Facsimile communication system

A facsimile communication system for communicating picture data among facsimile machines including two types of facsimile machines having different coding algorithms for picture data and different resolutions. One type of facsimile machine is directly connected to a store and forward switching network and the other type of facsimile machine is connected to the store and forward switching network through a facsimile terminal controller. When the facsimile terminal controller receives picture data from the other type of facsimile machine, it decodes the received picture data, encodes it by the coding algorithm of the first type of facsimile machine and sends it to the store and forward switching network. When the facsimile terminal controller receives the picture data from the store and forward switching network, it decodes the received picture data, encodes it by the coding algorithm of the other type of facsimile machine and sends it to the other type of facsimile machine. When a resolution of the image data received from the store and forward switching network is different from a resolution of the picture data to be sent to the other type of facsimile machine or vice versa, the facsimile terminal controller converts the image data to the appropriate resolution.

BACKGROUND OF THE INVENTION 
The present invention relates to a facsimile communication system, and more 
particularly to a facsimile communication system suitable for a 
circumstance where different types of facsimile machines are used in a 
store and forward switching network such as a packet switching network. 
In a conventional facsimile communication system which uses a store and 
forward switching network such as a packet switching network, a G3 
facsimile machine cannot be directly connected to the packet switching 
network. As is know, packet switching is a data transmission process 
utilizing addressed packets whereby a channel is occupied only for the 
duration of transmission of the packet. A packet is a group of binary 
digits including data and control elements which is switched and 
transmitted as a composite whole. A G3 facsimile machine cannot receive 
data directly from a packet switching network. In order for a G3 facsimile 
machine to make use of the data in a packet the packet must be 
disassembled to its original form. Also, in order for a G3 facsimile 
machine to transmit data over a packet switching network, the data must be 
assembled into packets with the appropriate control and data elements. 
Such packet assembly and disassembly functions are performed by a device 
known in the art as a Packet Assemble and Disassembly (PAD) device. As 
shown in an article "Separate System for Facsimile Communication", STUDY 
OF INTERNATIONAL COMMUNICATION, No. 128, April 1986, pp 73-79, published 
by Kokusai Denshin Denwa Co. Ltd., a G3 facsimile packet assembly and 
disassembly (PAD) device is provided between the G3 facsimile machine and 
the packet switching network (G3 facsimile communication system). A 
standard specification of a G4 facsimile machine was recommended in 1984 
by CCITT as T.5 and T.6. This G4 facsimile machine can be directly 
connected to the store and forward switching network such as packet 
switching network. 
The G3 facsimile machine and the G4 facsimile machine have different design 
philosophies and there are many differences between them as shown in FIG. 
1. In order for the G3 facsimile machine and the G4 facsimile machine to 
communicate with each other through the store and forward switching 
network, it is necessary to absorb in the system all differences shown in 
FIG. 1 except for the facsimile signal form in item 3. The conversions of 
communication control system, terminal control system, modulation 
technique, transmission rate, transmission error control, frame 
configuration and one-line transmission time of the items 1, 2, 4, 5, 7, 8 
and 11 can be attained in the facsimile PAD device, but the conversions of 
redundancy compression, resolution and line synchronization signal of the 
items 6, 9 and 10 cannot be attained in the PAD device. Thus, the prior 
art network pays no attention to the circumstance where the G3 facsimile 
machines and the G4 facsimile machines are mixedly connected to the store 
and forward switching network, and even if a G4 facsimile machine is 
connected to the store and forward switcher, the G3 facsimile machine and 
the G4 facsimile machine cannot communicate with each other. 
In order to solve those problems, it has been proposed to absorb the 
differences shown in FIG. 1 in the store and forward switching network, 
but the store and forward switcher must communicate with a different 
protocol depending on whether the machine is a G3 facsimile machine or a 
G4 facsimile machine, and hence the control is complex. Since the 
facsimile machine handles a large volume of data, a load is heavy in 
encoding algorithm conversion or resolution conversion, and a throughput 
of the system is lowered because of a limitation to a processing 
performance of the store and forward switcher. Such a problem usually 
occurs in mutual communication between different types of facsimile 
machines. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a facsimile 
communication apparatus which allows mutual communication between 
different types of facsimile machines and in which each facsimile machine 
transmits and receives signals without recognizing the type of the partner 
facsimile machine and a store and forward switcher communicates with 
apparatuses connected thereto using only one protocol. 
