Write a set of non-functional requirements for the ticket-issuing system, setting out its expected reliability and response time.

What will be an ideal response?

Possible non-functional requirements for the ticket issuing system include:
1. Between 0600 and 2300 in any one day, the total system down time should
not exceed 5 minutes.
2. Between 0600 and 2300 in any one day, the recovery time after a system
failure should not exceed 2 minutes.
3. Between 2300 and 0600 in any one day, the total system down time should
not exceed 20 minutes.
All these are availability requirements – note that these vary according to the time
of day. Failures when most people are traveling are less acceptable than failures
when there are few customers.
4. After the customer presses a button on the machine, the display should be
updated within 0.5 seconds.
5. The ticket issuing time after credit card validation has been received should
not exceed 10 seconds.
6. When validating credit cards, the display should provide a status message
for customers indicating that activity is taking place.
This tells the customer that the potentially time consuming activity of
validation is still in progress and that the system has not simply failed.
7. The maximum acceptable failure rate for ticket issue requests is 1: 10000.
Note that this is really ROCOF. I have not specified the acceptable number of
incorrect tickets as this depends on whether or not the system includes trace
facilities that allow customer requests to be logged. If so, a relatively high failure
rate is acceptable as customers can complain and get refunds. If not, only a very
low failure rate is acceptable.
Obviously, these requirements are arbitrary and there are many other
possible answers. You simply have to examine their credibility.