Analysis of a Scan Service Policy in a Gated Loop System

Abstract

A communication system of n buffered input terminals, numbered 1,2,3,..., n, connected to a computer by a single channel, is analyzed. The n terminals are serviced according to a SCAN policy: the terminals are polled in sequence 1,2,3,..., n, n, n-1,...,2,1. Data are removed one unit at a time from the terminals’ buffer. Data arriving to the terminal during this time are stored in an auxilliary buffer and are served in the next poll to the terminal. When the buffer has been emptied, the channel is used for system overhead for a randomly determined length of time. The stationary distribution of buffer contents, assumed to exist if the total normalized arrival rate is less than one, is used to find the average buffer contents and the average intervisit time. General, independent arrival rates are assumed for the n terminals. The analysis follows that in Swartz [2].