Obtain public key infrastructure (PKI) certificates for the new servers and for the reverse proxy and new Edge Server roles. You need certificates for each computer running Office Communications Server 2007 R2. Certificates can be issued from an internal certification authority (CA) or you can obtain the required certificates from a publicly trusted certification authority. You need Subject Alternate Name (SAN) certificates for some server roles and network interfaces. If you are planning on a single edge version after you transfer your users to Office Communications Server 2007 R2, you may be able to reuse your existing Access Proxy certificates. For details about certificates, see in the Deployment documentation.
If you intend to allow users who are homed on the Office Communications Server 2007 R2 Enterprise pool to have external or remote access, you need to prepare a complete set of security certificates to support Office Communications Server 2007 R2, Edge Server. For details, see in the Planning and Architecture documentation.