Lync Server 2010 Call Resiliency

Lync Server 2010 provides voice call resiliency by creating a system of primary and secondary Registrars. This illustration shows two central sites, one running Lync Server Enterprise Edition and one using Standard Edition (the central sites are connected by a high-speed, low-latency WAN), and a branch site connected by a WAN link and the public switched telephone network (PSTN).

The Registrar role is collocated with the Front End role, including each Front End role in a pool of Front Ends, and manages connection and authentication of users and devices. It registers the Session Initiation Protocol (SIP) information needed to route calls to the correct endpoint.

Here a Lync endpoint at the central site (left) has a primary Registrar in the Front End pool Registrar of the central site (solid line); that primary Registrar has a secondary Registrar (dashed line) in the Front End of a Lync Standard Edition server at another central site.

If the Front End Server pool failed, voice services would fail over to use the backup Registrar in the Standard edition server so that calls could continue to be made and received. Instant messaging, presence information, and applications such as response groups or conferencing hosted in the failed Front End Server pool would not be available.