Priority-Based Queue Management Scheme to Reduce Overloads on SIP Servers

If a session initiation protocol (SIP) server receives enough SIP messages to exceed its processing capacity, it goes into overload. When a SIP server receives new SIP messages under overload, the SIP message queue in the server lengthens, which may cause significant throughput degradation in the network. An overload control mechanism using the 503 response code is specified in the SIP standard to improve throughput in the event of such an overload. However, it is known that this is insufficient to control overloading in a large SIP network. In this paper we propose a queue management scheme at a SIP server to improve throughput and prevent overload propagation when overload occurs. In the proposed scheme, SIP messages are dropped based on a dropping probability that is calculated by prioritizing the items in the SIP queue. We also show the effectiveness of the proposed scheme by simulation experiments.