JPS6365180B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for absorbing variations in transmission delay time of voice packets in a voice packet switching system.

In recent years, a voice packet switching system has been realized in which voice is digitized using a PCM method or the like, and further converted into packets and sent and received via a packet switching device. Figure 1 is a schematic diagram of a voice packet switching system, where 1 and 2 are telephones, and 3 is an A/C converter that converts analog signals from telephone 1 into digital signals.
D conversion device, 4 is a packet assembling device, 61, 6
2,..., 6n are packet switching devices; 5 is a packet switching network consisting of packet switching devices 61 to 6n; 7;
8 is a packet disassembly device, 8 is a D/A converter that converts a digital signal into an analog signal, 9 is a delay time fluctuation absorber, and telephone 1, A/D converter 3, and packet assembler 4 are on the transmitting side. , delay time fluctuation absorber 9, packet decomposer 7,
A D/A converter 8 and a telephone 2 represent the receiving side. The audio signal from the telephone 1 is digitized by the A/D converter 3, and further processed by the packet assembler 4 to be divided into transfer units, add header information (address information, etc.), and then converted into packets. It is sent to the switching network 5. In the packet switching network 5, the number of relaying packet switching devices varies depending on the setting of the call from the sending side to the receiving side, and voice packets are transmitted between the packet switching devices 61 to 6n.
are relayed and transmitted to the receiving side. On the receiving side, the audio packets are decomposed by a packet decomposer 7 and further decoded into audio signals by a D/A converter 8.

In a packet switching system, before a voice packet sent from the transmitting side reaches the receiving side, it mainly requires the fixation required to assemble the packet in the packet assembling device 4 on the transmitting side and to disassemble the packet in the packet disassembling device 7 on the receiving side. delay time and relaying packet switching devices 61 to 6
is delayed by waiting at n, and the latter delay time is not constant. Fluctuations in delay time in voice packet transmission not only result in poor audio quality, but in extreme cases can even make conversation impossible, so it is necessary to absorb fluctuations in delay time when receiving voice packets. This is essential, and even in the past, the delay time variation absorbing device 9 has been used to handle variations in delay time. Absorption of variations in the transmission delay time of voice packets in the conventional delay time variation absorbing device 9 is performed by sequentially accumulating received voice packets in a buffer memory and correcting the delay time of each voice packet to a constant fixed value D. I was worried. In other words, the audio packet input to the delay time variation absorbing device 9 on the receiving side at delay time D 1 stays in the buffer memory for a time of ₍ D-D ₁ ), and is input to the delay time variation absorbing device 9 on the receiving side at delay time D ₂ . The delay time of each audio packet was corrected to a constant value D by allowing the audio packet to stay for (D-D ₂ ) time. Also, audio packets with a delay time of D or more are discarded by the delay time variation absorber 9 because they cause deterioration of audio quality. but,
As mentioned above, the transmission delay of voice packets in a packet switching system is mainly due to the fixed delay time _t0 due to packet assembly on the transmitting side and packet disassembly on the receiving side, and the delay time due to packet disassembly at one or more relaying packet disassembly devices. It consists of varying delay times t _o due to waiting times, and the distribution of the combined delay times is shown in Figure 2. In Figure 2,
The horizontal axis shows the delay time (t), and the vertical axis shows the cumulative distribution of delays (%), and curves 1, 2, 3, 4, 5
The number of interrupted packet switching devices is 1, 2, and 3, respectively.
It corresponds to cases of 1, 4, and 5 machines. In the figure, for example, the cumulative distribution of delays within delay time _t1 is higher when the number of relay packet switching devices is small than when it is large. Therefore, it is clear that the variation in delay time is small when the number of relay packet switching devices is small, and on the contrary, the variation in delay time is large when the number of relay packet switching devices is large. Therefore, if the delay time is always corrected to a constant value regardless of the number of relaying packet switching devices on the receiving side as in the conventional system, when the number of relaying packet switching devices is small, voice packets may be stored in the buffer memory for a longer time than necessary. Furthermore, when the number of packet switching devices relaying is large, there is a high probability that voice packets will not arrive at the receiving side and will not be stored in the buffer memory at the time when they should be taken out of the buffer memory, which will affect the voice quality. There were some shortcomings such as:

An object of the present invention is to eliminate these drawbacks by enabling the transmission delay time of voice packets to be controlled on the receiving side in accordance with the number of relay packet switching devices, and will be described in detail below.

