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Group Communication Service

Group Communication Service. by Abhijeet Dharmapurikar Jesse Greenwald Sapna Gumidyala Shashidhar Rampally Varsha Mahadevan. Introduction. What is a Group Communication Service? Why do we need a Group Communication Service? Sample Applications Data Replication Process Groups.

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Group Communication Service

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  1. Group Communication Service by Abhijeet Dharmapurikar Jesse Greenwald Sapna Gumidyala Shashidhar Rampally Varsha Mahadevan

  2. Introduction • What is a Group Communication Service? • Why do we need a Group Communication Service? • Sample Applications • Data Replication • Process Groups

  3. Introduction (contd) • Existing Group Communication Services • Java Groups • Spread • Configurable protocol stack used by Java Groups • Scope for utilization of application specific information

  4. Our Group Communication Service • Using application specific information • Message Types • Message Patterns • Finding best-fit protocol stack for the above application • Optimization of number of messages

  5. Illustrative Examples • Tele-teaching Application • Card Game Application

  6. Tele-Teaching Application <protocol> <roles> <role name="Student" min="1" max="n"/> <role name="Teacher" min="1" max="1"/> </roles> <message-types> <message-type name="Question"/> <message-type name="Answer"/> <message-type name="Formula"/> <message-type name="Doubt"/> <message-type name="TeacherAnswer"/> </message-types> . . . </protocol>

  7. Tele-Teaching Application (contd) <message-patterns> <pattern> <query type="Question" role="Teacher" receiver="Student" min="1" max="1"/> <response type="Answer" role="Student” receiver="Teacher" min="0" max="#Student" timeout="60s"/> </pattern> <pattern> <query type="Formula” min="1" max="1"/> <response type="Doubt" min="0" max="#Student" timeout="120s"/> </pattern> </message-patterns>

  8. Card Game Application <protocol> <roles> <role name="Player1" min="1" max="1"/> <role name="Player2" min="1" max="1"/> <role name="Player3" min="1" max="1"/> <role name="Player4" min="1" max="1"/> </roles> <message-types> <message-type name="Play"/> </message-types> . . . </protocol>

  9. Card Game Application (contd) <message-patterns> <pattern> <message type="Play" role="Player1" min="1" max="1” receiver="Player1,Player2,Player3,Player4"/> <message type="Play" role="Player2" min="1" max="1” receiver="Player1,Player2,Player3,Player4"/> <message type="Play" role="Player3" min="1" max="1” receiver="Player1,Player2,Player3,Player4"/> <message type="Play" role="Player4" min="1" max="1” receiver="Player1,Player2,Player3,Player4"/> </pattern> </message-patterns>

  10. Related Concepts • Proactive Messages • Reactive Messages

  11. System Design Application Protocol Group Membership Protocol Correlation Protocol Ordering Protocol Filtering Protocol Event Service

  12. Message Send Sequence Diagram

  13. Group Manager Clients

  14. System Design Application Protocol Group Membership Protocol Correlation Protocol Ordering Protocol Filtering Protocol Event Service

  15. CORBA • Common Object Request Broker Arch. • Object Management Group (OMG) • Defines IDL Language • Defines the API for ORB

  16. Object Services • Name Service • Event Service • Notification Service • Time Service • Transaction Service • Persistent State Service

  17. Event Service Supplier Supplier Supplier Event Channel Consumer Consumer

  18. Push Communication Model Push Supplier Push Consumer Initiative I wish to decide when the data is to be sent Just call my method whenever you have data for me DATA

  19. Pull Communication Model Pull Supplier Pull Supplier Initiative I wish to decide when to go for data Just call my method whenever you want data DATA

  20. System Design Application Protocol Group Membership Protocol Correlation Protocol Ordering Protocol Filtering Protocol Event Service

  21. Filtering Protocol • Filters based on • Message Type • Destination • Operates in two modes • JOIN_MODE • ONLINE_MODE

  22. Filtering Protocol cond.. JOIN_MODE:  Allows only JOIN_GROUP messages  Allows only UpdatedView messages ONLINE_MODE:  Allows all the messages  Allows all messages except the messages to which its not a destination.

  23. System Design Application Protocol Group Membership Protocol Correlation Protocol Ordering Protocol Filtering Protocol Event Service

  24. struct Message { long messageId; long source; long destination; string message; char messageType; boolean isProactive; }; struct SequenceMessage { long messageId; long source; long destination; long sequenceId; }; Message Format

  25. Ordering Protocol • Sequencer based algorithm • Send broadcast message to all the members in the group and the sequencer • Sequencer assigns ids to these broadcast messages in a strictly increasing order • Member delivers the broadcast messages in the increasing order of sequencer ids

  26. System Design Application Protocol Group Membership Protocol Correlation Protocol Ordering Protocol Filtering Protocol Event Service

  27. Correlation Protocol • Buffered ordering of reactive messages with respect to proactive messages • Tele-Teaching Example • Question (proactive message) • Answer (reactive message)

  28. Correlator • Handles relationship between messages • Could be imagined as a smart tree-structured buffer • Patterns X –Y5 - Z2

  29. z Y z z Y z z Y X z z Y z z Y z

  30. System Design Application Protocol Group Membership Protocol Correlation Protocol Ordering Protocol Filtering Protocol Event Service

  31. Group Membership Roles • Roles for the membership protocol • Groups Administrator • Group Manager • Member • Related Concept • View

  32. Groups Administrative Class

  33. struct JoinGroup { long member; }; struct LeaveGroup { long member; }; struct UpdateView { long messageId; long source; viewSeq view; }; Membership Message Formats

  34. Group Membership Protocol NM M1 M2 M3 GManager GM GM GM GM JoinGroup UpdateView UpdateView UpdateView Event Channel

  35. Configurable Protocol Stack (1) DownQueue UpHandler DownHandler Protocol 1 UpQueue DownQueue UpHandler DownHandler Protocol 2 UpQueue

  36. Configurable Protocol Stack (2)

  37. Configurable Protocol Stack (3)

  38. Optimizations • Save round trip to sequencer for reactive messages • Tele-Teaching example • Card Game example • Selective build of required layers in the protocol stack

  39. Group Communication Issues • One channel per group concept • Atomicity of broadcast messages • Ordering of membership messages with respect to broadcast messages • Implicit notion of proactive membership messages • Support for uni-cast communication

  40. Conclusion • Possible extensions • Cross Group Communication • Fault-Tolerance issues • Group State Management

  41. References • Lecture Notes • http://www.cis.ksu.edu/~singh/CIS825/F02/cis825.html • Java Groups • http://www.cs.cornell.edu/Info/Projects/JavaGroupsNew/ • Event Service Specification • http://cgi.omg.org/docs/formal/01-03-01.pdf

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