Survey
* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project
Download slides
Document related concepts
no text concepts found
Transcript
Distributed Mobile Event Systems Sasu Tarkoma 30.11.2004 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 1. End-point change to mobile (User-mobility) 2. Access server handover (terminal-mobility) AC AC Desktop AC AC AC Event Domain A AC 3. Handover between domains (terminalmobility) Event Domain C TOPOLOGY UPDATE Event Domain B AC Desktop AC AC AC 4. End-pointchange (different access server) 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 105-110. • Sasu Tarkoma. Event Dissemination Service for Pervasive Computing. Pervasive 2004 Doctoral Colloquium, 18-19.4. 2004 Linz/Vienna, Austria. • Sasu Tarkoma and Jaakko Kangasharju. A Data Structure for Contentbased Routing. Accepted for publication in the IASTED International Conference on INTERNET AND MULTIMEDIA SYSTEMS AND APPLICATIONS (EuroIMSA 2005), February 21-23, 2005, Grindelwald, Switzerland.
