JPH10190681A - Asynchronous information communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a speech, etc., from deteriorating in data communication quality in the asynchronous information communication system which does not synchronize periodical transmission frame over the entire network. SOLUTION: A receiving station 3 of this information communication system extracts difference data of a transmit clock recorded in a specific field 150 of a packet received from an ATM communication network 1 and stores it in a register 210, and detects a jitter quantity as variance between delays at the last and current data reception time points on a reception side on the basis of the difference data stored in the register 210 and discharge abnormal data which is large in jitter quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an asynchronous information communication system for transmitting information such as audio and video in real time through a communication network.

[0002]

2. Description of the Related Art In recent years, communication technologies such as a synchronous communication system and an ATM communication system have been used for communication such as audio and video. The quality may be degraded, and there is an urgent need for measures against this jitter.

[0003] As a specific example of a synchronous communication system typified by an N-ISDN network or the like, a number of time slots are prepared in a fixed-period frame, and TDMA (TDMA) is transmitted in a time slot at a predetermined position. Time Division Mult
iple Access) method is common.

[0004] In the case of the TDΜΑ method, it is assumed that frames of a fixed period are synchronized in the entire network.
Although the jitter is limited to a small amount, it has a disadvantage that it is necessary to reserve a specific time slot in advance and it is necessary to occupy a certain communication band from the start to the end of communication.

On the other hand, as an asynchronous communication system which does not occupy a specific time slot, a fixed-length cell carrying data to a communication network is flowed at any time, and an empty cell (a cell to which data is not yet loaded) is used as necessary. ATM (Asynch) that carries data by using it as a valid cell (cell carrying data)
ronou Transfer Mode).

In the case of this ATM system, cells are not reserved at the start of communication irrespective of the state of communication traffic, so that transmission efficiency is improved. However, frame synchronization at a fixed period is not guaranteed. Therefore, jitter, that is, variation in delay of transmission data may occur. If the amount of jitter increases, communication quality may deteriorate in some cases, and the receiving side may not be able to hear the sound.

Therefore, when this measure against jitter is actually introduced into an asynchronous information communication system in which a transmitting station and a receiving station are connected to an ATM communication network, at least the receiving station is provided with a mechanism for detecting the amount of jitter. If the value exceeds a certain allowable value, the received data may be discarded. This is because, in the case of voice, even if data is discarded to some extent, if the data is discarded within a certain range, it can be recognized as voice on the receiving side.

[0008]

However, in the case of the conventional asynchronous communication system, that is, in the case of a system in which data is loaded on an empty cell flowing through the communication network without occupying a specific time slot, communication is performed. On the side,
It only receives data addressed to its own station based on the header information of the cell that has flowed over the communication network, and does not reach the point where it is possible to detect jitter, which is delay variation in transmission data. There is a problem that the possibility of occurrence is high.

The present invention has been made to solve such a problem, and periodic synchronization of transmission frames is not performed in the entire network, which may cause delay variation, that is, jitter, during data transmission. It is an object of the present invention to provide an asynchronous information communication system capable of detecting jitter when communicating information using a certain communication network.

It is another object of the present invention to provide an asynchronous information communication system capable of detecting jitter in performing the above-mentioned asynchronous communication and preventing deterioration of communication quality of data such as audio and video.

[0011]

To achieve the above object, an asynchronous information communication system according to the present invention comprises a transmitting station for transmitting data and a receiving station for receiving data from the transmitting station. Is connected on a communication network, and the same clock or synchronous clock is supplied from the communication network to the transmitting station and the receiving station. In the asynchronous information communication system, the transmitting station transmits data on the communication network. Transmitting means, a transmitting side clock counter that always counts a clock supplied from the communication network at a predetermined cycle,
Transmission count value storage means for storing a count value of the transmission side clock counter when the transmission means transmits data on the communication network; and transmission side clock when new data is transmitted by the transmission means. Difference calculation means for calculating the difference between the count value of the counter and the count value at the time of previous data transmission stored in the transmission count value storage means,
A difference information adding unit that adds difference information of the transmission clock calculated by the difference calculation unit to the new transmission data, wherein the receiving station receives data from the communication network; A receiving clock counter that constantly counts a clock supplied from a network at a predetermined cycle, and a receiving count value storing unit that stores a count value of the receiving clock counter when the receiving unit receives data from the communication network. Adding the difference information of the transmission clock included in the data received from the communication network by the reception means and the count value of the reception clock at the time of previous data reception stored in the reception count value storage means Means for calculating a difference between an added value added by the adding means and a count value of the receiving clock counter when data is received this time. It is characterized by comprising a jitter detecting means for detecting a jitter.

