Measurement-based admission control (MBAC)algorithm is designed for the relaxed real-time service. In contrast to traditional connection admission control mechanisms,the most attractive feature of MBAC algorithm is that it does not require a prior traffic model and that is very difficult for the user to come up with a tight traffic model before establishing a flow.Other advantages of MBAC include that it can achieve higher network utilization and offer quality service to users. In this article, the study of the equations in the MBAC shows that they can all be expressed in the same form. Based on the same form,some MBAC algorithms can achieve same performance only if they satisfy some conditions.