Voice Resiliency

Resiliency for voice was introduced through Survivable Branch Servers and Appliances starting in Lync Server 2010. This section discusses the various architectures available to organizations planning for voice resiliency.

To revisit the old approach for those performing migrations, back in Office Communications Server 2007 R2 the only way to provide resiliency for a branch site was to leverage dual WAN connections back to the datacenter, or deploy a full redundant set of pool services in the branch. Otherwise, a WAN outage would leave that branch completely offline.

Lync Server 2010 introduced the survivable branch components, which enable a branch to provide a minimal set of services to users in case the connection to the datacenter and main pool became unavailable. Branch components are paired or associated with a particular Front End pool, typically located in a datacenter or primary site.

Providing endpoints with a primary and backup registrar service achieves this redundancy. The registrar service existed in Office Communications Server 2007 R2 as part of the Front End Service, but has been separated into its own role in Lync Server 2010 and Lync Server 2013 to provide failover capabilities for voice features. When Lync endpoints sign in, they are informed through in-band signaling of both a primary and a backup registrar pool associated with their account. The primary registrar pool typically is the Front End pool where the user account is homed, except in branch office scenarios, in which the survivable branch component is the primary registrar and the associated Front End pool is the backup.