Universal telephony tones detector

1. A method of detecting single frequency and dual frequency signalling tones incorporated in communications voice traffic, the method comprising determining a mean frequency for said traffic via an automatic frequency control circuit, comparing said mean frequency with stored frequency values corresponding to said single frequency signalling tones and mean values of pairs of said dual frequency signalling tones, and, when a match of said mean frequency is determined by said comparison, confirming said match by determining whether said traffic incorporates said single or dual frequency signalling tones.

2. A method as claimed in claim 1 , wherein said single frequency signalling tones comprise continuity test (COT) tones and modem tones.

3. A method as claimed in claim 2 , and further comprising detecting phase reversals in said single frequency signalling tone identified as modem tones.

4. A method as claimed in claim 3 , wherein said phase reversals are detected via a phase locked loop.

5. A method as claimed in claim 4 , wherein said detection of said single and dual frequency signalling tones is effected from real and imaginary signal components.

6. A method of controlling echo cancellation in a communications network carrying voice traffic incorporating single frequency and dual frequency signalling tones, the method comprising determining a mean frequency for said traffic via an automatic frequency control circuit, comparing said mean frequency with stored frequency values corresponding to said single frequency signalling tones and mean values of pairs of said dual frequency signalling tones, when a match of said mean frequency is determined by said comparison, confirming said match by determining whether said traffic incorporates said single or dual frequency signalling tones, and disabling said echo cancellation responsive to the detection of that said single or dual frequency signalling tones.

7. A method as claimed in claim 6 , wherein said single frequency signalling tones comprise continuity test (COT) tones and modem tones.

8. A method as claimed in claim 7 , and further comprising detecting phase reversals in a said single frequency signalling tones identified as modem tones.

9. A method as claimed in claim 8 , wherein said phase reversals are detected via a phase locked loop.

10. A method as claimed in claim 9 , wherein said detection of said single and dual frequency signalling tones is effected from real and imaginary signal components.

11. A method as claimed in claim 6 , and embodied as software in machine readable form on a storage medium.

12. A signalling tone detector for use in a communications network carrying voice traffic incorporating single frequency and dual frequency signalling tones, the signalling tone detector comprising; an automatic frequency control circuit for determining a mean frequency of an input signal, comparison means for comparing said mean frequency with stored frequency values corresponding to said single frequency signalling tones and mean values of pairs said dual frequency signalling tones, first discrimination means for determining the presence of either a single frequency or a pair of frequencies, and second discrimination means responsive to said first discrimination means and said comparison means for providing a signal output indicative of the presence of said single frequency or pair of frequencies.

13. A signalling tone detector as claimed in claim 12 , and further comprising means for generating real and imaginary components from said input signal.

14. A signalling tone detector as claimed in claim 13 , and comprising phase locked loop means for detecting phase reversals in modem signalling tones.

15. A signalling tone detector for use in a communications network carrying voice traffic incorporating single frequency and dual frequency signalling tones, the signalling tone detector comprising; a first output path, a second output path, and a switch arranged to selectively couple an input signal to the first or the second output path, wherein said first output path comprises an automatic frequency control circuit for determining a mean frequency of said input signal, comparison means for comparing said mean frequency with stored frequency values corresponding to said single frequency signalling tones, and mean values of pairs of said dual frequency signalling tones, first discrimination means for determining the presence of either a single frequency or a pair of frequencies, and second discrimination means responsive to said first discrimination means and said comparison means for providing a signal output indicative of the presence of a said single frequency or pair of frequencies, and wherein said second output path comprises a phase locked loop arranged to respond in frequency and phase to modem signalling tones and output means responsive to the presence or absence of phase reversals in a said modem signalling tones.

16. A signalling tone detector as claimed in claim 15 , wherein the input signal to said switch comprises real and imaginary signal components generated by a Hilbert transformer.

17. An echo canceller arrangement for use in a communications network carrying voice traffic incorporating single frequency and dual frequency signalling tones, the arrangement comprising an echo canceller circuit, and a signalling tone detector arranged to selectively disable the echo canceller circuit in the presence of predetermined dual frequency signalling tones, wherein the signalling tone detector comprises an automatic frequency control circuit for determining a mean frequency of an input signal, comparison means for comparing said mean frequency with stored frequency values corresponding to said single frequency signalling tones and mean values of pairs of said dual frequency signalling tones, first discrimination means for determining the presence of either a single frequency or a pair of frequencies, and second discrimination means responsive to said first discrimination means and said comparison means for providing a signal output indicative of the presence of a said single frequency or pair of frequencies.

18. An ATM switch incorporating said echo canceller arrangement as claimed in claim 17 .

19. An echo canceller arrangement as claimed in claim 17 , wherein said echo canceller circuit is disposed at the boundary between a time division multiplex network and a connectionless network.

20. A communications system comprising a circuit based time division multiplex (TDM) network carrying voice traffic and audio tone signalling traffic, a connectionless network in which traffic is transported in cells, and an interface between said TDM network and said connectionless network, wherein said interface incorporates an echo canceller circuit arrangement comprising an echo canceller circuit, and a signalling tone detector arranged to selectively disable the echo canceller circuit in the presence of predetermined signalling tones, wherein the signalling tone detector comprises an automatic frequency control circuit for determining a mean frequency of an input signal, comparison means for comparing said mean frequency with stored frequency values corresponding to single frequency signalling tones and mean values of pairs of dual frequency signalling tones, first discrimination means for determining the presence of either a single frequency or a pair of frequencies, and second discrimination means responsive to said first discrimination means and said comparison means for providing a signal output indicative of the presence of a said single frequency or pair of frequencies.