Performance Measure Equation Average number in line (18–6) H(H – 1) (-) Probability of zero units in the system Po= 1- (18–7) Probability of n units in the system P,= Po (18–8a) --G)' Probability of less than n units in the system P = (18–8b) I This notation is commonly used to specify waiting-line models. The first symbol refers to arrivals, the second to service, and the third to the number of servers. M stands for a rate that can be described by a Poisson distribution or, equivalently, a time that can be described by an exponential distribution. Hence, M/M/1 indicates a Poisson arrival rate, a Poisson service rate, and one server. The symbol D is used to denote a deterministic (i.e., constant) service rate. Thus the notation M/D/1 would indicate the arrival rate is Poisson and the service rate is constant. Finally, the notation M/M/S would indicate multiple servers.
An airline is planning to open a satellite ticket desk in a new shopping plaza, staffed by
one ticket agent. It is estimated that requests for tickets and information will average
15 per hour, and requests will have a Poisson distribution. Service time is assumed to be exponentially distributed. Previous experience with similar satellite operations suggests
that mean service time should average about three minutes per request. Determine each of
the following:
a. System utilization
b. Percentage of time the server (agent) will be idle
c. The expected number of customers waiting to be served
d. The average time customers will spend in the system
e. The probability of zero customers in the system and the probability of four customers
in the system
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