIP, regular circuit switchedtelephone calls or even services like YouTube, while havinga client/serverimplementation, allows users to share content on equal terms.

• Resource level:On a resource level, peer-to-peer is referred to as architec-tures where peers are contributing to the network through direct connectionson equal terms. Common for resource level peer-to-peer applications is thatservers are relieved from content transfer, adressing or both.

This thesis will study peer-to-peer architectures where peers are contributing tothe network. Thus peer-to-peer will be referred to on the resource level unlessstated otherwise. The definition used in this thesis is only one of many possibledefinitions and cannot be said to be more true or false than alternative definitions.Resource level peer-to-peer architectures consist of two components:

• Peer discovery; how peers are located within the network

• Data transfer; the actual transfer of resources from one peer to another.

Data Transfer

Data transfers can be done in a one-to-one, many-to-one, one-to-many or many-to-many fashion. One-to-one transfers are straightforward. When the peer in posses-sion of the desired data has been located, a connection is setup directly between thetwo peers and data transfer is initiated. In addition to one-to-one transfers, someprotocols allow for many-to-one transfers by enabling users to add more sourcepeers for the current download. In order to achieve this, data can be divided intodifferent parts which are downloaded individually from different peers and assem-bled locally to form a complete file.

Many-to-many protocols take the concept of dividing data into small parts evenfurther by requiring peers to make partial downloads available for upload in orderto be able to continue downloading. An example is BitTorrent, where users simul-taneously uploads and downloads the same file, to and from multiple other users.BitTorrent, as a many-to-many protocol, has the unusual property that the transfercapacity of a particular file increases with the number of downloading peers.

Finally one-to-many transfers, or application layer multicast, could be imple-mented through peer-to-peer. In this case the peer sends theresource to a subset

3.1. COMMUNICATION MODELS 15

of the receiving peers, who in turn passes it on until the file is distributed to therecipents.

Peer Discovery

Peer-discovery can be done in a number of ways and each solution has differentcharacteristics, with respective strengths and flaws. Presented here is a selectionof possible strategies for locating resources in the peer-to-peer network. Peer-to-peer protocols can use either structured or unstructured discovery. Unstructureddiscovery methods can be either centralized, completely decentralized or have acombination of centralized and decentralized elements. Structured peer-to-peerarchitectures typically rely on hashing to maintain its network structure.

Centralized In a centralized peer discovery structure, a central serverstores in-formation about connected peers and the shared resources. Peer discovery is donethrough a central server, while the actual data transfer is done in a peer-to-peer fash-ion, relieving the server from content transfers. The original Napster applicationis a typical example of a service built upon a centralized peer-to-peer architecture.The centralized method has the advantage of reducing signaling overhead, but asthe number of peers grow, the central server capacity continuously need to be in-creased in order to avoid becoming a bottleneck in the system. The centralizedpeer-to-peer architecture is illustrated in Figure 3.1.

Figure 3.1:Centralized peer-to-peer structure.Step 1: Peer1 sends a request tothe server. Step 2: The server searches its index and replieswith the informationneeded to connect to Peer2, which is in possession of the desired resource. Step 3:Peer1 requests a file transfer from Peer2. Step 4: The file is transferred.

Decentralized Completely decentralized peer-to-peer structures are commonlyrefereed to as the only pure peer-to-peer architectures. Indecentralized structures,all peers have equal status and there is no central element for coordination. The


need for servers is eliminated all together and the network has no single pointof failure. An example of a decentralized protocol is Gnutella [6]. It relies onbroadcast messages for finding other peers. Peer discovery in Gnutella is initiatedthrough sending a request message to neighboring peers. Therequesting messagesare forwarded by the receiving peers as long as the desired resource is not found.To ensure that searches are terminated and to reduce stress on the network, eachmessage is stamped with a time-to-live that is decreased by one every time themessage is forwarded by a peer. In completely decentralizedstructures, peer dis-covery is complex and there are no guarantees that a resourcewill be found [1].It is possible that separate peer-to-peer islands are formed if the time-to-live is notsufficient for connecting them. Searches in a decentralizedstructure will be bothtime consuming and bandwidth consuming, producing more broadcast overheadthan centralized counterparts. A simplified decentralizedarchitecture is illustratedin Figure 3.2.

Figure 3.2:Decentralized peer-to-peer structure.Step 1: Peer1 sends a requestto Peer2 for data. Step 2: Since Peer2 does not have the desired resource it reducesthe time to live of the query and forward the request to its adjacent peers. Step 3:The peers respond to the query by issued by Peer2. Step 4: Peer2 replies to Peer1that the resource has been located at Peer 3. Step 5: Peer1 requests a data transferfrom Peer3. Step 6: The data is transferred.

Hybrid A third approach for peer-discovery is to use a mix of the centralizedand decentralized architectures. Peers are examined with respect to available re-sources and put into two categories: regular peers and superpeers. Regular peersare connected to super-peers in the same way as peers in a centralized peer-to-peerarchitecture are connected to servers. Super peers are responsible for connectingthe separate centralized peer-to-peer networks. From a regular peers perspective,the network works just as if it was centralized, taking advantage of efficient ad-dressing. On the other hand, the higher capacity peers will have to handle thequery messages for regular peers. A simplified hybrid architecture is illustrated inFigure 3.3.

3.2. PEER-TO-PEER AND IMS 17

Figure 3.3:Hybrid peer-to-peer structure. Step 1: A query is sent from Peer1 toSuperPeer1. Step 2,3: The query message is forwarded to other super peers untila peer with the suitable resource has been found. Step 4,5,6:A message with theidentity of the peer of interest is sent back to Peer1. Step 7:Peer1 requests a filetransfer. Step 8: The data is transferred.

Distributed Hash Table While the previously described peer discovery methodshave been unstructured, some peer-to-peer protocols aims to provide a structureddiscovery through the use of a distributed hash table (DHT).Two examples of DHTprotocols are Chord [7] and Can [8]. Each resource is associated with a name andvalue key, and the value associated with a given name can efficiently be retrievedthrough applying hash functions. An advantage of distributed hash table algorithmsis that they can offer guarantees of performance and be resistant to individual nodefailures [9].

3.2 Peer-to-Peer and IMS

The IP Multimedia Subsystem (IMS) is an architectural framework for service de-velopment by the Internet Engineering Task Force (IETF) andthe 3rd GenerationPartnership Program (3GPP). IMS provides a complete architecture of applicationservers, quality of service (QoS) management, billing control and integration ofservices [10]. Some potential services for IMS such as Instant Messaging, Voiceover IP (VoIP) can be classified as peer-to-peer on the content level (see section3.1.2). However, on the resource level, IMS represent an architectural concept thatis very different from peer-to-peer. Peer-to-peer architectures aim to reduce loadon centralized elements through distributing responsibilities to the end nodes ofthe network. IMS on the other hand moves functionality and intelligence in theother direction, toward the core of the network. IMS services are centralized andstandardized. Service providers can use the existing IMS functionality for commonfunctions and only implement functions that are missing [11]. However, through


using IMS functionality, service providers relies on infrastructure provided by op-erators. With peer-to-peer architectures, the infrastructure is instead provided bythe users of the peer-to-peer service.

3.3 Mobile Phones

Camponovo et al. [12] refers to mobility as the only advantage upon which mobileservices can build their value proposition and identifies the following benefits ofmobile devices: freedom of movement (can be used on the move), ubiquity (canbe used everywhere), localization (can use position to provide location based ser-vices), reachability (users can be reached anytime, anywhere), convenience (userscan carry mobile devices with them) and personalization (can exploit that mobiledevices typically are connected to its users identity). With mobility a number ofchallenges arise. This section will cover device limitations imposed by mobility,such as processing power, battery consumption and user interface limitations.

3.3.1 Device Capacity

Battery

While batteries enable mobile operation, it simultaneously imposes high demandson energy efficiency. A higher power consumption of a component in a mobilephone equals shorter battery life. The importance of battery life in peer-to-peerapplications has been studied by Matuszewski [13]. His findings indicate users arereluctant to share resources with unknown peers, even if theservice is provided forfree and the only drawback would be shorter battery life.

Processing Power

Processing power is a challenge in mobile devices. Not only do mobile processorsneed to be kept small, they also have very high demands on energy efficiency. Atrade-off needs to be made between battery performance and processing power. Anincrease of processing power will result in shorter batterylife, unless the processorefficiency is improved or the battery capacity is increased.On the other hand, poorprocessing power can result in unresponsive user interfaceand decrease end-usersatisfaction.

Memory

Memory capacity varies between different phone models and price ranges. As of2007, major cell phone manufacturers as Nokia, SonyEricsson and Motorola hasentry level cell phones in their product lines with limited memory of less than< 10Mb of memory. Many of them without high speed Internet access. For moreadvanced phones it is common with a larger memory capacity, either as standard

3.3. MOBILE PHONES 19

or through the use of external memory cards. With increased availability of digitalcameras and mobile phones with expandable memory, prices ofexternal memorycards have become more affordable.

3.3.2 Input/Output Capabilities

Input/output capabilities on mobile phones vary between different models. Bydefinition a mobile phone would include a microphone, a speaker and some methodof inputting telephone numbers. In recent years additionalfunctionality, such asbuilt in cameras, at varying resolutions, has become common. Text input methodsvaries from simple numbered buttons on simple phones to QWERTY keyboards onmore advanced smartphones. Even though input/output hardware is existent on aparticular device, another issue is how to access its functionality for use in mobilesoftware applications.

3.3.3 Platforms and languages

In contrast to desktop PC environments, where applicationsare usually imple-mented for a single operating system, mobile application developers face the chal-lenge of having to adapt services to different devices and platforms. There aremany operating systems available for use in mobile phones. Linux, Symbian andWindows Mobile are a few examples and many manufacturers provide phones withtheir own operating systems. This makes it more complicatedfor developers aseach platform may require an individual implementation [14].

