In this study, we investigated a signalling load control mechanism for SIP server networks and developed a corresponding queuing model. The so-called hop-by-hop overload control, known from recent IETF drafts and RFCs, was considered and a similar buffer overload control scheme which was developed for the SS7 signalling link in ITU-T Recommendation Q.704, was proposed. The mechanism is based on hysteretic load control with thresholds for reducing potential oscillations between the control-on and control-off states under certain loading conditions. Adjustment of three types of thresholds - the overload onset threshold, the overload abatement threshold, and the overload discard threshold - makes possible the regulation of signalling traffic to meet blocking requirements. In this study, we built and analyzed the M/M/1 queue with bi-level hysteretic input load control. A numerical example illustrating the control mechanism that minimizes the return time from overloading states satisfying the throttling and mean control cycle time constraints is also presented. © ECMS Klaus G. Troitzsch, Michael Möhring, Ulf Lotzmann (Editors).