The S interface or S reference point, also known as S₀, is a user–network interface reference point in an

ISDN Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Work ...

BRI environment, characterized by a

four-wire circuit In telecommunication, a four-wire circuit is a two-way circuit using two paths so arranged that the respective signals are transmitted in one direction only by one path and in the other direction by the other path. The four-wire circuit gets its ...

using 144kbit/s (2 bearer and 1 signaling channel; 2B+D) user rate. The S interface is the connection between ISDN terminal equipment (TE) or

terminal Terminal may refer to: Computing Hardware * Terminal (electronics), a device for joining electrical circuits together * Terminal (telecommunication), a device communicating over a line * Computer terminal, a set of primary input and output devi ...

adapters (TAs) and an NT1 (network terminator, type 1.) Not all TE or TAs connect externally to an S interface, but instead integrate an NT1 so they can connect directly to a U interface (local loop from central office.) Contrast to the T interface, which connects between an NT2 (PBX or other local switching device) and NT1. However, the S interface is electrically equivalent to the T interface, and the two are jointly referred to as the S/T interface. The S interface operates at 4000 48-

bit The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represente ...

frames per second; i.e., 192kbit/s, with a user portion of 36bits per frame; i.e., 144kbit/s.
Entry "S interface"
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References

{{Reflist ITU-T recommendations Integrated Services Digital Network

See also

References