For some applications, Java Micro Edition (ME) can prove useful to solvingthe problems of different operating systems. Java ME [15] provides a commonapplication platform for a variety resource constrained devices, such as PDAs, mo-bile phones and embedded devices. As different devices havedifferent properties,capacities and usage areas, Java ME has been divided into different configurations.Each configuration provide a specific set of devices with a virtual machine andclass libraries to enable access of basic functionality fordevelopers [16]. MobileInformation Device Profiles (MIDP) add APIs specific to mobile phones. In addi-tion, platform developers can chose to implement optional packages for supportingmore features.

Applications implemented in Java Standard Edition are known for their porta-bility. In Java ME, the situation is a bit different. A problem is that there arelarge differences among Java ME devices, including screen sizes, color depths anddifferences in multimedia capabilities. Kochnev [17] argues that the portabilityof Java ME is more to compare with the portability of C++ programs than JavaStandard Edition applications.


Table 3.1: Typical capacity of network configurations. Up (theory) andDown(theory) represents theoretical peak network bandwidth values. The user valuesrepresents peak achievable user rates. All values has been collected from the 3GAmerica white paper mobile broadband[19]

Network Down(theory) Down(user) Up(theory) Up(user) RTTGPRS 53.6kbps 40kbps 53.6kpbs 40kbps 700msEDGE 236.8 200kbps 236.8 200kbps 600ms

WCDMA 384kbps 350kbps 384kbps 350kbps 200msHSDPA 3.6Mbps >3Mbps 384kbps 350kbps 150msHSPA 7.2Mbps 5.76Mbps 100msLTE 100Mbps 50Mbps 50ms

3.4 Cellular Networks

The term cellular refers to a partition of a geographical area into smaller coverageareas, cells [4]. A base station, located in each cell communicates with mobileterminals within its designated coverage area. Cellular technologies are often clas-sified into generations, where first generation (1G) networks were analog systemsfor voice communication. Second generation networks (2G) were digital, but stillprimarily designed for voice communication. With the introduction of the GeneralPacket Radio Service (GPRS), 2G networks have evolved to handle data traffic.

Third generation (3G) networks are designed to provide bothvoice communi-cation and data communication at higher speeds.

3.4.1 Addressing

Reliance of on various Network Address Translator (NAT) solutions is common inboth fixed and mobile networks. A problem with NAT boxes in a peer-to-peer envi-ronment is that once a connection between two peers is closed, the NAT will updateits translation table. A peer located outside the NAT will have trouble locating thepeer behind the NAT after a connection has been closed, sincethe correspondingtranslation entry is gone. This means that if peers are located behind NATs, theconnection needs to be kept alive in order to avoid closing down the connection.An issue with keep-alive messages is their effect on batteryconsumption levels.According to Kessens [18] sending a keep-alive message every 30 seconds reducescell phone standby time by several days. The addressing problem and the needfor keep-alive messages would apply to both peer-to-peer and centralized architec-tures. Similar issues could arise from the usage of firewalls.

3.4.2 Network Capacity

GPRS introduced the possibility of developing data-based services to 2G networks,but the networking environment with poor bandwidth and latency measurements

3.4. CELLULAR NETWORKS 21

has been a limiting factor to the services that have been possible to provide (furtherreading in this area can be found in section 4.6.4). With current 3G (WCDMA andbetter) and upcoming 4G mobile networks, capacities are continuously increasing,making it possible to develop applications requiring higher bandwidth and lowerlatency. Typical performance characteristics of different cellular networks are pro-vided in table 3.1.

Actual throughput will be dependent on a range of factors such as cell prox-imity, number of users and the surrounding environment and can be significantlylower than the specified peak values. While it is difficult to state absolute values,an estimation used by Rysari at 3G Americas is that half the peak user achievablerate should be available to most users [19]. Due to the variations in latency andthroughput it can be difficult to guarantee levels of QoS in mobile networks.

Chapter 4

Applications for MobilePeer-to-Peer

In this chapter, a sample of potential application areas, where peer-to-peer tech-nologies can be applied in a mobile context, will be illustrated. The applicationshas been categorized into the following:

• Communication

• Distribution

• Sharing

• Gaming

• Indirect Peer-to-Peer services.

Each category of applications will be defined and exemplifiedwith existing ap-plications or through application concepts for services where no existing equivalenthas been identified. Applications will be analysed in respect to peer-to-peer, busi-ness opportunity, device feasibility, network feasibility and user value (see section2.3). The chapter is concluded with a summary of the analysisresults.

4.1 Communication

This category consists of applications that provide real-time exchange of messagesbetween peers. Several types of media can be used, includingtext, voice and video.It is possible for communication applications to provide communication through acombination of the identified media types.

4.1.1 Applications

Communication applications are very common and widely used, with a few exam-ples being Microsoft Network Messenger (MSN) [20], Google Talk [21] and ICQ

23

24 CHAPTER 4. APPLICATIONS FOR MOBILE PEER-TO-PEER

Figure 4.1:Skype architecture. (reference [25])

[22]. Many communication applications use centralized architectures. However,Skype [23] and Fring [24] are two applications based on peer-to-peer networkingconcepts.

Skype (Fixed)

Skype [23], founded in 2003, provides a service for Internettelephony based onpeer-to-peer principles. Based on a proprietary protocol,where addressing, load-balancing and NAT-traversal is handled by peers, the only required hardware forrunning Skypes internal network is a couple of login servers[25]. Calls withinthe Skype network are provided free for its users, while premium services, suchas calling to or accepting calls from the public switched telephone network, arecharged for. The application is available for a variety of platforms including Win-dows, MacOS, Linux and Windows Mobile. Skype versions for Symbian and JavaME are available, but as these connects to the Skype networksthrough gatewaysthey are described in section 4.5

Fring (Mobile)

Fring [24] is an application for instant messaging and VoIP,currently availablefor Symbian OS and Windows Mobile. Currently there are no charges for usersexcept for the data traffic charges from mobile operators. The application can beused through WiFi connections or cellular networks such as 3G or EDGE and hasbuilt in functionality for roaming. Just as Skype, Fring uses a proprietary peer-to-peer protocol for communication within its own network, andrelies on gatewaysin order to connect to other applications and protocols. Thearchitecture of Fringis shown in Figure 4.2. While Skype relies on super-nodes forpeer-discovery,it is assumed that Fring uses a centralized structure (see Section 3.1.2) in order

4.1. COMMUNICATION 25

to minimize the load of signaling and reduce battery consumption on end-userdevices.

Figure 4.2:Fring architecture

4.1.2 Evaluation

Peer-to-peer

According to the definition of peer-to-peer used in Section 3.1.2, all applicationsthat allow communication among equals are classified as peer-to-peer applicationson the communication level. However, on the resource level,communication ap-plications could be implemented in a number of ways. As notedin section 3.2,IMS enables use of centralized and standardized services and payment solutions,facilitating application deployment and offers advantages such as Quality of Ser-vice (QoS) management. IMS heavily relies on centralized elements, which canincrease the cost of architecture deployment. According toBraet et al. [26], inpeer-to-peer solutions, the cost of ownership is pushed toward the edges as it is thepeers that provide the infrastructure. Without relying on centralized elements, itwould be difficult for peer-to-peer VoIP to provide QoS.

As noted in section 3.4.1, addressing and NAT traversal is a widespread prob-lem in end-to-end applications. Peer-to-peer can offer benefits for service providerswishing to reduce effects of nodes behind NATs and firewalls.A technical ad-vantage of hybrid peer-to-peer structures (section 3.1.2)compared to centralizedstructures is that super nodes can act as relays and thus enabling the possibility oflocating relays closer to the unreachable node than would beachievable with relaysat central locations. As shown by Chiang et al. [27] the ability to keep the relayclose to the unreachable node has provided Skype with a performance advantagecompared to MSN, that uses centralized relays.


Business Opportunity

For independent service providers, peer-to-peer enables apotential opportunity tocompete with operators without having to build their own infrastructure. Peer-to-peer communication services could be competing with regular circuit-switchedservices today and possibly with future IMS based communication services. Adisadvantage compared to its operator based competition would be lack of QoS,which can have an effect on voice quality over mobile networks. Braet et. al.[26] argues that best effort has not stopped Skype from achieving success in fixednetworks. However, the impact of QoS service would be less prominent in fixedenvironments, as they typically have more stable networking conditions with lowerpacket loss, latency and jitter measurements.

For operators, implementation of IP-based voice calls add an additional over-head of about 19 percent [28] compared to a regular circuit switched call, whichwill increase traffic costs. This would apply to both IMS and P2P solutions. Toweigh up for the increased overhead, packet switched VoIP would be easier to in-tegrate with other services such as text messaging, video-chat and file sharing [28].

Device Feasibility

Even though many modern mobile phones are equipped with cameras, calendars,games and media players, the primary purpose for telephonesis communication.With built in microphones and speakers being core features of mobile phones,the obstacle for implementing multimedia communication services is in softwareimplementation. Text messaging only requires that the application can open IP-connections for incoming and outgoing text messages and that the phone keyboardcan be used for text input for the application. This can be andhas been imple-mented using basic functionality of Java ME. As described insection 3.3.2, ac-cessing other native hardware functionality, such as microphones and speakers,can provide a difficulty for service providers. This is reflected in that current im-plementations of VoIP such as Skype or Fring are presently (Oct, 2007) only avail-able for mobile phones with advanced mobile operating systems such as SymbianOS and Windows Mobile.

