The S interface or S reference point, also known as S
0, is a
user–network interface In telecommunications, a user–network interface (UNI) is a demarcation point between the responsibility of the service provider and the responsibility of the subscriber. This is distinct from a network-to-network interface (NNI) that defines a si ...
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. Wo ...
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 n ...
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 dev ...
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 A T-interface or T reference point is used for basic rate access in an Integrated Services Digital Network (ISDN) environment. It is a User–network interface reference point that is characterized by a four-wire, 144 kbit/s (2B+D) user rate.
...
, which connects between an NT2 (PBX or other local switching device) and NT1.
However, the S interface is electrically equivalent to the
T interface A T-interface or T reference point is used for basic rate access in an Integrated Services Digital Network (ISDN) environment. It is a User–network interface reference point that is characterized by a four-wire, 144 kbit/s (2B+D) user rate.
...
, 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
A frame is often a structural system that supports other components of a physical construction and/or steel frame that limits the construction's extent.
Frame and FRAME may also refer to:
Physical objects
In building construction
*Framing (con ...
; i.e., 144kbit/s.
Entry "S interface"
/ref>
See also
* R interface
R interface or R reference point defines the point between a non-ISDN device and a terminal adapter (TA) which provides translation to and from such a device.
See also
* S interface
* T interface
* U interface
U or u, is the twenty-first ...
* T interface A T-interface or T reference point is used for basic rate access in an Integrated Services Digital Network (ISDN) environment. It is a User–network interface reference point that is characterized by a four-wire, 144 kbit/s (2B+D) user rate.
...
* U interface
U or u, is the twenty-first and sixth-to-last letter and fifth vowel letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''u'' (pr ...
References
{{Reflist
ITU-T recommendations
Integrated Services Digital Network