JPS63305641A - Packet communication system - Google Patents

Abstract

PURPOSE:To attain the transmission of information with high quality by arranging a different time from each packet given to a packet received in a packet switching network to a prescribed value at the reception side to detect the missing packet in the network or a faulty packet receiving the transmission delay for a prescribed value or over in the network at the reception side. CONSTITUTION:A CPU 32 generates packet transmission information 37 in the order of sequence numbers obtains a difference of sequence numbers of adjacent packets based on the sequence numbers stored in a memory 33 and outputs the faulty packet information to a smoothing buffer 31 in addition of the packet sending information 37 if the faulty packet is detected. An inputted packet is divided into encoded signals at an input buffer 34 and outputted to a decoder 25 an encoded signal 39. Prescribed interpolation is applied by using the encoded signal of the packet before and after the missing packet by means of the fault information and the result is outputted as the encoded signal 39 with respect to the faulty packet or a retransmission request signal is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a packet communication system, and in particular, uses packets with variable bit lengths, and uses packets with different delay times on the receiving side for each packet received within a packet switching network. The present invention relates to a packet communication method that allows packets to be aligned to a constant value and to detect on the receiving side abnormal packets that have been lost within a network or have undergone a transfer delay greater than a certain value within the network.

[Conventional technology]

Traditionally, for example, transmitting low bit rate voice using packets has not been widely used, despite the significant savings in transmission and switching costs compared to circuit switching. , 1. The reason for this is that transmitting encoded information in packets causes various problems as described below.

One of the problems is that transmitting packets through a packet switching system typically results in different delays for each packet. Delay variations are introduced at switching nodes within a packet-switched network.

Unlike data, audio information must be decoded from a digital representation to an analog representation at the same speed as it was coded to achieve high quality audio reproduction.

When a variable delay is introduced during the transmission period of voice packets,
The above decoding cannot be performed unless some compensation is provided.

Conventionally, a method to solve this problem is to take advantage of the fact that conversational audio such as on a telephone has a sound part and a silent part, and generate packets only for the sound part of the sound.
Thereafter, no packets are transmitted during the period of silence, and after receiving the first packet of the sound portion, the receiving section delays that packet for a certain period of time (seconds), and after this initial delay, the packet is transmitted after receiving the first packet of the sound portion. There is a method of reproducing the original analog audio by decoding the packet 7) of the sound part at the same speed as the packet generation interval T (seconds).

FIG. 5 shows a time chart for this method. In FIG. 5, a is a voice signal, b is a coded signal obtained by encoding the voice signal by an encoder, C is a fixed-length transmission packet formed from the coded signal at a fixed time interval, and d is a received packet received on the receiving side, and e is a reproduced packet in which received packets d are arranged in a predetermined order and sent for reproduction.

In the conventional example shown in FIG. 5, when the delay time for a packet to arrive from the transmitting side to the receiving side is t8, and the delay time for the received packet to be played back is D', (t, +D' ) Packet 2 delayed by more than a certain value of time cannot be reproduced on the receiving side, and some kind of interpolation is required as necessary.

As explained above, in this conventional method, as shown in the coded signal diagram of FIG.
The b/s ADPCM (adaptive differential PCM) method was used. In other words, even when the amount of significant information generated changes over time, it is encoded at a constant bit rate and transmitted in fixed length packets, which has the problem of large waste from the perspective of information transmission efficiency. Ta.

As a solution to this problem, on the transmitting side, a packet with a variable bit length is formed whose length is made variable according to the number of information bits generated within a fixed time interval T (seconds), and a specific modulo A packet 7) communication method is being considered in which communication is performed using variable bit length packets, in which a sequence number consisting of a number is added and transmitted, and the receiving side arranges and reproduces the received packets according to the above sequence number.
For example, see Proceedings of the 1981 National Conference of the Institute of Electronics and Communication Engineers, Information Systems Division, 181 "Variable Quantum □ Bit Encoding Method between Audio Blocks").

[Problem that the invention seeks to solve]

As explained above, in conventional packet communication systems, when significant information changes over time, it is possible to improve information transmission efficiency by using packets with variable bit lengths.

