US5025469A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method and apparatus for reducing the turn-around time in facsimile transmission
Assignee: Telebit Corp
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Filing: 1990-02-06
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Granted: 1991-06-18
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Expires: 2010-02-06
Abstract
Abstract Previously recommended methods of transmitting facsimile data on the telephone network resulted in periods of time when there is no signal present in the network; one consequence of this was that the retraining time required for the facsimile modem's receiver after each quiet period was undesirably long. This problem is solved by the high-speed transmitter sending two or more holding tones whenever it is not sending training or facsimile signals; these tones prevent re-routing of a telephone connection and allow the high-speed receiver to continue to track data clock and carrier frequencies, thereby considerably reducing the time required for retraining.
Inventors
- 👤 John A. C. Bingham
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 03:47
CPC Classifications
H; H04; H04N; H04N1/00; H04N1/32; H04N1/327; H04N1/32795; H04N1/32702
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
158 words
In a device for sending facsimile data via a communication link from a source modem to a destination modem, each including a receiver and a transmitter, using a half-duplex protocol whereby, in sequence, said source modem sends a signal to said destination modem to synchronize and train its receiver, said destination modem sends a command signal back to said source modem, and said source modem sends a resynchronizing and retraining signal followed by data, a method of preventing the re-routing of some sections of said communication link and speeding the resynchronization and retraining of the receiver of said destination modem, said method comprising the steps of: recognizing the beginning and end of the time periods when said source modem is awaiting a response from said destination modem or is receiving and decoding said response; and transmitting, during said periods, a holding signal that occupies one or two bands of frequencies separate from that occupied by said command signal.
Claim 2
Dependent Claim
158 words
In a device for sending facsimile data via a communication link from a source modem to a destination modem, each including a receiver and a transmitter, using a half-duplex protocol whereby, in sequence, said source modem sends a signal to said destination modem to synchronize and train its receiver, said destination modem sends a command signal back to said source modem, and said source modem sends a resynchronizing and retraining signal followed by data, a method of preventing the re-routing of some sections of said communication link and speeding the resynchronization and retraining of the receiver of said destination modem, said method comprising the steps of: recognizing the beginning and end of the time periods when said source modem is awaiting a response from said destination modem or is receiving and decoding said response; and transmitting, during said periods, a holding signal that occupies one or two bands of frequencies separate from that occupied by said command signal.
Claim 3
Dependent Claim
33 words
The method of claim 1 wherein said holding signal comprises two tones, which are generated by constraining the data input to the transmitter of said source modem to be a simple repetitive pattern.
Claim 4
Dependent Claim
33 words
The method of claim 2 in which the frequency of one of said two tones that are generated is below the frequency band occupied by said command signal, and the other is above.
Claim 5
Dependent Claim
16 words
The method of claim 2 in which said tones are unmodulated carriers of a multicarrier set.
Claim 6
Independent Claim
161 words
An apparatus in a device for sending facsimile data via a communication link from a source modem to a destination modem, each having a receiver and a transmitter, using a half-duplex protocol whereby, in sequence, said source modem sends a signal to said destination modem to synchronize and train its receiver, said destination modem sends a command signal back to said source modem, and said source modem sends a resynchronizing and retraining signal followed by data, an apparatus for preventing the re-routing of some sections of said communication link and speeding the resynchronization and retraining of the receiver of said destination modem, said apparatus comprising: means for recognizing the beginning and end of the time periods when said source modem is awaiting a response from said destination modem or is receiving and decoding said response; and means for transmitting, during said periods, a holding signal that occupies a band or bands of frequencies separate from that occupied by said command signal.
Claim 7
Independent Claim
161 words
An apparatus in a device for sending facsimile data via a communication link from a source modem to a destination modem, each having a receiver and a transmitter, using a half-duplex protocol whereby, in sequence, said source modem sends a signal to said destination modem to synchronize and train its receiver, said destination modem sends a command signal back to said source modem, and said source modem sends a resynchronizing and retraining signal followed by data, an apparatus for preventing the re-routing of some sections of said communication link and speeding the resynchronization and retraining of the receiver of said destination modem, said apparatus comprising: means for recognizing the beginning and end of the time periods when said source modem is awaiting a response from said destination modem or is receiving and decoding said response; and means for transmitting, during said periods, a holding signal that occupies a band or bands of frequencies separate from that occupied by said command signal.
Claim 8
Dependent Claim
25 words
The apparatus of claim 5 including means for constraining the data input to the transmitter of said source modem to be a simple repetitive pattern.
Claim 9
Dependent Claim
15 words
The apparatus of claim 5 including means for transmitting unmodulated carriers of a multicarrier set.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1994-06-17 | 1994-12-17 | 1995-06-18 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1998-06-17 | 1998-12-17 | 1999-06-18 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2002-06-17 | 2002-12-17 | 2003-06-18 | $7700.00 | Window Closed / Lapsed |