JPH04113744A - Variable speed packet transmission system - Google Patents

Abstract

PURPOSE:To optimize the absorption of fluctuation at a variable rate terminal equipment by detecting the fluctuation of a network in response to a dummy packet width set at a prescribed interval and varying the capacity of a receiver side buffer. CONSTITUTION:A buffer control section 12 decreases the capacity of a variable buffer 11 when a reception average interval Tu of a dummy packet is slower than a transmission interval Td and keeps or increases the capacity of the variable buffer 11 when the reception average interval Tu of the dummy packet is faster than the transmission interval Td. Thus, the buffer control section 12 grasps the degree of congestion of the transmission line through the reception of the dummy packet in this invention and obtains the reception average interval Tu. Thus, a cell abort rate due to the fluctuation of the network is reduced by offering an optimum buffer capacity.

Description

[Detailed Description of the Invention] [Summary] Regarding a variable rate packet transmission method that performs voice packet communication at a variable rate, the purpose of this invention is to reduce network fluctuations and cell discard by providing an optimal buffer amount. On the side, there is a dummy packet generator that sends out dummy packets at regular intervals Td; on the receiving side, a variable buffer with a variable capacity that temporarily stores packets from the sending side and reads them into the receiving device; is slower than the transmission interval Td, the buffer amount of the variable buffer is decreased, and the average reception interval Tu of the dummy packets is equal to the transmission interval Td.
The configuration includes a speed control unit that maintains or increases the buffer amount of the variable buffer when the speed is faster.

3. Field of Industrial Application] The present invention relates to a variable speed bucket-node transmission system that performs packet communication at a variable rate.

In bucket communication, generated signals are transmitted as packets called cells, but when multiplexing processing is performed on the communication path, waiting time occurs and fluctuations (uncertain delay) occur, and fluctuation absorption is provided at the receiving terminal. Cell discard occurs when the allowable capacity of the buffer is exceeded. If the buffer capacity of the receiving terminal is large, the cell discard will be reduced, but the delay will be increased. On the other hand, if the capacity is small, the delay will be small, but the amount of waste will increase.

In packet communications such as audio and video that require real-time processing, the problem of cell delay and discard greatly affects the audio and video quality, so it is necessary to optimize the buffer capacity.

[Conventional technology]

FIG. 7 shows conventional variable rate packet communication. FIG. 7(a) is a diagram showing a system schematic diagram, and FIG. 7(b) is a diagram showing buffer processing. Now, consider the case in which terminals A and B communicate with terminal A' in FIG. 7(a).

Terminals A and B convert randomly generated voice data (transmission time interval T1, 8T2 in terminal A, transmission time interval ΔTΔT2' in terminal B) into packets called cells and send them to the line. The packet switch 21 multiplexes the packets from terminals A and B and sends them to the packet switch 22 via the line 23.
send to The packet switch 22 separates the multiplexed and transmitted messages and transfers them to the terminal A'.

At this time, terminal A' receives packets from terminals A and B that arrive at random (time interval ΔT, , Δ
T2, ΔT3'') are once stored in the buffer 24 shown in FIG. 7(b) and then read out at a constant speed U'.

This buffer capacity was determined by predicting network fluctuations in advance from past data and setting the buffer capacity to a capacity that could tolerate the maximum fluctuation, thereby dealing with cell discard.

[Problem to be solved by the invention]

Therefore, in the conventional system, the buffer amount is set to a fixed amount that can tolerate the maximum fluctuation, so the maximum delay will occur in any case.

Further, even if the buffer amount is reduced by preparing for a certain amount of cell discard in order to reduce the delay, a problem arises in that the number of cells discarded increases depending on the distribution of fluctuations in the network.

An object of the present invention is to reduce cell discard due to network fluctuations by providing an optimal buffer amount.

[Means to solve the problem]

FIG. 1 is a diagram explaining the principle of the present invention. In the figure, IO is a dummy packet generator, which sends dummy packets to the line at regular intervals Td.

Reference numeral 11 denotes a variable buffer, which has a variable capacity and temporarily stores packets from the transmitting side and reads them into the receiving device.

