An Interrogating Call Session Control Function (“I-CSCF”) server load balances Session Initiation Protocol (“SIP”) users over an Internet Protocol Multimedia Subsystem (“IMS”) network. The I-CSCF server establishes a Diameter connection between a first Serving Call Session Control Function (“S-CSCF”) server and receives a dynamically adjusted capacity and a status information from the first S-CSCF server. The I-CSCF server further receives from user equipment a request to initiate a SIP communication session over the IMS network. The I-CSCF server then selects an assigned S-CSCF server for the SIP communication session based at least on the dynamically adjusted capacity and the status information