JPH04179341A - Delay fluctuation absorbing control system - Google Patents

Abstract

PURPOSE:To prevent the deterioration of sound quality by reading a reception cell which arrives first from a FIFO memory after the time of delay fluctuation absorbing width and altering a reference point when a difference between cell transmission time and cell reception time is smaller than minimum delay time. CONSTITUTION:The content of a timer 3 is inserted into the header part of the reception cell as cell reception time and is written into the FIFO memory 1. The reception cell which arrives first is written into the FIFO memory 1 and a judgement reading control part 5 reads the reception cell after the time of the previously set delay fluctuation absorbing width. Then, the difference between cell transmission time added to the header part of the reception cell and cell reception time is judged to be smaller than minimum delay time or not. When it is judged to be smaller, the reference point of the minimum delay time is altered and the reading of the FIFO memory 1 is controlled. Thus, decoding is prevented from being interrupted and the deterioration of sound quality is prevented.

Description

[Detailed Description of the Invention] [Summary] Regarding a delay fluctuation absorption control method in an ATM multiplex transmission system, the purpose of this invention is to shorten delay fluctuation absorption pull-in time and minimize delay time. In a delay fluctuation absorption control method in a system, a first-in first-out memory writes a received cell, reads out the received cell, and sends only an information part to a decoding unit;
a timer that counts a decoding clock signal applied to the decoding unit; and a reception time insertion unit that inserts the contents of the timer as a cell reception time into a header part of the reception cell and sends it to the first-in first-out memory. , the cell transmission time added to the header section of the received cell read from the first-in/first-out memory, the cell reception time inserted by the reception time insertion section, the delay fluctuation absorption width, and the minimum delay. and a determination read control unit that performs read control of the first-in/first-out memory based on time, and after writing the first received received cell to the first-in/first-out memory, the determination read control unit The unit reads the received cell after a time of the delay fluctuation absorption width, and when it is determined that the difference between the cell transmission time and the cell reception time is smaller than the minimum delay time, changes the reference point of the minimum delay time. It was configured to do so.

[Industrial application field]

The present invention relates to a delay fluctuation absorption control method in an ATM multiplex transmission system.

ATM (Asynchronous Transfer)
r Mode; asynchronous transfer mode) multiplex transmission system is for audio signals.

It divides various information such as image signals and data into cells of a certain length, multiplexes them via a buffer, and transmits them.
When the number of sent cells increases, the time they stay in the buffer becomes longer, and conversely, when the number of sent cells decreases, the time they stay in the buffer becomes shorter. Therefore, delay fluctuations occur in cells that are multiplexed and transmitted. On the receiving side,
In order to absorb this delay fluctuation, a receiving buffer consisting of a first-in first-out memory (FIFO memory) is provided, and it is desired that the delay fluctuation absorption width is large and the absolute delay time is small.

[Conventional technology]

In the ATM multiplex transmission system, for example, as shown in FIG. The side includes a demultiplexing section 46, a reception buffer 47, a cell decomposition section 48, and a decoding section 49, and the transmission side and the reception side are connected via a transmission line 50 or an ATM switch (not shown), etc. ing.

On the transmitting side, a signal detection unit 43 detects whether the input signal is an audio signal or a modem signal, controls an encoding unit 41 and a cell processing unit 42, and performs processing corresponding to the audio signal or modem signal. After encoding the data, it is converted into cells. This cell has a 53-hide length consisting of a 5-byte header section and a 48-byte information section, is multiplexed via the buffer 44, and is sent out to the transmission path 50.

The cell processing section 42 is generally configured to determine whether the audio signal is a voiced cell or a silent cell, and to add only the voiced cells to the multiplexing section 45 . Furthermore, the multiplexing section 45 can add the cell number and cell transmission time to the header section when transmitting the cell.

The demultiplexer 46 on the receiving side separates the multiplexed cells, and the separated cells are added to the cell decomposer 48 via the receive buffer 47, where they are decomposed into a header part and an information part.
The information part is sent to the decoding section 49, and the decoding section 49 is controlled by determining whether it is a voice signal cell or a modem signal cell, and decoding corresponding to the voice signal or modem signal is performed.

