Transmission control system for facsimile transceiver

A transmission control system for a facsimile transceiver allows two facsimile transceivers having different buffer memory sizes and decoding rates different from encoding rates to intercommunicate within a short period of time. Start and stop of encoding and insertion of fill bits are controlled on the basis of an amount of data stored in a buffer memory of a transmitting transceiver, which temporarily stores encoded data, and various conditions associated with a receiving transceiver, so that the number of bits encoded data per line is averaged over a plurality of lines. This decreases the transmission time and, thereby, increases the transmission rate without resorting to an increase in the processing rate of a reader or that of a recorder or an increase in modem rate.

BACKGROUND OF THE INVENTION 
The present invention relates to a transmission control system for a 
facsimile transceiver which allows even facsimile transceivers furnished 
with different buffer memory sizes and/or decoding rates different from 
encoding rates to hold communications within a short transmission time. 
In facsimile communications, the higher the data transmission rate, the 
shorter the transmission time is. However, since the response rate is 
limited by a minimum scanning time designed for a receiver, i.e., a 
recording speed of a printer or like recording device, the transmission 
rate has a certain upper limit even if the modified Huffman (MH) system or 
similar encoding system is employed to transmit band-compressed data. It 
is therefore necessary to observe the minimum transmission time assigned 
to a transceiver at a receiving station and such has heretofore been 
implemented by the insertion of fill bits, for example. 
Usually, a transmitter of a facsimile transceiver is made up of a reader 
such as a scanner, an encoder, a buffer memory, a modem operable as a 
modulator, and a system control unit, while a receiver is made up of a 
modem operable as a demodulator, a buffer memory, a decoder, a recorder 
such as a printer, and a system control. Assume that the buffer memory of 
the transmitter, or transmit buffer memory, has a memory size Mt, the 
encoder has an encoding rate Ve, the buffer memory of the receiver, or 
receiver buffer memory, has a memory size Mr, the decoder has a decoding 
rate Vd, and the modems commonly have a modem rate Vm. 
Assume that two facsimile transceivers each having the above construction 
exchange picture data. In the transmitting transceiver, the reader 
develops binary black-white data representative of a picture to be 
transmitted (hereinafter sometimes referred to as raw data). The encoder, 
which may comprise a microprocessor, processes the binary data output from 
the reader with the MH principle. The MH data are delivered from the 
encoder to the buffer memory. The encoded data once stored in the buffer 
memory are continuously transferred to the modulator synchronized with 
modem clock, which is output from the modulator. The procedure described 
so far is controlled by the system control unit. 
The other or receiving transceiver demodulates the incoming encoded data by 
means of the demodulator. The demodulated data are continuously applied to 
the buffer memory in synchronism with modem clock, which is output from 
the demodulator. The data stored in the buffer memory are decoded by the 
decoder into the original binary data which are then reproduced by the 
recorder. 
The picture signal processing times of such facsimile transceivers are 
related with each other as will be discussed mathematically hereinafter. 
The transmitting transceiver station controls the generation interval of 
raw data (picture information) per line to within a predetermined range so 
that the generation rate of raw data at the reader may not exceed a 
plotter rate of the recorder at the receiving transceiver. This is, the 
control occurs such that the I/O rate Tp (ms/l) of the receiver of the 
receiving transceiver and the generation rate of raw data per line at the 
transmitting transceiver are in a relation 
EQU Ts.gtoreq.Tp (1) 
The control represented by the relation (1) is always performed between 
facsimile transceivers of the same type and is especially required for 
transceivers of different types. Also, where raw data are input from an 
external memory or the like, the rate of receiving the data supplied from 
the outside has to be controlled as represented by the relation (1). 
As previously described, a facsimile transceiver of the described type has 
a minimum transmission time Tmin per line (s/l) which is predetermined to 
match with a kind of the transceiver of a receiving facsimile transceiver; 
a control is performed such that the transmission time remains longer than 
the minimum transmission time by, for example, inserting fill bits. To 
improve the transmission rate, it is necessary to increase the processing 
rate of the reader and that of the recorder as well as the modem rate. 
This naturally results in a higher production cost. For given processing 
rates of a reader and recorder and a given modem rate, the transmission 
time cannot be shortened and, therefore, the transmission rate cannot be 
increased unless the number of fill bits to be inserted is made as small 
as possible. 
