A WAP-Based Session Layer Supporting Distributed Applications in Nomadic Environments
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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
KeywordsTerminal Mobility Transport Protocol Object Management Group Common Object Request Broker Architecture Object Request Broker
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