Internet telephony uses the Internet to send audio, video, and fax between users in real time. A basic IP telephone system has two components: IP phones for users and a media gateway controller that provides call control and coordination. For interconnection with traditional phone systems, media and signaling gateways translate between IP and public switched telephone networks. IP telephony works by digitizing, compressing, and packetizing telephone signals and routing them over the Internet using IP protocols. While offering lower costs, internet telephony has reliability issues and cannot currently support emergency calls.