1. Multimedia Services based on Mobile Agent
Presenter : Lee Chi Wai, Anson
Supervisors : Prof. Michael Lyu, Prof. Irwin King
Markers : Prof. Ng Kam Wing, Prof. Leung Ho Fung
Date : 28 Apr 2000

2. Outline of the presentation
Introduction
Survey of agent environments
Distributed Multimedia Services System
Agent based applications
Conclusion
Question and Answer Session

3. Introduction(1)
Distributed multimedia services systems tend to be heterogeneous
The heterogeneous environments differ in underlying hardware architecture
Main problems:
Discovery of remote resources and services
Configuration of the remote client or servers
Solutions:
Scripting language can cover the heterogeneity of environments

4. Introduction(2) Use of script:
Retrieve multimedia data in distributed environment
Create a common configuration between the communication parties
Reconfigure the systems which is already running
Mobile agent can provide flexibility to adapt themselves in heterogeneous environment

5. Introduction(3) Multimedia Transportable Agent System
Multimedia agent platform
provides an agent transport protocol for agent migration
provides an agent communication environment
Multimedia applications
retrieve multimedia data
transfer of various audio or video data

6. Survey of Agent Environments
Agent Tcl
support agents written in Tcl, Java, C and C++
agent server is multi-threaded
each agent is executed in a separate process
agent communication uses inter-process communication

7. D’Agents(Agent Tcl) Agent Tcl
agent server uses public-key cryptography to authenticate the identity of an incoming agent’s owner
resource manager agents assign access rights to agents based on authentication
enforcement modules enforce the access rights

8. Similarities and differences(1)
Same general architecture:
a server on each machine accepts incoming agents
start up an execution environment for each incoming agent
load agent’s state information into the environment
resume agent execution

9. Similarities and differences(2)
Multi-threaded servers and run each agent in a thread of the server process itself
Multi-process servers and run each agent in a separate interpreter process

10. Similarities and differences(3)
Nearly all mobile agent systems either interpret their language directly
Or compile their languages into bytecodes and interpret the bytecodes
Java is the most popular agent language
portable and efficient
existing security mechanisms allow safe execution of un-trusted code
wide-spread market penetration

11. Similarities and differences(4)
Two kinds of migration approach:
Captures agent object state, code and control state, allowing it to continue execution from the exact point at which it left off
Captures only agent object state and code, and restart execution on some known entry point inside its code

12. Similarities and differences(5)
Protecting an individual machine against malicious agents
Do not provide any protection for the agent
All systems are suitable for distributed information retrieval
Decision should be based on implementation language, level of security and performance

13. Distributed Multimedia Service System
The agent structure
transport header
agent header
agent script

14. Agent Structure AG-ID Type
name the directory where the agent and the load are stored
used as a reference when an agent or any files is lost in the network
Type
determines the type of the file
distinguish between agent files and different media files in agent load

15. Agent Structure Name Size Load length name of the file in agent load
size of the file in agent load
Load length
indicates the total number of files in the agent load

16. Agent Header Sender Identification Mission Information Agent State
user name, address
Mission Information
describes the mission, parameter needed for the mission
Agent State
stores number of sites already visited, type of information found
Route Info
a list of service site addresses that guide the agent during its mission

17. Multimedia Server Infrastructure(1)
Implementation Language:
Agent Tcl/Tk, C
System Specification:
Redhat Linux 6.2
Pentium II 333MHz w128MB RAM
4.3GB Harddisk
Tasks:
Search and retrieval multimedia data based on title matching
Delivery multimedia data including audio and video to end user

18. Multimedia Server Infrastructure(2)
An extension module : the Multimedia Agent Platform
Starting, executing, accessing multimedia data and management of agents
Code of multimedia server doesn’t need to be changed
server doesn’t need to understand any MAP related request
any changes in MAP requests don’t affect the server implementation

19. Multimedia Server Infrastructure(3)

20. Multimedia Server Infrastructure(5)
Working Principle
Agent startup and configuration phase
1. connect to multimedia server
2. request to start an agent
3. Server redirect request to MAP
4. MAP initializes and starts an agent
Agent service phase
1. communicate with other agent
2. migrate to other multimedia servers to access their multimedia data

21. Agent Startup

22. MAP Architecture(1) Five components: Agent Execution Environment
Migration Facilitator
QoS & multimedia module
Service Location Module
Agent Communication Module

23. MAP Architecture(2) Agent Execution Environment
Agent Tcl 2.0 interpreter
recognizes the structure of the agent and extracts information necessary to run the agent script
Agent scripts are written in Agent Tcl
able to execute on any platform

24. Migration Facilitator(1)
Agent Tcl 2.0 daemon listens to port 6138
Transport of the agent and its load
For incoming agent:
1. read the agent header
2. create a directory in the agent data store
3. stores agent and load files
4. activates the Agent Execution Environment
5. waits for new incoming agent

25. Migration Facilitator(2)
For departing agent:
1. it connects another migration facilitator in the destination machine
2. Transfers the agent file and all the files in the agent load

26. Migration Facilitator(3)

27. QoS and Multimedia Module
Problem in multimedia document delivery:
a media stream is continuous and of high bandwidth need
huge amount of data to transport
Solution:
get feedback from the receiver, e.g. available buffer space, network bandwidth
modify or change the coding scheme to lower or raise the quality and bandwidth needs for the stream

28. Service Location Module
Eliminates the need for a mobile agent to travel to destination which doesn’t have the requested resources
Working principle:
1. register itself with a service agent
2. supplies a set of attributes which describe the
service
3. get information about destination, such as next
hop address

29. Agent Communication Module
Get the AG-ID from the service agent
Make a connection

30. Agent Based Applications
Audio Delivery
System Specification
Pentium II 333 MHz with 128M RAM
4.3GB harddisk
Compression Algorithm
MPEG 1 layer III at 128kbps
Layer III
most complex but offers the best audio quality
bit rates around 64kbps per channel

31. Audio Decoder deciphers the encoded bitstream
restores the quantized values
reconstruct the audio signal

32. Transmission Plan pseudo code : sleep interval t’=0.03125sec;
while (server buffer not empty){
record the start time;
transmit audio packet;
record the stop time;
sleep for t’ sec;
compute next sleep interval t’; }

33. Transmission Plan

34. Buffer Management in Client Side
use a leaky bucket model to keep the bit rate of audio data at 128kbps
consists of a finite queue
when a packet arrives, append it at the end of queue if buffer is available
otherwise, discards the packet
at every clock tick, one packet is transmitted to decoder

35. Leaky Bucket Model

36. Video Delivery same system specification
use MPEG 1 decoder from
similar transmission plan as audio delivery, differ in bit rate requirement (1.5Mbps in MPEG 1 standard)
can modify it to some advanced bandwidth smoothing algorithms
similar buffer management strategy as audio delivery

37. Conclusion
Discuss similarities and differences of different agent environments
Propose to use mobile agent in searching and retrieving multimedia data
Discuss the system architecture and prototype of multimedia server
Present two multimedia data delivery application build on the top of MAP

38. Future Work Finish the implementation of MAP
Try to protect the multimedia server against malicious agent
Try to protect agent against malicious host