13Mobile Agents1

1
Lecture 13 Mobile Agents

• Topics
• Basics
• Mobile Agent Model
• Applications
• Discussions
• Case study - Aglet
• Some Other Mobile Agents
• Concordia
• MOA

2
Basics

• What is Mobile Agents?
• Mobile agents are programs that assist people and
  act on their behalf (agent), and they can travel
  in network
• Mobility Agents that can travel in network
• Autonomy migrate at times and to place of their
  own choosing
• Compare to ..
• Stationary agent
• Mobile code (Applets)
• Mobile object

3
Basics

• Network Computing Paradigms
• Client-Server Paradigm Code-onDemand
  Paradigm

Server
Know how
Download (Applet)
Client
Client
Know- how
Know- how
Server
Mobile Agent Paradigm
Agent
Agent
Network
Know- how
Know- how
Host
Host
4
Basics

• Limitation of Client/Server
• Scaling -- Multiple servers
• Quality of network connection
• Reliability , latency , bandwidth
• Protocol
• Advantage of Mobile Agents
• Every node is a server
• Request Network connection
• No application-level protocol

5
Basics

• Seven good reasons for Mobile Agents
• Reduce network load
• Overcome network latency
• Encapsulate protocols
• Execute asynchronously and autonomously
• Adapt dynamically
• Naturally heterogeneous
• Fault-tolerant

6
Mobile Agent Model

• Agent travel to Host work and interact with
  other agents in place (meeting place)

Host
Agent
Place
Resources
Engine
7
Mobile Agent Model

• Key concepts
• Agent
• the main entity in Mobile Agent System
• Place
• the environment where agents operate
• Security
• security policies for protecting agents,
  networks, and servers

8
Mobile Agent Model

• 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

9
Mobile Agent Model

• Place
• Engine
• Workhorse and 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 operation of a
  place

10
Mobile Agent Model

• Security
• Agent protection
• remote host, other agents, unauthorized third
  parties
• Host protection
• incoming agents, third parties
• Network protection
• -- incoming agents
• Security Services
• Authentication
• user, host, code, agent
• Integrity
• Confidentiality

• Authorization
• Non-repudiation
• Auditing

11
Mobile Agent Model

• Agent Behavior
• Agent Management
• Creation
• Disposal
• Agent Transfer
• Dispatch and Receive
• Agent class transfer

12
Mobile Agent Model

• Creation
• Instantiation and identifier assignment
• Initialization
• Autonomous execution
• Disposal
• Preparing for disposal
• Suspension of execution

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Mobile Agent Model

• Dispatch and Receive

Sender
Receiver
Resume Execution
Suspend Execution
Serialize Agent
Deserialize Agent
Encode Data
Decode Data
Transfer Data
Receive Data
Network
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Mobile Agent Model

• Agent Class Transfer

Server
Class at Server (code on demand)
Class code
Origin
Server
Agent
Agent
Class code
Class code
Class at origin
Class at destination
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Mobile Agent Model - Standard

• MASIF (Mobile Agent System Interoperability
  Facility) defines
• Agent management
• Agent transfer
• Agent and agent system names
• Agent system type and location syntax
• MASIF doesnt do
• Language interoperability
• Standardize local agent operations

16
Mobile Agent Model - Standard

• OSM (Open Service Model) A model for Global
  Information Brokerage and Distribution
• The next generation framework for globally
  distributed Electronic Commerce and virtual
  trading market systems
• Contain advanced Java based desktop components
  supporting a catalogue browsing, service
  inspection, monitoring and construction tools

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Mobile Agent Model - Standard
OSM - Open Service Model
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Applications

• Electronic Commerce
• Personal Assistance
• Distributed Information Retrieval
• Telecommunication Network Service

19
Applications

• Example mobile agent systems
• Java-based
• Aglets (IBM)
• Concordia (Mitsubishis)
• Odyssey (General Magic Inc.)
• Voyager (ObjectSpace)
• Others
• Agent Tcl (Dartmouth College)
• Tacoma (Univ.of Tromso and Cornell Univ.)

20
Applications

• Mobile Agent with Java

• Benefits
• Platform independence
• Secure execution
• Dynamic class loading
• Multithread programming
• Object serialization
• reflection

• Drawbacks
• Inadequate support for resource control
• No protection of references
• No object ownership of references
• No support for preservation and resumption of the
  execution state

21
Discussions

• Advantages of Mobile Agents
• Reduced network load
• Reduced resource usage of the client
• Asynchronous processing
• Reconfigurable services
• Active behavior
• Decentralized structure

22
Discussions

• Disadvantages of Mobile Agents
• Security threats
• Technical problems
• transport/migration
• efficiency
• standards/interoperability
• billing systems

23
Case Study - Aglet

• Aglet A mobile agent that conforms to a set of
  security restrictions
• A Java aglet is a mobile Java object
• It can move from one host to another
• It supports concepts of autonomous execution and
  dynamic routing on its itinerary.
• Has its own thread of control
• Is event-driven
• Communicates by message passing

