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Transcript of Mobile Agents Niranjan Suri [email protected] University of West Florida.
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida2
Outline
Overview of Agents and Mobile Agents Characterization of Mobility Advantages of Mobile Agents System Components Language / Design Issues Applications Challenges Survey of Mobile Agent Systems Summary
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida3
Definition of Software Agents
Computer program Autonomous behavior Represents some entity Has authority (delegation) Reacts and learns about environment Communicates using high-level Agent
Communication Languages (ACLs)
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida4
Mobile Agents
Definition– Software agents– Move from one computer to another
User-directed or autonomous
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida5
Outline
Overview of Agents and Mobile Agents
Characterization of Mobility Advantages of Mobile Agents System Components Language / Design Issues Applications Challenges Survey of Mobile Agent Systems Summary
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida6
Characterizing Mobility
Three capabilities– Mobile code– Mobile computation– Mobile state
Various combinations are possible
M obileC ode
Mo
bile
Co
mp
uta
tion
Mob
ile
State
R P C , S ervle ts,S tored P rocedures
R em oteInsta lla tion
C heckpo in ting
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida7
Mobile Code
Allows executable code to be moved to a new host
May use the push or pull model– Pull: Applets– Push: Remote Installation
Mobile agents use push– Sometimes, an agent push may result in a code pull
Code may be binary (intermediate or native) or source
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida8
Mobile Code
Advantages:– Dynamically change capabilities
Download new code to add / change / update capabilities of platform
Remove code when no longer needed
Problems:– Security concerns due to untrusted / unchecked
code Code could be malicious, buggy, and/or tampered
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida9
Mobile Computation
Evolution of Remote Computation– RPC, RSH, RMI, Servlets, Stored Procedures,
CORBA
Allows one system to run a computation on another system
Utilize resources on remote system– CPU, memory
Access resources on remote system– Files, databases, etc.
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida10
Mobile State
Evolution of State Capture– Checkpointing
Allows execution state of a process to be captured and moved
State may be machine specific or machine independent
May contain– State of single or multiple threads– Code
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida11
Combinations of Capabilities
M obileC ode
Mo
bile
Co
mp
uta
tion
Mob
ile
State
R P C , S ervle ts,S tored P rocedures
R em oteInsta lla tion
C heckpo in ting
W eakM obility
P rocessM igra tion
S trongM obility
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida12
Strong Mobility
Move execution state with agent Why is it important?
– Computationally equivalent to weak mobility– However, simpler, more natural abstraction– Therefore, easier to write mobile agents
More importantly –
mobile state allows
forced mobility
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida13
Weak Mobility Example
public class Example extends Aglet {
boolean _theRemote = false;
public void onCreation (Object init) {
addMobilityListener(
new MobilityAdapter() {
public void onArrival (MobilityEvent e) {
_theRemote = true;
}
}
);
}
public void run() {
if (!_theRemote) {
System.out.println (“On Source”);
dispatch(destination);
}
else {
System.out.println (“On Destination”);
}
}
}
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida14
Strong Mobility Example
public class Example extends Agent
{
public static void main (String[] args)
{
System.out.println (“On source”);
go (destination);
System.out.println (“On destination”);
}
}
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida15
Outline
Overview of Agents and Mobile Agents Characterization of Mobility
Advantages of Mobile Agents System Components Language / Design Issues Applications Challenges Survey of Mobile Agent Systems Summary
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida16
Client-Server Versus Mobile Agents
Client
Server Server
Client
Agent
Server
Client
Agent
Server
Client
Agent
Traditional Mobile Agent-Based
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida17
Advantages of Mobile Agents
Reduced network bandwidth Disconnected operation
– Short “On-Line” times– Low-power requirements– Support for mobile units
Low-latency interaction
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida18
Jini Versus Mobile Agents
Client
Device
Client
Device
Proxy
Client
Device
Client
Device
Agent
Client
Device
Agent
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida19
Advantages of Mobile Agents
Highly Dynamic and Flexible Systems– Enabled my mobile code– Download new capabilities / services– Remove old / unused capabilities
“Swapping” for memory constrained devices
– Structure systems around mobile code “Universal” server Open Services Gateway Initiative (OSGI)
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida20
Advantages of Mobile Agents
Unique capability:Send an executable program that does your bidding on someone else’s computer
Very powerful but… can be dangerous!– Only one step removed from a Virus
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida21
Agent Programming Paradigms
Itinerant Agents– Use an itinerary that dictates mobility of agents
Reactive Agents– Event-based approach– Events trigger mobility of agents
Agent-Minion– Minions: Small mobile agents spawned by larger
agents
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida22
Outline
Overview of Agents and Mobile Agents Characterization of Mobility Advantages of Mobile Agents
System Components Language / Design Issues Challenges Survey of Mobile Agent Systems Summary
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida23
System Components
ExecutionEnvironment
ExecutionEnvironment
Agent Transfer Protocol
DirectoryService
MessagingService
PolicyManager
Interpreter
VisualizationTools
AdministrationTools
Agent Messaging Protocol
AuthenticationEncryption
GlobalDirectoryService
LoggingService
GlobalLoggingService
Other Frameworks(DARPA CoABS Grid, etc.)
PersistenceService
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida24
Outline
Overview of Agents and Mobile Agents Characterization of Mobility Advantages of Mobile Agents System Components
Language / Design Issues Applications Challenges Survey of Mobile Agent Systems Summary
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida25
Languages for Mobile Agents
Java– Numerous Systems
TCL– D’Agents, SMIA
C/C++– Omniware
Miscellaneous– Telescript– Lisp, Scheme, custom, etc.
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida26
Advantages of Java
Platform independent
Virtual Machine execution environment– Important for isolation
Small footprint
“Real” programming language– Compared to TCL
Most security conscious– Though still not adequate!
