ABSTRACT
The Session Initiation Protocol (SIP), being an application layer protocol, forms the notion of end-to-end logical connections known as network flows, in the form of registrations or dialog-forming requests/responses between the SIP communicating functional entities, including user agents (UAs) and proxies. The management of these end-to-end connections in the form of network flows of SIP messages for reusing by proxies in the routing of SIP messages is very important, especially in the face of failures of SIP and network entities. The flow-based connection setup, keep-alive mechanisms, connection management by SIP entities, and illustrations of connection management are described in detail. In addition, the overload control of SIP entities, which is a prime requirement for the next-generation large-scale SIP networks, is articulated in great detail. Two types of overload control, known as loss-based and rate-based control algorithms, that complement each other are explained. The general behaviors of SIP entities for both overload control mechanisms are described in detail. The SIP extensions that are required for both connection management and overload control are also provided.
