Reasons Waiting Lines Occur - correct answer ✔✔When demand exceeds capacity, variability (high
arrival rate and long service time), services cannot be completed ahead of time and stored for later use
Goals of Waiting Line Management - correct answer ✔✔Adequate service (wait time) at a reasonable
cost, minimize total costs associated with customers waiting for service and capacity cost
Metrics for Evaluating Waiting Lines - correct answer ✔✔1. Average # of customers waiting (in line or in
the system)(length of the line Lq)
2. Average time customers wait (in line or in the system) (wq=Lq/λ)
3. System Utilization
4. Cost of a given level of capacity
5. Probability that an arrival will have to wait for service
Parameters Affecting Waiting & The Saturation Effect - correct answer ✔✔Utilizations and variability
Little's Law - correct answer ✔✔In a stable system, the average # of customers in the system (line)
equals the average customer arrival rate times the average time in the system (line)
Single Server System (M/M/1) - correct answer ✔✔Infinite source, poisson arrival rate, single server,
exponential service time, system in steady state
Single Server System, Constant Service Time (M/D/1) - correct answer ✔✔If a system can reduce
variability, it can shorten waiting lines noticeably, average # of customers waiting in line cut in half,
average time customers spend waiting in line is also cut in half, similar improvements can be made by
smoothing arrival rates, Lq= λ^2/ 2u(u-λ)
Means for Reducing Waiting Time - correct answer ✔✔Reduce waiting lines by actively managing one or
more system constraints, increase processing capacity, facility size, # of servers, use better methods and
equipment, look for a bottleneck, reduce variability, standardize the service, shift demand
, The Psychology of Waiting - correct answer ✔✔Waiting customers that have nothing else to occupy their
thoughts often focus of the fact they are waiting and can perceive waiting time as much longer than
actual waiting time
Forward Scheduling - correct answer ✔✔Scheduling ahead from some point in time, how long will it take
to complete this job
Backward Scheduling - correct answer ✔✔Scheduling backwards from some due date, when is the latest
this job can be started and still be completed on time
Infinite Loading - correct answer ✔✔Jobs are assigned to workstations without regard to the capacity of
the work center, overloading may require shifting work, overtime, contracting out
Finite Loading - correct answer ✔✔Jobs are assigned to work centers taking into account the work
center capacity and job processing times
Scheduling Difficulties and Methods to Minimize them - correct answer ✔✔Set realistic due dates, focus
on bottle neck operations, if not possible schedule bottleneck operations first, schedule non bottleneck
operations around the bottleneck operations, consider splitting larger jobs
First Come First Serve - correct answer ✔✔Allocates resources to those who are first in line
Shortest Processing Time - correct answer ✔✔Jobs with the shortest processing times are assigned first
Earliest Due Date - correct answer ✔✔Earliest due date jobs are performed first
Critical Ratio - correct answer ✔✔Time remaining until due date divided by work remaining to be done
Job Flow Time - correct answer ✔✔The amount of time from when a job arrives until its complete,
includes not only processing time but also any time waiting to be processed
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