S interface

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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[edit]


  1. ^  This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C"., Entry "S interface"
  2. ^ Becker, Ralph (2006-12-05). "ISDN Tutorial: Interfaces". ralphb.net. Retrieved 2014-01-22.