Real-Time Scheduling Support
		in Ultrix-4.2 for Multimedia Communication

				 Tom Fisher
			fisher@tenet.Berkeley.EDU

			      The Tenet Group
			 Computer Science Division
	Department of Electrical Engineering and Computer Sciences
			 University of California
			Berkeley, California 94720

				    and

		 International Computer Science Institute
			    1947 Center Street
			 Berkeley, California 94720

				 ABSTRACT

	     Advanced workstations are now being equipped to  handle
	various  types  of multimedia applications such as audio and
	video.  The quality  of  these  images  and  sounds  depends
	highly  on  the  timely  management  of multimedia data.  In
	order to provide such management, support for real-time pro-
	cess  scheduling  must exist.  In this paper we describe the
	fundamental mechanisms implemented in the  Ultrix4.2  kernel
	that  provide  the  real-time  scheduling support needed for
	multimedia applications.  Our primary goal is to reduce  and
	bound the overall delay in the response times to both inter-
	nal as well as external events.  To  achieve  this  goal  we
	have  modified  the  Ultrix4.2  kernel  to be preemptible at
	highly specific locations and have added a small  subset  of
	data structure locks to maintain data consistency.  Work has
	also been done towards reducing and bounding the time  spent
	resolving  lock conflicts.  The end result is that we have a
	kernel capable of the  real-time  processing  necessary  for
	multimedia  applications.  Finally, we demonstrate and vali-
	date through experimentation that the above claim is true.