The Mediation Server has the following dependencies:

• Registrar. Required. The Registrar is the next hop for signaling in the Mediation Server’s interactions with the Communications Server 2010 network. Note that Mediation Server can be collocated on a Front End Server along with the Registrar, as well as being installed in a standalone pool consisting only of Mediation Servers. The Registrar is collocated with a Mediation Server and PSTN Gateway on a Survivable Branch Appliance.
  
  
• Monitoring Server. Optional but highly recommended. The Monitoring Server allows the Mediation Server to record quality metrics associated with its media sessions.
  
  
• Edge Server. Required for external user support. The Edge Server allows the Mediation Server to interact with users who are located behind a NAT or firewall.
  
  

The Communications Server 2010 Mediation Server is by default collocated with an instance of the Communications Server Registrar on a Standard Edition Server, a Front Server Server in an Enterprise pool, or Survivable Branch Appliance. All Mediation Servers in an Enterprise pool must be configured identically.

Where performance is an issue, it may be preferable to deploy one or more Mediation Servers in a dedicated standalone pool. For guidelines on which topology to deploy, see Deployment Guidelines for Mediation Server.

The following figure shows a simple topology consisting of two sites connected by a WAN link. Mediation Server is collocated with the Registrar on an Enterprise pool at Site 1. The Mediation Servers at Site 1 controls both the IP-PSTN gateway at Site 1 andthe gateway at Site 2. In this topology, media bypass is enabled globally to use site and region information, and the trunks to each PSTN Gateway (GW1 and GW2) have bypass enabled.

The next figure shows a simple topology where the Mediation Server is collocated with the Registrar on an Enterprise pool at Site 1 and has a Direct SIP connection to the IP-PBX at Site 1. In this figure, the Mediation Server also controls an IP-PSTN gateway at Site 2. Assume that Communicator users exist at both Sites 1 and 2. Also assume that the IP-PBX has an associated media processor that must be traversed by all media originating from Communications Server endpoints before being sent to media endpoints controlled by the IP-PBX. In this topology, media bypass is enabled globally to use site and region information, and the trunks to the PBX and IP-PSTN gateway have media bypass enabled.

For information on planning for PBX topologies, see Deployment Guidelines for Mediation Server and Direct SIP Deployment Options.

The last figure in this topic shows a topology where the Mediation Server is connected to the SBC of an Internet Telephony Service Provider. For more information on SIP trunking topologies, see SIP Trunks.