24
Case Study - Aglet
Aglet and Proxy Client Interaction Proxy
Aglet

• Aglet Model
• Proxy a representative of an aglet
• Context an aglets workplace (place)
• Identifier

Host, Server process (Engine) and Context
Host
Context
Context
Server Process (Engine)
Network
25
Case Study - Aglet

• Aglet Life Cycle
• Creation
• Cloning
• Dispatching and Retraction (Mobility)
• Activation and Deactivation (Persistence)
• Disposal

Dispose
Context A
Context B
Clone
Dispatch
Aglet
Aglet
Retract
Create
Deactivate
Activate
Disk storage
Class File
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Case Study - Aglet

• Aglet Event Model
• Clone listener
• Mobility listener
• Persistence listener

Clone event
CloneListener
Aglet
Mobility event
MobilityListener
PersistenceListener
Persistence event
27
Case Study - Aglet

• Aglet Communication Model
• Allows aglets to create and exchange messages in
  flexible ways
• Key Components
• Aglet, AgletProxy, Message, Future reply, Reply
  set

Aglet/ Application
Message
Message
Proxy
Aglet
Reply
Reply
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Aglet Package a Quick Tour

• Aglet Class
• AgletProxy Interface
• AgletContext Interface
• Message Class
• FutureReply Class
• AgletID Class

29
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 Class

• What happens when dispatch?

• Object Serialization
• Transfer
• Deserialization and re-create state

State
Byte Code
Host
Host
Sending
Receiving
State
Byte Code
Host
Host
31
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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AgletContext

• An aglet uses AgletContext to
• Get information about its environment (place)
• Send message to the environment, including other
  aglets currently active in that environment
• How it works
• contextgetAgletContext()
• context.createAglet()
• context.retractAglet(remoteContextURL,agletID)

33
Message Class

• Aglets communicate by exchanging objects of the
  Message class
• kind field distinguishes messages
• Message myNamenew Message(my name, Jacob)
• Message yournamenew Message(your name?)
• Methods to send message (defined in AgletProxy
  class)
• Object sendMessage(Message msg)
• FutureReply sendFutureMessage(Message msg)
• Void sendOnewayMessage(Message msg)

34
Message Class

• Message handling
• 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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FutureReply Class

• Returned by the asynchoronous message-sending
  method
• Used to handle later receive the result
  asynchronously
• FutureReply future-proxy.sendFutureMessage(msg)
• While(!future.isAvailable())
• doPeriodicWork()
• Object reply future.getReply()

36
AgletID Class

• Identity
• Globally unique
• Throughout lifetime
• AgletID object
• Hides the implementation-specific representation
• Immutable
• Use
• AgletID aidproxy.getAgletID()
• proxycontext.getAgletProxy(aid)

37
Anatomy of an Aglet

• Creation Disposal
• Clone
• Mobility
• Dispatch and Retract
• Persistence
• Activate and Deactivate

38
Creation

• public final AgletContext Aglet.getAgletContext()
• //Example
• getAgletContext().createAglet(getCodeBase(),SomeA
  glet,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()
40
Event

• Event Types
• CloneEvent
• MobilityEvent
• PersistencyEvent
• Delegation-Based Event Model
• CloneListener CloneAdapter
• MobilityListener MobilityAdapter
• PersistencyListener PersistencyAdapter

41
Cloning

• Public final Object Aglet.clone()
• Public final void Aglet.addCloneListener(CloneList
  ener listener)
• Public final void Aglet.removeCloneListener(CloneL
  istener listener)
• 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 _theClonefalse
• public void onCreation(Object o)
• addCloneListener(new CloneAdapter()
• public void onCloning(CloneEvent e)
• // print to the console
• public void onClone(CloneEvent e)
• // print to the console
• public void onCloned(CloneEvent e)
• // print to the console
• )

public void run() if (! _theClone)
//the original runs here try clone()
catch (Exception e) System.out.println(e.
getMessage()) else //the clone runs here
run()
original
onCloning()
onCloned()
onClone()
clone
run()
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Mobility

• Dispatching
• Retracting

run( )
Origin
dispatch( )
onDispatching( )
onArrival( )
Destination
run( )
retractAglet( )
Local
onArrival( )
run( )
run( )
Remote
onReverting( )
44
Persistence

• Persistence

Aglet Context
Activate
Deactivate
run( )
deactivate( )
Before
onDeactivating( )
onActivation( )
After
run( )
45
Inside Aglets

• Architecture Overview

Services and User-defined aglets
Aglet API

• Aglet Runtime Layer
• Core Framework
• Management Components
• CacheManager
• SecurityManager
• 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

ATP
ATP
Host
Host
HTTP
HTTP Tunneling of ATP
47
Aglet Security

• Principals
• Aglet
• Context Server
• Network Domain
• Permissions
• Protection
• Policy Authority
• Aglet owner
• Context owner
• Network Domain owner

48
Some Other Mobile Agent Systems

• Concordia

49
Some Other Mobile Agent Systems

• MOA (Mobile Objects and Agents )