Guido Gehlen

Mobile Web services for peer-to-peer applications

The role of the service oriented architecture (SOA) is going to he more and more popular in the software design for distributed systems. This middleware framework tries to simplify as much as possible the software architecture of distributed applications. In infrastructure based networks like the Internet the SOA is successfully implemented by XML Web services in a client-server manner. In ad-hoc systems without any infrastructure, the peer-to-peer (P2P) paradigm is attractive. Thus, a Web service realization using the P2P paradigm is promising, since a uniform middleware can be achieved without any constraints of the underlying network and communication paradigm. In this article, we look at a heterogenous environment being composed of mobile nodes with computing and communication capabilities. Each (peer) node equally acts as both, server and client. These nodes provide their services to other nodes in the distributed environment, and they are able to use remote services. We distinguish and discuss different SOA realizations enabling P2P computing and introduce common software architecture for P2P Web services. On this basis, we introduce an implementation of P2P Web services on Java enabled mobile devices. We focus on the server implementation, enabling mobile devices (phones and PDAs) to provide and publish their services.

Mobile Web Service Communication Over UDP

A Web service based middleware for mobile applications is a promising platform to accelerate the application development for mobile systems. Currently, the Web service protocol stack is using by default the simple object access protocol (SOAP) on top of HTTP. Since HTTP is using TCP, the round-trip time of a Web service call in mobile networks is high due to the connection establishment of TCP (three-way- handshake) and the congestion and error control mechanisms (slow-start phase). Some applications do not require delivery guarantees of TCP. For these applications an unreliable transport of SOAP messages over the user datagram protocol (UDP) is a natural choice. If an application needs a reliable transport of SOAP messages a lightweight ARQ mechanism on top of UDP is the better choice than using HTTP over a mobile link. The session management of HTTP is substituted by introducing Web services addressing properties within the SOAP header. This paper will present the architecture and the realization of an unreliable and reliable UDP SOAP binding for a mobile Web service based middleware, which consumes Web services (client) and provides Web Services (server). Both bindings will map two basic MEP to UDP services. The reliable binding encapsulates a selective-repeat (explicit request) ARQ protocol on top of UDP which ensures even the transmission of SOAP messages over several datagrams. Some use cases and examples motivate the work and stress the importance according to the mobile middleware. A comparison of method invocation latencies of the reliable UDP binding and the HTTP binding illustrate the performance enhancements.

Mobile P2P Web Services using SIP

Telecommunication networks and the Internet are growing together. Peer-to-Peer (P2P) services which are originally offered by network providers, like telephony and messaging, are provided through VoIP and Instant Messaging (IM) by Internet service providers, too. The IP Multimedia Subsystem (IMS) is the answer of the telecommunication industry to this trend and aims at providing Internet P2P and multimedia services controlled by the network operators. The IMS provides mobility and session management as well as message routing, security, and billing. This article is a comprehensive version of a conference publication [1] and introduces a Mobile P2P Web Services framework which enables the creation of arbitrary P2P application on mobile devices within the IMS. The terminals are sharing and publishing a Web Service interface, which provides the capability of coupling arbitrary applications using Web Service technologies and the support of the {IMS} infrastructure. The concept, the necessary Web Service adaptations, and extension as well as the interworking of Web Services, {IMS} nodes, and protocols are described and proofed by an exemplary mobile chess game application. In addition, the performance of mobile P2P Web Services is evaluated by means of an analytical analysis.

A Rule Based Publish/Subscribe Context Dissemination Middleware

Context information is vital data coming from mobile devices to add a value for the application execution. Such applications are called context-aware or context-sensitive applications. To enable context-aware applications in a distributed environment, first the context raw data is measured from sensors. After interpreting and structuring the data, the context objects have to be disseminated all over the distributed system. This paper introduces a context dissemination middleware based on a mobile Web Service framework. It eases the development of context aware applications by providing an abstraction layer hiding complex protocols. In addition, the protocols are optimized in terms of reducing latencies and network load. Moreover, to provide observation (monitoring) service of arbitrary context information, a rule description (policy) language has been designed, developed and structured. Web services eventing has been implemented for sending event notifications. The architecture and a prototypical implementation of the context middleware is presented in detail.

A Mobile Context Dissemination Middleware

Context information is one of the most important data coming from, mobile devices to add a value for the application execution. This paper introduces a context dissemination middleware based on a mobile Web services framework. In a P2P environment, each context source/provider offers services to other devices. A monitor service is proposed which reduces the communication amount between devices and decreases the reaction time according to context changes. Moreover, to provide monitoring service of arbitrary context information, a rule description (policy) language has been designed. The paper presents an exemplary application in the health care domain to demonstrate the use of the middleware. Additionally, the application development process is described to point out the strength of the middleware for application developers

A rule based data monitoring middleware for mobile applications

In this article we look at the scenario of mobile nodes, e.g. cars, which are connected to a back-end system and an application running on the mobile back-end system which wants to monitor data of the mobile nodes, e.g. the position data of the cars. There are many options to realize such an application, but we have to take care of the costs and performance of the application, since a cost-intensive mobile link is used. We present a middleware architecture solving the problem described, and an implementation of this rule based data monitoring middleware by minimizing the communication frequency over the mobile link. The implementation is based on the service oriented architecture (SOA), a middleware framework which tries to simplify as much as possible the software architecture of distributed applications. The realization of our middleware and exemplary application uses Web service technologies to be platform and vendor independent. Finally, the rule based middleware is evaluated in respect of the application delay and the application communication costs.