MOBILE ACCESS TO THE SERVICES IN AMBIENTNETWORKS

A. Reyes*, R. Messeguer*, D. Royo*, C. Homar*

*Technical University of Catalonia, Spain, messeguer@ac.upc.edu

Keywords: Ambient Networks, Ambient Intelligence,Mobile Access, Web Services.

Abstract

Ambient Networks will enable mobile terminals tocommunicate in an environments populated by severalnetworks, devices, services and artefacts in a transparentway to the final user. In these scenarios, one way ofimplementing services uses web service architecture. So itis important to study how these mobile devices willintegrate efficiently to access web services. Because of thereduced capabilities of the mobile devices, their access toweb services is not easy and might have someperformance costs related to show data speeds andprocessing both HTTP commands and XML. Moreover,sOlne mobile devices could not support web service accessand if supported it lacks of web service search engine. Inorder to allow mobile devices to access web servicesefficiently, giving a solution to the previous problems, wepropose a new architecture based on a peer-to-peer withdistributed hash tables network, as a gateway between themobile device and web service. This architecture is a basesoftware simulator for an Anlbient Network environnlentdeveloped in our research group. Nodes of the peer-to­peer network publish services, allow finding them easilyand acting as a gateway to the mobile devices foraccessing web services more efficiently.

1 Introduction

Our research has been focused on the prototyping ofAmbient Networks (AN) [1] based on Peer to Peer (P2P)Distributed Hash Table (DHT) architectures that providesservices implemented using web service architecture [6].

Currently, several kind of mobile devices areindispensable tools in our daily life, so using mobiledevice for accessing services has much significance,because people that own the device can access to theservice anytime, anywhere.

In our prototype, services are implemented using webservice architecture. For desktop computer, there are nearmature software develop SDK and models to build, oraccess web services. However, things are not the same for

mobile devices, due to resource constraints for Inobiledevices such as memory and bandwidth.

One solution to this problem is to build a gateway that sitsbetween the mobile device and the web service to handlethese problems providing an efficient way to web serviceaccess. In [2] [5] [8] several strategies for deploying agateway are described, in all of them it is shown that usingthe gateway improves web service response time, but noneof them supports the web service finding engine.

In this paper, we propose P2P DHT- based architecture,which allows mobile devices to consume but also to findweb services efficiently.

2 Ambient Networks Scenario

In the last years, all technological development isfollowing the idea of creating full-connectedenvironments, where users will be able to access manyservices and devices iri a completely transparent way.

Ambient Networks (ANs) look for a nlobile networkdesign between heterogeneous networks leaving theparticular characteristics of each network in a subjacentlevel.

Figure 1: Ambient Net\vork environment.

Basically, there are four methods to simulate an ANscenario [4] [7]: Pattern-based approach, P2P approach,Plug and play approach and Closed-loop- based approach(also known as Traffic Engineering)

We have modelled an AN as a P2P network based onFreePastry [6]. So, the P2P paradigms are used for themaintenance of the hierarchy, as well as for solvingmanagement and control tasks.

Besides this, our network scenario benefits from somePastry characteristics such as: efficient request routing,

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Registry (P2P DHT Pastry)

discovery consume (via gateway----------------------

consume (direct)J2ME Requester

deterministic object location and load balancing in anapplication-independent manner.

In this way, P2P nodes publish services and the DHTfacilitates the work of finding the published services inour ambient network environment.

Services in our architecture are implemented through aweb service scheme, which provides high interoperabilitydue to all the interfaces are independent from hardwareand software.

The web services architecture has three distinct roles (Seefig. 2a) [5]: a provider, a requestor and a registry. Theprovider creates the web service and makes it available toclients who want to use it. A requestor is a clientapplication that consumes the web service. The registry,such a service registry, provides a way for the providerand the requestor of a web service to interact. Therequestor queries the registry to find services and theprovider sends the web service description to the registryfor publishing web services.

3 Mobile-DeviceArchitecture

Access Web Service Figure 3. Architecture to consume-discover Web Servicesfrom mobile devices

As we have pointed before, because of the reducedcapabilities of the mobile devices, their access to webservices is not easy and might have some performancecosts related to show data speeds and processing bothHTTP commands and XML. That is why, in ourarchitecture, mobile-devices have the option of consumingweb services through the gateway.

In next section, some experiments show that in mobilescenario, consuming web services via the gateway is fasterthan consuming directly from mobile-devices.

Figure 2. Web Service Architecture (fixed and mobile)

At this point, mobile-devices have enough informationabout web services for consuming them directly.

In all tests, our prototype SNAP [6] is in charge ofpublishing and discovering web services.

We have ituplemented two web services: CalculadoraWSand HolaMundoWS.

The characteristics we have evaluated are:

a) Number of bytes exchanged between web serviceand the client.

b) Time to invoke a web service method and time toreceive the response.

Three different clients, direct, proxy and fixed, have beenimpletuented for testing our architecture:

I. Proxy. The gateway (MIDlet ProxyWS) placed ina node of P2P network, consumes the service.The mobile device sends the parameters to thegateway and receives the response from thegateway.

2. Direct. Mobile-device consumes directly webservices (MIDlet DirectWS).

3. Fixed. A P2P DHT node consumes the webservice.

In this section we describe experiments for testing ourproposal. In order to gain a better understanding of theissues associated with web services consumption of ourarchitecture, we configured a mobile device Nokia N80Internet Edition to test the application. The device hadWLAN connectivity and supports Java MIDP 2.0 andCLDC 1.1.

