Andreas Zeidler

A peer-to-peer approach to content-based publish/subscribe

Publish/subscribe systems are successfully used to decouple distributed applications. However, their efficiency is closely tied to the topology of the underlying network, the design of which has been neglected. Peer-to-peer network topologies can offer inherently bounded delivery depth, load sharing, and self-organisation. In this paper, we present a content-based publish/subscribe system routed over a peer-to-peer topology graph. The implications of combining these approaches are explored and a particular implementation using elements from Rebeca and Chord is proven correct.

Supporting mobility in content-based publish/subscribe middleware

Publish/subscribe (pub/sub) is considered a valuable middleware architecture that proliferates loose coupling and leverages reconfigurability and evolution. Up to now, existing pub/sub middleware was optimized for static systems where users as well as the underlying system structure were rather fixed. We study the question whether existing pub/sub middleware can be extended to support mobile and location-dependent applications. We first analyze the requirements of such applications and distinguish two orthogonal forms of mobility: the system-centric physical mobility and an application-centric logical mobility (where users are aware that they are changing location). We introduce location-dependent subscriptions as a suitable means to exploit the power of the event-based paradigm in mobile applications. Briefly spoken, location-dependency refines a subscription to accept only events related to a mobile users current location. Implementations for both forms of mobility are presented within the content-based pub/sub middleware Rebeca, drawing from its refined routing capabilities (namely, covering and merging).

Looking into the past: enhancing mobile publish/subscribe middleware

Publish/subscribe (pub/sub) middleware facilitates loosely coupled cooperation and fits well the needs of spontaneous, ad-hoc interaction. However, newly started mobile applications have to be bootstrapped to interpret the current flow of notifications correctly and commence normal operation. This problem is aggravated in mobile environments where disconnections and context changes occur frequently.In this paper, we propose two forms of subscriptions that allow consumers to subscribe to past events to improve the bootstrapping process. The first form uses logical mobility to harness possible client movements and subscribe in future locations to bootstrap virtual counterparts before the application needs the data. The second form is based on buffers and offers a way to integrate data repositories distributed in the network.

Mobility support with REBECA

Publish/subscribe (pub/sub) proliferates loose coupling and is touted to facilitate mobility. The inherent loose coupling even allows existing applications to be transferred to mobile environments, if an appropriate infrastructure support is available. However existing pub/sub middleware are mostly optimized for static systems where users as well as the underlying system structure is rather fixed. In this paper we analyze the necessary steps to support mobile clients with publish/subscribe middleware. The REBECA content-based pub/sub service is extended to accommodate to physically mobile clients, offering a location transparent access to the middleware without degrading the previously guaranteed quality of service. The transparent access allows existing applications to be seamlessly transferred from a static to a mobile scenario without having to adapt client applications.

A Framework for the Integration of Legacy Devices into a Jini Management Federation

The administration of heterogeneous networks with many devices is a tedious and time-consuming task. Todays approaches only provide static configuration files and make the addition and removal of devices a manual chore. In this paper we present a framework for the integration of legacy devices based on Jini, Sun Microsystems new technology for federating network devices and services. We introduce extended proxy objects called nannies that take care of non-Jini-enabled devices and handle the relevant management events, guide a device through bootstrapping, register it with the lookup service, and provide the implementation of the administrative interfaces of the Jini API. Through this approach both Jini-enabled and legacy devices can be handled homogeneously in a Jini Management Federation.

A Jini-based Gateway Architecture for Mobile Devices

In the near future we expect a widespread deployment of mobile computational resources including network-enabled end devices like Laptops and PDAs. An interesting problem then and today is the transparent change of locality. Traditionally several manual actions are necessary to reconfigure the device and to rebind client-applications to services available in the host network. This paper presents the architecture of a Jini-based Application Level Gateway (ALGW) which avoids manual reconfiguration of a mobile device every time the user changes the host network. To do so, the ALGW makes use of key technologies provided by Jini. Jini is used for dynamic looking up and binding to services needed by the user and located in the host network. Moreover, Jini can be used for value-added services like our authenticating SMTP-Service.