Performance Study of an Input Queueing Packet Switch with Two Priority Classes

This paper studies an N x N nonblocking packet switch with input queues and two priority classes which can be used to support traffic with different requirements. The switch operation is slotted and, at each time slot, fixed size packets arrive at the inputs with distinct Bernoulli distributions for both the high and low priority classes. Two policies are studied. In the first policy, packets of both priority classes are queued when waiting for service. In the second policy, only low priority packets are queued, and high priority packets not delivered at first attempt are dropped from the system. Under both policies, high priority packets prevail over low priority packets at the inputs as well as the outputs. Because of the service dependencies introduced by the switch structure, an exact analysis of this system is intractable. This paper provides an approximate analysis based on some independence assumptions and uses an equivalent queueing system to estimate the service capability seen by each input. Using this approach, an expression for the input queue length distribution is obtained. The maximum system throughput is also derived and shown to exceed that of a single priority switch. Numerical results are compared to simulations and found to be in good agreement.Jeane S.-C. Chen (S'88-M'89) was born in Taipei, Taiwan. She received the B.S. degree from National Chiao-Tung University, Taiwan, the M.S. degree from Washington University, St. Louis, and the Ph.D. degree in 1990 from Columbia University, New York. Since 1982 she has been employed by IBM T. J. Watson Research Center, Yorktown Heights, NY, where she has been involved in data compression for storage of Chinese characters; optimal design and feedback control for electromagnetic devices;design, analysis, and prototyping of highspeed printer actuators; and,currently, modeling and performance analysis of communication networks.Her current research interests include packet switching architectures and dynamic routing in highspeed networks.Roch Guérin (S'84-M'86) was born in Paris, France, on June 26, 1959. He received the “Diplôme d'Ingénieur” from the Ècole Nationale Supérieure des Télécommunications, Paris, France, in 1983, and the M.S. and Ph.D. degrees from the California Institute of Technology, both in electrical engineering, in 1984 and 1986, respectively. Since August 1986 he has been with the IBM Research Division, T. J. Watson Research Center, Yorktown Heights, NY, where he now is a member of the Communication Network Analysis Group. His current research interests focus on design and analysis of switching systems and networks, dynamic routing algorithms, and their relation to bandwidth management and traffic/flow control in highspeed integrated networks. Dr. Guérin is a member of Sigma Xi, the IEEE Communications and Information Theory Societies, and he is the Editor for the Book Reviews Section of the IEEE Communications Magazine.