Agents & Mobile Agents

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

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

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

Agents - what are they?

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

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

Microsoft Agent persons Microsoft Agent

Basic Definitions

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.

Simple reflex agents

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... 12

What is a Mobile Agent ?

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

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

Evolution Mobile Agent – transfers 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

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

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.

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 Requests include data which are sent as arguments to the procedure Responses include data which are sent as results Protocol for communication : which procedures are remotely accessible, the types of arguments and results CLIENT SERVER network Mobile Agent Service

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

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

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

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

MAP ? MAP MAP MAP

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

Mobile IP Solution MAP MAP-Home Reg MAP MAP

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

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

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

Caching Mechanism MAP-1 MAP-2 MAP-3

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

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

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

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