Queueing Systems

, Volume 2, Issue 2, pp 115–145

Polling and greedy servers on a line

  • E. G. CoffmanJr.
  • E. N. Gilbert
Contributed Paper

DOI: 10.1007/BF01158396

Cite this article as:
Coffman, E.G. & Gilbert, E.N. Queueing Syst (1987) 2: 115. doi:10.1007/BF01158396


A single server moves with speed υ on a line interval (or a circle) of length (circumference)L. Customers, requiring service of constant durationb, arrive on the interval (or circle) at random at mean rate λ customers per unit length per unit time. A customer's mean wait for service depends partly on the rules governing the server's motion. We compare two different servers: thepolling server and thegreedy server. Without knowing the locations of waiting customers, a polling server scans endlessly back and forth across the interval (or clockwise around the circle), stopping only where it encounters a waiting customer. Knowing where customers are waiting, a greedy server always travels toward the current nearest one. Except for certain extreme values of υ,L, b, andλ, the polling and greedy servers are roughly equally effective. Indeed, the simpler polling server is often the better. Theoretical results show, in most cases, that the polling server has a high probability of moving toward the nearest customer, i.e. moving as a greedy server would. The greedy server is difficult to analyze, but was simulated on a computer.


Polling systemsdisk systemsdisk SCAN policyshortest-seek-time-first disk schedulingmoving-server systems

Copyright information

© J.C. Baltzer AG, Scientific Publishing Company 1987

Authors and Affiliations

  • E. G. CoffmanJr.
    • 1
  • E. N. Gilbert
    • 1
  1. 1.AT&T Bell LaboratoriesMurray HillUSA