When the number of cells of each channel input to the multiplexing section 45 increases, the queue of cells in the buffer 44 becomes longer, and conversely, when the number of transmitted cells decreases, the queue of cells in the buffer 44 becomes shorter. The delay time of the cells multiplexed from the multiplexing unit 45 and sent out to the transmission path 50 changes.

In other words, cell delay fluctuations occur. When such delay fluctuation occurs in the audio signal cell, the quality of the reproduced audio signal on the receiving side deteriorates. Therefore,
On the receiving side, a receiving buffer 47 is provided to absorb delay fluctuations.

This reception buffer 47 is a first-in first-out memory FIFO (First-InF1
rst-0ut) is used, for example, the capacity is twice the delay fluctuation absorption range, the first arriving cell is written in the center, shifted sequentially and read out, and the arrival of the next cell is the standard delay time. If it is after, write to the center again. If it is after a delay time that is larger than the standard, write from the center to the output end side. If it is after a delay time that is smaller than the standard, write from the center to the side opposite to the output end side. By inserting the signal into the cell, it is possible to output a cell that has absorbed delay fluctuations from the output terminal.

However, a FIFO memory with twice the capacity of the delay fluctuation absorption range is required, and if the delay fluctuation absorption range is increased, the residence time of the received cell becomes longer, so the absolute delay time increases. Therefore, a method can be considered to reduce the absolute delay time by first receiving a cell and writing it into the FIFO memory, then immediately reading it and decoding it.

FIG. 5 is a block diagram of the main part of a conventional example for explaining the above-mentioned method of reducing the absolute delay time, and 51 is a FIFO
52 is a timer, 53 is a read control section, 54 is a setting control section, 55 is a register, 56 is a reception processing section, 57 is a decoding section, and a part of this decoding section 57 and a part of the FIFO memory 51 are used. The cell disassembly section 4 in FIG.
The case where the function corresponding to 8 is realized is shown.

The reception processing unit 56 detects the beginning of the received cell, detects the verch cell path identifier VPI and the verch cell channel identifier VCI in the header section, adds only the received cell for its own channel to the FIFO memory 51, and stores the overflow flag 0 from this FIFO memory 51. When is not added,
By applying the write clock signal WCK to the FIFO memory 51, the received cells are written, and each reception processing section 56 has a multiplexing/demultiplexing function for separating cells of its own channel.

Further, the read control unit 53 adds a read clock signal RCK for reading the received cell to the FIFO memory 51 when the empty flag EP is not added from the FIFO memory 51, that is, when the received cell is written. In response to the cell head pulse HP of the received cell read out from the FIFO memory 51 in accordance with the read clock signal RCK, a timing pulse TP is output that sets the cell transmission time ST added to the header portion of the received cell in the register 55. The cell transmission time ST set in this register 55 is given to the setting control section 54.

Further, the information part of the received cell read from the FIFO memory 51 is added to the decoding section 57, and the information part of the received cell is applied to the decoding section 57,
The decryption process is performed according to the following. Also, the decoding clock signal C
LK is counted by the timer 52, and the count contents TT
By adding to the setting control section 54, the setting control section 54
compares the cell transmission time ST and the count content TT,
In order to keep the difference constant, the control signal R3 is applied to the read control unit 53 to perform control such as waiting for the read clock signal RCK to be applied to the FIFO memory 51.

FIG. 6 is an explanatory diagram of the operation of the conventional example, (al is the cell transmission time ST added to the header part of the received cell, (b) is F
The timing of cells 01 to C11 to be written to the IFO memory 51 is shown, and Ca indicates the case where a silent cell is not transmitted. Further, (C) shows the empty flag EP, and (d) shows the header portion of the cell read from the FIFO memory 51 with a bold line, and also shows the decoding time of cells C8 to C0. Also, TD indicates the decoding time of one cell, and (e) is the read waiting period.
is the content TT of the timer 52, and (6) is the difference between the cell reception time by the timer 52 and the transmission time ST of that cell.

