An SBA (Survivable Branch Appliance) is a device that increases communications resiliency in branch offices. In the event of a WAN link failure, SBAs switch VoIP calls from the network into the PTSN. However, this approach does not provide resilient presence and conferencing will also be affected during a WAN outage because these features depend on Front End Servers at the central site.

SBAs are third-party, all-in-one devices that consists of a PSTN gateway with the interface required for connectivity to the PSTN and a Lync Server Registrar and Mediation Server running on Windows Server 2008 R2. Data networks and factors such as bandwidth availability should be considered for designing an SBA.

SBAs are utilized in the following settings:
• Branch sites with up to 1000 users
• Have a T1/E1 or analog connection to the PSTN
• Limited IT staff on site
• Won’t miss conferencing or resilient presence during an outage