Abstract:
Facsimile transmission apparatus for transmitting and receiving facsimile messages over a network, the apparatus comprising a facsimile transmission control device operative, upon occurrence of a network transmission delay which would otherwise cause an associated local facsimile device to disconnect, to supply at least one disconnection-preventing signal to the associated local facsimile device until a signal arrives from a remote facsimile device via the network and the switchboard, a switchboard interface operative to interface between said facsimile transmission control device and the switchboard and a network interface operative to interface between said facsimile transmission control device and the network.

Description:
The present invention relates to apparatus and methods for facsimile transmission. 
     BACKGROUND OF THE INVENTION 
     Conventional solutions for using private networks or Internet for inter-site facsimile transmission are hard to integrate, expensive to implement and do not integrate existing, conventional fax machines with LANs. 
     State of the art fax servers, which effect binary file transfer to transmit faxes, are mainly suitable for new systems. They usually are not cost-effective for already-installed bases of standalone fax machines in most organizations. 
     A state of the art fax message system is described in U.S. Pat. No. 5,291,546 to Giller et al. 
     The disclosures of all publications mentioned in the specification and of the publications cited therein are hereby incorporated by reference. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide improved apparatus and methods for inter-site facsimile transmission over private networks or Internet, preferably including integration of existing, conventional facsimile machines and/or provision of fax routing capability. 
     The present invention also seeks to provide a facsimile transmission system which employs existing, conventional facsimile machines, such as standard G3 facsimile machines, to send standard fax messages over the Internet or any private Internet-protocol based network (LAN or WAN). 
     The facsimile transmission system of the present invention preferably provides at least some and preferably all of the following advantages: 
     a. Reduced costs, because faxes are sent over already-paid-for leased lines, 
     b. High quality of transmitted faxes since the digital network is more reliable than public phone lines, 
     c. Imitation of normal fax sending routines, such that retraining of fax operators is unnecessary, 
     d. Acknowledgement of each faxed message is received instantly and online directly from the receiving fax machine, 
     e. Online choice of carrier: Internet, LAN/WAN or PSTN (public switched telephone network). 
     There is thus provided, in accordance with a preferred embodiment of the present invention, facsimile transmission apparatus for transmitting and receiving facsimile messages over a network via a switchboard, the apparatus including a facsimile transmission control device operative, upon occurrence of a network transmission delay which would otherwise cause an associated local facsimile device to disconnect, to supply at least one disconnection-preventing signal to the associated local facsimile device until a signal arrives from a remote facsimile device via the network and the switchboard, a switchboard interface operative to interface between the facsimile transmission control device and the switchboard, and a network interface operative to interface between the facsimile transmission control device and the network. 
     Further in accordance with a preferred embodiment of the present invention, the disconnection-preventing signal includes a NULL signal which causes the local facsimile device to hold traffic for a predetermined period. 
     Still further in accordance with a preferred embodiment of the present invention, the disconnection-preventing signal includes a training sequence signal. 
     Additionally in accordance with a preferred embodiment of the present invention, the local facsimile device includes a receiving facsimile device, the remote facsimile device includes a sending facsimile device and the signal arriving from the remote facsimile device includes a portion of a facsimile message. 
     Further in accordance with a preferred embodiment of the present invention, the local facsimile device includes a sending facsimile device, the remote facsimile device includes a receiving facsimile device and the signal arriving from the remote facsimile device includes an acknowledgement of a portion of a facsimile message. 
     Still further in accordance with a preferred embodiment of the present invention, the at least one disconnection-preventing signal includes a false acknowledgement signal. 
     Additionally in accordance with a preferred embodiment of the present invention, the facsimile transmission control device also includes a facsimile transmission speed adjuster operative to cause the associated local facsimile device to reduce its speed of transmission. 
     Also provided, in accordance with a preferred embodiment of the present invention, is a facsimile transmission method for transmitting and receiving facsimile messages over a network via a switchboard, the method including transmitting a facsimile message over a network from a sending facsimile device to a receiving facsimile device, and upon occurrence of a network transmission delay which would otherwise cause a local one of the facsimile devices to disconnect, locally supplying at least one disconnection-preventing signal to the local facsimile device until a signal arrives from the remote facsimile device via the network. 
     Further in accordance with a preferred embodiment of the present invention, the disconnection-preventing signal includes a NULL signal which causes the local facsimile device to hold traffic for a predetermined period. 
     Still further in accordance with a preferred embodiment of the present invention, the disconnection-preventing signal includes a training sequence signal. 
     Additionally in accordance with a preferred embodiment of the present invention, the local facsimile device includes a receiving facsimile device, the remote facsimile device includes a sending facsimile device and the signal arriving from the remote facsimile device includes a portion of a facsimile message. 
