CA1108288A

CA1108288A - Facsimile communication system

Info

Publication number: CA1108288A
Application number: CA290,379A
Authority: CA
Inventors: Hirohide Miwa; Yoshio Iizuka; Kiyoshi Oikawa
Original assignee: Fujitsu Ltd
Current assignee: Fujitsu Ltd
Priority date: 1976-11-12
Filing date: 1977-11-07
Publication date: 1981-09-01
Also published as: GB1574513A; JPS5816668B2; US4153916A; JPS5361216A

Abstract

FACSIMILE COMMUNICATION SYSTEM

ABSTRACT OF THE DISCLOSURE
Disclosed is a facsimile communication system in which facsimile information from original documents is sequentially transmitted from a transmitter to a remote receiver. The transmitter is utilized for changing the data transfer speed of the facsimile information in accordance with an instruction signal provided by the remote receiver.
The remote receiver supervises the error rate level of each unit of facsimile information of the original documents and provides an instruction signal when the error rate level is detected to exceed a reference error rate level.

Description

The present invention rela-tes to a facsimile com-munication system and, more particularly to a method and apparatus for transmitting facsimile information without reducing the quality of the facsimile o~ the original documents reproduced in a remote receiver. This method and apparatus may preferably be applied to a facsimile com-munication system comprlsing a transmitter, a remote receiver and a transmission line connected therebetween, especially the transmission line is connected by not using a private line but by using a public transmission circuit network such as conventional telephone lines.
In a Eacsimile communication system, especially in a facsimile communica-tion system operating under a band compression method, the compressed diyital video signal is generally transferred over the transmission line at one of the data transfer speeds selected from 9600 bit/sect ~800 bit/sec, 2~0G bit/sec and 1200 bit/sec. A compressed digital video signal is generally transmitted from the transmitter to -the remote receiver by using a quadrature-~hase modulation method. However, when the transmission line has a good electric condition, the compressed digital video signal can be transferred thereover at a high data transfer speed such as 9600 bit/sec. Contrary to the above, when the transmission line has an extremely bad electric condition, the compressed digital video signal must be transferred thereover at a low data transfer speed such as 1200 bit/sec in order to obtain a high-quality facsimile of the original - document, although the transfer time may take longer than the transfer time of a digital video signal being transferred at a high data transfer speed such as 9600 bit/sec. The ' `:

2~;?`~3 ' data transfer sp~ed is usually determined by carrying out the so-called MODEM (Modula-tor-Demodulator) training process performed in both the transmitter and the remote receiver.
The process of the MODEM training is introduced into the system immediately before supplying the compressed digital video signal, containing the facsimile information to be reproduced by the remote reseiver, from the transmitter to the remote receiver. When the transmission line has good electric conditions for transferring facsimile information to the remote receiver, the MODEM training process will automatically determine transmission at a high data transfer speed. On the other hand, a low data transEer rate will be determined by the MODEM training process when -the transmission line has a bad electric condition. The selection of the data transfer speed in the transmitter according to the result of the MODEM training process, is usually performed manually.
As mentioned above, the r~ODEM training process is introduced immediately before the facsimile information to be reproduced is supplied from the transmitter to the remote receiver. ~urthermore, it should be noted that the MODEM training process is usually carried out only once per every transmission operation for transferring the facsimile information of one batch of documents. The MODEM training process is carried out by using a pseudo random pattern for testing the electric conditions of the transmission line and for equalizing the MODEM. Accordingly, the method of the prior art for determining the data transfer speed, as described above, is only useful for a facsimile communication system in which the transmission line is connected by a prlvate line, because the electric condition of a private line remains static for many years. ~ccordingly, the electric condition does not vary during the time from the beginning to the end of the transmission operation for transferring the facsimile information of at least one batch of documents.
However, in the facsimile communication system in which the transmission line is connected by means of the public transmission circuit network such as conventional telephone lines, the electric condition of the transmission line electrically connected between a transmitter and a remote receiver is not static but dynamic. The reason for this dynamic condi-tion is because, in the public transmission circuit network, the route of a transmission line from one transmitter to one remote receiver is often switched from one route to another route by a telegraph supervising office in accordance with the telegraph signal traffic condition of each of the routes of the transmission lines.
During transfer of facsimile information over the transmission line, it is not preferable -to switch the route of the transmission line. Furthermore, during transfer of facsimile - information, if a ~irst transmission line route having a relatively good electric condition is switched to a second transmission line route having a relatively bad electric 2S condition, the first s~t o one batch of documents transferred through the first route can be reproduced by the remote receiver into a high-quality facsimile. However, the remaining documents of this batch oE documents cannot be reproduced into a high-quality facsimile. In the above case, when the irst route over which facsimile information 2~

