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		   B O S T O N   U N I V E R S I T Y
                                       
		      Computer Science Department
                                       
			  C O L L O Q U I U M
                                       
			 Tuesday April 4, 1995
                                       
				 12:45pm
		       (Coffee served at 12:30 pm)
                                       
			 Seminar Room / MCS 135
                                       

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           Real-Time Distance-Constrained Scheduling and
                 Its Applications in Communications

                           Ching-Chih Han

                   Real-Time Computing Laboratory
     Department of Electrical Engineering and Computer Science
                     The University of Michigan

  In the conventional real-time periodic task model, every task needs to
  be executed once during each of its periods.  The execution of a task in
  one period is independent of the execution of the same task in another
  period.  As a result, the executions of the same task in two consecutive
  periods may be right next to each other, or at the far ends of the two
  periods.  For some real-time applications, e.g., multimedia
  applications, there exists an additional constraint which require two
  executions of a task be close enough to each other.  We call this kind
  of constraints the temporal distance constraint.

  In order to incorporate the temporal distance requirement, we propose a
  new model for real-time task systems, called the real-time
  distance-constrained task model.  In such systems, the temporal distance
  between the finish times of any two consecutive executions of the same
  task must be less than or equal to a given value.  Using the scheduling
  algorithms designed for the traditional periodic task model for
  distance-constrained tasks may not provide efficient solutions.  In this
  talk, I will formally define the distance-constrained task model,
  present a scheduling algorithm for the model, and give the
  schedulability condition for the algorithm.  I will also discuss how to
  apply the distance-constrained scheduling schemes to real-time
  communications.  In particular, I will show how to guarantee the timely
  delivery of isochronous messages in a Distributed Queue Dual Bus (DQDB)
  network using our proposed model and scheduling algorithm.

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For colloquium info, including directions, see http://cs-www.bu.edu/colloquium
   For more information contact Prof. Mark Crovella <crovella@bu.edu>
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