A Continuous Media Data Transport Service and Protocol for 
	      Real-Time Communication in High Speed Networks 

			      Bernd Wolfinger
				    and
				 Mark Moran

				  ABSTRACT

		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 trans-
	port service for CM  clients  and  its  underlying  protocol
	(within  the  XUNET  II project) is presented in this paper.
	The service makes use, in particular, of an a priori charac-
	terization  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 data 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  traffic
	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.