Network Feasibility

Bandwidth requirements of instant messaging depend on the length of the ex-changed messages, but are very low in comparison to exchangeof other media.While chat conversations can be executed in real-time, the delay requirements arenot as tight as real-time audio or video applications. According to Holma [28] con-versational audio and videos requires that end-to-end delays are kept below 400ms, while delay values at 150 ms or less are preferable. Bandwidth consumptionis dependent on the type of codec used for communication, buta lower bit ratelimit for conversational video on a normal size mobile phonedisplay is about 40-64 kb. For VoIP, the Adaptive Multi-Rate (AMR) codec that canbe used for circuit

4.2. DISTRIBUTION 27

switched or packet switched voice applications in 3G networks, has a typical band-width of 12.2 kbps. While VoIP becomes theoretically possible in 3G networks,where latency values are approaching the preferred 150 ms limit, variations of net-working conditions results in jitter and packet loss and render it difficult to provide3G VoIP without proper Quality of Service management.

User Value

In fixed networks, the main driver for VoIP calls has been price [28]. If the priceadvantage is still valid in mobile networks relies on the pricing policies of mobileoperators. With data prices approaching flat-rate, VoIP provided by independentservice providers could possibly provide an alternative toregular circuit switchedcalls. Compared to regular operator based voice calls, SMS and MMS, independentapplications based peer-to-peer will face other challenges. Users would have todownload and install applications, start the application in order to be able to calland keep the application running in order to be able to receive calls.

4.2 Distribution

This category consists of applications where peer-to-peeris used as a technique todistribute media or files among users. The main characteristic is that the sourceof media or files is a commercial content provider and not other peers. In contrastto communication applications, distribution applications can not be classified aspeer-to-peer on the content level. From the user’s point of view, the interaction isbetween the user and a centralized source of information. Peer-to-peer is merelyan architecture for the underlying transport mechanism to deliver that informationto the end user. Distribution services can be divided into two categories:

• Real-time Distribution: Real-time distribution services provide the userwith content that is typically not permanently stored afterthe application hasbeen terminated. Content is to be viewed instantaneously.

• Downloading services:In downloading services, the content is transferredand saved on the user terminal. Downloading services enables more freedomto users, since the downloaded data can be viewed or executedat any time.

4.2.1 Applications

Commercial services for distributing premium content havestarted to emerge infixed networks. Joost [29] represents an application for distributing streamingvideo, while VeOH [30] is an application that uses peer-to-peer mechanisms totransfer media files to the end-user. In addition to the applications presented here,there are several other distribution services using peer-to-peer technology includ-ing Azureus Vuze [31], BBC iPlayer [32] and Sky Anytime PC [33].


Joost (Fixed)

Joost [29] is an application that provides on-demand Internet television. The com-pany is collaborating with a number of television companieslike MTV, NationalGeographic, Warner Bros and Virgin and even though the service is still in Betastage, it has gotten much attention. Joost uses peer-to-peer to take advantage ofusers upload band-with and client-side load balancing.

While Joost is using a peer-to-peer transport protocol, content servers are stillused in order to fill the gap between down-link and up-link performance imposedby asymmetrical broadband connections.

Veoh (Fixed)

VeOH [30] is a media portal consisting of two parts. Their webportal is similar toYouTube in appearance, where a difference is that it can recommend and automat-ically play videos similar to the ones previously watched. The other part of VeOHis a TV application, where content is distributed through a peer-to-peer protocolsimilar to BitTorrent. Business models are not yet clear, but VeOH has plans forrevenue sharing of premium content and using advertising for financing its service.

4.2.2 Evaluation

Peer-to-Peer

A peer-to-peer approach for distributing content is arguably more complex thana client/server approach. In a client/server implementation, the client issues a re-quest to the server and the file is transmitted. The procedureis then repeated foreach client. If peer-to-peer distribution is to be implemented, each client will beresponsible for contribution for up-link performance. Where many simultaneousconnections are made, the coordination of peer resources will add to implementa-tion complexity. The need for content servers is reduced by letting peers handledistribution and load balancing.

Figure 4.3:Comparing client/server and peer-to-peer architecture for content dis-tribution.

4.2. DISTRIBUTION 29


According to Hausenblaus[34], peer-to-peer distributionservices such as Joostseems to be approved by the major parts of the media distribution value chain. Con-tent providers are provided a safe encrypted distribution method for their media;advertisers can use the same business models as in regular television and end-usersare provided with free entertainment. Peer-to-peer distribution can cut distribu-tion costs for service providers, shifting bandwidth coststoward users and mobileoperators (see fig 4.3).

However, peer-to-peer distribution is based on the assumption that there are re-sources to spare, and the starting point of in telecommunication is rather limitationof resources than abundance [26]. Mobile operators and users will experience anincreased up-link usage, which may not be desirable.

Device Feasibility

Peers need to be able to both request information and allow for incoming con-nections. By contributing up-link capacity, device resources are used more inten-sively than in alternative implementations. Common for theapplication examplesreferred to in this category is that they rely on many-to-many connections for trans-ferring files, where users are simultaneously uploading anddownloading parts toand from other peers in the network. It can be argued that thisapproach, withmany simultaneous connections in both directions would be taxing on mobile de-vices, leading to higher CPU usage and battery consumption.

Network Feasibility

Downstream performance of peer-to-peer distribution systems would be limitedto the upstream capacity of nodes participating in the network. For peer-to-peerdownloading services bandwidth measurements only affect the time it takes forusers to receive content. For real-time distribution, there are additional require-ments on the transmitter, such as jitter and steady upload rates. Poor networkconditions can have an effect on the user perceived quality of streamed media.According to Holma et. al [28], streamed television requires at least 112 kbpsbandwidth, and radio needs at least 64 kbps for used on mobiledevices.

User Value

Compared to client/server distribution, the difference isthat peer-to-peer distribu-tion requires users to upload content. The cost of upload is transferred from theservice provider to the user, both in terms of bandwidth and device resources, inthe form of CPU and battery life.


4.3 Sharing

The sharing category consists of applications where content is shared directly be-tween peers. A characteristic is that users can provide the network with additionalfiles or media resources and are able to locate content made available by otherpeers.

• Unrestricted file sharing: No restrictions are imposed on the shared media.All types of content are allowed, regardless of type, size ororigin.

• File sharing of user generated content: Enables peers to exchange files,but still under control of the service provider. The application can be limitedin the amount of data that can be uploaded or which types of files that areallowed.

4.3.1 Applications

Peer-to-peer is by many strongly affiliated with file sharing. Next, a number of ap-plications that relies on peer-to-peer sharing will be described. Napster and Sym-Torrent represents file sharing as it has become known to the general public, as theyenable or has enabled sharing of premium content without theconsent of contentproviders. Social FM represents an alternative way of sharing music without vi-olating copyright laws and the Photo Share concept represents an application thatenables sharing of user generated photos.

Napster(Fixed)

Napster was released in 1999 and allowed users to find and share music with eachother through a centralized peer-to-peer structure. Not long after Napsters launch,the Recording Industry Association of America (RIAA) filed alawsuit against Nap-ster for copyright infringement [35] and eventually had to restrict its usage and losta large amount of users. Although Napster is no longer available in its originalform, the application was only the first of many to come unrestricted peer-to-peerfile sharing applications. Napster raised tremendous attention in media and hasbecome a strong contributor to the strong peer-to-peer affiliation with piracy.

SymTorrent(Mobile)

SymTorrent [36] is a free and open-source as mobile client for the BitTorrent proto-cols developed at Budapest University of Technology and Economics. SymTorrentusers have equal status as peers using other BitTorrent clients and provide upstreamresources in exchange for being able to download content. Currently, the applica-tion supports the Symbian OS S60 platform.

4.3. SHARING 31

SocialFM(Fixed/Mobile)

Social F.M. [37] is an Internet radio service based on peer-to-peer distribution.The application automatically searches for songs and simultaneously makes songsavailable for broadcast to other users. It is possible for users to create their ownradio stations by sharing play-lists. Social F.M. is an entirely legal service as itactually pays royalty fees generated by the application. Inorder to be able toclassify the application as an Internet radio, there are constraints on what users areable to listen to. For example, one can only listen to 3 songs from one album withina given time-frame and it is not possible to repeat the song that has been listenedto. Furthermore, it cannot be guaranteed that any given songis playing at a certainmoment. While Social F.M. currently does not support mobiledevices, a mobileversion is listed as soon to be released. Social F.M. mobile will enable user toaccess their own music collection and Social F.M. radio channels. An architecturaloverview of Social F.M. is provided in figure 4.4.

Figure 4.4:Architecture of Social F.M.

Photo Share (concept)

Photo Share is a concept of an application that offers customers the ability to syn-chronize folders of photographs and distribute them withina closed community.A specified group of friends, family or colleagues can have a way of automati-cally sharing pictures. Instead of exchanging pictures manually through sendingMMS messages to every group participant or through client/server based pictureexchange, pictures can be distributed through a peer-to-peer network.

4.3.2 Evaluation

Peer-to-peer

In addition to what has been stated in the evaluation the peer-to-peer in distri-bution applications (Section 4.2.2), peer-to-peer sharing systems can allow for a


potential lack of centralized control of the network. By definition, sharing in amobile environment implies that it is required that peers are able to upload content.Transferring a resource to directly to a peer instead of to a server will not affectthe complexity of implementation, except for possibly addressing if decentralizedmethods are used for peer discovery.

Figure 4.5: Comparing client/server and peer-to-peer architecture for contentsharing


When Subramian et. al [1] states that over 70 percent of the Internet traffic is peer-to-peer related, file sharing is mentioned as the most popular application. It can beassumed that a large portion of the exchanged files on peer-to-peer networks hasbeen copyrighted and that acquiring premium material at no charge has been oneof the main forces in the adoption of peer-to-peer applications in fixed networks.While content providers are missing out on royalties, arguably file sharing has beena driver in sales of high speed Internet connections.

