GB2240012A

GB2240012A - Transmission of data, such as telecopies, to a receiving apparatus having a limited processing speed

Info

Publication number: GB2240012A
Application number: GB9024091A
Authority: GB
Inventors: Georges Penalver
Original assignee: Sagem SA
Current assignee: Sagem SA
Priority date: 1989-11-07
Filing date: 1990-11-06
Publication date: 1991-07-17
Anticipated expiration: 2010-11-06
Also published as: GB9024091D0; FR2654282A3; IT9067870A1; FR2654282B3; IT1241006B; ES2024339A6; BE1005338A0; DE4035384A1; GB2240012B; IT9067870A0

Abstract

A receiving apparatus is provided with a buffer memory. The filling and emptying of this buffer memory is simulated (103, 104, 202, 203) at the transmission end, and the transmission speed of the useful data is decelerated (106), when the simulation indicates the occupancy by useful data of a determined fraction of the capacity of the buffer memory, to avoid overflow. The value of the capacity of the buffer memory, as well as that of its emptying speed, are acquired in the course of a protocol procedure which precedes the transmission of the useful data. <IMAGE>

Description

:2::--- cl C.) c J

DESCRIPTION

A METHOD OF TRANSMISSION OF DATA, SUCH AS TELECOPIES, TO A RECEIVING APPARATUS HAVING A EIMHED PROCESSING '9PEiE; AND AN APPARATUS FOR IMPLEMENTING THIS METHOD The present invention initially relates to a method of transmission, in particular of telecopies, to a receiving apparatus whose speed of processing useful data is limited, in which the transmission speed of the useful data transmitted in response to the realisation of a condition connected to the limiting value of said processing speed is decelerated.

Such a method enables it to be ensured that, for any document to be transmitted by telecopy, for example, the duration of transmission is as short as possible, taking into account the performance of the receiving apparatus to which it is transmitted.

A method of the type defined above is already known, which is used to transmit telecopies. This method uses in particular the fact that, at the transmission end, any document to be transmitted is broken down into a sequence of lines of pixels which are individually coded, and that, at the reception end, each line of pixels received is decoded and printed. On this subject, in the following text, a line is not a line of characters of a text possibly carried by the document, but a line of pixels of the document. Such a line is a strip of the document having a height equal to that of a pixel, or an elementary point of the image and the length equal to the width of the document, which corresponds, for example for a document in A4 format, to 1,728 pixels.

In the case of the telecopy, the speed of processing on reception is limited because the duration of printing of a line of pixels is not zero and is, for example, 10 ms whatever the configuration of the line.

In the known method, in the course of the protocol procedure which precedes the transmission of the useful data, the value of the necessary duration at the receiving apparatus for printing a line of pixels is acquired. Coding of each line of pixels is then effected. This coding is such that the volume of useful coding data is variable from one line to the next. For example, the volume of,useful coding data of one completely white line of pixels is very small, while the volume of useful coding data of a line of pixels having numerous black and white ranges is greater. The maximum transmission speed of the data transmitted being moreover imposed, prior to the transmission of useful coding data of one line of w pixels, the duration necessary on.transmission of these data at this maximum transmission speed is determined. If this duration is less than the duration of printing of one line by the receiving apparatus, the transmission speed for the useful data transmitted is decelerated so that the duration of transmission relative to one line remains at least equal to its duration of printing by the receiving apparatus.

Thus the overflow of the buffer memory is reliably avoided, which memory is of a size which is necessarily limited and is provided in the receiving apparatus, in particular because it has to wait until it has received all the useful data relative to one line of pixels before decoding them. In the known method, the transmission speed of the useful transmitted data is thus continuously adapted to the limiting value of the printing speed of the receiving apparatus, since the duration of transmission of a line of pixels, and thus the duration of its reception, is rendered at least equal to the duration of printing of this line. Thus, the filling speed for the buffer memory is definitely less than or equal to its emptying speed.

This known method has however a disadvantage which is connected to the fact that the transmission speed of useful data is systematically decelerated for any line for which the duration of transmission at the maximum transmission speed would be too short. For if such a line is followed by a line whose duration of transmission is long, such a deceleration is not necessary. In effect, in this case, the difference between the duration of printing and the duration of transmission at the maximum transmission speed of the first line could be used to commence transmission of the second line. In the known method, time is thus lost when alternating between lines having short transmission times and lines having long transmission times.

The present invention intends to overcome the preceding disadvantage.

