Mobile agents (2)

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Mobile agents (2)

• EEL 5937 Multi Agent Systems
• Lotzi Bölöni

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Weak mobility
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Weak mobility

• In the case of weak mobility, agents are allowed
  to transfer data only at specific instances.
• Weak mobility puts smaller requirements on the
  agent systems
• Traditional programming languages can be used
  Java, Perl, Python, Lisp
• Smaller performance penalty
• But there are still a number of challenges

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Challenges in soft mobility

• Platform independent code
• How do I handle heterogeneous systems?
• What about _extremely_ heterogeneous systems?
• How to collect state / data?
• How to mark checkpoints (when is mobility
  possible)?
• Authorization, security, resource management
• Reliability problems
• How do I handle open files and other local
  resources?
• How do I handle global names? How do I send a
  message to a mobile agent? What is the address of
  the agent?

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Agent systems with weak mobility

• Most agent system designers considered that
  migration is a relatively rare even in the life
  of the agent system.
• Thus weak mobility
• The agent system is allowed to migrate, but
  migration is not a fundamental type of operation,
  but a problem to be solved
• In Telescript, migration was the basic
  communication primitive!
• Examples
• Aglets, Jade, Concordia, Grasshopper, Bond 2,
  aIsland (JXTA)
• About 60 agent systems on the Mobile Agent List
• http//mole.informatik.uni-stuttgart.de/mal/mal.ht
  ml

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Standards for weak mobility

• Object Management Group (OMG), an international
  consortium dealing with interoperability
  specifications (e.g. CORBA)
• MASIF Mobile Agent Facility
• A specification, released in 2000, specifying how
  CORBA based agents should implement weak mobility
• There are a number of conformant agent systems
  (eg. Grasshopper, partially Aglets)
• As of yet, FIPA did not release any standard for
  agent mobility.
• But they did for mobile (nomadic) users, eg. PDAs
  etc.

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Aglets

• Java based mobile agent system
• I have chosen to present this because of its
  major focus on mobility
• Research project at IBM Japan (from 1996)
• Danny Lange and Mitsuro Oshima
• http//www.trl.ibm.com/aglets/index_e.htm
• As IBM decided to phase out the project it was
  released as an Open Source project
• http//aglets.sourceforge.net/

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Aglets (contd)

• Goal Provide an easy and comprehensive model
  for programming mobile agents without requiring
  modifications to Java VM or native code

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Aglet Lifecycle
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Agent lifecycle

• Instantiating
• Creating a new aglet from the codebase
• Cloning (the clone has the same state as the
  original but different identity)
• An aglet can dispatch itself to a remote server
  by calling the Aglet.dispatch(URL dest)
  primitive. To be more precise, an aglet occupies
  the aglet context and can move from this context
  to others during its execution. Because the
  server may serve multiple contexts within one
  Java VM, and one host may serve multiple servers
  in one host the context are named as the
  following set
• the address of the host, typically IP-address.
• the port number to which the server is listening.
• the name of context within the server.
• Example atp//aglets.ibm.com1434/context_name
• ATP// Aglets Transport Protocol

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Aglet lifecycle (contd)

• Dispatching causes an aglet to suspend its
  execution, serialize its internal state and
  bytecode into the standard form and then to be
  transported to the destination. On the receiver
  side, the Java object is reconstructed according
  to the data received from the origin, and a new
  thread is assigned and executed.
• Aglets can be persistent. Since a mobile aglet
  needs to be serializable into a bit-stream, all
  mobile aglet can be persistent in nature. The
  Aglet.deactivate(long timeout) primitive causes
  an aglet to be stored in secondary storage and to
  sleep for a specified number of milliseconds.

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Migration events in Aglets
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Security issues in aglets / mobile agents

• For secure agent execution, the agent system must
  provide the following security services
• Authentication of the Sender, the Manufacturer
  and the Owner of the Agent.
• Who is responsible for this agent?
• Who is responsible for the agent code?
• Has the agent (code and state) been tampered
  with?
• Authorization of the Agent (or Its Owner)
• What can this agent do? (E.g, can this agent
  access files?)
• Secure Communication between Agent Systems.
• Can the agent protect its privacy?
• Non-repudiation and Auditing.
• How can we ensure that a deal has been actually
  carried out?
• Security-sensitive activities of agents must be
  recorded, and an administrator must be able to
  audit them.