For sharing premium content, assessing that digital rightsare protected is achallenge. Record labels and movie companies may be reluctant making their ma-terial available unless there is a way that the contributionwill generate revenue.One approach is to release content with Digital Rights Management (DRM) pro-tection, but there are challenges. First of all, in order to play a copyrighted file,there needs to be a way of authenticating the user. This meansthat the mediaplayer of choice, PC application or external device, needs to support the specificDRM protocol. According to Mulligan et al[38], DRM systems impose severelimitations on normal personal usage.

For operators, peer-to-peer distribution has the disadvantage of utilizing moreup-link bandwidth than centralized solutions. Renjih et. al [39] studied the effectsof peer-to-peer content delivery from the operator’s perspective and concluded thatpeer-to-peer delivery methods would be less suitable than centralized methods if,in both cases, transaction charges would be the same.

Mobile phones are equipped with microphones and cameras. Peer-to-peer ser-vices can give application providers opportunities to develop platforms to facilitatethe exchange of user generated content, competing with MMS messaging.

4.3. SHARING 33

Table 4.1:Estimated upload times in seconds of different mediaGPRS EDGE WCDMA/HSDPA HSPA LTE

Picture(10kb) 4 0.8 0.5 0.03 <0.01Picture(300kb) 120 24 14 0,8 <0.01Music(5Mb) 2000 400 228 14 0,8

Video Clip(25Mb) 10000 2000 1140 70 4Movie(700Mb) 280000 56000 32000 1940 112

Device Feasibility

Matuszewski et. al [40] implemented a SIP based file sharing application on Sym-bian series 60 and concluded that device capacity and signaling overhead wouldnot impose any visible restrictions on the application. Another Symbian imple-mentation is SymTorrent. Limitations of file sharing applications can be assumedto be keeping battery consumption low, rather than processing power. A Java MEimplementation will be dependent on Whether or not there areAPIs that allowaccess to the mobile phone file system.

Network Feasibility

Just as in distribution applications, effects of network characteristics are dependenton the type of content to be shared. User generated content such as pictures aretypically small compared to commercial content such as music and video. Esti-mated typical upload times are shown in Table 4.1 and are based on half the userachievable peak up-link performance (see Section 3.4.2).

User Value

Disregarding the legal aspects, a peer-to-peer file sharingapplications would bemore resource consuming as it would require users to allow for both incoming andoutgoing connections. Furthermore, in a peer-to-peer application, in order to trans-fer files, the application needs to be running on both peers. For example, if a picturein a social file sharing application would have been uploadedto a server, the mo-bile client could close the application and other users could still access the picture.If the peer-to-peer transfer would have been executed it on the other hand wouldrequire both parts to be online at the same time. In a study by Matuszewski [13] in-experienced users strongly favored a client/server approach instead of peer-to-peerconnections. Experienced peer-to-peer users, while stillpreferring client/server so-lutions, were a bit more positive toward peer-to-peer sharing. Battery consumptionand pricing was seen as inhibiting factors.


4.4 Gaming

This category consists of interactive applications designfor competing againstother peers in a virtual environment.

4.4.1 Applications

There are a variety of games for mobile platforms, ranging from advanced 3D fight-ing games on Nokia N-gage [41], to simple turn-based Java Micro Edition boardgames and anything in between. In addition to mobile phones,Sony PlaystationPortable [42] and Nintendo DS [43] provide wireless multi-player gaming throughWiFi connections. Many games can be divided into the following categories:

• Real-time action games:Real-time action games are dependent on fast ac-tion. Typically the user is controlling one game character at a time.

• Real-time-strategy games: Gameplay can consist of resource gatheringand abstract control over game units.

• Turn-based strategy games:In turn based games each player makes a moveand then the game is locked until the opponent has made his/her move. Thewaiting process makes turn based games slower than real timevariants.

4.4.2 Evaluation

Peer-to-Peer

A decentralized approach for gaming arguably increases complexity for large scalegaming. When game information is stored on a common server, game data stayssynchronized. Distributed architectures are more sensitive to timings and owner-ship of data. As the number of users grows, complexity increases since more usersneed to be kept synchronized. Neuman et al identifies cheating as one of the majorchallenges [44], as peer-to-peer architectures are more sensitive to network attacksof eavesdropping, delaying or dropping packets. Furthermore, since game statesare stored on the client side, it means that control is put on peers and not a trustedcentralized resource.

In small scale two-player gaming, increased complexity of apeer-to-peer im-plementation is less apparent. Every player is required to be able to send andreceive game states, regardless on how they are transmittedto each other. A bene-fit of a server in two-player games would be that game scores and decisions wouldbe decided on neutral ground, but that functionality could easily be transferred toone of the clients.


Fairly low bandwidth combined with increased complexity indicates that serviceprovider cost savings from implementing peer-to-peer gaming over the Internet

4.4. GAMING 35

Table 4.2:Network requirements for common types of games. Source: WCDMAfor UMTS [28]

Application Bandwidth Latency Data-Loss

GamingAction 10-20kbps <300ms loss-tolerant

Strategy <20kbps1 <900ms loss-tolerantTurn based few kbps <40s no loss

1: Based on the assumption that strategy games does not consume more bandwidth than actiongames

would be small for large scale gaming. Subramanian [1] refers to peer-to-peer asideal for small ad-hoc networks. Peer-to-peer enables completely server-less multi-player gaming and is not necessarily harder to implement fortwo-player games.

Device Feasibility

Gaming performance on mobile devices is very much dependenton the type ofgame and the particular platform the game is to be deployed on. Cell phone gamesare common, ranging from Java ME games that are able to be deployed on simplemobile devices, to the Nokia N-gage platform designed for 3Dgaming.

Network Feasibility

In Table 4.2, network requirements for the different game categories are speci-fied. Comparing gaming requirements with characteristics of mobile networks insection 3.4.2, shows that throughput requirements are fulfilled by most cellularnetworks. However, the high latency of GPRS and EDGE networks renders themunsuitable for real-time action gaming. Less demanding applications, as turn basedand possibly real-time strategy, should be playable in slower networks. More expe-rienced gamers generally have higher demands on low latency. To satisfy demand-ing gamers, latency values at 70-80 ms could be required [28]. It should also benoted that the specified network requirements are based on generalizations madeby Holma et al. [28] and that there can be large variations among individual gametitles.

User Value

Mobile gaming provides an opportunity to provide users withcasual entertainmenton the go. While throughput requirements might be low, it might be hard for cus-tomer to translate time spent gaming to actual data traffic generated. With flat-rateor subscription payments, multi-player gaming introducesopportunities to inter-act with others, with the only additional cost being a possible subscription fee andincreased battery consumption resulting from use of the phones network connec-tivity.


4.5 Indirect Peer-to-Peer Services

This category consists of applications where the mobile node is not directly a partof the peer-to-peer network, but instead acts as an extension of the peer-to-peerapplication that is running in other devices. Two subcategories can be identified:

• Proxy based: One way of achieving interaction with peer-to-peer systemswithout actually contributing resources to the network is to use relays toconnect to the peer-to-peer network. While the mobile client in this casemaintains a client/server relation to the relay or proxy, the proxy itself actsas a regular node in the peer-to-peer network.

• Remote control of home node:Another indirect way of interacting with apeer-to-peer network, is by controlling it, without necessarily transmittingor receiving data from the peer-to-peer network. The purpose is instead toremotely control how a single node interacts with the peer-to-peer network.

4.5.1 Applications

Next, two mobile applications that take advantage of peer-to-peer networks throughhome nodes or gateways will be presented. Skype X-series [45] and the Skype-phone [46] provides transparent interaction with other Skype users. MovieRentrepresents a concept in which the mobile phone essentially works as a remote con-trol.

Skype X-series, Skypephone (Mobile)

X-series [45] is packet of services, bundled with flat-rate mobile Internet accessby mobile carrier Three. One of the services included in the package is a mobileversion of Skype. The mobile client does not use VoIP. Instead regular circuit-switched calls are connected to Skype’s peer-to-peer network through gateways.

Skypephone [46] is a recently announced collaboration project between Skypeand Three, where a mobile phone has been designed around Skype and is bundledwith a number of other services including Facebook, YouTubeand Google Mail.Just as with the X-series, the Skypephone uses gateways to connect to the Skypenetwork.

MovieRent (Concept)

MovieRent is a concept for a movie rental service that is based on TV sets withInternet connections, hard drives and integrated peer-to-peer software. A moviein HD-DVD or Blu-ray format can easily take up 20 gigabytes ofstorage space,which can take more than 30 minutes with a 100 Mbit connectionor more thantwo hours at a download rate of 24 Mbit. Through adding mobileinteraction withthe home TV set, renting movies can be done at a remote location, resulting in thatthe movie download can be initiated before arriving at home.

4.5. INDIRECT PEER-TO-PEER SERVICES 37

Figure 4.6:Possible architecture of the Movie Rent concept

4.5.2 Evaluation

Peer-to-Peer

In indirect peer-to-peer services, the mobile node is not used as a resource. Anadvantage for the mobile device is that the resource utilization could be pushedaway from the mobile node toward the proxy/home node. That the host applicationis deployed using a peer-to-peer architecture will have little affect on the indirectnode.


Indirect peer-to-peer provides a different entry point to peer-to-peer applicationscompared to other identified application areas. Services can be provided for fixednetworks, building up an infrastructure. At a later stage mobile services can beadded and utilize the resources provided by the built-up fixed peer-to-peer network.Support for mobile phones can be added gradually.

