J. WEB INFOR. SYST. VOL. 2, NO. 1, MARCH 2006 51

Web Services and Multimediain M-Business Applications:Opportunities and Concerns

CHRISTOS K. GEORGIADIS, PANAYOTIS E. FOULIRAS, IOANNIS MAVRIDISand ATHANASIOS MANITSARIS

Department of Applied Informatics, University of Macedonia, 540 06 Thessaloniki, GreeceEmail: �geor,pfoul,mavridis,manits�@uom.gr

Received: January 16 2006; revised: March 21 2006

Abstract—Web services refer to a specific set of technologiesused to implement a Service Oriented Architecture. Thanks tomaturing Web-services standards, and to new mobile devicesand application solutions, progress is being made in presentingsimilar Web-services offerings in both mobile and fixed networks.To bring that architecture and the solutions it will support tothe world of mobility is indeed a significant issue in m-businessapplications, because mobile Web services present various advan-tages: Reduction of the overall cost of development (by reusingexisting system components), faster time to market introductionof products (provided by applications’ rapid development anddeployment) and remarkable possibilities to emerge new appli-cations with increased functionalities. In addition, the new andforthcoming mobile networks, with native IP connection andhigh speed transmission capability, allow the development of avariety of modern multimedia services. Multimedia MessagingServices (capable to mix the media types in order to enablemore intuitive messaging operation), and Instant Messaging andPresence Services (dedicated for presence, instant messaging,and distribution and sharing of multimedia content in groupsof users), provide suitable underlying capabilities to supportlocation-based and context-sensitive multimedia services. In thispaper we will present the current approaches regarding archi-tectural, functional and security features that allow enterprisesto enjoy the benefits of traditional Web services in the mobilemultimedia domain.

Index Terms—Web services, M-business, multimedia

I. INTRODUCTION

Integration, cooperation, and interaction are characteristicproblems to overcome in the collaboration of diverse dis-tributed systems: Service Oriented Architecture (SOA) hasbeen anticipated as an architecture model to assist and en-courage the cooperation of two or more generic systems. SOAdemands any cooperating system to expose interfaces consist-ing of services and expressed in a standard common language[1]. In recent years, the application of SOA on the Webis manifested by Web Services (WS). Using widely-adoptedWeb standards (HTTP communications and XML-based datadescription) to realize SOA models, WS are evolving from thebasic operations in the foundation layer, to support businessinteractions in the composition layer [2].

WS are re-usable web-based applications that are a meansto share services and information between other applications.Businesses can save money by reducing the overhead costs,and create new opportunities with other businesses. WS areenvisioned as building blocks for accomplishing broad inter-operability both in the domain of business-to-business (B2B)and business-to-customer (B2C) e-commerce transactions. Assuch, they need to inherently support reliable and securetransactions. At the base of all WS are the respective transportprotocols, of which UDP is useful in the case of multi-media real-time traffic, where considerable amount of two-way interaction is needed. However, most of the supportede-/m-business transactions involve reliable exchange of filesand data, hence TCP is the protocol that must be revisitedor even enhanced to achieve this goal. Due to limited re-sources on mobile devices, WS technology is an appropriatechoice in the mobile setting. It encourages the delegationof some tasks to external service providers to save localresources. However, XML-based messaging is at the heartof the current WS technology, and this brings considerableperformance problems. In addition, multimedia applicationsneed and consume considerable resources because of their highrate data exchange and media processing. High performanceSOAP encoding is an open research area [3], and WS inmobile environments also need to overcome such performancelimitations.The introduction of mobile devices has added a series of

issues that must be addressed:

� variability in communication delays due to communica-tion errors, handoffs and interference,

� lack of reliability in transactions, since mobile devicesmay go out of network range,

� demand for simpler and faster transactions due to lowcomputing and electrical power,

� higher security problems.

Nevertheless, significant efforts are already made and a lotof research attempts are currently in progress at all levels,demonstrating architectures in which WS support multimedia

52 J. WEB INFOR. SYST. VOL. 2, NO. 1, MARCH 2006

Fig. 1. The SOA and Web-Services interaction model

content and services in m-business applications.

II. MOBILE WEB SERVICES

A. Service Oriented Architecture

Services imply one party performing work for another.Indeed, services are the fundamental concepts of outsourcing,and their use changes the traditional model of software de-velopment. Creating applications by linking modules duringdevelopment is an approach that gradually is substituted bycombining services at run-time. In this way, the componentsof the applications interact in a very different style than in thepast [4]. At the highest level, virtually all WS are based onthe SOA model illustrated in Fig. 1.In this model, three essential operations exist: Publish, Find,

and Bind (or Interact). Service Providers publish services toa registry called Service Broker (or Discovery Agency). Theregistry entity stores service-related naming information, suchas service access points or interface definition locations. Onthe other side, Service Requestors find required services usinga service broker and bind to them. Service instances mayserve multiple roles concurrently. Indeed, each peer serviceserves in both the service requestor and service providerroles in a peer-to-peer scenario. One intermediary (or more)may exist in a message path between requestor and provider.Intermediaries may perform certain functions associated withthe message (such as security, routing, or management) [5].Interactions between SOA entities typically follow a tradi-tional synchronous request-response model: Requestor sendsa service request to a provider that executes the invokedoperation and then returns a response to the requestor [1]. Inaddition of this capability to provide support for programmaticinteractions like remote procedure calls, SOA allows for amore asynchronous “document exchange” mode of interactionthat provides flexibility and extensibility. The WS architecturerealize the SOA model using largely adopted Web protocols:Once a WS is created, it is advertised in a registry calledUDDI (Universal Description, Discovery and Integration),where it can be searched. A response from the UDDI willcontain the description of a service and the location (URL)to the service provider’s WSDL (Web Services DescriptionLanguage) file that describes the methods that can be invokedand the parameters required [6]. In fact, WSDL constitutesthe API (Application Programming Interface) of the WS. Inthe current WS architecture there exist a small number ofwell known global UDDIs that maintain information about

Fig. 2. WSDL and UDDI: XML documents passing via SOAP over HTTP

available WS and replicate data among themselves. Since thecode for a UDDI registry is freely available, it is possibleto deploy UDDI registries locally in order to reduce Internettraffic. This is especially interesting for services that are to behidden from anyone outside the local domain [7].Messages are exchanged through the protocol SOAP (Sim-

ple Object Access Protocol). In fact, all previously mentionedWeb protocols are XML-based grammars for exchanged dataformat definition. So, the transmitted parameter names, valuesand possible error conditions are encoded through XML.In addition, SOAP works by exchanging information usingGET/POST over HTTP. This allows the data to be exchangedregardless of where the client is in a network.

