The extent and diversity of systems provided by IP networks have made various technologies to approach integrating various types of access networks and converting to next generation network. The Session Initiation Protocol (SIP) with respect to facilities such as being in text form, end-to-end connection, independence from the type of transmitted data, and supporting various forms of transmission, is an appropriate choice for signaling protocol in order to make connection between two IP network users. These advantages have made SIP to be considered as a signalling protocol in IMS, a proposed signalling platform for next generation networks. Despite having all these advantages, SIP protocol is in lack of appropriate mechanism for addressing overload.Overload can cause serious problems for SIP servers. SIP overload occurs when a SIP server does not have enough resources to process messages. It is a proven fact that the performance of SIP servers is largely degraded during overload periods because of the built in message retransmission mechanism of SIP. In this Thesis, we propose an advanced method which is an improved method of the Windows Based Overload Control. In the Windows based Overload Control method, the window is used to limit the amount of messages that are generated at once by SIP proxy server. An adaptive window based overload control algorithm, which does not use explicit feedback from the downstream server, is proposed. The number of confirmation messages is used as a measure of the amount of load on the downstream server by upstream ones. Thus, the proposed algorithm does not impose any additional complexity or processing on the downstream server which is overloaded, making it a very robust approach. Our proposed algorithm is developed and implemented on Asterisk open source proxy and evaluated. The results indicate that the related server maintains its throughput at the maximum capacity in under-load conditions. Also it is concluded that the suggested method can change the maximum windows size dynamically through considering the number of confirmation message.
