IP Multimedia Subsystem (IMS) Handbook

IP MultimediaSubsystem

Handbook

(IMS)

CRC Press is an imprint of theTaylor & Francis Group, an informa business

Boca Raton London New York

Edited by

Syed A. AhsonMohammad Ilyas

IP MultimediaSubsystem

Handbook

(IMS)

CRC PressTaylor & Francis Group6000 Broken Sound Parkway NW, Suite 300Boca Raton, FL 334872742

2009 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business

No claim to original U.S. Government worksPrinted in the United States of America on acidfree paper10 9 8 7 6 5 4 3 2 1

International Standard Book Number13: 9781420064599 (Hardcover)

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Library of Congress CataloginginPublication Data

IP multimedia subsystem (IMS) handbook / editors, Syed A. Ahson, Mohammad Ilyas.

p. cm.Includes bibliographical references and index.ISBN 9781420064599 (alk. paper)1. Internet Protocol multimedia subsystem. I. Ahson, Syed. II. Ilyas,

Mohammad, 1936 III. Title.

TK5105.15.I64 2008006.7dc22 2008032888

Visit the Taylor & Francis Web site athttp://www.taylorandfrancis.comand the CRC Press Web site athttp://www.crcpress.com

Contents

Preface...........................................................................................................ixThe.Editors....................................................................................................xiContributors............................................................................................... xiii

Section 1 Concepts

1 IMS Service, Models, and Concepts.................................................... 3Emmanuel Bertin and Nol Crespi

2 IMSA Secure Architecture for All IP Networks.......................... 27Muhammad Sher and Thomas Magedanz

3 Peer-to-Peer Features in the IP Multimedia Subsystem................. 73Adetola Oredope and Antonio Liotta

4 On the Support of Media Functions within the IMS..................... 87Jean-Charles Grgoire and Admela Jukan

Section 2 Technologies

5 The FOKUS Open IMS CoreA Global IMS Reference Implementation................................................................................ 113Peter Weik, Dragos Vingarzan, and Thomas Magedanz

6 Next-Generation Grid Support over the SIP/IMS Platform........ 133Vicente Olmedo, Antonio Cuevas, Victor Villagr, and Jos I. Moreno

7 Policy-Based QoS Control for a Convergence Network............... 157Younghan Kim and.Youngsuk Lee

8 OSA Service Capability ServerParlay/Parlay X......................... 169Moo Wan Kim and.Ryozo Ito

9 Internetworking of 3GPP and WLAN and Wimax Networks..... 191Fangmin Xu, Luyong Zhang, Zheng Zhou, and Wei Zhong

i Contents

10 IM-SSF Application ServerInterworking with CAMEL......... 215Moo Wan Kim and Ryozo Ito

11 Distributed IMS............................................................................... 243Marcin Matuszewski

Section 3 Services

12 Service Delivery Platforms and Multimedia Service Design... 265Christopher J. Pavlovski

13 The Integration of IMS into Service Delivery Platforms Based on Service-Oriented Architectures.................................... 307Niklas Blum, Peter Weik, and Thomas Magedanz

14 Service Orchestration in IMS......................................................... 329Anahita Gouya and Nol Crespi

15 Instant Messaging and Presence Service (IMPS)........................ 345Whai-En Chen

16 Multiparty Services in the IP Multimedia Subsystem............... 363Ivn Vidal, Ignacio Soto, Francisco Valera, Jaime Garca, and Arturo Azcorra

17 IMS-Based Conferencing Services: An Engineering Approach........................................................................................... 383Alessandro Amirante, Tobia Castaldi, Lorenzo Miniero, and Simon Pietro Romano

18 IMS-Based IPTV.............................................................................. 411Oliver Friedrich, Stefan Arbanowski, Adel Al-Hezmi, and Robert Seeliger

19 IPTV Modeling and Architecture over IMS................................ 443David Lpez, Eugen Mikoczy, Jos Ignacio Moreno, Antonio Cuevas, and Enrique Vzquez

20 SIP-Based Prepaid Application Server......................................... 473Mario Weber

21 JAIN SLEE Platforms for IMS Application Servers.................... 493Igor Vukomanovi

Contents ii

22 Role of OSS/BSS in the Success of IMS....................................... 509Jithesh Sathyan

Index........................................................................................................... 531

ix

Preface

Fixed-mobile.convergence.and.voice-data.networks.have.merged.next-gen-eration,.value-added.applications.and.integrated.multimedia.services,.com-bining. Web. browsing,. instant. messaging,. presence,. voice. over. IP,. video.conferencing,. application. sharing,. telephony,. unified. messaging,. multi-media. content. delivery,. etc..on. top.of.different. network. technologies.. The.convergence.of. the.communications.networks. is.motivated.by. the.need.to.support.many.forms.of.digital.traffic.as.well.as.to.amortize.implementation.and.operational.costs.of.the.underlying.networks..Historically,.the.approach.to. build. and. deploy. multimedia. services. has. focused. upon. single-point.solutions..These.solutions.worked.well.to.address.the.specific.needs.of.the.intended.service.or.related.set.of.services;.however,.they.possess.shortcom-ings.in.extensibility.to.cater.to.the.newer.and.emerging.multimedia.services..A.more.pragmatic.approach.is.to.develop.a.single.consolidated.platform.that.is.capable.of.supporting.a.wide.variety.of.multimedia.services.over.several.communication.networks.

The.IP.multimedia.subsystem.(IMS).is.a.standardized.next-generation.net-working.architecture.that.has.been.conceived.for.telecom.operators.willing.to.provide.advanced.services.on.top.of.both.mobile.and.fixed.networks..The.IMS.is.a.service-oriented.architectural.framework.that.aims.to.provide.exist-ing.and.future.Internet.services.to.both.fixed.and.mobile.end.users.over.a.multi-access,.all-IP.platform..The.3rd.Generation.Partnership.Project.(3GPP).and.3GPP2.have.developed.the.IMS.to.provide.service.delivery.platforms.for.a.converged.communication.paradigm..The.IMS.provides.ways.for.integrat-ing.existing.Internet.services.with.future.ones..It.is.a.well-designed.service.platform,.using.open.and.standardized.Internet.protocols.and.respecting.the.Internet.paradigm.of.data. transport.and.application.separation.with. links.between.these.two.layers..The.IMS.offers.telecom.operators.the.possibility.to.build.an.open.IP-based.service.infrastructure.that.will.enable.easy.deploy-ment.of.new,.rich.multimedia.communication.services.mixing.telecom.and.data.services.

The.IP.multimedia.subsystem.grants.the.network.operator.the.role.of.ser-vice.broker..Multimedia.calls.are.a. service. inherent. to. the. IMS,.but.many.more. services. are. being. developed. on. top. of. the. IMS. service. platform. to.build.a.rich.service.environment.enticing.the.users.to.employ.it..The.IMS.is.an.IP-based.architecture.designed.to.provide.a.set.of.essential.functionalities.that.support.the.delivery.of.the.next-generation.multimedia.services.that.are.envisioned.in.the.future.of.third-generation.networks.

The.IMS.architecture.has.been.defined.to.provide.the.user.with.access.to.a. wide. range. of. services,. which. are. implemented. by. means. of. application.servers..The. IMS.has. resulted. in.an.environment. that. introduces.new.ser-vices.more.quickly.than.ever.before.as.well.as.exciting.new.concepts.such.as.

x Preface

reusable.service.components.and.real-time.integration..The.IMS.fills.the.gap.between.the.existing.traditional.telecommunications.technology.and.Inter-net.technology,.allowing.operators.to.offer.new,.innovative,.and.compelling.services;.it.represents.a.standardized,.reusable.platform.that.provides.a.better.way.to.roll.in,.roll.out,.deploy,.integrate,.and.expand.consumer.and.enterprise.voice.and.data.services..There.is.increased.interest.in.the.IMS.due.to.its.ability.to.revolutionize.the.end-user.experience.with.new.and.innovative.services.

The.IP Multimedia Subsystem (IMS) Handbook.provides.technical.informa-tion.about.all.aspects.of.the.IMS..The.areas.covered.in.the.handbook.range.from.basic.concepts.to.research-grade.material,.including.future.directions..The.handbook.captures.the.current.state.of.IMS.technology.and.serves.as.a.source.of.comprehensive.reference.material.on.this.subject..There.are.three.sections. in. the.handbook:.Concepts,.Technologies,. and.Services.. It.has.a.total.of.22.chapters.authored.by.50.experts.from.around.the.world..The.tar-geted.audience.for.the.handbook.includes.professionals.who.are.designers.or.planners.for.IMS.systems,.researchers.(faculty.members.and.graduate.stu-dents),.and.those.who.would.like.to.learn.about.this.field.

This.handbook.has.the.following.specific.salient.features:

to.serve.as.a.single.comprehensive.source.of.information.and.as.ref-erence.material.on.IMS.technology;to.deal.with.an.important.and.timely.topic.of.emerging.technology.of.today,.tomorrow,.and.beyond;to.present.accurate,.up-to-date.information.on.a.broad.range.of.top-ics.related.to.IMS.technology;to.present.material.authored.by.the.experts.in.the.field;.andto. present. the. information. in. an. organized. and. well-structured.manner.

Although.the.handbook.is.not.precisely.a.textbook,.it.can.certainly.be.used.as.a.textbook.for.graduate.courses.and.research-oriented.courses.that.deal.with.the.IMS..Any.comments.from.readers.will.be.highly.appreciated.

Many.people.have.contributed.to.this.handbook.in.their.unique.ways..The.first.and.the.foremost.group.that.deserves.immense.gratitude.is.the.group.of.highly.talented.and.skilled.researchers.who.have.contributed.22.chapters.to.this.handbook..All.of.them.have.been.extremely.cooperative.and.profes-sional..It.has.also.been.a.pleasure.to.work.with.Nora.Konopka,.Jessica.Vakili,.and.Judith.Simon.of.CRC.Press.and.we.are.extremely.grateful.for.their.sup-port.and.professionalism..Our. families.have.extended. their.unconditional.love.and.strong.support.throughout.this.project.and.they.all.deserve.very.special.thanks.

