An important class of applications with real-time data transport requirements is defined by applications requiring transmission of data units at regular intervals. These applications, which we call continuous media (CM) clients, include video conferencing, voice communication, and high-quality digital sound. The design of a data transport service for CM clients and its underlying protocol (within the XUNET U projecO is presented in this paper. The service makes use, in particular, of an a priori characterization of future data transmission requests by CM clients.First, we will give a few examples of CM clients and their specific data transmission needs. From these clients, we then extract a generalized list of data transport requirements for CM and describe the basic features of a service designed to meet these requirements. This service provides unreliable, in-sequence transfer (simplex, periodic) of so-called stream _dat_a units (STDUs) between a sending and a receiving client, with performance guarantees on loss, delay, and throughput. An important feature of the solution is the use of shared buffers to eliminate most direct client/service interactions and to smooth waffle patterns, which may be bursty due to fluctuations in the arrival process of data and variability of network delays. The paper concludes with some aspects of implementation.
1, IntroductionApplications with real-time data transport requirements fall into two categories: those which require transmission of data units at regular intervals, hereafter referred to as continuous media (CM) clients, and those which generate data for transmission at relatively arbitrary times, hereafter referred to as (real-time) message-oriented clients. Examples of the former are video conferencing, in which video frames (of fixed or variable length) are sent from source to destination once per frame time (e.g. 33 ms), voice communication, playback of high-quality digital sound, and transmission of sensor data that is measured and transferred with strict periodicity. Examples of real-time messageoriented clients are those which require urgent messages or transactions, and mail service with guaranteed delivery latency.It is generally accepted that dedicated transport protocols are necessary for high speed networks. Adaptation of existing transport protocols, originally designed for lower speed networks (such as OSI Transport Protocol Class 4 or TCP), to high speed environments is not straight-forward, and may not provide satisfactory performance to transport *
