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Mobile Agents
An Introduction with Examples in Java


Prof. David Bernstein
James Madison University

Computer Science Department
bernstdh@jmu.edu

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Definitions
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  • In General:
    • People disagree about the definition of the term "agent" and the definition of the term "mobile agent"
  • For Our Purposes:
    • A mobile agent is an object that has the ability to move from host to host and execute one or more operations on each host
RMI vs. Mobile Agents
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  • Remote Method Invocation:
    • An object on one host requests that an object on another host perform some operation
  • Mobile Agents:
    • The object itself moves from one host to another (i.e., the code to be executed moves between the hosts)
The Process
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A UML Sequence Diagram

images/mobile_agent_sequence.gif
Minimal Requirements for Mobile Agents
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  • Serialization:
    • To be able to freeze an object it, transmit it, and unfreeze it
  • A Class Loader:
    • To be able to load the code required by an object
A Simple Implementation - States
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  • An agent starts out in the NewAgent state
  • After being initialized, it moves into the BeforeDeparting state (and executes a series of operations on its "home" host)
  • It then moves to another host and enters the Arrived state (which can happen any number of times)
  • When it runs out of hosts to visit it moves to its "home" host and enters the ReturnedHome state
A Simple Implementation - States (cont.)
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images/mobile_agent_states.gif
A Sandbox for Mobile Agents
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Using a Variant of the Strategy Pattern or Command Pattern

images/mobile_agent_sandbox.gif
A Simple Implementation
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The Sandbox

javaexamples/agents/Sandbox.java
 
A Simple Implementation (cont.)
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The Sandbox Server

javaexamples/agents/SandboxServer.java
 
A Simple Implementation (cont.)
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The Agent

javaexamples/agents/Agent.java
 
A Simple Implementation (cont.)
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A Particular Agent - Kilroy

javaexamples/agents/Kilroy.java
 
Advantages of Mobile Agents
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  • A Clear Case:
    • It is more "expensive" to transmit the data than it is to transmit the code; and
    • The code is complicated enough that it is difficult to indicate the operations that need to be performed using a "simple" protocol or scripting language
  • People Have Made The Following Arguments:
    • Mobile agents are appropriate for mobile devices because they: are only connected to the network intermittently, they tend to have low bandwidth, and they have limited storage/processing.
    • Mobile agents are appropriate for some searches because they are "closer to" the data and can "learn" about the data.
    • Mobile agents are appropriate for real-time interaction with remote hardware when latency of the communications network is high (e.g., space missions).
    • Mobile agents are appropriate when it is difficult to maintain the system state in other ways.
Extensions
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  • Security:
    • Authentication of the agents and the hosts
    • The host must be able to determine what kinds of operations each agent is authorized to perform
  • Directory Services:
    • For finding hosts/sandboxes
    • For finding other agents (remote and local) to communicate with
    • For finding other objects (local) to communicate with
Extensions (cont.)
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  • Class Loading:
    • Allow the agent to make use of multiple classes from multiple sources
  • Logging:
    • Have the host keep a log of the agents that use it (and how they use it)
There's Always More to Learn
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