JPH10200531A - Realtime abr communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To synchronize a data-generating rate of a host layer with an ATM cell rate and to suppress a resident time of cells of a buffer in an ATM cellularized part within a prescribed time, even in the data communication without having a window control function such as, dynamic image transmission. SOLUTION: A communication equipment is provided with a host layer information-generating means 11, an ATM cellularized means 10 that applies an ATM cellularized process to the generated information to transmit the result and a display rate increase/decrease display means 17 that displays rate increase/decrease indicating whether or not a generated rate should be decreased from the ATM cellularized means 10 to the information generating means 11. Furthermore, the ATM cellularized means 10 checks the number of cells not yet transmitted and stored in a buffer 14 periodically and decides the rate increase/ decrease display content, depending on whether or not the number of cells not yet transmitted exceeds a prescribed threshold.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a real-time ABR communication device for converting information to be transmitted into ATM cells on a transmission side and transmitting the ATM cells via an ATM line.

[0002]

2. Description of the Related Art ATM (Asynchronous T)
transfer Mode asynchronous transfer mode)
U-TI. 361, which divides a wide variety of information into short packets of fixed length with a header called a cell, multiplexes them in units of an efficient statistical multiplexing system, and transfers them. Is what you do.
The cell is an STM (Synchronous Trans)
fer Mode synchronous transfer mode), but it does not appear periodically in time.
Called asynchronous transfer mode. The cells are dynamically allocated in response to a request for information transmission that fluctuates with time, and the communication speed can be variably set by changing the number of cells. Accordingly, this is a transfer mode in which all digital information from voice / data to images can be transmitted in a unified manner. In the ATM, instead of deterministically allocating a band to each terminal, a communication mode in which a plurality of terminals share a transmission band is possible. This communication form is referred to as band sharing type communication. In the bandwidth sharing type communication, a plurality of terminals transmit a large number of cells simultaneously,
If the number of cells input to the M switch exceeds the transfer capability of the switch, the cells may be discarded. In order to prevent this, there is a communication method in which the switch notifies the terminal whether or not the transmission rate of the ATM cell may be increased from the current value according to the current traffic situation. ATM communication using this method is called ABR (Ava
This is referred to as “able bit-rate” communication.

When performing data transfer by ABR communication,
The terminal is required to have a function of controlling the transfer rate of the data of the upper layer according to the fluctuation of the cell rate. TCP
/ IP (Transmission Control)
Protocol / Internet Protocol
When a transfer control protocol having a window control function such as l) is used as an upper layer, the data transfer rate of the upper layer follows the cell rate by window control. That is, unless the ACK is transmitted from the receiving side, the transmitting side does not transmit a new packet.
If the transfer rate of the ATM layer is reduced, the time until the ACK is received becomes longer, and the transfer rate of the upper layer naturally decreases. FIG. 2 is an explanatory diagram of a conventional data transfer by ABR. The transmitting terminal 24 and the receiving terminal 25 each have a T
AT which actually performs ATM communication as a lower layer with CP / IP layers 26 and 28 and performs ABR cell rate control
The case where M layers 27 and 29 are provided is shown.
When the cell rate of the ATM layers 27 and 29 is reduced,
Since the interval of the arrival time of the ACK notification from the TCP / IP layer 28 becomes longer, the packet transmission rate of the TCP / IP layers 26 and 28 also becomes lower. On the other hand, ATM layer 2
When the cell rates of 7, 29 are increased, the arrival time of the ACK notification of the TCP / IP layers 26, 28 is shortened, so that the packet transmission rates of the TCP / IP layers 26, 28 are also increased.

