Microsoft Office Communicator establishes a connection with the estos CallControlGateway via the Office Communications server (OCS). The estos CallControlGateway needs its own URI SIP for this. This URI SIP of the estos CallControlGateway has to be configured in the OCS as a static route. Afterwards the IP address which was configured in the static route must be added as authorized Host in the OCS.
The configuration of a static route in the Office Communications Server permits only routes for a complete domain (*@callcontrol.yourdomain.com). For the route to the estos CallControlGateway an own Sub-Domain has to be used.
When selecting the SIP URI, note the SIP Routing:
Configure the Static Route for TCP.
Configure the Static Route for TLS.