Method and apparatus for reducing the turn-around time in facsimile transmission
First Claim
1. 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.
1 Assignment
0 Petitions
Accused Products
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.
48 Citations
7 Claims
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1. 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:
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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. - View Dependent Claims (2, 3, 4)
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5. 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:
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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. - View Dependent Claims (6, 7)
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Specification