[0004]

FIG. 3 shows a conventional ABR.
FIG. 9 is a diagram illustrating a problem when moving image communication is performed using technology. When information having real-time properties, such as encoded information of a moving image, is transmitted using ABR, the following problems occur. That is, (1) Generally, a transfer control protocol for performing window control such as TCP / IP is not used. Therefore, the moving image information is usually represented by UDP / IP (User Datagr).
am Protocol / Internet Prot
ocol) After the IP packetization at the layer 30, the AAL
5 (ATM Adaptation Layer 5) processing unit or directly into AAL5 processing unit for transmission. When the ABR communication is performed by such a transmission method, there is no mechanism for the data transfer rate (generation rate) of the upper layers 30 and 31 to follow the cell rate of the ATM layers 27 and 29. , 31 are not reduced, and A
Data may be discarded in the TM cell unit. (2) Real-time information such as a moving image or information that has received a large delay cannot be correctly reproduced. When the rate is reduced by the ABR, the time during which cells stay in the buffer in the ATM cell unit becomes longer, and there is a possibility that information transmission delay becomes longer. That is, as shown in FIG. 3, since there is no flow control in the UPI / IPs 30, 31, it is impossible to follow the cell rate of the ATM layers 27, 29, buffer overflow occurs in the ATM layer 27, and the delay time in the receiving terminal 25 is reduced. Exceeded (indicated by ×).
Therefore, an object of the present invention is to solve these conventional problems,
In order to enable moving picture transmission by ABR communication, even in data communication that does not perform a window control function as in moving picture transmission, the ATM cell rate and the data generation rate of the upper layer are synchronized, and the cells in the buffer in the ATM cell conversion unit are controlled. An object of the present invention is to provide a real-time ABR communication device having a mechanism for suppressing the stay time to a certain value or less.

[0005]

In order to achieve the above object, a real-time ABR communication apparatus according to the present invention comprises: an information generating means (11) for generating information;
ATM cell conversion means (10) for converting into M cells and sending them out
And a rate increase / decrease display means (17) for displaying information indicating whether the information generation rate should be reduced from the ATM cell conversion means (10) to the information generation means (11). And Further, the ATM cell conversion means (10) includes a buffer (1) for accumulating untransmitted cells.
4) and means for comparing the number of untransmitted cells with a certain threshold value, periodically checking the number of untransmitted cells stored in the buffer (14), and It is also characterized in that the content of the rate increase / decrease display is determined depending on whether or not the number exceeds the threshold. The ATM cell conversion means (10) has means (19) for storing the number of unsent cells, and displays a rate increase / decrease display when the current number of unsent cells exceeds a certain threshold value. Multiply the constant obtained by subtracting the number of unsent cells at the previous rate increase / decrease display from the current number of unsent cells by a constant, and multiply the multiplied value by the number obtained by subtracting the threshold from the current number of unsent cells. It is also characterized in that it is determined by the sign of the added value (Equation 1). Further, the ATM cell forming means (10) is provided with an information generating means (1).
Means (1) for receiving an allowable delay of information to be transferred from (1)
7), wherein a threshold for determining the rate increase / decrease display is determined based on the permissible delay.

[0006]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram of a terminal showing one embodiment of the present invention. In FIG. 1, 10 is an ATM cell unit, 11 is an information generating unit, 12 is an information receiving unit,
Installed inside the terminal. Reference numeral 13 in the ATM cell conversion unit 10 denotes a transmission-side AAL5 processing unit, 14 denotes a transmission cell buffer, 15 denotes a reception-side AAL5 processing unit, 16 denotes a reception cell buffer, 17 denotes a transfer control unit, 19 denotes a communication state storage table, 18 is a physical layer processing unit, 20 is an output port, 21
Is an input port. The information generating section 11 is a section having a function of generating information to be transmitted, such as a moving picture coding function, in the terminal. The information generated by the information generating section 11 is transmitted to the ATM cell by the AAL5 processing section 13 or the like. After the conversion, the processing of the present invention is performed in the ATM cell conversion unit 10 and then transmitted to the outside. In the ATM cell forming unit 10, the transmission cell buffer 14 stores the untransmitted cell buffer. The transfer control unit 17 of the ATM cell unit 10 stores, in the transfer state storage table 19, the number of untransmitted cells (b ') when the rate increase / decrease display was performed last time and the number of untransmitted cells when determining the rate increase / decrease display. The threshold (Bth) is stored. In addition, the communication status storage table 19 additionally includes ABR
PCR (Peak Cel) is used as the rate control state value.
l Rate), MCR (Minimum Cell)
Rate), RDF (Rate Decrease F)
actor), RIF (RateIncrease F)
actor), NRM (Number of RM c)
cells), ACR (Allowed Cell Ra)
te), etc., and VPI (V
actual Pass Identificatio
n), VCI (Virtual Channel Id)
(entification) are stored. Further, the transfer control unit 17 has an arithmetic function, and performs an arithmetic operation (see the following equation 1) based on the current number of untransmitted cells and the value of b'Bth when determining the rate increase / decrease display, and performs communication. When the allowable delay (D) is received from the upper layer at the time of the start, the calculation (see the following equation 2) is performed based on the MCR.

