New Jersey Institute of Technology   	   	 
           Department of Electrical and Computer Engineering,
  	       New Jersey Center for Multimedia Research  
 	   Center for Communications and Signal Processing Research
	     North Jersey Chapter of IEEE Communications Society


    				present

   	NETWORKS WITH DETERMINISTIC QUALITY-OF-SERVICE GUARANTEES

			Professor Jorg Liebeherr
			 University of Virginia
   
       			    January 29, 1997
      			 2:30 PM, ECEC Room 202
  
         

Abstract:

The most demanding applications in a Quality-of-Service network require a
bounded-delay service that provides deterministic(i.e., worst-case) bounds on
network latencies for all packets.  Since traffic sources may have a variable
bit rate (VBR) with a high degree of burstiness, the network must carefully
allocate its resources in order to ensure a high achievable network
utilization.  The talk presents two recent results:  (1) a traffic
characterization method for VBR video, and (2) a novel scheduler that
transmits packets without violating the worst-case delay bounds. 

The traffic characterization method is designed to accurately specify the
traffic of stored VBR video sources, with low computational overhead. Using
actual MPEG traces, we demonstrate that using our method achieves higher
network utilizations than any other known characterization scheme.  We
present a new packet scheduling discipline, referred to as
Rotating-Priority-Queues+ (RPQ+), that attempts to combine the low
implementation overhead of a priority scheduler with the high efficiency of
the optimal Earliest-Deadline-First (EDF) scheduler.  RPQ+ is the only known
packet scheduler that is both superior to a priority scheduler and has an
achievable network utilization that increases with queue rotation frequency,
approaching that of EDF in the limit. 
 
 
Short Bio:
 
Jorg Liebeherr received the Diplom-Informatiker (M.S.) degree from the
University of Erlangen, Germany, in 1988 and the Ph.D. degree in Computer
Science from the the Georgia Institute of Technology in 1991. During 1990 and
1991 he did his dissertation work partly at the IBM T. J. Watson Research
Center. In 1992 he was a Postdoctoral Fellow in the Computer Science Division
at the University of California, Berkeley. Since September 1992 he is an
Assistant Professor in the Computer Science Department at the University of
Virginia. He received an NSF Research Initiation Award in 1993 and an NSF
CAREER Award in 1996.