JPH01175432A - Delay difference absorption system for packet switching - Google Patents

Abstract

PURPOSE:To decrease an underflow occurrence rate by adding a sequence number to each packet, providing a packet absence and packet error counter and an underflow counter on a reception side, and deciding whether or not regeneration timing is corrected at the time of underflow occurrence according to the values of both counters. CONSTITUTION:A transmission side adds sequence numbers 1-8 to respective packets and sends the packets at equal intervals. The reception side while checking errors of received packets and the sequence numbers stores them in a buffer 14 for delay difference absorption and reads those received packets in order at equal intervals at specific time. For a packet which is discarded in the network or does not reach the reception terminal until regeneration timing, dummy packets 2', 4', and 7' such as a soundless packet and a background noise packet are regenerated instead at the time of a sound. Then even if a true packet arrives, this packet is discarded. Consequently, the underflow probability is reduced below the packet loss and packet error probability in the network.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention provides a method for supporting continuous communication of audio, video, etc. in a high-speed packet switching network that supports communication of various different media [prior art ] The packet switching method is originally suitable for data communication where information is generated in discrete bursts, and is suitable for voice communication.

It was considered unsuitable for continuous communication such as videos.

In continuous communication such as audio and video, a fixed amount of information is constantly generated at fixed intervals, but in packet exchange, the exchange is performed on a queuing basis, so fluctuations in delay (delay difference) occur. This is because the receiving side needs to absorb the fluctuations and restore the original continuous communication.

However, in recent years, high-speed packet switching, which has become possible due to faster and higher quality digital and optical communications, has significantly shortened delays and, as a result, has reduced delay fluctuations, making continuous communications more effective. In principle, it is now possible to accommodate the same information, and we are approaching the realization of literal multimedia communications.

Delay difference absorption is performed by providing a delay difference absorption buffer, but in continuous communication, once playback has started, it is necessary to continue playback at a constant speed, so it is difficult to determine at what point after packets start arriving. The problem is how to start the process, and how to control when the delay difference absorbing buffer overflows or underflows. Furthermore, in a packet network, packets may be discarded due to a transmission error or an overflow of a buffer memory within the network, and how to deal with this is also a problem. When a packet is lost in a packet network, if only the received packet is reproduced at the receiving end, the time point at which the packet is reproduced will be advanced by the amount of the lost packet. Therefore, as the loss of packets accumulates, the playback time point is moved forward more and more, and eventually a buffer underflow occurs in which the packets to be played back have not yet arrived at the receiving end at the time they should be played back.

In response to this, various delay difference absorption methods have been considered in the past, but the first method is the simplest method;
There is a method of reproducing dummy packets at the time of underflow, equivalently increasing the number of reproduced packets, and delaying the reproduction timing. In the second method, the sending side adds a sequence number to each packet belonging to one call and sends it to the network, and the receiving side sends it to the network after an appropriate time delay from the arrival of the first packet related to that call. If the sequence number jumps due to a packet being lost or discarded due to an error in the network, a dummy packet is inserted for that amount, and the delay difference absorption buffer underflows. Sometimes, there is a method of inserting a dummy packet and then discarding the packet when the packet arrives. In the case of voice, the dummy packet may be a packet corresponding to silence information, a packet corresponding to background noise, or a repeat of the previous packet.

[Problem that the invention seeks to solve]

According to the first conventional method, the playback timing is delayed each time an underflow occurs.
It is possible to keep the probability of underflow very small. However, although the probability of underflow is small, it leads to an increase in the amount of buffer memory and an increase in delay, so it cannot be said that it should be set to O in general. It is sufficient that the probability is equal to or lower than the probability of packet errors and discards in the network.

On the other hand, according to the second conventional method, it is possible to suppress fluctuations in playback timing caused by packet errors and discards in the network as well as underflow of the memory for absorbing delay differences on the receiving side. If the playback timing deviates from the optimal value due to bias in network delays, underflow will occur frequently.

An object of the present invention is to adaptively control the delay difference in bucket exchange in the second method described above so that the probability of underflow is equal to or less than the probability of packet sorting errors and discards in the network. The goal is to provide a method.

