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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Agent Header Sender Identification Mission Information Agent State user name, e-mail 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

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

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

Multimedia Server Infrastructure(3)

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

Agent Startup

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

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

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

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

Migration Facilitator(3)

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

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

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

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

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

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’; }

Transmission Plan

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

Leaky Bucket Model

Video Delivery same system specification use MPEG 1 decoder from http://www.mpegtv.com 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

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

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