Mobile Agent-1

8/7/2019 Mobile Agent-1

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Mobile Agent


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Main Content

Introduction of Mobile Agent

Aglets Tcl Agent


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Introduction

An information agentis charged with the

task of managing all or a portion of a users

information space.

The resources in this space are distributed

across a network and can contain

tremendous quantities of data.


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What is a Mobile Agent ?

A mobile agent is an executing program that can migrate from

machine to machine in a heterogeneous network under its own

control.

Here an agent has migrated to interact with a search engine ,an agent will

migrate again to bring the results back to its owner.


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A Mobile Agent Can Suspend execution at any point, transport its code and state

to another machine, and resume execution on the new

machine. An agent can access the resource locally and eliminate the

network transfer of all intermediate data.

Move the programmer away from the rigid client-server

model to the more flexible peer-peer model. Programs communicate as peers

Act as either clients or servers depending on their

current needs


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Introduction to

Mobile Agents What is Mobile Agents?

Mobility: Agents that can travel in network

Autonomy: migrate at times and to place oftheir own choosing

Compare to ..Stationary agent

Mobile code (Applets)

Mobile object


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Network Computing ParadigmsClient-Server Paradigm Code-onDemand Paradigm

Know-

how

ClientServer

ClientKnow-

how

Know

how Server

Download

(Applet)

Agent Agent

Know- how Know- how

Host Host

Network

Mobile Agent Paradigm


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Compare Client/Server & Mobile Agent

Model

Limitation ofClient/Server

Scaling -- Multiple servers

Quality of network connection

Reliability , latency , bandwidth

Protocol

Advantage of Mobile AgentsEvery node is a server

Request Network connection (decentralized)

No application-level protocol (flexible, not

standard)


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Seven good reasons forMobile Agents

Reduce network load (average in distributed db)

Overcome network latency (network management)

Encapsulate protocols (customized protocols) Execute asynchronously and autonomously

Adapt dynamically

Naturally heterogeneous Fault-tolerant


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Mobile Agent Systems

Java-based:

Odyssey. General Magic Inc.

Concordia. Mitsubishis

Aglets. IBM

Voyager. ObjectSpace

Others:Tacoma: Univ.of Tromso and Cornell Univ.

Agent TCL: Dartmouth College


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Mobile Agent Model

Key concepts:

Agent

-- the main entity in Mobile Agent System

Place

-- the environment where agents operate


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Agent

State: needed for resume computation after traveling

Implementation:

needed for location-independent agent execution

Interface needed for agent communication

Identifier needed for recognize and locate traveling agents

Principals needed to determine legal and moral responsibility


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Engine Virtual machines for one or more places

Resources

Databases,processors,and other services provided by the host

Location The network address of a given place

Principals

Those legally responsible for the opration of a place

Place


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The Agent Model Pyramid

Host

Engines

Places

Agents


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Place and Engine

Host

Engine

Agent

PlaceResources


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Agent Behavior(1)Creation and Disposal

Creation:

Instantiation and identifier assignment

InitializationAutonomous execution

Disposal

Preparing for disposalSuspension of execution


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Agent Behavior(2)

Transferdispatching/receiving Dispatch and Receive:

Sender

Suspend Execution

Serialize Agent

Encode Data

Transfer Data

Receiver

Resume Execution

Deserialize Agent

Decode Data

Receive Data

Network


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Agent Behavior(2)

Transferagent class transfer Agent Class Transfer

Server

Class code

Origin

Class code

Server

Class code

Agent Agent

Class at destinationClass at origin

Class at Server(code on demand)


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Security of Mobile Agent

What can go wrong?Agent protection

remote host , other agents, unauthorized third parties

Host protection incoming agents, third parties

Network protection

-- incoming agents

Security ServicesAuthentication

user, host, code, agent

Integrity

Confidentiality

AuthorizationNon-repudiation

Auditing


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Aglets Platform & Aglet


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Aglet Model

Basic Elements:

Aglet a mobile Java object

Proxy a representative of an aglet

Context an aglets workplace

Identifier

Aglet and Proxy:

Client Interaction Proxy Aglet

Context Context

Host

Server Process(Engine)

Network

Host,Server process(engine) and Context


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Aglet : Life Cycle Model

Fundamental

operations:Creation

Cloning

Dispatching

Retraction

Activation and

deactivation

Disposal

AgletC

lone

Class File

Aglet

Disk storage

Dispose

Dispatch

Retract

Create DeactivateActivate

Context A Context B


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Aglet : Event Model

Clone listener

Mobility listener

Persistence listener

Aglet

Clone event

Mobility event

Persistence event

CloneListener

MobilityListener

PersistenceListener


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Aglet : Communication Model

Message passing:

Allows aglets to create and exchange

messages in flexible ways.