However, when using variable bit length packets, the sizes of the packets vary, so if a variable delay is introduced during the packet transmission period, the reception side , it becomes difficult to smooth the delay, and the occurrence of abnormal packets 7) in which transmitted packets are lost for some reason or are delayed for more than a certain period of time and cannot be sequentially reproduced increases. The important issue is to accurately detect the occurrence of this abnormal packet and perform interpolation or retransmission.
Conventionally, this problem has not been sufficiently solved.

The purpose of the present invention is to solve the above problems.
An object of the present invention is to provide a packet communication system using variable bit length packets that allows delay smoothing and abnormal packet detection to be easily performed on the receiving side.

[Means for solving problems]

The present invention provides a packet communication method in which communication is performed using variable bit length packets in which the number of information bits in a packet is varied according to the number of information bits generated within a fixed time interval T (seconds). A sequence number modulo n (n is a natural number) is assigned to the packets in the order in which they occur, and the receiving side assigns a sequence number of modulo n (n is a natural number) to the packets. time (Dm +T) (seconds) (however, D6 is the allowable delay time for each packet, 0, ≦T)
Later, the apparatus is characterized in that it sequentially reproduces the arranged packets in accordance with the sequence numbers at a timing of every T (seconds), and detects abnormal packets from the difference in the sequence numbers of the arranged adjacent packets.

Further, in the present invention, it is preferable to detect an abnormal packet when the difference in sequence numbers is 2.

[Effect]

On the receiving side, the permissible per-packet delay time D8 allowed for playback is determined as the per-packet delay time D8, which is unique to each packet by subtracting the common delay time for each packet from the packet delay time, as 0 < D m ≦ Set to satisfy T. That is, the present invention is applied to a system in which the delay time for each packet is small and the variation in packet length and packet transfer route is small.

Then, on the receiving side, the arriving packet is received for a certain period of time (
After Dm +T) (seconds), the packets are arranged and sequentially reproduced according to the sequence number added to the packets at a timing of every T (seconds).

Therefore, each packet takes a certain amount of time (Dm +T) (seconds)
The signal will definitely arrive at the receiving end within 10 minutes, and delay smoothing will be performed correctly.

On the other hand, regarding the sequence numbers of the arranged packets, the difference Δ between the sequence numbers of two adjacent packets is determined. However, the difference between number n and number 1 is 1. Thus, the difference Δ is, if no abnormal packet occurs,
Δ=1, and when an abnormal packet occurs,
Δ≠1, and the occurrence of an abnormal packet can be detected.

In this case, Δ=2 occurs when the previous packet is lost and becomes an abnormal packet, and if necessary, interpolation can be performed using reproduced signals from previous and subsequent packets, or retransmission can be performed.

Further, the case of Δ<1 or Δ>2 may also occur, but the probability thereof is usually very small.

〔Example〕

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

FIG. 1 is a time chart showing one embodiment of the present invention, and FIG.
The figure is a diagram showing the delay characteristics of the packet.

First, FIG. 2 will be explained. In Figure 2, the horizontal axis represents time t (seconds), and the vertical axis represents packet delay probability.
3 shows a packet end-to-end delay probability distribution function in a packet communication system to which the present invention is applied. In Figure 2, t is a fixed packet common delay time common to all received packages, such as transmission path delay in each packet network and node processing delay, and D is a fixed packet common delay time that is unique to each packet. is the delay time (where Dm is the delay time per allowable packet and Pa is the probability at that time). Further, T is a fixed time interval for packet generation, and in this case is the packet length.

Here, on the receiving side, the ratio P. When the delay time for a packet with (po≦1) to settle down is (ta + D, ) (seconds) (where 0<D,≦T), the first packet or a specific reference packet on the transmitting side next T (seconds)
If there are still packets in between, the packets at a rate of P arrive at the receiving side with a delay time of (t, +D, ) (seconds), and an additional delay time of T (seconds) is added. As a result, almost 100% of the packets arrive. That is, on the receiving side, after the arrival of the first packet or a certain reference packet, a delay of (Dm+T) is added, and the packet is subsequently played back at a timing of <T (seconds). smoothing is performed, and the digital signal is regenerated into an analog signal at the same speed as it was coded.