Reference numeral 12 denotes a buffer control unit that controls increase/decrease in the buffer amount of the variable buffer 12.

The buffer control unit 12 of the present invention reduces the buffer amount of the variable buffer 11 when the average reception interval T, u of dummy packets is slower than the transmission interval Td, and when the average reception interval Tu of dummy packets is faster than the transmission interval Td. The buffer amount of the variable buffer 11 is maintained or increased.

Further, the buffer control unit 12 of the present invention reduces the buffer amount of the variable buffer 11 when the average reception interval Tu of dummy packets is slower than the transmission interval Td, and when the average reception interval Tu of dummy packets is faster than the transmission interval Td. A confidence interval Tuc centered on the average reception interval Tu is calculated, and if the reception interval ΔT of the next received dummy packet belongs to the confidence interval Tuc, the buffer amount of the variable buffer 11 is maintained, and if it does not belong to the confidence interval Tuc, it is changed. No＼fa 11 no＼7
Increase the amount of fur.

[Operation] Therefore, according to the present invention, the buffer control unit 12 can grasp the congestion state of the transmission path by receiving the dummy packet, and can also determine the average reception interval Tu. When this average reception interval Tu is slower than the transmission interval T(I), the buffer amount of the variable buffer 11 is decreased, and the average reception interval Tu
When is greater than or equal to the transmission interval Td, the buffer amount of the variable buffer 11 is maintained if it is within the confidence interval of the average reception interval Tu, and if it is outside the confidence interval of the average reception interval Tu when the average reception interval Tu is greater than or equal to the transmission interval Td. Processing to increase the buffer amount of the variable buffer 11 is performed.

〔Example〕

FIG. 2 is a configuration diagram of an embodiment of the present invention. Figure 2(a)
is a functional block diagram, and FIG. 3(b) is a detailed functional block diagram of the buffer control section. In FIG. 2(a), 21 is an encoding section and 22 is a cell forming section. Reference numeral 23 denotes a dummy packet generation unit, which generates and transmits dummy packets 31 to 34 at regular intervals Td, as shown in the upper part of the time chart of dummy packet transmission and reception times in FIG. The transmission band of this dummy packet must be sufficiently smaller than the transmission band of the terminal in order to maintain voice quality.
For example, if the average transmission bandwidth of a voice terminal is 16 kbps, the transmission bandwidth of dummy packets is 42 kbps per packet.
It is assumed to be 4 bps. 24 is a multiplexing section, and 25 is a demultiplexing section. 26 is a buffer control unit, which controls the reception dummy packet arrival time T(31) to T(34) shown in the lower part of FIG.
The arrival time intervals ΔT(31) to ΔT(34) are calculated to control the increase/decrease in the buffer capacity of the variable buffer 27.

The variable buffer 27 is composed of a plurality of buffers (for example, one buffer can accommodate one buffer), and during communication, the buffer amount increases or decreases in units of one buffer under the control of the buffer control unit 26. 28 is a cell decoding section, and 29 is a decoding section.

FIG. 2(b) shows the detailed configuration of the buffer control section, in which the buffer control section 26 includes the reception interval average time Tu calculation section 2.
6a, confidence interval Tuc calculation unit 26b, reception interval average time Tu/transmission interval time Td comparison unit 26c, confidence interval Tuc
It consists of a comparing section 26d.

The reception interval average time Tu calculation unit 26a calculates the reception interval time ΔT (i) −T (i) − from the arrival time T (i) of the dummy packet i received this time and the dummy packet l) received last time.
T(i-1) is obtained, and the average value Tur -ΣΔT(j)/i of this reception interval time from the start of communication is calculated.

The confidence interval Tuc calculation unit 26b calculates the confidence interval Tu from the standard normal distribution of dummy packets determined by the average reception interval time Tu, which is the output of the Tu calculation unit 26a, with the discard rate being T.
This is to calculate c=2TuX7.

Reception interval average time Tu/transmission interval time Td comparison unit 26c
compares the current average reception interval time Tu with the dummy packet transmission interval time Td.

