Conclusion

In this paper, a prototype VOD application that distributes MPEG video over ATM network was developed to investigate design issues such as rate control and error control. Performance measurements, such as the achieved frame rate and the number of concurrent clients a single server can handle, indicate that the ATM networks can effectively transport compressed video (MPEG) for VOD application.  Experiments also show that random network errors and network burst errors (i.e. due to congestion) degrade the video quality severely and to an unacceptable level.  Thus error control must be provided. The two proposed error control methods­RS FEC and HEC­have their own advantages and disadvantages.  The RS FEC error control method maintained perfect image quality, but imposed a large overhead redundancy.  HEC had a small overhead redundancy and maintained the integrity of video format.  However, in the latter image quality was not guaranteed. A hybrid error control method involving both is probably optimal.  The VOD application may start by providing the high overhead redundancy RS FEC error control and switch to HEC error control as the number of concurrent clients handled increases.  Recall that fewer concurrent clients can be supported if the overhead redundancy is large.

Possible future work could be done to implement and verify the performance of the hybrid error control method described above. Also, researchers could investigate further the error control issues for VOD application. Another possible future endeavor might be to investigate further the rate control issues to provide interactive operations such as pause and stop, slow and fast forward, and rewind.

Endnotes

1ISO/IEC JTC 1/SC 29. Revised Text for ITU-T Recommendation H.262 (ISO/IEC: Japan, 1995).

2S. Sengodan and V. Li, "A Quasi-Static Retrival Scheme for Interative VOD Servers." In IEEE IC3N 96 (Washington DC, October 1996).

3R. Handel, M. Huber, and S. Schroder, ATM Networks­ Conepts, Protocols Applications (New York: Addison-Wesley, 1995).

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