Key Components: Aglet, Aglet Proxy, Message,Future reply, Reply set

Aglet/

Application

Message

Reply

Message

Reply

Proxy Aglet


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Aglet Package :a Quick Tour

Aglet Class

AgletProxy Interface AgletContext Interface

Message Class

FutureReply Class AgletID Class


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Aglet API: Aglet Class

Create a customized aglet:

import com.ibm.aglet.*;

Public class MyFirstAglet extends Aglet{

//put aglets methods here}

Overriden methods:

public void onCreation(Object init){

//do some initialization here

}

public void run() { //do something here; }//main entry point

//e.g. call dispatch(new URL(atp://some.host.com//context));


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Aglet API:Aglet Class

What happens when dispatch?

State

Byte Code

Host Host

Sending Receiving

State

Byte Code

HostHost

Object Serialization

Transfer

Deserialization and

re-create state


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Aglet API: AgletProxy

Why AgletProxy?

Acts as a shield object that protects an aglet from malicious aglets

Provide the aglet with location transparency

How to get a proxy?Get proxy from a newly created aglet:

AgletContext.createAglet(),

AgletProxy.clone()

Get proxy from existing aglets

Aglet.getProxy() get its own proxy

AgletContext.getAgletProxies() retrieve an enum. of proxies in a context

AgletContext.getAgletProxy() get an aglet proxy for a given aglet ID

Message passing passed as an argument

AgletContext.setProperty put proxy into context property and share it.


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Aglet API: AgletContext

An aglet context is the equivalent of a place.

An aglet uses AgletContext interface to:

Get information about its environment

Send message to the environment, including other

aglets currently active in that environment

How it works:context=getAgletContext();

context.createAglet();

context.retractAglet(remoteContextURL,agletID);


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Aglet API: Message Class

Aglets communicate by exchanging objects of the

Message class.

kind field: distinguishes messagesMessage myName=new Message(my name, Jacob);

Message yourname=new Message(your name?);

Methods to send message(defined in AgletProxy class):

Object sendMessage(Message msg)

FutureReply sendFutureMessage(Message msg)

Void sendOnewayMessage(Message msg)


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Aglet API: Message Class

handleMessage method:Public boolean handleMessage(Message msg){

if(msg.samekind(my name)){

String name=(String)msg.getArg();return true; //Yes, I handled this message

} else if(msg.samekind(your name?)) {

msg.sendReply(Yina); //Return its name

return true; //Yes, I handled this message} else

return false; //No, I did not handle this message

}


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Aglet API: AgletID Class

Identity:Globally unique

Throughout lifetime

AgletID objectHides the implementation-specific representation

Immutable Use :

AgletID aid=proxy.getAgletID();

proxy=context.getAgletProxy(aid);


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Anatomy of an Aglet

Creation & Disposal

C

lone Mobility

Dispatch and Retract

Persistence Activate and Deactive


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Creation

public final AgletContext Aglet.getAgletContext()

//Example:

getAgletContext().createAglet(getCodeBase(),SomeAglet,null);

Methods that can be overridden

protected Aglet.Aglet()Public void Aglet.onCreation(Object init)

Public void Aglet.run()

createAglet()Aglet()

onCreation

run()


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Disposal

public final void Aglet.dispose();

public void Aglet.onDisposing();

Dispose()

onDisposing()

run()


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Event

Event Types:

C

loneEventMobilityEvent

PersistencyEvent

Delegation-Based Event Mode

CloneListener CloneAdapter

MobilityListener MobilityAdapter

PersistencyListener PersistencyAdapter


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Cloning

Public final Object Aglet.clone()

Public final void Aglet.addCloneListener(CloneListener

listener)

Public final void Aglet.removeCloneListener(CloneListenerlistener)

public CloneAdapter.CloneAdapter()

public void CloneAdapter.onCloning(CloneEvent event)public void CloneAdapter.onClone(CloneEvent event)

public void CloneAdapter.onCloned(CloneEvent event)


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Cloning (continued)public class CloningExample extends Aglet{

boolean _theClone=false;public void onCreation(Object o) {

addCloneListener(new CloneAdapter(){

public void onCloning(CloneEvent e){

// print to the console }

public void onClone(CloneEvent e){


public void onCloned(CloneEvent e){


} );

}

public void run() {if (! _theClone) {

//the original runs heretry{

clone();} catch (Exception e)

{ System.out.println(e.getMessage());

}

else {//the clone runs here}

}

run()

onCloning()onCloned()

onClone()

run()

original

clone


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Mobility

-- Dispatching

-- Retracting

run( )

dispatch( )

onDispatching( )

onArrival( )run( )

Origin

Destination

retractAglet( )

onArrival( )

run( )

run( )onReverting( )

Local

Remote


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Persistence

Persistence

run( )

deactivate( )

onDeactivating( )onActivation( )

run( )

Before

After

Aglet Context

Deactivate

Activate


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Inside Aglets

Architecture Overview

Services and User-defined aglets

Aglet APIAglet Runtime Layer

Core FrameworkManagementComponents

CacheManagerSecurityManager

PersistanceManager

Communication API

Communication Layer


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Communication Layer

Communication API

Agent Transfer Protocol(ATP)

An ATP request consists of : a request line,header fields, content.

