Mobile Agents - Multi Agent Systems - Lecture Slides, Slides of Multiagent Systems

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Mobile agents

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

Motivations for mobility (cont’d)

• 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.

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.

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

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.

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)

Custom language: Telescript

• Proprietary language, created by General Magic around 1994- - Highly influential, without being highly successful
• Interpreted language, which runs on a Telescript engine. - The company implemented engines running on PDA’s, PC’s etc
• “High Telescript”:
  • Object oriented language, inspired by Smalltalk
  • Compiled to Low Telescript Docsity.com

Telescript (cont’d)

• 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)

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,Docsity.com

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 Docsity.com