Page 221 - DCOM303_DMGT504_OPERATION_RESEARCH

Operations Research

Notes We infer that queues form because the service facilities are inadequate. If service facilities are
increased, then the question arises how much to increase? For example, how many buses would
be needed to avoid queues? How many reservation counters would be needed to reduce the
queue? Increase in number of buses and reservation counters requires additional resource. At
the same time, costs due to customer dissatisfaction must also be considered.
In designing a queuing system, the system should balance service to customers (short queue)
and also the economic considerations (not too many servers). Queuing theory explores and
measures the performance in a queuing situation such as average number of customers waiting
in the queue, average waiting time of a customer and average server utilization.

11.1 Queuing System

The customers arrive at service counter (single or in groups) and are attended by one or more
servers. A customer served leaves the system after getting the service. In general, a queuing
system comprises with two components, the queue and the service facility. The queue is where
the customers are waiting to be served. The service facility is customers being served and the
individual service stations. A general queuing system with parallel server is shown in
Figure 11.1 below:

Figure 11.1: A Typical Queuing System

(x)
S 1 Customers
Customers
Arrival (x) S (x)
2
xxxxxxxxxxxxxxxxxxxx .
.
.
(x) Customers
Sn.
Departure

Queue Service Facility

Queuing System

11.1.1 Characteristics of Queuing System

In designing a good queuing system, it is necessary to have a good information about the
model. The characteristics listed below would provide sufficient information.
1. The arrival pattern.
2. The service mechanism.
3. The queue discipline.
4. The number of customers allowed in the system.

5. The number of service channels.

216 LOVELY PROFESSIONAL UNIVERSITY