Providing multimedia services to users assumes perfect quality of transfer and modern processing equipment that involves need of development of new methods of the analysis and forecasting of functioning of a communication network. In the paper we investigate the problem of the overload that occurs on a SIP (Session Initiation Protocol) server. SIP overload mitigation is based on RBOC (Rate-based overload control) schema, which was designed by IETF SIP overload control workgroup. The aim of RBOC schema is to restrict signaling message flow rate from the client side towards the server side. Hysteretic overload control algorithm is used to define trigger point for sending control information by the server to the client. Token bucket algorithm is applied to restrict the number of the tokens that the server grants the client. Simulation model for estimation main performance metrics is developed. Traffic with different type of distribution is used for investigation the behavior of the system with tandem servers. The optimization problem for maximization of processor utilization of SIP server on the dependence of threshold values and the number of token is formulated. © ECMS Valeri M. Mladenov, Petia Georgieva, Grisha Spasov, Galidiya Petrova (Editors).