Remote Authentication Dial In User Service (RADIUS) is a widespread used Authentication, Authorization and Accounting (AAA) protocol. With RADIUS, the network users are able to access the Internet in security and the operators can record the information of network activity such as login time, logout time and traffic, etc. This paper presents some observations of the real operational CDMA network in a certain city by analyzing the characteristics of the RADIUS packet-level data captured by monitoring system deployed between AAA server and PSDN server of the network. The distribution of activated mobile users, the characteristics of online mobile users such as traffic, online duration and login times were analyzed. Finally we acquired some valuable conclusions that might be useful for the mobile network operators.