Based on the functionality provided by the servers, each Lync server runs one or more roles.
- User authentication and registration
- Presence information and contact card exchange
- Address book services and distribution list expansion
- IM functionality, including multiparty IM conferences
- Web conferencing and application sharing (if deployed)
- Application hosting services, for both applications included with Lync Server (for example, Conferencing Attendant and Response Group application) and third-party applications
A/V Server allows user to have Audio and video conference.
Mediation Server is a necessary component for implementing Enterprise Voice and dial-in conferencing. Mediation Server translates signaling and, in some configurations, media between your internal Lync Server infrastructure and a public switched telephone network (PSTN) gateway, IP-PBX, or a Session Initiation Protocol (SIP) trunk.
Edge Server enables your users to communicate and collaborate with users outside the organization’s firewalls. These external users can include the organization’s own users who are currently working offsite, users from federated partner organizations, and outside users who have been invited to join conferences hosted on your Lync Server deployment. Edge Server also enables connectivity to public IM connectivity services, including Windows Live, AOL, and Yahoo!.
Directors can authenticate Lync Server user requests, but do not home user accounts, or provide presence or conferencing services. Directors are most useful in deployments that enable external user access, where the Director can authenticate requests before sending them on to internal servers. Directors can also improve performance in organizations with multiple Front End pools.
Monitoring Server collects data about the quality of your network media, in both Enterprise Voice calls and A/V conferences. This information can help you provide the best possible media experience for your users. It also collects call error records (CERs), which you can use to troubleshoot failed calls. Additionally, it collects usage information in the form of call detail records (CDRs) about various Lync Server features so that you can calculate return on investment of your deployment, and plan the future growth of your deployment.
Archiving Server enables you to archive IM communications and meeting content for compliance reasons. If you do not have legal compliance concerns, you do not need to deploy Archiving Server.
Lync 2010 has two versions: Standard Edition and Enterprise Edition. Standard Edition is designed for small organizations (less than 5,000 users). It provides the full functionalities, but does not support high-availability and scalability. e.g. It collocates Frond End Server, A/V server, Back End Server (SQL Express) on a single server, and does not allow user to change.
For large scale deployment, Lync Server 2010 Enterprise Edition is recommended. Enterprise Edition allows user to collocate some roles depending on user’s scenario. (see more)