Syed AhsonPlantation, Florida

Mohammad IlyasBoca Raton, Florida

xi

The Editors

Syed Ahson.is.a.senior.staff.software.engineer.with.Motorola,.Inc..He.has.played.a.leading.role.in.and.contributed.significantly.to.the.creation.of.several.advanced.and.exciting.cellular.phones.at.Motorola..He.has.extensive.expe-rience.with.wireless.data.protocols. (TCP/IP,.UDP,.HTTP,.VoIP,.SIP,.H.323),.wireless.data.applications.(Internet.browsing,.multimedia.messaging,.wire-less. e-mail,. firmware. over-the-air. update),. and. cellular. telephony. proto-cols. (GSM,.CDMA,.3G,.UMTS,.HSDPA)..Prior. to. joining.Motorola,.he.was.a.senior.software.design.engineer.with.NetSpeak.Corporation.(now.part.of.Net2Phone),.a.pioneer.in.voice.over.IP.telephony.software.

Ahson.is.a.co-editor.of.the.three-volume.WiMAX Handbook.(CRC.Press).and.has.authored.Smartphones,.a. research. report. that. reflects.on. the.smart-phone.market.and. technologies. for. the. International.Engineering.Consor-tium.(IEC)..He.has.published.several.research.articles.and.teaches.computer.engineering.courses.as.adjunct.faculty.at.Florida.Atlantic.University.in.Boca.Raton,.Florida,.where.he.introduced.a.course.on.smartphone.technology.and.applications..He.received.his.MS.degree.in.computer.engineering.in.1998.at.Florida.Atlantic.University.and.his.BSc.degree.in.electrical.engineering.from.Aligarh.University,.India,.in.1995.

Mohammad Ilyas.received.his.BSc.degree.in.electrical.engineering.from.the.University.of.Engineering.and.Technology,.Lahore,.Pakistan,.in.1976..From.March.1977.to.September.1978,.he.worked.for.the.Water.and.Power.Develop-ment.Authority.in.Pakistan..In.1978,.he.was.awarded.a.scholarship.for.his.graduate.studies.and.completed.his.MS.degree.in.electrical.and.electronic.engineering.in.June.1980.at.Shiraz.University,.Shiraz,.Iran..In.September.1980,.he.joined.the.doctoral.program.at.Queens.University.in.Kingston,.Ontario,.Canada..He.completed.his.PhD.degree. in.1983..His.doctoral.research.was.about. switching. and. flow. control. techniques. in. computer. communication.networks..Since.September.1983,.he.has.been.with.the.College.of.Engineer-ing.and.Computer.Science.at.Florida.Atlantic.University,.Boca.Raton,.Flor-ida,.where.he.is.currently.associate.dean.for.research.and.industry.relations..From.1994.to.2000,.he.was.chair.of.the.Department.of.Computer.Science.and.Engineering..From.July.2004.to.September.2005,.he.served.as.interim.associ-ate.vice.president.for.research.and.graduate.studies..During.the.19931994.academic.year,.he.was.on.sabbatical.leave.with.the.Department.of.Computer.Engineering,.King.Saud.University,.Riyadh,.Saudi.Arabia.

Dr.. Ilyas. has. conducted. successful. research. in. various. areas,. including.traffic.management.and.congestion.control.in.broadband/high-speed.com-munication.networks,.traffic.characterization,.wireless.communication.net-works,.performance.modeling,.and.simulation..He.has.published.one.book,.eight.handbooks,.and.more.than.150.research.articles..He.has.supervised.11.

xii TheEditors

PhD.dissertations.and.more.than.37.MS.theses.to.completion..He.has.been.a.consultant.to.several.national.and.international.organizations..Dr..Ilyas.is.an.active.participant.in.several.IEEE.technical.committees.and.activities,.a.senior.member.of.IEEE,.and.a.member.of.ASEE.

xiii

Contributors

Adel Al-Hezmi Fraunhofer.FOKUS.Research. Institute. for.Open.Com-munication.Systems,.Berlin,.Germany

Alessandro Amirante Universit.di.Napoli.Federico.II,.Napoli,.Italy

Stefan Arbanowski Fraunhofer.FOKUS.Research.Institute.for.Open.Com-munication.Systems,.Berlin,.Germany

Arturo Azcorra IMDEA.Networks,.Madrid,.Spain.Universidad.Carlos.III.de.Madrid,.Madrid,.Spain

Emmanuel Bertin Orange.Labs,.France.Telecom,.Caen,.France

Niklas Blum Fraunhofer.FOKUS.Research.Institute.for.Open.Commu-nication.Systems,.Berlin,.Germany

Tobia Castaldi Universit.di.Napoli.Federico.II, Napoli,.Italy

Whai-En Chen National.I-Lan.University, Taiwan,.Republic.of.China

Nol Crespi GET-INTInstitut.National.des.Tlcommunications, Evry,..France

Antonio Cuevas Universitt.Stuttgart, Stuttgart,.Germany

Oliver Friedrich Fraunhofer.FOKUS.Research.Institute.for.Open.Com-munication.Systems,.Berlin,.Germany

Jaime Garca Universidad.Carlos.III.de.Madrid,.Madrid,.Spain

Anahita Gouya Institut.National.des.Tlcommunications,.Evry,.France

Jean-Charles Grgoire EMT-INRS.University.of.Quebec,.Quebec,.Canada

Ryozo Ito Hewlett-Packard,.Tokyo,.Japan

Admela Jukan EMT-INRS.University.of.Quebec,.Quebec,.Canada

Moo Wan Kim Tokyo.University.of.Information.Sciences,.Tokyo,.Japan

xi Contributors

Younghan Kim Soongsil.University,.Seoul,.South.Korea

Youngsuk Lee Soongsil.University,.Seoul,.South.Korea

Antonio Liotta University.of.Essex,.Colchester,.United.Kingdom

David Lpez Universidad.Carlos.III.de.Madrid,.Madrid,.Spain

Thomas Magedanz Fraunhofer.Institute.FOKUS,.Berlin,.Germany

Marcin Matuszewski Nokia,.Espoo,.Finland

Eugen Mikoczy Slovak.University.of.Technology,.Bratislava,.Slovakia

Lorenzo Miniero Universit.di.Napoli.Federico.II,.Napoli,.Italy

Jos Ignacio Moreno Universidad.Carlos.III.de.Madrid,.Madrid,.Spain

Vicente Olmedo Universidad.Politcnica.de.Madrid,.Madrid,.Spain

Adetola Oredope University.of.Essex,.Colchester,.United.Kingdom

Christopher J. Pavlovski IBM,.St..Leonards,.New.South.Wales,.Australia

Simon Pietro Romano Universit.di.Napoli.Federico.II,.Napoli,.Italy

Jithesh Sathyan Infosys.Technologies.Limited,.Bangalore,.India

Robert Seeliger Fraunhofer.FOKUS.Research.Institute.for.Open.Commu-nication.Systems,.Berlin,.Germany

Muhammad Sher Technical.University.of.Berlin,.Berlin,.Germany

Ignacio Soto Universidad.Carlos.III.de.Madrid,.Madrid,.Spain

Francisco Valera Universidad.Carlos.III.de.Madrid,.Madrid,.Spain

Enrique Vzquez Universidad.Carlos.III.de.Madrid,.Madrid,.Spain

Ivn Vidal Universidad.Carlos.III.de.Madrid,.Madrid,.Spain

Victor Villagr Universidad.Politcnica.de.Madrid,.Madrid,.Spain

Dragos Vingarzan Fraunhofer.FOKUS.Research.Institute.for.Open.Com-munication.Systems,.Berlin,.Germany

Contributors x

Igor Vukomanovi KATE-KOM,.Zagreb,.Croatia

Mario Weber KATE-KOM,.Zagreb,.Croatia

Peter Weik Technical.University.of.Berlin,.Berlin,.Germany

Fangmin Xu Beijing.University.of.Posts.and.Telecommunications,.Beijing,.Republic.of.China

Luyong Zhang Beijing.University.of.Posts.and.Telecommunications,.Beijing,.Republic.of.China

Wei Zhong Duke.University,.Chapel.Hill,.North.Carolina

Zheng Zhou Beijing.University.of.Posts.and.Telecommunications,.Beijing,.Republic.of.China

Section 1

Concepts

1IMSService,Models,andConcepts

Emmanuel Bertin and Nol Crespi

CONTENTS

Introduction..............................................................................................................3The.Foundations.of.IMS.Services..........................................................................4

From.IN.to.NGN.............................................................................................4From.NGN.to.IMS...........................................................................................7IMS.Service.Capabilities.and.OMA.Enablers.............................................9

IMS.Service.Model................................................................................................. 12IMS.Brings.New.Types.of.Services............................................................ 12The.Link.between.Services.Seen.by.the.User........................................... 13Technical.Functions...................................................................................... 14Relationship.between.Service.and.Technical.Function.......................... 16

Example.of.the.Push-to-Talk.over.Cellular........................................................ 17PoC.Service.Seen.from.the.Users.Perspective......................................... 18PoC.Service.and.Service.Enablers.............................................................. 19Technical.Functions.for.PoC.Service.......................................................... 19A.Comprehensive.View.of.IMS.Services...................................................22

Conclusion...............................................................................................................22Glossary................................................................................................................... 24References............................................................................................................... 24

Introduction

NGN.(next-generation.network).is.a.concept.that.has.been.introduced.to.take.into.account.the.new.situation.and.changes.in.the.telecommunications.fields..This.new.situation.is.characterized.by.a.number.of.aspects:.the.deregulation.of.markets,.the.new.demand.from.users.for.innovative.services.to.meet.their.needs,.and.the.explosion.of.digital. traffic. (increase.of. Internet.usage)..The.introduction.of.NGN.comprises.economic.and.technical.aspects..Economi-cally,. it.allows.increasing.productivity.by.creating.new.usage.[1].based.on.user.preferences.and.related. to.voice.and.data.services. (e.g.,.voice.over. IP,.

IPMultimediaSubsystem(IMS)Handbook

instant. messaging,. presence,. streaming,. and. push. to. talk).. It. also. permits.reducing.costs.for.infrastructure.maintenance,.with.only.one.type.of.trans-port.network.instead.of.specific.ones.for.each.access.network..Technically,.NGN.makes.the.network.architecture.flexible.in.order.to.define.and.intro-duce.new.services.easily.

