TE2 devices are non-ISDN terminal equipment such as personal computers. These devices interface to a TA by way of an R interface. These devices interface to the ISDN network by way of an S interface. An example would be a PBX that terminates a PRI connection and provides several BRI interfaces. An NT2 interfaces to a TA or TE1 via an S interface and to an NT1 via a T interface.
Reference Points are conceptual points used to separate groups of ISDN function.
Some of these reference points are purely conceptual abstractions while others are defined as physical interfaces between functional blocks. Examples include RS232, V.35, and X.21. The interface between an NT1 and NT2. It is functionally equivalent to the S interface. The interface between the ISDN customer premises equipment and the public ISDN network.