This chapter provided a technical overview of six major areas of Office Communications Server 2007 technology: SIP, SIP routing, GRUU, enhanced presence, authentication, and security. These fundamental areas are necessary for establishing secure communications in your deployment. Now that you have read this chapter, you should have a better understanding of the main SIP verbs that are used to establish communication sessions. You should also now know what these call flows looks like, and you should be familiar with authentication technologies used when signing into Office Communications Server 2007, the different call flows for these technologies, and the routing logic used by Office Communications Server 2007 to route these main SIP requests inside and outside the enterprise. Finally, the chapter introduced you to some security concepts and some actions you can take to protect your environment. There are additional resources you can leverage to gain a deeper understanding of each of these areas, and this information is provided in the next section.