[This is pre-release documentation and subject to change in future releases. This topic's current status is: Milestone-Ready]

Topic Last Modified: 2010-07-18

A Microsoft Communications Server 2010 Director authenticates user requests and then refers them to their home pools, but is not home to any user accounts and provides SIP Registrar, SIP Proxy, and Web Services only. If your deployment includes multiple Front End pools in a central site, a Director can reduce the authentication workload on one of the pools and thereby improve overall performance.

For external user access, a Director authenticates inbound Session Initiation Protocol (SIP) requests forwarded by the Edge server, determines the user’s correct home pool, and proxies the SIP traffic to a Front End server in the user’s home Enterprise pool or Standard Edition server.

When a Director is used to authenticate external users, it relieves Enterprise pool servers from the overhead of performing authentication of these users. It also helps insulate internal Front End pools from malicious traffic such as denial-of-service attacks; if the network is flooded with invalid external traffic in such an attack, this traffic ends at the Director, which minimizes any performance impact on internal users.

If a Director or Director Pool is deployed, by default it is configured as the internal next-hop to which an Edge Server routes inbound SIP traffic destined to internal servers. Furthermore, Front Ends can be configured to proxy outgoing SIP requests to Federated partners from the various pools to the Edge Server(s) via a Director, thereby limiting the numbers of servers from which the internal firewall needs to permit outgoing SIP traffic.

Directors can be deployed as one-off servers or can be deployed as multiple server pools (they can use DNS load balancing for SIP traffic, but must use Hardware Load Balancing for the HTTP/HTTPS Web Service traffic) for higher availability and capacity. Once you have deployed the Front End and the Back End, and confirmed that it is working, you can deploy a Director. This section describes that process.

Directors have the same hardware and software requirements as Front End servers.

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