     Further in accordance with a preferred embodiment of the present invention, the local facsimile device includes a sending facsimile device, the remote facsimile device includes a receiving facsimile device and the signal arriving from the remote facsimile device includes an acknowledgement of a portion of a facsimile message. 
     Still further in accordance with a preferred embodiment of the present invention, the at least one disconnection-preventing signal includes a false acknowledgement signal. 
     Additionally in accordance with a preferred embodiment of the present invention, the facsimile transmission control device also includes a facsimile transmission speed adjuster operative to cause the associated local facsimile device to reduce and preferably subsequently restore its speed of transmission. 
     Further in accordance with a preferred embodiment of the present invention, the speed adjuster is operative to indicate to the local facsimile device that a training session has failed. 
     Still further in accordance with a preferred embodiment of the present invention, the facsimile message includes a last page and also including transmitting, after the last page, an additional page having a predetermined contents known to the receiving facsimile device. 
     Additionally in accordance with a preferred embodiment of the present invention, the additional page includes a blank page. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be understood and appreciated from the following detailed description, taken in conjunction with the drawings in which: 
     FIG. 1 is a simplified pictorial illustration of a facsimile transmission system constructed and operative in accordance with a preferred embodiment of the present invention; 
     FIG. 2 is a simplified pictorial illustration of &#34;on-net&#34; operation of the system of FIG. 1; 
     FIG. 3 is a simplified pictorial illustration of &#34;off-net&#34; operation of the system of FIG. 1; 
     FIGS. 4A and 4B, taken together, form a timing diagram for transmission of a facsimile message using the system of FIGS. 1-3; 
    
    
     Attached herewith are the following appendices which aid in the understanding and appreciation of one preferred embodiment of the invention shown and described herein: 
     Appendix A is a netlist of hardware components of facsimile transmission apparatus constructed and operative in accordance with a preferred embodiment of the present invention; 
     Appendix B is a partlist for the netlist of Appendix A; and 
     Appendix C is a computer listing of software components of the facsimile transmission apparatus of Appendices A-B. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 
     FIG. 1 is a simplified pictorial illustration of a facsimile transmission system constructed and operative in accordance with a preferred embodiment of the present invention. In all of the figures, the same numbers are utilized to designate like parts. However, unprimed numbers are used to show a first sending end, prime numbers and double prime numbers are used to show the subsequent receiving end in sequence. However, it should be appreciated that communication can take place from either side to the other side and thus, either side can be used as the sending end and the other side as the receiving end. 
     The system of FIG. 1 includes a plurality of fax machines 10 communicating via switchboards 20 (such as PABXS), facsimile transmission control devices 30, and a network 40 such as the Internet or an IP (Internet protocol) LAN or WAN. 
     Each facsimile transmission control device 30 is associated with the network by means of a conventional LAN interface 50 which, in the illustrated embodiment, connects the facsimile transmission control device to any Ethernet based IP network, such as a 10BaseT/UTP or a 10Base2/BNC. Each facsimile transmission control device acts as any IP node on the network, having its own IP address and being able to access any remote facsimile transmission control device 30 across the network 40. 
     Each facsimile transmission control device 30 is associated with its corresponding switchboard by means of a serial interface 60 which connects the device 30, via an external fax-modem (not shown), to a local extension of the corresponding switchboard 20. Alternatively, the facsimile control device 30 may be operative to perform both switching and D/A-A/D conversions, in which case the facsimile control device may connect directly to a facsimile machine. 
     Preferably, each fax transmission control device 30 is operative to receive inputs from a fax operator which are provided using the internal fax keypad or an attached handset, and which do not require physical access of the fax operator to the device 30. 
     In the illustrated embodiment, each facsimile transmission control device 30 uses the standard G3 facsimile protocol to communicate with one or more corresponding facsimile devices 10 and uses the standard IP protocol to communicate among themselves. In this embodiment, the network 40 may comprise any LAN/WAN environment that supports IP, such as private networks based on routers or the Internet public network. 
     The system of FIG. 1 may be used to send a fax in either of the following ways: 
     a. Via PTT (public telephone) service--through the external line of switchboard 20; or 
     b. Via the network 40, in which case the fax operator dials the local extension of the receiving fax transmission control device. 
     Typically, the following events occur when a call is made from a sending facsimile machine 10 to its corresponding facsimile transmission control device 30: 
     a. The sending facsimile control device 30 creates an IP session with the receiving control device 30 (the control device 30 associated with the receiving fax machine 10). Some initial parameters are transferred between the two control devices 30 including the number that the receiving facsimile control device has to dial in order to access the receiving fax machine 10. 
     b. The receiving facsimile control device 30 uses the information it received in order to call the receiving fax. 
