S interface

The S interface or S reference point, also known as S₀, is a User–network interface reference point for basic rate access in an Integrated Services Digital Network (ISDN) environment, that

• is characterized by a Four-wire circuit, 144 kbit/s (2B+D) user rate,
• serves as a universal interface between ISDN terminals or terminal adapters and the network channel termination,
• allows a variety of terminal types and subscriber networks, such as PBXs, local area networks (LANs), and controllers, to be connected to the network, and
• operates at 4000 48 bit frames per second, i.e., 192 kbit/s, with a user portion of 36 bits per frame, i.e., 144 kbit/s.^[1]

The S interface is electrically equivalent to the T interface, and the two are jointly referred to as the S/T interface.^[2]

See also

• R interface
• T interface
• U interface

References