Installation At first glance, OCS seems daunting to install, but many of the required components are likely already in existence in corporate networks.You'll need an Active Directory server, hosting core network services (such as DNS), and a Certificate Services server. You also need Exchange Server 2007 configured with the Unified Mailbox role, plus SharePoint Server and SQL Server.The OCS 2007-specific components include the primary OCS system (including an A/V MCU), a Mediation Server that transcodes outbound calls destined for the PSTN (Public Switched Telephone Network) (I used an AudioCodes MP-114 Analog Gateway), a Communicator Web Access Server and a Quality of Experience Monitoring Server (more on that below). Both the primary OCS system and the Quality of Experience servers require SQL Server on the back end. Microsoft provides copious amounts of literature to help organizations right-size their OCS deployment. In general, most OCS components in a geographically distributed network could be hosted centrally. However, Microsoft representatives definitely recommend the Mediation Servers be distributed to where the trunks are located, and they also suggest distributing A/V MCU servers to aid in multiparty calls. However, I'd recommend at least talking to qualified third-party resources as a sanity check before going too far with OCS deployment plans, to ensure the project meets both current and future performance requirements. Integration Microsoft currently supports two avenues of integration with SIP- (Session Initial Protocol) based equipment. PSTN gateway devices bridge calls between the SIP-based telephony network and the analog PSTN. In addition to the AudioCodes equipment I tested with, OCS can work with PSTN gateways from Cisco Systems, Dialogic, Network Equipment Technologies and Quintum Technologies. OCS also integrates with certain IP PBXes. Enterprise customers that are not ready to perform a forklift replacement of existing telecom equipment in favor of OCS-either because the existing system has not reached end of life or because OCS does not provide all the enterprise telephony features expected from a voice system-may want to investigate OCS' PBX integrations to marry OCS' desktop functionality with existing desktop phones and backed systems. At this time, Nortel Networks is the only third-party PBX vendor qualified to work with OCS. However, the integration happens via SIP, so other solutions may work to some extent. As I saw in person at Nortel Networks' facility in San Ramon, Calif., a Nortel CS1000 PBX-running the most up-to-date code-supports dual forking with remote call control. This means that a Nortel phone and an OCS Communicator session can share a twinned extension-one that rings through in both places, allowing a user to seamlessly move from one device to the next, with OCS' presence capabilities being aware of activity on the PBX extension.