The confidence interval Tuc comparison unit 26d compares the confidence interval Tuc of the reception interval average time Tu obtained by the Tuc calculation unit 26b with the reception interval time ΔT of the next received dummy packet.

The operating principle of the buffer control section 26 will be explained below with reference to FIG. 4, which shows the relationship between fluctuation time and buffer absorption time. In the figure, the horizontal axis indicates the fluctuation time of the dummy packet,
The vertical axis indicates the buffer absorption time. If the transmitting device sends out dummy packets at fixed intervals Tcl, each dummy packet causes a -like delay on the line, so the reception interval time ΔT of the dummy packets actually received by the receiving device
The fluctuation distribution constitutes a standard normal distribution centered on the transmission interval time Td. This is represented by the curve ■ in the figure. Further, standard normal distribution curves (1) to (2) indicate fluctuations of the dummy packets centered on average reception interval times Tu+ to T u 3, respectively.

Next, the relationship between fluctuation time and buffer amount will be described. When packets arrive according to the standard normal distribution curve ■ and when they arrive according to the standard normal distribution curve ■, the overall arrival time is slower when the packets follow the standard normal distribution curve ■. To accommodate the packets, a large capacity ■' is required. For example, the amount of buffer required for each of the standard normal distribution curves ■ to ■ is indicated by ■' to ■ in the figure. Now, fluctuation time ΔT
If we consider a packet that arrives at
If the absorption time follows the standard normal distribution curve {circle around (2)} having t, the absorption time will be t■, which is faster than t■. In other words, if the packets have the same fluctuation time ΔT, the buffer absorption time is proportional to the buffer amount.

In view of the above-mentioned points, the buffer control unit 26 of the present invention determines whether to increase or decrease the buffer amount of the variable buffer 27 depending on whether the current reception interval average time Tu is faster or slower than the transmission interval time Td.

(1) Reduce the buffer amount.

The speed of the current reception interval average time Tu is the transmission interval time Td
When slower (Td<Tu).

(11) Maintain and increase buffer amount.

Current reception interval average time Tu speed or transmission interval time Td
When the above condition is satisfied (Tu≦Td).

In the present invention, as a method of process (11), the farther the average reception interval time Tu is from the transmission interval time Td, the more processing is performed to increase the buffer amount than the maintenance process; The closer it is to the interval time Td, the more processing for maintaining the buffer amount is performed than the processing for increasing it. This is because the purpose of the present invention is to reduce the buffer amount as much as possible, so the period in which the buffer amount is increased is minimized.

FIG. 5 is an explanatory diagram of the control method (11) above.

In the figure, the standard normal distribution curve ■ is centered at the transmission interval time Td, and shows the original form of the dummy packet. On the other hand, the standard normal distribution curve (2), 0.0, indicates the case where the average reception interval time Tu is faster than the transmission interval time Td. Processing (ii) of the present invention is such that when the current average reception interval time is Tu, the reception interval ΔT of the next received dummy packet is a signal interval T of the average reception interval time Tu.
We are focusing on the probability of falling outside uc. In other words, each confidence interval TucI of the standard normal distribution curve @, ■, [phase]
1. Considering Tu Cat and Tu CIs,
The next dummy packet is for each transfer interval Tu CII+
Tu cl□.

Considering that the dummy packet arrives according to the standard normal distribution curve ■, the probability of entering TuC+z is ■, @
, becomes smaller as it goes to 0. Therefore,
If the reception interval Δt of the next received dummy packet falls outside the transmission interval Tuc of the reception interval average time Tu, the buffer amount will be increased, and if it falls within the transmission interval Tuc, the buffer amount will be maintained. . By doing the above, the closer the reception interval average time Tu is to the transmission interval time Td, the more
More processing is performed to maintain the buffer amount, and as the reception interval average time Tu becomes faster than the transmission interval time Td, more processing is performed to increase the buffer amount.