In the facsimile communication system of the present invention, one of two 
different types of facsimile machines which may have different picture 
data encoding algorithms and different resolutions is directly connected 
to the store and forward switching network and the other type of facsimile 
machine is connected to the store and forward switching network through a 
facsimile terminal controller, which decodes the encoded picture data sent 
from the other type of facsimile machine, encodes it with the encoding 
algorithm of the one type of facsimile machine and sends it to the storage 
switching network. The facsimile terminal controller handles the encoded 
picture data supplied from the store and forward switching network in the 
opposite manner. Namely, it encodes the decoded data with the encoding 
algorithm of the other type of facsimile machine and sends it to that 
facsimile machine. When the resolution of the picture data received from 
the store and forward switching network is different from the resolution 
of the picture data to be sent to the other type of facsimile machine, the 
resolution is converted. The facsimile terminal controller uses the same 
protocol as that which the one type of facsimile machine uses when it 
transmits and receives the picture data, when the picture data is 
transmitted and received to and from the store and forward switching 
network. 
In the present facsimile communication system, each of different types of 
facsimile machines can transmit and receive signals without recognizing 
the type of partner facsimile machine, and the store and forward switching 
network need to follow only the protocol of the one type of facsimile 
machine. 
In one embodiment of the present invention in which a G3 facsimile machine 
and a G4 facsimile machine communicate with each other, the G4 facsimile 
machine is directly connected to a store and forward switching network, 
the G3 facsimile machine is connected to the store and forward switching 
network through a facsimile terminal controller, and the facsimile 
terminal controller is provided with a PAD function as well as a picture 
data encode/decode function for mutual conversion of picture data of the 
G3 facsimile machine and the G4 facsimile machine, and a resolution 
conversion function. The resolution conversion is made by converting the 
number of dots per line in the main scan direction, that is in the 
direction of line, and by converting number of lines in the sub-scan 
direction perpendicular to the main scan direction. The facsimile terminal 
controller connected between the G3 facsimile machine and the store and 
forward switching network operates in the following manner. 
When the facsimile terminal controller receives the picture data from the 
G3 facsimile machine, it converts the attributes of the received picture 
data (items 6, 9 and 10 of the G3 facsimile machine of FIG. 1) to the 
attributes of the items 6, 9 and 10 of the G4 facsimile machine by the 
picture data decode function and the picture data encode function, stores 
one sheet of picture data in a memory, and then sends it to a store and 
forward switching network. When the picture data is to be sent to the G3 
facsimile machine, the controller stores the picture data received from 
the store and forward switching network (and having the attributes of the 
items 6, 9 and 10 of the G4 facsimile machine of FIG. 1 for both the 
document sent from the G3 facsimile machine and the document sent from the 
G4 facsimile machine) into the memory, recognizes the attributes of the G3 
facsimile machine in accordance with the procedures of the G3 facsimile 
machine and the CCITT Recommendation T.30, and converts the picture data 
to a picture data having the attributes of the items 6, 9 and 10 of the G3 
facsimile machine of FIG. 1 by using the picture data decoding function, 
the number of dots per line conversion function and the picture data 
encoding function. The packet assembly and disassembly are basically 
identical to those of the conventional facsimile PAD device. 
In this manner, the G3 facsimile machine and the G4 facsimile machine can 
communicate with each other without recognizing the type of the partner 
facsimile machine. Since the facsimile terminal controller, the store and 
forward switching network and the G4 facsimile machine are connected 
through the G4 mode protocol, the control in the store and forward 
switcher is simple and the load is reduced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
One embodiment of the present invention will now be explained with 
reference to the drawings. 
FIG. 2 shows a configuration of an embodiment of the facsimile store and 
forward switching system of the present invention. In the present 
embodiment, facsimile communication is made in a network in which G3 
facsimile machines and G4 facsimile machines coexist. In FIG. 2, a G3 
facsimile machine 6 is connected to a facsimile terminal controller (FTC) 
4 having a facsimile PAD function and an image data conversion function, 
through a telephone switching network 5. The FTC 4 is connected to a store 
and forward switcher (DP) 2 through a packet switching network (PSN) 1. A 
G4 facsimile machine 3 is also connected to the. DP 2 through the PSN 1. 
The communication protocol between the FTC 4 and the G3 facsimile machine 
6 follows the CCITT T.30, the communication protocol between the FTC 4 and 
the PSN 1 follows the CCITT X.25, and the communication protocol between 
the FTC 4 and the DP 2 follows the mail service protocol (MSP). Since the 
FTC 4 has the facsimile PAD function, the FTC 4 communicates with the PSN 
1 and the DP 2 using the same protocol which the G4 facsimile uses when 
communicating with the PSN 1 and the DP 2. 