According to a second aspect of the present invention, in the asynchronous information communication system, a transmitting station for transmitting data and a receiving station for receiving data from the transmitting station are connected on a communication network. In the asynchronous information communication system in which the same clock or a synchronous clock is supplied from the communication network, the transmitting station transmits data on the communication network; A transmission-side clock counter that constantly counts in a cycle; a transmission count value storage unit that stores a count value of the transmission-side clock counter when the transmission unit transmits data over the communication network; The count value of the transmission side clock counter when data is transmitted, and the count at the time of previous data transmission stored in the transmission count value storage means And a difference information adding means for adding the difference information of the transmission clock calculated by the difference calculating means to the new transmission data, wherein the receiving station comprises: Receiving means for receiving data from the communication network, a receiving clock counter that always counts a clock supplied from the communication network at a predetermined cycle, and a receiving clock counter when the receiving means receives data from the communication network. Receiving count value storing means for storing a count value, difference information of the transmission clock included in data received from the communication network by the receiving means, and the last data reception time stored in the receiving count value storing means. Adding means for adding the count value of the reception clock of the receiving clock, the added value added by the adding means, and the reception value when the current data is received. Jitter detection means for determining the difference from the count value of the clock counter and detecting jitter, based on the value of the jitter detected by the jitter detection means, to determine whether to discard the received data, it was determined to discard And discarding means for discarding the received data.

According to a third aspect of the present invention, there is provided an asynchronous information communication system, wherein a transmitting station for transmitting data and a receiving station for receiving data from the transmitting station are connected on a communication network, and the transmitting station and the receiving station are connected to each other. In an asynchronous information communication system that performs communication without using a synchronous clock of the communication network, the transmitting station includes a clock generation source that generates a clock of a predetermined frequency, and a clock generated by the clock generation source at a predetermined period. A transmitter clock counter that always counts,
First transmission count value storage means for storing a count value of the transmission side clock counter when the transmission means has transmitted data on the communication network; and Second transmission count value storage means for storing the count value of the transmission side clock counter; count value of the transmission side clock counter when new data is transmitted by the transmission means; and transmission count value storage means. A difference calculating means for calculating a difference from the stored count value at the time of the previous data transmission, a difference information of the transmission clock calculated by the difference calculating means, and a second transmission count value storing means. Information adding means for adding a count value of a transmission side clock counter to the new data, wherein the receiving station receives data from the communication network, A clock recovery unit that reproduces a clock controlling the transmission-side clock counter based on a count value of the transmission-side clock counter included in the data received by the reception unit; A receiving clock counter that constantly counts a clock at a predetermined cycle; a receiving count storage unit that stores a count value of the receiving clock counter when data is received from the communication network by the receiving unit; Adding means for adding the difference information of the transmission clock included in the data received by the above and the count value at the previous data reception stored in the reception count value storage means, Sum and
And a jitter detecting means for detecting a difference between the data and the count value of the receiving clock counter when data is received this time to detect jitter.

According to a fourth aspect of the present invention, there is provided an asynchronous information communication system, wherein a transmitting station for transmitting data and a receiving station for receiving data from the transmitting station are connected on a communication network, and the transmitting station and the receiving station are connected to each other. In an asynchronous information communication system that performs communication without using a synchronous clock of the communication network, the transmitting station includes a clock generation source that generates a clock of a predetermined frequency, and a clock generated by the clock generation source at a predetermined period. A transmitter clock counter that always counts,
First transmission count value storage means for storing a count value of the transmission side clock counter when the transmission means has transmitted data on the communication network; and Second transmission count value storage means for storing the count value of the transmission side clock counter; count value of the transmission side clock counter when new data is transmitted by the transmission means; and transmission count value storage means. A difference calculating means for calculating a difference from the stored count value at the time of the previous data transmission, a difference information of the transmission clock calculated by the difference calculating means, and a second transmission count value storing means. Information adding means for adding a count value of a transmission side clock counter to the new data, wherein the receiving station receives data from the communication network, A clock recovery unit that reproduces a clock controlling the transmission-side clock counter based on a count value of the transmission-side clock counter included in the data received by the reception unit; A receiving clock counter that constantly counts a clock at a predetermined cycle; a receiving count storage unit that stores a count value of the receiving clock counter when data is received from the communication network by the receiving unit; Adding means for adding the difference information of the transmission clock included in the data received by the above and the count value at the previous data reception stored in the reception count value storage means, Sum and
Jitter detecting means for detecting a difference between the count value of the receiving clock counter when data is received this time and detecting jitter, and discarding means for discarding received data according to the amount of jitter detected by the jitter detecting means Are provided.