A higher transmission rate may be implemented by a prior art transmission 
control system in which a transceiver at a transmitting station is 
furnished with a reader capable of reading a bunch of "N" lines at a time, 
and a multi-line memory for temporarily storing data read by the reader, 
i.e., raw data before compression, while a transceiver at a receiving 
station is furnished with a recorder capable of recording "N" lines at a 
time, and a multi-line memory for temporarily storing reproduced data. In 
this system, a minimum transmission time Tmin.times.N is predetermined for 
each "N" lines and, only when the transmission time has become shorter 
than the minimum transmission time, fill bits are inserted. In this 
manner, the system inserts fill bits on the basis of each "N" lines to 
maintain the minimum transmission time Tmin instead of inserting fill bits 
on a line-by-line basis to maintain the minimum transmission time Tmin, 
thereby averaging the density of read data. The result is a decrease in 
the number of inserted fill bits and, therefore, an increase in the 
transmission rate. Concerning such as a transmission control system, the 
larger the number of lines N, the greater the transmission time shortening 
effect is. However, an increase in the number of lines N is unattainable 
without an increase in the capacity of the line memory for storing raw 
data and, hence, without an increase in memory cost. 
Another known implementation for a higher transmission rate is a 
transmission control system which constantly monitors a relationship 
between a quantity of encoded data temporarily stored in a buffer memory 
at a transmitting transceiver, i.e. memory size Mt, and a quantity of 
decoded data stored in a buffer memory at a receiving transceiver, i.e. 
memory size Mr. When the receive buffer memory is about to overflow, the 
system informs the transmitting transceiver of that storage condition to 
cause it to stop encoding operation or insert fill bits, thereby 
increasing the transmission rate. In detail, the system control is such 
that when the quantity of encoded data in the buffer memory at the 
receiving transceiver has exceeded a first value M.sub.1 (M.sub.1 &lt;Mr), 
the encoding operation is interrupted and, when the quantity of data has 
decreased beyond a second value M.sub.2 (M.sub.2 &lt;M.sub.1), the encoding 
operation is resumed and, when the data quantity has decreased beyond a 
third value M.sub.3 (0&lt;M.sub.3 &lt;M.sub.2), fill bits are inserted. 
In the second prior art transmission control system, a response from the 
receiving transceiver has to be sent before the receive buffer memory 
overflows, in order to prevent the overflow. Again, this increases the 
costs becaust exchange of such responses between remote transceivers is 
unachievable without employing a signal generator or a receiver or 
installing an additional channel for the transmission of the responses. 
As discussed above, the first-mentioned prior art transmission control 
system, which increases the transmission rate when the processing rates of 
a reader and recorder or the modem rate is constant, cannot achieve the 
purpose unless an expensive line memory having a large capacity is used. 
The second-mentioned prior art system requires the transmitting 
transceiver to send out information indicative of overflow of its buffer 
memory, increasing the system cost for the generation and exchange of 
response signals. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a 
transmission control system for a facsimile transceiver which allows 
remote facsimile transceivers to intercommunicate within a short 
transmission time even though their buffer memory sizes, encoding rates 
and decoding rates may be different from each other. 
It is another object of the present invention to provide a transmission 
control system for a facsimile transceiver which shortens a transmission 
time without resorting to increases in the processing rates of a reader 
and recorder or the modem rates of transmitting and receiving facsimile 
transceivers. 
It is another object of the present invention to provide a generally 
improved transmission control system for a facsimile transceiver. 