The.cornerstone.of.the.service.architecture.for.next-generation.networks.is. the. IMS.(IP.multimedia.subsystem).architecture,.standardized.by.3GPP.(3rd.Generation.Partnership.Project)..The.IMS.offers.telecom.operators.the.possibility.to.build.an.open.IP-based.service.infrastructure.that.will.enable.easy.deployment.of.new,.rich.multimedia.communication.services.mixing.telecom.and.data.services.

The. conception. of. IMS. services. is. a. key. challenge. for. the. telecom. mar-ket..IMS.services.are.fundamentally.tailored.to.user.preferences,.rely.seam-lessly.on.multiple.access.networks,.and.bundle.multiple.service.features.(e.g.,.voice/video.connectivity,.community.tools,.presence,.conferencing,.gaming,.and.TV.broadcasting).

The. architecture. and. technical. aspects. of. the. IMS. architecture. are. well.addressed. by. the. standardization. bodies.. However,. a. clear. model. of. what.an. IMS.service. is. (and.what. it. is.not). is.not.proposed.by. these.bodies..The.objective. of. this. chapter. is. to. detail. the. concepts. behind. IMS. services. and.to.propose.a.way.to.link.IMS.service,.service.building.blocks,.and.technical.functions.

This.chapter.is.divided.into.three.sections..In.the.first.section,.we.present.a.survey.of.IMS.services,.starting.by.briefly.introducing.NGN.architecture.and.then.describing.IMS.service.architecture.and.the.OMA.(Open.Mobile.Alliance).achievements..In.the.second.section,.we.present.how.IMS.services.can.be.linked.with.service.building.blocks.and.with.technical.functions..In.the.third.section,.we.illustrate.the.previous.section.with.the.case.study.of.the.push-to-talk.over.cellular.service.(PoC),.specified.by.the.OMA.

The Foundations of IMS Services

From IN to NGN

The.concept.of.intelligent.networks.(INs).developed.in.the.1980s.was.a.pre-cursor.of.the.NGN..The.principle.of.INs.is.to.separate.clearly.the.switching.functions.from.the.service.data.and.logic.located.in.an.external.entity:.the.service. control.point. (SCP)..A.new. functional. entity. is.added. to. the.TDM.(Time.Division.Mutiplexing).switch,.the.service.switching.point.(SSP),.which.interfaces.between.the.service.logic.and.the.switch.itself..An.interface.based.on.the.intelligent.network.application.part.(INAP).protocol.family.is.intro-duced.between.the.SSP.and.the.SCP..The.services.are.no.longer.developed.in.the.TDM.switchas.with.the.concept.of.global.system.for.mobile.com-

IMSService,Models,andConcepts

munications.(GSM).and.integrated.services.digital.network.(ISDN).supple-mentary. servicesbut. rather.are. implemented. in. the.SCP..The. INAP.and.associated.procedures.allow.the.SCP.to.control.and.monitor.the.switch.

The.intelligent.network.introduced.the.concept.of.a.service.independent.building. block. (SIB). for. reusable. service. functions.. A. service. could. thus.be.thought.of.as.a.composition.of.various.SIBs..But.this.goal.was.not.fully.achieved.because.of.a. lack.of. independence.with.INAP.protocol,.a. lack.of.software.reusability,.and.a.lack.of.openness.by.manufacturers.and.operators..As.a.consequence,.INs.deployed.today.rely.on.a.monolithic.architecture.and.service. platforms. do. not. offer. flexible. services.. In. addition,. as. the. service.logic.is.executed.in.external.entities,.triggering.multiple.services.for.one.call.requires. having. service. interaction. management. mechanisms.. This. issue,.known.as.feature.interaction,.is.one.of.the.most.complex.problems.encoun-tered.in.IN.and.considerable.work.has.been.done.on.it..However,.this.work.cannot.be.directly.applied.to.the.NGN.because.of.the.service.and.architec-tural.differences.between.IN.and.NGN.

The.promise.of.the.NGN,.as.defined.in.the.late.1990s,.was.to.offset.these.shortcomings. by. moving. from. a. vertical. approach. (where. access,. control,.and. services. are. closely. tied). to. a. horizontal. approach. (where. each. layer.provides.reusable.elements.to.other.layers)..Specification.work.is.ongoing.at.the.International.Telecommunication.Union.(ITU)-T.(as.described.in.Knight-son,.Morita,.and.Towle. [2]). to. formalize. the.separation. (e.g.,. through.stan-dard.protocols.or.application.programming.interfaces.[APIs]).between

the. transport.stratum.that. is.composed.of. transfer. functions. from.various. access. networks. (UMTS. terrestrial. radio. access. network.[UTRAN],.wireless.local.area.network.[WLAN],.xDSL).and.from.the.core. networks,. control. functions. for. these. transfer. functions. (e.g.,.network. attachment. control. or. resource. and. admission. control),.the.transport.user.profiles.(e.g.,.to.store.the.data.linked.to.network.attachment),. and. the. media. handling. functions. (e.g.,. for. playing.announcements.or.for.transcoding);.andthe.service.stratum.composed.of.access-independent.service.control.functions. (e.g.,. session. establishment. control. or. service. triggering.control),.application.functions,.and.service.user.profiles..Application.functions.should.be.independent.from.the.service.control.functions.and. should. offer. flexibility. (e.g.,. by. using. open. software. mecha-nisms).to.answer.user.needs.

This.NGN.architecture.with.two.strata.is.defined.at.the.International.Tele-communication. Union. Telecommunication. Standardization. Sector. (ITU-T).(Figure.1.1)..The.NGN.architecture.may.also.be.represented.with.three.layers.instead.of.two.strata.(this.is,.for.instance,.the.case.at.the.European.Telecom-munications.Standards. Institute. [ETSI]).. In. this. case,. service. control. func-tions.and.transport.control.functions.are.grouped.into.a.control.layer..The.


separation.thus.involves.a.transfer.layer.(with.transfer.functions),.a.control.layer.(with.transport.control.functions.and.service.control.functions),.and.an.application.layer.(with.application.functions).

We.can.draw.a.parallel.between.IN.and.NGN.architectures:.The.service.control. function. (usually. implemented. with. a. session. initiation. protocol.[SIP].proxy).is.the.NGN.counterpart.of.the.TDM.switch/SSF.(service.selec-tion.function).and.the.application.function.(for.example,.implemented.with.a.SIP.application.server).is.the.NGN.counterpart.of.the.service.control.func-tion.(SCF)..In.both.architectures,.the.triggering.criteria.have.been.defined.in.order.not. to. invoke.services.systematically.but.only.when.required..How-ever,. there. is. a. key. difference. between. those. architectures. regarding. the.triggering.mechanisms..In.IN,.the.SCF.controls.the.SSF.using.INAP,.which.is. independent.of.the.call.control.protocols.. In.the.NGN.architectures,. the.application.function.is.inserted.in.the.signaling.path;.therefore,.all.SIP.sig-naling.requests.and.responses.can.be.intercepted.by.the.entity.controlling.the.services..Indeed,.the.IN.concept.of.point.of.control.(i.e.,.an.entity.that.can.control.the.SSP.and.modify.the.signaling.at.any.time).does.not.exist.in.the.NGN.context..This.concept.is.replaced.by.the.notion.of.application.func-tion.present.in.the.signaling.path,.which.can.modify.SIP.messages.to.execute.a.service.logic..The.consequence.of.this.fundamental.difference.in.signaling.and.architecture.is.that.mechanisms.defined.in.IN.for.feature.interaction.are.mostly.not.applicable.for.SIP.

ServiceUser Profiles

Service Stratum ApplicationFunctions

Service ControlFunctions

Transport ControlFunctions

TransferFunctions

Control flows Media flows

Media HandlingFunctions

TransportUser Profiles

Transport Stratum

End-UserFunctions

FIGure 1.1NGN.technical.architecture.[2].


From NGN to IMS

The.IMS.architecture.is.a.realization.of.NGN.principles,.relying.on.the.SIP.protocol.for.the.session.control..The.IMS.specifications.[3].define.the.whole.multimedia.session.control.architecture.on.top.of.the.universal.mode.telecom-munications.system.(UMTS).packet-switched.domain..With.IMS,.operators.provide.both.reliable.session.control.and.better.integrated.services..Because.IMS.is.solving.architectural.issues.for.SIP.deployments.(as.detailed.in.Bertin,.Bury,.and.Lesieur.[4]),.it.is.now.seen.as.a.guideline.for.all.SIP.deployment.using.the.client/server.paradigm..While.the.IETF.(Internet.Engineering.Task.Force).has.standardized.the.SIP.protocol.but.not.the.associated.architectures.[5],. the. 3GPP. has. defined. with. precision. the. architectures. and. the. proce-dures.to.ensure.roaming,.scalability,.security,.and.reliability..Moreover,.the.IMS.specifications.are.not. intrinsically. linked.to.mobile.networks. [6].. IMS.was,. for. the. most. part,. conceived. independently. from. the. UMTS. packet-switched. domain. and. can. be. adapted. to. other. types. of. access. networks..3GPP.has.specified.the.interface.between.IMS.and.WLAN.access.networks.(IMS.release.6).[7]..The.ETSI.TISPAN.(Telecommunications.and.Internet.Con-verged.Services.and.Protocols.for.Advanced.Networking).project.specifies.the.adaptations.controlling.xDSL.access.networks.with.IMS.[8]..In.addition.to.IMS,.TISPAN.is.also.defining.other.subsystems.such.as.public.switched.telephone. network. (PSTN)/ISDN. emulation. for. PSTN. replacement. (which.will.be.needed.in.Europe.between.2008.and.2012).

The.major.elements.related.to.service.architecture.are.the.following:

S-CSCFs. (serving. call. state. control. functions). implement. service.control.functions.(session.control.and.service.triggering).HSS. (home. subscriber. server). is. the. central. service. and. network.database..It.implements.the.service.user.profiles.(as.well.as.the.trans-port.user.profiles).ASs.(application.servers).implement.the.application.functions,.pro-viding. session-related. services. to. users.. The. ASs. offer. APIs. like.OSA/Parlay.or.SIP.servlet.for.application.execution.