B. Web Services in the Mobile World

Initial developments in the WS area tend to concentrate onserver-to-server interactions in fixed networks. However, forWS to become a universal communications paradigm, its rangeshould also include mobile devices with wireless connectivity.In fact, with the most recent advances in wireless technologies,new WS are presented for the benefit of persons who aremost of the time on the move. These persons heavily relyon mobile devices to conduct their operations. Mobile Webservices (MWS) denote these WS and are meant to be eitherremotely triggered from mobile devices for their execution ortransferred from provider sites to users’ mobile devices onwhich their execution takes place [8]. It is worth mentioningthat mobile devices can both request (consume) and provideMWS.Standardization of MWS is lead by OMA (Open Mobile

Alliance) [9]. OMA in general drives service enabler archi-tectures and open enabler interfaces that are independent ofthe underlying wireless networks and platforms. Its mission isto facilitate global user adoption of mobile data services byspecifying market driven mobile service enablers that ensureservice interoperability across devices, geographies, serviceproviders, operators, and networks, while allowing businessesto compete through innovation and differentiation. A specialworking group (OMA Mobile Web Services) aims to developspecifications that define the application of WS within theOMA architecture. According to [9], the use of WS on mobiledevices includes three basic usage patterns:1) Invocation of network-based WS (e.g. location service,push notification service, billing service) from mobiledevices.

2) Hosting of WS (e.g. personal authentication service,payment service) on mobile devices.

GEORGIADIS ET AL.: WEB SERVICES AND MULTIMEDIA IN M-BUSINESS APPLICATIONS 53

3) Mobile-to-mobile communication using WS technologyend-to-end (effectively a combination of the first two).

The integration of mobile devices into WS-based architectureshas to take into consideration a number of parameters. We maydistinguish the following mobile device characteristics [10],[7]:

� Changing location – Depending on location of the mobiledevice, the possibilities and the requirements may vary.

� Restricted resource capabilities – Mobile devices havelower storage capacities, minor processing capabilities,limited energy supply, inconvenient input/output facilities(smaller screens/keyboards) and lower network connec-tion speeds than desktop computers. Network bandwidthcapability in particular, is dependent on the previouscharacteristic (changing location)

� Adoption motivation – This is a direct consequence of theprevious characteristic. As the input/output capabilitiesof the mobile devices are restricted, their use is uncom-fortable in many cases. Therefore, mobile applicationsmust provide added value for getting accepted. Significantmobile device usage characteristics have been identified[11], which must be taken into consideration. Mobileusers:

– have a tendency to treat their mobile device in a quitepersonal way,

– have limited attention as they manage their mobiledevices. This is because they usually involved at thesame time in other tasks, and

– manage their mobile devices in broadly mixed en-vironments. So mobile devices have to detect theuser’s setting (such as location and resources nearby)and subsequently have to offer task-relevant services(context-sensitivity of mobile device operations).

A number of considerations (related with the use of WS onmobile devices), have already been identified [9], [7], [10]:

� Scalable means of service advertisement: A single, centralUDDI registry is probably unable to accommodate thelarge aggregate number of WS that may be hosted onmobile devices; protocols for ad-hoc service discovery orfederations of registries with localized coverage may bemore appropriate in terms of administration, flexibility,and performance. This will also allow other devicesor services to discover/invoke WS originating from thedevice in a peer-to-peer fashion.

� Economical (small-footprint) WS implementations: Re-stricted capabilities require optimized implementations ofWS stacks, including SOAP message handling, messagedispatching, and XML serialization/deserialization. Forinstance, compressed over-the-air encodings for serializedSOAP traffic may help to reduce bandwidth requirementsand/or parsing overhead on (constrained) mobile devices.

� Location-based service discovery: This will allow mobiledevices to get instant access to WS that are particularlyrelevant to their present location/context, by taking devicelocation information into account during the discoveryprocess in order to list most relevant/proximate services(first). This may work, for example, by broadcasting

lookup requests only within a local network perimeteror by consulting a (local) registry.

� Interoperability issues: SOAP stack implementations maynot fit all sizes, and there are different runtime environ-ments to consider. Furthermore, device constraints maynecessitate particular interoperability profiles for certainclasses of mobile devices.

� Service instance disambiguation: When WS becomeubiquitous many similar candidate service instances maybe available inside close perimeters; for instance, theremay be many on-device payment services in proximityof a single point of sale. Convenient ways for identifyingappropriate service instances are then required (e.g. rely-ing on closeness or pointing rather than identification byburdensome unique names).

� Tuned programming model: Unlike current bandwidthlimitations, (which is expected that will decrease overtime), communication latencies over wireless links willalways remain significant. This requires a programmingdiscipline that favors calls to coarse-granular methods andaggregation of functionality within such methods, in orderto keep messages as short as possible and the overallnumber of over-the-air message exchanges low.

� Intermittent connection: Mobile devices may be tem-porarily switched off or become otherwise unreachableduring normal use. So, handling of connection loss isan important topic. In addition, the services offered onmobile device may not be accessible all the time. Thecommunication software should offer means to masksuch intermitted connectivity as far as possible (e.g.by replicating state information belonging to WS), andclients should tolerate longer round trip times.

� Quality of Service: WS on mobile devices, among otherthings help to drive user interfaces. Quality of ser-vice parameters (such as bounds on delays, bandwidthreservations, error levels, etc.), become critical, becauseinfringements directly impact user experiences.

In the next section, we will focus on multimedia content. So,we will look closer issues related to MWS and multimedia.A significant topic here is a particular type of MWS: WSparticipating in multimedia mobile services architectures.

III. MULTIMEDIA AND MOBILE WEB SERVICES

A. Mobile Multimedia Services

Multimedia permits users to increase their comprehensionof the presented information and amplifies the prospective ofboth person-to-system and person-to-person communication.Mobile multimedia services aim to combine the Internet,telephones, and broadcast media into a single device. Inorder of increasing data rate, six broad classes of service aredistinguished [12]:

� Speech/Voice: Call quality at least as good as the fixedtelephone network is provided. Voicemail belongs also inthis class (eventually integrated fully with email throughcomputerized voice recognition and synthesis).

� Messaging: It is an extension of paging, combined withInternet email. Unlike the older ’text only’ messaging

54 J. WEB INFOR. SYST. VOL. 2, NO. 1, MARCH 2006

services, email attachments are allowed. Because of itsnature, messaging service attracts the research efforts ofseveral approaches exploiting MWS capabilities.

� Switched data: includes faxing and dialup access to cor-porate networks or the Internet. With always-on connec-tions available, this is mainly included to support devicesthat do not support a fully packet-switched network.

� Medium multimedia: used for Web surfing. Its down-stream data rate is also perfect for games, collaborativeworking, and location-based maps.

� High multimedia: used for very high-speed Internet ac-cess, for CD-quality audio and high definition video ondemand and for digital products-oriented online shopping.

� Interactive high multimedia: used for reasonably high-quality videoconferencing or videophones.

B. Multimedia Messaging Service (MMS)

In particular, (mobile) MMS include various technologiesand services enabling the exchange of messages betweenmobile users. It has been designed to leverage capabilities ofthe previous messaging systems (SMS and EMS). With MMS,users are not restricted anymore to the exchange of short textmessages but are able to exchange messages with multimediacontents such as sounds, images, animations, videos as foundover the Web. Moreover, elements of a multimedia messagecan be choreographed over time and appropriately placed overa graphical layout by content designers [13]. In comparisonwith previous messaging protocols, a message in the MMSenvironment is composed of truly multimedia elements. Thisincludes the possibility to compose multimedia messages as’slideshow’ presentations (i.e. combination of pictures, text,and audio, all coordinated over time).However, design objectives for MMS support the use of

existing transport protocols and content formats widely usedin the Web. MMS supports indeed many standard multimediaformats like JPEG, GIF, MPEG and MIDI, which can becombined in one message using a presentation language (e.g.SMIL). MMS makes use of existing protocols (e.g. WAP,SMTP, HTTP) and message formats (SMIL, MIME) as far aspossible, but requires operators to invest in new network ele-ments. The MMS architecture includes the software messagingapplication in the MMS-capable mobile device necessary forthe composition, sending and reception of messages. Besides,other elements in the network infrastructure are required toroute messages, to adapt the content of messages to thecapabilities of receiving devices, etc [13], [14].Even though most new mobile devices contain support

for MMS and many network operators already offer MMSfunctions, the amount of sent messages has so far beenreasonably small. People are still unwilling to use the serviceas they can not be sure that the corresponding person has anMMS compliant device. Given that the cost of sending MMSmessages is kept rational, it is likely that MMS will obtainan important part of the messaging market as soon as thedissemination level of MMS enabled devices is sufficient highfor mass use [14].