To this end, the present invention provides a method of the type defined above, wherein the receiving apparatus is provided with a buffer memory, the filling and emptying of said buffer memory is simulated. and said condition is the occupancy of a determined fraction of the capacity of said buffer memory.

In the method oi the invention, the transmission speed of the useful data transmitted is only decelerated when the buffer memory on the receiving end threatens to overflow. The result is that the duration of transmission of a document is on average shorter in the method of the invention than in the known method. It should be noted that this remarkable result is obtained in particular because, on the transmission end, the filling and emptying of the buffer memory of the receiving apparatus is simulated. In effect, without this simulation, it would be necessary, in order to avoid useless decelerations at the transmission end, for the receiving apparatus to let the transmitting apparatus know that its buffer memory was approaching saturation. This would lead to a loss of time, in particular for the return of each of the modulator- demodulators or modems, put into telecopy mode, which return is necessary for the transmission of data from the receiving end to the transmitting end. In such a case, there is a risk that the time thus lost is not compensated by the time gained because of the absence of useless decelerations of the transmission speed at the transmission end.

In the preferred embodiment of the method of the invention:

- any document to be.transmitted is broken down into a sequence of lines of pixels, - each line of pixels is coded using binary coding elements variable in number from one pixel line to the next, - the number of binary coding elements of each line to be transmitted is added to a variable which is representative of the total number of binary elements stored in said buffer memory, in order to simulate the filling thereof, - the number of binary coding elements of each line to be transmitted is memorised, the number of binary coding elements per line to be transmitted which has been stored the longest is subtracted periodically, with a period equal to the duration of printing of a line by the receiving apparatus. in order to simulate emptying of said buffer memory, and - the number of binary coding elements per line to be transmitted which has just been subtracted is no longer memorised.

One such embodiment is particularly simple. Advantageously: - data are transmitted at a fixed transmission speed, said transmitted data comprising usefuldata and -7packing data, and - the proportion of packing data in said transmitted data is increased in order to decelerate the transmission speed of the useful data transmitted.

The embodiment of the method of the invention is in this case facilitated even further by the fact that it can be used on apparatuses which are already known to vary the transmission speed of the useful data.

In a further advantageous manner, in the course of a protocol procedure preceding the transmission of useful data. the limiting value of said processing speed and the value of the capacity of said buffer memory are acquired.

Adaptation to the characteristics of the receiving apparatus is thus possible.

The present invention also provides an apparatus for transmitting telecopies-for implementing the preceding method, which is intended for transmitting telecopies to a receiving apparatus whose speed of processing the useful data is limited, said transmission apparatus comprising means for decelerating the transmission speed of the useful data in response to means for determining the realisation of a condition which is connected to the limiting value of said processing speed, said receiving apparatus being provided with a buffer memory, and -8said means for determining the realisation of the condition comprising means for simulating the filling and emptying of said buffer memory and means for determining the occupancy of a determined fraction of the capacity of said buffer memory.

The present invention is described further hereinafter, by way of example only, using the following description of the preferred embodiment of the method of the invention, and the preferred embodiment of the apparatus of the invention, with reference to the attached drawings, in which:

Fig. 1 is a block diagram of.an apparatus for transmitting telecopies, and Figs. 2 and 3 show schematic diagrams of various stages of operation of the apparatus of Fig. 1.

Fig. 1 shows a transmission apparatus, in this case for telecopies. for transmitting documents over a distance to a receiving apparatus (not shown) by way of a telephone line 5.

As has already been indicated, the invention relates to a method of adapting the transmission speed of useful data transmitted to the performance of the receiving apparatus, which performance is relative to its speed of processing the useful data. the latter speed being limited in this case by the printing speed. In this case, and in a known manner, the -9receiving apparatus prints the document which it receives pixel line by pixel line, and its printing speed is limited by the fact that the duration of printing of one line of pixels is 10 ms.

The transmission apparatus of Fig. 1 comprises a device 1 for analysing the document 6 to be transmitted, a circuit 2 for coding the data resulting from the analysis of the document 6, a circuit 3 for controlling communications, and a modem 4, which is connected to a telephone line 5.

The analysis device 1 is of a known type which analyses a document 6 pixel line by pixel line. It is provided with an output which delivers an analysis signal A for each line of pixels analysed.

The coding circuit 2 is of a known type which is provided with an input which receives the analysis signal A and an output which delivers a coding signal C for each line of pixels. The implemented coding results, for example, in a known manner, from the breaking down of each line of pixels into a sequence of ranges of pixels, the pixels of one range all being of the same value, either black or white, in the most frequent case binary pixels of black or white value. The signal C thus indicates for each line of pixels and in a coded manner the number and value of the pixels in each of the successive ranges of the line.