Device Feasibility

Device feasibility is dependent on how the mobile devices are interacting withthe peer-to-peer network. Two possibilities are to use circuit switched telephoneconnections or regular IP-connections. Indirect servicescan be designed so thatthe resource impact on the mobile node is minimized.


Network Feasibility

Since mobile nodes can interact with the peer-to-peer network in variety of waysit is not possible to state absolute requirements. Voice calls that connect to VoIPnetworks through proxies only require the ability for a phone to make an ordinaryphone call. Traffic generated by applications for remotely controlling peer-to-peerapplications could consist of basic messages not requiringa significant amountof bandwidth, but if the content is to be transferred to or from the mobile phonerequirements becomes comparable to those of file sharing applications (section4.3.2).

User Value

The mobile user is allowed to interact with the existent peer-to-peer applicationwithout being required to contribute with resources. If theapplication is introducedto existing fixed peer-to-peer services it could mean that resource usage on thestronger fixed nodes will increase compared to an application without the mobilenodes, possibly affecting performance of computer users.

4.6 Evaluation Summary

This section summarizes the analysis results for the identified application areas.

4.6.1 Peer-to-Peer

Peer-to-peer implementations of the above mentioned application have in commonthat they typically are less reliant on network infrastructure. In many cases, thisis compensated by an increased complexity in software implementation as moreresponsibility must be put on each client. As noted by Braet et al. [26] qualityof service management can be hard to achieve in a peer-to-peer architecture asend-nodes tend to label their own packets as important, which makes it hard toimplement traffic priorities.

4.6.2 Business Opportunity

For service providers, bandwidth costs will be decreased since the up-link band-width at the customer is used in favor of bandwidth at the central content servers.The cost of operation will be transferred toward users and operators and both willsee an increase of utilized up-link capacity. The lack of network infrastructure canlead to rapid service deployment once a mobile peer-to-peerapplication has beenimplemented.

4.6. EVALUATION SUMMARY 39

Table 4.3:Network requirements for mobile peer-to-peer applications. Sources:WCDMA for UMTS [28] and Computer Networking [4]

Application Bandwidth Latency Data-LossCommunication

IM few kbps few seconds no lossVoIP 12kbps1 150ms loss-tolerant

Videochat >40kbps1 <400ms loss-tolerantDistribution

Radio >64kbps 100’s of msec loss-tolerantTelevision >112kbps 100’s of msec loss-tolerantDownloads elastic2 - no loss

SharingUnrestricted elastic2 - no lossRestricted elastic2 - no lossIndirect

Share Control few kbps - no lossGamingAction 10-20kbps <300ms loss-tolerant

Strategy <20kbps3 <900ms loss-tolerantTurn based few kbps <40s no loss

1: Depending on the type of media and selected codecs. Low quality audio can be sent using only afew kbps while high quality video can consume megabit bandwidth

2: Applications cope with a variable bandwidth. Typically they will use as much bandwidth as isavailable to the application

3: Based on the assumption that strategy games does not consume more bandwidth than actiongames

4.6.3 Device Feasibility

Applications requiring access to native functionality of mobile phones such as mul-timedia capabilities and file systems can be difficult implement on mobile plat-forms. This would apply to both peer-to-peer and other applications. However,complexity will arguably increase if more functionality ispushed toward the client-side. CPU and memory might be a limitation in resource intensive applicationssuch as video streaming and gaming. Achieving low battery consumption levelswill be a major challenge when developing peer-to-peer applications.

4.6.4 Network Feasibility

In table 4.3 network requirements for each identified application area are speci-fied. It should be noted that the bandwidth requirements are not including headerinformation and that bandwidth consumption might be slightly higher in real-lifeapplications. A comparison of application requirements and network performancevalues (see Section 3.4.2) are shown in Table 4.4. For applications with fixed


Table 4.4:Estimated application applicability cellular networksApplication GPRS EDGE WCDMA HSDPA HSPA LTE

CommunicationIM Yes Yes Yes Yes Yes Yes

VoIP No No Yes/No1 Yes/No1 Yes YesVideochat No No Yes/No1 Yes/No1 Yes Yes

DistributionStreaming Radio No No Yes/No2 Yes/No2 Yes/No2 YesStreaming TV No No Yes/No2 Yes/No2 Yes/No2 Yes

Remote controlShare Controls Yes Yes Yes Yes Yes Yes

GamingAction No No Yes Yes Yes Yes

Strategy Yes Yes Yes Yes Yes YesTurn based Yes Yes Yes Yes Yes YesSharing/

DistributionPicture(10kb) 4 0.8 0.5 0.5 0.03 <0.01Picture(300kb) 120 24 14 14 0,8 <0.01Music(5Mb) 2000 400 228 228 14 0,8Video(25Mb) 10000 2000 1140 1140 70 41: Providing adequate quality of service might be difficult to achieve in specified networks

2: Depending on the bit-rate of media that is to be streamed

requirements, the table shows if the application is estimated to run at all with ac-ceptable quality on the specified network. For elastic applications estimated typicalupload times are shown. The impact of quality of service management has beendisregarded. Calculations are only based on estimated requirements and estima-tions of network performances and should be seen as indications, rather than ab-solute facts. As noted in section 3.4.2 network conditions in cellular networks canvary with a number of factors. Thus the impact of quality of service management,that has been disregarded in the simplistic calculations, needs to be investigatedbefore making absolute statements on the network feasibility on applications withhigh demands on latency and consistent throughput.

4.6.5 User Value

In fixed networks, a main driver for peer-to-peer usage has been price[26]. Usershave been offered cheap communication and free (although possibly not legal) ac-cess to commercial content. This is based on an assumption that it does not costto contribute to the network. In a mobile environment, this is usually not the case,as mobile data access tariffs can be high and that user in addition will pay forcontribution in terms of CPU, memory and battery power.

Chapter 5

Operators and Service Providers

This chapter looks in to the relation between service providers and operators andhow that possibly can affect the adoption of mobile peer-to-peer technologies.Viewpoints from six actors representing mobile operators and service providershas been examined through interviews and complemented through simple calcu-lations and literature studies to form a basis for estimating business relations andconditions. Background information on interview respondents can be found in sec-tion 2.4.1 and brief interview summaries are located in appendix A.

5.1 Operator Pricing Strategies

“Today operators try to earn much money on little use. It might bemore profitable to cut margins and aim to catch a larger crowd.” (In-terview respondent 4)

The above quote only represents one of many viewpoints on mobile pricing today.Nevertheless, high end-user mobile data access tariffs were agreed upon as a ma-jor inhibiting factor for end-user adoption of mobile services by a majority of theinterview respondents. Roto et al. [47] stated that research has shown billing mod-els to have a dramatic effects on data consumption patterns and end-user levels ofsatisfaction of mobile Internet services.

There are many possible variations of operator pricing strategies. One strategyis for operators to charge solely based on the data volume generated by its mobilephone users. Another strategy is to charge a flat-rate for unlimited usage within aspecified time-frame. A third option is to use a combination of volume based andflat-rate pricing, where services provided through operators can be offered for afixed price, while volume based charging is applied to trafficoutside the operatorsservice network. In addition, there can be many variations on the above mentionedthemes. Pure volume based and flat rate charging will be discussed in this sectionand the mixed strategy will be discussed Section 5.2 as it is strongly connectedwith revenue sharing between service providers and operators.

41

42 CHAPTER 5. OPERATORS AND SERVICE PROVIDERS

Table 5.1:Typical one way end-user distribution costs based on IM-message (0,05kb), low-resolution photo (10 kb), high-resolution photo (300 kb) and a music file(5 Mb) Prices are specified in Swedish kronor

IM -message Photo(low-res) Photo(high-res) Music20kr/Mb 0.001 0.2 6 10015kr/Mb 0.00075 0.15 4.5 7510kr/Mb 0.0005 0.1 3 505kr/Mb 0.00025 0.05 1.5 25

2.5kr/Mb 0.00012 0.025 0.75 12.51kr/Mb 0.00005 0.01 0.3 5

Ref. SMS 0.691 MMS 2.251 MMS 2.251 -

1: Based on Swedish TeliaSonera prices when using prepaid phone credit (28-10-2007)

5.1.1 Volume based

A common way for mobile operators to charge for mobile phone data traffic is to doso by measuring the band-width consumed for each user and charge accordingly.Peer-to-peer systems could increase the impact of high volume-based data accesstariffs. This effect was illustrated by respondent 1.

“by shifting the cost from a client/server approach into a peer-to-peer system, end-users have to, on average, receive as much as theytransmit back into the peer-to-peer cloud; effectively doubling theirbill over a conventional client/server system.” (Interview Respondent1)

Table 5.1 show the relation between price per megabyte and end user transfer costfor a single upload/download. Calculations are based on Swedish operator Telia-Sonera prices when using prepaid phone credit. Pricing differs between operatorsand countries. Therefore, the results should only be seen asindications on howpricing levels could affect the range of data that is to be shared on mobile peer-to-peer networks.

When comparing text messages to SMS messages it can be noted that, at themost expensive data rate, the transfer cost of a single text message is still lower thereferenced SMS charge by a large margin. For low-resolutionimages the situationis similar, while high resolution images can be more expensive than MMS mes-sages based on data costs alone. Larger files, such as music ormovies, producesone way traffic costs higher than of the retail cost of the specified media.

For applications that are not based on file exchange, but rather produce a streamof data that should be handled in real-time, a cost per minuteof usage has beencalculated and is shown in Table 5.2. It should be noted that with traffic basedpricing, charges would apply for both outgoing and incomingconnections. Thismeans that end users are charged, not only for transmitting but also for receiving.