FIG. 3 shows a block diagram of one embodiment of the facsimile terminal 
controller (FTC) and a flow of picture data. The FTC 4 comprises a 
microprocessor (MPU) 7 which stores and processes the picture data, a main 
memory (MM) 8, a hard disk controller (DKC) 9, a hard disk (DK) 10, a 
network control unit (NCU) 13 having a telephone switching network 
controller and a G3 facsimile modem, a facsimile control unit (FCU) 14 
having a T.30 protocol and a picture data conversion function, and a line 
controller (LC) 15 for carrying out the X.25 protocol, all of which are 
connected through an internal bus 11. The NCU 13 is connected to the 
telephone switching network 5 through a telephone switching network 
connection cable 12, and the LC 15 is connected to the pocket switching 
network 1 through a PCN connection cable 16. 
FIG. 4 shows a detail of the facsimile control unit (FCU) 14 and a flow of 
picture data therein. The FCU 14 comprises a modem control unit (MCU) 17 
having a signal serial/parallel conversion function, encoder/decoders 
(CODEC) 18 and 20, a number of dots per line converter (LNC) 19, a DMA 
controller (DMAC) 21, a local main memory (LMM) 22, a local microprocessor 
unit (LMPU) 23 and a bus coupler (BC) 24, all of which are connected 
through a local bus (L bus) 25. 
The operation of the facsimile terminal controller (FTC) 4 is primarily 
explained. Transmission from the G3 facsimile machine 6 to the DP 2: 
a flow of the image data in the FTC 4 is first explained with reference to 
FIG. 3. The image data 26 received by the protocol of T.30 from the G3 
facsimile machine 6 through the telephone switching network 5, connection 
cable 12 and NCU 13 is code-converted in the FCU 14 and the resolution is 
converted. Then, it is buffered into the MM 8 8K bytes at a time ( 
.circle.1 ). The picture data in the MM 8 is designated by A. When the 
picture data A in the MM 8 reaches 8K bytes, or the data terminates, the 
picture data A is stored in the DK 10 through the DKC 9 ( .circle.2 ). 
When one sheet of picture data has been stored in the DK 10, the MPU 7 
establishes a session with the DP 2 by the X.25 and MSP through the LC 15, 
and reads out the picture data from the DK 10, 8K bytes at a time, into 
the MM 8 through the DKC 9 ( .circle.8 ). This picture data is 
designated by B. Then, the 8K-bytes picture data B is divided into 
one-packet data (128-4096 bytes), which are sent to the DP 2 through the 
LC 15 as the picture data 27 ( .circle.4 ). When the MPU 7 receives the 
acknowledgement of reception from the DP 2, it erases the picture data of 
the DK 10. The picture data stored in the DP 2 is sent as it is to the G4 
facsimile machine 3. 
Referring to FIG. 4, the coding algorithm conversion and the resolution 
conversion in the FCU 14 will be explained. The picture data from the NCU 
13 is serial-parallel converted by the MCU 17 and the converted image data 
is stored in the LMM 22 ( .circle.a ). This image data is designated by 
a. The image data a is coded data, which is decoded by the CODEC 18 ( 
.circle.b ) and returned to the LMM 22 one line at a time (one line has 
dots at 8 pels/mm) ( .circle.c ). This picture data is designated by b. 
The decoded picture data b is encoded to MMR by the CODEC 20 ( .circle.d 
) and returned to the LMM 22 ( .circle.e ). This picture data is 
designated by d. The picture data d is read from the LMM 22 and 
transferred to the MM 8 through the BC 24 and the internal bus 11 ( 
.circle.e ). Transmission from the DP 2 to the G3 facsimile machine 6: 
The flow of picture data in FIG. 3 is completely opposite to the flow in 
the transmission from the G3 facsimile machine 6 to the DP 2 and the 
picture data flows in the order of .circle.4 , .circle.4 , 
.circle.2 , .circle.1 . 
The coding algorithm conversion and the resolution conversion in the FCU 14 
of FIG. 4 are also in the opposite order to that in the transmission from 
the G3 facsimile machine 6 to the DP 2. When the resolution of the G4 
facsimile machine 3 is not equal to the standard 200 pels/25.4 mm, the 
number of dots per line conversion by the LNC 17 may be carried out. 
