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 environment, that
- is characterized by a four-wire circuit, 144kbit/s 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, and controllers, to be connected to the network, and
- operates at 4000 48-bit frames per second; i.e., 192kbit/s, with a user portion of 36bits per frame; i.e., 144kbit/s.
The S interface is electrically equivalent to the T interface, and the two are jointly referred to as the S/T interface.