4 Experiment on accessing Web Servicefrom Mobile-Device

Registry

Requestor Providerb) J2ME Web Service

Registry

Requestor Providera) General Web Service

To solve these problems we propose the architecturedescribed in figure 3. In this architecture our AmbientNetwork prototype based on Pastry P2P DHT (SNAP [6])performs registry role. All nodes of the prototype havecapabilities for publishing, discovery and consume webservices.

To efficiently integrate our prototype with service­oriented architecture for Java mobile-devices one P2PDHT node, the gateway, interacts with mobile-devices.Through this gateway mobile-devices are capable ofquerying the registry (discovery) to get web serviceinformation.

In a basic service-oriented architecture for Java mobile­devices (See fig 2.b), the requestor is the mobile-device.In this scenario, there are to main problems: standardJ2ME for mobile-devices (JSRI72) [3] does not providediscovery services for mobile devices and becausehardware and software limitations of mobile-devicesconsuming web services are very inefficient.

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c) Number and type of messages exchangedbetween client and web services.

a) Number of bytes

Figure 4 shows the number of exchanged bytes whenclients consume web service method.

-------- Cliente Cliente ClienteFijo Proxy Directo

CalculadoraWS 24 29 23HolaMundoWS 20 24 20

This research partially supported by the Spanish MECproject P2PGrid TIN2007-68050-C03-0 1.

In this paper, we contribute to increase the potential forweb services on mobile devices. There are severalchallenges on this area due to mobile devices have muchlower processor power, limited bandwidth and lessmemory than desktop computers. Besides this, webservices specifications do not consider some mobilityissues such as service discovery. Therefore, we haveimplemented a gateway-based architecture that distributesthe web services along network nodes which performspublish, discovery and consumption web service roles.

Currently, web service consumption on mobile devicesbasically can be done in two ways: mobile deviceconsumes the service directly by itself or lTIobile devicethrough a web service gateway technology, which makesconsume more efficient.

Finally, we have described how service search andconsumption functions are made through out our proposedgateway and have proved that our architecture helps toovercome the lack of standard J2SE specifications todiscover web services from mobile devices as well asdevice limitations.

Acknowledgements

5. Conclusions and future work

Table 1: Number of exchanged messages.

• Direct client starts a TCP connection with the webservice and later exchanged SOAP messages over HTTP.

• Gateway client only exchanges its own TCP messages ofthe socket-proxy connection.

Performance tests of different web services in highdemand produced similar results in execution time.

With these results, we conclude that mobile web serviceconsumption using our architecture is much faster thanusing J2ME.

HolaMundoWSCalculadoraWS

0,5

o

Figure 5: Web services execution time.

• Execution time from fixed clients is lower than timefrom mobile clients due to several reasons, for examplethe throughput of wireless connection is lower than thethroughput of fixed systems.

• The gateway client needs less time than direct client.The reason is that direct client decodifies the WSDL file,while in case of gateway clients the pastry node decodifiesthe WSDL file.

1000

4,5

3000

4000

7000

8000

3,5

3

2,5

6000

2000

1,5

Byte.

9000

Calculadora\IVS HoiaMundo\AJS

Figure 4: Number of transmitted Bytes for each service.

• Fixed and direct clients exchange a very similar numberofbytes because both of them do the same operations.

• The number of exchanged bytes depends on the webservice, the more are the functions of the web service thebigger is its WSDL file.

• When we use a proxy client, it has to unload the WSDLfile and to communicate with the web service. So the loadof the Pastry network is increased.

b) Time to invoke/receive a method

Figure 5 shows the time to invoke a web service methodand the required time to receive web service response.

http://www.ambient-

c) Messages exchanged between client and service

Next table shows the number of exchanged messagesusing two different web services. As we can see there isno significant variation between them.

References• Decoding time increases according with the number offunctions that have the web service, so the execution time [1] Ambient Networksalso is increased. networks.org/

[2] S. Berger, S. McFaddin, C.Narayanaswami,M.Raghunath. Web Services on Mobile Devices ­Implementation and Experience Proceedings of theFifth IEEE Workshop on Mobile Computing Systems& Applications. 2003

[3] J2ME Specification for Web Serviceshttp://developers.sun.com/mobility/apis/articles/wsa/

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[4] P. Kersch, R. Szabo, Z. Lajos, Self OrganizingAmbient Control Space. An Ambient NetworkArchitecture for Dynamic Network Interconnection,International Conference on Mobile Computing andNetworking. Dynamic Interconnection of Networks.2005

[5] Luqun Li, Minglu Li, Xianguo Cui. The Study onMobile Phone-Oriented Application IntegrationTechnology of Web Services. Second InternationalWorkshop of Grid and Cooperative Computing, pp.867-874, Shanghai China, December 2003.

[6] D. Royo, A. Reyes, R. Messeguer, R. Martinez.SNAF: A Service Naming and AddressingFramework for SerAN Platform, 3rd lETInternational Conference on IntelligentEnvironments. VIm Germany 2007.

[7] A. Schieder, L. Eggert, N. Papadoglou, F. Pittmann,Components and Concepts of the Ambient NetworksArchitecture. Wireless World Research Forunl(WWRF). 2004

[8] Yoshiro Imai, Yuichi Sugiue, Yukio Hori, YutakaIwamoto, Shin'ichi Masuda: An EnhancedApplication Gateway for some Web services toPersonal Mobile Systems, International Conferenceon Computational Intelligence for Modelling Controland Automation, pp. 1055-1060, Vienna Austria,November 2005.

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