[Means for solving problems]

The present invention is a method for absorbing delay differences in packets for continuous communication in packet switching, in which the transmitting side adds a sequence number to packets belonging to the same call and transmits the packets, and calculates delay difference absorbing packets and underflow counting. The receiving side, which is provided with a counter for counting packets and a counter for counting packet omissions and packet errors, monitors transmission errors in the received bucket and the sequence number, stores correctly received packets in the buffer for absorbing delay differences, and The received packets are read from the delay difference absorbing buffer at a constant speed, and when the received packets are monitored, if the received packet is incorrect or the sequence number of the received packet is missing, dummy packets are read by the number of incorrect or missing packets. is stored in the delay difference absorption buffer, and the counter for counting missing packets/packet errors is counted by the number of packets lost, and when the counter for counting missing packets/packet errors reaches its maximum count value. , reset the counter for counting missing packets/packet missing I-errors and the counter for counting underflow, and insert a dummy bucket when the buffer for absorbing delay difference underflows.
While reproducing, the counter for counting underflow is counted up, and as a result, when this output reaches its maximum count value, this counter and the counter for counting missing packets/packet errors are reset; When the value of the underflow counting counter is less than the maximum count value, after inserting the dummy bucket,
The present invention is characterized in that when a packet having a sequence number that should have been reproduced at the time of the underflow is received, the received packet is discarded.

[Effect]

In the present invention, a sequence number is added to each packet, and during normal times, transmission errors within the packet console 1-18 can be avoided.

The receiving side detects missing packets/nodes due to buffer overflow etc. by missing sequence numbers and inserts dummy buckets for the missing packets/nodes due to buffer overflow, etc., and when a buffer underflow occurs, inserts and reproduces the dummy buckets. Thereafter, when a packet having a sequence number that should have been reproduced at the time of underflow is received, the received packet No+ is discarded so that the reproduction timing does not change, which is the same as in the conventional method.

In the present invention, a counter for counting missing packets/packet errors and a counter for counting underflow are further provided on the receiving side, and it is determined based on the values of both counters whether or not to correct the reproduction timing at the time of underflow. Specifically, the maximum count value of the packet dropout/packet error counter is set as N1, the maximum count value of the underflow counter is set as N2, and when the packet dropout/packet error count counter reaches full amplification first, both counters are reset. However, when the underflow counting counter reaches full capacity first, both counters are reset and
When an underflow occurs, the real packet that should have been reproduced at the time of the underflow after inserting a dummy packet is not discarded, and the reproduction timing is delayed by one bucket. With this method, the underflow occurrence rate can be reduced by
The packet error occurrence rate can be reduced to approximately N2/N1 or less.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an explanatory diagram showing an embodiment of the packet delay difference absorption method according to the present invention, and shows time charts on the transmitting side, receiving side, and reproduction when supporting continuous communication. As shown in FIG. 1, on the transmitting side, sequence numbers ``■'' to ``■'' are added to each packet and the packets are transmitted at equal intervals. These packets arrive at the receiving end with different delays for each packet, as shown in the figure, due to queuing within the network. On the receiving side, receive bucket No. 1.
While checking for errors and sequence numbers, these received packets are stored in the delay difference absorbing function sofa, and at a predetermined time, these received packets are read out in order at equal intervals. The playback start timing is, for example, a delay time 99%D that satisfies 99% of the packets after the first packet of each call arrives at the receiving side. - Once playback is started, packets are read out continuously thereafter. Packet ■ in Figure 1.

As shown in ■ and ■, packets that are discarded within the network or do not reach the receiving end by the playback timing are replaced with dummy packets such as silent packets, background noise packets, or previous packets in the case of audio ■′ ■′
,■' are played. After this, even if a genuine packet ■ arrives, this packet will be discarded. For example,
The probability of packet discard or error in the network is controlled to be equal to the probability of underflow, and the maximum count value N1 of the counter for counting packet loss/packet error is set to 2, and the probability of underflow counting is set to 2. If the maximum count value is 2, as shown in Figure 1, the packet ■
When the underflow occurs, the underflow counting counter is fully increased and both counters are reset, and the packet ■ that arrives late is not discarded, but is written as it is to the delay absorption buffer and reproduced. In other words, when the packet ■ underflows, it is determined that the underflow probability is higher than the packet discard/packet error rate in the network, and to correct this, the playback timing is delayed and the underflow probability is reduced. control so that This is achieved by not discarding packet ■.

