Feature negotiation protocol and dynamically adjustable retraining sequence for a high speed half duplex modem

In half-duplex communications between a first modem and a second modem, a method of operating said second modem, comprising the steps of:

• establishing communications with said first modem;
• negotiating with said first modem to select a table of retraining sequence durations, each retraining sequence duration of said retraining sequence durations being for a predetermined range of values for a period of non-reception, said table being one of a plurality of tables contained in a memory;
• obtaining a measurement of each said period of non-reception;
• obtaining from said table which was selected a value for said retraining sequence duration corresponding to said measurement;
• entering a resynchronization mode;
• using a signal from said first modem for said retraining sequence duration to effect resynchronization after said period of non-reception;
• and
• entering a data transfer mode.

In half-duplex communications between a first modem and a second modem, a method of operating said modems to improve resynchronization of a receiver in said second modem to a transmitter in said first modem after a period during which said transmitter of said first modem has not sent a signal to said receiver of said second modem, comprising:

• a first modem procedure comprising the steps of:
• obtaining a first measurement of said period;
• determining a first duration dependent upon said first measurement;
• providing to said second modem a retraining sequence for said first duration;
• and
• sending data to said second modem;
• and
• a second modem procedure comprising the steps of:
• obtaining a second measurement of said period;
• determining a second duration dependent upon said second measurement, said second duration being less than said first duration when said second measurement is not greater than said first measurement;
• operating in a resynchronization mode for said second duration and using said retraining sequence from said first modem to effect said resynchronization;
• and
• operating in an online mode.

An improved half-duplex modem, comprising:

• a modem transmitter comprising:
• first means for measuring a first elapsed time since a preceding signal transmission;
• second means responsive to said first elapsed time for determining a transmitted retraining sequence duration;
• and
• third means responsive to said retraining sequence duration for generating a retraining sequence;
• and
• a modem receiver comprising:
• fourth means for measuring a second elapsed time since a preceding signal reception;
• fifth means responsive to said second elapsed time for determining a received retraining sequence duration, said received retraining sequence duration being less than said transmitted retraining sequence duration when said second elapsed time is not greater than said first elapsed time;
• and
• sixth means for effecting resynchronization of said receiver during said received retraining sequence duration by using a received retraining sequence.

In half-duplex communications between a first modem and a second modem, a method of operating said modems, comprising:

• a first modem procedure comprising the steps of:
• establishing communications with said second modem;
• negotiating with said second modem to select a table of transmitted retraining sequence duration values, each of said transmitted retraining sequence duration values being for a predetermined range of values for a first elapsed time, said table being one of a plurality of tables contained in a memory;
• obtaining a value for said first elapsed time, said first elapsed time being measured from termination of a preceding transmission;
• obtaining from said table which was selected a value for said transmitted retraining sequence duration corresponding to said value for said first elapsed time;
• transmitting a retraining sequence for said transmitted retraining sequence duration;
• and
• transmitting data to said second modem;
• and
• a second modem procedure comprising the steps of:
• establishing communications with said first modem;
• negotiating with said first modem to select a table of received retraining sequence duration values, each of said received retraining sequence duration values being for a predetermined range of values for a second elapsed time, said table being one of a plurality of tables contained in said memory;
• obtaining a value for said second elapsed time, said second elapsed time being measured from termination of a preceding reception;
• obtaining from said table which was selected a value for said received retraining sequence duration corresponding to said value for said second elapsed time;
• entering a resynchronization mode;
• retraining circuits in said second modem for a period at least equal to said value for said received retraining sequence duration;
• and
• entering a data transfer mode.