A digital circuit multiplication system for interconnecting a transmission trunk link having a plurality of bearer channels to a second plurality of telephone communication trunks, with the second plurality exceeding the first. The system comprises transmission apparatus at a first end of the transmission link within which there is apparatus for detecting signals on the second plurality of telephone communication trunks and apparatus for assigning each trunk on which signals are present to an available one of the first plurality of bearer channels and for providing assignment messages indicating such assignments. The speech signals are transmitted in bit reduced form by adaptive differential pulse code modulation (ADPCM) transmitting apparatus which is operative to be coupled to the first plurality of bearer channels. The output of the ADPCM transmitting apparatus is combined with the assignment messages along the first plurality of bearer channels, and the assignment messages are stripped from the speech signals at the other end of the transmission link by a signal receiving and message detection apparatus. A receiving apparatus operates to assign each of the first plurality of bearer channels carrying signals to a corresponding one of the second plurality of trunks in accordance with the assignment information received from the transmission apparatus. The signal receiving and detection apparatus contains delay circuitry for temporarily storing the received signals and detecting whether there are assignment messages contained in them, whereupon if these are detected, a message extractor apparatus replaces them with output signals constituting a predetermined signal pattern.

The DTMF receiver sense and control arrangement collects and stores multiple customer originated data for determination of customer identification, validity and billing purposes. This arrangement is part of a telecommunications switching office and monitors up to 24 DTMF receivers (channels) to determine whether each channel contains valid data. This data is stored in temporary storage for subsequent transmission to a processor of the switching office. Each of the DTMF receivers asynchronously presents data for collection by this arrangement. This arrangement provides the proper timing required to operate up to 24 receivers to obtain their data, while it is stable at the receiver. Once a receiver transmits data, this arrangement then synchronizes its operation to that receiver so that, sequential monitoring of each of the 24 channels is guaranteed and no loss of valid data will result. In addition, each DTMF receiver may be enabled selectively for special monitoring.

The DTMF receiver sense and control arrangement collects and stores multiple customer originated data for determination of customer identification, validity and billing purposes. This arrangement is part of a telecommunications switching office and monitors up to 24 DTMF receivers (channels) to determine whether each channel contains valid data. This data is stored in temporary storage for subsequent transmission to a processor of the switching office. Each of the DTMF receivers asynchronously presents data for collection by this arrangement. This arrangement provides the proper timing required to operate up to 24 receivers to obtain their data, while it is stable at the receiver. Once a receiver transmits data, this arrangement then synchronizes its operation to that receiver so that, sequential monitoring of each of the 24 channels is guaranteed and no loss of valid data will result. In addition, each DTMF receiver may be enabled selectively for special monitoring. In order to insure the effective operation of the receiver arrangement, this invention provides for transmitting selected maintenance data. The maintenance data transmitted is compared with the data sent by the processor to determine whether the receiver arrangement is operating properly.

An efficient system for simultaneously conveying a large number of telephone conversations over a much smaller number of relatively low-bandwidth digital communication channels is disclosed. Each incoming telephone speech signal is filtered, periodically sampled, and digitized. An efficient computational speech compression algorithm is applied to transform a sequence of digitized speech samples into a much shorter sequence of compression variables. The compression variables sequence is further processed to construct a minimum-length bit string, and an identifying header is appended to form a packet. Only a few packets containing information on representative background noise are generated during pauses in speech, thereby conserving digital bandwidth. The packets are queued and transmitted asynchronously over the first available serial digital communication channel. Numerical feedback to the compression algorithm is employed which results in the packet size being reduced during periods of high digital channel usage. Packet header information is utilized to establish a "virtual circuit" between sender and receiver.