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida27
Limitations of Java
No state capture Importance:
– Mobile state Mobile agent systems Load balancing (distributed systems) Forced migration Cloning (fault tolerance)
– Checkpointing Faster VM startup Restarting crashed applications Persisting processes for later resumption
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida28
Limitations of Java
No resource control Importance:
– Protect against denial-of-service attacks Malicious code Buggy code
– Prioritize tasks– Foundation for providing QoS guarantees
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida29
Limitations of Java
No resource accounting Importance:
– Measuring resource consumption Charging / billing resource usage
– Observing behavior of code
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida30
Directory Service Issues
Difficult to find an agent– Chase agent around
Fast Moving Agents– May be difficult/inefficient to update directory service
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida31
Authentication Issues
Agent Anonymity– Agent may want to be anonymous on a host– Analogy: Window shopping
Multiple Hop– Agent may not want to carry credentials
Credentials could be stolen by malicious hosts
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida32
Outline
Overview of Agents and Mobile Agents Characterization of Mobility Advantages of Mobile Agents System Components Language / Design Issues
Applications Challenges Survey of Mobile Agent Systems Summary
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida33
Applications of Mobile Agents
Information Retrieval– Mobile agents reduce network bandwidth– Depends on:
Quantity of information searched Quantity of information retrieved Size of mobile agent
– Comprehensive study for DARPA Dartmouth College, Lockheed Martin ATL,
University of West Florida
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida34
Applications of Mobile Agents
Monitoring– Computer programs can be very patient
Remote Control Dynamic Systems
– Universal servers
Active Mail– Send executable content as email
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida35
Outline
Overview of Agents and Mobile Agents Characterization of Mobility Advantages of Mobile Agents System Components Language / Design Issues Applications
Challenges Survey of Mobile Agent Systems Summary
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida36
Challenges for Mobile Agents
Security Issues– Protecting network communication– Protecting hosts from agents
Illegal access Denial of service
– Protecting agents from hosts Tampering Extracting information Capture / Replay
System-wide Administration / Management– Policies– Tracking / Visualization
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida37
Challenges for Mobile Agents
Access to non-mobile resources– Network endpoints– Files
Deployment (of environments) Interoperability
– OMG MASIF – Not successful– DARPA CoABS – We shall see…
Debugging– Highly Asynchronous
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida38
Outline
Overview of Agents and Mobile Agents Characterization of Mobility Advantages of Mobile Agents System Components Language / Design Issues Applications Challenges
Survey of Mobile Agent Systems Summary
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida39
Survey of Mobile Agent Systems
Commercial Systems
– Telescript/Odyssey - General Magic
– Voyager - ObjectSpace
– Aglets - IBM
– Concordia - Mitsubishi Electric ITA
– Jumping Beans - AdAstra
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida40
Survey of Mobile Agent Systems
Research Systems– NOMADS– KAoS– D’Agents– Agents for Remote Action (ARA)– Mole– Sumatra– Many others...
Mobile Agent List:http://www.informatik.uni-stuttgart.de/ipvr/vs/projekte/mole/mal/mal.html
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida41
NOMADS
Java-based mobile agent system– Strong mobility
Capture full execution state of running agents Provides anytime mobility – simplifies writing mobile
agents Provides forced mobility – arbitrary Java code can be
moved
– Strong security Dynamically control resource usage (rates and quantities) Allows platform owner full control over agent execution Protect against denial of service attacks
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida42
Strong Security
Limitations of current Java systems– Rely on JDK security
Does not provide resource control
– Either assume agents are safe Does not scale
– Or rely on code signing Not a preventive measure
Goal: Build secure execution environments– Run untrusted or partially-trusted code
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida43
Aroma Virtual Machine
Clean-room implementation State capture mechanism Dynamic, fine-grained resource control
– Disk, Network, CPU
JDK 1.2.2 compatible– Uses Java Platform API from JRE 1.2.2– No AWT / Swing
Ported to Win32 (x86), Linux (x86), Solaris (SPARC) No Just-In-Time compilation (Almost) No optimization
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida44
State Capture
Aroma supports two modes– Full VM state
All threads, loaded classes, objects State may be restored into a “blank” VM Size: Approx 1.5 MB
– Individual thread state Method stack and all reachable objects Thread may be restored into running VM Size: Approx 4 KB
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida45
State Capture
State capture is fine-grained– Between any two Java bytecode instructions– Supports blocked, waiting, sleeping, and suspended
threads
State is platform independent State may be stored in memory, saved to disk,
or streamed over the network
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida46
Resource Control
Rate control– Control rate at which resources are used– Dynamically adjustable– Fine grained– Examples:
CPU limited to 10% Disk write rate limited to 30 KB/sec Network read rate limited to 10 KB/sec
Disk Usage Rate
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida47
Resource Control
Quantity control– Control quantity of resources used– Dynamically adjustable– Fine grained– Examples:
Disk space limited to 1.8 MB Total network writes limited to 1024 KB
– Still needed: memory
Disk Usage Quantity
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida48
Benefits of Resource Control
Protect host from malicious agents– Prevent denial of service attacks
Simplify agent writer’s task– Agents do not need to worry about resource
control / limits Means of prioritization
– Raising limits increases priority Basis for Quality of Service Means of accounting
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida49
Outline
Overview of Agents and Mobile Agents Characterization of Mobility Advantages of Mobile Agents System Components Language / Design Issues Applications Challenges Survey of Mobile Agent Systems
Summary
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Mobile Agents Tutorial - Niranjan Suri - Cognition Institute/University of West Florida50
Summary
Mobile Agents are Good – Code mobility adds significant flexibility
Security is Critical Deployment is Difficult No Interoperability
MH MP MPD