Concerning.user.identity,.the.user.is.represented.in.IMS.by.several.identi-fiers..Public.identities.are.routable.addresses.that.can.be.communicated.to.the.contacts.of.the.user.and.can.be.used.to.reach.this.user.(e.g.,.sip:[email protected]:+33123456789)..Private.identities.belong.to.the.IMS.operator.and.are.stored.in.the.SIM.(subscriber.identity.module).card..The.same.user.may.have.several.private.user. identities.and.several.public.user. identities,.but.only.one.private.identity.is.stored.per.SIM.card.(Figure.1.2).

Concerning. service. triggering,. IMS. provides. an. application. triggering.architecture.based.on.filter.criteria.and.service.points.triggers.(SPTs).[9]..Ini-tial.filtering.criteria.(iFC).allow.the.S-CSCF.to.decide.which.services.should.be. invoked. during. a. SIP. session. or. transaction. and. in. which. order. they.should.apply..The.SPTs.are. the.points. in. the.SIP.signaling.on.which.filter.


criteria.can.be.set..The.filter.criteria.are.distributed.among.the.S-CSCF,.HSS,.and.IMS.application.server,.as.shown.in.the.Figure.1.3.

iFCs.are.stored.in.the.HSS.as.a.part.of.the.service.profile..They.are.down-loaded.to.the.S-CSCF.upon.user.registration.or.upon.a.terminating.initial.request.for.an.unregistered.user..They.are.active.during.the.registration.life-time.or.until.the.service.profile.is.changed..Filter.criteria.should.contain.the.following.information,.structured.in.an.XML.format:

the.address.of.the.AS.to.be.contacted;the.priority.of.the.filter.criteria.providing.the.sequence.in.which.the.criteria.will.be.applied;

IMSSubscription

PrivateUser Identity

PublicUser Identity

PublicUser Identity

PublicUser Identity

ServiceProfile

ServiceProfile

FIGure 1.2IMS.user.identities.in.IMS.release.5.[3].

SIP SIP

SIP

Filter CriteriaSPT

HSS

iFC

S-CSCF

Application Server

Service Logic

Service Platform Trigger Points

SIP Interface

FIGure 1.3Application.server.triggering.architecture.[9].


the.SPTs,.which.may.contain.the.following.information:.SIP.method,.presence. or. absence. of. any. header,. content. of. any. header,. session.description.information,.etc.;default.handling.if.the.AS.is.not.reachable;.andoptional.service.information,.added.to.the.message.body.before.it.is.sent.to.the.AS.

During.the.registration.phase,.an.S-CSCF.is.assigned.to.control.user.ser-vices..The.service.profile.(containing.iFCs).of.the.user.is.downloaded.from.the.HSS.to.the.S-CSCF..When.the.S-CSCF.receives.a.SIP.request.matching.the.iFC,.it.invokes.the.associated.service.by.forwarding.this.SIP.request.to.the.AS.indicated.in.the.iFC..iFCs.are.only.applied.to.initial.SIP.requests.(i.e.,.the. requests. initiating. a. SIP. session. or. transaction:. INVITE,. SUBSCRIBE,.REGISTER,.OPTION,.etc.);.consequently,.the.service.invocation.can.be.done.only.statically.in.the.SIP.session.or.transaction.initiation.phase.

A. user. may. subscribe. to. several. services,. and. as. a. consequence. several.iFCs. may. be. present. in. the. service. profile.. When. the. S-CSCF. receives. an.initial.SIP.request,.it.checks.whether.it.matches.the.iFC.that.has.the.highest.priority.for.this.user..If.it.does.not.match,.the.S-CSCF.checks.the.next.iFC,.in.the.predefined.priority.order..If.it.matches,.the.S-CSCF.forwards.the.request.to.the.indicated.AS..This.AS.executes.the.service.logic,.eventually.modifies.the.request,.and.sends.it.back.to.the.S-CSCF..The.S-CSCF.performs.the.same.processing.with.the.next.unexecuted.iFC..The.S-CSCF.continues.this.process.until.all. the. iFCs.are.checked..The.AS.may.also.suppress. the. information.required.to.trigger.the.iFC.(e.g.,.replacement.of.public.identity.by.a.globally.routable.user.agent.[UA].uniform.resource.identifier.[URI]).or.locally.end.the.request.as.a.part.of.the.service.logic.(e.g.,.a.prepaid.account.without.remain-ing.credit)..These.mechanisms.will.be.used.to.build.future.communication.services.with.the.IMS.

3GPP.had.specified.a.SIP.AS.called.service.capability.interaction.manager.(SCIM).for.managing.the.interactions.between.application.servers,.but.nei-ther.the.service.invocation.functionalities.over.ISC.nor.the.service.interac-tion.management.functionalities.of.SCIM.are.specified.in.the.standards.[14]..These.points.are.detailed.in.Chapter.14,.Service.Orchestration.in.IMS.

IMS Service Capabilities and OMA enablers

The.business.purpose.of.the.IMS.is.to.enable.the.building.of.innovative.ser-vices.in.a.flexible.way..IMS.services.will.include.multiple.service.features.like.chat,.instant.messaging,.voice,.video,.presence,.address.book,.and.TV.broad-casting.[10,11]..If.all.these.features.are.deployed.in.an.uncoordinated.way.by.a.service.provider,.the.user.will.have.to.handle.the.interaction.between.the.services. (e.g.,.by.entering. the.same.personal.preferences. several. times).. In.addition,.advanced.services.that.combine.many.service.features.(like.routing.voice.calls.according.to.the.originating.community.and.the.availability.state).

10 IPMultimediaSubsystem(IMS)Handbook

are.not.possible.if.there.is.no.coordination.between.features..The.answer.to.improving. user. experience. is. to. build. a. coherent. service. environment. by.standardizing.the.applications.functions.

Standardization.of.application.functions.is.today.mainly.driven.by.ITU-T,.3GPP,.and.OMA..Telecom.and.IT.companies.regroup.within.OMA.to.specify.interoperable.advanced.mobility.services..OMA.was.created.in.June.2002.as.a.combination.of.the.WAP.forum,.the.SyncML.Initiative,.the.MMS.Interoper-ability.Group,. the.Wireless.Village. Initiative,. the.Mobile.Wireless. Internet.Forum,.and. the.Mobile.Games. Interoperability.Forum..The.goal.of. ITU-T,.3GPP,.and.OMA.is.not.to.standardize.complete.services.but,.rather,.to.stan-dardize.functional.service.building.blocks.that.are.reusable.at.runtime.by.various.services,.as.defined.in.Bertin,.Bury,.and.Lesieur.[13]..This.approach.enables. the. building. of. innovative. and. evolving. services. mostly. indepen-dently.of.network.considerations..These.service.building.blocks.provide.key.capabilities.to.ensure.interoperability.of.devices,.operators,.and.service.pro-viders..As.seen.before,.ITU-T.and.3GPP.are.standardizing.the.mechanisms.that.trigger.these.building.blocks,.either.separately.or.in.a.coordinated.way,.including. the. management. of. interactions. between. these. capabilities,. as.shown.in.Gouya,.Crespi,.and.Bertin.[14]..These.service.building.blocks.are.called.service.capabilities.at.3GPP,.service.support.capabilities.at.ITU-T,.and.service.enablers.at.OMA..Service.support.capabilities.studied.at.ITU-T.[15].typically.include.presence,.location,.group.management,.message.handling,.broadcast/multicast,.push.and.session.handling,.or.device.management..Ser-vice.enablers.at.OMA.[16].include,.for.example,.data.synchronization,.device.management,.digital.rights.management,.downloading,.e-mail.notification,.instant.messaging,.presence.and.mobile.location,.or.multimedia.messaging..Service.capabilities.defined.at.3GPP.typically.include.presence.[17].and.mes-saging.[18].or.conferencing.[19].

The.OMA.specifications.for.service.enablers.are. the.most.advanced.and.complete..According.to.the.OMA,

An.enabler.is.defined.as].a.technology.intended.for.use.in.the.devel-opment,.deployment.or.operation.of.a.service;.defined.in.a.specifica-tion,. or. group. of. specifications,. published. as. a. package. by. OMA.[20].An.enabler.should.specify.one.or.more.public.interfaces..Examples.of.OMA.enablers.include.location.or.device.management.[16].

These.definitions.highlight.the.normative.character.of.an.enabler..A.com-ponent.or.a.technology.is.an.enabler.because.it.has.been.defined.as.an.enabler..Moreover,.when.individual.enablers.are.defined.independently,.each.enabler.has.to.define.all.functions.required.to.fulfill.its.requirements..This.implies.several.issues.for.the.service.providerespecially.the.difficulty.of.providing.user-centric.services:.Integration.and.deployment.of.services.is.complicated.and.expensive;.high.implementation.efforts.for.applications.wanting.to.use.

IMSService,Models,andConcepts 11

several.capabilities;.there.is.no.common.integration.of.the.different.services.from.the.point.of.view.of.the.end.user.(e.g.,.no.common.group.management.or.user.profile.across.multiple.services).[16]..An.OMA.enabler.should.thus.contain.only.intrinsic.functions.that.can.interact.with.other.functions.from.the.service.architecture.or.from.underlying.network.architecture..Intrinsic.functions.are.defined.as.those.functions.that.are.essential.in.fulfilling.the.intended.task.of.the.specified.enabler..For.example,.the.position.calculation.function.is.intrinsic.to.secure.user.plane.location;.authentication.is.intrinsic.to.single.sign.on;.encryption.is.an.intrinsic.function.of.digital.rights.manage-ment.[16].

