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Digital Library Accessing Techniques. Supervisors : Prof. Michael Lyu, Prof. Irwin King Presenter : Lee Chi Wai, Anson Date : 7-12-1999. Outline of the presentation. Introduction Bandwidth smoothing algorithms Mobile agent communication model Audio server/client delivery system Conclusion

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Digital library accessing techniques
Digital Library Accessing Techniques

Supervisors : Prof. Michael Lyu, Prof. Irwin King

Presenter : Lee Chi Wai, Anson

Date : 7-12-1999

Outline of the presentation
Outline of the presentation

  • Introduction

  • Bandwidth smoothing algorithms

  • Mobile agent communication model

  • Audio server/client delivery system

  • Conclusion

  • Question and answer


  • Live video delivery techniques:

    • Challenges : decisions must be made in real-time and delay must be minimized

    • Solution : weaker guarantees of service or degradation in quality of service

  • Stored video delivery techniques:

    • used in digital libraries and video-on-demand systems


  • Stored video delivery techniques(cont.):

    • the full video is know in advance

    • use pre-fetching techniques to control the picture quality

  • What is pre-fetching techniques?

    • create a pre-fetch buffer in client side

    • fill the pre-fetch buffer with more bytes in advance of each burst


  • How to fill the pre-fetch buffer?

    • Server uses some bandwidth smoothing algorithms

    • Critical bandwidth allocation (CBA)

      • introduced by W. Feng and S. Sechrest in 1995

    • Minimum changes bandwidth allocation (MCBA)

      • introduced by W. Feng and S. Sechrest in 1995


  • Bandwidth smoothing algorithms (cont.)

    • Minimum variability bandwidth allocation

      • introduced by J. Salehi, Z. Zhang, J.Kurose, and D. Towsley in 1996

    • Piecewise Constant Rate Transmission and Transport Algorithm

      • introduced by J. Mcmanus and K.Ross in 1996


  • Problem of the client/server communication model :

    • static and inflexible

    • interaction between clients and servers requires permanent network connections

    • can’t support mobile computers


  • Solution :

    • use Mobile Agent communication model

    • support asynchronous interaction of searching for information

    • support for mobile computers or lightweight devices

Bandwidth smoothing algorithm
Bandwidth smoothing Algorithm

  • Aim : reduce the burstiness of the network traffic by pre-fetching video data to the client side at a series of fixed rates in advance of each burst (transmission plan)

  • Different bandwidth smoothing algorithms use various strategy to generate their transmission plan

Transmission plan
Transmission plan

  • Suppose a compressed video stream consists of n frames, where frame I requires fi bytes of storage

  • The server must always transmit quickly enough to avoid pre-fetch buffer underflow, where

Transmission plan1
Transmission plan

  • The server must not transmit more data than

  • It prevent the overflow of the pre-fetch buffer (of size b)

Transmission plan2
Transmission plan

  • Hence, any valid transmission plan should follow the following constraint

  • where ci is the transmission rate during frame slot i of the smoothed video stream

Transmission plan3
Transmission plan

  • Creating a transmission plan involves generating m consecutive runs each with a constant bandwidth allocation rj and duration tj

Critical bandwidth allocation
Critical bandwidth allocation

  • For the need of decrease bandwidth, the CBA algorithm starts a rate decrease at the leftmost point of the frontier

Critical bandwidth allocation1
Critical bandwidth allocation

  • For the need of increase bandwidth, the CBA performs a search along the frontier to locate the starting point that allows the next trajectory to extend as far as possible

Critical bandwidth allocation2
Critical bandwidth allocation

  • smallest possible peak bandwidth requirement

  • minimum number of bandwidth increases

  • does not necessary have the minimum number of bandwidth decreases, since the algorithm selects the leftmost starting point

Minimum changes bandwidth allocation
Minimum changes bandwidth allocation

  • Extends the CBA scheme to perform the linear search operation on all rate changes

  • smallest possible number of rate changes

  • minimum peak bandwidth


Minimum variability bandwidth allocation
Minimum variability bandwidth allocation

  • Reduce the variability in the rate requirements across the lifetime of the transmission plan

  • Initiates bandwidth changes at the leftmost point along the frontier, for both rate increases and rate decreases

Run boundary example
Run boundary example

  • Selection of starting point of different bandwidth smoothing algorithm

Piecewise constant rate transmission and transport algorithm
Piecewise Constant Rate Transmission and Transport Algorithm

  • Aim : Generate a single run for each intervals by connecting the interaction points on the Funder curve

Piecewise constant rate transmission and transport algorithm1
Piecewise Constant Rate Transmission and Transport Algorithm

  • Slope of the dotted line corresponds to the rate rj in the resulting transmission plan

  • vertically offsets the plan until all runs lie above Funder curve

  • introducing an initial playback delay in the pre-fetch buffer

Mobile agent
Mobile agent

  • Definition of mobile agent

    • a program that is able to migrate from node to node on a network under its own control for the purpose of completing a task specified by a user

    • The agent chooses when and to where it will migrate and may interrupt its own execution and continue anywhere on the network

Reasons for using mobile agent
Reasons for using Mobile Agent

  • Asynchronous interaction by sending one active message to the service site

  • Reduction of network traffic

Reasons for using mobile agent1
Reasons for using Mobile Agent

  • Support for mobile and lightweight devices

Audio server client delivery system1
Audio Server/Client delivery system

  • The system is implemented under Linux

  • Use MPEG 1 layer 3 compression technique to compress the audio file

  • mp3 files are stored in the same machine where the audio server is running

Transmission plan4
Transmission plan

  • mp3 bit rate = 128kbps

  • try to approximate the bit-rate by introducing sleep intervals between successive sending attempts

  • Maximum Transfer Unit(MTU)= 512 bytes

  • Sleep interval = MTU/(mp3 bit rate)


Transmission plan5
Transmission plan

  • While (server buffer not empty){

  • sleep interval =0.03125sec;

  • Record the start time;

  • Transmit audio packet;

  • Record the stop time;

  • Sleep for sec;

  • }

Buffer management in client side
Buffer Management in Client Side

  • Need to buffer audio data at the beginning of playback process since some packets may arrive too late

  • Or some packets may arrive in burst

  • Use Leaky bucket Model in the client side buffer to produce a constant output bit rate (128kbps) to the decoder


  • We have presented four bandwidth smoothing algorithms

  • We have discussed the possibility of substituting client/server model with mobile agent communication model

  • The audio server/client delivery system has been presented

Future work
Future Work

  • Implement video server/client delivery system

  • Use mobile agent in the multimedia applications to delivery audio or video data