Topic Last Modified: 2011-03-28

There are obvious advantages to providing branch-site resiliency to your organization, namely that if you lose the connection to the central site, branch site users will continue to have Enterprise Voice service and voice mail (if you configure voice mail rerouting settings; for details, see Branch-Site Resiliency Requirements). However, for sites with fewer than 25 users a resiliency solution may not provide return on investment.

If you decide to provide branch-site resiliency, you have three options for how to do so. Use the following table to help you determine which option is right for you.

If you… We recommend that you use a…

Host between 25 and 1000 users at your branch site, and if the return on investment does not support a full deployment or where local administrative support is unavailable

Survivable Branch Appliance



The Survivable Branch Appliance is an industry-standard blade server with a Microsoft Lync Server 2010 Registrar and Mediation Server running on Windows Server 2008 R2. The Survivable Branch Appliance also contains a PSTN gateway. Qualified third-party devices (developed by Microsoft partners in the SBA qualification/certification program) provide a continuous PSTN connection in the event of WAN failure, but it does not provide resilient presence and conferencing because these features depend on Front End Servers at the central site.



For details about Survivable Branch Appliances, see “Survivable Branch Appliance Details”, later in this topic.



Note: If you decide to also use a SIP trunk with your Survivable Branch Appliance, contact your Survivable Branch Appliance vendor to learn about which service provider is right for your organization.

Host between 1000 and 2000 users at your branch site, lack a resilient WAN connection, and have trained Lync Server administrators available

Survivable Branch Server or two Survivable Branch Appliances



The Survivable Branch Server is a Windows Server meeting specified hardware requirements that has Lync Server 2010 Registrar and Mediation Server software installed on it. It must connect to either a PSTN gateway or a SIP trunk to a telephone service provider.



For details about Survivable Branch Servers, see “Survivable Branch Server Details,” later in this topic.

If you require presence and conferencing features in addition to voice features for up to 5000 users, and have trained Lync Server administrators available

Deploy as a central site with a Standard Edition server rather than as a branch site.



A full-scale Lync Server deployment provides a continuous PSTN connection and resilient presence and conferencing in the event of WAN failure.



For details about preparing for this solution, see Planning Primer: Planning for Your Organization, Determining Your System Requirements, Determining Your Infrastructure Requirements, and other relevant sections of the Planning documentation.

Resiliency Topologies

The following figure shows the recommended topologies for branch-site resiliency.


Voice Branch Resiliency Options

Survivable Branch Appliance Details

The Lync Server 2010 Survivable Branch Appliance includes the following components:

  • A Registrar for user authentication, registration and call routing

  • A Mediation Server for handling signaling between the Registrar and a PSTN gateway

  • A PSTN gateway for routing calls to the PSTN as a fallback transport in the event of a WAN outage

  • SQL Server Express for local user data storage

The Survivable Branch Appliance also includes PSTN trunks, analog ports, and an Ethernet adapter.

If the branch site’s WAN connection to a central site becomes unavailable, internal branch users continue to be registered with the Survivable Branch Appliance Registrar and obtain uninterrupted voice service using the Survivable Branch Appliance’s connection to the PSTN. Branch site users connecting from home or other remote locations will be able to register with a Registrar server at a central site in the event the WAN link to the branch site is unavailable. These users will have full unified communications functionality with the sole exception that inbound calls to the branch site will go to voice mail. When the WAN connection becomes available, full functionality should be restored to branch site users. Neither the failover to the Survivable Branch Appliance nor the restoration of service requires the presence of an IT administrator.

Lync Server supports up to two Survivable Branch Appliance at a branch site.

Survivable Branch Appliance Deployment Overview

The Survivable Branch Appliance is manufactured by original equipment manufacturers in partnership with Microsoft and deployed on their behalf by value added retailers. This deployment should occur only after Lync Server 2010 has been deployed at the central site, a WAN connection to the branch site is in place, and branch site users are enabled for Enterprise Voice.

For details about these phases, see Deploying a Survivable Branch Appliance or Server in the Deployment documentation.

Phase Steps User Rights

Set up Active Directory Domain Services for the Survivable Branch Appliance

At the central site:

  1. Create a domain user account (or enterprise identity) for the technician who will install and activate the Survivable Branch Appliance at the branch site.

  2. Create a computer account (with the applicable FQDN) for Survivable Branch Appliance in Active Directory.

  3. In Topology Builder, create and publish the Survivable Branch Appliance.

The technician user account must be a member of RTCUniversalSBATechnicians. The Survivable Branch Appliance must belong to the RTCSBAUniversalServices group, which happens automatically when you use Topology Builder.

Install, and activate the Survivable Branch Appliance.

At the branch site:

  1. Connect the Survivable Branch Appliance to an Ethernet port and PSTN port.

  2. Start the Survivable Branch Appliance.

  3. Join the Survivable Branch Appliance to the domain, using the domain user account created for the Survivable Branch Appliance at the central site. Set the FQDN and IP address to match the FQDN created in the computer account.

  4. Configure the Survivable Branch Appliance using the OEM user interface.

  5. Test PSTN connectivity.

The technician user account must be a member of RTCUniversalSBATechnicians.

Survivable Branch Server Details

In Topology Builder create the branch site, add the Survivable Branch Server to that site, and then run the Lync Server Deployment Wizard on the computer where you want to install the role.

See Also

Other Resources

Deploying Lync Server 2010


    Branch site resiliency options