According to a fifth aspect of the present invention, there is provided the asynchronous information communication system according to any one of the third and fourth aspects, wherein the receiving side clock counter for clock recovery provided in the receiving station is provided for jitter detection. It is characterized by being shared as a counter for

According to a sixth aspect of the present invention, in the asynchronous information communication system according to the second or fourth aspect, the discarding means is set in advance to a value of the jitter detected by the jitter detecting means. A comparison means for comparing the received data with a predetermined allowable value; and a received data discarding means for discarding received data when the value of the jitter exceeds the allowable value as a result of the comparison by the comparing means.

In the above invention, in the case of an asynchronous information communication system in which the same or phase-synchronized clock is provided from the communication network to the transmitting station and the receiving station, the transmitting station uses the clock counter for counting the clock from the communication network. In other words, prepare a transmission clock counter that is incremented or decremented by the transmission clock, and when transmitting data from the transmitting station, calculate the difference of the transmission clock counter value from the previous data transmission and add that information to the data And send.

On the other hand, the receiving station prepares a receiving clock counter which is incremented or decremented by the clock from the communication network, and calculates the difference between the transmission clock counter value included in the data received from the communication network and the reception data at the time of the previous data reception. Addition of the count value of the clock counter to obtain the sum of each other, and calculating the difference between the sum value and the value of the receive clock counter at the time of data reception this time, the amount of jitter when data is transmitted over the communication network. Is detected. Then, the detected jitter amount is compared with a preset allowable jitter value, and when the detected jitter amount exceeds the allowable jitter value, the data is discarded.

When the transmitting station and the receiving station communicate from the communication network without detecting the same or phase-synchronized clocks, it is necessary to generate a reference clock at the transmitting station and reproduce it at the receiving station.

In this case, the transmitting station counts the transmission clock counter based on the clock generated from its own clock generation source, and when transmitting data, calculates the difference between the transmission clock counter value and the previous transmission data counter value. After the calculation, the difference data and the value of the clock generated from the clock generation source are added to the data at a constant or less than a predetermined interval and transmitted.

When the receiving station receives the data transmitted from the transmitting station, the receiving station reproduces the clock controlling the transmitting clock counter from the count value of the transmitting clock counter included in the data, and receives the received clock with the reproduced clock. Count clock counter. Then, the difference data of the transmission clock included in the data received from the communication network and the reception clock counter value at the time of the previous data reception are added to obtain a mutual sum, and the sum and the reception clock counter value at the time of the current data reception are obtained. The jitter is detected by calculating the difference between

Then, the detected jitter value is compared with a preset allowable jitter value, and when the detected jitter value exceeds the allowable value, the data is discarded.

Therefore, the amount of jitter can be detected in real time even in a communication network in which periodic transmission frames are not synchronized in the entire network such as an AT @ communication network. Then, when data such as audio and video is transmitted from the transmitting station to the receiving station using such a communication network, the receiving station detects the amount of jitter.
By discarding data when the amount of jitter exceeds a certain limit, deterioration of communication quality can be prevented.

[0024]

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

FIG. 1 is a diagram showing a configuration of a first embodiment of an asynchronous information communication system of the present invention, FIG. 2 is a diagram showing a configuration of a transmission preparation function unit of a transmitting station of the asynchronous information communication system,
FIG. 3 is a diagram showing a configuration of a jitter detection / abnormal data discarding function unit of the receiving station of the asynchronous information communication system, and FIG. 4 is a diagram showing a layer function model.

