Voip Providers by Protocol
SIP (Session Initiation Protocol) An application-layer control protocol, a Signaling protocol for Internet Telephony. SIP can establish sessions for features such as audio/videoconferencing, interactive gaming, and call forwarding to be deployed over IP networks thus enabling service providers to integrate basic IP telephony services with Web, e-mail, and chat services. In addition to user authentication, redirect and registration services, SIP Server supports traditional telephony features such as personal mobility, time-of-day routing and call forwarding based on the geographical location of the person being called.
IAX (Inter-Asterisk eXchange protocol) is an alternative to the SIP and H323 protocols for initiating and transmitting voice (and other) data over IP.
It's a protocol which has been produced by the group developing the Linux-based PBX software Asterisk rather than being a standards-based system.
It was developed because it was felt that SIP insufficiently supported: Interoperability with firewalls, a high performance, low overhead protocol, internationalization support, remote dialplan polling, flexible authentication, multimedia support, call statistic gathering, and call parameter communication.
MGCP (Media Gateway Control Protocol) A protocol complementary to H.323 and SIP, designed to control media gateways from external call control elements in decomposed gateway architectures. Working in conjunction with the Gateway Location Protocol (GLP), MGCP enables a caller with a PSTN phone number to locate the destination device and establish a session. It provides the gateway-to-gateway interface for the Session Initialization Protocol (SIP). MGCP is meant to simplify standards for the new Voice over Packet technology by eliminating the need for complex, processor-intense IP telephony devices, thus simplifying and lowering the cost of these terminals.
H.323 is a protocol standard for multimedia communications. H.323 was designed to support real-time transfer of audio and video data over packet networks like IP. The standard involves several different protocols covering specific aspects of Internet telephony. Most voice over IP (VoIP) applications utilize H.323. H.323 supports call setup, teardown and forwarding/transfer. Architectural elements of a H.323 based system are Terminals, Multipoint Control Units (MCUs), Gateways, an optional Gatekeeper and Border Elements. Different functions of H.323 run over either TCP or UDP. Overall, H.323 competes with the newer Session Initialization Protocol (SIP), another proven standard often found in VoIP systems.