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Mobile agents

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This is a stronger concept than 'code mobility' such as Java applets, or ... clones of themselves, exhausting resources, or other such anti-social behaviour. ... – PowerPoint PPT presentation

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Title: Mobile agents


1
Mobile agents
  • EEL 5937 Multi Agent Systems
  • Lotzi Bölöni

2
Mobile agents
  • Mobile agents are autonomous programs which move
    though a network and maintain their identity
    through this move.
  • This is a stronger concept than code mobility
    such as Java applets, or client-side Javascript.
  • Many agent systems were implemented with support
    for mobility.
  • And for many researchers, agents mobile agents

3
Motivation for mobility (contd)
  • Mobile agents can provide better support for
    mobile clients.
  • Reduction of network traffic
  • Asynchronous interaction (good in case of
    intermittent connection)
  • Remote searching and filtering
  • Mobile agents facilitate semantic information
    retrieval.
  • Move one step above simple keyword based search.
  • Mobile agents facilitate real-time interaction
    with a server
  • Eg. space probes, real time control of a machine
    tool
  • Mobile agent based transactions avoid the need to
    preserve process state in clients and servers
  • Instead, the process state is carried in an agent

4
Motivations for mobility (contd)
  • Agent based transactions scale better than
    RPC-based transactions
  • Secure agent-based transactions have lower
    overhead than secure RPC.
  • Mobile agents allow users to personalize server
    behaviour.
  • Agents enable semantic routing.
  • Not all these arguments are valid.

5
Counter arguments and answers
  • Most counter arguments are based on the fact that
  • What can be done with mobile agents can be done
    with RPC or
  • What can be done on the server, you can do it on
    the client.
  • The software engineering counterargument
    whereas each individual case can be addressed in
    some (ad-hoc) manner without mobile agents, a
    mobile agent framework addresses them all of them
    at once.

6
Mobile code
  • ! mobile agents
  • But, the majority of mobile agent systems imply
    mobile code
  • Transferring code between (heterogeneous)
    machines.
  • Implies machine independent code.
  • Usually, it is implemented with some kind of
    virtual machine
  • But it can be also implemented with adaptation,
    recompilation etc.
  • Types of mobile code
  • Partially Turing machine complete languages (e.g.
    SQL, SVG)
  • Interpreted programming languages (Perl, Python,
    Javascript)
  • Virtual machine based compiled languages (Java,
    Telescript)

7
Mobile code - applications
  • Client-server queries (SQL)
  • Client side browser applets
  • Java applets
  • Javascript
  • ActiveX controls
  • Remote code updates
  • Software updates
  • Plugins
  • Active E-mail
  • Confirmations
  • Javascript, Visual Basic for Applications
  • E-mail viruses and worms
  • Mobile agents

8
Mobile agents without code mobility
  • Seeing control handoff as mobility
  • No code mobility involved.
  • Multithreading involves problems.
  • Distributed systems as mobile agent systems
  • In this approach, mobility is an analysis
    approach, not a design principle.

9
Strong mobility
10
Strong mobility
  • Strong mobility assumes that agents can move at
    any point during their execution
  • They are usually relying on
  • Specially designed programming languages (eg.
    Telescript).
  • Modified virtual machines (eg. NOMADS / AromaVM)

11
Custom language Telescript
  • Proprietary language, created by General Magic
    around 1994-95
  • Highly influential, without being highly
    successful
  • Interpreted language, which runs on a Telescript
    engine.
  • The company implemented engines running on PDAs,
    PCs etc
  • High Telescript
  • Object oriented language, inspired by Smalltalk
  • Compiled to Low Telescript
  • Low Telescript
  • Postfix syntax for stack based implementation

12
Telescript (contd)
  • The basic network configuration is to run a
    Telescript Engine on each node of the network.
  • A network of Telescript Engines provides a
    homogenous environment on which to build
    distributed systems.
  • Basic class Process. Telescript supports
    preemptive, prioritized multi-tasking of Process
    objects. A Process instance can be thought of as
    an object with a life of its own.
  • A Place object represents a virtual space in
    which other objects can interwork (through local
    communication). Each Telescript Engine can
    support a number of places.

13
Telescript (contd)
  • An Agent object is a Process object which can
    migrate between Places. An agent may move between
    Places on the same Engine, or between Places
    which exist on different Engines.
  • The Telescript notion of a distributed system is
    a number of distinctly located places and a
    number of Agents which move between these Places.
  • Places provide meeting locations for Agents. At a
    Place, Agents can exchange information and
    perform computation. Places also route travelling
    Agents.
  • Persistent Objects --- Telescript Engines
    implicitly save and recover object state
    information.
  • The Telescript world is divided into "regions".
    Each Engine uses a "regions" database to route
    migrating Agents. Places and Agents are
    identified using "Telenames"
  • Telename(Locally-Unique-Name, Region-Name)

14
Telescript security
  • Agents have "attributes" such as "identify" and
    "owning authority" which uniquely identify the
    Agent and the entity responsible for it. These
    attributes may be used for authentication.
    Telescript objects also have a "permit" attribute
    which may be used to limit the amount of
    resources which they may consume (e.g. a Place
    may ask an Agent to pay it 30 "Teleclicks" before
    granting it access to some resource).
  • A secure "permits" feature is crucial to stop
    Agents from creating a crash-limited number of
    clones of themselves, exhausting resources, or
    other such anti-social behaviour.
  • Apparently you can't define a legal Telescript
    Place which holds visiting Agents to ransom
    unless you can circumvent security features and
    hack the Interpreter code!)

15
Specialized JVM NOMADS/Aroma
  • NOMADS/Aroma is a Java based agent system with
    strong mobility support, developed at Boeing and
    University of West Florida.
  • The standard Java JVM does not allow explicit
    execution state capture, thus we can not
    implement hard mobility.
  • There are several solutions
  • Modify (patch) the Sun JVM
  • Difficulty because of the native thread usage.
  • Implement a new JVM
  • Use preprocessors and a standard JVM.

16
NOMADS
  • Is composed of two parts the agent execution
    environment (called Oasis) and the AromaVM. This
    provides two key enhancements
  • Strong mobility the ability to capture and
    transfer the full execution state.
  • Safe execution the ability to control the
    resources consumed by the agents thereby
    facilitating guarantees of quality of service and
    protecting against denial of service attacks.
  • These features, however come with a performance
    penalty.
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