[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

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 voicemail (if you configure voicemail rerouting settings; for more information, 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 Communications Server 2010 Registrar and Mediation Server running on Windows Server 2008 R2. The Survivable Branch Appliance also contains an IP-IP/PSTN gateway. This non-Microsoft device provides 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 more information about Survivable Branch Appliances, see “Survivable Branch Appliance Details,” 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 5000 users at your branch site, lack a resilient WAN connection, and have trained Communications Server admins available

Survivable Branch Server



The Survivable Branch Server is a Windows server that has Communications Server 2010 Registrar and Mediation Server software installed on it. It must connect to either an IP/PSTN gateway or a SIP trunk to a telephone service provider.



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

Host more than 5000 users at your branch site and have trained Communications Server admins available

Full-scale Communications Server 2010 deployment at the branch site and an IP/PSTN gateway or SIP trunk



A full-scale Communications Server deployment provides a continuous PSTN connection in the event of WAN failure, as well as resilient presence and conferencing. Note that you do NOT need to include Mediation Server in your branch-site Communications Server deployment if you’re using an IP/PSTN gateway that supports media bypass.



For more information about preparing for this solution, see Planning for Your Organization, Preparing Your Environment, Determining Your Infrastructure Requirements, and other relevant sections of this guide.

Resiliency Topologies

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


Survivable Branch Appliance Details

The Communications 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 an IP-PSTN gateway

  • An IP-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.

The following figure shows the basic architecture of the Survivable Branch Appliance.


If the branch site’s WAN connection to a central site becomes unavailable, internal branch users should 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. Remote branch site users should be able to register with a Registrar server at a central site. 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.

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 Communications 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 detailed information about these phases, see Deploying a Survivable Branch Appliance or Server, in the Deployment Guide.

Phase Steps Permissions

Install prerequisite software

At the central site:

  1. Install Communications Server 2010 at the central site.

  2. Set up permissions for an installation technician at the branch site.

  3. Create a Survivable Branch Appliance computer account in Active Directory and add Survivable Branch Appliance to topology.

The technician must belong to the RTCUniversalSBATechnicians group.



The computer 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 turn it on.

  2. Log on to the Survivable Branch Appliance, and join it to domain.

  3. Use the Web UI to install and activate the Survivable Branch Appliance.

  4. Test PSTN connectivity.

The technician must belong to the RTCUniversalSBATechnicians group.

Survivable Branch Server Details

Install the Survivable Branch Server the same way you install any Communications Server role.

See Also


    Survivable Branch Appliance components and connectivity
    Topologies enabling voice survivability in a branch site