A back-end server farm is a group of homogeneous back-end servers. A client making a request through the Relay Server farm must specify the back-end server farm it is targeting.

The load balancer directs requests from the mobile devices to a Relay Server running in the Relay Server farm. The load balancer is not required if there is only one Relay Server.

The Relay Server Outbound Enabler runs on the same computer as the back-end server. Its primary function is to initiate an outbound connection to all Relay Servers in the Relay Server farm on behalf of the back-end server. There is one Outbound Enabler per back-end server. See Outbound Enabler.