In FIG. 1, reference numeral 1 denotes an ATM communication network (network). A transmitting station 2 and a receiving station 3 are connected to the ATM communication network 1. The transmitting station 2 has a transmission preparation function unit 21 for processing data before transmission, and a transmission function unit 22 for transmitting the processed transmission data to the ATM communication network 1 as a packet. The receiving station 3 is an ATM
A packet is received from the communication network 1 and the ATM communication network 1
Reference clock (reference CLK) supplied from
) The receiving function unit 31 that constantly detects 120, and restores (reproduces) the transmission clock based on the difference information included in the data of the received packet, detects jitter from the transmission clock, and uses unnecessary received data (abnormal data) And a jitter detection / abnormal data discarding function unit 32 for discarding the data. The means for realizing the transmission function unit 22 and the reception function unit 31 may be hardware or software. In this embodiment, the means is realized by application software (hereinafter, referred to as an application).

As shown in FIG. 2, the transmission preparation function unit 21 of the transmission station 2 comprises a counter 110, registers 130 and 14,
0, a subtractor 115, and the like, which calculates the difference between the count values of the transmission clocks and adds the difference information to the transmission data. Register 13 as transmission count value storage means
The counter 11 at the time when the immediately preceding data was transmitted is set to 0.
A count value of 0 is stored. The difference between the value of the register 130 for the previous time and the clock count value for the current time (the count value of the counter 110) is stored in the register 140.
After the calculation by step 15, the difference data is stored. Thereafter, the difference data is added to the transmission data and transmitted from the transmission function unit 22 as a packet. The transmission of the difference data is not necessarily performed every data transmission, and the difference may be calculated and transmitted at intervals of a certain time or less.

As shown in FIG. 3, the jitter detecting / abnormal data discarding function unit 33 of the receiving station 3 includes a buffer 280 for storing packets received by the receiving function unit 31 from the ATM communication network 1, and a receiving function unit 31. , A register 210 for temporarily storing differential data extracted from a specific field of a received packet, a counter 220 for reproducing a received clock for counting the reference clock 120 supplied from the ATM communication network 1, and a counter 2 for receiving a packet.
20, a register 230 for storing the count value of 20, an adder 240 for adding the value of the register 230 and the value of the register 210, and subtracting the count value of the counter 220 and the output of the adder 240 when receiving the next data. Subtractor 250 for detecting the amount of jitter (jitter value 225), a register 270 in which an allowable value of the jitter amount is stored in advance, and the allowable value (b) of this register 270 and the jitter output from the subtractor 250. The comparator 260 compares the value 225 (a) and outputs a control signal (if a ≦ b, outputs an ON signal (ON)) according to the comparison result, and the comparator 26
A gate 290 for outputting received data stored in the buffer 280 to an application according to a control signal from 0
And

Here, the overall operation of the asynchronous information communication system will be described with reference to FIG. FIG. 5 is a diagram showing a layer function model of the ATM communication network 1.

As shown in the figure, the transmitting station 2 converts the data input from the application layer into an L-PD
The data is transmitted on the payload of U. In the ATM communication network 1, the data is further decomposed into fixed-length cells of 53 octets and cell exchange (data exchange) is performed based only on the header value of the fixed-length cells. In the communication network 1, jitter cannot be detected on the receiving side.

On the other hand, a 155.52 MHz common clock is supplied from the ATM communication network 1 to the receiving station 2 and the transmitting station 3, and the receiving station 2 and the transmitting station 3 detect this clock and 19.44MHz, which has been frequency-divided by 8, is used as the reference clock.

The transmission clock counter 110 provided in the transmission station 2 is composed of 32 bits, and is incremented by a clock of 19.44 MHz.
The register 130 is also composed of 32 bits. The storage value (difference data) 140 of the register obtained by subtracting the value of the register 130 from the value of the counter 110 is, for example, $ LP
The specific field 150 is set and written in the trailer section of the DU, and transmitted to the ATM communication network 1. In receiving station 3,
The differential data recorded in the specific field 150 of the data received through the ATM communication network 1 is extracted (extracted). Note that a specific field 150 may be prepared in the payload portion of the L-PDU itself to embed the difference data of the counter 110. At this time, since the transmitting station 2 uses 19.44 MHz as the reference clock, the accuracy of the jitter detection is 1 / (19.44 × 10 ⁶ ) = 5.1 × 10
⁻⁸ [s], and assuming that the field length of the specific field 150 is 8 bits, 1 / (19.44 × 10 ⁶ ) × 256 = 1.3 × 1
0 ^-5 [s], and jitter can be measured (detected) when data is transmitted in a cycle shorter than this value. Assuming that the allowable value of jitter is 10 × 10 ^-6 [s],
Since 10 × 10 ^-6 / 5.1 × 10 ^-8 = 196.1, register 2
OxCO may be set as the value of 70.