In FIG. 1, b is a coded signal with a fixed time interval T
This shows how the data is encoded according to the number of information bits every (second). C is a transmission packet, the bit length of which is determined at fixed time intervals T (seconds) according to the number of information bits included in the encoded signal. Then, in the order of generation, sequence numbers of modulo 4 (n=4) are added to the formed packets in order, starting with 1 for the first packet and 2.3.4, and these numbers 1 to 4 are repeated in order. will be added. Note that this sequence number is provided in the header portion of the packet, and the modulo number n of the sequence number is appropriately set depending on the situation of the packet network.

FIG. 1d shows a received packet, and each packet arrives from the transmitting side after being delayed by a common packet delay time t and a delay time for each packet. Here, the second modulo sequence number 3 packet shown by the dotted line was lost, indicating that it was an abnormal packet and did not arrive.

FIG. 1e shows the playback packets arranged for playback. After a certain period of time (D□10T) after the first packet 1 arrives, the packets are arranged in sequence number order. That is, the sequence numbers are 1.2.3.4.1.2.4.
1, and there is no abnormal packet 3. In other words, the packets that arrive at the receiving side are buffered for -tan, and after (DmI + T) time, are sent out and played back every T (seconds). Playback is performed correctly with the same time relationship.

On the other hand, when these reproduced packets are arranged, the difference Δ between the sequence numbers of two adjacent packets is determined. Note that this difference Δ is 1 between the 1st (4th in this embodiment) of modulo n and the next 1st. The value of the difference Δ thus obtained is as shown in FIG. According to this, the next packet with sequence number 4 is the packet with sequence number 4 after the second packet with sequence number 2 in modulo, and the difference between the sequence numbers is Δ=2, and the packet with sequence number 3 that was lost immediately before the packet with sequence number 4 is is detected as an abnormal packet.

Therefore, according to this embodiment, a variable bit rate encoding method is used to encode the information source, communication is performed using variable length packets without reducing information transmission efficiency, and delay smoothing is performed appropriately on the receiving side. At the same time, when an abnormal packet is detected and consecutive packets are generated every T (seconds) on the sending side, and the difference in sequence numbers is Δ = 2, the immediately preceding lost abnormal packet is retrieved from the previous and subsequent packets as necessary. By interpolating using the reproduced signal or arranging retransmission, high-quality information transmission becomes possible.

Note that the probability that two or more immediately preceding packets become abnormal packets consecutively, that is, Δ=3 or more, is (1-P
o) 2 or less, generally P. is set as a value very close to 1 that is acceptable in practice even if there are delayed packets, so (1-Pa)'' = 0, and in practice this kind of thing only happens very rarely ( For example, P
, =0.999, (1-Po)'', 10-
').

In addition, the probability that n packets become abnormal packets and Δ=1 makes it appear as if there were no abnormal packets is (
t-Pa)'', and by increasing n as necessary, it can be set to (1-Po)→0, which is a value that poses no problem in practice.

Furthermore, by using Δ=2 as the detection standard for abnormal packets, it is possible to prevent an increase in the packet buffer time, which would be a problem if Δ>2 or Δ×1, and a decrease in packet transmission efficiency can be avoided.

FIG. 3 is a block configuration diagram of a packet communication system to which an embodiment of the present invention is applied, and FIG. 4 is a block configuration diagram showing details of the packet disassembly device.

The packet communication system of this embodiment includes a variable length encoder 2
1 and a packet assembly device 22, and a receiving side including a packet disassembly device 24 and a decoder 25 are connected through a packet network 23.

Here, the variable length encoder 21 encodes the input analog human input signal with a variable bit length depending on the amount of information thereof, and outputs the encoded signal shown in FIG. Packet assembly device 2
In step 2, this output encoded word a is input, and at fixed time intervals T (seconds), packets with variable packet lengths are sequentially generated according to the number of information bits contained therein. At the same time, a modulo 4 sequence number is added, for example, to the header, and the packets are sequentially sent to the packet network 23.