C. Instant Messaging and Presence Service (IMPS)

IMPS is a set of specifications motivated to ensure inter-operability in mobile instant messaging. Instant messaging(IM) is a type of communication service providing users withtwo elements: presence information and real-time messaging.Presence may be defined as the ability to detect whether otherusers are online and whether they are available. It is a way forfinding, retrieving, and subscribing to changes in the presenceinformation (e.g. ‘online’ or ‘offline’) of other users. The aimof IMPS is not only to provide exchange of messages andpresence information in mobile networks, but also to makepossible the creation of gateways to other instant messagingservices.IM can be seen as some kind of combination of features

from voice calls and email. Like voice calls, IM providesreal-time communication but at a price equivalent to email.When it comes to archiving, email systems provide the mostrefined solutions. Presence information is one of the greatestadvantages for users of instant messaging. Surveys show that40-60% of business related phone calls fail due to the calleebeing busy or absent [14]. Presence information practicallyreduces these incidents for IM, assuming that users keep theirpresence information up-to-date. In addition, voice calls affectthe productivity of parties involved, as often they interrupt thework of the callee. On the contrary, emailing is more proneto suspend caller’s work for a while. IM is more like voicecalls in this aspect, but presence information provides a wayto prevent unnecessary interruptions.The current strong trend involves use of presence servers in

push-to-talk (PTT) applications for preventing mobile networkoverloads, improving users’ motivation to expand PTT callvolumes when the user on the other end is accessible, andtransmitting location-based services and contents over PTT.

D. MWS Supporting Multimedia

A MWS may be considered as a specific type of WS whoseexecution takes place on top of a mobile device, and so itshould be able to be [8]:� executed efficiently and adapted according to the com-puting features of mobile devices,

� composed with other MWS and/or WS,� executed securely on mobile devices, and� transported through wireless networks, but eventuallyparticipating in a mixed (wired and wireless setting).

In addition, multimedia particular nature (voluminous datasize, time-dependency and hard-to-infer semantics) raises sup-plementary considerations in all previous requirements.1) Efficient Execution: XML’s self-describing nature has

considerable benefits, particularly in platform-independentweb application, however XML-based messages are larger andrequire more processing than existing Java-oriented protocolssuch as RMI (Remote Method Invocation), RMI/IIOP (RMIover Internet Inter-Orb Protocol) or CORBA/IIOP: Data isrepresented inefficiently, and binding requires more compu-tation processing and sending XML messages can not avoidcoming at the price of bandwidth and performance. Underthe environment of desktop computer and wired wide internet

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network, the deficiencies of XML mentioned above are not soapparent. Almost the three roles in WS architecture (requestor,provider, and broker) accept the fact it is worth sacrificingsome efficiency to get better web application architecture. Thisis the main mode of interaction between a WS requestor anda WS, namely the direct architecture model. And it is alsothe right way, as it keeps both the WS provider and the WSconsumer in standard forms.However the things are different to wireless mobile phones

[15]. The inevitable mobile computing characteristics (narrowbandwidth, limited computation, and small memory space)make processing SOAP messages (parsing, validation andtransformation) consume valuable resources [3]. Researchersexploring Java mobile phones, examine in detail the realizationarchitectures for mobile phone-oriented application integrationtechnology of WS. KSOAP and KXML are third party opensource solutions for Java (or J2ME - Java2 Micro Edition)phones to access WS. But it must be noted that neither ofthose support the WS “finding” engine. Thus, the programmerhas to act as the roles for finding WS in the system. In suchsituations, where the WS requestor may not support the fullWS messaging and discovery functionality, an indirect modeof interaction (indirect architecture model) takes place [9].Requestor devices communicate with a WS via an inter-

mediate element (proxy). A proxy in turn, acting in the roleof a WS requestor will communicate with the WS provider,using a standard WS interface. This is actually the directionto avoid the low efficiency of Java mobile phone parsingSOAP and XML. Sun’s fast web services is an approachthat aims at eliminating the low efficient of SOAP and XMLencode, using another protocol the Abstract Syntax Notation1 (ASN.1). Work entitled “ASN.1 Support for SOAP, WebServices and the XML Information Set” (referred to as X.695),is in progress that aims to define a number of proposedspecifications to ensure that ASN.1 encoding rules can beused in Web service environments. Using fast web service,the Java phone can access WS in a much efficient way,however fast web service is now a not standard protocol[15]. ASN.1 schemas allow defining various binary or textualformats, so it may be used for multimedia content. But stillit doesn’t use universal format of data model, they are notXML schemas. Another approach is provided from the state-of-the-art technologies for WS attachments. They deal withbinary data associated with a primary XML document. In thiscategory, W3C SOAP Message Transmission OptimizationMechanism (SOAP MTOM) enables SOAP bindings to opti-mize the transmission and/or wire format of a SOAP messageby selectively encoding portions of the message, whilst stillpresenting XML data to the SOAP application [16]. Thisapproach often is combined with the XML-binary OptimizedPackaging (XOP) specification. XOP defines a means of moreefficiently serializing XML documents that have certain typesof content, such as multimedia. A XOP package is createdby placing a serialization of the XML data inside of anextensible packaging format, such as the MIME (MultipurposeInternet Mail Extensions) Multipart/Related content-type [17],[18]. MTOM and XOP preserve the basic structure of XMLdocuments. They keep tagged data model and only document

contents are encoded in any binary format. Thus, they producesmaller size of data than equivalent ASCII encoding. They,however, impose the same parsing overhead because theypreserve hierarchical structure of their contents.Finally, it is worth mentioning the approach used at the

Handheld Flexible Representation (HHFR) as a part of Hand-held Message Service (HHMS) mobile communication frame-work. It serializes SOAP/XML structure in binary formatwith tokens, but still keeps data transparency with the datadescription file. It actually preserves the SOAP semantics,with a binary data format for high performance messagetransmission and processing [3]. In addition to performanceissues, Flexible Representation specification includes a QoS(Quality of Service) framework in the architecture to supportreliability and security2) Service Composition (Agents and WS): It is largely

accepted that composing services, rather than accessing asingle service, is essential. Searching for the relevant WS,composing them into a composite service, triggering them,and monitoring their execution are among the operationsthat users will be in charge. Most of these operations arecomplex, although repetitive with a large segment suitable tocomputer aids and automation. Therefore, software agents areappropriate candidates to assist users in their operations [8].Two major types of agents may be considered: User-agents,acting on behalf of users, and provider-agents, acting on behalfof providers (thus, offering WS to users). The integrationof agents and WS into the same environment raises theimportance of a specification method. In this context, serviceaggregators may use the Business Process Execution Languagefor Web Services (BPEL4WS) to create new WS by defininginternal processes of existing services and corresponding com-positions of the interfaces. Apart BPEL, specifications such asWS-Coordination, and WS-Transaction, illustrate how WS canbe used together in the composition layer [2].3) Security Issues: While WS offer significant benefits

for SOA-based applications, they also set significant securityissues. To use the advantages of WS for its informationsystems needs, an organization must trust the security of WSin order to provide access to its information assets, whichare usually attractive targets for malicious hackers, industrialespionage, and fraud [19].There are many security issues when adopting WS and vari-

ous WS security mechanisms are involved in the developmentof a secure WS environment, besides the existing securitymechanisms in legacy systems that are updated to join the SOA[20]. However, the main objective is to ensure that message-level transactions can be conducted by providing end-to-endsecurity of WS, according to the following requirements [21]:� Mechanisms for mutual authentication between serviceproviders and service invokers.

