This paper presents the first quantitative evaluation of the role of routing computations on performance when mobility is introduced to a content-based routing network. Additionally, the paper identifies the factors that affect the performance of a distributed publish/subscribe architecture supporting mobile publishers, formalizes publisher mobility protocols for distributed publish/subscribe systems, and develops and evaluates protocols that reduce the costs associated with supporting mobile publishers in publish/subscribe systems. Our results show that ignoring route computation time paints a false picture of the scalability of content-based routing networks, but that with appropriate protocols the adverse effects can be mitigated.

The publish/subscribe model of communication provides sender/receiver decoupling and selective information dissemination that is appropriate for mobile environments characterized by scarce resources and a lack of fixed infrastructure. We propose and evaluate three content-based routing protocols: CBR is an adaptation of existing distributed publish/subscribe protocols for wired networks, FT-CBR extends CBR to provide fault-tolerance, and RAFT-CBR provides both fault-tolerance and reliability. Using network simulations we analyze the applicability and test the tradeoffs of these algorithms. We show that RAFT-CBR can guarantee 100% delivery to small groups, at the expense of transmission delay. CBR, with a low message overhead and low delay, is more suitable for larger groups at the expense of reliability. FT-CBR provides comparable delivery rates to RAFT-CBR, as well as low delay, at the expense of increased message cost.

RDF is increasingly being used to represent metadata. RDF Site Summary (RSS) is an application of RDF on the Web that has considerably grown in popularity. However, the way RSS systems operate today does not scale well. In this paper we introduce G-ToPSS, a scalable publish/subscribe system for selective information dissemination. G-ToPSS is particularly well suited for applications that deal with large-volume content distribution from diverse sources. RSS is an instance of the content distribution problem. G-ToPSS allows use of ontology as a way to provide additional information about the data. Furthermore, in this paper we show how G-ToPSS can support RDFS class taxonomies. We have implemented and experimentally evaluated G-ToPSS and we provide results in the paper demonstrating its scalability compared to alternatives.

The decoupling of producers and consumers in time and space in the publish/subscribe paradigm lends itself well to the support of mobile users who roam about the environment and have intermittent network connectivity. This paper identifies the factors that affect the performance of a distributed publish/subscribe architecture supporting mobility; formalizes mobility algorithms for distributed publish/subscribe systems and develops and evaluates optimizations that reduce the costs associated with supporting mobility in publish/subscribe systems. In our analysis, we focus on the "unicast" traffic generated to support mobile users, as opposed to the regular "multicast" traffic used for event dissemination to stationary clients. We find that the network capacity must be doubled to handle the extra load of just 10% of mobile users.