~`
can be transferred at a high data transEer speed, is switched to the second route over which facsimile information is transferred at a low da-ta transfer speed, the data transfer speed should also be simultaneously changed from high to low in order to maintain a high-quality facsimile of the - original documents. In the prior art method for determining the data transfer speed, as mentioned above, since the data transfer speed is determined by the ~ODEM training process which is carried out immediately before the facsimile ~ 10 information is transferred by using the above-mentioned ; pseudo random pattern, the determined data transfer speed is maintained as it is until one transmission operation for trans~erring the facsimile inEormation regardin~ one batch of documents is ~inished. Accordingly, the high-quality of the facsimile of the original documents cannot be maintained throughout the scanning of the original documents if the - above-mentioned route switch occurs.
Therefore, it is an object of the present invention to provide a facsimile communication system in which the quality of the ~acsimile of the original documents is always maintained at a high level even if the transmission line route having a good electric condition is switched to another transmission line route having a bad electric condition, dllring transmission of the facsimile information of one batch of documents from a transmitter to a remote receiver.
The details of the present invention will become apparent from the ensuing description with reference to the accompanying drawings wherein:

3~ Fig. 1 is a schematic illustration of an entire view of a conventional facsimile communicati~n system;
Fig. 2A depicts a timing chart of the communication processes performed in a facsimile communication system of the prior art;
Fig. 2B schematically depicts wave-forms created by the transmitter in accordance with the timing chart shown in Fig. 2A;
Fig. 3A depicts a timing chart of the communication processes performed in a facsimile communication system according -to the present invention;
Fig. 3B schematically deplcts wave-forms created by the~transmitter in accordance with the timin~ chart shown in Fig. 3A;
Fig. 4 is a schematic diagram showing a facsimile communication system according to the present invention;
- Fi~. S illustrates the data format of a transmission signal transmitted over a transmission line from a transmitter to a remote receiver;
Fig. 6 illustrates the data format of a transmission signa1 transmitted over the transmission line from the remote receiver to the transmitter in accordance with the present invention;
Figs. 7A, 7B and 7C respectively illustrate a detailed circult diagram of an error rate detector 56 shown in Fig. 4 and;
Fig. 8 depicts a timing chart of a modified communication process in a facsimile communication system according to the present invention.
In Fig. l illustrating a conventional facsimile communication system, reference numerals ll and 12 represent ~$~12~3 a facsimile unit acting as a transmitter and a facsimile unit acting as a remote receiver, respectively. Each of the two facsimile units can alternately act as a transmitter and a receiver. The transmitter 11 is comprised of a MODEM
(Modulator-Demodulator) 13, a conventional scanner (not shown) which scans documen-ts to be reproduced in the remote receiver, -a conventional document feeding unit (not shown), eleetronie eontrol units (not shown) and so on. The remote receiver 12 is comprised of a MODEM 1~, a conventional printing unit (not shown) for reproducing faesimile information transmitted from the transmitter 11, eleetrie eontrol units and so on. The transmitter 11 and the remote reeeiver 12 are conneeted by means of a transmission line. The trans-mission line is connected by a private line indicated by a dotted line 15 or by a public transmission circuit network 16 such as conventional telephone lines. The telephone lines are generally used to eonnect one telephone unit 17 with another telephone unit 18. The reference numerals 19 schematically indicate conventional switehing eenters. The telephone unit 17 (18) and the facsimile unit 11 (12) can alternately oceupy the -transmission line by means of a -switching element indicated by reference symbol S or Sl.
Fig. 2A depiets a timing chart of the communication processes performed in a facsimile communication system of the prior art. Fig. 2B schematically depicts wave-forms created by the transmitter in accordance wi~th the timing chart shown in Fig. 2A. Referring to Fig. 2A, the transmitter sends a call signal to the remote reeeiver (see eall signal 21 in Fig. 2B~. The remote receiver sends back a response signal to the transmitter. Therefore, a starting signal i~ ' .

(see starting signal 22 in Fig. 2B) is sent to the remote - receiver. When the remote receiver receives the starting signal, the remote receiver energizes the MODEM 14 (Fig.
1). As a result, the MOD~ training process i~ started between the transmitter and the remote receiver (see MODEM
training signal 23 in Fig. 2B). nuring the MODE~ training process, a pseudo random pattern is sequentially applied from the transmit-ter to the remote receiver. The remote receiver utilizes the pseudo random pattern for detecting the error rate level which varies in accordance with the electric condition of the transmission line and equalizing the MODEM. If the remote receiver detects that the error rate level exceeds -the reEerence error rate level due to a bad electric condition of the transmission line, then the remote receiver sends the so-called fall-back signal to the transmitter. When the transmitter receives the fall-back signal, it reduces the data transfer speed from 9600 bit/sec to 4800 bit/sec, 2400 bit/sec or 1200 bit/sec in order to decrease the error rate level. Secondly, if the data transfer speed is reduced to, for example, 4800 bit/sec, due to the above first step of the MODE~ training process~
a predetermined training bit pattern is sequentially applied from the transmitter to the remote receiver at a data transfer rate of 4800 bit/sec. The remo-te receiver is used to adjust an automatic equalizer (not shown) contained in the MODEM 14 (Fig. 1) by using the training bit pattern at the data transfer speed of 4800 baud. The above embodiment of the MODEM training process has recently been recommended by Interna-tional Teleyraph and Telephone Consultative Committee for performing a facsimile communication system.