Cell CI of cell transmission time 5T=0 to 130 shown in (a)
4C11 indicates a case where the cell arrives at an interval different from the interval of the cell transmission time ST due to delay fluctuation, and the cell CI with the cell transmission time 5T=O is sent to the FIF at the timing shown in et al.
When written to the O memory 51, the empty flag EP changes from "1" to "O" as shown in (C). Also, the contents T of the timer 52 that counts the decoding clock signal CLK
It increases at regular intervals as shown in T-gage). Furthermore, when the empty flag EP is "O", the header part of the cell is read out from the FIFO memory 51 at regular intervals, and the cell transmission time ST is stored in the register 55, as shown in (d). and the content TT of the timer 52 are compared in the setting control section 54, and the read clock signal RCK from the read control section 53 is controlled so that the difference between them is constant.

During the decoding time TD of the first cell C+, the cell transmission time 5T
-10 cell C, is written into the FIFO memory 51, and then when the content TT of the timer 52 is 10, that cell C2 is read out and decoded. Also, cell C1 with cell transmission time 5T-20 and cell C4 with cell transmission time 5T-30 also have the content T of timer 52.
It is read and decoded at times T-20 and T-30.

Since the next cell Ca is a silent cell and is not transmitted, the cell C5 with the next cell transmission time 5T=50 is stored in the FIFO memory 5.
1, and when the content TT of the timer 52 is 40, the header part H2 of the cell C9 is read out as shown in (d), and the cell transmission time 5T added to the header part H5 is 50. During the read waiting period shown in (e) until TT<ST and TT=ST, the read clock signal RCK is not applied to the FIFO memory 51, and the information part of the cell C3 becomes the decoding part. 57 will be added to the waiting list.

Then, when the timer 52 content TT=50, F
The information portion of the cell C6 from the IFO memory 51 is applied to the decoding section 57 and decoded. Similarly, cells C,...
C, is also decoded. In this case, the difference between the cell transmission time ST and the count content TT of the timer 52 is O as shown in (6).

The cell Ca next to cell C7 is a silent cell;
When the delay time of cell C7 is large, the FIFO memory 51 becomes empty due to the completion of decoding of cell C7, and the empty flag E
P becomes "1". In this case, since the decoding is interrupted for a period longer than the period of the silent cell Ca, the playback audio output is also interrupted.

Then, when the cell C6 with a cell transmission time of 5T=90 arrives at point A, it is written in the FIFO memory 51, the empty flag EP becomes "O", and its header section is read out and the cell transmission time is 5T. -90 is set in the register 55, and the timer 52 is set in the setting control section 54.
Since (ST-TT)<O, the reference point of the minimum delay time is changed. Then, the information section of cell C8 from the FIFO memory 51 is added to the decoding section 57 and decoded. Cells Cm and Cro arriving after this cell C6 are read out from the FIFO memory 51 so that the difference between the count TT of the timer 52 and the cell transmission time ST becomes a constant 15.

Also, cell C0 with cell transmission time 5T=130 is transmitted by timer 52.
If the arrival occurs at point B when the count content of timer 52 is TT = 150, since (ST-TT) < o, the reference point of the minimum delay time is changed, and the count content of the timer 52 and the subsequent count content TT are changed. The reading of the PIFO memory 51 is controlled so that the difference from the cell transmission time ST is 20.

[Problem to be solved by the invention]

In the conventional example described above, when a received cell is stored in the FIFO memory 51, it is immediately read out and decoded in accordance with the cell transmission time ST. , the absolute delay time can be made smaller. However, the distribution of cells arriving during a time delay by the delay fluctuation absorption width from the minimum value of the delay time is
There are many cases near the minimum value, and the delay is thick (it tends to decrease rapidly as it becomes larger), and as a result, it is unclear whether the arrival of the first received cell is near the reference point of the minimum delay time. As a result, until the subsequent received cells fall within the delay fluctuation absorption width, A in FIG.
The reference point for delay fluctuation absorption is changed, such as point or point B, so that, for example, decoding is interrupted during the period of timer 52 content TT=80 to 105, and the reproduced audio output is changed in time. The disadvantage is that the audio quality is degraded due to discontinuity.

An object of the present invention is to shorten the delay fluctuation absorption pull-in time and to minimize the delay time.

[Means to solve the problem]

The delay fluctuation absorption control method of the present invention is based on the first-in
A first-out memory is used to absorb delay fluctuations of received cells, and will be explained with reference to FIG.

