Importance

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Abstract

The operation modes of a plurality of modems in a communication system are matched with each other for connection of digital terminals to an analog telephone line on both the calling and answering sides of the analog telephone line. For example, operation modes of modems on both sides of the analog telephone line can automatically be matched with each other by transferring a mode instructing signal with DTMF, using multi-frequency DTMF symbols for a select signal employed in the telephone line, between digital terminals connected to both ends of the telephone line. More specifically, even in the case of the calling and answering sides being in different initial operation modes, the different operation modes are matched by setting a desired operation mode on the calling side and generating an off-hook signal on the answering side in response to a calling signal, followed by (1) transmitting an operation mode instructing signal in the form of a code with DTMF from the calling side to the answering side, setting the instructed operation mode on the answering side and returning if it can be set on that side, and then returning an answer tone to the calling side for completing the mode matching; or when the operation mode instructed from the calling side cannot be set on the answering side, transmitting an operable mode in the form of a code with DTMF from the answering side to the calling side, and transmitting again the code corresponding to that mode from the calling side to the answering side if that mode can be set on the calling side, thereby matching operation modes of both the calling and answering sides, or (2) transmitting an operation mode instructing signal in the form of a code with DTMF from the answering side to the calling side, and then carrying out a procedure similar to above (1).

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First Claim