Although a central site topology must include one Front End pool or Standard Edition server, each central site can also contain the following:

• Multiple Front End pools, which can be in the same domain or different domains. Although, all Front End Servers in a Front End pool and the Back End Server for that pool, must be in the same domain.
  
  
• Multiple Standard Edition servers.
  
  
• A/V Conferencing Server or pool, if you want to support A/V conferencing functionality at the central site. For a Standard Edition server deployment, the A/V Conferencing Server is automatically collocated with the Standard Edition server and you cannot use a stand-alone A/V Conferencing Server or pool. For a Front End pool, use of a stand-alone A/V Conferencing Server or A/V Conferencing pool is optional but recommended for deployments with more than 10,000 users. The servers in an A/V Conferencing pool do not require load balancing because they provide their own load balancing. All Front End Servers of a central site that do not have a collocated A/V Conferencing Server use the same stand-alone A/V Conferencing Server or pool.
  
  
• Edge Server or Edge pool in your perimeter network, if you want your deployment to support federated partners, public IM connectivity, remote user access, participation of anonymous users in meetings, or hosted UM . You cannot collocate any other server role with an Edge Server. DNS load balancing is recommended, where appropriate, but hardware load balancing is also supported. For details about load balancing requirements and support, see Planning for External User Access in the Planning documentation and Deploying Edge Servers in the Deployment documentation.
  
  
• Mediation Server or pool, if you want to support Enterprise Voice or dial-in conferencing in a Front End pool at the central site. Depending on how you deploy Enterprise Voice support, you can collocate the Mediation Server in a Front End pool (the default) or deploy a stand-alone Mediation Server or pool. For details about the planning the appropriate Mediation Server topology, including collocation options, see Deployment Guidelines for Mediation Server in the Planning documentation. You can use DNS, hardware or application load balancing (when appropriate) to distribute traffic from a Mediation Server pool’s gateway peer, including a PSTN gateway, IP-PBX, or SIP trunk Session Border Control (SBC).
  
  
• Monitoring Server, if you want to support data collection about of your audio/video Quality of Experience (QoE) and call detail recording (CDR) for Enterprise Voice and A/V conferences in your deployment. Optionally, you can also install the Microsoft System Center Operations Manager (formerly Microsoft Operations Manager), which uses Monitoring CDR and QoE data to generate near real-time alerts showing the health of call reliability and media quality. A Monitoring Server can be collocated with an Archiving Server, with a SQL Server store of an Enterprise Edition Front End pool, or with a file store of a Front End pool. The Monitoring Server requires a database, but the database can be collocated on the Monitoring Server, with the database server for the Archiving Server, or on the Back End Server of an Enterprise Edition Front End pool. A Monitoring Server cannot be collocated with a Standard Edition server in a production environment.
  
  
• Archiving Server, if you want to archive IM communications and meeting content (for compliance reasons) in your deployment. An Archiving Server can be collocated with a Monitoring Server, with a SQL Server store of an Enterprise Edition Front End pool, or with a file store of an Enterprise Edition Front End pool. The Archiving Server requires a database, but the database can be collocated on the Archiving Server, with the database server for the Monitoring Server, or on the Back End Server of a Front End pool. An Archiving Server cannot be collocated with a Standard Edition server in a production environment.
  
  
• Director or Director pool, if you want to facilitate resiliency and redirection of Lync Server user requests to the user’s home pool, which can be either an Enterprise Edition Front End pool or a Standard Edition server. We recommend that you deploy a Director or Director pool in each central site that supports external user access and in each central site in which you deploy one or more Front End pools. Each Director pool can contain a maximum of ten Directors. A Director cannot be collocated with any other server role.
  
  
• Reverse proxy, which is not a Lync Server component but is required if you want to support sharing of web content for federated users. You cannot collocate a reverse proxy server with any Lync Server 2010 server role, but you can implement reverse proxy support for a Lync Server deployment by configuring the support on an existing reverse proxy server in your organization that is used for other applications.
  
  

All Front End pools and Standard Edition servers that you deploy at a central site share any of the following that you deploy for the central site:

• Director or Director pool
  
  
• Monitoring Server
  
  
• Archiving Server
  
  
• Stand-alone A/V Conferencing Server or pool (Enterprise Edition Front End pool only)
  
  
• Stand-alone Mediation Server or pool
  
  
• Edge Server or Edge pool
  
  

Note:
An Exchange UM Server can be implemented with your Lync Server 2010 deployment if you want to support integration of Microsoft Exchange unified messaging, but it is not a component of the Lync Server site.

Multiple central sites can also share any of the following that you deploy in one central site:

• Archiving Server
  
  
• Monitoring Server
  
  
• Stand-alone Mediation Server or pool
  
  
• Edge Server or Edge pool
  
  

Note:
An Exchange UM Server can be implemented with you Lync Server 2010 deployment and shared by multiple central sites, but it is not a component of the Lync Server site

For details about Lync Server 2010 server roles, see Server Roles in the Planning documentation.

For a summary of which Lync Server 2010 server roles can be collocated with other server roles, see Supported Server Collocation.

In addition to the server roles covered previously in this section, Lync Server 2010 has additional components and options, which can include some or all of the following:

• Firewalls
  
  
• PSTN gateways (if deploying Enterprise Voice)
  
  
• Exchange UM Server
  
  
• DNS load balancing
  
  
• Hardware load balancers
  
  
• SQL Server databases
  
  
• File shares
  
  

For details about all of the Lync Server 2010 components and options, see the Planning documentation.

A branch site is associated with a central site and each Survivable Branch Appliance in a branch site is associated with an Enterprise Edition Front End pool or a Standard Edition server in the associated central site. Branch sites depend on the central site for most of their functionality, so components at a branch site contain only the following:

• A Survivable Branch Appliance, which combines a public switched telephone network (PSTN) gateway with some Lync Server functionality. Mediation Server can be collocated with the instance of the Registrar on the Survivable Branch Appliance, you can deploy a stand-alone Mediation Server or pool of Mediation Servers.
  
  
• A Survivable Branch Server, which is a Windows server that has Lync Server 2010 Registrar and Mediation Server software installed.
  
  
• A stand-alone PSTN gateway (not part of the Survivable Branch Appliance) and stand-alone Mediation Server.
  
  

The requirements for Survivable Branch Servers are the same as the requirements for any Lync Server 2010 server role.