BS 7940:1999

This standard BS 7940:1999 Analogue PSTN terminal support interface is classified in these ICS categories:

• 33.040.35 Telephone networks

This British Standard is applicable to apparatus incorporating an interface for the connection of terminal equipment intended for connection to a single 2-wire analogue line interface of the PSTN (known commonly as a Direct Exchange Line, and using loop calling, loop clearing) and specifies the performance requirements of the interface so as to make it appear to the attached terminal equipment that is inter-working with a single 2-wire analogue interface of the PSTN.

NOTE 1 A single 2-wire analogue interface of the PSTN is one which does not use the commonly provided PBX signalling protocols of either loop calling-guarded clearing, loop calling-disconnect clearing, or earth calling.

This standard is applicable to apparatus where the loop current provided to the terminal equipment is not directly derived from a PSTN connection and includes apparatus where the internal connection between the terminal support interface and the NCP uses radio communication means such as CT2 and PCN.

This standard is applicable to apparatus where any terminal equipment connected to the terminal support interface is connected via a cable with a maximum loop resistance of 100 Ω.

NOTE 2 Cable with a loop resistance of 100 Ω is equivalent to approximately 500 m of cable with 0.5 mm diameter copper conductors.

This standard applies to apparatus having an interface for the connection of Terminal Equipment (T.E.) intended for a Direct Exchange Line (D.E.L.) and specifies the performance requirements of the interface which make it appear to the attached T.E. that is interworking with a single 2-wire analogue PSTN D.E.L.