32~3 In the ne~t step r the transmitter sends a first con-trol signal (see control signal 24-1 in Fig. 2B) to the remote receiver. The control signal confirms whether or - not the machine parts of the remote receiver are ready for reproducing and printing the facsimile information from the transmitter. Also, the control signal commands the remote receiver to reproduce~the facsimile information at a particular scanning line density, for example, 4 lines/mm or 8 lines/mm, according to the picture element density of the document when the machine parts exhibit a ready status, the remote receive~ sends a response signal to the transmitter. When the transmitter receives the respon.se slgnal, facsimile information from the first page of the documents ~see facsimile information 25-1 in Fig. 213) is fed to the remote receiver. When feeding of the facsimile information from the first page of the documents is finished the transmitter then sends a first end-of-page signal (EOP) to the remote receiver (see end-of-page signal 26-1 in Fig. 2B). Therefore, the remote receiver sends back a response signal to the transmitter. When the transmitter receives the response signal, a second control signal (see control signal 24-2 in Fig. 2B) is supplied therefrom. Accordingly, the facsimile information from a second page o documents (see facsimile - information 25-2-in Fig. 2B) is fed to the remote receiver.
Similarly, each unit oE facsimile inEormation corresponding to a respective scanning line is sequentially fed to the remote receiver. Finally, ~hen feeding of the facsimile information of an "Nth" page of documents (see facsimile information 25 N in Fig. 2B) to the remote receiver is ".,~ .
;~; 30 finished, and an Nth end-of-page signal EOP (see end-of-page .'~ , .
g _ '~;
.. . ,, ~

signal 26-N in Fig. 2B~ is received thereby, then one transmission operation for transferring one batch of documents is completed.
Referring to Fig. 2B, if the previously-mentioned route switch of the transmission lines occurs at a time, for example "to" and, further if the route I (Fig. 1) of the transmission line having a good electric condition is switched to another route II (Fig. 1) of the transmission line having a bad electric condition at the time "to1', the successive pages of the facsimile information of the documents may not be transmitted correctly from the transmitter to ~he remote receiver. Accorclingly, the ~uality of the facsimile oE the original documents which are fed into the remote receiver after the time l'tol' will be reduced, because the digital video signal signals containing the facsimile information from these original documents may exhibit a ; high error rate (see hatched wave-forms 25-2, 25-3 ....... 25-N
in Fig. 2B).
Fig. 3A depicts a timing chart of the communication processes performed in a facsimile communication system according to the present invention. Fig. 3B schematically depicts wave-forms created by the transmitter in accordance ` with the timing chart shown in Fig. 3A. Most of the com--~ munication processes shown in Fig. 3A are the same as the processes depicted in Fig. 2A. In Fig. 3B, the wave-forms designated by the same reference numerals as those in Fig.

.~, ;~ 2B are exactly the same as the wave-forms shown in Fig. 2B.

;~ In Fig. 3B, the wave-forms 31-1, 32, 31-2, 33, 34, 31-N

are newly created according to the present invention. The ~ 30 wave-forms 31-1, 31-2 .... 31-N indicating error checking ,;
~ - 10 --2 ~

processes are simultaneously produced wlth the execution of the corresponding facsimile information feeding processes 25-1, 25-2, 25-3 ... 25-N, respectively. In each of the error checking processes, the error rate level with respect to the digital video signal of the acs:imile inormation is supervised in the remote receiver. If the error rate level with respect to, or example, the digital video signal of the facsimile information 25-1 is below the reference error rate level, the facsimile information is determined to be correct. Then, the remote receiver sends back an ACKNOWLEDGE
signal (see "ACK" in Fig. 3A and the wave-form 32 in Fig.
3B). Similarly, the error checking process (see wave-form 31-2 in Fig. 3B) is carried out simultaneously with the feeding of the facsimile information (see facsimile information lS 25-1 in Fig. 3B). If the previously-mentioned rou-te switch of the transmission lines occurs at a time for example '7to'l and further the route of the transmission line having a good electric condition is switched to another route of the transmission line having a baa electric condition at the time lltolll then the error rate level of the Eacsimile inormation 25-2 soon exceeds the reerence error rate level. Such a condition can be detected in the error checking process 31-2 after the time ll-to'l by the remote receiver. In this case, the remote receiver sends back a NON-ACKNOWLEDGE signal tsee "NACK" in Fig. 3A and also . .. ~
' NON-ACKNOWLEDGE signal 33 in Fig. 3B). The NON-ACKNOWLEDGE
- signal 33 includes the aforementioned all-back signal.
When the transmitter receives the all-back signal, it ~ reduces the data transfer speed rom 9600 hi-t/sec to 4800 ; 30 bit/sec, 2400 bit/sec, or 1200 bit/sec in order to decrease the error rate of the diyital video signals regarding the facsimile information 25-3 -to 25-N and to obtain correc-t facsimile inEorma-tion 25-3 to 25-N. After the NON~ACKNOWLEDGE
signal 33 is received by the transmitter, the MODEM training process .(see Fig. 3A and also wave-form 34 in Fig. 3B) is again carried ou-t by both the transmitter and the remote receiver. This rlODE~ training process is carried out at the reduced da-ta transfer speed of, for example, 4800 bit/sec. Thus, although the route switch occurs at a time ~Itoll/ correct facsimile information 25-3 .. 25-N is still obtained by the remote receiver. Contrary to this, in the prior art, incorrect facsimile information 25-3 ... 25-N
is fed after the time llto" to the remote receiver.
As mentioned above, the facsimile communication system of the present invention can transmit facsimile information without reducing the quality of the facsimile of the original documents except for only one page of the documents (see corresponding wave-form 25-2 in Fig. 3B).

