Adding a Mediation Server to a pool is much like creating the initial pool. The topology must first be updated and published to reflect the change. Follow the steps described previously to import the existing topology in Topology Builder, and then follow these steps to add another pool member:
1. Expand the Mediation Pools node.
2. Right-click the Mediation Pool name and select New Server.
3. Enter the fully qualified domain name of the new Mediation Server.
4. Select either Use All Configured IP Addresses or Limit Service Usage to Selected IP Addresses and enter the IP addresses to be used by the Lync Server 2013 services.
5. Optionally, select the IPv6 check box if IPv6 is in use on the network.
6. Click OK ...