Editorial

Recent Advances in Network Convergence

Recent years have witnessed an increasing trend to-wards the convergence of networks, services, and applica-tions. In contrast to a telecommunications landscapewhere different services are delivered through separate ac-cess technologies, each tailored to a specific application,network convergence aims at providing a unified networkplatform for the efficient coexistence of previously distinctmedia accessible through common interfaces on single de-vices. The convergence trend is further stressed by users’increasing demand for ubiquitous access to any serviceanytime, anywhere and on any device. This, however, im-plies that one device should be able to connect with a mul-titude of specialized services, access technologies, andpossibly different network operators as illustrated in Fig. 1.

As network convergence involves many different par-ties, its technical and economical success depends on theability to agree on a common set of standard interfaces.Moreover, the convergence of different access technologiesalong with users’ increasing mobility and demand for con-nectivity at all times at high data rates raise the need fornew monitoring, control and management approachesessential for providing converged services with quality-of-experience (QoE) assurance. At the same time, networkconvergence is expected to serve as an enabler for newbusiness models for network operators and service provid-ers, a means to reduce operations and management costs,and a platform for faster deployment of new multimediaapplications. Convergence attracted even more interestwith the advent of Cloud Computing in the recent fewyears where a converged view of infrastructure is emerg-ing in which all resources whether computing, storage ornetworking are viewed as being part of shareable resourcepools that can be controlled and managed using the samesystems. The converged infrastructure is envisioned toencompass remote datacenters, dense small-cell wirelessaccess integrated with optical backhaul where the tradi-tional point-to-point backhauling may be partly replacedby multi-point technologies, and deployment of a FutureInternet architecture. The realization of this vision how-ever faces many technical challenges that need to be ad-dressed in order to ensure failsafe network operations, toefficiently support user mobility, and to guarantee QoE.

This special issue has as its main purposes the presen-tation of recent developments in the area of network

convergence, and providing a view of the field’s state-of-the-art today. It is composed of eleven papers selectedfrom 50 submissions. The contributions span IP multime-dia subsystems (IMS), media independent handover(MIH), fixed-mobile convergence, convergence of differentwireless standards, vertical handover, quality-of-service(QoS) and QoE, and convergence in the network core.

QoE is the ultimate measure of user satisfaction. In thepaper ‘‘QoE assurance in converged networks.’’, R. Stan-kiewicz and A. Jajszczyk discuss several quality measures,specifically QoS, Grade-of-Service (GoS), and Quality-of-Resilience (QoR), and their impact on QoE assurance inconverged networking environments. The authors focuson convergence between fixed and wireless as well as con-vergence between heterogeneous wireless technologies,and elaborate on the requirements for any service, any-where, anytime and on any device.

The IP multimedia subsystem (IMS), standardized by3GPP, plays a key role in network convergence and pro-vides a platform for converged voice, video, and data-applications over fixed and mobile networks based on IP.In the paper ‘‘TRIM: An architecture for transparent IMS-based mobility,’’ I. Vidal, A. de la Oliva, J. Garcia-Reinosoand I. Soto consider IP mobility in IMS networks and showhow a new architecture called TRIM extends mobile termi-nals such that seamless IMS-based mobility can be pro-vided transparently to end-user applications. TRIMsupport for mobility is evaluated on the basis of an IMStest-bed with 3G and WLAN access networks.

The transition towards new mobile communicationstandards is characterized by the co-existence of differentwireless standards such as GSM and UMTS in addition to3GPP LTE and IEEE 802.16 during the roll-out of 4G net-works. This problem is addressed in the paper ‘‘Reinforce-ment learning for joint radio resource management in LTE-UMTS scenarios.’’ by N. Vucevic, J. Pérez-Romero, O. Sal-lent, and R. Agustı́. In particular, the authors consider theconvergence of 3G and 4G networks using the exampleof co-existing UMTS and LTE technologies and present adynamic joint radio resource management algorithm span-ning both technologies. Based on a reinforcement learningtechnique, the algorithm determines the most appropriateRadio Access Technology for user sessions in a multi-service scenario under dynamic conditions. The low

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Computer Networks 55 (2011) 1455–1458

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complexity of the proposed algorithm makes it a likelycandidate for implementation in real-time systems.

