In this chapter, the most important protocols that controls the operation of the end-to-end system and has implications on the overall performance aspects will be presented. Then, performance issues will be demonstrated. the performance issues and the challenge of enhancing SIP services performance will be highlighted and briefly discussed. The protocol related performance metrics will be identified to determine the way SIP is utilizing the system resources and how to maximize it. Moreover, the architectural design challenges will be targeted to enhance the SIP performance.
TopIntroduction
In this section, the most important protocols that controls the operation of the end-to-end system and has implications on the overall performance aspects will be presented. Then, performance issues will be demonstrated.
There are mainly two types of protocols; the control plane set of protocols and the data plane protocols. The Session Initiation Protocol (SIP) is one of the control domain protocols and was fully standardized and specified by Internet Engineering Task Force (IETF) in RFC 2543 for the first version SIP 1.0 and in RFC 3261 for the second version SIP 2.0 (Rosenberg, et al., 2002). SIP operates over IP protocol and considered as a communication protocol for signalling of real-time multimedia services such as voice and video and non-real-time services such as text messages and presence notifications. The protocol, which is text-based, mainly defines the signalling order between end users for call initiation, termination, in addition to modifying the call setup instantly during the call. It is also used for registering the users before the call being initiated.
In this report, the SIP message headers and signalling details will not be presented. But the performance issues and the challenge of enhancing SIP services performance will be highlighted and briefly discussed. Figure 1 shows the signalling diagram for registering users, initiation and termination of a call between caller, callee, and back to back SIP server.
TopThe protocol related performance metrics need to be identified to determine the way SIP is utilizing the system resources and how to maximize it. Moreover, the architectural design challenges need to be targeted to enhance the SIP performance. Some of the protocol-related metrics in addition to implementation related metrics is discussed in (On SIP Performance, 2004), it shows different set of tests that measures the processing time for SIP messages, memory allocation, thread performance, and call-setup time. The results show that the performance of the proxy server changes by varying SIP related parameters and thus affecting the number of calls by seconds that the proxy server can handle at a time. It also shows that the performance of SIP related architectures, such as the IP Multimedia Subsystems (IMS) that will be presented later, is more affected due to the heavy dependence of SIP signaling and SIP messages structure compared with a simple Proxy/Registrar Server. Furthermore, it is important to note that the performance of SIP signalling is significantly affected by the delay at different stages of registration, call initiation, and call termination processes. The performance of SIP signalling will also affect the QoS of the offered service. Hence, the need to define the metrics that identify the performance measure for SIP is crucial for evaluation and performance comparison purposes.
IETF proposed the criteria for the end-to-end SIP performance measures in RFC 6076 (Malas & Morton, 2011).
Figure 2. SIP signalling flow and performance metrics