From the model Ⅰ we can see: c_s1 refers to the cost of handling service which is provided by handling facilities in unit time, when〖 µ=1 . c〗_s1µ refers to the cost of handling service which is provided by the single desk in the unit time. However, in model Ⅱ, c_s2 refers to the cost of handling service which is provided by every service desk in the unit time. The refore, the meaning of 〖 c〗_s1µ in model Ⅰ is equivalent