1. Chained Negotiation for Distributed Notification Services
Richard Lawley, Michael Luck and Luc Moreau
Intelligence, Agents, Multimedia Group
School of Electronics & Computer Science
University of Southampton

2. Chained Negotiation for Distributed Notification Services
Outline
Introduction
Notification Services
Negotiation
Chained Negotiation
Evaluation of Negotiation Engine
Future Work & Conclusion
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Chained Negotiation for Distributed Notification Services

3. Chained Negotiation for Distributed Notification Services
Introduction
Notification services (NSs) provide asynchronous communication between services in distributed environment
Consumers and providers may conflict over delivery preferences (QoS)
Negotiation enables mutually acceptable QoS levels to be found
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Chained Negotiation for Distributed Notification Services

4. Chained Negotiation for Distributed Notification Services
Introduction
Previous work introduced automated service-oriented negotiation engine suitable for use with notification service
Distributed notification services require different kind of negotiation
Chained negotiation supports reselling or redistribution of existing services
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Chained Negotiation for Distributed Notification Services

5. Notification Services (1)
Message-oriented middleware layer using publish-subscribe model
Publishers publish information on a topic
Consumers subscribe to that topic
Notifications are delivered by NS to consumer
Can process notifications before sending
Filtered notifications
Notifications combined into a digest
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Chained Negotiation for Distributed Notification Services

6. Notification Services (2)
Example notification topics:
Changes in database content
Release of new tools or services
Change in workflow execution state
Many existing notification services
MSMQ, MQSeries, Grid Monitoring Architecture, NaradaBrokering
Negotiation not supported
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Chained Negotiation for Distributed Notification Services

7. Distributed Notification Services
Centralised NSs leads to scaling problem
Overloaded with many consumers
Single point of failure
Distributed NS allows loads to be spread and effect of failure to be reduced
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Chained Negotiation for Distributed Notification Services

8. Distributed Notification Services
Consumers & publishers connect to different NS
Enables notifications to be redistributed
Less bandwidth used
Consumers use local NS instead of remote
NS1
NS2 P2 C1
Publisher
Notification Service C2 P1
NS3
Consumer
NS4
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Chained Negotiation for Distributed Notification Services

9. Chained Negotiation for Distributed Notification Services
myGrid
e-Science project aimed at Bioinformatics
Allows workflow-based in-silico experiments
Automated workflow management through personalisation, notification of change and publication of experiments
Increasing focus on data-intensive bioinformatics
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Chained Negotiation for Distributed Notification Services

10. myGrid Notification Service
JMS-based notification service
Persistent message delivery model
Push/Pull subscribers
Supports federated topics
Topics at each NS are part of a virtual topic
Consumer subscribing to virtual topic receives notifications from all member topics
Uses service directory for virtual topic data
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Chained Negotiation for Distributed Notification Services

11. Chained Negotiation for Distributed Notification Services
QoS in Distributed NS
Consumers still want to request QoS levels in a distributed NS
If QoS requests are simply granted, can’t redistribute notifications
Some form of negotiation needed to find acceptable levels of QoS
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Chained Negotiation for Distributed Notification Services

12. Chained Negotiation for Distributed Notification Services
“The process by which two or more parties exchange proposals in order to reach a mutually acceptable agreement on a particular matter”
Components of negotiation
Item – the object under negotiation
Terms – attributes of item under negotiation
Proposals – set of values suggested by one party
Preferences – values acceptable to a party
Utility functions – a method of evaluating the utility of a particular proposal
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Chained Negotiation for Distributed Notification Services

13. Chained Negotiation for Distributed Notification Services
Negotiation formally described as:
Negotiation Protocols – Rules governing a negotiation
Types of participants
Valid negotiation states & actions
Negotiation Strategies – How participants behave within protocol
Proposal Generation
When to accept a proposal
Specification of negotiation enables automated negotiation to take place
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Chained Negotiation for Distributed Notification Services

14. Chained Negotiation for Distributed Notification Services
Conventional negotiation (direct) involves negotiation between client and supplier
Chained negotiation involves middlemen between supplier and client
Enables reselling or redistribution
Made up of multiple subnegotiations
Item can be supplied by supplier or middlemen
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Chained Negotiation for Distributed Notification Services