The circuit 3 for controlling communications is provided with a first input which receives the signal C, a second input which receives a signal R, and an output which delivers a signal E. It will be described in more detail below.

The modem 4 is provided with an input which receives the signal E, an output which delivers the signal R. and a bi-directional access, which is connected to the telephone line 5. In a known manner, it modulates the signal E in order to transmit it by way of the line 5 to the receiving apparatus. Likewise, the modem 4 demodulates the signals which it receives on the line 5 coming from the receiving apparatus in order to give rise to the signal R.

It should be noted that. most frequently. the transmission apparatus of Fig. 1 is also equipped to receive telecopies. However, this is not obligatory and does not arise in the present invention. For this reason, any circuits and devices necessary to the functioning of the apparatus of Fig. 1 as a receiving apparatus are not shown in this figure.

The function of the apparatus described above is as follows:

Firstly. the transmission apparatus calls the receiving apparatus to which it is to transmit the document 6. Once communication has been established, -11there takes place, in a known manner, between the two apparatuses a protocol procedure which precedes the transmission of the useful data relative to the document 6, and which permits a mutual exchange of data, which exchange is intended to prepare this transmission. This protocol procedure is standardised by the Comite Consultatif International pour le Telegraphe et le Telephone, or C.C.I.T.T.

In the course of this protocol procedure, acquisition is provided for in a known manner by the transmission apparatus of the value of the duration of printing of a line by the receiving apparatus.

The method of the invention also provides for the acquisition by the transmission apparatus of the value of the capacity of the buffer memory with which the receiving apparatus is provided. It will be remembered that this buffer memory is necesary because, as the receiving apparatus prints the document received pixel line by pixel line, it has to wait until it has received and decoded a complete line of pixels before printing it. In principle, the capacity of the buffer memory corresponds to several lines of pixels. For example, the capacity of the buffer memory is 432 octets.

During the course of the protocol procedure, and in a known manner, the quality of the telephone -12channel of transmission is tested, and the max' transmission speed is determined at which the data on this channel can be transmitted in such a way that the error rate on the reception end remains acceptable. If the quality of the transmission channel is goodr the transmission speed is 9, 600 bits/s. If the quality of the transmission channel is average, the transmission speed is 4,800 bits/s, and so on.

After the protocol procedure, the duration of printing of one line by the receiving apparatust the capacity of the buffer memory of the receiving apparatus, and the maximum transmission speed of the data on the transmission channel are known by the transmission apparatus, and more precisely by the circuit 3 for controlling communications, which is a microprocessor circuit.

The transmission of useful data for coding of the pixel lines of the document 6, represented by the signals C, then starts.

In order for the duration of transmission of the document to be as short as possible, the first useful data are transmitted at the maximum transmission speed, which is assumed to be equal, for example, to 9,600 bits/s.- However, if the first lines of pixels of the document are simple lines whose coding only requires a -13few bits, the duration of transmission of each of these lines risks being less than 10 ms, and in this case, there is the risk of overflow of the buffer memory of the receiving apparatus. In effect, the duration of reception of each of these lines will be less than 10 ms, and the filling speed of the buffer memory greater than its emptying speed, since the latter depends on the duration of printing of a line, which in this case is equal to 10 ms.

If, on the contrary, the first lines of pixels of the document are complex lines whose coding requires a large number of bits, the duration of transmission of each of these lines will definitely be greater than 10 ms, even at a transmission speed of 9,600 bits/s. On the reception end, there will be no risk of overflow of the buffer memory, since its emptying speed will be greater than its filling speed.

Thus, in certain situations, it is necessary to decelerate the transmission speed of the useful data transmitted, while in other situations this transmission speed should be left equal to the maximum transmission speed which is compatible with the quality of the transmission channel, if it is desired that the total duration of transmission of a document should be as short as possible.

In order to decide in which situations it is necessary to decelerate the transmission speed of the useful data transmaitted, the present invention proposes the simulation, on the transmission end, of the filling and emptying of the buffer memory which is on the receiving end, the decision to decelerate being taken when simulation indicatesthat a determined fraction of the capacity of the buffer memory is occupied.

The fraction of the capacity of the buffer memory whose occupancy triggers deceleration is determined in particular with regard to the value of the maximum transmission speed used, so that the risk of the buffer memory overflowing following deceleration is practically zero. This fraction may for example be 1/10e with a maximum transmission speed of 9,600 bits/s, and 1/6e with a maximum transmission speed of 4,800 bits/s, and so on.