When the data transmitted by the application is transmitted at a cycle of 125 μsec,
Since 125 × 10 ⁻⁶ /5.1×10 ⁻⁸ = 2451, the field length may be 12 bits or more.

Hereinafter, a specific operation of the asynchronous information communication system according to the first embodiment will be described. In the case of the asynchronous information communication system, in the transmitting station 2, the reference clock 120 from the ATM communication network 1 is input to the counter 110 and is constantly incremented.

Then, when newly transmitting data, the count value at the time of the immediately preceding data transmission (the value stored in the register 130) is subtracted from the count value of the counter 110 at that time by the subtractor 115, and this subtracter The value (difference data) subtracted in 115 is stored in the register 140, written into the specific field 150 of the transmission data, and transmitted from the transmission function unit 22 to the ATM communication network 1 as a packet. After the data transmission, the count value of the counter 110 at that time is newly written in the register 130. On the other hand, also in the receiving station 3, the reference clock 120 is supplied from the ATM communication network 1, and the counter 220 is constantly incremented. The count value is stored in the register 230 every time data is received.

In the receiving function unit 31 of the receiving station 3, when a packet is received from the ATM communication network 1, the received data (received data) is temporarily stored in the buffer 280.
Then, difference data is extracted from the specific field 150 in the received data and stored in the register 210.

When the data is received, the count value counted by the counter 220 is stored in the register 230.

Then, the adder 240 calculates the sum of the value of the register 230 and the value of the register 210. When the sum of the stored values at the time of receiving the new data is obtained by the adder 240, the difference between the sum value and the count value of the counter 220 is obtained, and the jitter value 255 at the time of receiving the new data is calculated. The amount is detected.

The jitter value 255 is compared with the allowable value of the register 270 by the comparator 260.

As a result of this comparison, for example, when a> b, that is, when the jitter value 255 exceeds the allowable value of the register 270, no on signal is output from the comparator 260, the gate 290 is disabled, and the received data (For one packet) are discarded. When a ≦ b,
That is, when the jitter value 255 is equal to or smaller than the allowable value of the register 270, an ON signal is output from the comparator 260, whereby the gate 290 is enabled,
The received data in the buffer 280 is output to the application through the gate 290.

On the other hand, the data (received data) stored in the buffer 280 is output to the application function via the gate 290 by the control signal from the comparator 260.

As described above, according to the asynchronous information communication system of the first embodiment, in the case of the asynchronous communication system in which periodic transmission frame synchronization is not performed in the entire ATM communication network 1, the transmitting station 2 and the receiving station are used. For example, a transmission clock is generated based on the common reference clock 120 supplied from the ATM communication network 1 to the counter 3 and counted by the counter 110 to calculate a difference between the previous and current data transmission clocks. The difference is added to the transmission data and transmitted to the receiving station 3, while the receiving station 3 transmits the data based on the difference data included in the received data and the reference clock 120 supplied from the ATM communication network 1. The jitter can be detected in real time by reproducing the side clock on the receiving side and calculating the clock difference between the previous time and the current time. As a result, even in the case of asynchronous communication in which periodic transmission frame synchronization is not performed in the entire ATM communication network 1, it is possible to detect jitter, which is a delay variation in data transmission, in real time. In addition, since the detected jitter value is compared with the allowable value and the data is discarded when the jitter value exceeds the allowable value, if the received data is audio data or the like, the discard rate is within a certain range. Abnormal data having a large amount of jitter is not restored, so that deterioration of communication quality can be prevented.

Next, a second embodiment of the asynchronous communication system of the present invention will be described with reference to FIGS. FIG. 5 is a diagram showing a configuration of a second embodiment of the asynchronous communication system of the present invention, FIG. 6 is a diagram showing a configuration of a transmission preparation function unit of a transmitting station of the asynchronous communication system, and FIG. FIG. 3 is a diagram illustrating a configuration of a phase synchronization circuit of a station.
The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

The second embodiment is an example in which a transmitting station and a receiving station connected to a communication network detect jitter and discard abnormal data without using a reference clock of the communication network.

