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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 EnvironmentsAgent 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
A G - ID T yp e N a m e S izeL o a d
L e ngthA ge ntS ta te
M iss io nInfo
S e nd e r- ID R o uteInfo
A ge nt S c rip t
T ra nsp o rtH e a d e rA ge nt
H e a d e r
Agent StructureAG-ID
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 StructureName
name of the file in agent loadSize
size of the file in agent loadLoad length
indicates the total number of files in the agent load
Agent Header Sender Identification
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)
A g e n t
A g e n tR e q u e s t
A g e n tR e s p o n s e
M u lt im e d iaS e rv e r
R e d ire c t
U s e rIn t e r fa c e
M A P
Multimedia Server Infrastructure(5) Working Principle
Agent startup and configuration phase1. connect to multimedia server2. request to start an agent3. Server redirect request to MAP4. MAP initializes and starts an agent
Agent service phase1. communicate with other agent 2. migrate to other multimedia servers to access
their multimedia data
Agent Startup
act iveA gent
G ETA gent
A gent sends it sG U I to user
M ult imediaServer
R edirect
U serInt erface
M A P
G et G U I
A gent G U I
C onfigurat ionInformat ion
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
6138Transport 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)
M ig ra tio n F a c ilita to r ( s e n d e r )
A g e n t d a ta s to re
In te rp re te r
N e tw o rk
A g e n ts c r ip t
M ig ra tio n F a c ilita to r (d e s tin a tio n )
A g e n t d a ta s to re
In te rp re te r
c a ll th e a g e n t_ ju m pc o m m a n d to m ig ra te toa n o th e r h o s t
In th e n e w h o s t, it w illr e s to re s th e s ta te o f th ea g e n t a n d c o n tin u e th ee x e c u tio n
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 ModuleGet the AG-ID from the service agentMake a connection
S e rv ic eA g e n t
A g e n t B
S e rv ic eA g e n t
A g e n t A
M u lt im e d ia A g e n tP la t fo rm
M a c h in e A M a c h in e B
1 ) re g is t e r A g e n t A
2 ) re q : w h e re is A g e n t A ?
3 ) re p : A g e n t A o n A
4 ) s e n d m e s s a g e s t o A g e n tA o n M a c h in e A
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
B its tr e a mu n p a c k in g
F re q u e n c ys a m p le
re c o n s tru c tio n
F re q u e n c y totim e m a p p in g
Encodedbit s t ream
D ecodedP C Maudio
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’;
}
t = 0s l ee p i n t e rv a l 1 s l ee p i n t e rv a l 2
t = 0 .0 3 1 2 5 s ec .
t = 0 .0 3 1 2 5 s ec . + t '
t ra n s mi t t h e fi rs tp a ck e t o f a u d i o d a t a
(5 1 2 b y t e s )
t ra n s mi t t h e s ec o n dp a ck e t o f a u d i o d a t a
(5 1 2 b y t e s )
t ra n s mi t t h e t h i rdp a ck e t o f a u d i o d a t a
(5 1 2 b y t e s )
Buffer Management in Client Side
use a leaky bucket model to keep the bit rate of audio data at 128kbps
consists of a finite queuewhen a packet arrives, append it at the
end of queue if buffer is availableotherwise, discards the packetat every clock tick, one packet is
transmitted to decoder
Leaky Bucket Model
N etw ork
t ime t
P acket U nregulat edflow
T he bucket holds p acket s
R egulat edflow
M P EG decoder
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