� Mechanisms for authorization to control invoker accessto system resources.

� Encryption technology and digital signature techniquesfor transmitted data confidentiality and integrity, respec-tively.

� Mechanisms for integrity of transactions and commu-nications to ensure that the business process was done

56 J. WEB INFOR. SYST. VOL. 2, NO. 1, MARCH 2006

properly and the flow of operations was executed in acorrect manner.

� Mechanisms for non-repudiation so that a party to atransaction cannot deny the occurrence of the transaction.

� Mechanisms for end-to-end integrity and confidentialityof messages, even in the presence of intermediaries.

� Provision of security and audit trails in order to trace useraccess, behavior and system integrity verification.

� Distributed enforcement of security policy across variousplatforms with varying privileges.

A number of standard bodies are developing specificationsto address WS security [22]. The XML Key ManagementServices (XKMS) support clients to securely access publickey-related services such as key generation, registration andrevocation, and validation of certificates and signatures. TheSecurity Assertions Markup Language (SAML) is used for ex-changing with SOAP messages authentication and authoriza-tion information (in the form of tokens that represent securityassertions) and policy information between WS. The XMLAccess Control Markup Language (XACML) expresses accesscontrol rules in XML format and can be used with SAML forarticulating and conveying policy information linked to accesscontrol. The XML signature and XML encryption providerules for encrypting or signing of documents, respectively,in order to ensure that only legitimate entities can access agiven document. The WS-Security specification provides aframework for using existing techniques to add encryption andintegrity information to SOAP messages [23].

Besides the security aspects of using WS in general ITapplications, WS technology has also been proposed by theMedianet project to be used in a distributed architecture forcontrolling and managing the access to multimedia contentwith Digital Rights Management (DRM) techniques. Me-diaNet is a 6th Framework Programme Integrated Projectof European Union in the area of Networked AudiovisualSystems and Home Platforms, that is dealing with the issuesof Digital Rights Management [24]. The MediaNet projectaddresses the domain of digital multimedia personal com-munication and content distribution, as well as cooperationschemes between content owners, service providers, networkaccess operators, and telecommunication, computer, compo-nents and consumer electronics industries [25]. The objectiveis to remove the obstacles to end-to-end digital communica-tions and content exchange, from content/service providersto customers and between persons, over shared broadbandaccess and home network infrastructures at the same time.To achieve this, MediaNet integrates a DRM architecture,referred to as OpenSDRM, that provides an open service-oriented platform for controlling and managing the intellectualproperty rights (IPR) associated with multimedia content ina completely distributed environment. OpenSDRM integratessome critical DRM elements that include: content protection,rights expression, license management, content and metadataregistration and payment [26]. OpenSDRM uses two differentsecurity layers. The first security layer is established at thecommunication level to provide the necessary secure andauthenticated communication medium. The second security

layer is established at the application level, ensuring the secu-rity, integrity, authentication and non-repudiation mechanismsneeded by the different components to provide the OpenSDRMservices by exchanging SOAP messages.

IV. NETWORK ISSUES

New technologies in wireless networks have allowed thedevelopment of new standards with larger available bandwidthper channel. For example, the most widely deployed standardat present is IEEE 802.11b at 11 Mbps, although standardswith even higher speeds are available. Such bandwidth avail-able at the LAN level and at very low cost allows thedevelopment of new services, unrealistic in the past, suchas video streaming, p2p file sharing and simultaneous websurfing and e-/m-commerce transactions. Assuming that jitterand latency can be kept lower than 200 msec, even VoIP (bothvoice and video) can be supported. This situation presents anew window of opportunity for many added-value services thatcan be built on top of this infrastructure. It is, therefore, notsurprising that both small and large communities (e.g., the cityof Chicago) have recently announced their intention to deploya complete set of hot spots covering their area of jurisdiction.Assuming that the underlying backbone can support the

expected network traffic, it is imperative that we revisit ourviews on MWS and their protocols for the most importantunderlying components, since these are the important buildingblocks that can offer both low adaptation cost for existingapplications as well as better network utilization. Such astudy is non-trivial, given the diversity of wireless networktechnologies, with varying error-rates, available bandwidth perchannel and area coverage. In this section we are examiningthe main components of such WS architecture of issues,namely the transport layer, as well as the role of new standardsat lower levels. TCP and UDP are the protocols at thetransport. The former is important due to services related toreliable file sharing and e-/m-commerce transactions, whereasthe second due to services related to real-time traffic (e.g.,video streaming). Although ad hoc networks are generallyimportant, the deployment of wireline hot spots, has guidedour focus to networks where wireless clients are directlyconnected to a certain fixed (or base) node, which in turn ispart of a backbone. However, there are important exceptions,especially in the case of Wireless Personal Area Networks(WPANs), such as Bluetooth with piconets and scatternets.

A. TCP and UDP Overview

TCP and UDP are the de facto standard protocols used atpresent on the Internet at the Transport Layer.UDP is basically a best effort service providing almost

nothing on top of IP. As such it intended for best-effort (thusnot guaranteed) delivery of datagrams, providing a connection-less service among the communicating parties. Nevertheless,this lack of reliability is its strength in the case of real-timetraffic, where speedy rather than reliable service is soughtafter. In addition, UDP supports multicasting, whereas TCPdoes not. TCP on the other hand offers connection-oriented,reliable service, based on positive acknowledgements from

GEORGIADIS ET AL.: WEB SERVICES AND MULTIMEDIA IN M-BUSINESS APPLICATIONS 57

the recipient and retransmissions of lost segments. Therefore,it is better suited for reliable file exchange, necessary forapplications ranging from e-mail to web-based ones. TCPhas undergone many changes with various flavors, trying toimprove its performance, as well as its fairness to other TCPconnections running in parallel [27]. Therefore, TCP is quitecomplex, incorporating mechanisms for flow and congestioncontrol. In all cases, the basic characteristics have not changed,so that compatibility with different versions can be maintained.Such research effort was justified, since TCP was the most

widely used transport protocol in the Internet, comprisingan estimated 95% of the traffic [28]. However, this is nolonger the case, since voice and video over IP are provingincreasingly popular, consequently increasing the share oftraffic attributed to UDP. Since UDP does not include any self-policing rules, the net effect is that in the case of congestionTCP tends to choke itself. Although considerable researcheffort has been put on possible modification of UDP [29], inorder to make it fairer to TCP, this is still in its early stages.

