Abstract: QOS parameter definitions are the basis for furthering QOS control. But QOS parameters defined by ISO and ITU are incoherent and incompatible, which leads to the inefficiency of QOS control. In terms of the characteristics of multimedia real time applications, the minimum QOS parameter set in transport layer is proposed and defined for the first time. It is demonstrated that QOS parameters defined by ISO and ITU can be represented by parameters or a combination of parameters of the set. It is also shown that the set is open and manageable and can be the potential unified basis for QOS parameters.