As shown in FIG. 5, the transmitting station 4 of this asynchronous communication system has the same configuration (transmission function unit 22) as in the first embodiment, and also includes clocks in a plurality of different fields of data before transmission. A transmission preparation function unit 23 for writing data for reproduction and an independent clock generation source 24 are provided. The clock generation source 24 is a crystal oscillator or the like.

The receiving station 5 of the asynchronous communication system has the same configuration as that of the first embodiment (the receiving function unit 31).
In addition to the jitter detection / abnormal data discarding function unit 32), a phase synchronization circuit 33 is provided as clock recovery means for recovering the transmission clock on the receiving side.

As shown in FIG. 6, in addition to the configuration of the first embodiment, the transmission preparation function unit 23 stores a count value itself of the counter 110 and stores a second value for adding the count value to the transmission data. A register 170 is provided as transmission count value storage means. As shown in FIG. 7, the phase synchronization circuit 33 of the receiving station 5 includes a register 320 that stores the count value of the transmission clock extracted from the field 160 in the received data, and a clock 370 that is a reference clock of the receiving station 5. And a voltage controlled crystal oscillator (hereinafter referred to as VCXO) 360 for generating
A counter 310 that is incremented by a clock 370 output from 360, a subtractor 330 that subtracts the count value of the counter 310 from the count value stored in the register 320, and calculates a difference between transmission clocks;
Based on the difference signal output from the subtracter 330, V
It comprises a digital filter circuit (Digital Filter) 340 for controlling the clock output of the CXO 360 and a D / A converter (D / A Converter) 350.

That is, the phase synchronization circuit 33 extracts the count value of the transmission clock included in the received data and generates the receiving clock based on the extracted count value. In the case of this embodiment, the count value of the transmission clock included in the data transmitted first via the communication network 1 is loaded into the counter 310 in the phase synchronization circuit 33 and the value of the counter 310 is Initialized. After this initialization, the counter 310 is incremented by the clock 370 input from the VCXO 360.
After the counter 310 is initialized once, the count value of the counter 110 received from the communication network is
The value is temporarily stored in the register 320 instead of 0.

In this case, the value of the clock generated from the clock generation source 24 of the transmitting station 4 at the time of data transmission is counted by the counter 110 of the transmission preparation function unit 23, and the count value is stored in the register 170 at intervals of a predetermined time or less. Is stored. Then, the count value is recorded in a field 160 different from the specific field 150 on the transmission data. As the field 160, for example, the counter 110 is 32 bits, and if the value is to be transmitted as it is, 4 octets may be prepared on the transmission data.

Hereinafter, a specific operation of the asynchronous communication system according to the second embodiment will be described.

In the case of this asynchronous communication system, the transmitting station 4
In this embodiment, the clock generated by the clock source 24 provided in the ATM communication network 1 is input to the counter 110 without using the reference clock 120 of the ATM communication network 1, and the counter 110 is always incremented by the clock. The register 130 stores the count value of the counter 110 at the time of transmission of the data transmitted immediately before.

When newly transmitting data, the count value of the counter 110 at that time is stored in the register 170.
Is stored. Further, the subtractor 115 subtracts the value stored in the register 130 (the count value at the time of the immediately preceding data transmission) from the count value of the counter 110 at this time to obtain the difference between the previous and current transmission clocks. Is stored. It is written in the specific field 150 of the transmission data, and the count value of the transmission clock stored in the register 170 is written in the field 160 different from the specific field 150, and the packet is transmitted from the transmission function unit 22 to the ATM communication network 1. Sent as After the data transmission, the count value of the counter 110 at that time is newly written in the register 130.

On the other hand, in the receiving station 5, when a packet is received from the ATM communication network 1 by the receiving function unit 31, the data (received data) of the received packet is passed to the jitter detection / abnormal data discarding function unit 33. The jitter detection / abnormal data discard function unit 33 temporarily stores the received data in the buffer 28.
Store to 0. Then, difference data is extracted from the specific field 150 in the received data and stored in the register 210.

The count value of the transmission clock is extracted from the field 160 in the received data and is loaded into the counter 310 in the phase synchronization circuit 33 only in the initial state, and thereafter outputted to the register 320 and stored. .

In the initial state, when the count value of the transmission clock is loaded into the counter 310, the counter 31
0 is initialized. After that, the counter 310 becomes VCX
It is incremented by the clock 370 output from O360.