Co-existence and convergence of different mobile accesstechnologies implies the need for seamless handover be-tween these technologies commonly referred to as verticalhandover. IEEE 802.21 provides a standard framework forvertical handover and defines the mechanisms of mediaindependent handover. In the paper ‘‘Context-aware mediaindependent information server for optimized seamlesshandover procedures.’’ P. Neves, J. Soares, S. Sargento, H.Pires, and F. Fontes consider vertical handover betweenIEEE 802.11 (WiFi), IEEE 802.16 (WiMax), 3GPP UMTS,HSPA, and LTE. Their proposal extends IEEE 802.21 mediaindependent handover by introducing a context manage-ment server used to dynamically acquire and maintaininformation from the network and the mobile terminalssuch as the number of and requirements of currently run-ning services, established radio bearers, user preferences,and others. The context information is then exploited tooptimize the handover process, e.g., the handover duration.

On a similar topic, the paper ‘‘Autonomic personalizedhandover decisions for mobile services in heterogeneouswireless networks.’’ by J.-M. Kang, J. Strassner, S.-S. Seo,J.W.-K. Hong focuses on personalized and automated verti-cal handover decisions in heterogeneous mobile networks.In this proposal, the handover is not solely based on thesignal strength but considers two additional metrics: theaccess-point-acceptance and access-point-satisfaction.The former is a vector of individual channel quality mea-sures such as delay and power consumption, and the lattercombines these individual measures based on the user’sneeds. Accordingly, the access point which maximizes

these metrics and thereby user satisfaction is selected.The proposal is evaluated through simulations and com-pared to other decision metrics.

While previous contributions consider the co-existenceof different mobile communication standards, the paper‘‘Vertical handovers among different wireless technologiesin a UMTS radio access-based integrated architecture’’ by N.Vulic, S.M. Heemstra de Groot, I.G. Niemegeers extends theproblem to the co-existence of mobile access technologiesand broadcast systems. In particular, the authors focus onthe integration of UMTS, IEEE 802.11, IEEE 802.16, andDVB-H at the radio access level. The authors describe thenecessary handover mechanisms and conduct performanceevaluations for different vertical handover scenarios.

Heterogeneous wired/wireless networks rely on com-plex wired mesh backbones with gateway nodes connect-ing to the Internet. These gateway nodes act as convergingpoints for heterogeneous network traffic heading to andfrom the Internet and can turn into bottlenecks once theirresources are exhausted. In this context, the paper ‘‘Re-source competition in a converged heterogeneous net-working ecosystem.’’ by A. Jamalipour, F. Javadi, and K.S.Munasinghe asks the important question of how a systemcan maintain stability over a period of time in a resourcediminishing environment, provided the resources are fairlyallocated at the time of admission. To answer this ques-tion, the authors conduct an ecologically inspired analysiswhere the converged heterogeneous network is modeledas an ecosystem of diverse networks with limited resourceconstraints and competing communication sessions. Basedon the result of their analysis and the key observationof competitive exclusion between sessions, the authors

Fig. 1. Typical wireless and fixed networks involved in network convergence.

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propose a novel admission control policy to allow fair co-existence among sessions.

In the paper ‘‘Evaluation of two integrated signalingschemes for the Ultra Flat Architecture using SIP, IEEE802.21, and HIP/PMIP protocols.’’ Z. Faigl, L. Bokor, P.M.Neves, K. Daoud, and P. Herbelin discuss a new networkarchitecture, called UFA (Ultra Flat Architecture), whichdistributes some of the core network (e.g., 3GPP) functionsto the edge (close to the base stations) in order to betterscale to the ever growing traffic demand. Specifically thepaper extends UFA with support for non-SIP based applica-tions for more flexibility in converged networks as well aslegacy Internet applications including IMS compliantapplications.

The heterogeneous landscape of wireless access tech-nologies does not only imply the necessity of co-existencebut also provides the possibility to integrate different ac-cess technologies using the same infrastructure. This notonly relates to the radio access but also to the core net-work, which may be shared by different operators. In‘‘On the role of infrastructure sharing for mobile networkoperators in emerging markets.’’ D.-E. Meddour, T. Ras-heed, and Y. Gourhant discuss the different options ofinfrastructure sharing their implications and potentialsavings of operational expenditures (OPEX) as well as cap-ital expenditures (CAPEX) under technical, practical andregulatory constraints.