5.1. OPERATOR PRICING STRATEGIES 43

Table 5.2:Typical costs per minute of using constant bit-rate services. Prices arespecified in Swedish kronor

VoIPCall Gaming(Action) Radio20kr/Mb 2,67 3 19,2015kr/Mb 2 2,25 14,4010kr/Mb 1,33 1,5 9,605kr/Mb 0,67 0,75 4,80

2,5kr/Mb 0,33 0,375 2,401kr/Mb 0,133 0,15 0,96

Ref. 0.691 - 9kr\24h2

1: Based on Swedish TeliaSonera prices when using prepaid phone credit (28-10-2007)

2: Based on TeliaSonera max tariff for data services throughtheir service portal Telia

Surfport(28-10-2007)

The calculations are based on end-user data charges only. Inaddition to thedata charges, there need to be a service provider business model. The calculationsindicate that, at the referenced pricing level, there is headroom for independentservice providers to offer services competing with SMS and MMS messaging, butthat higher bandwidth services require very low rates per megabyte in order to befeasible.

5.1.2 Flat-rate

Flat rate charges for mobile data was a topic in which all interview respondents re-lated to mobile industry had strong opinions. Service providers were confident thatflat-rate pricing would eventually take over for Internet access in mobile phones.This view was often justified with looking at the developmentin fixed networks.One respondent representing a mobile operator agreed that prices for mobile datahas been a problem, but disagreed on the notion of flat-rate pricing.

“I think we will see a business model where users are charged for acertain amount of usage per time unit. In flat-rate models, some userstake much more than their fair share of bandwidth. We don’t wantthose customers” (Interview respondent 3)

Roto et al. [47] stated in 2006 that mobile operators are reluctant to offerflat rate subscriptions as the cellular networks at the time did not have capacityto handle VoIP calls, music sharing and other high bandwidthservices that wouldfollow as a result of flat-rate pricing models. According to Roto, it was not likelythat we would see flat-rate models in mobile phones within thenext five years.

However, in Sweden, there are signs of development in the other direction.Flat-rate has already started to find its way to the mobile spectrum as all four majormobile operators are currently offering flat-rate for mobile broadband subscriptionsfor computers.


“We though that mobile broadband would be a complement to fixedbroadband, but it is definitely more of a competitor. Since the launchof flat-rate mobile broadband, the growth of ADSL has completelystopped” (Interview Respondent 2)

The popularity of mobile broadband services was confirmed byrespondent 3

“The rise of data traffic has been huge the last few months, as weintroduced flat-rate mobile broadband ”(Interview Respondent 3)

However, Swedish operators distinguish the flat-rate data-only subscriptionsfor mobile broadband and volume based data charges for mobile phones. Flat rateshave been introduced for mobile phones, but only for operator driven services suchas mobile television and radio.

For peer-to-peer applications, flat data rates eliminate additional monetary costsfor peer contribution. However, while users are not chargedwith payments, theystill pay for contribution to the peer-to-peer network in terms of device resources,such as CPU and battery power. Besides the effects on usage ofapplications, re-spondent 4 argued that flat-rate pricing is important to openup for new serviceproviders and usages of mobile networks.

“Flat-rate is a key to enable experimentation. Today it is toexpensiveto try out new things ”(Interview respondent 4)

5.2 Revenue Sharing

Mobile operators have an important role to play in the development of mobileservices, as it is the operator that has the billing relationto the customer [48].Not only is data access charged for, but operators are also incontrol of paymentmethods connected to the user SIM card. When using these payments, operatorsare effectively paid twice, both for the traffic generated byusers and for paymentaggregation toward the service provider, resulting in the revenue flow shown infigure 5.1. To make things more complicated, if a service provider wishes to useoperator payment methods, it has to establish business relations with each andevery operator. Alternatively the service provider could introduce an additionalactor to the value chain by turning to an independent paymentaggregator, handlingpayments for more than one operator. The dominant position of mobile operatorswas highlighted by a majority of interview respondents.

“In the mobile world today, it is the operator that dictates the mar-ket”(Interview Respondent 3)

“Operators are kings, since they control the payment methods” (Inter-view respondent 6)

5.3. CONTROL 45

Figure 5.1:Simplified revenue flow of mobile service provider

There are large variations on how revenue is shared among operators and ser-vice providers. According to Soninen [49], the largest mobile carrier in Japan,DoCoMo, charges a 9 percent premium for payment aggregation. In other mar-kets, the operators share can be significantly higher. Respondent 5 presented aview on the situation for mobile service providers in Sweden:

“Handling micro payments for an independent service provider is tooexpensive. About 50 percent of the income is lost due to paymentaggregations” (Interview Respondent 5)

For data traffic, the pure volume based and flat-rate pricing strategies describedsection 5.1 represented two extremes. Often charges fall inbetween those cate-gories, where operators can choose to exclude data traffic costs generated by theirown services, while other traffic is charged per volume [47].As noted in section4.2.2, besides being limited by peer upstream capacity, peer-to-peer distributionwould generate more traffic at the edges than a centralized solution. This wouldshift the load from service provider’s application serversto the mobile operator’snetwork, leading to increased costs for operators and decreased for application de-velopers. This could have an affect on the revenue sharing deal between serviceproviders and operators, as a peer-to-peer solution would be more expensive interms of traffic than a client/server equivalent.

In addition to payment related issues, working with operators is of importanceas it can provide service providers with other benefits, suchas access to an existingcustomer base. Respondent 6 stated the following:

“Collaboration can be of great benefit when making applications ac-cessible. Working with manufacturers could result in pre-installedsoftware and operators can help promote services.” (Interview respon-dent 6)

5.3 Control

“A benefit of peer-to-peer is that it does not necessairly have a centralpoint of control. This is why peer-to-peer is sometimes associated


with piracy” (Interview respondent 1)

Whether or not the possible lack of central control mentioned by the respondentis a benefit or not is debatable. Operators wishing to controlthe network usagecan use a number of approaches. In pure volume based chargingmodels, usersare driven away from usage of high bandwidth services due to high prices. Ina completely flat-rate scenario this pricing method of control is removed. NATboxes, firewalls, blocking of ports and capping bandwidth usage might be a way ofkeeping some of that control. Attempts to block peer-to-peer services can be moreor less effective. A study by Fraleigh et al. [50] showed an increase of unknowntraffic with a corresponding decrease of peer-to-peer traffic compared to earliermeasurements. It was being argued that this was a result of American universitiesattempts to block peer-to-peer traffic. Regarding blockingof certain services orusers, respondent 2 and 3 presented the following views:

“What i know it has never happened, but if someone uses their sub-scription in a way that it disturbs others we want to have an opportu-nity to warn and limit speeds” (Interview respondent 2)

“We find and do easily detect and shut down users that share files”(Interview respondent 3)

The Next Generation Mobile Networks alliance represents a joint effort bysome of the largest mobile operators in the world to provide standardization bodieswith operator views on requirements for future networks. Intheir white paper “be-yond HSPA and EVDO”[51] the vision of service based pricing is supported as itis stated that the next generation mobile network should support a variety of charg-ing methods including time-based, volume-based, event-based, and session-basedcharging. This would require the ability to tell the difference between differenttypes of content.

In section 5.2 it was mentioned that operators have differentiated pricing mod-els, setting their own services apart through offering flat-rate subscriptions, whileother services have to rely on a higher volume based tariff. This can be seen as amethod of control, where users are more or less locked into services provided bytheir respective operator if the services require substantial bandwidth. Respondent5 expressed his opinion on how operators and attempts to lockin users to theirservices.

“Operators tries to pinch users to their own services and portals, butthe Internet does not work that way” (Interview Respondent 5)

Most interview respondents stated operator openness as something that hasbeen a problem with mobile service development.

“That the mobile operators grip to hard is a classic” (Interview respon-dent 3)

5.3. CONTROL 47

The importance of openness was illustrated by respondent 2.

“Different subsidiaries in the world selected different strategies to be-gin with and with the results in hand we have seen that the moreopen-ness toward the network, the better. You can’t out-content the Internet”(Interview respondent 2)

The view of convergence among fixed and mobile Internet was shared amongmost interview respondents, but not all. Respondent 3, madea clear distinctionbetween fixed and mobile Internet usages and argued that the devices and businessenvironments of fixed and mobile networks were very different and would remainthat way.

Chapter 6

Discussion

In this chapter, peer-to-peer is discussed based on resultsfrom application analy-ses combined with common themes emerged from interviews with operators andservice providers.

6.1 Difficulty of Defining Peer-to-Peer

The first fundamental difficulty in exploring the area of mobile peer-to-peer is at-tempting to define what peer-to-peer really is. Peer-to-peer is widely used phrasethat can mean different things to different people. For someit is synonymous withfile sharing. For some it represents person-to-person services. For others, peer-to-peer can refer to a concept of implementing services throughdecentralized struc-tures. Braet [26] talks about IMS and peer-to-peer architectures as two radicallyopposed paradigms. Akhavan et al [51], on the other hand, states that the peer-to-peer paradigm should be supported through IMS, two seemingly contradictingstatements. Upon further examination it becomes apparent that Braet and Akhavanare looking at peer-to-peer on different levels. Using the definition of peer-to-peerin section 3.1.2 it can be assumed that Akhavan talks of peer-to-peer on a contentlevel, while Braet speaks of peer-to-peer on the resource level.

When following the convention of dividing services into separate levels, ser-vices like Instant Messengers, that can be referred to as peer-to-peer applicationson content level, can be implemented by using client/serverparadigms. On theother side of the spectrum we have Joost, which from the content level appears tobe a client/server application, but is based on peer-to-peer architecture. While itcannot be said that the definition used in this thesis is more correct than any others,to be aware the different levels in which peer-to-peer can bedefined can lead to anincreased understanding of peer-to-peer in different contexts.