A facsimile transceiver to which the present invention is applicable 
comprises a transmitter which has a reader for reading picture 
information, an encoder for removing redundancy of the picture 
information, a buffer memory for temporarily storing encoded data, and a 
receiver having a buffer memory for temporarily storing the encoded data, 
a decoder for reproducing the redundancy of the encoded data, and a 
recorder for recording the picture information. In accordance with the 
present invention, the transmitter comprises a first control device for 
performing a control such that a relation Tsm.gtoreq.Tpm holds between a 
reading interval per line Tsm of the reader and a picture information 
recording time Tpm per line of the recorder, a fill bit insertion device 
for inserting fill bits Nf (Nf.gtoreq.0 and integer) line by line in the 
encoded data such that a relation Nc+Nf.gtoreq.VM.times.Tdm holds between 
the fill bits Nf inserted line by line in the encoded data, a modem rate 
Vm of the receiver, and a minimum decode processing time Tdm per line of 
the decoder, and a second control device for performing a control such 
that a relation Tc.gtoreq.(Nc+Nf)/Vd holds between an encoding interval 
per line Tc, a number of bits Nc of encoded data per line, the fill bits 
Nf to be inserted in the encoded data line by line, and the decoding rate 
Vd of the decoder. The transmitter and receiver being controlled such that 
during a protocol procedure at least the recording time Tpm of the 
recorder at the receiver, the modem rate Vm, a memory size Mr of the 
buffer memory of the receiver, the decoding rate Vd of the decoder, and 
the minimum decode processing time Tdm of the decoder are notified to the 
transmitter, during transmission of picture information the transmitter 
causes the first and second control means and said fill bit insertion 
means to satisfy the respective conditions, upon increase of an amount Mt 
of encoded data stored in the buffer memory beyond a first reference value 
M.sub.1 (M.sub.1 &lt;Mr) an encoding operation is interrupted, upon decrease 
of the amount Mt of encoded data beyond a second reference value M.sub.2 
(M.sub.2 &lt;M.sub.1) the encoding operation is resumed, and upon decrease of 
the amount Mt of encoded data beyond a third reference value M.sub.3 
(0&lt;M.sub.3 &lt;M.sub.2) a predetermined number of fill bits are inserted. 
The above and other objects, features and advantages of the present 
invention will become apparent from the following detailed description 
taken with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
While the transmission control system for a facsimile transceiver of the 
present invention is susceptible of numerous physical embodiments, 
depending upon the environment and requirements of use, a substantial 
number of the herein shown and described embodiment have been made, tested 
and used, and all have performed in an eminently satisfactory manner. 
Referring to FIG. 1 of the drawings, a picture information processing 
system of a facsimile transceiver 10 to which the present invention is 
applicable is shown. The transceiver 10 includes in its transmitting 
section a reader 12, an encoder 14, a buffer memory 16, a modem 
(modulator) 18 and a system control unit 20, and in its receiving section 
a recorder 22, a decoder 24, a buffer memory 26, a modem (demodulator) 28 
and a system control unit 30. The memory size of the buffer memory, or 
transmit buffer memory, 16 is indicated by Mt, the memory size of the 
buffer memory, or receive buffer memory, 26 by Mr, the encoding rate of 
the encoder 14 by Ve, and the decoding rate of the decoder 24 by Vd, while 
the modem rates of the modems 18 and 28 are commonly indicated by Vm. 
Although various encoding sytems are available for such a facsimile 
transceiver, the description will focus to the MH system by way of 
example. 
At the transmitter side, the system control unit 20 controls the start and 
stop of operation of the reader 12 on a line-by-line basis so that the 
following relation may hold between a reading interval per line Tsm and a 
recording time for recording one line of picture information assigned to a 
facsimile transceiver which received at the time of facsimile protocol: 
EQU Tsm.gtoreq.Tpm (2) 
The system control unit 20 controls the encoder 14 to insert fill bits 
after calculating fill bits Nf to be inserted in one line of encoded data 
(Nf.gtoreq.0 and integer) from a total number Nc of bits of encoded data 
per line and the modem rate (communication modem rate) Vm (bits/s), such 
that the following relation holds between the total number of bits Nc, the 
modem rate Vm, a minimum encode processing time Tdm per line (ms/l) of the 
decoder 24, and the fill bits Nf: 
EQU Nc+Nf.gtoreq.Vm.times.Tdm (3) 
The control over the insertion of fill bits described above is directed to 
insuring a certain minimum period of time necessary for the decoder 24 to 
decode one line of encoded data, however short the one line of data may 
be. Stated another way, such a control compensates for the incapability of 
the decoding rate of linearly approximating itself to the number of bits 
of encoded data. At the same time, the encoder 14 is controlled to set up 
an interval Tc of starts of encoding per line data as shown below in 
accordance with the decoding rate Vd of the decoder 24: 
EQU Tc.gtoreq.(Nc+NF)/VD (4) 
Such a control over the interval Tc of starts of line-by-line encoding is 
adapted to prevent the receive buffer memory 26, i.e. receive FIFO buffer 
memory, from overflowing. Using a ratio .alpha. of the decoding rate to 
the modem rate, the decoding rate Vd may be expressed as: 
EQU Vd=.alpha..times.Vm (5) 
In a practical example of the interval control, the number of bits Nc of 
line-by-line encoded data is counted, a required period of time from the 
start to the end of one line of encoding is predetermined in terms of a 
count Nm of modem clock (Vm), and encoding the next line is started when 
the count Ni of the modem clock after the start of encoding has reached a 
relation: 
EQU Ni.gtoreq.Nm/.alpha. (6) 
The control described above satisfies the condition (4). The encoder 14 
does not perform encoding unless the reader 12 develops a binary picture 
signal. 