When the resolution of the G4 facsimile 3 is 200 pels/25.4 mm, the picture 
data flows in the direction of .circle.f , .circle.e , .circle.b 
, .circle.c .circle. , .circle. , , .circle.b , .circle.a 
of FIG. 4. The CODEC 20 decodes the picture data and the CODEC 18 encodes 
the picture data for transmission to the G3 facsimile machine 6. 
When the resolution of the G4 facsimile machine 3 is different from the 
standard resolution, that is, when it is 240 pels/25.4 mm, 300 pels/25.4 
mm or 400 pels/25.4 mm, and the picture data of such resolution is 
transmitted, the coded picture data d stored in the LMM 22 through the BC 
24 is decoded by the CODEC 18 ( .circle.e ), it is returned to the LMM 
22 as the picture data c ( .circle.g ), and it is sent to the LNC 19 to 
convert it to 8 pels/mm ( .circle.h ). Then, the 8 pels/mm picture data 
is returned to the LMM 22 as the picture data b ( .circle.i ). Then, the 
flow is in the order of .circle.c , .circle.b , .circle.a and 
the picture data is sent to the NCU 13. 
Since the resolution 8 pels/mm is the standard specification of the G3/G4 
facsimile machines, the processing by the LNC 19 is not necessary for the 
transmission from the G3 facsimile machine 6 to the DP 2 and the 
transmission from the DP 2 to the G3 facsimile machine 6. The conversion 
of the number of lines in the sub-scan direction may be done by deleting 
lines or adding lines by the software control of the LMPU 23. 
FIG. 5 shows a block diagram of the CODEC 18 in the FCU 14. A processor 26 
refers a code table stored in a memory 28 by a microprogram stored in a 
memory 27 to decode the picture data and process for encoding. A command 
register 29 stores an encode command or decode command sent from the LMPU 
23. A data register A 31 stores the picture data to be decoded or encoded 
sent from the LMM 22. A data register B 30 stores decoded or encoded data 
to be sent to the LMM 22. A parallel/serial converter 32 converts parallel 
data stored in the data register A 31 to serial data for encoding. A pixel 
change detector 33 detects that pixel of the serial picture data converted 
by the parallel/serial converter 32 which has changed from "0" (white) to 
"1" (black) or from "1" to "0". 
The decode operation in the CODEC 18 is explained with reference to FIG. 5. 
When one sheet of image data (a) is stored in the LMM 22, the decode 
command is sent from the LMPU 23 to the command register 29 of the FCU 14 
and one line of picture data (A) is set into the data register A 31. The 
processor 26 reads out the picture data (a) from the data register A 31 in 
accordance with the command stored in the command register 29 and 
processes it in accordance with the microprogram stored in the memory 27, 
and refers the code table in the memory 28 to decode it by the algorithm 
of the CCITT Recommendation T.4. The decoded data is set into the data 
register B 30 and sent to the memory 22 as the picture data (b). The 
processor 26 erases the synchronization signal contained in the picture 
data (a) when it decodes the same. It repeats the above operation for each 
line of picture data. 
The encode operation will now be explained. When the picture data (b) is 
stored in the LMM 22, the encode command is sent from the LMPU 23 to the 
command register 29 of the FCU 14, and one line of picture data (b) to be 
encoded is set into the data register A 31. The data set in the data 
register A 31 is converted to serial data by the parallel/serial converter 
32 and supplied to the pixel change detector 33. The processor 26 
processes in accordance with the microprogram stored in the memory 27 and 
the encode command stored in the command register 29, reads the detection 
result from the pixel change detector 33, and encodes the picture data 
read from the data register A 31 by the algorithm of the CCITT 
Recommendation T.4 in accordance with the code table stored in the memory 
28. When it encodes, it inserts an EOL signal as a line synchronization 
signal. The encoded data is set into the data register B 30 and sent to 
the LMM 22 as the picture data (a). The above operation is repeated for 
each line of picture data (b). 
The configuration of the CODEC 20 is the same as that of the CODEC 18. The 
components of the CODEC 20 are designated by the same numerals as those of 
the components of the CODEC 18. The memory 28 stores a code table for 
decoding and encoding the picture data by the algorithm of the CCITT 
Recommendation T.6. Like the CODEC 18, the CODEC 20 decodes the picture 
data (d) stored in the LMM 22 by the algorithm of the CCITT Recommendation 
T.6 and sends it to the LMM 22 as the picture data (b) or (c), and encodes 
the picture data (b) stored in the LMM 22 by the algorithm of the CCITT 
Recommendation T.6 and sends it to the LMM 22 as the picture data (d). 