Now, the procedure of the buffer control unit according to the present invention will be explained below. As shown in Figure 4, when only a few dummy packets have been received, such as at the start of communication, although the dummy packets arrive uniformly according to the standard normal distribution curve ■, the reception interval time ΔT varies. Therefore, the average reception interval time Tu may deviate from the actual average reception interval time Td (hereinafter referred to as transmission interval time Td). The Tu and Td comparing unit 26c determines whether the average reception interval time Tu is on the right side or the left side of the transmission interval time Td.

Now, consider (11) when Tu+, where the average reception interval time Tu is smaller than the transmission interval time Td. Buffer control unit 2
The Tuc calculation unit 26b of No. 6 calculates the current reception interval average time Tu.
, the distribution of the reception interval time of the dummy packet/node is predicted as shown in the standard normal distribution curve ■, and the reliable interval Tuc-2Tu, Xr of the standard normal distribution curve ■ (however, T=0.
95).

At this time, if the distribution actually follows this standard normal distribution curve ■, the required buffer will be a buffer amount as large as ■', but since the actual distribution is the standard normal distribution curve ■, According to the present invention, the amount is controlled to approach ■'.

In other words, the probability that the Tuc comparator 26d has the reception interval time ΔT of the next received dummy packet within the confidence interval TuC of the standard normal distribution curve (2) is indicated by A in the figure. Also,
The probability of being outside the confidence interval Tu c is indicated by the opening in the figure.

In other words, when controlling the increase or decrease of the buffer amount when the reception interval average time is Tu, the buffer amount is maintained with probability A, and the buffer amount is increased with probability A.

On the other hand, when the average reception interval time Tu of the dummy packets received by the receiving device is Tuz larger than the transmission interval time Td, the Tu, Td comparator 26c calculates the distribution of the reception interval times of the dummy packets according to the standard normal distribution curve ■. Predict. If the distribution of dummy packets actually follows this standard normal distribution curve ■, the required buffer size will be as large as ■', but since the actual distribution follows the standard normal distribution curve ■, the buffer size will be ■ It is controlled so that it approaches ′′.

FIG. 6 shows the processing flow of the buffer control section, which will be explained below using a specific example.

A randomly generated signal from a terminal is encoded by an encoding unit 21 shown in FIG. 2, and converted into a packet called a cell by a cell generator 22. Then, the multiplexing processing section 24 multiplexes the signal packet from the terminal and the dummy packet from the dummy packet generation section 23 together.

The multiplexed packets are separated by the separation unit 25, the signal packets are stored in the variable buffer 27, and the dummy packets are received by the buffer control unit 26. The variable buffer 27 has a maximum capacity that can tolerate a maximum delay at the start of communication,
For example, if the maximum capacity is 12, it is set to half of that, 6.

The buffer control unit 26 receives the dummy packets 31 to 34 sent out at regular intervals Td and judges the fluctuation of the receiving network; now, in FIG.
．． It is assumed that dummy packet 32 has been received and dummy packet 33 has arrived this time.

The reception interval average time Tu calculation unit 26a calculates the dummy packet 3
The reception interval time ΔT (
33) Calculate =T (33) -T (32) (step 61), consider the reception interval time ΔT (33) to the average reception interval time Tu3□ up to the dummy packet 32, and calculate the reception when the dummy packet 33 arrives. Interval average time Tu, 3-
ΣΔT(i)/3 is determined (Stebu 62).

Next, the reception interval average time Tu/transmission interval time Td comparison unit 26c compares the updated reception interval average time Tu33 with the transmission interval time Td (step 63).

When the updated reception interval average time Tu:l:l is larger than the transmission interval time Td (YES at step 63), this means that the reception interval average time Tu33 is shifted to the right with respect to the transmission interval time Td in FIG. A certain reception interval average time Tu2 (
The standard normal distribution curve (■) is shown. In other words, the reading speed U of packets from the variable buffer 27 is faster than the writing speed ■, and the process of reducing the buffer capacity by one in order to reduce the delay caused by the buffer A=A-
1 (step 64).