As shown in FIG. 4, the packet disassembly device 24 includes a smoothing buffer 31, a CPU 32, a memory 33, a backup buffer 34 for a lost reproduction and decoder, and a clock supply device 35.

Packets transmitted from the transmitting side and arriving through the packet network 23 are input to the smoothing buffer 31 and buffered for a certain period of time (Dm +T) (seconds). During this time, sequence number information 36 added to the packet
is manually input to the CPU 32 and further stored in the memory 33. Then, in the CPU 32, packet sending information 37 is created in order of sequence number, and the memory 3
Adjacent packet 7 according to the sequence number stored in 3
), and when an abnormal packet is detected, the abnormal packet information is added to the packet transmission information 3.
7 and output to the smoothing buffer 31. In the smoothing buffer 31, this packet sending information 37
Accordingly, every T (seconds), as shown in FIG. In the power buffer 34, the input reproduction bucket) e is divided into encoded signals 39.
It is output to the decoder 25 as Also, based on the abnormality information, predetermined interpolation is performed using the encoded signals of the packets before and after the lost packet, and the encoded signal 39 for the abnormal packet is generated.
or a retransmission request signal.

The decoder 25 reproduces and outputs the input encoded signal into the original analog signal. Note that the clock supply device 35 supplies necessary clocks to each part.

As described above using FIGS. 3 and 4, the present invention can be easily realized as an apparatus using known techniques.

〔Effect of the invention〕

As explained above, the present invention uses variable bit length packets to efficiently transmit information by taking advantage of the burst nature of the information source, smoothing the delay of each packet on the receiving side, and detecting abnormal packets. According to
It becomes possible to interpolate the information of the missing packet from previous and subsequent values or to request retransmission as necessary, which has the effect of enabling high-quality information transmission without reducing transmission efficiency.

[Brief explanation of the drawing]

FIG. 1 is a time chart showing one embodiment of the present invention. FIG. 2 is a characteristic diagram of the packet delay time distribution. FIG. 3 is a block diagram showing a packet communication system according to an embodiment of the present invention. FIG. 4 is a block diagram showing details of the packet disassembly device. FIG. 5 is a time chart showing a conventional example. 1 to 5...Sequence number, 21...Variable length encoder, 22...Packet assembly device, 23...Bucket+-4, 24...Packet disassembly device, 25...Decoding smoothing device, 31... smoothing buffer, 32... CPU, 33... memory, 34...
Powerful buffer, 35... Clock supply device, 36...
・Sequence number information, 37...Packet transmission information,
38... Sending packet and loss information, 39... Encoded signal, D, D'... Delay time for each packet,
D... Permissible delay time per packet, T... Fixed time interval, a... Audio signal, b... Coded signal, C
...Transmission packet, d...Reception packet, e...
Playback packet, t, ...Packet common delay time. Patent applicant Nippon Telegraph and Telephone Corporation -1 agent
Patent attorney Nao Takashi Ide: Pa7. Tosho and extended time D: bug, 2 tou Jl Enkei time Dm - measurement pair nodogo 21 - 5 ML time 7 example (
Bug 2 To 01 Court waiting) 箆 2 Figure big brother example (Pub 2 To shota system A)? F+3 Diagram size @ S
4 Cause

Claims (2)

[Claims] (1) In a packet communication method that communicates using variable bit length packets that change the number of information bits in a packet according to the number of information bits generated within a fixed time interval T (seconds), each packet is The above packets are assigned a sequence number modulo n (n is a natural number) in the order in which they occur, and the receiving side assigns a sequence number of modulo n (n is a natural number) to the above packets. After time (D_m+T) (seconds) (where D_m is the allowable delay time for each packet, 0<D_m≦T), playback is performed sequentially according to the above sequence number at a timing of every T (seconds), and the adjacent A packet communication method characterized in that abnormal packets are detected from the difference in sequence numbers of the matching packets. (2) The packet communication method according to claim (1), in which an abnormal packet is detected when the difference in sequence numbers is 2.