Telephony Standards

An international organization that’s part of the United Nations, the International
Telecommunications Union (ITU) plays a major role in standardizing the technology of the
PSTN. Initially providing standards and agreements for connecting telegraph links between
countries starting in the 1800s, the ITU has evolved to oversee many areas of standards
development within the global telecom industry.
The ITU includes a specific division known as the Telecommunications Standardization
Sector, or ITU-T. This division comprises many companies and organizations with interests
in telecommunications standards. Once they’re grouped into similar functional areas, the
ITU-T standards are called recommendations, and they share an assigned letter of the
alphabet. Some of the ITU-T recommendations that are relevant to our discussion are:
G: Transmission systems and media, digital systems and networks
H: Audiovisual and multimedia systems
P: Telephone transmission quality, telephone installations, local line networks
The recommendation category letter is typically followed by a period and a number, such as
G.711 or H.323. An ITU-T standard recommendation is said to be “In Force” when the
standard has been approved by ITU-T membership.
Standards are absolutely crucial to the success of technologies like VoIP. Without standards,
your phone call would very likely be dropped when it passed from Vendor A’s network to
Vendor B’s network. Accordingly, many VoIP vendors have drawn on the expertise of the
ITU-T and built VoIP products based on well-known standards.