 Mobility management uses the SIP protocol and describes the messages and procedures necessary for RFSSs to perform registration, and affiliation across the ISSI for roaming SUs.Call control also uses the SIP protocol and describes the messages and procedures necessary for RFSSs to set up and tear down a call, and manage RTP resources.Transmission control uses the RTP protocol and describes the messages and procedures necessary for RFSSs to convey voice information, and manage voice call requests.