The documentation covers in detail the many decisions organizations must make when planning a deployment. For organizations with fewer than 5000 users who intend to deploy only instant messaging (IM), presence, A/V conferencing, and Web conferencing, a deployment that contains a single Standard Edition server with a single Edge Server is normally sufficient. If you intend to use a Web-based client instead of deploying Microsoft Office Communicator 2007 R2 to all your users, you also need to deploy Communicator Web Access and a reverse proxy. Figure 1 shows the reference topology that we use in this walkthrough.
In this deployment, the Standard Edition server supports IM, presence, A/V conferencing and Web conferencing. The Edge Server provides remote user access, federation, and conferencing with anonymous users. Communicator Web Access provides a browser-based client that extends IM and presence information to internal and external users, including users who are running operating systems other than Microsoft Windows.