SBA Versus SBS

A Survivable Branch Server is a Lync role that includes a limited Front End service for the registrar functionality, and a Mediation Server. It is installed and deployed like any other Lync role and requires a dedicated physical or virtual server to be created.

A Survivable Branch Appliance is a single piece of hardware that contains a media gateway and a Lync Survivable Branch Server. These appliances are produced by Microsoft partners and are similar to a Survivable Branch Server, but include the Survivable Branch Appliance server and IP/PSTN gateway all in one hardware device. These devices are typically more economical and take up less space than deploying a separate server and IP/PSTN gateway, so it makes sense to leverage these devices in small branch offices.

As with the Survivable Branch Server, users in the branch office use the Survivable Branch Appliance as the primary registrar service.

To recap, an SBA and SBS provide the same features to the end users, but the primary difference is that the SBA is bundled with a media gateway, whereas the SBS and the gateway are separate devices.

The other difference between an SBA and an SBS is scale. SBAs have some scale themselves and come with various amounts of RAM, intended for branch sites of 25 to 1,000 users. For branch sites of 1,000 to 5,000 users, Microsoft recommends using a dedicated Survivable Branch Server, mainly because it can perform better with more RAM and processing power.