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

Claim 2

An improved half-duplex modem, characterized by: 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.

Claim 3

The improved half-duplex modem of Claim 1 wherein said second means comprises a look-up table.

Claim 4

The improved half-duplex modem of Claim 1 wherein said second means determines a first partial duration and a second partial duration, the sum of said first partial duration and said second partial duration being equal to said transmitted retraining sequence duration.

Claim 5

The improved half-duplex modem of Claim 3 wherein said third means generates a first retraining sequence for said first partial duration and a second retraining sequence for said second partial duration.

Claim 6

The improved half-duplex modem of Claim 4 wherein said first retraining sequence comprises a first series of logical 1's using a first constellation and a second series of logical 1's using a second constellation.

Claim 7

The improved half-duplex modem of Claim 5 wherein said first constellation is a 4 point constellation and said second constellation is a 32 point constellation.

Claim 8

The improved half-duplex modem of Claim 1 wherein said fifth means comprises a look-up table.

Claim 9

The improved half-duplex modem of Claim 1 wherein said fifth means determines a first partial duration and a second partial duration, the sum of said first partial duration and said second partial duration being equal to said received retraining sequence duration.

Claim 10

The improved half-duplex modem of Claim 8 wherein said sixth means uses said received retraining sequence received during said first partial duration to effect a coarse resynchronization and uses said received retraining sequence received during said second partial duration to effect a fine resynchronization.

Claim 11

The improved half-duplex modem of Claim 1 and further comprising: means for switching to an on-line mode of operation after sending said transmitted retraining sequence.

Claim 12

The improved half-duplex modem of Claim 1 and further comprising: means for switching to an on-line mode of operation after receiving said received retraining sequence for said received retraining sequence duration.

Claim 13

The improved half-duplex modem of Claim 1 wherein said second means comprises a plurality of look-up tables, each of said look-up tables comprising a plurality of transmitted retraining sequence duration values, each of said transmitted retraining sequence duration values being for a predetermined range of values for said first elapsed time.

Claim 14

The improved half-duplex modem of Claim 12 and further comprising: means for communicating with a connected modem and determining which look-up table of said plurality of look-up tables will be used in conjunction with data transfers.

Claim 15

The improved half-duplex modem of Claim 1 wherein said fifth means comprises a plurality of look-up tables, each of said look-up tables comprising a plurality of received retraining sequence duration values, each of said received retraining sequence duration values being for a predetermined range of values for said second elapsed time.

Claim 16

The improved half-duplex modem of Claim 14 and further comprising: means for communicating with a connected modem and determining which look-up table of said plurality of look-up tables will be used in conjunction with data transfers.

Claim 17

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

Claim 18

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

Claim 19

The method of Claim 16 wherein said received retraining sequence duration is less than said transmitted retraining sequence duration when said second elapsed time is not greater than said first elapsed time.

Claim 20

The method of Claim 16 wherein said transmitted retraining sequence comprises a series of scrambled logic 1's for said transmitted retraining sequence duration.

Claim 21

The method of Claim 16 wherein said transmitted retraining sequence comprises: a first series of scrambled 1's using a first constellation for a first predetermined portion of said transmitted retraining sequence duration; and a second series of scrambled 1's using a second constellation for a second predetermined portion of said transmitted retraining sequence duration.

Claim 22

The method of Claim 19 wherein said first constellation is a 4 point constellation and said second constellation is a 32 point constellation.

Claim 23

The method of Claim 16 wherein said transmitted retraining sequence comprises: a first series of unscrambled 1's using a first constellation for a first predetermined portion of said transmitted retraining sequence duration; a second series of scrambled 1's using said first constellation for a second predetermined portion of said transmitted retraining sequence duration; and a third series of scrambled 1's using a second constellation for a third predetermined portion of said transmitted retraining sequence duration.

Claim 24

The method of Claim 21 wherein said first constellation is a 4 point constellation and said second constellation is a 32 point constellation.

Claim 25

The method of Claim 16 wherein said step of retraining circuits comprises: using a first predetermined portion of a received retraining sequence to obtain a coarse resynchronization; and using a second predetermined portion of said received retraining sequence to obtain a fine resynchronization.

Claim 26

The method of Claim 23 wherein said second modem determines said first predetermined duration and said second predetermined duration from said measurement of said second elapsed time.

Claim 27

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, characterized by: 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.

Claim 28

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, characterized by: 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.

Claim 29

The method of Claim 25 wherein said retraining sequence comprises a series of scrambled logic 1's for said first duration.

Claim 30

The method of Claim 25 wherein said retraining sequence comprises: a first series of scrambled 1's using a first constellation for a first predetermined portion of said first duration; and a second series of scrambled 1's using a second constellation for a second predetermined portion of said first duration.

Claim 31

The method of Claim 27 wherein said first constellation is a 4 point constellation and said second constellation is a 32 point constellation.

Claim 32

The method of Claim 25 wherein said retraining sequence comprises: a first series of scrambled 1's using a first constellation for a first predetermined portion of said first duration; a second series of scrambled 1's using said first constellation for a second predetermined portion of said first duration; and a third series of scrambled 1's using a second constellation for a third predetermined portion of said first duration.

Claim 33

The method of Claim 29 wherein said first constellation is a 4 point constellation and said second constellation is a 32 point constellation.

Claim 34

The method of Claim 25 wherein said step of determining said first duration comprises: entering a look-up table in memory in said first modem; and obtaining from said look-up table a value for said first duration.

Claim 35

The method of Claim 25 wherein said step of determining said second duration comprises entering a look-up table in memory in said second modem; and obtaining from said look-up table a value for said second duration.