In an ATM multiplex transmission system, writing received cells,
A first-in first-out memory (FIFO memory) 1 that reads out the received cell and sends only the information part of the received cell to the decoding section 2; and a timer 3 that counts the decoding clock signal given to the decoding section 2. , a reception time insertion unit 4 which inserts the contents of this timer 3 into the header part of the received cell as the cell reception time and adds it to the FIFO memory 1; and a cell transmission time which is added to the header part of the received cell read from the FIFO memory 1. It is equipped with a judgment read control unit 5 that performs read control of the FIFO memory 1 based on the time, delay fluctuation absorption width, and minimum delay time, and after writing the first received cell to the FIFO memory 1, The judgment readout control unit 5 reads out the received cell after a delay fluctuation absorption width time, and after that, the difference between the cell transmission time and the cell reception time is
When it is determined that the delay time is smaller than the minimum delay time, the reference point of the minimum delay time is changed.

Further, the judgment read control section 5 reads out the header section of the received cell from the FIFO memory l every time the decoding section 2 finishes the decoding process, and calculates the difference between the cell transmission time and the cell reception time added to the header section. It is determined whether the delay time is smaller than the minimum delay time, and when it is determined that it is smaller, the reference point of the minimum delay time is changed, the information part of the received cell in the header part is read out, and the information part is sent to the decoding unit 2. It is something to add.

[Effect]

Regarding claim 1, the content of the timer 3 is inserted into the header part of the received cell as the cell reception time and written to the FIFO memory 1, and after writing the received cell that arrived first to the FIFO memory 1, the determination is made. The readout control unit 5 reads the received cell after a preset delay fluctuation absorption width, and from then on, the difference between the cell transmission time added to the header of the received cell and the cell reception time is the minimum delay. It is determined whether or not the delay time is smaller than the minimum delay time, and when it is determined that it is smaller, the reference point of the minimum delay time is changed and the readout of the FIFO memory 1 is controlled. Therefore, since decoding is initially delayed by the delay fluctuation absorption width, there will be no interruption of the reproduced audio output when the reference point of the minimum delay time is shifted in accordance with the magnitude of the delay fluctuation thereafter. become.

Regarding claim 2, the determination read control unit 5 sequentially reads the header part of the received cell from the FIFO memory 1 every time the decoding process is completed, and calculates the difference between the cell transmission time and the cell reception time added to the header part, It is compared and determined whether the difference is smaller than the minimum delay time, and if it is determined to be smaller, the reference point of the minimum delay time is changed and the information part of the received cell is sent from the FIFO memory 1 to the decoding section 2. It is for decoding.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram of main parts of an embodiment of the present invention, and 11
First in, first out, Me-E-'J (
12 is a timer, 13 is an insertion circuit, 14 is an insertion control section, 15 is a judgment readout control section, 16 is a register, 1
7 is a reception processing section, and 18 is a decoding section.

When a received cell arrives, the reception processing unit 17 determines the vertical cell bus identifier VPI and the vertical cell channel identifier VCI in the header section of the received cell, and inserts only the received cell of the own channel into the FIFO memory 11 via the insertion circuit 13. When the overflow flag Ov from the FIFO memory 11 is not added, the write clock signal WCK is sent.
Give. A received cell is written into FIFO memory 11 according to write clock signal WCK.

Also, the timer 12 counts the decoding clock signal CLK given to the decoding section 18, and sends the content TT to the insertion control section 14, which receives the cell head pulse H.
Based on the PI, timer 1 is installed at a predetermined position in the radar part of the receiving cell.
Insert the content TT of 2 as the cell reception time. Therefore,
The header portion of the received cell includes the cell transmission time added on the transmitting side and the cell reception time inserted by the insertion circuit 13, and is written into the FIFO memory 11.

The determination readout control unit 15 has a delay fluctuation absorption width set,
This delay fluctuation absorption width can also be changed depending on whether the cell is a voice signal cell or a modem signal cell.

Also, an empty flag E indicates that the FIFO memory 11 is empty.
This control controls whether or not to apply the read clock signal RCK when P is not applied to the FIFO memory II.
In response to the cell head pulse HP2 of the received cell read out from the cell, a timing signal TP is output which sets the cell transmission time ST and cell reception time TT added to the header section in the register 16. Then, the cell transmission time ST and cell reception time TT set in the register 16 are read, and the read clock signal RCK is sent to the FIFO memory 11 after the set delay fluctuation absorption width for the first received cell. is given, and the information part of the first received cell is read out and sent to the decoding section 18. From then on, the cell transmission time S
Depending on whether the difference between T and the cell reception time TT is smaller than the minimum delay time, the reference point of the minimum delay time is controlled to be changed or not, and the read clock signal RC of the FIF○ memory 11 is controlled.
This is to control K.