B. Transport Layer Protocols and Wireless Networks

1) TCP: TCP is practically the single most importantprotocol in use today by web services, since they are inturn based on HTTP. Due to negligible error-rates in present-day wireline networks, TCP has been fine-tuned to attributeany segment losses to congestion. Nevertheless, in wirelessnetworks this assumption is not true. Consequently, segmentsare either lost and have to be retransmitted or the data-linklayer provides reliability at the expense of higher observeddelays.The problem here is not only the additional delay itself, but

the fact that such delays are not of constant duration. Suchvariability in response time on behalf of the receiver causesthe TCP to attribute it to congestion and thus multiplicativelyreduce its sending rate, during which it enters the phase ofadditive increase. Consequently indications of a short burst ofcongestion cause TCP to reduce its sending rate considerably,after which it takes a very long time to reach its original point.To address this situation, new approaches have been pro-

posed that can be classified in three broad categories:

� Modifications at the Data-Link layer. As stated earlier,such an approach is transparent to the transport layer.It typically involves packet buffering at the base stationbetween the wireline backbone and the wireless portionof the network. Reliability is achieved by automaticallyretransmitting lost frames. The main disadvantage is thatthey introduce additional delays of varying duration thatreduce the overall TCP throughput. Snoop [30] is such aTCP-aware protocol that suppresses duplicate ACKs fromthe wireless receiver and performs fast retransmission.In this way, the original TCP sender does not observeduplicate ACKs, thus halving its congestion threshold. Atthe same time it detects lost segments asking the wirelessnode to retransmit them. Performance results show thatSnoop is better than plain TCP at error rates ranging from� � ��

�� to ����. At higher error rates its performance

becomes worse than that of TCP.

� Indirect Protocols. This approach is similar to the oneabove, with the notable difference of ending the TCPconnection at the base station and establishing a secondconnection between the base station and the wireless re-ceiver. In this sense, TCP does not need any modificationfor the first portion of the total path and any suitableprotocol may be deployed at the second portion. One suchexample is the I-TCP [31] with similar performance thanthat of TCP. I-TCP performs better only in the case ofwide-area networks and prolonged blackouts.

� End-to-End Protocols. Under this approach the end-to-end semantics of TCP are retained, but the protocol stackneeds to be changed at both sender and receiver ends.WTCP has been proposed as one such example [32].WTCP is more complex than TCP, placing additionalcomputational burden on the receiver for congestioncontrol in order to reduce the effect of reverse pathcharacteristics from the congestion control. Furthermore,it makes a clear distinction between congestion relatedand other losses, and does not use retransmission timeoutsbut an elaborate selective acknowledge scheme to providereliability. Compare to normal TCP, it can achieve 100%higher performance for packet error rates of 4%; thisfigure increases for higher percentages of error rate.Nevertheless, WTCP uses inter-packet separation as agood metric to detect congestion, something that is validonly if the congestion point is the wireless link. More-over it has been shown that its heuristic for detectingnormal losses can fail under several scenarios [33]. Inthis respect one should evaluate its performance in thegeneral case (i.e., when the sender communicates witha wireline receiver which uses a normal TCP version),since compatibility is important.

Most of the approaches outlined above base their responsive-ness on duplicate ACKs and a maximum waiting time, whichis in turn based on the Round Trip Time (RTT) measured inprevious responses. A more accurate measurement for the pastvalues of RTT can be made using the timestamps option at theexpense of an additional 12 bytes field, inserted in both theoutgoing segment as well as its acknowledgement. For largewindows, such an option allows more frequent measurements,providing higher accuracy. WTCP actually uses this option.Partial acknowledgement is another novel idea [34]. Under

normal circumstances, the sender receives two acknowledge-ments: A partial from the base station and a complete from themobile receiver. If a partial acknowledgement is received, butnot a complete one, then the sender detects that the problemexists in the wireless link and thus no congestion control actionis taken, which would require the slow start threshold to behalved. Nevertheless, this makes TCP more complicated andincompatible to existing versions.Apart from congestion and errors, wireless networks may

experience problems due to frequent handovers. Freeze-TCP[35] exploits the fact that if the receiver sets the window sizeto zero, the sender leaves its congestion parameter unchanged.Therefore, when a handover is about to take place, the receiveradvertises a receiver window of zero, preventing congestioncontrol from being used by the TCP sender. Thus, the trans-

58 J. WEB INFOR. SYST. VOL. 2, NO. 1, MARCH 2006

mission rate remains unchanged.In all cases, it is evident that there is a trend towards rate-

based congestion control techniques, rather than ACK-based.However, there are two important issues that must be addressedfor any new TCP variant to be universally acceptable, namelycompatibility with other existing TCP variants and goodthroughput for hybrid networks, which involve both a wiredand a wireless part.2) UDP and Lower Layer Protocols: In the case of UDP

there is no congestion, flow control or other inherent mecha-nisms, which may impose any kind of restriction by default.As such, UDP is essentially nothing but IP with the additionof port numbers.Viewed from the wireless network perspective, UDP de-

pends upon its network layer service in order to be appropriatein such environments. Mobile IP [27] is well known as themost appropriate candidate for both wireline and wireless net-works with all its merits and shortcomings. Nevertheless thereare other possibilities, as well. One such important alternativeis UDP over Bluetooth [36], especially since Bluecasting(marketing by spamming Bluetooth enabled mobile phones)has already been established as a term of specific importancein m-business and marketing.Bluetooth is officially known as IEEE 802.15.1 and is

designed for use as a wireless personal area network (WPAN).In this respect its designated range is from a few centimetersto approximately 100 meters, but using very low cost hardwareand power consumption compared to IEEE 802.11b, for exam-ple. Moreover Bluetooth has known considerable deploymentin all sorts of mobile as well as other devices. It exists inseveral versions, the most recent being version 2.0, which iscompatible with earlier versions, but offers a transmission rateof up to 2.1 Mbps, lower power consumption and lower biterror rate. Future versions are planned offering improvementsin QoS, security and other features. Products adhering tothis standard belong to one of three classes, namely: Class1 (100 mW and 100 meters range), Class 2 (2.5 mW and 10meters range) and Class 3 (1 mW and 10 cm range). Possibleapplications depend upon the establishment and interpretationof specific Bluetooth profiles that include PAN, video andaudio distribution among others.The performance of UDP over Bluetooth depends mainly on

the two factors as demonstrated by [36], namely the numberof slaves in a piconet (Bluetooth ad hoc network with onemaster node and up to six slave nodes) and the UDP segmentsize. In the former case, the higher the number of slaves, thehigher the frequency of the inquiry period to the master; thisconsequently degrades performance. The UDP segment sizecan degrade its overall performance, because of the numberand type of Bluetooth packets (which can be of different size)used to transmit it as payload.

