High-speed modem synchronized to a remote CODEC

Apparatus comprising:

• an D/A converter operating under control of a first clock, for communicating signals to a A/D converter having a second clock,
• control means for receiving information from the A/D converter,
• means, responsive to said control means, for synchronizing the first clock to the second clock, and
• means, responsive to said control means, for adjusting levels of the output signal of the D/A converter.

Apparatus comprising:

• an A/D converter operating under control of a first clock, for receiving signals from a D/A converter having a second clock,
• control means for deriving information from the signal received by the A/D converter,
• means, responsive to said control means, for synchronizing the first clock to the second clock, and
• means, responsive to said control means, for adjusting the slicing levels of the A/D converter.

An modem including a transmitting section for developing an analog signal in response to an applied digital stream, which analog signal is destined to a remote clocked conversion means, a receiving section for developing a digital string in response to an analog signal from the remote clocked conversion means, means for developing a clock in synchronism with the clock in the remote conversion means, and means for employing the developed clock in the transmitting section, the receiving section comprising:

• a switched filter,
• a transmission-medium-emulating filter responsive the output of the switched filter,
• a codec connected to the output of the transmission-medium-emulating filter,
• a combiner for subtracting the output of the codec from the output of the transmission-medium-emulating filter,
• a band limiting filter responsive to an output signal of the combiner, and
• an input subtracter, for subtracting the output of the band limiting filter from incoming signals to form a symbol signal, the symbol signal being applied to the switched filter and to A/D means for developing said digital string.

A method for modifying operational parameters of a modem connected to a digital channel bank via analog lines, where the modem has a receiving portion and a transmitting portion, the method comprising the steps of:

• connecting the modem, through the channel bank, to a predefined destination, which connecting is effected over digital facilities following the channel bank, having communication and signal processing capabilities,
• the modem receiving a known signal, through the digital facilities through the channel bank, from the predefined destination,
• the modem processing the received signal to develop first control signals for the receiving portion and second control signals for the transmitting portion,
• the modem equalizing the receiving portion in response to the first control signals developed by the step of processing, and
• the modem equalizing the transmitting portion in response to the second control signals developed by the step of processing.