.
The differences between the facsimile communication systems of the prior art and the present invention are as follows.
In the prior art, only one MODE~ training process is carried ~ out during completion of one Eacsimile transferring operation ,~` immediately before the feeding facsimile information of one ~,~ batch of documen-ts from the transmitter to the remote receiver. Accordingly, the data transfer speed cannot be changed during when one facsimile transferring operation is being carried out.
Contrary to the above, in the present invention, the data transfer speed can be changed, if necessary, during when one facsimile transferring operation is being carried ,' ~

out, because, the error rate of the digital video signal of each unit of facsimile information of one group of documents is con`tinuously supervised by the remote receiver.
Fig. 4 is a schematic diagram showing a facsimile communication system according to the present invention.
- In Fig. 4, the reference numerals 11, 12 and 16, respectively indicate the transmitter, the remote receiver and the transmission line, as shown in Fig. 1. A scanner 41 scans a document D to be reproduced in the remote receiver 12 by way of the transmission line 16. A line memory 42 momentarily stores the digital video signal from the scanner 41. Such digital video siynal, that is, the ~acsimile information, is obtained every time the scanner 41 scans one scanning line on the document D. The facsimile inEormation stored in the line memory 42 is then compressed by a band compressory 43.
- The compressed facsimile information is applied to the MODE~I 13 by way of a buffer memory 44. The MODEM 13 can supply the compressed facsimile informa-tion to the transmission line 16 at one of the desired data transfer speeds selected from 9600 bit/sec, 4800 bit/sec, 2400 bit/sec and 1200 bit/sec.
The above members 41 through 44 and 13 are conventional i~ members, and the details of theses members are disclosed in, for example, Canadian Patent Application No. 270,798.
A control circuit 45 controls the scanner 41 and the band compressor 43 by way of lines Ll and L2 respectively. The . ;. .
- control signal -transferred over the line Ll commands, for example, the time at which the scanner 41 s-tar-ts to operate.
The control signal transferred over the line L2 controls the starting and the stopping operations of the band compressor 43.
A response signal is transferred over a line L3 from the band compressor 43 to the control circuit 45. ~ response detector 46 receives control information transmi-tted from the remote receiver 12 by way of the transmission line 16 ; and a line L4 The response detector 46 extracts the response signal from the control information. The response signal is then applied to a line L5 The response signal contains information pertaining to,for example, the completion of the MODEM training process in the remote receiver, the completion of the reproduction of the facsimile information and so on. The reference nùmeral 47 indicates a novel feature of the present invention, that is, the fall-back signal detector which extracts the fall-back signal (cor-responding to the NON-~CKNOWLEDGE signal 33 in Fig. 3B) from the control information. When the detector 47 detects the fall-back signal, the fall-back signal is then applied to a transmission control circuit 48 by way of a line L6 The transmission control circuit 48 commands the MODEM 13 to reduce the data transfer speed, for example, from 9600 bit/sec to 4800 bit/sec. Thereafter, the facsimile information :,.................................. . .
sotred in -the buffer memory 44 is transferred at 4800 bit/sec by means of the MODEM 13.
In the remote receiver 12, the modulated and compressed facsimile information supplied from the transmission line 16 : is demodulated by the MODEM 14. Furthermore, the compressed facsimile information is demodulated by a band compression de~modulator 51 by way of a line Llo and the facsimile information from the original documents is reproduced therein.
The facsimile information is supplied to a memory 52 by way of a line Lll and temporarily stored therein. The stored - facsimile information in the memory 52 is fed to a printing unit 53 via a line L12. The printing unit 53 prin-ts the re-produced document D' on a shee-t of paper. The above members 51 and 52 are conventional members, and details of these members are also disclosed in the speci.fication of the aforesaid patent application. A control circuit 54 controls the band compression demodulator 51, the memory 52 and the printing uni.t 53 by means of lines L13, L14 and L15, respectiveIy. The control signal transferred over the line L13 commands the band compression de-modulator 51 to start its demodulat.ion operati:on when there is no error in the facsimile information, and also commands the demodulator 51 to provide the facsimile information to the mem-ory 52. The control s.ignal transferred over the line I,l~ indi-cates the address in the memory 52 in which each unit of the :; facsimile information is stored. The control signal transferred ~: 15 over the line L15 controls the time for printing the document D' in the printing unit 53. A response signal to the control signal transferred over the line L14 is sent back. to the : control circui.t 54 by way of a line L16. The control circuit ~:., 54 also pro~ides a response signal to a response generator 55 by way of a line L17, which response signal contains informa-tion pertaining to, for example, the completion of the MODEM
training process in the remote receiver, the completion of ~ the reproduction of the facsimile information and so on.
,:
~ This response signal is transmitted from -the remote receiver : 25 to the response detector 46 in the transmi.tter 11 via the .~ response generator 55, a line L18, the MODEM 14 and the transmission line 16. On the other hand, the control circuit 54 receives control information by way of a line Llg, which control information includes the command from the transmitter 11 : -:

