As mentioned in Primary Rate Interface (PRI) section, T1 is one of the bases of the interface standard of PRI. T1, (also written as T-1), is considered as the most commonly used digital transmission service of different highly-technological advanced countries like Canada, United States, and Japan. During its early days, T1 uses copper wire before it came to use optical and wireless media. These are what today ‘s time is being accustomed to. This is among the very first successful systems that are being used in producing digitized voice transmission.

A T1 line that is owned by a major telephone network is most common among the lines being used by an internet access provider. This is because T1 line best serves the purpose of establishing connection to internet as a POP or point-of-presence.

T1 functions as its pair of wires (one for transmission and the other for receive) and time division multiplexing intersperse voice of 24 64-Kbps or data channel work.

A standardized T1 frame measures 193 bits long with the capacity to hold for up to 24 8-bit voice samples. An integrated T1, however, is a type of T1 carrier that serves different applications.

T1 is most recommended to business with more than 8 lines as it can be looped around the business locations from a local phone company.