Hereinafter, the processing contents of the ATM cell forming section 10 will be described in detail. (1a) The ATM cell conversion unit 10 gives a function of displaying to the upper layer whether or not the data generation rate should be reduced. Here, the upper layer is the information generator 11.
This function is called a rate increase / decrease display function, a display indicating that the rate should be reduced is referred to as a decrease, and a display indicating that the rate should not be reduced is referred to as an increase. The information generation unit 11 reduces the data generation rate if the rate increase / decrease display decreases, and increases the data generation rate if the rate increase / decrease display increases. (2a) When performing the rate increase / decrease display, the display content is determined by the following method. Here, the current ATM cell conversion unit 1
It is assumed that the number of untransmitted cells staying in the transmission cell buffer 14 within 0 is b, and the value of b when the previous rate increase / decrease display is performed is b '. (2a-1) If b ≦ Bth, the display is increased. (2a-2) If b> Bth, the value of x is calculated according to the following equation (1). If the value of x is positive, it is decreased, and if it is negative, it is increased. x = (b−Bth) + k (bb ′) Equation (1) where Bth and k are predetermined system parameters, and Bth is an ATM cell. K, which is lower than the number of cells that can be stored in the conversion unit buffer, is an appropriate real number (for example, 1). (3a) The ATM cell forming unit 10 receives the allowable value of the transfer delay from the information generating unit 11. This tolerance is D
Bth is determined by the following equation (2). Bth = MCR × D × p (2) where MCR is the minimum cell rate in ABR transfer,
p is a predetermined system parameter, and is set to an appropriate number between 0 and 1 (for example, 0.2). For the selection of k and p, an experiment is performed by appropriately selecting candidate parameters,
Thereby, the optimum value is selected and determined.

In FIG. 1, an H261 encoding device is considered as an example of the information generating unit 11. The H261 encoder is an HTU standardized by the ITU-T for TV conferences and telephone calls.
This device encodes an image based on the H.261 image encoding method, and can convert an input image of 360 pixels in the horizontal direction, 288 pixels in the vertical direction, and 30 frames per second from 64 Kbps to 2048 K.
Encode at a rate between bps. The H261 encoding device encodes an image at a certain encoding rate, and transmits the generated information to the ATM cell forming unit 10 as transfer information.
The coding rate is determined by periodically transmitting a rate increase / decrease display request to the ATM cell forming unit 10 and then transmitting the ATM cell forming unit 1.
A rate increase / decrease indication is received from 0, and if the indication is increased, the coding rate is increased, and if the indication is decreased, the coding rate is reduced. Further, prior to the start of communication, the allowable delay (D) is transmitted to the ATM cell forming unit 10. ATM
The celling unit 10 converts the information received from the information generating unit 11 into ATM cells in the AAL5 processing unit 13 on the transmission side, and stores the generated cells in a shaping buffer (transmission cell buffer) 14. ATM cell transmission unit (output port 2
0) has an ABR communication function, and sends cells stored in the shaping buffer 14 to the outside at a cell rate determined by the ABR procedure. A rate increase / decrease display determination unit (not shown) in the transfer control unit 17 stores the threshold value Bth for buffer accumulation and the previous number b 'of untransmitted cells,
When the rate increase / decrease display request from the information generator 11 is transmitted, the current number of cells stored in the shaping buffer 14 is detected, and the display content is determined according to the method (2a) described above. After the contents of the rate increase / decrease display are determined,
The current number of cells is stored in the b 'storage memory. Also, A
Upon receiving the permissible delay (D) from the information generator 11, the TM cell generator 10 determines the threshold Bth based on the value (D) according to the method (3a) described above.