49

50 CHAPTER 6. DISCUSSION

6.2 Service Deployment

Subramanian refers to reduced costs for the service provider as one of the majorbenefits of peer-to-peer architectures [1]. In fixed PC environments, with few dom-inant operating systems, service providers can develop a single version of softwarethat can potentially be spread over the Internet to millionsof users worldwide in-stantly. For these service providers, peer-to-peer networks can mean rapid servicedevelopment as the infrastructure is provided by the joining peers.

However, as shown in Chapter 4, peer-to-peer implementation often movesfunctionality to the end node of the network. In a mobile environment, increas-ing the already high complexity of mobile application development can lead toincreased costs for software implementation. The difficulty of developing mo-bile applications was confirmed by the interview respondents, which repeatedlymentioned that keeping up with new models and devices was a major obstacle forcommercial success of mobile applications.

An attempt to satisfy the need for rapid service implementation is the conceptof IMS. As described in Section 3.2, the IMS framework relieson centralized ap-plication servers for common functionality and leaves application developers onlyhaving to implement additional features. While this standardization of servicescan facilitate and accelerate development, it is not without disadvantages. IMSrequires considerable infrastructure before any servicescan be launched, whichpeer-to-peer services do not. Peer-to-peer enables service providers that lack hard-ware infrastructure to implement services, possibly competing with infrastructuredependent offerings. An increase of implementation complexity will be a chal-lenge for software designers, but if adequate common platforms or standards aredeveloped, peer-to-peer could enable rapid global distribution of services withoutconsiderable hardware investments. This can be observed inthe case of Napsterand Skype and it cannot be said that something similar will never happen in themobile community, although the development conditions might presently be lessfavorable.

6.3 Designing a Mobile Peer-to-Peer Application

Even if platform issues are solved, a challenge is how to design the software im-plemented infrastructure. Overhead introduced by pure decentralized peer-to-peersystems renders them unsuitable for mobile networks. Coordination among peerscan make peer discovery more resource efficient. Using a centralized approachfor discovery through adding servers will diminish the peer-to-peer advantage as itrelies on dedicated servers. Using a hybrid approach may seem like a worthy com-promise, but designing a network of super peers and regular peers is not withoutdifficulty in a resource constrained environment. A simple comparison in Figure6.1 shows how signaling traffic will be reduced in the networkfor all nodes ex-cept for the stronger node assigned to act as a centralized coordinator. An issue

6.4. USER CHALLENGES 51

Figure 6.1:Illustrates signaling traffic in completely decentralizedvs centralizedpeer discovery protocols)

is how to decide who is to take the increased responsibilities from being labeledas a stronger peer. While being a supernode might not affect wall powered desk-top computers with flat-rate broadband subscriptions, handling signaling for lesserpeers might be both expensive in terms of money and battery consumption in amobile environment.

An alternative view on mobile peer-to-peer is to look at where mobile devicescan take advantage of an existing peer-to-peer structure. In this case, a peer-to-peer application in fixed networks forms a basis on which to build mobile services.Service providers can take advantage of stable platforms and networking environ-ments, and providing mobile services as additions to desktop applications. Mobilenodes can either be excluded from the peer-to-peer structure as in the indirect peer-to-peer services explained in Section 4.5 or act as weaker peers in a hybrid peer-to-peer structure, if the application is requiring contentlevel contribution from themobile node.

Figure 6.2:Using resources is fixed peer-to-peer networks for mobile services

6.4 User Challenges

As noted in Section 3.3.1 a study by Matuszewski [13], show that users are re-luctant toward sharing resources with unknown peers. Assuming that all peers are


equally cooperative, users will on average transmit as muchas they receive. If usersare charged for both upload and download traffic, this would mean that peers wouldactually have to pay for contributing resources. Free-riding would still be an issue,even if battery power was the only cost, and would not be limited to distributionservices, but rather any peer-to-peer service where users are responsible for con-tributing resources. However, some mobile services, by definition, require clientand server functionality on each mobile node and end-to-endconnectivity. Thiswould apply to communication services, such as VoIP, text messages and socialfile sharing of content generated on the mobile device, such as photos and videoclips. All of which can be classified as peer-to-peer applications on the content-level. Common for this class of applications is that their usage would be driven byusers needs to communicate and share experiences through limited groups and thatcontent is pushed from one end-user toward another, possibly increasing willing-ness to contribute.

As indicated by Roto et al. [47] pricing is of great importance for the adoptionof mobile services. This view was confirmed by interview respondents, as they allstressed the importance of accurate pricing for mobile dataservices. Just as in thecase of possible increased battery consumption, the effectof pricing might even beincreased in peer-to-peer implementations if peers are contributing with resourcesto the network. Two central questions in the user adoption ofany mobile servicesare the following:

• How will operators charge for mobile data access?

• How will service providers charge for service usage?

Finding a good pricing strategy for mobile operators is of great importance.Too high rates might inhibit usage, while a too low rate with apossible resultingincrease of traffic, might strain the operator network and allow for competition withthe operators own services. Roto [47], for example, mentioned VoIP as a possiblereason that operators are not adopting to flat rate billing models. Fring, mentionedin Section 4.1.1, is an example of a mobile VoIP application that allow for makingcalls that are free of charge except for operator data charges. With flat-rate dataand increased network speeds, the conditions for Fring and similar of applicationsare improved. While best-effort mobile VoIP might not provide the same qualityof service as regular calls, a combination of future networkimprovements andflat-rate pricing might drive an increased usage of similar services at the expenseof mobile operator revenue. However, operator services as voice and SMS willstill have some advantages compared to an independent service provider offeringsimilar services through a peer-to-peer application. Operator based services can bebased on standardized voice calls, SMS and MMS messaging. These services usefunctionality that is built in to the phone. Peer-to-peer VoIP based on proprietarytechnology requires both sender and receiver to have the application installed andrunning in order to communicate.

6.4. USER CHALLENGES 53

Accessibility and usability for mobile applications were repeatedly brought upby interview respondents as two of the most important criterion for success of mo-bile applications. Another issue is to identify suitable business models, a problemthat will be shared by both peer-to-peer service providers and other mobile serviceproviders. Even if we have good services that are easy to use,accessible and re-source efficient and mobile operators have deployed flat-rate pricing, a fundamentalquestion is how services will be financed.

“On the Internet, users expect everything to be free” (Interview re-spondent 2)

Chapter 7

Conclusions

This study has explored potential mobile peer-to-peer applications. A number ofpossible application areas has been identified and analyzed. While driver for thedevelopment of commercial peer-to-peer services in fixed networks has mainlybeen cost reduction, this effect might diminish in mobile networks. Applicationdevelopers of mobile peer-to-peer services will face the same challenges as othermobile service providers, developing applications for different devices and plat-forms. As the idea of peer-to-peer networking is shifting the resource utilizationfrom the service provider toward the edges of the network, implementing suchservices can add to the already high complexity of mobile service development.Bandwidth costs will be shifted from the service provider toward the operator andultimately the user, increasing usage of up-link capacity.Battery consumption andhigh mobile data prices have been found to be important challenges to be over-come for development of peer-to-peer services. If those challenges are overcome,peer-to-peer can offer a benefit of rapid service deployment, where services canbe offered without considerable investments in infrastructure. However, quality ofservice management, needed for real-time communication and gaming services,will be difficult to achieve without centralized network control.

One way of limiting stress on mobile devices is to introduce centralized el-ements for addressing and coordination which will lessen impact on signalingoverhead on mobile devices. Integrating mobile services into fixed peer-to-peerapplications can offer service providers an alternative way forward, where a hy-brid peer-to-peer architecture can allow for resources in fixed networks can be har-nessed, while mobile resources are spared. Service providers can take advantageof application development in a more consistent desktop environment and considermobile services as additions.

55

56 CHAPTER 7. CONCLUSIONS

Chapter 8

Recommendations

This thesis has given an insight into possible application areas of mobile peer-to-peer in cellular networks. In such networks, the relation between mobile operatorsand service providers is of great importance. While conditions might not allowfor mobile peer-to-peer applications in cellular networkstoday, there are severalaspects to consider that can change the dynamics between service providers andoperators. Operator networks can be either partially bypassed, through using a mixof fixed and mobile networks, or bypassed altogether using short-range networkingtechnologies such as WiFi and Bluetooth. This could open up for new possibleapplication areas.

In cellular networks, it can be studied how current limitations of mobile peer-to-peer applications might be changed in future networkingenvironments. An ex-ample would be to look at how the speed of upcoming 3GPP LTE networks, thatare aiming for a theoretic maximum downstream rate of 100Mbit, will this affectmobile data pricing and mobile phone battery life.

Finally, a fundamental perspective that has been left out inthis thesis is theimpact on, and how to solve, user related challenges. One aspect to look into is howto make cell phone applications accessible. Another aspectis to study the severityof battery consumption and pricing. And finally user preferences for exchangingcontent through peer-to-peer can be compared to client/server solutions.

57

58 CHAPTER 8. RECOMMENDATIONS

References

[1] R. Subramanian and B. D. Goodman,Peer-to-Peer Computing: TheEvolution of a Disruptive Technology. Idea Group Puplishing, 2005.

[2] D. R. Cooper and P. S. Schindler,Business Research Methods. IrwinMcGraw-Hill, 1998.

[3] M. Saunders, P. Lewis, and A. Thornhill,Research Methods for BusinessStudents. Pearson Education, 2000.

[4] J. F. Kurose and K. W. Ross,Computer Networking: A Top-down ApproachFeaturing the Internet. Addison Wesley, 2005.

[5] H. M. Fattah,P2P: How Peer-to-Peer Technology Is Revolutionizing the WayWe Do Business. Dearborn Trade, A Kaplan Professionsl Company, 2001.