FIG. 3 shows an embodiment of the present invention, which corresponds to the delay time fluctuation absorbing device 9 in FIG. control circuit, 1
Reference numeral 3 denotes a delay time storage section for storing delay times corresponding to the number of relay packet switching devices, 14 a buffer memory for absorbing delay time fluctuations, 15 an audio packet input terminal, 16 a timer circuit, and 17 an audio packet output terminal. To operate this, first, the number of relay packet switching devices is input to the relay packet switching device number input terminal 10 when a call is connected. In this embodiment, since voice packets are transferred through the same route for one call, the number of relay packet switching devices can be easily known at the receiving station using various methods such as the common line signaling method. A relay packet switching device number receiving circuit 11 receives the number of relay packet switching devices and provides it to a control circuit 12. The control circuit 12 reads the delay time corresponding to the number of relay packet switching devices given by the relay packet switching device number receiving circuit 11 from the delay time storage unit 13. FIG. 4 shows the storage contents of the delay time storage section 13 in FIG.
Delay times are stored in correspondence with the number of relay packet switching devices. Next, the delay time from when the voice packet is transferred from the transmitting side to when it is received at the receiving side and appears at the voice packet output terminal 17 is determined by the delay time corresponding to the number of relay packet switching devices read from the delay time storage unit 13. The audio packets input to the audio packet input terminal 15 are sequentially stored in the buffer memory 14 for absorbing delay time fluctuations so that the audio packets are delayed by the control circuit and the timer circuit 16, and then the stored audio packets are first-in. ―First―Out
The audio packet is output to the audio packet output terminal 17 using the following method.

FIG. 5 shows a time chart from the transmission of a voice packet on the transmitting side to the output of the buffer memory 14 for absorbing delay time fluctuations on the receiving side.
Figure 5.1 shows each audio packet from the transmitting side.
, 〓, are transmitted at equal time intervals T. FIG. 52 shows the reception state of voice packets on the receiving side, where voice packets are received with a delay of transmission delay time D ₁ , voice packets are received with a delay of transmission delay time D ₂ , and voice packets are received with a delay of transmission delay time _Do. to show that In the above explanation, if the delay time read from the delay time storage unit 13 is D, then the time from when each audio packet is transmitted on the transmitting side to the output of the buffer memory 14 for absorbing delay time fluctuations on the receiving side is D. It is controlled by the control circuit 12 and the timer circuit 16 so that this occurs. In other words, as shown in FIG. 5, since the voice packet is received with a delay of _D1 hour from the transmitting side, the delay time fluctuation absorbing buffer memory 1
4, after being accumulated for (D-D ₁ ) time, the audio packet is output to the audio packet output terminal 17, and similarly, the audio packet is received with a delay of D ₂ hours (D-D ₂ ).
After being stored in the delay time fluctuation absorbing buffer memory 14 for an amount of time, the signal is outputted to the audio packet output terminal 17. Therefore, if the transmission delay time of audio packets sent from the transmitting side is within D, the output of the buffer memory 14 for absorbing delay time fluctuations will be delayed by only the time D from the time the packet is received on the transmitting side, and each audio It will be the same as if the packets were received at regular intervals T, and the voice quality would be greatly improved. (Actually, in FIG. 5, the delay time D≫T) If the audio packet sent from the transmitting side is received with a delay of more than the delay time D, the delay time fluctuation absorbing buffer memory 14
Since it is not input at the time when it should be output at the same timing T, it is discarded after being input to the buffer memory 14 for absorbing delay time fluctuations, but as explained in FIG. Since the packet rate is within an allowable range based on the overall cumulative distribution, it does not pose a problem to voice communication. In the case of this embodiment, the time from when the transmitting side transmits an audio packet until the receiving side receives it can be easily calculated by providing packet transmission time information in the header section of each packet. Furthermore, in this embodiment, for the sake of explanation, a case has been described in which the accumulation time (D-D _o ) is calculated for all audio packets and the accumulation time is accumulated in the buffer memory 14 for absorbing delay time fluctuations, but other methods may also be used. , the voice packets received successively from the first voice packet in the call are stored in the buffer memory 14 for absorbing delay time fluctuations, and after the voice packet is received, the transmission delay time of the voice packet is
The same result can be obtained by sequentially reading data from the buffer memory 14 for absorbing delay time fluctuations at equal time intervals T after the difference (D - D ₁ ) between D 1 and the delay time D read from the delay time storage unit ₁₃ has elapsed. .

As explained above, according to this embodiment, by controlling the delay time of voice packets by the number of relay packet switching devices, it is possible to maintain voice quality regardless of the number of relay packet switching devices. Furthermore, when the number of relay packet switching devices is small, the delay time can be shortened, so it is possible to eliminate the disadvantage that the voice of the other party is heard with a delay, making it difficult to have a conversation.

