Middleware is provided as a control plane for WiMAX control messaging. Each ASN in a WiMAX system is associated with a Session Initiation Protocol (SIP) server. A plurality of Functional Entities (FEs) are distributed across the ASNs, wherein each FE (or a group of FEs) associated with a SIP agent. Each FE is operable to control a function associated with a subscriber station (SS). The function controlled by a first FE is transferred to a second FE by employing the SIP agents to establish a SIP session between the first and second FEs. WiMAX control messages are then exchanged over the established session to transfer the SS function from the first FE to the second FE. The first and second FEs may be in the same ASN, or the first and second FEs may be in different ASNs.