In this case, it is the communications control circuit 3 which effects simulation. To this end, it calculates contipuously the value of a variable UT which is representative of the total number of bits stored in the buffer memory of the receiving apparatus. In order to simulate the filling of this buffer memory, as soon as a line of pixels is coded and has to be transmitted, the circuit 3 adds the number of coding bits of this line to the variable NT.

L 1 i 1 1 -15At the same time, the circuit 3 memorises the number of bits of this line.

In order to simulate the emptying of the buffer memory, the circuit 3 periodically subtracts, with a period in this case equal to 10 ms, which is the duration of printing of a line by the receiving apparatus. the number of bits relative to one line to be transmitted, whic it has memorised the longest, it being understood that as soon as the subtraction has been done, the circuit 2 deletes from its memory. that is to say ceases to store, the number of bits which it has just subtracted. In this way, there is good simulation of the exit from the buffer memory of the receiving apparatus of the line which itself had been memorised the longest, this exit occurring with a periodicity of 10 ms.

As soon as the number NT, which is calculated as described above, exceeds a threshold S, whose value is itself calculated as a fraction of the value of the capacity of the buffer memory acquired in the course of the protocol procedure, the circuit 3 orders the deceleration of the transmission speed of the useful data transmitted.

To do this, the circuit 3 could control the modem 4 in order to decelerate the transmission speed. but in this case it is done in a known manner by inserting 0 -16packing bits.

Thus, the data transmitted remain at a fixed transmission speed, for example 9,600 bits/s, but these data comprise both useful data for coding the lines of pixels and packing data.

In order to decelerate the transmission speed of the useful data transmitted, the proportion of packing data in the data transmitted is increased.

In this case, and for example, when the circuit 3 decides on decleration of the transmission speed of the useful data, it adds, following the coding bits of each line of pixels, packing bits which do not carry any data.

Of course, and in a known manner, the receiving apparatus is arranged so as not to store the packing bits in the buffer memory, since these packing bits do not carry any useful data.

In order to decide on the number of packing bits to be added to each line, the circuit 3 can use the known criterion of completing the lines whose duration of transmission is less than the duration of printing at the receiving end, since this criterion ensures that the buffer memory does not overflow.

Fig. 2 shows, in the form of blocks, the stages relating to the simulation by the transmission apparatus of the filling of the buffer memory at the 1 z, 1 receiving end.

Firstly, the block 101 schematises the stage of breaking down the document into a sequence of pixel lines, which breaking down is carried out in this case principally by the analysis device 1.

The block 102 schematises the stage of coding each line of pixels to be transmitted, which is carried out by the coding circuit 2. It is assumed in this case that the line of rank k is coded using a number of bits equal to "k The block 103 schematises the stage of addition of each number of bits 14k to the variable WT, which represents the total number of bits in the buffer memory of the receiving apparatus, as has already been indicated. This stage is carried out by the circuit 3.

The block 104 schematises the stage of memorising the number of bits Nk of each line of pixels, which is carried out by the circuit 3.

The block 105 schematises the stage, again carried out by circuit 3, of comparing the number NT with the threshold S, which is calculated in response to the value of the capacity of the buffer memory of the receiving apparatus, and which represents a determined fraction of this capacity.

If the number NT is less than the threshold S, 1 -18the circuit 3 immediately orders the modem 4 to transmit the Nk bits for coding the line of pixels of rank k. as schematised by block 107.

If. on the contrary, the number NT is greater than the threshold S, the circuit 3 inserts packing bits after the Nk bits for coding the line of pixels of rank k, as is schematised by the block 106. Thus the transmission speed of the useful data is decelerated. The circuit 3 then passes to the stage schematised by the block 107.

Fig. 3 shows the stages relative to the simulation, by the transmission apparatus, of emptying the buffer memory.

Block 201 schematises an interruption in operation of the circuit 3 as schematised by Fig. 2, which interruption occurs periodically, in this case with a period of 10 ms corresponding to the duration of printing of one line by the receiving apparatus.

During this interruption, the circuit 3 subtracts from the number NT the number Ni of bits coding the line of rank i, which number has been stored the longest.

Then, during the stage schematised by the block 203, the circuit 3 deletes the number Ni which has just been subtracted. In practice, and in a known manner, the circuit 3 will carry out the stages 104, -19202 and 203 by memorising the numbers of bits such as Ni or Nk in a memory of the First Input First Output, or F.I.F.O.. type.