15. Chained Negotiation for Distributed Notification Services
Middlemen choose which sub-negotiation to proceed with at each step
Upstream = away from client
Downstream = towards client
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Chained Negotiation for Distributed Notification Services

16. Chained Negotiation Protocol
Rule: “Proposals may be sent upstream only if there is time for the reply to get back to the client”
Messages contain distance of sender from client
Rule: “NC cannot confirm downstream without having a commitment in place upstream”
Prevents consumers committing to something unavailable
Propose, Accept, Confirm-Accept messages
Enables getting everyone “prepared to accept”
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Chained Negotiation for Distributed Notification Services

17. Chained Negotiation for Distributed Notification Services
Proximity function determines whether one proposal is satisfiable by another
Used to find suitable existing commitments
Actions created each time proposal received
Selecting existing commitments
Passing across proposal
Scoring functions choose best action
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Chained Negotiation for Distributed Notification Services

18. Chained Negotiation for Distributed Notification Services
Scoring functions used
Proximity – how close is the proposal in each action to the last received proposal?
Acceptable? – would this action directly lead to an acceptable state?
Favour least used – if the previous few rounds have resulted in upstream negotiation, this favours downstream more
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Chained Negotiation for Distributed Notification Services

19. Chained Negotiation Evaluation
Evaluate different types of negotiation
Direct (client – supplier)
Forwarded (middleman forwards proposals)
Chained (middlemen uses existing commitments)
Experiment setup similar to evaluation of previous negotiation engine
Common interval-based time model
Only time-dependent tactics used
Single tactics used for proposal generation
Only client utility considered
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Chained Negotiation for Distributed Notification Services

20. Chained Negotiation for Distributed Notification Services
Variable Deadline
“What effect does varying the deadline have on utility and success rate?”
Vary deadline (1-100 messages).
Measure utility and success rate for different types of negotiation
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Chained Negotiation for Distributed Notification Services

21. Chained Negotiation for Distributed Notification Services
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Chained Negotiation for Distributed Notification Services

22. Chained Negotiation for Distributed Notification Services
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Chained Negotiation for Distributed Notification Services

23. Chained Negotiation for Distributed Notification Services
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Chained Negotiation for Distributed Notification Services

24. Chained Negotiation for Distributed Notification Services
Variable Deadline
Problem with “spikes”
Client doesn’t know distance from supplier
Final concession not reaching destination
Failed negotiation
Predictable troughs
2n(m + 1) – 1
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Chained Negotiation for Distributed Notification Services

25. Variable Negotiation Terms
Easy to match to existing commitment when using a single term
All terms in a proposal need to match commitment in order to reuse it
Increase number of terms and measure success rate for each type of negotiation
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Chained Negotiation for Distributed Notification Services

26. Chained Negotiation for Distributed Notification Services
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Chained Negotiation for Distributed Notification Services

27. Chained Negotiation for Distributed Notification Services
Supplier Capacity
Multiple connected middlemen
Clients spread between them
Compared to negotiating with publisher’s NS M M M M M S S C S C S C S C S C
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Chained Negotiation for Distributed Notification Services

28. Chained Negotiation for Distributed Notification Services
Supplier Capacity
Most chained negotiations satisfied by existing commitment (<5% direct)
Load on supplier greatly reduced
Negotiations more successful and better utility when using chained negotiation
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Chained Negotiation for Distributed Notification Services

29. Chained Negotiation for Distributed Notification Services
Future Work
Reduce impact of deadline problem
Integrate with myGrid Notification Service
Use myGrid Notification Service to provide better performance in some test cases
Alternate interaction patterns between NSs?
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Chained Negotiation for Distributed Notification Services

30. Chained Negotiation for Distributed Notification Services
Conclusion
Distributed negotiation services need a new type of negotiation to select QoS levels
Better success rate & client utility can be obtained by reusing existing commitments
Benefits of chained negotiation decrease with larger numbers of terms
Chained negotiation suffers from a periodic poor result with certain values for the deadline
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Chained Negotiation for Distributed Notification Services

31. Chained Negotiation for Distributed Notification Services
Questions?
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Chained Negotiation for Distributed Notification Services