2~

to be applied to the control circuit 54~ The reEerence numeral 56 indicates a novel feature of the present inven-tion, that is, the error rate detector which supervises the error rate of the facsimile information via a line L20 The facsimile information is reproduced in the band compression demodulator 51. If the error rate detector 56 detects that the level of the error rate regarding certain facsimile information exceeds the reference error rate level, the error rate detector 56 sends a fall-back signal to the response generator 55 by way of a line L21 The fall-back signal applied to the transmitter 11 and the response signal are combined in the response generator 55. ThereaEter, the combined signals are fed to the transmitter 11 as control information Erom the remote receiver 12 to the transmitter 11.
The response signal and the fall-back signal are processed by the response detector 46 and the fall-back signal detector 47, respectively.
:.;
~; Fig. 5 illustrates the data format of a transmission , signal transmitted over the transmission line 16 (Fig. 4) from the transmi.tter 11 (Fig. 4) to the remote receiver 12 (Fig. 4) by means of the control circuit 45 (Fig. 4) by and via line L8 (Fig. 4). In Fig. 5, the data format 50 is ; comprised of a start flag byte (Fs) 57s, a discrimination byte 58, data bytes 59 and an end flag byte (Fe) 57e. The s-tart flag byte ~Fs) 57s is used as a synchronizing signal in the remote receiver. The end flag byte (Fe~ 57e indicates the end of the transmission signal to the remote receiver.
The discrimination byte 58 indicates what kind of information is being transferred in the data bytes 59. If the data bytes 59 contain facsimile information, the discrimination byte 58 indicates a flag "F". If the data bytes 59 contain control information, the discrimination byte 58 indicates a flag "C". When the discrimination byte 58 indicates the flag "F" (bit "1"), the data bytes 59 comprised of 2048 bits transf~er a set of facsimile information corresponding to one scanning line on the document D (Fig. 4), which scanning line is scanned by the scanner 41 (Fig. 4)O When a lalge number of data formats 50 obtained by scanning an entire page of document are sequentially transferred to the remote receiver, each of the information feeding processes 25-1, 25-2 ... 25-N (see Fig. 3B) is created. When -the discrimination byte 58 indicates the flag "C" (bit "0"), the data bytes 59 transfer to the remo-te receiver the call signal 2]., starting signal 22, ~ODEM training signals 23, 34, control signals 24-1, 24-2 .. , 24-N, and end of page signals 26-1, 26-2 .... 26-N
^ (see Fig. 3B). This control information is mainly supplied to the control circuit 54 in the remote receiver 12 (see Fig. 4).
Fig. 6 illustrates the data format of a transmission signal transmitted over the transmission line 16 (E~ig. 4) from the remote receiver 12 (Fig. 4) to -the transmitter 11 (Fig. 4) by means of the response generator 55 (Fig. 4).
The data format 60 is comprised of a flag byte 61, a first byte I and a second byte II. The flag byte 61 is used as a synchronizing signal in ~he transmitter. A first dis-crimination bit 62 indicates whether the corresponding data format 60 contains a response signal R (hit "1") to be sent to the transmitter or a command signal C (bit "0") to be sent to the transmitter. A second discrimination bit 63 indicates a response signal to be sent -to the transmitter.