     According to one embodiment of the present invention, each facsimile control device can dial to any fax machine 10 accessible to it. Alternatively, for security reasons, configuration parameters may be used to limit access to predefined destinations. 
     c. The connection and handshake stages of the fax transmission are effected. 
     d. A virtual connection is created between the sending fax machine, the fax control device 30 associated therewith, the receiving fax machine and the fax control device 30 associated therewith. The page images are now sent from the sending fax to the receiving fax. 
     The connection made is an end-to-end connection between the two fax machines. The sending fax control device 30 is operative to digitize the information from the sending fax machine, packetize it into IP messages and send it through the network 40. The receiving fax control device 30 reverses the above procedure and sends the resulting information to the receiving fax machine 10. 
     e. Once the page images are transferred, the receiving fax sends a positive or negative confirmation via the facsimile transmission control devices 30 to the sending fax machine. 
     The procedure for facsimile transmission using the system of FIG. 1 is described in more detail below with reference to FIGS. 4A-4B. 
     Preferably, each fax transmission control device 30 has security configuration options that protect a network from misuse by unauthorized users. Preferably, a Firewall mechanism may be provided which allows the fax transmission control device to be configured in different ways to accept transmission commands, such as the following: 
     a. The control device 30 may be configured to call only specific IP addresses; 
     b. The control device 30 may be configured to accept calls from specific IP addresses; 
     c. The control device 30 may be configured to send faxes to internal faxes only (i.e. the off-net mode of operation described below with reference to FIG. 3 is not permitted). 
     FIG. 2 is a simplified pictorial illustration of &#34;on-net&#34; operation of the system of FIG. 1 in which the sending facsimile machine 10 and its associated fax transmission control device 30 are physically connected to the same switchboard 20 as the receiving facsimile machine 10 and its associated fax transmission control device 30. 
     Alternatively, the facsimile control device 30 may be operative to perform both switching and D/A-A/D conversions, in which case the facsimile control device may connect directly to a facsimile machine. 
     When a fax operator calls a fax transmission control device 30, s/he preferably gets a special dial tone prompting him or her to specify the fax transmission control device which is to receive the fax transmission. This may be effected in any suitable manner. For example: 
     Each fax transmission control device 30 may include an internal dial table 70 which stores associated pairs of short &#34;destination numbers&#34; 80 and network addresses (IP addresses) 90, or associated triplets of short numbers 80, network addresses 90 and telephone numbers 94. The operator inputs a relatively short destination number 80 which is translated by the dial table in the control device 30 into the IP address of the receiving fax control device 30. 
     In the illustrated example, if it is desired to send a fax from Hong Kong to Paris over the network 40, the operator dials the internal extension of the associated fax control device 30, waits for 2 beeps and then dials #02##, where 02 is the entry in the table of the Hong Kong fax control device that represents the Paris fax control device. 
     FIG. 3 is a simplified pictorial illustration of &#34;off-net&#34; operation of the system of FIG. 1 in which the sending facsimile machine 10 and its associated fax transmission control device 30 are not physically connected to the same switchboard. Instead, the sending facsimile machine 10 calls the control device 30 using the public telephone network 100. 
     In the illustrated example, the operator wishes to send a fax from Paris to New York. The New York office is not connected to the corporate backbone and has a regular phone/fax connection to the public telephone network (e.g. phone number 201 555 1212). The nearest office with a fax control device 30 connected to the corporate backbone is in Washington. Instead of placing an expensive call from Paris to New York, the operator can use the corporate backbone from Paris to Washington and the public telephone service only from Washington to New York. 
     To do this, the operator gains access to the local fax control device by dialing a local extension, then dials the short number of the Washington fax control device, then dials the New York phone number. 
     FIGS. 4A-4B, taken together, form a timing diagram for transmission of a facsimile message using the system of FIGS. 1-3. The following terminology is used in the description of FIGS. 4A-4B: 
     A sending facsimile machine (&#34;sending fax&#34;) with an associated fax transmission control device (&#34;PASSaFAX A&#34; or &#34;PaF-A&#34;) sends a message, via a network (&#34;IP network&#34;) to a receiving facsimile machine (&#34;receiving fax&#34;) with an associated fax transmission control device (&#34;PASSaFAX B&#34; or &#34;PaF B&#34;). 
     The following table lists conventional messages that may be exchanged between the two fax machines in the diagrams of FIGS. 4A-4B. &#34;Recv&#34; indicates the receiving fax machine whereas &#34;Send&#34; indicates the sending fax machine. 