FIG. 2 is a flowchart representative of a control over the transmit buffer 
memory 16 in accordance with the transmission control system of the 
present invention. FIG. 3 is a flowchart representative of a compensation 
control which is associated with a minimum encode processing time of the 
decoder 24 and also executed at the transmitting side. 
In the drawings, Mt is an amount of encoded data stored in the transmit 
buffer memory 16 and the unit of which is a number of bits, Nc is a number 
of bits of encoded data per line. Vm is a modem rate, Tdm is a minimum 
decode processing time per line of the decoder 24, Nf is a number of fill 
bits to be inserted in encoded data on a line-by-line basis, and M.sub.1 
-M.sub.3 are reference data amounts associated with the transmit buffer 
memory 16 and preselected to be in a relation 0.ltoreq.M.sub.3 &lt;M.sub.2 
&lt;M.sub.1 .ltoreq.Mr. Further, EOL indicates an end-of-line code. 
In the transmission control system of the present invention, the encoder 14 
performs MH encoding while controlling the transmit buffer memory 16 
according to the flowchart of FIG. 2. That is, the control over the 
transmit buffer memory 16 is such that the number of bits Mt of encoded 
data stored in the buffer memory 16 is prevented from increasing beyond 
the first reference value M.sub.1 or decreasing beyond the third reference 
value M.sub.3. When the number Mt has decreased beyond the third reference 
value M.sub.3, a required number of fill bits are inserted to maintain the 
former larger than the latter. In the MH system, a fill bit is a logical 
"0". The encoding operation is stopped when the number Mt exceeded the 
first reference value M.sub.1 and resumed when it has become smaller than 
the second value M.sub.2. 
In relation with such a case, assume that the memory size Mt of the 
transmit buffer memory 16, i.e. FIFO buffer memory, and the memory size Mr 
of the receive buffer memory are in a relation: 
EQU Mt.gtoreq.Mr (7) 
Then, selecting the first reference value M.sub.1 
EQU M.sub.1 =Mr-.beta. (8) 
the encoding operation is stopped as soon as the amount of data Mt stored 
in the transmit buffer memory 16 exceeds M.sub.1. 
Where the comparison between the data amount Mt and the first reference 
value M.sub.1 is to be performed with respect to a black/white color 
transition point, it is performed at 
EQU M'.sub.1 =M.sub.1 -(bit length of maximum code of same color) (9) 
On the other hand, where the comparison is performed on a line-by-line 
basis, the stop control over the encoding operation is performed with 
EQU M'.sub.1 =M.sub.1 -(bit length of largest code per line) (10) 
While the encoding operation is resumed upon coincidence of the data amount 
Mt with the second reference value M.sub.2 (M.sub.2 &lt;M.sub.1), the 
following relation may be selected in order to avoid frequent starts and 
stops of the encoding operation: 
EQU M.sub.2 =M.sub.1 -(256 to 1024 bits) (11) 
Further, fill bits are inserted when the data amount Mt has decreased 
beyond the third reference value M.sub.3 (M.sub.3 &lt;&lt;M.sub.2), according to 
the flow of FIG. 3 and immediately before an EOL code. 
Comparison of the data amount Mt with the third value M.sub.3 occurs at the 
end encoding of each line and immediately before the generation of an EOL 
code. For example, assuming 
##EQU1## 
the number of fill bits to be inserted is produced by 
##EQU2## 
Meanwhile, where the memory sizes of the transmit and receive buffers are 
related as 
EQU Mt&lt;Mr (14) 
the equation (8) is replaced with 
EQU M.sub.1 =Mt-.beta. (15) 
for thereby controlling the data amount Mt in the buffer memory 16. The 
other controls are common to those previously described. 
Hereinafter will be described the value .beta. included in the equations 
(8) and (15). 
