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Agents & Mobile Agents

Agents & Mobile Agents

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Agents & Mobile Agents

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  1. Agents & Mobile Agents

  2. Agents • An agent is anything that can be viewed as perceiving its environment through sensors and acting upon that environment through actuators • Human agent: eyes, ears, and other organs for sensors; hands, • legs, mouth, and other body parts for actuators • Robotic agent: cameras and infrared range finders for sensors; • various motors for actuators

  3. Agents and environments The agentfunction maps from percept histories to actions: [f: P* A] The agentprogram runs on the physical architecture to produce f agent = architecture + program

  4. Vacuum-cleaner world Percepts: location and contents, e.g., [A,Dirty] Actions: Left, Right, Suck, NoOp

  5. Agents - what are they?

  6. Objects and Agents – An Analogy • Objects encapsulate state, Agents encapsulate state + execution behaviour • Objects have no control over the execution of methods • Invocation of method m on object o – involuntary – whether object o likes it or not

  7. Objects and Agents – An Analogy • Agents have control of whether or not to perform any given action • Request actions rather than invoke methods

  8. Microsoft Agent • persons Microsoft Agent

  9. Basic Definitions

  10. Rational agents An agent should strive to "do the right thing", based on what it can perceive and the actions it can perform. The right action is the one that will cause the agent to be most successful Performance measure: An objective criterion for success of an agent's behavior E.g., performance measure of a vacuum-cleaner agent could be amount of dirt cleaned up, amount of time taken, amount of electricity consumed, amount of noise generated, etc.

  11. Simple reflex agents

  12. Agents - Applications many due to: agent research spans disciplines: artificial intelligence, distributed computing, software engineering (ABSE), sociology, psychology, economics, object-oriented systems, artificial life, game theory, ... a sampling...

  13. What is a Mobile Agent ?

  14. What is a Mobile Agent ? • Software program • Moves from machine to machine under its own control…. • Suspend execution at any point in time, transport itself to a new machine and resume execution • Once created, a mobile agent autonomously decides which locations to visit and what instructions to perform • Continuous interaction with the agent’s originating source is not required • HOW? • Implicitly specified through the agent code • Specified through a run-time modifiable itinerary

  15. Mobile Agent • Derives from AI and distributed systems • Agent that migrates under its own control in a heterogeneous environment • Mobility can be • Strong: move code with current execution state • Weak: move only code Agent Server Client Server

  16. Evolution • BOTTOMLINE: Mobile Agents are a distributed computing paradigm • End point in the incremental evolution of mobile abstractions such as mobile code, mobile objects, mobile processes. • Mobile Code – transfers code • Mobile Object – transfers code + data • Mobile Process – transfers code + data + thread state • Mobile Agent – transfers code + data + thread + authority of its owner

  17. Inter-Agent Message Passing- Requirements • Efficiency • Low location updating overhead • Low message delivery overhead • Asynchrony • Asynchronous execution • Little constraint on the mobile agent mobility. • Adaptability • Suit different Communication and Migration Pattern

  18. Inter-Agent Message Passing- Requirements • Location Transparency • Message sender does not need to know the physical location of the receiver agent, whose address changes frequently by moving from one host to another. • Reliability • The concurrent and asynchronous nature of message forwarding and agent migration may cause message loss or chasing problem. • By reliability we mean the message can reach the target agent by a bounded number of forwarding.

  19. SERVER Mobile Agent Service network CLIENT RPC Vs Mobile Agents • Mobile Agents • Instead of calling a procedure, supply the procedure as well • Messages: Mobile Agent ( procedure + data + state) • “Sending” computer may have begun the procedure and the receiving computer will continue the procedure • On-going interaction, but NO on-going communication

  20. Applets, Servlets and Mobile Agents • Applet – Downloaded from server to client • Servlet – Uploaded from client to server • Mobile Agents – Detached from client, can have multiple hops

  21. Advantages of the Mobile Agent Paradigm • reduce bandwidth consumption and network loads • allow dynamic deployment of application components to arbitrary network sites • encapsulate protocols • execute asynchronously and autonomously • can adapt by moving • run on heterogeneous platforms • most distributed applications fit naturally into the mobile agent model • intuitively suitable for mobile users and disconnected operations • Mobile agents combine the strengths of techniques such as RPC, java applets etc. into a single, convenient framework

  22. Levels of Mobility • Weak Mobility • When moving a mobile agent carries code + data state • On moving, execution has to start from the beginning

  23. Levels of Mobility • Strong Mobility • When moving a mobile agent carries code + data state + execution state • Execution State – local variables and threads • On moving, execution can continue from the point it stopped on the previous host


  25. Design of ARP (Adaptive and Reliable Protocol) • Mobile IP solution • Extention1: Mobile IP + Synchronization • Extension2: Distributed Home Scheme • Extension3: Mailbox-Based Scheme = ARP

  26. Reg Mobile IP Solution MAP MAP-Home MAP MAP

  27. Design of ARP • Mobile IP solution • No Reliability Support • Extention1: Mobile IP +Synchronization • The agent home coordinates message passing and agent migration • Extension2: Distributed Home Scheme • Extension3: Mailbox-Based Scheme = ARP

  28. ACK Reg Dereg Mobile IP + Synchronization MAP MAP-Home MAP MAP

  29. ACK Reg Dereg Mobile IP + Synchronization MAP MAP-Home MAP MAP

  30. Caching Mechanism MAP-1 MAP-2 MAP-3

  31. Properties of ARP • Location Transparency • Home + Caching Mechanism • Reliability • Synchronization is used • Asynchronous Migration • Adaptability • Mobile IP + Synchronization • Distributed Home Scheme • Efficiency

  32. IBM’s Aglet Toolkit • An Applet-like programming model for mobile agents • Java (as many mobile agent toolkits are! ) • Aglet = Agent + Applet • Aglet’s API facilitates mobile technology • Aglet:mobile java object that visits aglet enabled hosts in a computer network • An Aglet = Instance of a Java class extending the Aglet Class

  33. IBM’s Aglet Toolkit • An Aglet =Aglet state (values in variables) + Aglet code (class implementation) • Autonomous – runs its own thread after arriving at a host • Reactive – responds to incoming messages • Weak Mobility

  34. Thank you for lessening