Abstract
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.