1. vs. Object-Process Methodology Written by Linder Tanya Rubinshtein Leena Nazaredko Anton Research Report Work Flow Management System

2. AgendaAgenda  Presenting the problem  Solution  Main idea  Technologies  Concepts  Example by Group Instant Messaging System

3. Presenting the Problem  Dependency on single central server  Low fault tolerance  Unsuitable for critical business systems  A possible solution for such a Fault tolerant system could be an Ad-hoc solution.

4. Solution – Main Idea  Generic API that will handle all replication issues

5. Solution – Technologies Means for providing multi-point to multi-point communication, by organizing processes in groups. Group Communication: Group Communication provides:  Group membership and dissemination of messages  Reliability and ordering of messages

6. Solution – Technologies cont’d  Is one of the implementations of the GC concepts. SPREAD:  In local area network settings, can handle over 8,000 1Kbytes messages a second  Reliable multicast from any number of senders to lots of receivers.  Scalable group services that allow thousands of active groups.

7. Solution Concepts – System State Solution Concepts – System State Intelligent Data Structure which holds all critical system information (that is to be shared)

8. Solution Concepts – State Machine Replication Solution Concepts – State Machine Replication  The system state is replicated at several sites  The operations which access the service state  Delivered in the same total order  Delivered without gaps at each site  Thus the replica states are kept consistent.  This is achieved by using SPREAD toolkit.

9. Solution Concepts – System State cont’d Solution Concepts – System State cont’d  Applies changes  Divides itself to small parts  Combines itself from small parts  Can be extended to answer different applications needs Features: Intelligent Data Structure which holds all critical system information (that is to be shared)

10. Solution Concepts – Master Server Solution Concepts – Master Server Deterministically elected server within a group which is responsible of supporting servers’ join features  Transfer system state to a new server  Get elected Responsibilities:

11. Solution Concepts – State Transfer Protocol Solution Concepts – State Transfer Protocol SPREAD Server AServer BMaster Server New Server

12. Solution Concepts – State Transfer Protocol Solution Concepts – State Transfer Protocol SPREAD Server AServer BMaster Server New Server

14. Top Level

15. GIM – Fault Tolerance Server side:  Group Host Server One for each of the client groups  Host Server failure  Distribution of fallen server responsibilities  Dynamic IP for Master Server Client side:

16. ResourcesResources  “Secure Group Communication Using Robust Contributory Key Agreement” by Yair Amir, Yongdae Kim, Cristina Nita-Rotaru, John Schultz, Jonathan Stanton and Gene Tsudik  “Group Communication” by Idit Keidar