This response signal is classified into two signals, that is, the ACKNOWLEDGE signal (ACIC) and the NON-ACKNOWLEDGE
signal (NACK). The ACKNOWLEDGE signal (bit "1") is the same as the ACKNOWLEDGE signal 32 in Fig. 3B, and the NON-ACKNOWLEDGE
signal (bit "0") is the same as the NON-AGKNOWLEDGE signal 33 in Fig. 3B. When the error rate LEVEL is detected to be lower than the re~erence, ERROR RATE level by me.ans of the .;
error rate detector 56 (Fig. 4), and if the facsimile in-formation transmitted to the remote receiver is correct, the error rate detector 56 will send an ACKNOWLEDGE signal to the response generator 55 (Fig. 4). Contrary to this, when .. . .
the error rate level is detected to be higher than the reEerence error rate level, and iE the facsimile information transmitted to the remote receiver is not correct, the error 15 rate detector 56 will send the ~ON-ACKNOWLEDGE signal to the response generator 55 (Fig. 4). This NON-~CKNOWLFDGE signal ~`~ can be the so-called fall-back signal or the line switch ~ .
instruction signal. The .fall-back signal instruc-ts the transmitter to reduce the data transfer speed in the MO~EM 13 (Fig. ~). When the error rate level is much higher than the .
reference error rate level, the line switch ins-truction signal instructs the transmitter to select another line havlny a good electric condition. When the fall-back signal is sent back to the transmitter, a bit (FB) 64 becomes a logic "1". ~hen the.line switch instruction signal is sent back to the transmitter, a bit (LS) 65 becomes a logic "l".
Other bits 66 and 67 may be used for transmitting auxiliary information to the transmitter, for example, the bit (TL) 66 can be used for informing the transmitter that the remote receiver 48 requires a change in the operation Erom -the facsimile information transmitting mode to the telephone conversation mode.
Figs. 7A, 7B and 7C respectively illustra-te a detailed block diagram of the error rate detector 56 shown in Fig. 4.
The error rate detector 56 shown by the circuit diagram of ; Fig. 7A detects whether or not each unit of the facsimile information produced by respective scanning lines includes errors. Such facsimile information is contained in the data bytes 59 (Fig. 5). The circuit shown in Fig. 7B is'provided ~ 10 Eor counting the number of error-contalning facsimile in-,-' formation units'produced by respective scanning lines.
Furthermore, this circuit produces a fall-back signal when the counted number exceeds the reEerence number. The circuit . , .
' shown in Fig. 7C provides a reset pulse applied to counters I5 71, 72, 73 and to a J-K flip-flop 74 shown in E`ig. 7A. In Fig. 7A a first stage counter 71 comprised of a conventional hexadecimal counter receives data clock pulses "DCK" of the demodulated facs'imile information from the band compression ' demodulator 51 (Fig. 4) by way of a line L20 (Fig. 4). When the facsimile in:Eormation of one scanning line contains no errors, the number of the data clock pulses (DCK~ will be exactly 2048. While, when the facsimile information of one scanning line includes errors, the number of the data clock pulses of the demodulated facsimile information will be lower or hi~her than 2048. A second stage counter 72 and a third stage counter 73 are both comprised of conventional hexadecimal counters. Accordingly, the first, second and third stage counters 71, 72 and 73 can count up to 2048 or even more. The J-K flip-flop 74 receives at its J~input terminal selected output bit pulses from the outputs of the ' counters 71, 72 and 73 via the logic gate circui~s 75. When the counters 71, 72 and 73 finish counting 2047 data clock pulses of the facsimile information corresponding to respective scanning lines, a logic "1" is applied to the J-input terminal of the J-K flip-flop 74. Therefore, when -the 2048th data clock pulse is applied to the CLK terminal (clock terminal) of the J-K flip-flop 74, the Q-output terminal thereof ~ becomes a logic "1". The logic status of this 9~output is ; sampled by a NOR gate 70 during when a data enable signal (DEN) disappears. An EDL (End of line) signal is applied to the NOR gate 70 when the data enable signal (DEN) disappears.
The data enable signal (DEN) iS supplied from the band compression clemodulator 51 by way of a D~N line (Fig. 4) and maintains a logic "1" state only during when the facsimile L5 information is being supplied from the data bytes 59 (Fig. 5).
IE the logic status of the Q-output terminal becomes a logic "1" when the EDL signal is being changed to a logic "1", the NOR gate 70 produces an ERL (Error of line) signal which is now a logic "0". The logic "0" of the ERL signal indicates that the facsimile information of one scanning line includes no errors. If the facsimile inEormation includes errors, for example, if 2049 or more data clock pulses are included in the facsimile information, the 2048th data clock pulse is supplied to the CLK terminal of the J K
flip-flop 79 before the data enable signal (DEN) disappears.
Accordingly, the Q-output terminal of the flip-flop 74 provides a logic "1" ou-tput before the data enable signal disappears, and the logic status of the Q-output terminal changes from a logic "1" to a loglc "0" when the 2049th data clock pulse is applied to the CLK terminal of the flip-flop 74.