V. WEB SERVICES AND MULTIMEDIA IN M-BUSINESSAPPLICATIONS

A. WS as an Application Integration Technology in E-/M-Business

It is clear that from the information technology (IT) perspec-tive, SOA is a flexible emerging set of technological standards

which provides Web-delivered functionality. However, apartfrom the technological aspects, numerous business challengesare additionally presented: WS paradigm can be seen as a nat-ural outcome of e-commerce. It is an outstanding applicationintegration technology [37]. High-level efficient applicationintegration is a key success factor for all businesses, sinceit represents the single largest expense of most IT budgetsin business organizations: Forrester Research estimates that asmuch as 35% of IT staff resources are used for gluing togetherheterogeneous applications. In addition, Gartner Research es-timates that the average programmer spends 65% of his/hertime performing integration tasks [4].Enterprise Resource Planning (ERP) was one of the first

steps along the evolutionary path of application integrationin business organizations: a single integrated system built,based on separate modules for each department or function.Using ERP, each department gets a customized application thatprovides its own window into the corporate system. Naturally,ERP packages could not solve all business automation needs.Soon there were other systems, such as those for CustomerRelationship Management (CRM) and Supply Chain Manage-ment (SCM). The closed architecture of ERP packages did notallow any other system to modify the data of ERP database:the ERP paradigm is based on the idea that the centralizeddatabase is authoritative for all data and transactions, acrossall business units and departments [4]. In other words, anyexternal system not part of the ERP system itself, was entirelydependent upon the ERP database system.The next step for application integration was Enterprise

Application Integration (EAI). EAI packages act as softwaredata translators that take information from ERP and convert itinto formats that other applications can understand, and viceversa. Initially, the only problem with EAI was its very highcost. But when e-commerce appeared as the latest applicationrequiring integration into existing infrastructures, both ERPand EAI confronted new challenges they couldn’t handle.WS are in fact the current step in application integrationtechnology, and they are considered a significant contributionto it.WS technology with its application integration benefits, may

serve as the foundation of a new generation of B2B architec-ture. The service-oriented computing paradigm migrates thetraditional standalone hosting model to a networked one, byallowing WS to dynamically discover and hook up to WSoffered by different providers. In this way, WS can be blendedto implement customized virtual supply chains or smaller-scalebusiness processes confined to a single enterprise [38].In addition, WS are supposed to be offered in such a way

that a large community of users can browse, select, and triggerto satisfy their needs. So, B2C transactions are also supported,and in fact, from the product marketing perspective, WS arecapable to support a new business model for organizationsoperating in the electronic environment. A business model(namely the e-service model) which is based less on reducingcosts through automation and increased efficiency and moreon expanding revenues through enhancing service and buildingprofitable customer relationships.E-service is a customer-centric concept, and is defined as

GEORGIADIS ET AL.: WEB SERVICES AND MULTIMEDIA IN M-BUSINESS APPLICATIONS 59

the provision of service over electronic networks. Electronicnetworks enable the transformation of all products (physicaland digital) to service products [39]. This transformation hasmajor implications for exploring new service opportunitiesand markets, especially in the domain of information-basedproducts. WS are the building blocks and the enablers ofbusinesses with e-service orientation. At the strategic level ane-service orientation shifts the highlighting from products andtransactions to service and relationships. These are supportedat the tactical level by personalization and customization,privacy and security risk management, and e-service measure-ment [39].

B. Multimedia and MWS in M-Business Environments

Focusing in m-business environments, one of the majoraims of the MWS effort is to create a new situation thatenables the computer industry and the mobile industry tocreate/deliver multimedia products and services that meetcustomer needs in a way not currently practicable withinthe existing WS framework. Mobile multimedia (defined asthe set of standards and protocols for multimedia informa-tion exchange over wireless networks), transmit and processcombined information (presented by various media types suchas text, pictures, sounds, graphics, animations and videos) tosupply the mobile user services from various mobile settingareas (such as entertainment, the working place, informationretrieval and context-based utilities) [12].Many of the opportunities for mobile multimedia will arise

when mobile operators and service providers work moreclosely with businesses, content providers and device man-ufacturers, for example [40]:

� product and marketing awareness, via fun interactivegames and downloads,

� a channel to market as part of an enterprise’s multimediacall centre strategy,

� a channel to market for the media industry (building onthe success of ring tones to include audio-track streamingand download, video clip download, ’mobile merchan-dise’, sports highlights, and cartoons),

� vertically integrated devices and applications (e.g. cam-eras/camera phones, surveillance),

� location-based multimedia, travel news, maps and pic-tures, picture messages sent to subscribers within a loca-tion.

Delivery of services (applications and content) is critical tothe future success of mobile multimedia. Well designed mobileapplications are those that are well integrated with the networkand use the special features of it (e.g. the user’s location).On the other hand, mobile networks have components frommany vendors, and do not have the same APIs for applicationdevelopers. For this reason, solutions and approaches arecurrently evolving capable to integrate WS in order to exposeAPIs that are easy for application developers to work with.1) Usability Challenges: Dealing with usability challenges

is an example of integrating WS in mobile applications tosupport multimedia capabilities on mobile devices. MWS mayprovide a flexible solution to add voice control and audio

feedback to the traditional mobile telephone interface in orderto make it multimodal. WS-based solutions do not requirethe devices (acting as VoiceXML-enabled clients), to be madephysically larger.We already underline the characteristic of mobile users’ lim-

ited attention. Using speech recognition technology, navigationthrough an application becomes easy with voice commands,while data entry is made hugely simpler. Audio feedback canbe used to supplement what can be shown on the limitedscreens. However, speech recognition is computationally ex-pensive and the more complex recognition tasks are beyondthe capabilities of current MMS devices. Modern distributedprocessing solutions (based on SOA and WS approaches) aretherefore required to deliver the full range of multimodalenabled applications, with the demanding speech recognitiontasks carried out on network based servers [40].2) Telecommunication Services (The Parlay X Specifica-

tion): The Parlay X specification describes a number ofWS that provide a simple interface to telephony and othersystems. The idea is simple: If telecommunications servicesare exposed as WS, it becomes easier to build applicationscombining both Internet-based and telecoms-based services.Using WS can reduce development costs if code, interfaces, ordevelopment models can be re-used for different projects. TheParlay X WS are intended to encourage the development ofnext generation network applications by IT developers who arenot essentially specialists in telecommunications. The choiceof WS will be driven not so much by technical sophisticationas by commercial utility. The main goals of Parlay X are [41]:

� Parlay X WS will be judged on the 80/20 rule, meaningthat the WS will aim to support 80% of applications using20% of available functionality (i.e. methods will not beunreasonably complicated or overloaded),

� each WS will be abstracted from the set of telecommuni-cations capabilities exposed by the Parlay APIs, but mayalso expose related capabilities not currently supported inthe Parlay APIs where there are compelling reasons,

� it is desirable for the messages to follow the synchronousrequest/responses model, initiated by the application,

� the capabilities offered by a building block may behomogeneous (e.g. call control only) or heterogeneous(e.g. mobility and presence),

� it is desirable for Parlay X WS invocations to be uncorre-lated and for the WS to be stateless from the perspectiveof the application,

� the Parlay X set of interfaces shall be extensible (integra-tion of third-party-provided interfaces must be supportedusing proven, reliable, and WS-standard technologies).

� a Parlay X WS will be neither application specific nornetwork specific.

The Parlay X specification is separated into a number ofdifferent application functionalities. MMS, IMPS (the term’terminal location’ is actually used in Parlay X specification todescribe the mobile version of services like ICQ which offervoice chat and text conferencing), and user status (enablinguser-status-aware applications) are among of the most impor-tant of them.