Claim 36

The method of Claim 25 wherein said step of operating in said resynchronization mode comprises: using a first predetermined portion of said retraining sequence to obtain a coarse resynchronization; and using a second predetermined portion of said retraining sequence to obtain a fine resynchronization.

Claim 37

The method of Claim 33 wherein said first predetermined portion of said retraining sequence comprises a first constellation and said second predetermined portion of said retraining sequence comprises a second constellation.

Claim 38

The method of Claim 34 wherein said first constellation is a 4 point constellation and said second constellation is a 32 point constellation.

Claim 39

For use with a first modem and a second modem, said first modem and said second modem conducting a predetermined handshake sequence, waiting for a predetermined period of time after completion of said predetermined handshake sequence, and then switching to an online mode of operation, a feature negotiation protocol executed during said predetermined period, characterized by: a first modem procedure comprising the steps of: (a) generating a first modem list of features which are supported by said first modem; (b) sending said first modem list to said second modem; (c) waiting for a reply from said second modem; (d) inspecting said reply from said second modem; (e) if said reply is a predetermined reply then switching to said online mode of operation and using said features on said first modem list; (f) if said reply is a second modem list of features, all of which are supported by said first modem, then sending said predetermined reply to said second modem, switching to said online mode of operation, and using said features on said second modem list; and (g) if said reply is a second modem list of features, less than all of which are supported by said first modem, then generating a first modem list of said features on said second modem list which are supported by said first modem and returning to step (b); and a second modem procedure comprising the steps of: (a) waiting for a communication from said first modem; (b) if said communication is a first modem list of features, all of which are supported by said second modem, then sending said predetermined reply to said first modem, switching to said online mode of operation, and using said features on said first modem list; (c) if said communication is a first modem list of features, less than all of which are supported by said second modem, then generating a second modem list of said features on said first modem list which are supported by said second modem, sending said second modem list to said first modem, and returning to step (a); and (d) if said communication is said predetermined reply then switching to said online mode of operation and using said features on said second modem list.

Claim 40

For use with a first modem and a second modem, said first modem and said second modem conducting a predetermined handshake sequence, waiting for a predetermined period of time after completion of said predetermined handshake sequence, and then switching to an online mode of operation, a feature negotiation protocol executed during said predetermined period, characterized by: a first modem procedure comprising the steps of: (a) generating a first modem list of features which are supported by said first modem; (b) sending said first modem list to said second modem; (c) waiting for a reply from said second modem; (d) inspecting said reply from said second modem; (e) if said reply is a predetermined reply then switching to said online mode of operation and using said features on said first modem list; (f) if said reply is a second modem list of features, all of which are supported by said first modem, then sending said predetermined reply to said second modem, switching to said online mode of operation, and using said features on said second modem list; and (g) if said reply is a second modem list of features, less than all of which are supported by said first modem, then generating a first modem list of said features on said second modem list which are supported by said first modem and returning to step (b); and a second modem procedure comprising the steps of: (a) waiting for a communication from said first modem; (b) if said communication is a first modem list of features, all of which are supported by said second modem, then sending said predetermined reply to said first modem, switching to said online mode of operation, and using said features on said first modem list; (c) if said communication is a first modem list of features, less than all of which are supported by said second modem, then generating a second modem list of said features on said first modem list which are supported by said second modem, sending said second modem list to said first modem, and returning to step (a); and (d) if said communication is said predetermined reply then switching to said online mode of operation and using said features on said second modem list.

Claim 41

The feature negotiation protocol of Claim 36 wherein, in steps (e) and (f) of said first modem procedure, said first modem waits until said predetermined period has expired before switching to said online mode of operation.

Claim 42

The feature negotiation protocol of Claim 37 wherein said first modem sends a predetermined idle signal until said predetermined period has expired.

Claim 43

The feature negotiation protocol of Claim 38 wherein said predetermined idle signal comprises a retraining sequence, a flag, an idle character, and a frame check sequence.

Claim 44

The feature negotiation protocol of Claim 36 wherein, in steps (b) and (d) of said second modem procedure, said second modem waits until said predetermined period has expired before switching to said online mode of operation.

Claim 45

The feature negotiation protocol of Claim 40 wherein said second modem sends a predetermined idle signal until said predetermined period has expired.

Claim 46

The feature negotiation protocol of Claim 40 wherein said predetermined idle signal comprises a retraining sequence, a flag, an idle character, and a frame check sequence.

Claim 47

The feature negotiation protocol of Claim 36 wherein said first modem is an originating modem and said second modem is an answering modem.

Claim 48

The feature negotiation protocol of Claim 36 wherein said first modem procedure further comprises the step of: (h) if said predetermined period expires before said first modem sends or receives said predetermined reply then switching to said online mode of operation and using a predetermined set of default features.

Claim 49

The feature negotiation protocol of Claim 36 wherein said second modem procedure further comprises the step of: (e) if said predetermined period expires before said second modem sends or receives said predetermined reply then switching to said online mode of operation and using a predetermined set of default features.

Claim 50

The feature negotiation protocol of Claim 36 wherein said first modem executes said first modem procedure only if said first modem is configured for synchronous operation and has a high speed half duplex mode of operation.

Claim 51

The feature negotiation protocol of Claim 36 wherein said second modem executes said second modem procedure only if said second modem is configured for synchronous operation and has a high speed half duplex mode of operation.

Claim 52

The feature negotiation protocol of Claim 36 wherein said first modem list of features is user programmable.

Claim 53

The feature negotiation protocol of Claim 36 wherein said second modem list of features is user programmable.

Claim 54

The feature negotiation protocol of Claim 36 wherein said predetermined reply comprises a retraining sequence, a flag, a null character, and a frame check sequence.