VoIP comprises many standards and protocols. Basic terminology must be understood in order to comprehend the applications and usage of VoIP. The following definitions serve as a useful starting point (the protocols are listed in alphabetical order):

• H.248 is an ITU Recommendation that defines "Gateway Control Protocol." H.248 is the result of a joint collaboration between the ITU and the IETF. It is also referred to as IETF RFC 2885 (MEGACO), which defines a centralized architecture for creating multimedia applications, including VoIP. In many ways, H.248 builds on and extends MGCP.

• H.323 is an ITU Recommendation that defines "packet-based multimedia communications systems." In other words, H.323 defines a distributed architecture for creating multimedia applications, including VoIP.

• IETF refers to the Internet Engineering Task Force (http://www.ietf.org), a community of engineers that seeks to determine how the Internet and Internet protocols work, as well as to define the prominent standards.

• ITU is the International Telecommunication Union (http://www.itu.int/home), an international organization within the United Nations System (http://www.unsystem.org) where governments and the private sector coordinate global telecom networks and services.

• MEGACO, also known as IETF RFC 2885 and ITU Recommendation H.248, defines a centralized architecture for creating multimedia applications, including VoIP.

• MGCP, also known as IETF RFC 2705, defines a centralized architecture for creating multimedia applications, including VoIP.

• Real-Time Transport Protocol (RTP), also known as IETF RFC 1889, defines a transport protocol for real-time applications. Specifically, RTP provides the transport to carry the audio/media portion of VoIP communication. RTP is used by all the VoIP signaling protocols.

• SIP, also known as IETF RFC 2543, defines a distributed architecture for creating multimedia applications, including VoIP.