Ch 4- Waiting Lines Flashcards
(19 cards)
waiting line
1 or more “customers” waiting for service. Occurs because of an imbalance between demand for service and capacity of system to provide service.
- “Customers” can be people, machines, inventory, etc.
- Variability in rate of demand determines size of lines (if no variability and enough capacity is provided –> no lines)
4 elements of a waiting situation
1) customer population (input)
2) waiting line of customers
3) service facility
4) a priority rule
customer population
An input that generates potential customers
service facility
A person (or crew), a machine (or group), or both necessary to perform the service for the customer.
priority rule
A rule that selects the next customer to be served by the service facility
- first-come, first-served
- earliest promised due date
- shortest expected processing time
service system
The number of lines and arrangement of the facilities.
channel
One or more facilities required to perform a given service
phase
a single step in providing the service
preemptive discipline
A rule that allows a customer of higher priority to interrupt the service of another customer
ex. emergency room
interarrival times
the time between customer arrivals
Implications of line length
Short lines could be good customer service or too much capacity. Long lines could be inefficiency or need to increase capacity.
Implications of number of customers in the system
A large number of customers can cause congestion and lead to customer dissatisfaction if more capacity is not added
Implications of waiting time in line
If the service time is fast, long lines can be served efficiently.
- if the wait time is long, managers can either change the arrival rate or try to make lines seem shorter than they really are (through entertainment) to minimize dissatisfaction
Implications of total time in the system
Total time in system can indicate problems with customers, server efficiency, or capacity. Might be necessary to change priority discipline, increase productivity, or adjust capacity.
Implications of service facility utilization
The collective utilization of the service facilities reflects percentage of time busy. Goal is to maintain high utilization and profitability without messing up other aspects of operations.
5 operating characteristics of the system
- Line Length
- Number of Customers in System
- Waiting Time in Line
- Total Time in System
- Service Facility Utilization
λ
average number of customer arrivals per period
μ
mean service rate
7 decision areas for management (after analyzing a waiting line problem)
- Arrival Rates
- Number of Service Facilities
- Number of Phases
- Number of Servers per Facility
- Server Efficiency
- Priority Rule
- Line Arrangement