     
         ______________________________________Name Type       Sent by   Description______________________________________CED  Tone       Recv      Indicating that the answering                     machine is a faxNSF  HDLC/300   Recv      Indicating what type of non-baud       (optional)                     standard facilities will be                     usedCSI  HDLC/300   Recv      ID of the receiving faxbaud       (optional)DIS  HDLC/300   Recv      Capabilities offered bybaud                 receiving faxTSI  HDLC/300   Send      ID of the sending machinebaud       (optional)DCS  HDLC/300   Send      Capabilities that will be usedbaudTCF  HDLC/Vari  Send      Training sequence (1.5 secondsable                 of 0&#39;s)CFR  HDLC/300   Recv      Confirm the trainingbaudFTT  HDLC/300   Recv      Reject the trainingbaudEOP  HDLC/300   Send      End of last pagebaudMPS  HDLC/300   Send      End of not last pagebaudMCF  HDLC/300   Recv      Confirmation of pagebaudRTN  HDLC/300   Recv      Rejection of pagebaudRTP  HDLC/300   Recv      Acceptance of page, return tobaud                 TCF______________________________________ 
    
     Conventional fax transmissions include the following 4 phases: 
     Phase A--Sending machine dials, and waits for CED tone 
     Phase B--Receiving fax sends NSF (optional), CSI (optional) and DIS (always present). Sending fax sends TSI (optional), DCS and TCF (training sequence of 1.5 seconds of nulls) according to the speed declared in the DCS. Receiving fax machine answers with CFR (positive) or FTT (negative). 
     Phase C--Sending fax sends the page image. 
     Phase D--Sending fax sends EOP (after last page) or MPS (after not last page) and waits for MCF or RTN. If MPS was sent, return to phase C. 
     According to a preferred embodiment of the present invention, the transmission process proceeds as follows: 
     1. The sending fax device dials to PASSaFAX &#34;A&#34;, and specifies the destination fax, typically by dialing DTMF codes. 
     2. PASSaFAX &#34;A&#34; creates a TCP/IP or UDP/IP session with PASSaFAX &#34;B&#34;. Alternatively, the session may be conducted in accordance with any other suitable communications protocol. 
     3. PASSaFAX &#34;B&#34; dials to the receiving fax. 
     A &#34;pipe&#34; now exists between the two faxes, through the PASSaFAX units. The data sent by any of the fax devices is digitized, typically by a fax modem, and sent in IP packets to the other side. Each IP packet includes one original HDLC frame, or a segment from the page image, which is very large piece of data. Both PASSaFAXs typically do not store the fax transmission but send the information as soon as it arrives at the destination. 
     Typical timing problems and solutions therefor are now described. 
     Regular fax transmissions are conducted over telephone links and can therefore assume constant and low delay transmission time. Fax devices have internal, relatively short time-outs that are regulated for the telephone links environment. 
     Facsimile transmission conducted via packet switching networks are subject to frequent and intermittent delays. 
     The following table lists timing sensitive locations in a fax transmission, according to the ITU T-30 standard: 
     
         ______________________________________                       Time out valuePhase   Description         (seconds)______________________________________A       Sending waits for CED                       30B       Receiving waits for DCS                        2   Receiving waits for TCF                        2C       Receiving fax should get image data                       --   continuouslyD       Sending waits for response                       10______________________________________ 
    
     The present invention provides several methods which can be employed either separately or in any combination to overcome the timer sensitive locations. Each PASSaFAX may function either as PASSaFAX &#34;A&#34; or &#34;B&#34;, according to the direction of the fax transmission for a specific fax session. These methods include: 
     1. Sending NULL TSIs (TSIs which do not contain any real information) to keep the fax waiting until the real data arrives from the other side. 
     2. Generating a training sequence phase at least once, or more than once, when waiting for the beginning of a page transmission other than the first page transmission, even though the training is not needed for the fax session, to induce the associated local fax machine to wait for information from the other side. 
     3. Forcing the sending fax to repeat the training after each page, if no confirmation from receiving PASSaFAX &#34;B&#34; has arrived within a predetermined time period, thus gaining more time to receive the confirmation. The predetermined time period is determined by the time interval within which the transmitting fax expects to receive confirmation. 
     4. Using the training sequence to reduce the speed in case of slow networks, e.g. by sending a negative &#34;FTT&#34; signal falsely indicating that a training session has failed. Conventional fax machines slow their speeds upon receipt of a negative &#34;ack&#34; signal. 
