The Lync Director role provides functionality for users accessing Lync internally and externally. The Lync Director role is one of the most confusing roles in the Lync environment. This follows on from the confusion that existed in OCS where I for one was never sure of when a Director should be deployed. One thing that has changed is that Microsoft have made an explicit Director role in Lync, whereas in OCS, the Director was simply a pool without users homed on it. Therefore Microsoft obviously believe that the Director has a role to play in Lync designs. The function of the Director is different dependent on whether the clients are internal or external.

Internal Users

Lync Server is deployed as one or more pools, based on Standard Edition or Enterprise Edition Lync Server. Users can be homed on only a single pool. Clients can be configured to find their Lync pool automatically. However, the DNS records that support this functionality can point to only a single pool. In a multi-pool environment, this 'primary' pool will have to redirect users to their correct home pool. This is an overhead on the 'primary' pool. The Lync Director is used to offload this redirection functionality. The Director does not home any users itself but redirects the user to their correct pool home. The requirement for the Lync Director is therefore for multi pool environments with high user numbers.

Once the user has been redirected to their correct pool, the Director plays no further role in communications between the client and the pool server.

External Users

For users accessing the Lync deployment from the Internet, the Director is set as the next hop server on the Lync Edge. In this situation, the Director will authenticate the users and only authenticated sessions will be forwarded to the internal pool servers. The Director stays in the communications path. For this reason, the Director can scale to 15,000 remote users. The Director is both offloading the authentication and providing an extra layer of security against DoS attacks (DoS attacks will affect the Director but internal users will continue to work as the internal pool servers will not be affected).

The platform requirements for the Director role are the same for other Lync roles with the exception of requiring only 4 GB of memory.