Apparatus for digital transmission of facsimile calls using echo protection tone detection and regeneration

摘要

A transmission arrangement is disclosed which facilitates compression of modem modulated facsimile signals for transmission on digital facilities. The presence of a facsimile call is detected and facsimile control messages are obtained by demodulating and interpreting the facsimile call control protocol. A controller is responsive to the obtained control messages for controlling a voiceband encoder to encode the control portion of the facsimile call and for controlling a so-called facsimile page demodulator to demodulate any facsimile page portions of the facsimile call to obtain a baseband digital bit stream. The presence of prescribed tone signals, i.e., echo protection tone (EPT) signals, is detected in the facsimile call. EPT control messages representative of the EPT signals are generated. The encoded control portion of the facsimile call and the baseband digital bit stream representative of the demodulated, i.e., compressed, facsimile page portion of the facsimile call are transmitted along with control information (as side information) and the EPT control messages to a receiver. At the receiver, a replica of the original modem modulated facsimile signal is reconstructed in response to the control information and by decoding the control portion of the facsimile call and by remodulating the digital bit stream representative of the facsimile page portion of the facsimile call. If EPT control messages are received, the corresponding echo protection tone signal is regenerated for inclusion in the remodulated facsimile signal.