Rainer Ruggaber

Π 2 -- a generic proxy platform for wireless access and mobility in CORBA

Distributed applications in a wireless environment often suffer from sudden connection losses. Furthermore, scarce bandwidth and high error rates may affect data transmission so that traditional Internet protocols like TCP show unwanted behaviour. However, one of todays most popular middleware architectures, namely the Common Object Request Broker Architecture CORBA, is built on top of TCP. Hence, its extension into the wireless and mobile environment has to be carefully designed. This paper introduces &Pgr;2, a proxy platform for CORBA-based applications in the mobile environment that copes with the mentioned problems. It can be transparently integrated into existing distributed systems without changes to clients or servers using a generic interface and dynamic type determination. Furthermore, this platform flexibly provides services for context- and location-aware applications, thus broadening the scope of the CORBA-based middleware.

Using WAP as the enabling technology for CORBA in mobile and wireless environments

CORBA is currently the most popular middleware platform. Due to the progress and acceptance of mobile communications, it is inevitable to offer CORBA services for mobile terminals, especially over a wireless link. The Object Management Group, the standardization body for CORBA, already requested proposals for extending CORBA in the wireless environment, leading to several submissions. However, the standardization process is far from being completed. Therefore, we propose the adaptation of an outstanding approach to supply a range of services in the mobile environment, the Wireless Application Protocol (WAP) framework. In the paper, we show how the CORBA standard and the WAP framework can converge, leading to a comprehensive middleware platform for distributed applications in a wireless and mobile environment.

A transparent network handover for nomadic CORBA users

This paper introduces a generic disconnection handling and network handover mechanism for nomadic CORBA applications. The disconnection handling provides a transparent or explicit mode. In the explicit mode, a special class provided by the user or application is informed if a disconnection occurs and can take appropriate actions. The handover mechanism supports an active handover, where the handover decision is based on application and user needs as well as a passive handover which is needed if after a disconnection the original network is not available. Both mechanisms provide a solution for the lost reply problem occurring if the mobile node is disconnected before the reply to an outstanding request has arrived. The presented mechanisms are integrated into the generic proxy platform /spl Pi//sup 2/. /spl Pi//sup 2/ transparent encapsulates the wireless link and splits the connection between the client on the mobile node and the server into separate parts. /spl Pi//sup 2/ can be transparently integrated into existing distributed systems without changes to clients or servers using a generic interface and dynamic type determination.

Using CORBA applications in nomadic environments

Introduces /spl Pi//sup 2/, a proxy platform for CORBA-based applications in a nomadic environment. Nomadic computing presumes ubiquitous access to network services. An infrastructure providing the framework for nomadic users, therefore, has to support different network technologies and protocols. Wireless access networks offer widespread connectivity to nomadic users. However, distributed applications in a wireless environment often suffer from sudden connection losses, scarce bandwidth and high error rates when using TCP/IP. Hence, /spl Pi//sup 2/ transparently encapsulates the wireless link and splits the connection between the client on the mobile node and the server into separate parts. /spl Pi//sup 2/ can be transparently integrated into existing distributed systems without changes to clients or servers using a generic interface and dynamic type determination. It provides seamless handover between different networks, taking advantage of protocols especially tailored for wireless links, like WAP, and uses compression to reduce the required bandwidth. Furthermore, this platform flexibly provides value-added services for distributed applications like context- and location-awareness or caching, thus broadening the scope of the CORBA-based applications.

Supporting Secure and Transparent Delegation in the CORBA Proxy Platform pi2

π2 is a generic CORBA proxy platform that is used to support applications in mobile and wireless environments. π2 consists of two proxies which are transparently integrated into the application. Due to the broadcast characteristics of wireless communication, mobile users have very high security requirements. Since the CORBA security service as the standard approach for securing CORBA applications does not support the transparent integration of proxies between client and server, we introduce proprietary solutions with end-to-end authentication based on the services of a public-key infrastructure.

A WAP-Based Session Layer Supporting Distributed Applications in Nomadic Environments

Nomadic computing imposes a set of serious problems and new requirements onto middleware platforms supporting distributed applications. Among these are the characteristics of wireless links like sudden and frequent disconnection, long roundtrip times, high bit error rates and small bandwidth. But there are also new requirements like handover support and the necessity to use different networks (bearers). All these problems and requirements lead to the demand for an association between client and server that is independent of a transport connection. In this paper, we present a session layer that provides such an association for the middleware platform CORBA based on the Wireless Application Protocol (WAP) that is especially designed for mobile and wireless devices. It turns out that the session protocol in WAP called WSP is not able to fulfill our requirements, thus, it was necessary to define our own session layer. The session layer provides explicit and implicit mechanisms to suspend and resume a session, a reconnection to the session after the bearer was lost or changed and a solution to the lost reply problem. Furthermore, it contains an interface to be used by session-aware applications to control the presented mechanisms themselves on a fine-grained level. This paper presents a detailed description of the session layer, its integration into CORBA, a mapping of GIOP messages onto WTP and selected implementation details

∏2: Unterstützung mobiler und drahtlos angebundener Teilnehmer in verteilten CORBA-Architekturen

Die hier vorgestellte Proxyplattform II2 hat zum Ziel mehrere unabhangigen Entwicklungen zu vereinen und effizient zu unterstutzen: kurzere Time-to-Market-Zyklen, die zu einer starkeren Verzahnung und Integration von Anwendungen, Prozessen und Daten fuhren hohe Anforderungen an die Mobilitat von Mitarbeitern, die zu jeder Zeit und an jedem Ort Zugriff auf Unternehmensanwendungen und -daten benotigen heterogene drahtlose Zugangsnetze, die im lokalen Bereich sehr leistungsfahig sind, im Weitverkehrsbereich mit GSM jedoch nur eine geringe Leistungsfahigkeit aufweisen

Flexible Vermittlung von skalierbaren Dienstobjekten in verteilten Systemen

Die zunehmende arbeitsteilige Integration zwischen weitraumig verteilten Anwendungen bei gleichzeitiger Partitionierung zuvor monolithischer Anwendungen in feingranularere (Dienst-)-Objekte erfordert eine systemtechnische Unterstutzung, um zur Laufzeit flexibel das jeweils benotigte Dienstobjekt zu ermitteln und darauf zuzugreifen. Diese Flexibilitat wird in verteilten Systemen durch eine Vermittlungsschicht auf Basis verteilter Trading-Dienste bereitgestellt. Der Nachteil dieses Ansatzes liegt in seiner Beschrankung auf die Vermittlung von Objektreferenzen. In dem folgenden Artikel wird ein in Java realisierter erweiterter Trading-Ansatz vorgestellt, der neben der Referenz zudem den Objektzustand und die Implementierung vermittelt und damit eine flexible Erstellung verteilter Anwendungen unterstutzt.