The SCCP client runs on an IP phone, also called an End Station, which uses SCCP for signaling and for making calls. For an SCCP client to make a call, it must first register with a Primary CallManager (and a secondary, if available). The connection between the client and the CallManager is over TCP on port 2000. This connection is then used to establish calls to or from the client. Transmission of media is over RTP, UDP, and IP.