The clustering and fixed allocation of the available spec-trum over the years has resulted in an inefficient use of thescarce spectral resources. To alleviate this problem, dy-namic spectrum management techniques such as cognitiveradio have received a lot of attention recently. B. Ishibashi,N. Bouabdallah, and R. Boutaba in their paper ‘‘QoS Capac-ity of Virtual Wireless Networks’’, introduce the concept ofVirtual Wireless Networks (VWNs) created and operatedwithout obtaining any dedicated spectrum resources oftheir own. VWNs exploit residual bandwidth left underuti-lized by licensed users. However, it is unclear whetherVWNs can provide QoS guarantees since the residual re-sources can be reclaimed anytime by the primary users.The authors extend a classical wireless system withcognitive radio capabilities and use Markov chain-basedanalysis and simulations to demonstrate that VWNs areindeed capable of providing QoS and allowing for new ser-vices provided by virtual wireless operators.

In the last paper presented in this special issue ‘‘SWISH:Secure WiFi Sharing.’’, D. Leroy, G. Detal, J. Cathalo, M.Manulis, F. Koeune, and O. Bonaventure present an effi-cient and fully deployed solution, SWISH, enabling secureWiFi sharing with visiting mobile users. The key motiva-tion behind the development of SWISH is to enable mobileusers to connect to the Internet via a nearby foreign net-work without jeopardizing the security of the visited net-work. There exist indeed many WiFi networks withunused resources, which visiting mobile users can use toconnect to the Internet if the owners of these networkswere not reluctant due to security concerns. Using crypto-graphic authentication of the involved parties (mobileuser, her/his home network and the visited WiFi network),the authors demonstrate how WiFi networks can be fullysecured with minimal impact on their performance which

is demonstrated by deploying and testing their solution ina production campus network.

In presenting these diverse research efforts on converg-ing communication systems and services, we hope toprovide some possible directions to future network con-vergence research and to excite future research explora-tions in this promising field. It is also our hope that theselected papers have shown to you, the readers, thebreadth and depth of the challenges we face and the exis-tence of many open research issues.

We express our gratitude to the Editor-in-Chief, Dr.Harry Rudin, for giving us the opportunity to put togetherthis special issue, and for his continuous support through-out this project from establishing a successful call for pa-pers to the time-consuming editorial work he put oneach accepted paper. We also express our thanks to themany authors who responded to the call for papers. Weare particularly grateful to the authors of the four invitedpapers for kindly agreeing to write papers: A. Jajszczyk,A. Jamalipour, D.-E. Meddour, J. W.-K. Hong and their co-authors. All the papers went through a rigorous reviewprocess and we are grateful to the many obliging reviewerswhose timely efforts were essential for the selection of thepapers. As much as we enjoyed working on this special is-sue, we hope you will enjoy reading it.

Peter Rost received his Ph.D. degree in elec-trical engineering from Technische UniversitätDresden, Dresden, Germany, in 2009 and hisM.Sc. degree in information technology fromUniversity of Stuttgart, Stuttgart, Germany, in2005.From 1999 to 2002, he was with FraunhoferInstitute for Beam and Material Technolo-gies, Dresden, Germany where he developedaugmented and virtual reality based con-trolling systems. From 2002 to 2005 he waswith IBM Deutschland Entwicklung GmbH,

Böblingen, Germany, where he contributed to the IBM Tivoli system. InJune 2005 he joined the Vodafone Chair of Prof. Gerhard Fettweis atTechnische Universität Dresden and focused on different aspects ofrelaying in the context of mobile communications systems. He was alsoa leading member of the organizing team of IEEE ICC 2009, preparedmultiple successful EU FP6 and FP7 proposals, and was actively con-tributing to the European research project WINNER since 2005 as taskleader. Since April 2010 Peter is member of the Mobile and WirelessNetworks group at NEC Laboratories Europe, where he is working in BUprojects as well as the EU FP7 project FLAVIA.Currently, he is conference coordinator of the first IEEE online conference(2010 IEEE Online Conference on Green Communications). He published30 + contributions to books, journals, conferences, and public projectreports, and he is author of multiple patents and patent applications.