Four standard request method:

Dispatch

Retract

Fetch

Message

Host HostATP ATP

HTTP

HTTP Tunneling of ATP


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Aglet Security

PrincipalAglet

Context & Server

Network Domain

Permissions

Protection

Policy & Authority

Aglet owner

Context owner

Network Domain owner


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Tcl Agent

A flexible and secure mobile-agent system


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Overview

Introduction

Agent Tcl Architecture

Tcl and Agent Tcl

Security in Agent Tcl


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Introducing Agent Tcl

Mobile agent system developed at Dartmouth

College.

Uses a flexible scripting language Tclas its mainlanguage but provides a framework for

incorporating addiotional languages.

Provides migration and communication primitives

that dont require the programmer to explicitly

capture state information and hides actual

transport mechanisms


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Agent Tcl continued

Uses Safe Tcl security modelto protect a machine from a

malicious agent and agents from each other.

Allows agents To migrate from machine to machine orremain stationary and

access resources from across the network.

To create child agents to perform subtasks.

To communicate with other agents on the local and remote

machines.

Intended as a general environment for

distributed applications.


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The Architecture

4 main goals

Reduce migration to a single instruction.Provide transparent communication among

agents.

Support multiple languages and transport

mechanisms.Provide effective security in the uncertain

world of the Internet.


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Architecture continued

Agents

Tcl .. Java

Server or engine

TCP/IP .. Electronic

mail

Interpreter

State

Capture

Server

API

Security


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Levels in Architecture

4 Levels to architecture

API

Server

Interpreter

Agents


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Server Level

Server performs following tasks:

Status - keeps track of the agents on machines

Migration - accepts each incoming agent, authenticatesidentity of its owner, passes to appropriate interpreter

Communication- provides a hierarchical namespace for

agents and allows agents to send messages to each other

within this name spaceNonvolatile Store - provides access to a nonvolatile

store so agents can back up their internal state as

desired.


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Interpreter Level

One interpreter for each available language

Four components to interpreter

interpreter

security module

state module

captureState

restoreState

API


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Tcl and Agent Tcl

Current implementation does not provide

event messages or the nonvolatile store

Has a single language (Tcl)

Single transport mechanism (TCP/IP)

Incoming agents are authenticated using

PGP


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Tcl

High level scripting language

Advantages as a mobile agent language

Easy to learn Interpreted thus highly portable and easy to make secure

Can be embedded in other applications

Can be extended with user-defined commands

Disadvantages of Tcl

Interpreted - thus much slower than machine language No facilities for capturing the complete internal state of an executing

script

This was modified by adding to the Tcl core


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Agent Tcl

Two components

Server

Runs at network site

Implemented as two cooperating processes

One watching the network

Other maintaining a table of running agents

Modified version of Tcl 7.5 and a Tcl extension

Provides explicit stack and state-capture routines

Extension provides commands for an agent to

migrate, communicate, and create child agents.


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How does it work ?

Agent simply a Tcl script running on top of

a modified version of Tcl 7.5

agent_begin - register with server and obtain a

name in flat namespace

agent_submit - used to create a child agent on

a particular machineagent_jump - migrates an agent to a particular

machine

agent_send, agent_receive - to send and

receive messages


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How does it work, continued

agent_meet - used by source agent to send

a connection request to the destination agent

agent_accept - used by destination agent to

receive the connection request and send

with an acceptance or rejection.

Acceptance includes sending a TCP/IP port numberto which the source agent connects


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Agent Tcl and Security

Main Problems are to

Protect the machine

Protect other agents

Protect the agent

Protect a group of machines


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Authentication

Based on PGP (Pretty good Privacy)

Encrypts a file using the IDEA private key

algorithm and random private key Encrypts the private key using RSA and public key

Sends encrypted key and file to recipient

Initiated by the agent_begin command


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Authorization and Enforcement

Resources divided into 2 types

Indirectresources

Only accessed through another agent

Built-in resources

Directly accessible through language primitives

Security maintained using Safe Tcl and A set ofresource manageragents

Safe Tcl creates trusted and untrusted

interpreter


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Conclusion

Future work includes incorporating Java

into the architecture

Agent Tcl

Secure mobile agent system which gains

flexibility and simplicity from use of hih-level

scripting language Tcl

Documents

Mobile Agent-1