High speed half duplex modem with fast turnaround protocol

A V.22 bis compatible handshake method for an originating modem for establishing communications with an answering modem at a selected speed of 1200 bps, 2400 bps, 4800 bps, or 9600 bps, comprising:

• (a) said originating modem sending a first sequence for a first predetermined period;
• (b) said originating modem sending a second sequence for a second predetermined period while listening for said first sequence from said answering modem;
• (c)
• (1) if said first sequence from said answering modem was not heard by said originating modem, said originating modem commencing communications with said answering modem at 1200 bps;
• (2) if said first sequence from said answering modem was heard by said originating modem, said originating modem sending a third sequence for a third predetermined period while listening for said second sequence from answering modem;
• (d)
• (1) if said second sequence from said answering modem was not heard by said originating modem, said originating modem continuing to send said third sequence for an additional period of time and then commencing training and communications with said answering modem at 2400 bps;
• and
• (2) if said second sequence from said answering modem was heard by said originating modem, said originating modem then sending a fourth sequence followed by a rate request sequence;
• (e) said originating modem listening for said fourth sequence from said answering modem and training an adaptive equalizer in said originating modem in accordance with said fourth sequence;
• (f) said originating modem listening for said rate request sequence from said answering modem;
• (g)
• (1) if said rate request sequence sent by said originating modem is different from said rate request sequence received from said answering modem, said originating modem commencing communications at 4800 bps;
• (2) if said rate request sequence sent by said originating modem and said rate request sequence received from answering modem both specify 4800 bps, said originating modem commencing communications at 4800 bps;
• and
• (3) if said rate request sequence sent by said originating modem and said rate request sequence received from said answering modem both specify 9600 bps, said originating modem commencing training and communications at 9600 bps.

A V.22 bis compatible handshake method for an answering modem for establishing communications with a calling modem at a selected speed of 1200 bits per second (bps), 2400 bps, or greater than 2400 bps, comprising:

• (a) said answering modem listening for a first sequence from said calling modem;
• (b)
• (1) if said first sequence from said calling modem was not heard by said answering modem, said answering modem commencing communications with said calling modem at 1200 bps;
• (2) if said first sequence from said calling modem was detected by said answering modem, said answering modem sending said first sequence to said calling modem and listening for a second sequence from said calling modem;
• (c)
• (1) if said second sequence from said calling modem is not heard by said answering modem, said answering modem commencing training and communications at 2400 bps;
• (2) if said second sequence from calling modem was heard by said answering modem, said answering modem sending said second sequence and commencing training and communications at a rate greater than 2400 bps.

A V.22 bis compatible handshake method for an answering modem for establishing communications with a calling modem at a selected speed of 1200 bits per second (bps), 2400 bps, or greater than 2400 bps, comprising:

• (a) said answering modem listening for a first sequence from said calling modem;
• (b)
• (1) if said first sequence from said calling modem was not heard by said answering modem, said answering modem commencing communications with said calling modem at 1200 bps;
• (2) if said first sequence from said calling modem was detected by said answering modem, said answering modem sending said first sequence to said calling modem and listening for a second sequence from said calling modem;
• (c)
• (1) if said second sequence from said calling modem is not heard by said answering modem, said answering modem commencing training and communications at 2400 bps;
• (2) if said second sequence is heard from said calling modem by said answering modem, said answering modem sending said second sequence and then listening for said third sequence from said calling modem;
• (d) said answering modem using said third sequence from said calling modem to train the adaptive equalizer in said answering modem;
• (e) said answering modem listening for a rate request sequence from said calling modem;
• (f)
• (1) if said rate request sequence from said calling modem designates 4800 bps, said answering modem sending said thrid sequence to said calling modem, sending said rate request sequence designating 4800 bps to said calling modem, and then commencing communications at 4800 bps;
• (2) if said rate request sequence from said calling modem designates 9600 bps and said answering modem cannot accomodate 9600 bps then said answering modem sending said third sequence, sending said rate request sequence designating 4800 bps, and commencing communications at 4800 bps;
• and
• (3) if said rate request sequence from said calling modem designates 9600 bps, and said answering modem can accommodate 9600 bps, sending said third sequence, sending said rate request sequence designating 9600 bps, and then said answering modem commencing training and communications at 9600 bps.

A fast line-turnaround method for transferring data between two modems operating in the half-duplex mode, comprising:

• (a) a data transfer protocol comprising:
• (1) sending a first idle signal for a first predetermined period;
• (2) sending at least one of a predetermined flag;
• (3) sending a data frame, said data frame not exceeding a predetermined number of bytes;
• (4) repeating steps (a) (2) and (a) (3) until a predetermined number of said data frames have been sent;
• (5) sending at least one of said predetermined flag;
• and
• (6) sending a second idle signal for a second predetermined period;
• and
• (b) a no-data line turnaround protocol, comprising:
• (1) sending said first idle signal for a third predetermined period;
• (2) sending at least one said predetermined flag;
• and
• (3) sending said second idle signal for a fourth predetermined period.

For use with a calling modem and an answering modem engaged in half-duplex communications, a method for correcting for a loss of equalization in an equalizer in said calling modem, comprising:

• a calling modem procedure comprising:
• detecting said loss of equalization in said equalizer in said calling modem;
• waiting until said answering modem has completed transmitting;
• sending a tone for a first predetermined period;
• detecting said tone sent by said answering modem;
• being silent for a third predetermined period;
• sending a training sequence to said answering modem for a fourth predetermined period;
• and
• receiving said training sequence from said answering modem and using said training sequence to adjust said equalizer in said calling modem;
• and
• an answering modem procedure comprising:
• detecting said tone sent by said calling modem;
• sending said tone for a second predetermined period;
• being silent during said third predetermined period;
• being silent during said fourth predetermined period;
• and
• sending said training sequence to said calling modem for a fifth predetermined period.

For use with a calling modem and an answering modem engaged in half-duplex communications, a method for correcting for a loss of equalization in an equalizer in said answering modem, comprising:

• an answering modem procedure comprising:
• detecting said loss of equalization in said equalizer in said answering modem;
• waiting until said calling modem has completed transmitting;
• sending a tone for a first predetermined period;
• detecting said tone sent by said calling modem;
• being silent for a third predetermined period;
• receiving a training sequence from said calling modem and using said training sequence to adjust said equalizer in said answering modem;
• and
• a calling modem procedure comprising:
• detecting said tone sent by said answering modem;
• sending said tone for a second predetermined period;
• being silent for said third predetermined period;
• and
• sending said training sequence to said answering modem for a fourth predetermined period.