Let it be assumed that the various parameters have the following values: 
Vm=9600 bps 
Tp+Ts=10 ms/l 
.alpha.=1/2 
Tdm=5 ms 
A possible case which renders the data amount in the receive buffer memory 
26 substantial is one in which a line with the most complicated pattern 
and a subsequent line with the simplest pattern continuously appear as 
long as structurally permitted. Typical of such a situation may be one in 
which checkers (2048 bits per line) are encoded by the MH system and 
followed by 64 successive lines (generated number of bits being smaller 
than 9600 bps.times.5 ms/l) each being in a line smaller than 24 bits. 
Where the encoding operation and the modem transfer begin at the same time, 
the number of generated bits will coincide with the number of transmitted 
bits when 
##EQU3## 
For the generation of such a number of bits, there is required a period of 
time produced by 
##EQU4## 
In the case concerned, assuming that a decoding operation is started when a 
quantity of data of 10772 bits has been reached in the receive buffer 
memory 26, the content does not exceed 10772 even though the pattern of 
the 65 lines may be repeated. Therefore, the value of .beta. in the 
equation (8) or (15) which suffices the purpose in practice is: 
.beta.=10772 bits 
In the manner described, in accordance with the transmission control system 
of the present invention, a facsimile transceiver at a transmitting 
station performs controls in response to various conditions which are sent 
thereto from a facsimile transceiver at a receiving station during a 
protocol procedure. The encoder 14 starts and stops encoding and inserts 
fill bits while sensing the number of effective data bits, which are 
status signals output from the buffer memory 16. Meanwhile, encoded data 
stored in the receive buffer memory 26 are sequentially applied to the 
decoder 24 in response to the modem clock without having their amount 
controlled, the decoder 24 decoding the data at the decoding rate Vd. The 
fill bits inserted at the transmitting station are removed at the 
receiving station as has been the case with prior art systems. 
While the present invention has been shown and described in relation with a 
facsimile transceiver, such is only illustrative and it is also applicable 
to the transmission of encoded data which have undergone compression. The 
data to be encoded at the transmitting station may even be the data stored 
in another data generating device or an external memory, instead of those 
which are output from the reader. 
Concerning the receiving station, too, the present invention may be 
practiced in the case where data are stored in a memory instead of routed 
to a recorder. In such a case, the control will be effected employing the 
recording time Tpm per line as represented by the equation (2) or the like 
as a period of time for recording data in one line of the memory. 
As described hereinabove, while a prior art transmission control system for 
a facsimile transceiver controls a minimum transmission time by inserting 
fill bits line by line, a system embodying the present invention makes the 
number of inserted fill bits as small as possible by controlling the start 
and stop of encoding as well as fill bit insertion based on an amount of 
encoded data stored in a transmit buffer memory and various parameters 
associated with a facsimile apparatus at a receiving station. Such a 
control over the encoding operation and insertion of fill bits is 
effective to average the number of bits of one line of encoded data over a 
plurality of lines, the average value being longer than a minimum 
transmission time for each line. 
Hence, the transmission control system of the present invention reduces the 
number of fill bits to be inserted and, thereby, shortens the transmission 
time and speeds up transmission, even with a facsimile system in which the 
processing rate of a reader and/or that of a recorder is the same as prior 
art one or with a modem rate also common to prior art one. 
For example, assume that the communication modem rate is 9600 bps, and that 
in the MH coding system the I/O rate is 10 ms/l and the minimum 
transmission time is 10 ms/l. Then, the prior art transmission control 
system consumes 19.2 seconds for sending a CCITT #1 document, while the 
transmission control system in accordance with the present invention 
reduces the transmission time to 15.6 seconds, meaning an about 20% 
cutdown of the transmission time. For the transmission control system of 
the present invention, use is made of a system configuration in which the 
memory size Mr of the receive buffer memory 26 is 16 kilobits, the 
decoding rate Vd is 9600 bps.times.1.5, and the minimum processing time of 
the decoder is 5 ms/l. 
In contrast to the first-mentioned prior art control system which uses a 
line memory for storing raw data, the control system of the present 
invention uses a buffer memory for storing encoded data and, therefore, 
allows the memory size to be reduced in proportion to the compression 
ratio provided by encoding, resulting in a proportionally lowered memory 
cost. 
Furthermore, since the present invention eliminates the need for 
controlling a buffer memory at a receiving station as has been practiced 
by the second-mentioned prior art system, it is unnecessary for a 
transmitting station to send a response during transmission of picture 
information and this eliminates an increase in cost due to addition of 
devices. 
Various modifications will become possible for those skilled in the art 
after receiving the teachings of the present disclosure without departing 
from the scope thereof.