Facsimile and static presentation processing – Facsimile – Facsimile system interface
Patent
1997-09-11
1999-03-02
Lee, Thomas D.
Facsimile and static presentation processing
Facsimile
Facsimile system interface
358405, 358407, 379103, 455 121, H04N 132, H04N 100
Patent
active
058778713
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a communication method and apparatus and particularly, but not exclusively, to a facsimile interface apparatus for communication via a communication link, such as a satellite link or cellular telephone system.
Conventional facsimile terminals are designed for communication over a public service telephone network. Standard protocols have been adopted for communication between calling and called facsimile terminals. Examples of such protocols are those defined by the International Telegraph and Telephone Consultative Committee (CCITT) under Recommendations T.3 and T.4, known respectively as the Group 2 and Group 3 facsimile protocols. Recommendation T.30 defines a protocol for Group 2 and 3 facsimile equipment for communication over a telephone network.
An alternative means for communication between facsimile terminals has been proposed, in which each facsimile terminal is connected to a facsimile interface unit which converts analog modulated facsimile signals, suitable for communication via a public service telephone network, to encoded data suitable for transmission over a digital network, for example a digital satellite link or a cellular telephone system. However, the introduction of facsimile interface units into the circuit increases the delay between transmission and reception of a facsimile signal. This increased delay may cause failures in communication between the calling and called facsimile terminals. A standard for overcoming this increased delay is not provided under the Group 3 fax protocol.
The document WO 92/02100 discloses a facsimile interface unit which automatically sends a "command repeat" signal to a facsimile terminal on receipt of a command therefrom, in order to allow more time for a response signal to be received.
The article "Real-time transmission of group 3 facsimile over interconnected public switched digital mobile satellite networks", Comsat Technical Review 22 (1992) Spring, No. 1, pages 125 to 145, proposes programming a facsimile interface unit to send a sequence of flags to a facsimile terminal if no response signal is detected within a predetermined period of receiving a command therefrom so that the time limits for response set out in Recommendation T.30 are not exceeded at the facsimile terminal.
However, the facsimile terminal may still time out if no response is received at all or if the sequence of flags continues for too long.
The present invention provides a facsimile interface unit which detects a transmitted signal from a transmitting facsimile apparatus and detects whether a response signal to said transmitted signal is received from another facsimile apparatus within a predetermined period. If no response signal is detected after a predetermined period, a holding signal is sent to the transmitting apparatus and, if there is no response after a further period of time, a repeat signal is sent to the transmitting apparatus by the facsimile interface unit, such that the transmitting facsimile apparatus repeats the transmitted signal.
Preferably, the repeat signal is generated by the facsimile interface unit connected to the transmitting facsimile apparatus.
Thus, the transmitting facsimile apparatus may reliably communicate with the receiving apparatus over a circuit having a long delay.
Other aspects and preferred embodiments will be apparent from the following description and claims.
Embodiments of the present invention will now be described with reference to the accompanying drawings in which:
FIG. 1 is a diagram of a communications link between two facsimile terminals, including a satellite link, according to an embodiment of the invention;
FIG. 2 is a block diagram of a facsimile terminal, a facsimile interface unit, and a mobile earth station forming part of FIG. 1;
FIG. 3 is a time chart showing a late response to a signal transmitted over the satellite link;
FIG. 4 is a time chart showing a case in which no response is received to a signal transmitted over the satellite link; and
FIG. 5 is a flowchart of the operation of a
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Mitsubishi, Acces Cell Fax Machines; brochure; 1991.
Dimolitsas et al., "Real-Time Transmission of Group 3 Facsimile over Interconnected Public Switched Digital Mobile Satellite Networds", Comsat Technical Review, vol. 22, No. 1, pp. 125-145(1992).
K.C. Halton, "The Evolution and Future of Group 3 Facsimile Standards", BT Technology Journal, vol. 12, No. 1, pp. 53-60 (1994).
Dimolitsas et al., "Group 3 Facsimile Transmission over Digital Satellite Land Mobile Networks", Vehicular Technology Society, 42nd VTS Conference, vol. 1, pp. 240-246 (1992).
Procedures for Documents facsimile Transmission in the General Switched Telephone Network. "Recommendation T.30", pp. 77-173.
Besset Jean-Benoit
Smith Richard Douglas Lane
Grant II Jerome
International Mobile Satellite Organization
Lee Thomas D.
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