According to the above (2a-2), the number of untransmitted cells exceeds the threshold Bth, and the number of untransmitted cells tends to increase, or the number of non-transmitted cells significantly increases the threshold Bth.
is greater than th, the ATM cell forming unit 10
The information generation unit 11 is notified to reduce the information generation rate. On the other hand, if the number of untransmitted cells is equal to or less than the threshold value Bth, or the number of untransmitted cells exceeds the threshold value Bth, but the number that exceeds the threshold value is small and the number of untransmitted cells tends to decrease, the ATM is used. The cell generator 10 notifies the information generator 11 to increase the information generation rate. As a result, the information generation rate follows the cell rate. As a result, the number of untransmitted cells in the buffer 14 fluctuates near the threshold value Bth. This threshold B
According to the above (3a), th is a value sufficiently lower than the number of cells that can be transferred in the allowable delay time when the transfer is performed at the minimum value of the cell rate. As a result, the cell transfer delay can be kept below the allowable value.

[0010]

As described above, according to the present invention,
Even in data communication that does not perform the window control function such as moving image transmission, the ATM cell rate and the data generation rate of the upper layer can be synchronized, and the stay time of cells in the buffer in the ATM cell conversion unit can be suppressed to a certain value or less. While a plurality of terminals share a band in an ATM network, communication such as a TV conference can be efficiently performed at a transmission speed commensurate with the load of the current communication network.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a terminal showing one embodiment of the present invention.

FIG. 2 is an explanatory diagram of an operation of data transfer by a conventional ABR.

FIG. 3 is a diagram illustrating a problem when moving image communication is performed using the conventional ABR technology.

[Explanation of symbols]

10: ATM cell conversion unit, 11: information generation unit, 12: information reception unit, 13: transmission AAL5 processing unit, 14: transmission cell buffer, 15: reception AAL5 processing unit, 16: reception cell buffer, 17: transfer Control unit, 18: physical layer processing unit, 19: communication state storage table, 20: output port,
21 input port, 24 transmission terminal, 25 reception terminal,
26, 28 ... TCP / IP layer, 27, 29 ... ATM
Layers 30, 31,... UDP / IP layer.

Claims (4)

[Claims] 1. An information generating means for generating information, an ATM for converting the generated information into ATM cells and transmitting the ATM cells to the outside
A real-time ABR communication apparatus comprising: cell-forming means; and rate increase / decrease display means for displaying information indicating whether or not the information generation rate should be reduced from the ATM cell-forming means to the information generating means. . 2. The ATM cell converting means has a buffer for storing untransmitted cells and a means for comparing the number of untransmitted cells with a certain threshold value. 2. The real-time ABR according to claim 1, wherein the number of unsent cells is checked, and the content of the rate increase / decrease display is determined based on whether the number of unsent cells exceeds the threshold. Communication device. 3. The ATM cell conversion means has means for storing the number of untransmitted cells, and displays a rate increase / decrease display when the current number of non-transmitted cells exceeds a certain threshold value. The value obtained by subtracting the number of unsent cells at the time of the previous rate increase / decrease display from the number of unsent cells is multiplied by a constant, and the value obtained by subtracting the threshold from the current number of unsent cells is added to the multiplication result. 2. The method according to claim 1, wherein the value is determined by the sign of the value.
Or the real-time ABR communication device according to 2. 4. The ATM cell conversion means has means for receiving an allowable delay of information to be transferred from the information generation means,
4. The real-time ABR communication device according to claim 1, wherein a threshold value for determining the rate increase / decrease display is determined based on the allowable delay.