This.separation.into.intrinsic.and.nonintrinsic.functions.is.a.way.of.ensur-ing.that.various.enablers.will.not.include.the.same.function.(e.g.,.authentica-tion.function.in.each.enabler)..As.specified.in.reference.16,.any.requirements.or.features.that.are.not.intrinsic.to.an.enabler.should.not.be.specified.within.the.enablers.specification..An.enablers.specification.should.only.specify.the.intrinsic.functionality.required.to.fulfill.its.actual.function..This.specifica-tion. of. service. functions. with. enablers. that. are. responsible. only. for. their.intrinsic.functions.enhances.the.ability.of.service.providers.to.offer.a.con-sistent. user. experience. (i.e.,. reuse. of. user. information,. service. continuity,.etc.)..However,.the.separation.into.intrinsic.and.nonintrinsic.functions.is.not.obvious.but.remains.subjective,.as.recognized.in.reference.16.(the.classifi-cation.of.intrinsic.and.non-intrinsic.is.subjective.and.needs.to.be.done.on.a.per.enabler.basis)..This.implies.again.that.the.definition.of.enablers.should.result.from.a.normative.process.

The. OMA. has. specified. the. OMA. service. environment. (OSE). [16]. that.provides.a.common.architecture.for.the.integration.of.enablers.and.service.creation..As.shown.in.Figure.1.4,.the.OSE.architecture.consists.of.enablers.that.run.on.an.execution.environment.and.are.accessible.to.applications.and.other.enablers.through.a.policy.enforcer.

Enablers.are.intended.for.use.in.the.development,.deployment,.or.opera-tion.of.a.service..They.provide.their.intrinsic.functionality.through.one.or.more.public.interfaces.called.I0.interfaces.and.may.use.underlying.network.resources.through.I2.interfaces.(such.as.IMS.interfaces).The.execution.envi-ronment.logically.encompasses.various.functions.such.as.process.monitoring,.software.life.cycle.management,.system.support.(e.g.,.thread.management,.load.balancing,.and.caching),.operation,.management,.and.administration..The.interface.between.the.execution.environment.and.enablers.is.called.an.I1.interface..The.policy.enforcer.provides.a.policy-based.management.mecha-nism. to.protect. resources. from.unauthorized. requests. and. to.manage. the.use.of.these.requestsfor.instance,.through.appropriate.charging,.logging,.and.enforcement.of.user.privacy.or.preferences..The.policy.enforcer.function.allows.the.domain.owner.to.extract.and.separate.policy.rules.from.architec-tural.elements..This.element.exposes. I0.+.P. interfaces. to.applications.and.enablers,.where.P.is.additional.parameters.that.must.be.provided.along.with.a.request.to.an.enablers.I0.interface,.when.the.policies.that.are.to.be.enforced.


require.additional.parameters..Applications.can.be.located.inside.or.outside.the.service.delivery.environment.

IMS Service Model

IMS Brings New Types of Services

Traditionally,.telecommunications.services.are.divided.into.bearer.services,.teleservices,.and.supplementary.services..A.bearer.service.is.a.type.of.tele-communication.service.that.provides.the.capability.for.the.transmission.of.signals.between.user-network.interface.and.a.teleservice.is.a.type.of.ser-vice. that. provides. the. complete. capability,. including. terminal. equipment.functions,. for.communication.between.users.and.supplementary.service.modifies.or.supplements.a.basic.teleservice.[26]..Examples.of.basic.teleser-vice.are.telephony,.facsimile,.or.emergency.calls.

These.notions.are.still.in.use.in.some.3GPP.or.TISPAN.standards.but.can.no.longer.be.used.by.a.service.provider.to.design.services..Indeed,.the.added.value.of.IMS.for.service.providers.is.the.ability.to.build.user-centric.services.that.flexibly.combine.several.features.and.enable.the.sharing.of.user.infor-mation.between.these.features.to.form.a.coherent.service.environment.for.the.user.[12]..As.explained.in.the.previous.section,.the.OMA.enabler.or.the.3GPP.service.capabilities.are.the.necessary.building.blocks.for.such.services..However,.a.model.for.IMS.services,.linking.the.services.from.users,.enablers,.and.technical.functions,.is.not.defined.in.standards.

ApplicationsService Provider

I0+P

I0 I0

I2I2I2

I0

EnablerI1

Policy Enforcer

EnablerEnabler

Exec

utio

n En

viro

nmen

t

FIGure 1.4The.OMA.service.environment.architecture.[16].


Transfer.and.control.functions.are.extensively.addressed.by.IMS.and.NGN.studies..Application.functions.are.partially.addressed.by.the.OMA.concern-ing. the. service. delivery. aspects. (with. the. OSE).. The. foreseen. services. for.IMS.will.require.a.coherent.integration.of.multiple.loosely.coupled.features..The.integration.between.these.features.should.be.considered.not.only.at.the.technical.level.(i.e.,.the.integration.within.a.service.delivery.environment.like.OSE).but.also.at.a.service.level.(i.e.,.how.the.composition.of.various.technical.functions.and.enablers.will.provide.a.coherent.service.experience.to.the.user)..If. the. integration.at. the. technical. level. is.well.addressed.by.the.OMA.and.ETSI.studies,.the.integration.at.the.service.level.has.not.been.investigated.

To. answer. these. needs,. we. should. describe. the. relationships. between. a.service.perceived.by.the.user.and.the.technical.functions.and.enablers.used.to.implement.it.

The.modeling.approach.is.organized.as.follows:

modeling. the. link.between.services. that. is. seen.by. the.users. (e.g.,.a.user.is.aware.that.his.or.her.personal.information.is.shared.between.his.services);modeling. the. technical. functions. that. are. the. foundation. of. IMS;.technical.functions.are.those.carried.out.by.the.systems.(e.g.,.service.platforms,.terminals).controlled.by.the.service.providers;.andmodeling.IMS.service.architecture.based.on.service.enablers..Service.enablers.are.designed.for.the.reuse.of.the.user.information.between.services.and.for.easy.integration.of.new.services..As.seen.before,.ser-vice.enablers.contain.and.wrap.technical.functions.(intrinsic.func-tions)..We.propose.to.characterize.an.enabler.by.the.information.it.handles.and.by.the.technical.functions.it.wraps..For.instance,.only.one.service.enabler.can.produce.the.presence.information.and.can.wrap.the.technical.functions.linked.to.presence,.or.only.one.service.enabler.can.produce.the.location.information.and.can.wrap.the.tech-nical.functions.linked.to.location.

The Link between Services Seen by the user

The.first.step.is.to.define.clearly.what.a.service.is..There.is.a.lot.of.research.on.the.notion.of.servicenot.that.much.in.the.IT.area.but,.rather,.in.the.eco-nomic.and.business.sciences,.as.surveyed.in.Ben.Yahia.et.al..[21]..In.a.generic.way,.a.service.can.be.defined.as.any.business.actions.or.business.activities.that.have.a.value-added.result.for.a.user.(a.person.or.a.system)..This.action.or.activity.is.offered.by.a.service.provider.(another.person,.entity,.or.system),.which.profits.from.providing.this.action.[22,23].

In.the.telecommunications.field,.a.telecom.service.is.defined.by.3GPP.as.a.component.of.the.portfolio.of.choices.offered.by.service.providers.to.a.user,.functionality.offered.to.a.user.[24].

The.focus.area.of.this.study.is.service.usage;.hence,.we.concentrate.on.the.user.while.the.customer.is.outside.the.scope.of.IMS.services..The.customer.is.


a.person.or.organization.that.purchases.products.and.services.[25];.the.user.is.the.person.(or.system).who.uses.the.service.and.can.be.different.from.the.customer..For.example,.in.a.family,.the.customer.may.be.one.of.the.parents,.and.a.child.may.be.the.user.of.the.purchased.service..The.customer.usually.assigns.rights. to.users. to.use.the.services.he.or.she.has.obtained,.and.the.customer.can.be.a.user..Although.the.user.is.typically.a.person,.it.may.also.be.another.actor.(e.g.,.another.service.provider).

Relying.on. the.preceding.service.definition,.we.propose.a.definition. for.IMS.services.as.follows:

IMS.services.are.activities.that.take.place.in.interactions.between.a.user.(i.e.,. IMS. user). and. systems. controlled. by. service. providers. (e.g.,. IMS.user. equipment,. IMS. platforms).. These. activities. have. a. value-added.result.for.the.user;.and.the.service.providers.profit.from.providing.these.activities.

In. this.definition.we.highlight. two.parties:. the.user.and. the.systems.con-trolled.by.the.service.providers.

From.a.user.perspective,.the.purpose.of.IMS.services.is.to.establish.a.com-munication.session.between.users. that. is.adapted. to.user.preferences.and.context..The.session.manipulated.by.IMS.services.may.be.voice.sessions.but.can.also.be.video.sessions,.instant.messaging.sessions,.or.collaboration.ses-sions.. The. term. session. here. means. only. an. interactive. exchange. between.two.or.more.persons.in.order.to.communicate..From.a.user.perspective,.an.IMS.service.is.linked.to.his.or.her.identity.and.not.to.his.or.her.access.device.because.the.user.may.access.the.same.services.from.several.IMS.devices.

When.using.IMS.services,.the.user.is.aware.that.applications.within.his.or.her.user.equipment.or.within.service.platforms.are.sharing.and.reusing.his.or.her.personal.information.such.as.presence.information,.availability.rules,.personal.profile,.contact.list,.or.location.information..A.given.service.will.be.responsible.for.the.creation.and.the.modification.of.each.type.of.information.(e.g.,.presence.service. for.presence. information,. location.service. for. location.information).. An. IMS. service. can. thus. consult. a. users. personal. informa-tion.(according.to.privacy.policies).and.may.be.responsible.for.defined.user.information.

Figure.1.5. proposes. relationships. of. an. IMS. service,. an. IMS. public. user.identity,.and. the.users.personal. information..The. terms.of. IMS.service. in.this.figure.do.not.name.a.service.in.a.general.way.(e.g.,.presence.service).but.name.the.service.instance.of.one.specific.user.(e.g.,.Bobs.presence.service).

Technical Functions

From.a.service.provider.technical.perspective,.a.service.is.implemented.with.technical.functions..Technical.functions.are.the.functions.carried.out.by.sys-tems.controlled.by.the.service.providers.(e.g.,.service.platforms,.terminals)..As. seen. before,. the. IMS. service. architecture. may. be. divided. into. several.technical. functions..The.first.division. is.among.service.stratum.functions,.


transport.stratum.functions,.and.end-user.functions..As.we.are.not.dealing.here.with.networking.issues,.we.will.focus.only.on.the.service.stratum..As.seen.in.the.first.section,.this.service.stratum.is.divided.among.service.control.functions,. service. user. profiles,. and. application. functions. [2].. In. addition,.end-user.functions.have.to.be.considered..They.are.not.part.of.the.service.stratum.but.are.closely.related.for.the.delivery.of.the.services.through.the.user.interface.