On the other hand, when the answer in step 63 is NO, FIG. 4 shows the average reception interval time Tu (standard normal distribution curve ■) in which the average reception interval time Tu is to the left with respect to the transmission interval time Td. In other words, the arrival time of the pake-nod is becoming faster. At this time, 1ΔT(33) of the reception interval time ΔT(33) of the dummy packet 33 received this time.
)l and the confidence interval Tuc (region a of the standard normal distribution curve ■)
Compare.

Here, when 1ΔT(33) l > T u c (YES in step 65), process A to increase the buffer amount by one
=A+1 (step 66). In this case, as described above, the dummy packets arrive according to the actual standard normal distribution curve, so most of the packets fall within region C of the standard normal distribution curve (2).

If NO in step 65, in FIG.
Show that it is within. In other words, when the average reception interval time Tu is faster than the transmission interval time Td, and the reception interval time ΔT(33) of the dummy packet 33 received this time is within the reliable interval of the standard normal distribution curve ■, the result will be as predicted. Since the dummy packet has arrived, the buffer amount is maintained at the current state A=A (step 67). 20F 4 The variable size filter 27 discards packets exceeding the capacity A.

In the example described above, the initial capacity of the variable buffer 27 is set to half the buffer capacity that can tolerate the maximum delay, assuming that a dummy packet arrives with the maximum delay at the start of communication.

In other words, if the dummy packet arrives with the maximum delay (standard normal distribution curve ■ in Figure 4), the required buffer capacity is such that it can tolerate the dummy packet whose reception interval average time Tu3 is the maximum delay. There must be. That is, it is sufficient that the absorption time t can be tolerated, and half of the buffer capacity ■' is sufficient.

[Effects of the Invention] As described above, in the present invention, fluctuations in the rope are detected in accordance with the delay width of dummy packets sent out at regular intervals, and the capacity of the Hanwha on the receiving side is changed. Therefore, it is possible to optimize the absorption of Ig errors in a variable rate terminal, and there is no need for unnecessary absorption delays or packet discards.

[Brief explanation of drawings]

Fig. 1 is a diagram explaining the principle of the present invention, Fig. 2 is a configuration diagram of an embodiment according to the invention, Fig. 3 is a time chart of dummy packet transmission/reception time, and Fig. 4 is a diagram of fluctuation time and buffer absorption time. Figure 5 is a diagram illustrating the buffer amount control of the present invention; Figure 6 is a diagram illustrating the processing flow of the buffer control unit; Figure 7 is a diagram illustrating conventional variable speed voice packet transmission. (a) System Figure (b) showing a schematic diagram is a diagram showing buffer processing. In FIG. 1, the symbols of main parts are as follows. IO... Dummy bucket generation unit 11... Variable hump 7 12... Buffer control unit 11 Q (o) Functional block haze L- (sh) Hardware false Zagoto's V mill HgJ7J wooden function Figure 2 shows the flow of the chipped buffer control push part.TugJ Figure 2

Claims (1)

[Claims] 1. A dummy packet generator (10) on the transmitting side that sends out dummy packets at regular intervals Td, and a variable capacity unit on the receiving side that temporarily stores packets from the transmitting side and reads them into the receiving device. a buffer (11); when the average reception interval Tu of the dummy packets is slower than the transmission interval Td, the buffer amount of the variable buffer (11) is reduced;
is faster than the transmission interval Td, the variable buffer (
11) A variable speed packet transmission system characterized by comprising a buffer control unit (12) for maintaining or increasing the buffer amount. 2. The buffer control unit (12) reduces the buffer amount of the variable buffer (11) when the average reception interval Tu of the dummy packets is slower than the transmission interval Td, and the average reception interval Tu of the dummy packets is When the transmission interval is faster than the transmission interval Td, a confidence interval Tuc centered on the average reception interval Tu is calculated, and if the reception interval ΔT of the next received dummy packet belongs to the confidence interval Tuc, the buffer amount of the variable buffer (11) is determined. and maintain the confidence interval Tu
2. The variable rate packet transmission system according to claim 1, wherein the buffer amount of the variable buffer (11) is increased if the variable rate does not belong to c.