FIG. 3 is an explanatory diagram of the operation of the embodiment of the present invention, in which (a) shows the cell transmission time ST added to the header part of the received cell, [
]) are received cells 01 to C to be written to the FIFO memory 11.
1l timing is shown, and Ca shows the case of not transmitting a silent cell. Further, (C) shows the difference between the cell reception time TT and the cell transmission time ST, (6) shows the contents TT, Hp, and cell reception time of the timer 12, and TD shows the decoding time of one cell. Also, (e) shows the empty flag EP, (f) shows the decoding time of the receiving cells C5 to C8, and the thick line shows the FIFO memory 1.
Header section H1 of received cell CI%CI+ read from 1
〜Hl l, Fd indicates the delay fluctuation absorption width, and the time axis of (a) coincides with the time axis of (a) to (e) only at the beginning, but after that, the delay fluctuation absorption width Fd is shortened. It's off by that amount. Further, (6) shows the initial state 30 of the reference point of the minimum delay time and the change points 31 to 35.

When the first received cell CI with cell transmission time 5T=0 arrives, the reception processing unit 17 gives the write clock signal WCK to the FIFO memory 11 since the overflow flag Ov has not been added from the FIFO memory 11. . Also, cell reception time TT of the contents of timer 12 at that time =
0, the insertion control unit 14 inserts the cell reception time TT-0 at a predetermined position in the header section according to the cell leading pulse HPI, and transfers the received cell C2 to the FIF.
It will be written to the O memory 11.

Then, as the empty flag EP of the FIFO memory 11 changes from "1" to "0" as shown in (e), the determination readout control section 15 provides the readout clock signal RCK to the FIFO memory 11 and receives the readout clock signal RCK. Cell CI header H
5 is read out, a timing pulse TP is applied to the register using the cell head pulse HP2, and the cell transmission time 5T=0 and cell reception time TT-0 of the header section H1 are set.

Since it is the first received cell, the determination readout control unit 15 applies the readout clock signal RCK to the FIFO memory 11 after a time of delay fluctuation absorption width Fd, and reads the information part of the reception cell C1 as shown in (f). is read out and sent to the decoding section 18, where it is decoded into an audio signal. Meanwhile, receiving cells C1 and C with cell transmission time 5T=10.20°30.50
2, Cm and Cs are the contents of timer 12 TT=5.12.
It arrives at 20.32 and is written to the first @order FIFO memory 11 as shown in ).

After the decoding time of the received cell C1, the header section H2 of the next received cell C2 is read out, and the cell transmission time 5T=10 and cell reception time TT=5 of the received cell C2 are set in the register 16 as described above. , 1 The determination readout control unit 15 is
D,=TT-3T=-5, and the previous received cell CI
When compared with the glue, =TT-3T=O, D,>
D2, so change the reference point of the minimum delay time and get D
After a time corresponding to the time r D x, the receiving cell C2
The information part of the data is read out from the FIFO memory 11 and decoded. Similarly, after the decoding time of this received cell C2, the hennoder section H3 of the next received cell C3 is read out, and its cell transmission time 5T=20 and cell reception time TT=12 are set in the register 16, and D3= When TT-3T=-8 is obtained, D z > D :l, so the reference point for the minimum delay time is changed, and after a time corresponding to D2-D, the information part of the receiving cell C3 is transferred to FIFO. It will be read from the memory 11 and decoded.

The next received cell C4 has cell transmission time 5T=30 and cell reception time TT=20, so D,=TT-3T=-1
0 and D3>D, the reference point of the minimum delay time is changed, and the information section of the receiving cell C4 is read out from the FIFO memory 11 and decoded after a time of -D.

The next received cell C3 has a silent cell Ca, its cell transmission time 5T=50, and cell reception time TT-32, so D,=TT-3T=-18, and D4>DS, so the minimum Change the reference point of delay time and change the receiving cell C1
-D.

