چكيده به لاتين
Session Initiation Protocol (SIP) is an application layer protocol designed to create, manage, and terminate multimedia sessions in the IP multimedia subsystem. The variety of features and popularity of this protocol have resulted to its extensive use and high traffic volume in SIP proxies. However this protocol lacks the proper mechanism for overload control, and the quality of signaling is severely affected in cases of overload. This thesis aimed to improve the methods of controlling overload in SIP proxies, in such a way that the goodput of SIP signaling is not reduced and in addition, to observe issues such as stability, maximum use of proxies' capacity and fairness between flows.
In order to achieve these goals, this thesis was divided into three distinct parts. In the first part, the fluid model in the queues of two tandem SIP proxies and the stability conditions using the theory of Lyapunov were studied analytically. In the second part, two explicit methods were proposed using fluid flow equations and stability conditions, as well as an implicit method based on transaction response time and the number of previous retransmissions. These methods were evaluated by simulation and also operationally with implementation in the testbed and compared with similar methods. Another examined case of this stage is to improve the sustainability of proxies against overload, which was achieved by rejecting surplus requests in the operating system kernel with minimal cost, prior to further processing in the application layer.
In the third part, the policy of resource allocation to flows was evaluated with the optimization problem of network utility maximization in scenarios with proportional fairness, max-min fairness and also with regards to minimum service rates. In order to benefit from these policies practically, the classification of flows and message prioritization are used, which are applicable at the proxy level or at the operating system level.
