Distributed Mobile Event Systems Sasu Tarkoma MiNEMA Workshop

Contents Introduction –Motivation, Challenges Mobile Event Systems Fuego Event Service –Content-based Routing –Mobility support Conclusions

Introduction Event-based systems are a good candidate for mobile and wireless environments –Asynchronous, anonymous one-to-many communication –Expressive semantics with filters Content-based routing and addressing –Primitives: adv, unadv, sub, unsub, pub Subscription-semantics –Subscriptions are propagated throughout the system, notifications are sent on the reverse path Advertisement-semantics –Advertisements are propagated throughout the system, subscriptions on the reverse path, notifications on the reverse path of subscriptions

Challenges How to cope with mobile users? –Disconnected operation Buffering and queue management –Mobile subscribers / producers Handover protocol for relocating subscriptions and updating the topology Multiple indirection points How to manage large numbers of filters? –Covering relations, filter merging –Efficient routing algorithms are needed General requirements –fast convergence of the subscription topology –mobility-safety: no false negatives and positives

Mobility-aware Systems Recently, mobility protocols and extensions have been proposed for different pub/sub systems: Trivial solution is to used flooding (topology update) Jedi –Hierarchical topology, move-in and move-out commands, mobility not main focus Elvin –Centralized proxy for supporting disconnected operation, no roaming between proxies Siena –Generic mobility service on top of the pub/sub layer –Relies on ping/pong synchronization and has a high cost in terms of latency and exchanged messages Rebeca –Acyclic graph topology with advertisements

Fuego Event System Scalable distributed event framework for mobile computing The Fuego event router consists of two parts: –access server functionality with buffering and handover support for mobile clients, and –extensible routing core for distributed operation New data structures for efficient content-based routing: –poset (partially ordered set)-derived forest –weakly merging forest –the forest is considerably more efficient than dag (directed acyclic graph) - based structures Rendezvous-based mobility support for fast handovers and subscription topology updates –RP or paths to RP are updated instead of the whole topology

Mobility Architecture AC 4. End-point- change (different access server) 3. Handover between domains (terminal- mobility) 2. Access server handover (terminal-mobility) Event Domain A Event Domain B Event Domain C Desktop 1. End-point change to mobile (User-mobility) Desktop AC TOPOLOGY UPDATE

Demonstration at WMCSA 2004

Conclusions In order to develop flexible systems we have divided the event router into two parts: access part and the routing part –A router may support several routing and mobility protocols The topology update and synchronization between access servers is costly in pub/sub mobility We propose a rendezvous-based mobility protocol –Rendezvous points may be updated efficiently –It is possible to leverage overlay systems, such as Hermes, for scalability Efficient algorithms are crucial for content-based routing –The poset-derived forest and variants, filter merging Future and current work: federation, load balancing

Related Publications Sasu Tarkoma, Jaakko Kangasharju, Kimmo Raatikainen. Client Mobility in Rendezvous-Notify. International Workshop for Distributed Event-Based Systems (DEBS03), in conjunction with the ACM SIGMOD/PODS Conference, San Diego. Available at ACM Digital Library. Sasu Tarkoma. Distributed Event Dissemination for Ubiquitous Agents. Proceedings of the 10th ISPE International Conference on Concurrent Engineering (CE-2003), Madeira, Portugal. Pages Sasu Tarkoma. Event Dissemination Service for Pervasive Computing. Pervasive 2004 Doctoral Colloquium, Linz/Vienna, Austria. Sasu Tarkoma and Jaakko Kangasharju. A Data Structure for Content- based Routing. Accepted for publication in the IASTED International Conference on INTERNET AND MULTIMEDIA SYSTEMS AND APPLICATIONS (EuroIMSA 2005), February 21-23, 2005, Grindelwald, Switzerland.