[This is pre-release documentation and subject to change in future releases. This topic's current status is: Milestone-Ready]

Topic Last Modified: 2010-07-14

In Communications Server 2010, you define network sites that contain Communications Server components. A site represents a geographical location of your network, and is a set of computers well-connected by a high-speed, low-latency network, such as a single local area network (LAN) or two networks connected by a high-speed fiber optic network. Note that the concepts of sites in Communications Server is different from the concept of sites in Active Directory Domain Services and Microsoft Exchange Server.

Each site is either a central site, which contains at least one Front End pool or Standard Edition server, or a branch site. Each branch site is associated with exactly one central site, and the users at the branch site get most of their Communications Server functionality from the servers at the associated central site.Each branch site contains at least a public switched telephone network (PSTN) connection and can also include a Mediation Server. Alternatively, a branch site could run a Survivable Branch Appliance, which is a new device introduced in Communications Server 2010 that combines a PSTN gateway with some Communications Server functionality.

Branch sites with a Survivable Branch Appliance deployed are resilient in times of wide-area network failures. For example, in a site with a branch office appliance deployed, users can still make and receive Enterprise Voice calls if the network connecting the branch office site to the central site is down. For details about the Survivable Branch Appliance and this resiliency, see Branch-Site Voice Resiliency.