Accordingly, when the EDL signal (logic "1") is applied to the NOR gate 70, the logic status of the Q~input terminal will have already been changed to a logic "0". Thereafter, the NOR gate 70 produces the ERL signal which now has a logic "1" status. The logic "1" status of the ERL signal ~ indicates that the facsimile information of one scanning - line includes errors. If the facsimile information includes errors, for example, if 2047 or fewer data clock pulses are included in the facsimile information, the 2048th data clock pulse is supplied to the CLK terminal of the flip-flop 74 after the data enable signal disappears. ~ccordingly, the - Q-output terminal of the flip-flop 74 provides a logic "1"
; output after the data enable signal (DEN) disappears.
Therefore, when the EDL signal (logic "1") is applied to the ,.. . .
NOR gate 70, the logic status of the Q terminal will still remain a logic "0". Thereafter, the NOR gate 70 produces the ERL signal which now has a logic "1" status. The logic "1"
of the ERL signal indicates that the fascimile information of one scanning line includes errors.
As mentioned above, when the facsimile information ; includes errors, the ERL signal which is a logic "1" is produced from the N~R gate 70. This ER~ signal is, on one hand, applied to a counter 76 shown in Fig. 7B, and on the other hand, applied to the control circuit 54 in Fig. 4.
In Fig. 7B, the counter 76 counts the number of ERL signals.
If the reference error rate level is predetermined to be 16, an FB signal is provided from a Q-output terminal of a J-K
flip-flop 77 to the response generatorA55 by way of a line L21 (see Fig. 4) when the number of facsimile information units including errors exceeds 16 in per every page of 2~`~
..i documents to be sent to the remote rece,ver. In this case the counter 76 may be comprised of a conventional hexadecimal counter. The 15th ou-tput bit o~ the counter 76 is applied to a CLK terminal (clock termina]) of the flip-flop 77.
^~ 5 A J-input terminal of the flip-flop 77 receives a page enable signal PEN which is a logic "1" during transmission of the facimile information from one page of the documents to the remote receiver. The PEN signal is provided from the control circuit 54 (Fig. 4) by way of a PEN line (see Fig. 4).
The PEN signal is also used to reset the counter 76 to its , .
initial state. An r~R signal resets the flip-flop 77 to its initial state, which MR signal becomes a logic "1" at the beginniny of the PEN si~nal of the next successive unit oE
facsimile information from the following page of the documents - 15 or at the beginning of a LEN signal (explained hereinafter).
In Fig. 7A, the counters 71, 72, 73 and the J-K flip-flop 74 are simultaneously reset to their initial states by an LRS
(Line Reset) pulse. The I,RS pulse is produced at the beginning of the next successive DEN signal. Fig. 7C illustrates a circu.it for creating the LRS pulse. In Fig. 7C, the reference numerals 78 and 79 respectively designate J-K flip--flops.
The main clock pulse MC is applied to both of the CLK (clock) terminals of the flip-flops 78 and 79. A J-input terminal of the flip-flop 78 receives the VEN signal. A NAND gate 80 receives the output signals from the Q-output terminal of the flip-flop 78 and from the Q-ou-tput terminal of the flip-flop 79, and produces the LRS pulse. A NAND gate 81 produces the EDL signal which is applied to the NOR gate 70 shown in Fig. 7A. A start signal ST (Fig. 7C)- ls supplied to the band compression demodulator 51 (Fig. 4) by way of 2~`~
~'- ' ' .
the control circuit 54 (Fig. 4) and the line L13 (Fiy. 4).
This signal ST starts the operation of the band compression ; demodulation in the band compression demodulator 51 (Fig. 4).
;~, Fig. 3A depicts the timing chart in which the fall--back signal can be supplied to every page of the documents, if necessary. It should be noted that the fall-back signal can be supplied to each of a predetermined number of scanning ~ .
lines, if necessary. Fig. 8 depicts a timing chart of the - modified communication processes in a facsimile communication ., ~
system, according to the present invention. ~lost of the ~ processes shown in Fig. 8 are the same as the processes , shown in Fig. 3A. However, in F:ig. 8, the error checking process is carried out with regard to each of the predetermined scanning lines. If the error rate level is lower than the reference error rate level, the remote receiver sends back , .
an ACKNOWLEDGE signal (see "ACK" in Fig. 8). Contrary to this, if the error rate level exceeds the reference error rate level, the remote receiver sends back a NON-ACKNOWLEDGE
signal (see "NACK" in Fig. 8). The NON-ACKNOWLEDGE signal NACK includes the previously-mentioned all-back signal.
The fall-back signal commands the fali-back signal detector 47 (Fig. 7) to reduce the data transfer speed o:E the MODEM 13 (Fig. 4). Then the MODE.M training process is carried out before the beginning of the process for transmitting the facsimile information of the successive predetermined scanning lines to the remote receiver (see ~ODEM training in Fig 8).

In this case, a line enable signal LE~ is applied to both the counter 76 and the flip-flop 77 instead of the PEN
signal (see Fig. 7B). This line enable signal LEN is a logic "1" during when each one of a predeterminecl number of .
~ ~ 23 -, ~3 .

