 6: Presentation Layer 6 controls the format or how the information Layer looks on the user's screen. Hypertext Markup Language (HTML), which is used to format web pages and some e-mail messages, is a Layer 6 standard. Layer 7: Application Layer Layer 7 includes the application itself plus specialized services such as file transfers or print services. HTTP is a Layer 7 protocol. This page intentionally left blank Data Centers and IP Private Branch Exchanges In this chapter: Introduction Next-Generation Data Centers: Virtualization and Gigabit Speeds Managing Virtualization Backbone and Individual Local Area Network Structures IP Private Branch Exchange Systems for Internal Use The Technology behind IP Telephony IP Private Branch Exchange Architecture Value-Added Applications for Telephone Systems Summary Appendix Data Centers and IP Private Branch Exchanges INTRODUCTION desire to improve staff and computing productivity as well as technological advances motivates enterprises to adopt technologies to increase efficiencies across the organization. Organizations are no longer locked into supporting the majority of functions in-house. They can outsource them to cloud providers and hosting services (see Chapter 1, "Computing and Enabling Technologies," for more information about cloud computing), leading to savings in energy, staffing, and space requirements. How- ever, this creates pressure on IT directors to demonstrate that applications in the data center can be run as cost-effectively as those operated by cloud providers. CEOs and chief financial officers are aware that public cloud providers' offerings such as Amazon Web Services, Google Apps, and Rackspace Hosting can potentially save money on in-house computing and increase the speed of developing software applications. IT directors are often called upon to justify operating or developing certain appli- cations in-house as some large enterprises are reluctant to outsource mission-critical core applications. With these pressures in mind, data center managers are