In the first embodiment, a delay time corresponding to the number of relaying packet switching devices is stored in the delay time storage unit 13, and the audio packet is delayed by a time equal to the difference between the delay time and the transmission delay time of the received audio packet. Although fluctuations in transmission delay time are corrected by storing them in the buffer memory 14 for absorbing time fluctuations and then taking them out, the delay time storage section 13 stores the time itself for storing audio packets in the buffer memory 14 for absorbing delay time fluctuations. Similarly, fluctuations in transmission delay time can be corrected by That is, as shown in FIG. 4, the delay time storage unit 13 stores delay times that increase in size as the relay packet switching device becomes larger, so that the delay time that increases as the relay packet switching device becomes larger is stored in the delay time storage unit 13. The delay time corresponding to the number is read from the delay time storage unit 13, and the first received audio packet is stored in the buffer memory 1 for absorbing delay time variation by the delay time.
In this method, the audio packets are stored in the buffer memory 14 for absorbing delay time fluctuations, and then the audio packets are sequentially taken out at regular intervals. Therefore, this method also corrects the variation in the transmission delay time of each audio packet, and has the same effect as described for the first embodiment.

Furthermore, instead of the delay time, the delay time storage unit 13 stores the number of received voice packets corresponding to the delay time (≒delay time/voice packet transmission time interval) in correspondence with the number of relay packet switching devices. The above-mentioned method can also be achieved by sequentially extracting the audio packets stored in the buffer memory 14 for absorbing delay time variations after receiving the first audio packet and subsequently receiving the audio packets for the number of receptions read out from the delay time storage unit 13. There are effects similar to those described in the embodiment.

By controlling the delay time of voice packets by the number of relay packet switching devices, the present invention can maintain voice quality regardless of the number of relay packet switching devices. When the delay time is small, the delay time can be shortened, which eliminates the drawback that the voice of the other party is heard with a delay and it becomes difficult to carry out a conversation.This provides a very effective voice packet transmission delay control method. be.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a voice packet switching system.
FIG. 2 is an explanatory diagram showing the cumulative distribution of packet delay times corresponding to the number of relay packet switching devices, and FIG. 3 is an illustration of a delay time fluctuation absorbing device 9 according to an embodiment of the present invention.
4 is an explanatory diagram of the storage contents of the delay time storage section 13, and FIG. 5 is a block diagram of the buffer memory 1 for absorbing delay time fluctuations from packet transmission to the receiving side.
4 shows a time chart of audio packet transmission and processing up to the output of step 4. 9...Delay time variation absorber, 10...Relay packet switching device number input terminal, 11...Relay packet switching device number receiving circuit, 12...Control circuit, 13...Delay time storage unit, 14...Buffer memory for absorbing delay time variation, 15 ...Audio packet input terminal, 16...Timer circuit, 17...Audio packet output terminal.

Claims (1)

[Claims] 1. In a voice packet switching system in which voice packets having time information related to transmission are relayed through one or more packet switching devices and transmitted through the same route for each call, the relay packet is transmitted to the receiving side. means for receiving the number of switching devices; means for storing a delay time corresponding to the number of relay packet switching devices and increasing in value as the number of relay packet switching devices increases; and a buffer memory for sequentially storing received voice packets. and a control means for extracting voice packets input to the buffer memory at fixed time intervals after accumulation for a specified time, reading a delay time corresponding to the number of received relay packet switching devices from the storage means, An audio packet transmission delay control method, characterized in that the read delay time is used to control the storage time of audio packets stored in the buffer memory in accordance with time information of the audio packets. 2. The control means uses the time difference between the delay time read from the storage means and the transmission delay time of the first voice packet received after the call is set up, and adjusts the voice packets inputted to the buffer memory thereafter by the time difference. 2. The voice packet transmission delay control system according to claim 1, wherein the voice packet transmission delay control method is characterized in that the voice packets are sequentially retrieved after being accumulated. 3. In a voice packet switching system in which voice packets are relayed through one or more packet switching devices and transmitted through the same route for each call, means for receiving the number of relay packet switching devices on the receiving side, and the relay packet switching device. Means for storing a delay time that increases as the number of relay packet switching devices increases in accordance with the number of devices; a buffer memory for sequentially storing received voice packets; and a means for specifying voice packets to be input to the buffer memory. a control means for storing the delay time corresponding to the number of received relay packet switching devices and then extracting the delay time at regular intervals; A voice packet transmission delay control method, characterized in that the storage time of voice packets stored in the buffer memory is controlled. 4. The means for storing the delay time stores the number of received voice packets corresponding to each of the delay times, and the control means further stores the number of received voice packets corresponding to each of the delay times, and further, the control means stores the first voice packet received after the call is set up as the first voice packet. The audio packets received subsequent to packet reception are stored in the buffer memory until they reach the number of received audio packets read out, and then the audio packets stored in the buffer memory are sequentially extracted to correct fluctuations in transmission delay time. A voice packet transmission delay control system as claimed in claim 1.