Figure.1.6.classifies.the.IMS.(or.NGN).technical.functions,.according.to.the.NGN.standards.presented.in.the.first.section..The.service.stratum.functions.are.a.particular.type.of.technical.function..A.service.stratum.function.may.be:

-is linked to-is responsible for

*

*

IMS Public User Identity

1

1

1

*

*

*

User Personal Information

IMS Service

-consult

FIGure 1.5Links.seen.by.the.user.

Transport Stratum Function

Technical Function

Service Stratum Function

Service Control Function Service User Profile

End-user Function

Application Function

FIGure 1.6IMS.technical.functions.


a. service. control. function. that. handles. common. control. functions.like.session.establishment.control.or.service.triggering.control;an. application. function. that. contains. the. service. logic. and. the.manipulation. rules. for. session. establishments. (e.g.,. transfers,. call-back,.reachability,.call.log);a.service.user.profile.that.stores.the.information.on.user.identities.and.on.service.triggering;.andan.end-user.function.that.includes.not.only.the.connection.to.the.IMS.(using.SIP.and.bearer.protocols).but.also.the.service.interface.part.that.resides.in.the.client.device..This.interface.performs.the.trans-formation.of.the.technical.messages.from.the.application.functions.into.something.usable.by.the.user.(and.vice.versa).and.thus.provides.the.end.user.with.the.ability.to.initiate.and.participate.in.a.session..For.example,.an.interface.for.presence.will.transform.the.presence.protocols.messages.into.a.user.interface.displaying.the.presence.of.the.users.contacts.

relationship between Service and Technical Function

An.IMS.service.is.the.junction.between.user.personal.information.and.tech-nical.functions..To.illustrate.this.in.Figure.1.7,.we.can.consider.the.example.of.an.IMS.presence.service..The.presence.service.is.seen.by.the.user.as.the.notification.of.presence.information.between.a.consumer.of.presence.infor-mation.and.sources.of.presence.information,.where.the.presence.information.is.a.set.of.attributes.characterizing.current.properties.of.the.sources.(such.as.status. or. communication. address). [17].. The. presence. service. is. performed.with.technical.functions.such.as.end-user.presence.clients.(a.presence.source.client.and.a.presence.watcher.client),. service.control.mechanisms. to. route.

**

1

*

*

*

-consult

Technical Function


-is responsible for

-utilizesIMS Service

FIGure 1.7IMS.service.


presence.messages.(the.SIP.SUBSCRIBE,.PUBLISH,.and.NOTIFY.messages),.and.presence.application.servers.(to.process.the.presence.state.from.the.pres-ence.sources.and.to.store.and.send.it.to.the.watchers.that.have.subscribed.to.this.presence.event).

The.services.are.directly.responsible. for. the.users.personal. information.and.are.utilizing. the. technical. functions.directly..As.mentioned,. this.may.lead.to.building.silo.architecture,.where.each.service.relies.on.its.own.tech-nical. functions..Service.enablers. (or.service.support.capabilities.or.service.capabilities). are. designed. to. address. this. issue. by. focusing. only. on. their.intrinsic.functions..This.means.that.there.should.be.no.overlap.between.the.service.enablers,.both.from.the.user.perspective.and.from.the.technical.func-tions.perspective.

No.overlap.from.the.user.perspective.implies.that.different.service.enablers.should.not.be.responsible.for.the.same.type.of.users.personal.information..For.example,.only.one.service.enabler.can.produce.the.presence.information.and.only.one.service.enabler.can.produce.the.location.information.

No.overlap.from.the.technical.functions.perspective.implies.that.the.differ-ent.service.enablers.should.not.use.the.same.IMS.functions.in.an.incoherent.way..For.example,.only.the.presence.service.enabler.can.process.the.presence.messages.and.store.the.presence.state.and.only.the.location.service.enabler.can.process.and.aggregate.user.location.from.various.location.sources.

In.IMS.service.architecture,.the.IMS.services.have.to.rely.as.much.as.pos-sible.on.IMS.service.enablers..These.IMS.service.enablers.wrap.a.set.of.tech-nical. functions.and.provide.a. consistent. service. interface. to. IMS.services..An. IMS. service. might. also. use. some. technical. functions. directly. (e.g.,. an.application. server. dedicated. to. a. specific. service).. In. addition,. only. IMS.service.enablers.should.be.responsible. for. the.users.personal. information.(Figure.1.8).

Example of the Push-to-Talk over Cellular

In.order. to. illustrate. this.model,.we.apply. it.here. to. the.push-to-talk.over.cellular.(PoC).described.in.the.OMA.release.program.and.specifications.[27]..The.PoC.service. is.a.walkie-talkie. type.of.service. that.allows.rapid,.short,.and. spontaneous. communications.. It. is. a. half. duplex. voice. service. that.allows.person-to-person.and.person-to-group.communications..This.service.is. considered. an.early. example. of. IMS.application. in. the.market..Because.PoC.is.specified.as.both.a.service.and.an.enabler,.we.show.the.distinction.between.the.service.perceived.by.the.user.and.the.functional.service.build-ing.blocks.

This.illustrates.the.separation.of.concern.from.what.is.seen.by.the.user,.the.service.enabler,.and.the.technical. functions.that. implement.these.enablers..


This.separation.will.benefit.service.providers.for.the.whole.service.life.cycleespecially.service.composition,.service.interaction,.and.service.management.

PoC Service Seen from the users Perspective

From.a.user.perspective,.a.typical.PoC.session.is.as.follows:

The. PoC. user. opens. his. contact. list,. where. presence. features. indicate.whether. contacts. or. groups. of. contacts. are. available. or. not.. The. user.selects.one.or.more.contacts.in.his.contact.list,.creates.a.PoC.group.with.these.contacts,.starts.the.PoC.service,.and.then.talks.simultaneously.to.all.the.contacts.of.his.PoC.group.

This.basic.session.shows.that.the.PoC.service.is.based.on.the.user.identity,.which. is.necessary. to.access. the.contact. list.and. invite.other.PoC.users. to.participate. in.a.session..Besides. identity,. from.a.user.perspective,. the.PoC.service.uses:

presence. information. to. be. aware. of. contact. availability. and.reachability;contact.lists.to.create.groups.for.PoC.sessions;.anduser.profiles.

Figure.1.9.shows.the.PoC.service.as.seen.by.user.Bob.Smith..This.view.contains.the.information.that.the.user.owns.and.that.is.reused.in.the.PoC.ser-vice..His.personal.information.could.be.reused.as.in.another.IMS.service.

IMS Service


IMS Service Enabler

Technical Function

-utilizes

-wrap1

-is responsible for

-consult-consult

-utilizes

*

**

*

*

**

*

**

**

1-requires

FIGure 1.8IMS.services.and.service.enablers.


PoC Service and Service enablers

As.described. in. the.OMA.specifications,. the.PoC.service. requires. several.service.enablers.that.perform.specific.actions.and.are.responsible.for.spe-cific.information:

push-to-talk.over.cellular.enabler.[27].that.manages.the.service.logic.of.the.PoC.service;XDM.(XML.document.management).enabler.[28].to.handle.the.con-tact.groups.in.particular;presence.enabler.[29];IMS.enabler.[30].to.support.the.service;.anddevice.management.enabler.[31].

The.dependencies.between.the.PoC.service.and.the.service.enablers.and.also.between.the.service.enablers.are.described.in.Figure.1.10.with.dotted.arrows..Each.service.enabler.is.responsible.for.some.type.of.personal.information.

Technical Functions for PoC Service

As.mentioned.before,.each.service.enabler.is.implemented.and.carried.out.via.a.set.of.technical.functions.that.are.shown.in.Figure.1.11..In.this.section.we.split.each.enabler.into.its.corresponding.technical.functions.

The.XML.document.management.(XDM).enabler.is.implemented.with.an.XDM.client.(XDMC),.a.shared.XDM.server.(shared.XDMS),.and.an.aggrega-tion.proxy..The.XDMC.is.an.XCAP.(XML.configuration.access.protocol).client.

Another Service of Bob : IMS Service

Bob Identity : IMS Public User Identity

Bob Presence Information : User Personal Information

PoC Service of Bob : IMS Service

Bob Profile : User Personal Information Bob Contact List : User Personal Information

FIGure 1.9PoC.service.as.seen.by.Bob.Smith.

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that.gives.access.to.XML.documents.stored.in.the.network.(e.g.,.PoC-specific.documents.in.the.PoC.XDMS,.contact.lists.in.the.shared.XDMS)..The.aggrega-tion.proxy.acts.as.the.single.contact.point.for.the.XDMC..It.performs.authenti-cation.of.the.XDMC.and.routes.individual.XCAP.requests.to.the.correct.XDMS..The.shared.XDMS.is.an.XCAP.server.that.manages.XML.documents.(e.g.,.con-tact.lists).that.are.shared.with.other.service.enablers.(e.g.,.presence).

The.PoC.enabler.is.implemented.into.a.client.part,.a.server.part,.and.a.PoC-.specific.XDM.server..The.PoC.client.resides.on.the.terminal.and.is.used.to.access.the.PoC.service..The.PoC.server.implements.the.application.logic.for.the.PoC.service..The.PoC-specific.XDM.server.is.an.XCAP.server,.which.man-ages.XML.documents.that.are.specific.to.the.PoC.service.(e.g.,.PoC.groups).

The. presence. enabler. is. implemented. on. a. presence. server,. a. presence.source,.and.a.watcher..A.presence.server.is.an.entity.that.accepts,.stores,.and.distributes.presence.information.about.PoC.clients..A.presence.source.is.an.entity. that.provides. (publishes).presence. information,.and.a.watcher. is.an.entity.that.is.notified.from.presence.information.