Raouf Boutaba received the M.Sc. and Ph.D.degrees in computer science from the Uni-versity Pierre & Marie Curie, Paris, in 1990and 1994, respectively. He is currently a pro-fessor of computer science at the University ofWaterloo (Canada) and a distinguished visit-ing professor in the division of IT convergenceengineering at POSTECH (Korea). His researchinterests include network, resource and ser-vice management in wired, and wireless net-works. He is the founding editor in chief of theIEEE Transactions on Network and Service

Management (2007–2010) and on the editorial boards of other journals.He has received several best paper awards and other recognitions such asthe Premier’s Research Excellence Award, the IEEE Hal Sobol Award in

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2007, the Fred W. Ellersick Paper Prize in 2008, the Joe LociCero awardand the Dan Stokesbury in 2009.

Klaus Doppler received his Ph.D. degree inElectrical Engineering from Aalto UniversitySchool of Science and Technology, Helsinki,Finland, in 2010 and his M.Sc. degree inElectrical Engineering from Graz University ofTechnology, Austria, in 2003.He joined Nokia Research Center in 2002.Currently he is leading the Wireless Systemsteam of the Radio Systems Laboratory inBerkeley, California. He has been leading andcontributing to research activities on thedesign and integration of novel radio concepts

into cellular systems, including device-to-device communication, (coop-erative) relaying and multiband operation. He was among the top teninventors in Nokia in the years 2008–2009 and received a Nokia topinventor award in the years 2007–2008.He has been the proof-of-conceptsubtask leader within the relaying task of the European research projectWINNER II and he has been leading the device-to-device communicationand network coding task within WINNER+. He has authored and co-authored 25 + conference and journal articles, two book chapters andmore than 40 pending patent applications.

Ashwin Gumaste is currently the James R.Isaac Chair and faculty member in theDepartment of Computer Science and Engi-neering at the Indian Institute of Technology(IIT) Bombay. He is currently also a consultantto Nokia Siemens Networks, Munich where heworks on optical access standardizationefforts. He was a Visiting Scientist with theMassachusetts Institute of Technology (MIT),Cambridge, USA in the Research Laboratoryfor Electronics from 2008 to 2010. He waspreviously with Fujitsu Laboratories (USA) Inc

in the Photonics Networking Laboratory (2001–05). He has also worked inFujitsu Network Communications R&D (in Richardson TX) and prior to

that with Cisco Systems in the Optical Networking Group (ONG). Hiswork on light-trails has been widely referred, deployed and recognized byboth industry and academia. His recent work on Omnipresent Ethernethas been adopted by tier-1 service providers. Ashwin has 20 granted USpatents and over 30 pending patent applications. Ashwin has publishedabout 120 papers in referred conferences and journals. He has alsoauthored three books in broadband networks called DWDM NetworkDesigns and Engineering Solutions (a networking bestseller), First-MileAccess Networks and Enabling Technologies and Broadband Services:User Needs, Business Models and Technologies for John Wiley. Owing tohis many research achievements and contributions, Ashwin was awardedthe Government of India’s DAE-SRC Outstanding Research InvestigatorAward in 2010 as well as the Indian National Academy of Engineering’s(INAE) Young Engineer Award (2010). He has served Program Chair, Co-chair, Publicity chair and workshop chair for IEEE conferences and asProgram Committee member for IEEE ICC, Globecom, OFC, ICCCN, Grid-nets etc. Ashwin is also a guest editor for IEEE Communications Magazine,IEEE Network and the founding Editor of the IEEE ComSoc ONTC’snewsletter Prism. He is the Chair of theIEEE Communication Society’sTechnical Committee on High Speed Networks (TCHSN) 2011–2013. Hehas been with IIT Bombay since 2005 where he convenes NetworkingLaboratory (GNL): www.cse.iitb.ac.in/gnl. The Gigabit Networking Labo-ratory has secured over 8 million USD in funding since its inception andhas been involved in 4 major technology transfers to the industry. Ashwincan be reached through www.ashwin.name.

P. RostR. BoutabaK. Doppler

A. Gumaste

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