This is for operation and supply chain . I need the answer to be related to chapter 9 (Variability and Its Impact on Process Performance: Waiting Time Problems)

Many companies including banks have customer service departments that receive a large number of calls (and inquiries) from their customers on a daily basis. One of the biggest challenges for such departments is to reduce the waiting time that their customers experience (needless to say that waiting time may have direct relationship with customer dissatisfaction). Explain what factors can affect the waiting time length in a typical customer service operations? And, what are the potential ways to reduce waiting time?