After a period of time, the data will be read out from the FTFO memory 11 and decoded. For the next received cell C4, D6=-20
Since D s > D b, the reference point for the minimum delay time will be changed in this case as well. In the case of the next receiving cell C1, it becomes D7-18 and Db<D, so the information part of that receiving cell C1 is read out from the FIFO memory 11 and decoded without changing the reference point of the minimum delay time. It turns out. Therefore, in steps 31 to 35 of (g), the reference point of the minimum delay time is changed.

In addition, in the case of receiving cell C6, D,=-15, and D,>
D, so the reference point of the minimum delay time is not changed, but the presence of the silent cell Ca next to the receiving cell C7 means that
Since it can be identified by the cell transmission time ST, the information part of the receiving cell C3 is stored in the FIFO memory 1 after one cell's time.
It will be read and decoded starting from 1.

Thereafter, in the same manner, it is determined whether or not to change the reference point of the minimum delay time, and by controlling the readout of the FIFO memory 11, the reference point is adjusted so as to fall within the delay fluctuation absorption width. Therefore, it is possible to absorb delay fluctuations without causing discontinuous reproduction of audio.

The present invention is not limited to the above-described embodiments, but can also be applied to moving image signal cells and the like.

[Effects of the Invention] As explained above, the present invention provides FIFO memo IJ 1
When writing a received cell, the count contents of the decoding clock signal of timer 2 are inserted into the header section as the cell reception time, and the first received cell is read out from the FIFO memory 1 after the delay fluctuation absorption width, and then From then on, that F
When the difference between the cell transmission time added to the header section of the received cell read from the IFO memory 1 and the cell reception time is smaller than the minimum delay time, the reference point is repeatedly changed, and the FIFO memory 1 Since the delay fluctuation of the receiving cell in the ATM multiplex transmission system has a distribution characteristic that concentrates near the reference point of the minimum delay time, this reference point can be quickly and automatically adjusted to the optimal position. death,
In addition, since there is no interruption of reproduced audio output during this period, there is an advantage that deterioration of audio quality can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the principle of the present invention, FIG. 2 is a block diagram of main parts of an embodiment of the present invention, FIG. 3 is a diagram explaining the operation of the embodiment of the present invention, FIG. 4 is a system diagram, and FIG. The figure is a block diagram of main parts of the conventional example, and FIG. 6 is an explanatory diagram of the operation of the conventional example. 1 is a FIFO memory, 2 is a decoding section, 3 is a timer, 4 is a reception time inserting section, and 5 is a judgment reading control section.

Claims (2)

[Claims] (1) In the delay fluctuation absorption control method in the ATM multiplex transmission system, a first-in first-out memory writes received cells, reads out the received cells, and sends only the information part to the decoding unit (2). (1); a timer (3) for counting the decoding clock signal given to the decoding section (2); and inserting the contents of the timer (3) into the header section of the received cell as the cell reception time. a reception time insertion section (4) to be sent to the first-in/first-out memory (1); and the first-in/first-out memory (1).
Based on the cell transmission time added to the header section of the received cell read from the cell, the cell reception time inserted by the reception time insertion section (4), the delay fluctuation absorption width, and the minimum delay time, A judgment read control section (5) that controls reading of the first-in/first-out memory (1) is provided, and the first-in/first-out memory (1) is provided with a judgment read control section (5) for controlling the reading of the first-in/first-out memory (1), and the first-in/first-out memory (1) is provided with a judgment read control section (5) for controlling the reading of the first-in/first-out memory (1).
After writing in the first-out memory (1), the received cell is read out by the judgment read control unit (5) after a time of the delay fluctuation absorption width, and the difference between the cell transmission time and the cell reception time is A delay fluctuation absorption control method characterized in that when it is determined that the minimum delay time is smaller than the minimum delay time, a reference point of the minimum delay time is changed. (2) The judgment read control unit (5) reads the header part of the received cell from the first-in/first-out memory (1) every time the decoding unit (2) completes the decoding process, and It is determined whether the difference between the cell transmission time and the cell reception time is smaller than the minimum delay time, and when it is determined that the difference is smaller, the reference point of the minimum delay time is changed and the received cell information in the header section is changed. 2. The delay fluctuation absorption control system according to claim 1, wherein the information part is read out and the information part is sent to the decoding part (2).