Distributed Mobile Event Systems

1
Distributed Mobile Event Systems

• Sasu Tarkoma
• 30.11.2004
• MiNEMA Workshop

2
Contents

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

3
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

4
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

5
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

6
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

7
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
Event Domain C
TOPOLOGY UPDATE
AC
AC
3. Handover between domains (terminal-mobility)
Event Domain B
Desktop
AC
AC
4. End-point-change (different access server)
AC
8
Demonstration at WMCSA 2004
9
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

10
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 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.