60 J. WEB INFOR. SYST. VOL. 2, NO. 1, MARCH 2006

Fig. 3. Delivering ITWS traveler information to mobile phone display

3) Handheld Flexible Representation: In previous para-graph we outline HHFR scheme, as an approach of avoid-ing performance holdups of SOAP (preserving at the sametime SOAP semantics) for mobile computing. In [3], a WS-based, integrated videoconferencing system (that allows het-erogeneous, mobile clients to join the same session) whichexploits HHFR features is presented. HHFR scheme offersperformance benefits in most of collaboration applicationsthat is session-based including audio/video conferencing andwhiteboard [3].4) Intelligent Transportation Web Services: Intelligent

Transportation Web Services (ITWS) is another significantapproach of integrating WS in mobile applications to supportmultimedia (and not only) capabilities on mobile devices [42].Different from conventional Advanced Traveler InformationSystems (ATIS) applications, ITWS is designed to be a WSinfrastructure. Not only to provide traveler information tousers, has it also aimed to be used as a modular component byother enterprises or WS providers for application development.It can deliver real-time traffic information to MMS-enabledmobile phones. MMS can deliver messages of audio, voice,or colorful graphics, so it will make the delivery of visualtraveler information to mobile users easily, and promote them-commerce with successful business models.ITWS through MMS is capable to support access of the

system to mobile travelers with visualized real-time trafficinformation for pre-trip planning or ’en route’ referencing tohelp drivers avoid congestion and choose timesaving and saferoute. To generate graphical traffic visualizations (using thetraffic data from the ITWS Server via the SOAP protocol), atraffic diagram server is used. These traffic visualizations canbe generated online or offline and pre-stored on the server.Users can use personal computers or portable devices suchas PDA and mobile phones to access ITWS through wirelessInternet or MMS gateway [42]. Thus, WS technology canserve as an inexpensive platform for providing location-basedmultimedia and regional navigation services. Figure 3 depictsthe displays of a mobile phone after ITWS transmits requestedinformation back to the user. From left to right: arrival time atcorresponding major cities on the way, a quick look of overalltraffic speed, and on board traffic state forecast.

VI. CONCLUSION

WS technology is well suited for integration, and it seemsto be well on the way to achieving broad acceptance (thekind of universal acceptance that TCP/IP, HTTP, HTML, andXML, have by now achieved) as a way to implement SOA.The reason is that WS design is independent as much as

possible from specific platforms and computing paradigms anddeveloped both for inter-organizational situations (internal andintra-system WS) as well as for intra-organizational situations(external WS) [4].In m-business environments, the basic idea remains the

same: any particular MWS can be seen as a component that anorganization provides wirelessly in order to be assembled andre-used in a distributed, Internet-based environment [8]. More-over, mobile devices challenge us to exploit MWS solutions byredesigning conventional WS operational architectures: Newconveniences for users and new business opportunities areopening (e.g. using WS to extend blogging on mobile phones[43]). But designing for the limited mobile platforms, presentsunique demands especially for supporting multimedia content.Considerable research is under way at all networking levelsin order to improve overall network performance. Bluetoothand TCP variants for the mobile environment are the strongestcandidates for the infrastructure on which to base the variousWS. Moreover, the security and authentication qualities madepossible by WS, will allow organizations to create reliable newservice offerings.However, the largest barriers to enterprise and consumer

adoption have to do with business and support models ratherthan technological difficulties. Concerning consumer adoption,services must be delivered that meet real customer needsthrough a user interface that delivers an acceptable experi-ence. Current customer experience research methodologies arelimited in the mobile domain. And the methods that makebusiness (desktop) software successful are probable to provideinsignificant results when applied to the mobile products andservices market [44]. Especially for multimedia content andservices, the established popularity of ring tones and growingpopularity of games downloads show that people are happy tospend small amounts of money per item for relatively small-scale multimedia components. Yet, there are open questionsregarding, e.g. how much people will be willing to pay, orwhat is the ceiling for mass-market multimedia pricing [40].On the other side, concerning the enterprise adoption, inte-

grating MWS into the corporate infrastructure it is certainlya challenge. However, this type of integration is a majoringredient for any enterprise in becoming on-demand e-/m-business that can respond intelligently, efficiently, appealinglyand flexibly to any kind of information (text, audio, video,speech, and images) from disparate sources. Also, key issuewill be whether and how well telecommunication companiessupport and deploy MWS architectures.

REFERENCES

[1] P. Bellavista, A. Corradi and S. Monti (2005) Integrating Web Servicesand Mobile Agent Systems. Proceedings of the 25th IEEE InternationalConference on Distributed Computing Systems Workshops, 283–290.

[2] M. P. Papazoglou and D. Georgakopoulos (2003) Service-Oriented Com-puting. Communications of the ACM, 46(10): 25–28.

[3] S. Oh, H. Bulut, A. Uyar, W. Wu and G. Fox (2005) OptimizedCommunication using the SOAP Infoset For Mobile Multimedia Col-laboration Applications. JProceedings of the International Symposium onCollaborative Technologies and Systems.

[4] D. Kaye (2003) Loosely Coupled: The Missing Pieces of Web Services.Boston, USA:Addison Wesley.

GEORGIADIS ET AL.: WEB SERVICES AND MULTIMEDIA IN M-BUSINESS APPLICATIONS 61

[5] Y. C. Chang, J. L. Chen and W. M. Tseng (2005) A Mobile CommerceFramework Based on Web Services Architecture. Proceedings of theIEEE International Conference on Information Technology: Coding andComputing, 403–408.

[6] W. Zahreddine, and Q. H. Mahmoud (2005) An Agent-based Approachto Composite Mobile Web Services. Proceedings of the 19th IEEEInternational Conference on Advanced Information Networking and Ap-plications, 189–192.

[7] S. Berger, S. McFaddin, C. Narayanaswami and M. Raghunath (2003)Web Services on Mobile Devices - Implementation and Experience.Proceedings of the Fifth IEEE Workshop on Mobile Computing Systems& Applications, 100–109.

[8] Z. Maamar, F. Akhter and M. Lahkim (2003) An Agent-based Ap-proach to Specify a Web Service-oriented Environment. Proceedings ofthe Twelfth IEEE International Workshops on Enabling Technologies:Infrastructure for Collaborative Enterprises, 48–49.

[9] Open Mobile Alliance (2005) OMA Web Services Enabler (OWSER):Overview, Candidate Version 1.1. http://www.openmobilealliance.org/.

[10] I. Duda, M. Aleksy and T. Butter (2005) Architectures for MobileDevice Integration into Service-Oriented Architectures. Proceedings ofthe International Conference on Mobile Business, 193–198.

[11] C. K. Georgiadis (2006) Handbook of Research on Mobile Multimedia,pp. 266–277. Hershey, PA: Idea Group Inc.

[12] G. Kotsis, A. Ferscha, W. Schreiner and I. K. Ibrahim (2004) MobileMultimedia: A Communication Engineering Perspective. Radiomatics:Journal on Communication Engineering, 1(1): 1–11.

[13] G. Le Bodic (2002) Mobile Messaging: SMS, EMS and MMS. IEEEVehicular Technology Society News, 13–21.

[14] P. Salin (2004) Mobile Instant Messaging Systems - A ComparativeStudy and Implementation. Master’s Thesis, Department of ComputerScience and Engineering, Helsinki University of Technology.