Unlike the CODEC 18, no deletion or addition of the line synchronization 
signal is done during the encoding. 
FIG. 6 shows a block diagram of the number of dots per line converter 19. A 
processor 34 charges a rate of picture data change in accordance with a 
program stored in a memory 35. A command to indicate a rate of change of 
dot number per line of the picture data supplied from the LMPU 23 is set 
into a command register 36. A data register A 38 stores picture data whose 
dot number per line is to be changed, and a data register B 37 stores data 
whose dot number per line has been changed. 
In the resolution conversion, the command to indicate the rate of change of 
dot number per line of the picture data is set from the LMPU 23 into the 
command register 36. The rate of change of dot number per line is shown in 
the column of process in the main direction of FIG. 11. As the command is 
set into the command register 36, one line of image data (c) from the LMM 
22 is set into the data register A 38. The processor 34 recognizes the 
picture data based on the content of the command register 36, and changes 
the rate of change of dot number per line of the picture data stored in 
the data register A 38 to a rate of change designated by the content of 
the command register 36 and sets it into the data register B 37, in 
accordance with the microprogram stored in the memory 35. The data set in 
the data register B 37 is sent to the LMM 22 as the image data (b). The 
above operation is repeated for each line of image data (c). 
LMPU 23 carries out deletion or addition of lines, when such conversion of 
resolution is necessary, by processing the decoded picture data. 
The MCU 17, DMAC 21, LMM 22, BC 24 and LMPU 23 in the NCU 14 are configured 
in the same manner as those of conventional apparatus and detailed 
explanation thereof is omitted. 
FIG. 7 shows an encoding algorithm conversion pattern. In each block, a 
right top section indicates a process when the FTC 4 sends picture data to 
a receiving facsimile machine (FTC 4.fwdarw.G3 facsimile machine 6), and a 
left bottom section indicates a process when the FCU receives the picture 
data from a sending facsimile machine (G3 facsimile machine 6.fwdarw.FTC 
4). MH, MR and MMR are parameters to indicate data compression systems, 
and the contents of processes (A), (B), (C) and (D) are shown at the 
bottom of FIG. 7. Since the FTC 4 is not connected to the G4 facsimile 
machine, the blocks corresponding to the transmission/reception to and 
from the G4 facsimile machine have symbols "-" which indicate not 
applicable. As to the parameters MH, MR and MMR, the value of any of such 
parameters obtained during the protocol process with the G3 facsimile 
machine 6 is supplied from the LMPU 23 to the CODEC 18 and 20 in the form 
of a command. Since the picture data from the DP 2 is in MMR, no 
recognition of the parameter is necessary in the process when 
communicating with DP 2. 
FIG. 8 shows a resolution conversion pattern, or main direction scan line 
density/sub-direction scan line density conversion pattern. The main 
direction means a line direction in scanning a sheet, and the 
sub-direction means a column direction in scanning the sheet, and 8 p/mm 
means 8 points/mm. Again, in each block, a right top section indicates a 
resolution conversion process when the image data is sent from the FTC 4 
to the G3 facsimile machine 6, and a left bottom section indicates a 
resolution conversion process when the image data is sent from the G3 
facsimile machine 6 to the FTC 4. The contents of the processes (A) to (J) 
are shown in FIG. 11. When the resolution of the G4 facsimile machine 
connected to the DP 2 is 240 pels/ 25.4 mm, 300 pels/25.4 mm or 400 
pels/25.4 mm, the resolution conversion process when the picture data is 
sent to the G3 facsimile machine is different from the process when the G4 
facsimile machine having a standard resolution of 200 pels/25.4 mm is 
connected to the DP 2. FIG. 11 shows the resolution conversion processes 
of the FTC 4 when a document to be sent is the size A4 and the size B4, 
respectively. 
FIG. 9 shows the number of pixels per main direction scan line and ratio 
for each resolution, and FIG. 10 shows the number (l) of scan lines per mm 
in the sub-scan direction and ratio for each resolution. In the processes 
(A) to (J) of FIG. 11, the main direction relates to the conversion of the 
number of pixels per scan line, and the sub-direction relates to the 
conversion of the number of scan lines per mm. The remarks in FIG. 11 
indicate the resolution conversions when the picture data is received from 
the facsimile machine having the resolution shown in the remark column, 
and when the picture data is sent to such a facsimile machine. 
While particular embodiments of the invention have been shown and 
described, it will be obvious to those skilled in the art that various 
changes and modifications may be made without departing from the present 
invention in its broader aspects.