This chapter provided a technical overview of four major areas of Office Communications Server technologies: SIP, SIP routing, GRUU, and authentication. 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 requests that are used to establish communication sessions and what SIP call flows look like. You should also be familiar with routing logic that Office Communications Server uses to route these main SIP requests inside and outside the enterprise. Finally, you should have an understanding of authentication technologies used when signing in to Office Communications Server and the different call flows for these technologies. 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.