[15] L. Li, M. Li and X. Cui (2003) The Study on Mobile Phone-Oriented Application Integration Technology of Web Services. Springer,3032: 867–874.

[16] W3C SOAP MTOM (2005) SOAP Message Transmission OptimizationMechanism. W3C Recommendation, http://www.w3.org/TR/2005/REC-soap12-mtom-20050125/, 01-12-2006.

[17] W3C XOP (2004) XML-binary Optimized Packaging. W3C Can-didate Recommendation 2004, http://www.w3.org/TR/2004/CR-xop10-20040826/, 01-12-2006.

[18] W3C BCUC (2004) XML Binary Characterization Use Cases. W3CWorking Draft 2004, http://www.w3.org/TR/2004/CR-xop10-20040826/,01-12-2006.

[19] R. J. Boncella (2004) Communications of the Association for Infor-mation Systems. Communications of the Association for InformationSystems, 14: 344–363.

[20] E. Newcomer and G. Lomow (2004) Understanding SOA with WebServices. Boston: Addison Wesley Professional.

[21] A. Barbir (2003) Web Services Security: An Enabler of Semantic WebServices. Proceedings of Business Agents and the Semantic Web.

[22] OASIS Public Groups (2006) http://www.oasis-open.org/committees/,01-11-2006.

[23] OASIS Web Services Security (2005) http://www.oasis-open.org/committees/workgroup.php?wg abbrev=wss, 01-10-2006.

[24] [24] S. Travert and M. Lemonier (2004) The MediaNet Project.http://www.cs.cornell.edu/Info/Projects/MediaNet/, 01-11-2006.

[25] C. Serrao, M. Dias and J. Delgado (2005) Using Web-Services toManage and Control Access to Multimedia Content. Proceedings of The2005 International Symposium on Web Services and Applications, 23–28.

[26] C. Serrao, D. Neves, P. Kudumakis, T. Barker and M. Balestri (2003)Open SDRM – An Open and Secure Digital Rights Management Solution.Proceedings of the IADIS 2003, Lisboa, Portugal.

[27] J. Kurose and K. Ross (2004) Computer Networking: A Top-DownApproach Featuring the Internet (3rd Edition), Boston: Addison Wesley.

[28] H. Y. Hsieh and R. Sivakumar (2002) Transport over Wireless Networks.Handbook of Wireless Networks and Mobile Computing. Boston: Wiley-Interscience: 289–308.

[29] S. Floyd, M. Handley and E. Kohler (2005) Problem Statementfor DCCP. http://www.icir.org/kohler/dccp/draft-ietf-dccp-problem-03.txt,01-10-2006.

[30] S. Vangala and M. A. Labrador (2003) The TCP SACK-Aware SnoopProtocol for TCP over Wireless Networks. Proceedings of IEEE VTC,4: 2624–2628.

[31] R. Abdelmoumen, M. Malli and C. Barakat (2004) Analysis of TCPlatency over wireless links supporting FEC/ARQ-SR for error recovery.Proceedings of IEEE ICC’04, 3994–3998.

[32] P. Sinha, N. Venkitaraman, R. Sivakumar and V. Bharghavan (1999)WTCP: A Reliable Transport Protocol for Wireless Wide-Area Networks.Proceedings of ACM MOBICOM, 213–241.

[33] S. Biaz and N. H. Vaidya (1999) Discriminating Congestion Losses fromWireless Losses using Inter-Arrival Times at the Receiver. Proceedingsof IEEE Asset, 10–17.

[34] J. A. Cobb and P. Agrawal (1995) Congestion or Corruption? A Strategyfor Efficient Wireless TCP Sessions. Proceedings of the IEEE Symposiumon Computers and Communications, 262–268.

[35] T. Goff, J. Moronski, D. Phatak and V. V. Gupta (2000) Freeze-TCP:A True End-to-End Enhancement Mechanism for Mobile Environments.Proceedings of IEEE INFOCOM, 1537–1545.

[36] M. Connolly and C. J. Sreenan (2003) Analysis of UDP Performanceover Bluetooth. Proceedings of IT&T.

[37] T. E. Stafford (2003) E-Services. Communications of the ACM,46(6): 27–28.

[38] W. J. Van Den Heuvel and Z. Maamar (2003) Intelligent Web services(moving toward a framework to compose). Communications of the ACM,46(10): 103–109.

[39] R. T. Rust and P. K. Kannan (2003) E-Service: A new paradigm forbusiness in the electronic environment. Communications of the ACM,46(6): 37–42.

[40] J. A. Harmer (2005) Mobile Multimedia Services. BT TechnologyJournal, 21(3): 169–180.

[41] H. Lofthouse, M. J. Yates and R. Stretch (2004) Parlay X Web Services.JBT Technology Journal, 22(1): 81–86.

[42] C. H. Wu, D. C. Su, J. Chang, C. C. Wei, J. M. Ho, K. J. Linand D. T. Lee (2003) An advanced traveler information system withemerging network technologies. Proceedings of the 6th Asia-Pacific Conf.Intelligent Transportation Systems Forum, 230–231.

[43] Cosmorion Weblog Server System (2005) White paper.http://whitepapers.zdnet.com/abstract.aspx?scname=HTML&scid=1044&docid=95626, 01-12-2006.

[44] T. S . Balaji, B. Landers, J. Kates and B. Moritz (2005) A Carrier’sPerspective on Creating a Mobile Multimedia Service. Communicationsof the ACM, 48(7): 49–53.

Christos K. Georgiadis Christos K. Georgiadis is currently a Lecturer in theDepartment of Applied Informatics at the University of Macedonia, Greece.He received a PhD in security for information systems & web databases fromAristotle University of Thessaloniki (AUTh), Greece (2002); a postgraduatescholarship in informatics, Universita di Pisa, Italy (1989); and a BSc inmathematics from AUTh (1987). Dr Georgiadis also worked in the Universityof Thessaly in Greece as a lecturer and in the AUTh, as a research associate.He is a member of the Greek Computer Society and ACM-SIGEcom. Hisresearch interests focus on the area of electronic commerce technologies.

Panayotis E. Fouliras Panayotis Fouliras is a Lecturer in the Departmentof Applied Informatics at University of Macedonia (Greece). His researchinterests focus on the area of computer networks.

Ioannis Mavridis Ioannis Mavridis is a Lecturer in the Department ofApplied Informatics of University of Macedonia (UoM). He has a Diplomain Computer Engineering and Informatics from the University of Patras(1985) and a Doctor’s (Ph.D., 2000) degree in Mobile Computing Securityfrom Aristotle University of Thessaloniki (AUTh), Greece. He has taughtinformatics and information systems security in UoM, AUTh, Hellenic OpenUniversity and TEI of Thessaloniki. He is a member of Greek ComputerSociety, Technical Chamber of Greece and WG 11.3 on Database Security ofIFIP. His research interests focus on the area of information system security.

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Athanasios Manitsaris Athanasios Manitsaris is currently an AssociateProfessor in the Department of Applied Informatics at the University ofMacedonia, Greece. He has a Ph.D. from University of Macedonia, Greece(1992); a DEA Matematiques Statistiques, from Univ. de Paris VI, France(1977); and a B.Sc. in mathematics, Aristotle University of Thessaloniki,Greece (1975). His research interests focus on the area of multimedia andInternet technologies - applied statistics.