Video transfer application transport protocol design over ATM networks

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Virginia Tech

This report analyzes the transport layer protocol functional requirements needed to support a video file transfer application over the proposed Broadband Integrated Services Digital Network (ISDN) network. The B-ISDN network will be capable of supporting very high speed transmissions (up to 100s of Mbps to individual users). The Asynchronous Transfer Mode (ATM) protocol is intended to be the transmission and switching standard upon which the next generation high speed integrated network will be based. The transport layer protocol supports the end-to-end communication channel and provides the application access to the B-ISDN network.

The video transfer application will essentially act as a file transfer service, where the file will be a digitized compressed form of the video. This file must then be transferred in a reasonable time with a very low probability of error (a requirement of the high compression ratios). High compression ratios are desired to minimize file length, transmission duration, and buffer requirements. The unique transfer requirements for the video transfer application are described in Section 3.0.

In order to achieve the application requirements, the transport protocol must minimize overhead, maximize the fixed application transfer data rate, and make full use of the ATM functions. Section 2.0 of this report provides a overview of B-ISDN and insight into the ATM protocol functions and processing times.

As a result of the transport layer analysis, a dedicated video transfer application transport protocol can be designed to operate without additional overhead fields other than what is provided by ATM. To minimize transmission duration, the file transfer data rate is fixed at 60.16 Mbps, this rate is then subdivided into sub-channels in order to utilize the ATM modulo 7 sequencing number header field. The transport protocol will use a Go-Back-7 window error control algorithm assigned to each sub-channel. With the low error rates associated with fiber transmission (or non-fiber transmission system with similar BER values), the probability of exhausting the window, and hence decreasing the transmission rate, is insignificant with respect to the overall transmission duration. Section 4.0 of this report, analyzes each transport layer function and describes its implementation tailored to supporting the video transfer application. Numerical analysis and simulations support the conclusions derived in this section.

Current transport protocols, primarily designed for circuit switched or datagram environments, are designed for relatively low speed, high error rate transmission systems. As a result, current transport protocols add a significant amount of overhead, hence increasing overall transmission duration and processing complexity. From a functional standpoint, it is concluded that the unique transport protocol design specified in Section 4.0 is superior to current/modified transport protocols in terms of resource utilization, processing simplicity, and total transmission duration.