Abstract
This paper provides a unified approach that can directly verify the following results related to First-Come-First-Served (FCFS): (a) in the case of a single server system, FCFS is optimal for max of C (completion time) and max of F (flow time), (b) in the case of a multi server system with identical servers, when customers have the equal processing time, any optimal discipline for the total (sum) of C, F and W (waiting time) has the same service starting times as FCFS, and (c) in the later case, FCFS is optimal for max of C, max of F and max of W.