The interviewer wants to be assured that you will be able to meet the scheduling commitments associated with being a dispatcher. Before you answer, be sure that you understand how often you will be on call. It's absolutely okay to ask the interviewer to clarify any scheduling expectations.
If you fully understand the schedule and expectations: "I understand that this dispatch position requires shift work, overtime, and being on call every other weekend. I am certainly able to meet those expectations."
If you do not fully understand the schedule and expectation: "I am available to work a variety of hours and am accustomed to being on call. Could you clarify for me the exact hours expectations for this role?"