Digital composite tone alerting

DETAILED DESCRIPTION It is desirable for various reasons to provide tone alerting that is more diverse and not restricted to two-tone combinations of five fixed tones.
For one thing, it is then possible to provide tone alerting that is tailored to the particular environment within which a PBX system operates.
For example, there may be a number of telephone stations or extensions in an office within earshot of each other where it is an irritant to have all extensions ringing at the same composite tone.
It would be much more meaningful to provide distinctive tone ringing to extensions particularly within the open office concept.
The present invention, therefore, endeavors to provide flexibility in tone alerting be it for the above-mentioned reason or for other, user determined, reasons.
The present invention provides minimal apparatus for reconstructing in the digital telephone extension or station an arbitrary tone having a frequency within the permitted band of PCM encoded signals within the system.
The arbitrary tone may, of course, be generated within the PBX or key system itself, or it may be relayed from a remote switching center or system.
Accordingly, the present invention provides an apparatus for digital composite tone alerting comprising: logic means for deciding whether a PCM encoded signal has attained or exceeded a predetermined value; latching means, responsive to said logic means for latching a bit in a predetermined bit position in said PCM encoded signal to yield a latched bit; and means for combining said latched bit with a predetermined tone to provide said digital composite tone.
In a narrower aspect of the invention, said predetermined bit position is the sign-bit position.