The. IMS.enabler. includes.a.number.of.SIP.proxies.and.SIP.registrars.. It.performs. functions. such. as. authentication,. authorization. of. PoC. user,. or.maintaining.of.the.registration.state.

The.device.management.enabler. is. implemented.with.a.device.manage-ment.client. that.receives.the. initial.parameters.needed.by.the.service.pro-vider.for.the.PoC.client.and.a.device.management.server.that.initializes.the.entire.configuration.and.updates.necessary.for.the.PoC.client.

DM Client

DM Server

Presence Source

PoC Subscriber/User

Watcher

XDMC

PoC Client

UE

Presence Server Shared

XDMS

Aggregation Proxy

PoC XDMs

PoC Server

SIP/

IP C

ore

FIGure 1.11Technical.functions.of.the.PoC.service.(simplified).


All. technical. functions. described. here. belong. to. the. service. stratum..They.are.thus.end-user.functions,.service.control. functions,.or.application.functions..PoC.client,.XML.document.management.client,.presence.source,.watcher,.and.device.management.client.are.end-user.functions..IMS.core.is.a. service. control. function.. PoC. server,. PoC. XML. document. management.server,. aggregation. proxy,. shared. XML. document. server,. presence. server,.and.device.management.server.are.application.functions.

A Comprehensive View of IMS Services

Figure.1.12.is.an.example.of.the.three.enablers.OMA.XDM,.IMS.in.OMA,.and.OMA.presence.SIMPLE..It.defines.the.suitable.dependencies.of.these.three.enablers.and.with.the.services.that.make.use.of.these.enablers..We.take.here.the.examples.of.the.PoC.service.and.of.an.instant.messaging.service..All.the.enablers.used.by.these.services.are.not.represented.in.order.to.simplify.the.figure.

Conclusion

IMS. services. cannot. be. considered. independently. from. the. whole. service.environment.of.the.user.[32]..This.environment.includes.at.least.features.such.as.identity.management,.community.management,.availability.management,.or.context.management..This.service.environment.should.be.able.to.integrate.third-party.service.elements..The.service.value.will.reside.in.the.quality.of.the.interactions.between.all.the.service.elements.and.in.seamless.accessibil-ity.in.a.user-centric.way..A.service.control.framework.handling.these.interac-tions.is.therefore.needed.for.the.interactions.between.the.operator.services.and.for.intermediation.with.other.service.providers..This.framework.should.rely.on.a.common.modeling.for.services,.service.enablers,.and.resources.

The. main. interest. of. the. proposed. approach. lies. in. the. identification. of.the.dependencies.between.the.services.and.the.service.enablers..This.allows.better.design.of.the.IMS.services.by.defining.clearly.which.service.enabler.is.involved.in.which.service.and.how.a.service.enabler.is.linked.to.techni-cal.functions..This.approach.optimizes.the.treatment.of.service.interaction.between.IMS.service.enablers.by.tracing.the.impact.on.the.user.perception.of. the.service.. It.will.also.enhance.service.management.aspects.by.detect-ing. how. the. failure. of. one. or. many. technical. functions. can. affect. service.enablers.and.the.use.of.the.IMS.service..It.is.a.tool.to.identify.the.user.per-sonal.information.that.should.be.shared.between.services,.to.define.which.service.enabler.is.responsible.for.which.information,.and.then.to.design.ser-vices.that.reuse.this.personal.information.through.these.service.enablers.


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Glossary

3GPP 3rd.Generation.Partnership.ProjectAPI. . application.programming.interfaceAS. . application.serverCSCF. . call.state.control.functionsDSL. . digital.subscriber.lineGSM. . global.system.for.mobile.communicationsGUI. . graphical.user.interfaceHSS. . home.subscriber.serverIETF. . Internet.Engineering.Task.ForceiFC. . initial.filter.criteriaIMS. . IP.multimedia.subsystemIN. . intelligent.networkINAP. . intelligent.network.application.protocolISDN. . integrated.services.digital.networkISUP. . ISDN.user.partIT. . information.technologyITU. . International.Telecommunication.UnionNGN. . Next-generation.networksOMA. . Open.Mobile.AllianceOSE. . OMA.service.environmentPSTN. . public.switched.telephone.networkS-CSCF.. serving.call.state.control.functionsSIB. . service.independent.building.blockSIP. . session.initiation.protocolSIM. . subscriber.identity.moduleSPT. . service.point.triggerTISPAN.. telecommunication.and.Internet.converged.services.and...

. protocols.for.advanced.networkingUMTS. . universal.mobile.telecommunications.systemWLAN.. wireless.local.area.networkXML. . extensible.markup.languageTMF. . TeleManagement.Forum

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. 27.. OMA..OMA.push.to.talk.over.cellular.(PoC)..Approved.enabler.version.1.0.2,.September.2007.

. 28.. OMA.. OMA. XML. document. management.. Approved. enabler. version. 1.0.1,.November.2006.

. 29.. OMA..OMA.presence.simple..Approved.enabler.version.1.0.1,.November.2006.

. 30.. OMA..IMS.in.OMA..Approved.enabler.version.1.0,.September.2005.

. 31.. OMA..OMA.device.management..Approved.enabler.version.1.2,.February.2007.

. 32.. Ryu,.S..et.al..2005..Research.activities.on.next-generation.mobile.communica-tions.and.services.in.Korea..IEEE Communications Magazine.43(9):122131.

27

2IMSASecureArchitectureforAllIPNetworks

Muhammad Sher and Thomas Magedanz

CONTENTS

Introduction............................................................................................................28IMS.Architectural.Overview................................................................................ 29IMS.Security.Challenges.and.Potential.Attacks................................................ 32IMS.Security.Mechanisms.and.Security.Associations.....................................35IMS.Authentication,.Key.Management,.and.Secrecy....................................... 39

IMS.Authentication.and.Key.Management.............................................. 39Encryption.and.Secrecy............................................................................... 41

Use.of.IPsec.ESP.for.SIP.Confidentiality.and.Integrity.Protection............................................................................43

SIP.Integrity.and.Confidentiality.Procedure................................44Interdomain.Security............................................................................................45

Network.Domain.Security.(NDS).Architecture....................................... 47Use.of.IPsec.in.an.NDS/IP.Environment..................................................50Public.Key.Infrastructure.(PKI)..................................................................53PKI-Based.NDS.Authentication.Framework.............................................55

Security.Management.for.HTTP-Based.Services.............................................. 59Generic.Bootstrapping.Architecture.(GBA).............................................. 59Bootstrapping.Authentication.Procedure................................................. 62Bootstrapping.Usage.Procedure.................................................................64Authentication.Proxy.Usage.for.Multimedia.Services............................64

References............................................................................................................... 67


Introduction

The.fixed-mobile.convergence.(FMC).and.voice-data.networks.have.merged.next-generation,. value-added. applications. and. integrated. multimedia. ser-vices,. combining. Web. browsing,. instant. messaging,. presence,. voice. over.Internet.protocol.(VoIP),.video.conferencing,.application.sharing,.telephony,.unified.messaging,.multimedia.content.delivery,.etc..on.top.of.different.net-work. technologies.. The. 3GPP. (3rd. Generation. Partnership. Project). [1]. and.3GPP2.[2].have.developed.the.IP.multimedia.subsystem.(IMS).[3].to.provide.a.service.delivery.platform.(SDP).for.a.converged.communication.paradigm..No.doubt,. the. convergence.of.voice.and.data.networks. is.a.great.achieve-ment.to.maintain.a.single.communication.platform.for.all,.but.the.greatest.challenge.is.to.maintain.an.adequate.level.of.security.in.the.heterogeneous.network.environment.to.protect.multiple.technologies.and.protocols.and.to.provide.data.confidentiality.and.protection.

Another.important.development.in.the.converged.networks.paradigm.is.the.introduction.of.IP.as.the.network.layer.in.the.GPRS.(general.packet.radio.service).and.in.the.UMTS.(universal.mobile.telecommunication.system).net-work.domain..The.IP-based.network.architecture.provides.open.and.flexible.interfaces.to.deploy.innovative.services..In.terms.of.security,.this.implies.an.array.of.new.threats.and.risks.inherited.from.the.Internet.world.

The.IMS.is.also.vulnerable.to.different.peer-to-peer.attacks.because.users.are.always.connected.and.online..The.possible.reasons.for.passive.and.active.attacks.in.IMS.are.that.an.attacker.could.easily.access.a.wireless.link,.launch.a.falsely.based.station,.and.redirect.attacks.to.intercept.and.redirect.a.users.confidential.information.somewhere.else.

IMS.utilizes.SIP.(session.initiation.protocol).[4].for.signaling,.which.is.open.architecture.and.vulnerable.to.different.attacks,.as.discussed.in.Calhoun.et.al..[5]..The.IMS.core.threats.include.flooding.attacks,.which.ultimately.keep.the.network.resources.busy,.and,.as.a.result,.these.sources.are.not.available.to.legitimate.users..The.IMS.application.servers.(ASs).are.also.valuable.targets.for. intruders. because. they. provide. value-added. services.. Due. to. the. text-based.nature.of.SIP,.the.IMS.and.AS.are.vulnerable.to.attacks.like.spoofing,.hijacking,.and.message.tampering..Moreover,.the.AS.may.suffer.from.HTTP-based.threats..Finally,.intruders.may.launch.denial.of.service.(DoS).attacks.against.applications.installed.on.the.AS.

In.order.to.minimize.the.risk.of.theft.of.information.and.data.from.hackers,.we.have.to.focus.on.an.independent.security.framework.for.IMS..According.to.3GPP.technical.specifications.and.standards,.IMS.security.provides.two.solutions.at.different.levels.of.protection:

. 1..The.early.IMS.security.solution.standardized.in.3GPP.release.5.pro-vides. limited.security. functionality.and.aims.to.protect.early.IMS.deployment. and. offers. less. security.. It. provides. authentication. of.

IMSASecureArchitectureforAllIPNetworks 2

subscribers. for. services. access. and. identity. confidentiality. on. the.radio.interface..It.also.provides.radio.interface.encryption.

. 2..The.complete.IMS.security.solution.is.standardized.in.3GPP.release.6.with. full. security. functionality.and.builds.on. the.early. security.solutions.with.the.objective.to.improve.them..It.offers.new.security.features.and.secures.new.services.to.protect.networks.and.terminals.with.data.protection.