~ line is being transmitted to the remote receiver.
-. Finally, i~ it is re~uired to process the reproduced facsimile information contaning errors, the control circuit 54 (Fig. 4) can be used to perform this correction. In Fig. 4, when the control circuit 54 receives the ERL (Error of line) ` signal from the error rate detector 56 by way of a line L22 (Fig. 4), the control circuit 54 instructs the memory 52 not to store the facsimile information containing errors.
The circuit 54 further lnstructs the memory 52 to again provide the stored facsimile information to the printing unit 53. This Eacsimile information is stored in the memory 52 immediately before the facsimile ineormation containing error is demodulated by the band compression demodulator 51.
The control circuit 54 can also instruct the control circuit 45 to again scan the scanning line correspond to the facsimile information containing errors, by way of the line Ll7 the response generator 55 the llne Ll8, the MODEM 14, the trans-mission line 16, the ~ODEM 13, the line L4 the response detector 4~ and the line L5 This instruction from the control circuit 54 to the control circuit 45 is -transferred by means of the data format 60 shown in Fig. 6. In Fig. 6, the discrimination bit 62 indicates a command signal C
; (bit "0"), and the instruction inEormation is contained in the bits 67.
As mentioned above, the facsimile communication system according to the present invention can be used to reproduce high-quality Eacsimile information even if the electric condition of the transmission line suddenly changes to a bad electric condition in the middle of transmit-ting a plurality of pages of documents from the transmitter to the remote receiver.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A facsimile communication system comprising a transmitter, having a scanner which scans documents to be transmitted, a buffer memory which temporarily stores facsimile information supplied from the scanner, transmitting means for modulating the facsimile information from the buffer memory and transmitting the facsimile information to a receiving site at one of specified data transfer speeds and a response signal detector which detects a response signal transmitted from the receiving site; and a remote receiver provided at the receiving site and having a memory which temporarily stores the facsimile information transmitted from the transmitter, a printing unit which reproduces the documents according to the facsimile information, an error rate detector and a response generator which produces the response signal to be transmitted to the response signal detector in the transmitter, said error rate detector including means for producing an instruction signal to be applied to the transmitting means, which instruction signal instructs the transmitting means to select a desired one of said specified data transfer speeds by way of the response generator and the transmission line.

2. A facsimile communication system as set forth in claim 1, wherein the instruction signal for instructing the transmitting means to select a desired one of the data transfer speeds is transmitted to the transmitting means between a time when the remote receiver finishes receiving the facsimile information obtained by scanning one page of the documents and a time when the remote receiver starts receiving the facsimile information obtained by scanning a successive page of the documents.

3. A facsimile communication system as set forth in claim 1, wherein the instruction signal for instructing the transmitting means to select a desired one of the data transfer speeds is transmitted to the transmitting means between a time when the remote receiver finishes receiving the facsimile information obtained by scanning a predetermined number of scanning lines on one page of the documents and a time when the remote receiver starts receiving the facsimile information obtained by scanning the predetermined number of successive scanning lines.

4. A facsimile communication system as set forth in claim 1, wherein the data format of a transmission signal from the transmitter to the remote receiver is comprised of at least a flag byte used as a synchronizing signal in the remote receiver and data bytes used for transferring facsimile information regarding each scanning line scanned by the scanner; while the data format of a transmission signal from the remote receiver to the transmitter is comprised of at least a flag byte used as a synchronizing signal in the transmitter, a discrimination bit for indicating an ACKNOWLEDGE
signal or a NON-ACKNOWLEDGE signal and an instruction bit for instructing the transmitting means to select a desired one the data transfer speeds; which ACKNOWLEDGE signal attains a certain logic status of "1" or "0" when the error rate detector detects that the error rate level of the facsimile information in the data bytes is lower than a predetermined reference error rate level; which NON-ACKNOWLEDGE
signal attains a certain logic status of "1" or "0" when the error rate level is higher than the predetermined reference error rate level; and the instruction bit becomes a certain logic "1" or "0" when the NON-ACKNOWLEDGE signal attains a certain logic status of "1" or "0".

5. A facsimile communication system as set forth in claim 4, wherein the instruction signal is produced from a flip-flop I; a clock terminal of the flip-flop I is connected to a predetermined output bit of a counter I; the counter I
counts the number of ERL (Error of Line) signals, each ERL
signal being produced when the facsimile information of the scanning line includes errors; and the flip-flop I is set during transmission of the facsimile information of one page of documents to the remote receiver, or during transmission of the facsimile information of a predetermined number of lines scanned on one page to the remote receiver.

6. A facsimile communication system as set forth in claim 5, wherein each ERL signal is produced from a NOR
gate; which NOR gate receives both signal from a flip-flop II
and an EDL (End of Line) signal produced when transmission of the facsimile information regarding each scanning line to the remote receiver is finished; which flip-flop II receives an input signal provided from a counter II by way of a logic gate circuit; which counter II counts the number of data clock pulses of facsimile information contained in the data bytes; which flip-flop II is reset by a LRS (Line Reset) signal produced when transmission of the successive facsimile information to the remote receiver is begun; and wherein the output of the flip-flop II attains a certain logic status of "1" only when the counter II has counted a fixed number of data clock pulses.

7. A facsimile communication system as set forth in claim 6, wherein the EDL signal is produced from a NAND
gate I and the LRS signal is produced from a NAND gate II;
which NAND gate I receives both an output from a Q-output terminal of a flip-flop III and an output from a Q-output terminal of a flip-flop IV; which NAND gate II receives both an output from a Q-output terminal of the flip-flop III and an output from a Q-output of the flip-flop IV; a J-input terminal of the flip-flop III receives a DEN (Data Enable) signal which attains a certain logic "1" during transmission of the facsimile information of each of the data bytes to the remote receiver; and the output terminals of the flip-flop III
are connected to respective input terminals of the flip-flop IV.