After the initialization, the count value received from the ATM communication network 1 is stored in the register 320, and the difference between this stored value and the count value counted by the counter 310 is calculated and input to the digital filter circuit 340. You. Further, the output of the digital filter circuit 340 is input to a D / A converter (D / A Converter) 350, and becomes a control input of the VCXO 360. With the above circuit, a clock synchronized with the reference clock of the transmitting station is obtained as the output clock 370 of the VCXO 360. As described above, the clock on the receiving side synchronized with the reference clock transmitted by the packet from the transmitting side is V
Obtained as a clock 370 by the CXO 360 and counted by the counter 310.

On the other hand, as in the first embodiment, the jitter detection / abnormal data discarding function unit 33 stores the data in the register 21 when receiving data.
The difference data stored in “0” is extracted, and the jitter value 255 is detected based on the difference data and the count value of the receiving clock counted by the counter 310. Then, the detected jitter value 255 is compared with the allowable value of the register 270 by the comparator 260, and unnecessary data having a large jitter value 255 is discarded by the gate 290.

As described above, according to the asynchronous communication system of the second embodiment, the asynchronous communication system in which the synchronization of the periodic transmission frame is not performed in the entire ATM communication network 1 is performed. When the receiving station 5 performs communication without detecting the reference clock 120 of the ATM communication network 1, a clock generating source 24 is provided in the transmitting station 4, a transmission clock is generated, and this is counted by the counter 110. The difference between the transmission clocks when the data is transmitted is calculated, and the difference data is calculated in the specific field 1 of the transmission data.
50, and the transmission clock count value counted by the counter 110 is recorded in a field 160 different from the specific field 150 of the transmission data and transmitted to the receiving station 5, while the receiving station 5 includes the transmission clock count value in the received data. The difference data and the count value of the transmission clock are extracted, and the clock of the reception side which is substantially synchronized with the clock of the transmission side is reproduced based on the count value of the transmission clock, and is obtained from the clock and the received difference data. By taking the difference from the transmitted clock, jitter, which is a delay variation in data transmission, can be detected in real time.

Also in this case, similarly to the first embodiment, the detected data is compared with the permissible value, and when the jitter value exceeds the permissible value, the data is discarded. In such a case, if the discard rate is within a certain range, abnormal data having a large amount of jitter is not restored, and deterioration of communication quality can be prevented.

Next, a third embodiment of the asynchronous communication system of the present invention will be described with reference to FIG.

The third embodiment of the asynchronous communication system simplifies the configuration of the receiving station of the second embodiment.

That is, in the second embodiment, the jitter detection / abnormal data discarding function unit 32 and the phase synchronization circuit 33 of the receiving station 5 are provided with counters 220 and 310, respectively. The above function is realized by one counter by integrating these two function units (jitter detection / abnormal data discard function unit 32 and phase synchronization circuit 33) into one.

That is, as shown in FIG. 8, registers 210 and 230 for performing jitter detection, an adder 240,
Subtractor 250, counter 310, register 320 for performing phase synchronization detection, digital filter circuit (Degi
tal Filter) 340, D / A Converter (D / A Converte)
r) 350, VCXO 360, and subtractor 330 as in the second embodiment, and a counter 3 for detecting phase synchronization.
By outputting the count value from 10 to the register 230 and outputting the count value from the counter 310 to the subtractor 250, the counter 220 for jitter detection can be omitted.

According to the asynchronous communication system of the third embodiment, the counter 310 for detecting phase synchronization is also used for detecting jitter, so that the counter 310 for detecting jitter provided in the receiving station 5 in the second embodiment is used. The counter 220 can be omitted, and the configuration of the receiving station can be simplified.

In this case, as in the first and second embodiments, the detected jitter value is compared with the allowable value, and when the jitter value exceeds the allowable value, the data is discarded. When the discard rate is within a certain range, abnormal data having a large amount of jitter is not restored, and deterioration of communication quality can be prevented.

[0066]

As described above, according to the present invention, in an asynchronous information communication system in which periodic transmission frame synchronization is not performed in the entire network, the transmitting station and the receiving station are shared by the communication network. The jitter can be detected whether or not the reference clock is supplied.

Since abnormal received data is discarded based on the detected amount of jitter, deterioration of communication quality can be prevented in the case of voice data or the like if the discard rate is within a certain range. Furthermore, since the counter for clock recovery is also used for jitter detection, the configuration of the receiving station can be simplified.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of an asynchronous communication system of the present invention.