FIG. 2 is an explanatory diagram schematically showing a circuit configuration on the receiving side for realizing the delay difference absorption method of the present invention. In FIG. 2, the reception control circuit 12 that has received the packet from the reception line 11 notifies the buffer memory control circuit 13 of the reception of the packet, and if the delay difference absorbing buffer memo January 4 is free, The reception control circuit 12 is commanded to write the packet to the delay difference absorption buffer memory January 4. When the receiving external circuit 12 detects a transmission error in a received packet or a missing sequence number in the received packet, the dummy packet generation circuit 17 sends dummy packets corresponding to the number of dummy packets to the dummy packet generation circuit 17 under the control of the sofa memory control circuit 13. Instruct to write to absorption buffer memo January 4,
A counter 15 for counting packet omissions and packet errors is counted up. Further, when the buffer memo January 4 underflows, a dummy packet is generated in the generating circuit 17 and outputted to the output terminal 19 via the selector 18, and the underflow counting counter 16 is counted up. If the underflow counting counter does not reach the maximum count value, the buffer control circuit 13 sends the received packet to the reception control circuit 12 to the delay difference absorbing buffer when the packet that should have been reproduced at the time of the underflow arrives late. It is discarded without being stored in the memory 14. Also,
When the underflow counting counter 16 reaches the maximum count value, simply resetting the packet loss/packet error counting counter 15 and the underflow counting counter 16 will eliminate the underflow probability of arriving late.
・Do not instruct the disposal of. On the other hand, when the packet loss/packet error counting counter 15 reaches the maximum count value, both counters are reset. With the above circuit configuration, it is possible to realize the delay difference absorbing function according to the present invention described above.

〔Effect of the invention〕

According to the present invention, the underflow probability can be suppressed to the same level as the packet loss/packet error probability in the network, and the quality of service for continuous communication can be maintained at an appropriate level, so the effects are remarkable. be.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the principle of the delay difference absorption method of the present invention, and FIG. 2 is an explanatory diagram showing a schematic circuit configuration for realizing the delay difference absorption method of the present invention. 12... Reception control circuit 13... Buffer memory control circuit 14...
Delay difference absorption buffer memory 15... Counter for counting missing packets and packet errors 16... Counter for underflow counting 17...
...Dummy packet generation circuit agent Patent attorney Iwa
Yoshiyuki Sae Figure 2

Claims (1)

[Claims] (1) A packet delay difference absorption method for continuous communication in packet switching, in which the sending side adds a sequence number to packets belonging to the same call and sends them, and the packets for delay difference absorption and the underflow counter are combined. The receiving side, which is provided with a counter for counting missing packets and packet errors, monitors transmission errors and the sequence number of received packets, stores correctly received packets in the buffer for absorbing delay differences, and stores packets that are received correctly in the buffer for absorbing delay differences. is read from the delay difference absorbing buffer at a constant speed, and when the received packet is monitored, if the received packet is incorrect or the sequence number of the received packet is missing, dummy packets are delayed by the number of incorrect or missing packets. The packet is stored in the difference absorption buffer, and the counter for counting missing packets/packet errors is counted up by the number of packets missing, and when the counter for counting missing packets/packet errors reaches its maximum count value, this missing packet/packet error is counted up. The counting counter and the underflow counting counter are reset, and when the delay difference absorption buffer underflows, a dummy packet is inserted and reproduced, and the underflow counting counter is counted up. When the count reaches its maximum count value, this counter and the counter for counting missing packets and packet errors are reset; on the other hand, when the value of the counter for underflow counting is less than the maximum count value, the dummy packet is inserted. A method for absorbing delay differences in packet switching, characterized in that, when a packet having a sequence number that should have been reproduced at the time of the underflow is subsequently received, the received packet is discarded.