Measurements and analysis of the performance characteristics of SIP proxy servers

The wide scale deployment of the Internet, combined with several advancements in hardware and software technologies, have created opportunities for several Internet based applications such as Voice Over IP (VoIP) that involve the delivery of voice, video and data to the end user. In recent years, Internet Protocol (IP) telephony has been a real alternative to the traditional Public Switched Telephone Networks (PSTN). IP telephony offers more flexibility in the implementation of new features and services. The Session Initiation Protocol (SIP) is becoming a popular signaling protocol for VoIP based applications. SIP is a peer-to-peer multimedia signaling protocol standardized by the Internet Engineering Task Force (IETF) and it plays a vital role in providing IP telephony services. The SIP Proxy Server (SPS) is a software application that provides call routing services by parsing and forwarding all the incoming SIP packets in an IP telephony network. The efficiency of this process can create large scale, highly reliable packet voice networks for service providers and enterprises. Efficient design and implementation of the SIP proxy server architecture is investigated in this research, which can enable significantly enhancing the performance characteristics of the SPS. Since SPS performance can be characterized by the transaction states of each SIP session, we studied an existing M/M/1-network performance model of the SIP proxy server in the light of key performance benchmarks such as average response time to process the SIP calls and mean number of SIP calls in the system. The first part of our research identifies the limitations of the M/M/1-network model and provides an alternative M/D/1-network analytical model. Following this, based on more recent advancement in SPS software architecture, we propose an M/M/c performance model of the SPS, and note that this change enhances SPS performance. In the latter part of this research, we study the performance and scalability of the SIP proxy server when the calls are routed though more than one SPS. Because the deployment and delivery of SIP value-added services in the public network carry significant security issues, we also evaluate the relative performance impacts on the SIP proxy server when secured and non-secured transport protocols are used to transport the SIP packets.