[6] “Gnutella website,” Nov. 2007. [Online]. Available:http://www.gnutella.com

[7] I. Stoica, R. Morris, D. Karger, F. M. Kaashoek, and H. Balakrishnan,“Chord: A scalable peer-to-peer lookup service for internet applications,” inProceedings of the 2001 SIGCOMM Conference, 2001.

[8] S. Ratnasamy, P. Francis, M. Handley, K. Richard, and S. Schenker, “Ascalable content-adressable network,” inProceedings of the 2001SIGCOMM Conference, 2001.

[9] H. Balakrishnan, M. F. Kaashoek, K. David, R. Morris, andI. Stoica,“Looking up data in p2p systems,”Communications of the ACM, vol. 46,2003.

[10] C. Gonzalo and M. A. Garcia-Martin,3G IP Multimedia Subsystem (IMS):Merging the Internet and the Cellular World. John Wiley and Sons,Incorporated, 2005.

[11] S. Chakraborty, P. Janne, and F. Tomas,IMS Multimedia Telephony OverCellular Systems: VoIP Evolution in a Converged Telecommunication World.John Wiley and Sons, Incorporated, 2007.

59

http://www.gnutella.com

60 REFERENCES

[12] G. Camponovo and Y. Pigneur, “Business model analysis applied to mobilebusiness,” inProceedings of the 5th International Conference on EnterpriseInformation Systems,IEEE, 2003.

[13] M. Matuszewski, “Understanding attitudes towards mobile peer-to-peer,” inProceedings of IEEE International Conference on Portable InformationDevices, 2007, 2007.

[14] M. Zyda, “Educating the next generation of game developers,” inProceedings of IEEE International Conference on Portable InformationDevices, 2007.

[15] S. Microsystems, “The java me platform,” Oct. 2007,http://java.sun.com/javame/index.jsp.

[16] M. d. Jode,Programming Java 2 Micro Edition on Symbian OS: ADeveloper’s Guide to MIDP 2.0. John Wiley and Sons, Incorporated, 2004.

[17] D. S. Kochnev and A. A. Terekhov, “Surviving java for mobiles,” PervasiveComputing, IEEE, vol. 2, 2003.

[18] D. Kessens and T. Savolinen, “3g and ipv6 impact on battery life,” 2006,french IPv6 Worldwide Summit, Cannes.

[19] P. Rysavi, “Mobile broadband,” 2006, white Paper, 3G americas.

[20] “Msn website,” Nov. 2007. [Online]. Available:http://im.live.com/messenger/im/home/

[21] “Google talk website,” Nov. 2007. [Online]. Available:http://www.google.com/talk/

[22] “Icq website,” Nov. 2007. [Online]. Available: http://www.icq.com

[23] “Skype website,” Nov. 2007. [Online]. Available: http://www.skype.com

[24] “Fring website,” Nov. 2007. [Online]. Available: http://www.fring.com

[25] S. A. Baset and S. Henning, “An analysis of the skype peer-to-peer internetprotocol,” in INFOCOM 25th IEEE International Conference on ComputerCommunications, 2006.

[26] O. Braet and P. Ballon, “Strategic design issues of ims versus end-to-endarchitectures,”Emerald, Info, vol. 9, 2007.

[27] W.-H. Chiang, W.-C. Xiao, and C.-F. Chou, “A performance study of voipapplications: Msn vs skype,” inMULTICOMM 2006, proceedings, 2006.

[28] H. Holma and A. Toskala,WCDMA for UMTS, Third Edition. John Wileyand Sons, 2005.

http://java.sun.com/javame/index.jsp

http://im.live.com/messenger/im/home

http://www.google.com/talk

http://www.icq.com

http://www.skype.com

http://www.fring.com

REFERENCES 61

[29] “Joost website,” Nov. 2007. [Online]. Available: http://joost.com

[30] “Veoh website,” Nov. 2007. [Online]. Available: http://www.veoh.com

[31] “Azureus vuze website,” Nov. 2007. [Online]. Available:http://www.vuze.com

[32] “Bbc iplayer website,” Nov. 2007. [Online]. Available:http://www.bbc.co.uk/iplayer/

[33] “Sky anytime website,” Nov. 2007. [Online]. Available:http://anytime.sky.com/

[34] M. Hausenblaus and N. Frank, “Interactivity = reflective expressiveness,”IEEE, Multimedia, vol. 14, 2007.

[35] M. Matuszewski, “Business study of mobile peer-to-peer contentdistribution,” inTowards the Next Wave of Mobile Communication:Proceedings of the Research Seminar on TelecommunicationsBusiness II,2005.

[36] “Symtorrent website,” Nov. 2007. [Online]. Available:http://symtorrent.aut.bme.hu

[37] “Socialfm website,” Nov. 2007. [Online]. Available: http://www.social.fm

[38] D. K. Mulligan, J. Han, and A. J. Burstein, “How drm-based contentdelivery systems disrupt expectations of personal use,” inProceedings of the3rd ACM workshop on Digital rights management, 2003.

[39] K. K. Renjish and H. Hammainen, “Peer-to-peer content delivery overmobile networks: A techno-economic analysis,” inProceedings on the 10thIEEE Symposum on Computers and Communication, 2005.

[40] M. Matuszewski, N. Beijar, J. Lehtinen, and H. Tuomo, “Mobilepeer-to-peer content sharing application,” inIEEE CCNC 2006 proceedings,2006.

[41] “Nokia n-gage website,” Nov. 2007. [Online]. Available: http://n-gage.com

[42] “Playstation portable website,” Nov. 2007. [Online].Available:http://www.us.playstation.com/PSP/About

[43] N. D. website, Nov. 2007. [Online]. Available:http://www.nintendo.com/channel/ds

[44] C. Neumann, N. Prigent, M. Varvello, and K. Suh, “Challenges inpeer-to-peer gaming,”ACM SIGCOMM Computer Communication Review,vol. 37, 2007.

http://joost.com

http://www.veoh.com

http://www.vuze.com

http://www.bbc.co.uk/iplayer

http://anytime.sky.com

http://symtorrent.aut.bme.hu

http://www.social.fm

http://n-gage.com

http://www.us.playstation.com/PSP/About

http://www.nintendo.com/channel/ds

62 REFERENCES

[45] “Skype x-series website,” Nov. 2007. [Online]. Available:http://xseries.three.com/

[46] “Skypephone website,” Nov. 2007. [Online]. Available:http://www.skype.com/intl/en/mobile/

[47] V. Roto, R. Geisler, A. Kaikkonen, A. Popescu, and E. Vartiainen, “Datatraffic costs and mobile user experience,” inMobEA IV workshop onEmpowering the Mobile Web, in conjunction with WWW2006 conference.(2006), 2006.

[48] P. Ballon, “Scenarios and business models for 4g in europe,” Info, Emerald,vol. 6, 2004.

[49] M. Soininen, “Segments of the mobile internet industry: Examples fromfinland and japan,” inMobile Business, 2005. ICMB 2005. InternationalConference on, 2005.

[50] C. Fraleigh, S. Moon, B. Lyles, C. Cotton, M. Khan, D. Moll, R. Rockell,T. Seely, and C. Diot, “Packet-level traffic measurements from the spring ipbackbone,”Network, IEEE, vol. 17, 2003.

[51] H. Akhavan, V. Badrinath, T. Geitner, H. Lennertz, Y. Sha, T. Utano, andB. West, “Next generation mobile networks - beyond hspa and evdo,” nextGeneration Mobile Networks Limited White Paper.

http://xseries.three.com

http://www.skype.com/intl/en/mobile

Appendix A

Interview notes

For each respondent, a brief summary of the interview is provided.

A.1 Respondent 1 - Service Provider Perspective

The respondent provided a perspective on the benefits and disadvantages of select-ing a peer-to-peer implementation of services. Potential cost savings, and a pos-sibility to develop services without centralized control was identified as the onlybenefits of peer-to-peer implementations, at the cost of increased implementationcomplexity.

A.2 Respondent 2 - Operator Perspective

The respondent sees positively on future mobile IP including VoIP applications.He believes operators should be open to new ideas regardlessand be neutral interms of technology choices as long as it is of benefit to the operator or customer.He welcomes IMS services, but is opposed to the idea of walledgardens oftenassociated with IMS technology. He states that “the more openness toward thenetwork, the better” and that it would be impossible to out-content the Internet.

A.3 Respondent 3 - Operator Perspective

The respondent clearly points out that application development for mobile phones,with adaption to different devices, is troublesome. In addition, he highlights theimportant of accessibility to end users an states mobile users are often reluctant touse new services. He is opposed to the idea of flat-rate pricing, as some users seemto use more than their fare share of bandwidth

63

64 APPENDIX A. INTERVIEW NOTES

A.4 Respondent 4 - Academic Perspective

The respondent states that flat-rate data pricing is a key to increase usage of mobileservices and make people experiment. He believes that the mobile world would bemuch more dynamic if it where more Internet like. Open sourcecommunities andgood platforms for developing mobile applications is something that the respondentthink is lacking today.


The respondent stressed the importance of revenue sharing with operators. Run-ning independent mobile services with alternative paymentoptions was seen asimpossible. The respondent stated that it was preferable touse standards and pro-tocols already supported by phones rather than trying to implement applications,due to the high development costs when forced to adapt software to different de-vices. Operator pricing was seen as way to high, but he saw flat-rate pricing asinevitable in the future.


The respondent stressed that collaboration can be of great benefit when makingapplications accessible. Working with manufacturers could result in pre-installedsoftware and operators could help promote services. Partnering was seen as crucialto the business case. The respondent did not seem concerned with battery con-sumption levels of mobile peer-to-peer applications as long as files are kept smalland the notion of peer-groups is introduced.

2007:257 civ master's thesis mobile peer-to-peer ...1024904/fulltext01.pdfthe opportunity to...

Documents