This. chapter. presents. an. IMS. overview. and. addresses. IMS. potential.attacks.. It.presents.an.overview.of. IMS.security.architecture.and.security.associations,.as.well.as.key.authentication,.key.generation,.and.use.of.keys.to.provide.confidentiality.and.integrity..Later,.it.discusses.interdomain.security.and.presents.IMS.HTTP-based.services.security..Finally,.it.presents.security.extension.for.new.threats.

IMS Architectural Overview

The. IMS. [3]. provides. SDP. for. mobile. multimedia. services. provisioning,.such. as. VoIP,. video-telephony,. multimedia. conferencing,. mobile. content,.and.push-to-talk..It.is.based.on.Internet.Engineering.Task.Force.(IETF).pro-tocols. like.SIP.[4],.DIAMETER.[8],.SDP,.real-time.transport.protocol.(RTP),.and.transfer.control.protocol.(TCP)/IP.protocol.stack..The.IMS.is.considered.as.the.next-generation.service.delivery.platform.framework..It.consists.of.a.modular.design.with.open.interfaces.and.enables.the.flexibility.for.provid-ing.multimedia.services.over.IP.technology..The.IMS.does.not.standardize.specific. services.but,. rather,.uses. standard.service.enablers. (e.g.,.presence).and.inherently.supports.multimedia.and.VoIP.

In.the.IMS.architecture,.the.SIP.protocol.[4].is.used.as.the.standard.signal-ing.protocol.that.establishes,.controls,.modifies,.and.terminates.voice,.video,.and.messaging.sessions.between.two.or.more.participants..The.related.sig-naling.servers.in.the.architecture.are.referred.to.as.call.state.control.functions.(CSCFs).and.are.distinguished.by.their.specific.functionalities..The.function-ality.related.to.authentication,.authorization,.and.accounting.(AAA).within.the. IMS.is.based.on.the. IETF.DIAMETER.protocol. [6].and. is. implemented.in. the. home. subscriber. system. (HSS),. CSCFs,. and. various. other. IMS. com-ponents.in.order.to.allow.charging.functionality.within.the.IMS..Instead.of.developing. the. protocol. from. scratch,. DIAMETER. is. based. on. the. Remote.Authentication. Dial-in-User. Service. (RADIUS). [7],. which. has. previously.been.used.to.provide.AAA.services.for.dial-up.and.terminal.servers.across.environments.

The.other.protocol.that.is.important.for.multimedia.contents.is.real-time.transport.protocol.(RTP).[8],.which.provides.end-to-end.delivery.for.real-time.data..It.also.contains.end-to-end.delivery.services.like.payload-type.(codec).


identification,.sequence.numbering,.time.stamping,.and.delivering.monitor-ing.for.real-time.data..The.RTP.provides.quality.of.service.(QoS).monitoring.using.the.RTP.control.protocol.(RTCP).[9],.which.conveys.information.about.media.session.participants.

The. IMS. entities. and. key. functionalities. can. be. classified. in. six. catego-ries.[10]:.session.management.and.routing.family.(CSCFs),.databases.(HSS,.SLF),.interworking.elements.(BGCF,.MGCF,.etc.),.services.(application.server,.MRCF,.MRFP),. support. entities. (THIG,. security. gateway. [SEG],. PDF),. and.charging.. The. most. important. components. and. parts. of. IMS. architecture.(shown.in.Figure.2.1).are.described.as.follows:

Proxy call state control function (P-CSCF).is.the.first.contact.point.within.the.IP.multimedia.core.network;.all.SIP.signaling.traffic.from.or.to.the.user.equipment.(UE).traverse.via.the.P-CSCF..Its.address.is.dis-covered.by.the.UE.following.the.packet.data.protocol.(PDP).context.activation..The.P-CSCF.behaves.like.a.proxy,.accepting.and.forward-

IMS Core

HSS Cx Cx

Sh

Mw

IMS Clients

Mw Mw

ISC

Mw

Media Server

Media GW

Legacy networks

GSM, PSTN

Signalling GW

IMS Application Platform

XDMS

Parlay X GW SIP AS

Presence Charging

P-CSCF

S-CSCF Mw

I-CSCF

Gm

FIGure 2.1IMS.architecture.


ing.requests.and.responses..It.performs.functions.like.authorizing.the.bearer.resources.for.the.appropriate.QoS.level,.emergency.calls,.monitoring,.header.(de)compression,.and.identification.of.I-CSCF.

Interrogating call state control function (I-CSCF).is.the.first.contact.point.within.an.operators.network..It.contacts.the.HSS.to.get.the.address.of.S-CSCF.to.serve.the.user.for.registration..It.forwards.SIP.requests.and.responses.to.S-CSCF..It.also.performs.network.topology.hiding.functionality.

Serving call state control function (S-CSCF).performs.the.session.control.services.for.the.end.point.and.maintains.session.state.as.needed.by.the. network. operator. for. support. of. the. services.. Within. an. oper-ators. network,. different. S-CSCFs. may. have. different. functional-ities.. The. important. functions. performed. by. S-CSCF. include. user.registration/interaction. with. service. platforms. for. the. support. of.services..The.S-CSCF.decides.whether.an.AS.is.required.to.receive.information. related. to. an. incoming. SIP. session. request. to. ensure.appropriate.service.handling..The.decision.at. the.S-CSCF.is.based.on. filter. information. received. from. the. HSS. [10].. This. filter. infor-mation.is.stored.and.conveyed.on.a.per-application-server.basis.for.each.user.

Home subscriber server (HSS).is.the.equivalent.of.the.HLR.(home.location.register). in. 2G. systems. but. extended. with. two. DIAMETER-based.reference.points..It.is.the.master.database.of.an.IMS.that.stores.IMS.user.profiles,.including.individual.filtering.information,.user.status.information,.and.application.server.profiles.

Application server (AS).provides.service.platforms.in.IMS.environments..It.does.not.address.how.multimedia/value-added.applications.are.programmed;.only.well.defined.signaling.and.administration.inter-faces. (IMS. service. control. [ISC]. and. Sh). and. SIP. and. DIAMETER.protocols.are.supported..This.enables.developers.to.use.almost.any.programming.paradigm.within.a.SIP.AS,.such.as.legacy.intelligent.network.servers.(i.e.,.CAMEL.support.environments);.open.service.access.(OSA)/Parlay.servers/gateways;.or.any.proven.VoIP.SIP.pro-gramming.paradigm.like.SIP.servlets,.call.programming.language.(CPL),.and.common.gateway.interface.(CGI).scripts.[11]..The.SIP.AS.is.triggered.by.the.S-CSCF,.which.redirects.certain.sessions.to.the.SIP.AS.based.on.the.downloaded.filter.criteria.or.by.requesting.filter.information. from. the. HSS. in. a. user-based. paradigm.. The. SIP. AS.comprises.filter.rules.to.decide.which.of.the.applications.deployed.on. the.server. should.be. selected. for.handling. the.session..During.execution.of.service.logic,.it.is.also.possible.for.the.SIP.AS.to.commu-nicate.with.the.HSS.to.get.additional.information.about.a.subscriber.or.to.be.notified.about.changes.in.the.profile.of.the.subscriber.[12].

Media resource function (MRF).can.be.split.into.media.resource.function.controller.(MRFC).and.media.resource.function.processor.(MRFP)..


It.provides.media.stream.processing.resources. like.media.mixing,.media.announcements,.media.analysis,.and.media. transcoding.as.well.as.speech.[10]..The.other.three.components.are.border.gateway.control.function.(BGCF),.media.gate.control.function.(MGCF),.and.media.gate.(MG),.which.perform.the.bearer.interworking.between.RTP/IP.and.the.bearers.used.in.the.legacy.networks.

IMS end-user system. provides. the. necessary. IMS. protocol. support,.namely.SIP,.and.the.service-related.media.codecs.for.the.multimedia.applications.in.addition.to.the.basic.connectivity.support.(e.g.,.GPRS,.wireless.local.area.network.[WLAN]).

IMS Security Challenges and Potential Attacks

The.security.challenges.facing.IMS.are.threats.from.different.domain.proto-colsfor.example,.SIP.signaling.attacks,.RTP.media.attacks,.and.IP.domain.attacks.. Some. of. the. potential. IMS. attacks. are. identified. in. reference. 13..The. IMS. security. challenges. are. DoS. attacks,. threats. from. open-based. IP.infrastructure,.and.SIP.signaling.and.media.flow.attacks,.as.depicted.in.Fig-ure.2.2..These.threats.are.summarized.as.follows:

Denial-of-service (DoS) attack:. This. jams. radio. signals. and. floods. by.authentication.requests.to.P-CSCF.and.other.devices..For.example,.in. a. REGISTER. flooding. attack,. the. attacker. sends. many. REGIS-TER.requests.to.the.P-CSCF.with.fake.or.spoofed.source.addresses.(e.g.,. SIP. URI. [uniform. resource. identifier]).. In. the. case. of. distrib-uted.REGISTER.flooding,.the.attacker.generates.multiple.REGISTER.requests.with.different.spoofed.and.faked.source.addresses.to.over-whelm.the.IMS.resources..It.causes.downfall.of.IMS.resources.and.the.legitimate.users.cannot.get.the.services.

Spoofing attack:.The.malicious.node.hides. its.presence. in. the.network.and. intercepts. traffic,. and. attackers. tamper. with. messages.. These.nodes.become.trusted.nodes.in.IMS.

Man-in-the-middle attack:. Hackers. search. the. breaches. and. break. the.authentication.process.and.integrity.protection.process.in.order.to.get.IMS.services.for.free.

Impersonation:.Impersonating.a.server.causes.misrouting.of.messages..The. existing. authentication. processes. are. unable. to. differentiate.between.the.intruder.and.the.legitimate.user..This.way.the.attacker.has. free. access. to. IMS. services. and. the. victim. is. charged. for. the.attackers.usage.of.services.


Eavesdropping:.Hackers.get.session.information.if.messages.are.sent.i

Documents

IP Multimedia Subsystem (IMS) Handbook