     5. Using the fax modem capability to hold traffic for periods of 5 seconds, by sending it a NULL (zero) character. 
     6. If confirmation still has not been received, allowing the associated local fax to send another page, by sending it a false confirmation signal. If, however, confirmation does not arrive during the transmission of next page, disconnect. 
     7. Add a blank or other redundant page to the transmission so the real last page of the transmission is not considered as such by the fax machine. Typically, adding a blank or other redundant page to the transmission causes the real last page to be followed by an MPS (multi-page segment) signal rather than an EOP (end of pages) signal. After an MPS signal is received, the above Method No. 3 can be employed, whereas after an EOP signal is received, the above Method No. 3 cannot be employed. 
     Returning again to FIGS. 4A-4B, the operation of PASSaFAX &#34;A&#34; (near the sending fax) is preferably as follows: 
     Phase Description 
     A Generate CED instead of getting it from PASSaFAX &#34;B&#34; 
     B Send NULL CSI until the real CSI and DIS of the receiving fax is received 
     Accept the training request (TCF) locally, generate response 
     C Nothing 
     D If sending fax machine sends MPS: 
     The page send operation is ended, but it takes time for the confirmation from the remote side to arrive. PASSaFAX &#34;A&#34; therefore generates RTP (instead of MCF) so the sending fax will start the TCF again, giving more time to the MCF from the other side to arrive, and if it does not arrive the PASSaFAX has a chance to terminate the session. 
     Reject the TCF (by DIS) if MCF still does not arrive (so this stage is repeated), and answer by CFR when it does arrive. 
     Use a blank or &#34;dummy&#34; page so the real last page is not considered as the physical last page by the sending fax. 
     The operation of PASSaFAX &#34;B&#34; (near the receiving fax) is preferably as follows: 
     Phase Description 
     A Initiate a call. 
     B Send NULL TSIs (as many as needed) until the real TSI and DCS sent by the sending fax are received. After each NULL TSI, restart the timer at the receiving fax. 
     Generate the TCF again and again, typically using the same speed, until the data buffer is filled. 
     C Each time the amount of data in the data buffer falls below a specific level, use the fax modem ability to hold the fax for 5 seconds. Thus when PASSaFAX &#34;B&#34; sees that it does not get enough data to feed the fax (the network throughput is lower than the fax session) it stops, wait for 5 seconds and continues. During this time more data arrives. 
     D Between pages, generate the TCF again and again, typically using the same speed, until the data buffer is filled with enough data. 
     A preferred method for constructing facsimile transmission apparatus operative in accordance with a preferred embodiment of the present invention, is now described. 
     The method is based on the following appendices: 
     Appendix A, which is a netlist of hardware components for facsimile transmission apparatus; 
     Appendix B, which is a partlist for the netlist of Appendix A; and 
     Appendix C, which is a computer listing of software components of the facsimile transmission apparatus of Appendices A-B. 
     Appendix C includes an image of the Altera U4 component of Appendix B, an image of the Altera U10 component of Appendix B and an image of code which is programmed into the EPROMs of Appendix B. The format of the first two items, which are files entitled U4.txt and U10.txt, respectively, is suitable for the Altera 7a32 component. 
     To construct facsimile transmission apparatus, a printed circuit is constructed based on the netlist of Appendix A and the partlist (BOM) of Appendix B, using a PCAD system. The images of Appendix C are programmed into the appropriate components. The EPROMs are programmed in Intel MCS-86 format with word width =16. The code is loaded onto two EPROMS: U12 and U13, where high bytes are on U12 and low bytes are on U13. 
     It is appreciated that the software components of the present invention may, if desired, be implemented in ROM (read-only memory) form. The software components may, generally, be implemented in hardware, if desired, using conventional techniques. 
     It is appreciated that the particular embodiment described in the Appendices is intended only to provide an extremely detailed disclosure of the present invention and is not intended to be limiting. 
     Abbreviations used in the present specification include the following, as defined in the T.30 standard (ITU-T Recommendation T.30) of the International Telecommunication Union (ITU), 3/93: 
     NSF--Nonstandard facilities 
     CSI--Called subscriber identification 
     DIS--Digital identification signal 
     TSI--Transmitting subscriber identification 
     DCS--Digital command signal 
     TCF--Training check 
     DCS--Digital command signal 
     TCF--Training check 
     CFR--Confirmation to receive 
     FTT--Failure to train 
     EOP--End of procedure 
     MPS--Multipage signal 
     MCF--Message confirmation 
     RTN--Retrain negative 
     RTP--Retrain positive. 
     It is appreciated that various features of the invention which are, for clarity, described in the contexts of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment may also be provided separately or in any suitable subcombination. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention is defined only by the claims that follow: ##SPC1##