Then, the block 204 of Fig. 3 schematises the end of the interruption and the return to operation as schematised in Fig. 2.

Programming the circuit 3 in order to carry out the tasks schematised by Figs. 2 and 3 is within the scope of a person skilled in the art and will therefore not be described further.

Of course, although the invention finds a useful application in the field of telecopying, it is not limited to this field and may be used between a transmitter and a receiver of any type, if the speed of processing of the useful data by the receiver is limited and the latt..r comprises a buffer. memory.

i

Claims

1. A method of transmission of data, such as telecopies, to a receiving apparatus whose speed of processing useful data is limited, in which the transmission speed of the useful data transmitted in response to the realisation of a condition which is connected to the limiting value of said processing speed is decelerated, said receiving apparatus being provided with a buffer memory, and the filling and emptying of said buffer memory being simulated, said condition being the occupancy of a determined fraction of the capacity of said buffer memory.

2. A method as claimed in claim 1, which is applied to the transihission of teiecopies, in which: - any document to be transmitted is broken down into a sequence of pixel lines, - each pixel line is coded using binary coding elements which are variable in number from one pixel line to the next, - the number (Nki of binary coding elements of each line to be transmitted is added to a variable (NT) which is representative of the total number of binary elements stored in said buffer memory, in order to simulate the filling thereof,- -21- the number (Nk) of binary coding elements of each line to be transmitted is memorised, - the number (Ni) of binary coding elements per line to be transmitted which has been stored the longest is subtracted periodically, with a period equal to the duration of printing of a line by the receiving apparatus, in order to simulate the emptying of said buffer memory, and - the number (Ni) of binary coding elements per line to be transmitted, which has just been subtracted, is no longer memorised.

3. A method as claimed in claim 1 or 2, in which: - data are transmitted at a fixed transmission speed, said transmitted data comprising useful data and packing data, the proportion of packing data in said transmitted data being increased in order to decelerate the transmission speed of the useful data transmitted.

4. A method as claimed in any of claims 1 to 3, in which, in the course of a protocol procedure preceding the transmission of useful data. the limiting value of said processing speed and the value of the capacity of said buffer memory are acquired.

5. A transmission apparatus for data, such as telecopies, for implementing the method of any of claims 1 to 4, which is intended for transmitting teleconies -22- to a receiving apparatus whose speed of procetsing u:eful data is limited, the transmission apparatus comprising means for decelerating the transmission speed of the useful data in response to means for determining the realisation of a condition which is connected to the limiting value of said processing speed, said receiving apparatus being provided with a buffer memory, and said means for determining the realisation of the condition comprising means for simulating the filling and emptying of said buffer memory and means for determining the occupancy of a determined fraction of the capacity of said buffer memory.

6. An apparatus.as claimed in claim 5, for transmitting telecopies, comprising: - means for breaking down any document to be transmitted into a sequence of pixel lines, - means for coding each line of pixels using binary coding elements varying in number from one pixel line to the next, - means for adding the number (14k) of binary coding elements of each line to be transmitted to a variable (NT) representative of the total number of binary elements stored in said buffer memory, in order to simulate the filling thereof. - means for memorising the number (Nk) of binary 1 1 -23coding elements of each line to be transmitted. - means for subtracting periodically, with a period equal to the duration of printing of a line by the receiving apparatus, the number (Ni) of binary coding elements per line to be transmitted which has been memorised the longest. in order to simulate the emptying of said buffer memory, and - means for. stopping memorisation of the number (Ni) of binary coding elements per line to be transmitted which has just been subtracted.

7. An apparatus as claimed in claim 5 or 6, comprising: - means for transmitting data at a fixed transmission speed. said transmitted data comprising useful data and packing data, and - means for increasing the proportion of packing data in said transmitted data in order to slow down the transmission speed of the useful data transmitted.

8. An apparatus'as claimed in any of claims 5 to 7, comprising means for acquiring, in the course of a protocol procedure preceding the transmission of useful data, the limiting value of said processing speed and the value of the capacity of said buffer memory.

9. A method of transmission of data, substantially as hereinbefore described with reference -24to the accompanying drawings.

10. A transmission apparatus for data, substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.

Published 1991 at 7be Patent 0171ce. State House. 66/71 High Holborn. London WC I R 47P. Further copies may be obtained from Sales Branch.:Jnit 6. N-ne Mile Point, Cwmfelinfach, Cross Keys. Newport NPI 7HZ. Printed by Multiplex techniques lid. St Mary Cray, Kent.