FIG. 2 is a diagram showing an example of a configuration of a transmission-side preparation function unit of the transmission station in the asynchronous communication system according to the first embodiment.

FIG. 3 is a diagram showing an example of a configuration of a jitter detection / abnormal data discarding function unit of the receiving station of the asynchronous communication system according to the first embodiment.

FIG. 4 is a diagram showing a layer function model.

FIG. 5 is a diagram showing a second embodiment of the asynchronous communication system of the present invention.

FIG. 6 is a diagram illustrating an example of a configuration of a transmission-side preparation function unit of a receiving station in the asynchronous communication system according to the second embodiment.

FIG. 7 is a diagram showing a configuration of a phase synchronization circuit of a receiving station of the asynchronous communication system according to the second embodiment.

FIG. 8 is a diagram showing a third embodiment of the asynchronous communication system of the present invention.

[Explanation of symbols]

1: ATM communication network, 2, 4: transmitting station, 3, 5: receiving station,
21: transmission preparation function unit, 22: transmission function unit, 31: reception function unit, 32: jitter detection / abnormal data discard function unit, 1
15, 250 ... subtractor, 130, 140, 170, 21
0, 230, 270 ... register, 110, 220, 31
0: counter, 240: adder, 260: comparator, 280: buffer, 340: digital filter circuit, 350: D / A converter, 360: voltage-controlled crystal oscillator (VCXO), 370: clock.

Claims (6)

[Claims] A transmitting station for transmitting data and a receiving station for receiving data from the transmitting station are connected on a communication network;
In an asynchronous information communication system in which the same clock or a synchronous clock is supplied to the transmitting station and the receiving station from the communication network, the transmitting station transmits data on the communication network, and the communication network A transmission-side clock counter that constantly counts a clock supplied from a predetermined period, and a transmission count value storage unit that stores a count value of the transmission-side clock counter when the transmission unit transmits data over the communication network. A difference calculation for calculating a difference between a count value of the transmission side clock counter when new data is transmitted by the transmission means and a count value at the time of previous data transmission stored in the transmission count value storage means. Means for adding difference information of the transmission clock calculated by the difference calculation means to the new transmission data; The receiving station comprises: receiving means for receiving data from the communication network; a receiving clock counter for constantly counting a clock supplied from the communication network at a predetermined cycle; and receiving means for receiving data from the communication network. Receiving count value storing means for storing a count value of the receiving side clock counter when receiving, a difference information of the transmission clock included in data received from the communication network by the receiving means, and the reception count value Adding means for adding the count value of the reception clock at the time of the previous data reception stored in the storage means; and the addition value added by the adding means, and the reception side clock counter when the current data is received. An asynchronous information communication system, comprising: a jitter detecting unit that obtains a difference from a count value and detects jitter. 2. A transmitting station for performing data transmission and a receiving station for receiving data from the transmitting station are connected on a communication network,
In an asynchronous information communication system in which the same clock or a synchronous clock is supplied to the transmitting station and the receiving station from the communication network, the transmitting station transmits data on the communication network, and the communication network A transmission-side clock counter that constantly counts a clock supplied from a predetermined period, and a transmission count value storage unit that stores a count value of the transmission-side clock counter when the transmission unit transmits data over the communication network. A difference calculation for calculating a difference between a count value of the transmission side clock counter when new data is transmitted by the transmission means and a count value at the time of previous data transmission stored in the transmission count value storage means. Means for adding difference information of the transmission clock calculated by the difference calculation means to the new transmission data; The receiving station comprises: receiving means for receiving data from the communication network; a receiving clock counter for constantly counting a clock supplied from the communication network at a predetermined cycle; and receiving means for receiving data from the communication network. Receiving count value storing means for storing a count value of the receiving side clock counter when receiving, a difference information of the transmission clock included in data received from the communication network by the receiving means, and the reception count value Adding means for adding the count value of the reception clock at the time of the previous data reception stored in the storage means; and the addition value added by the adding means, and the reception side clock counter when the current data is received. Jitter detection means for determining a difference from the count value and detecting jitter, and discarding received data according to the amount of jitter detected by the jitter detection means. Asynchronous information communication system, characterized by comprising a discarding means for. 3. A transmitting station for performing data transmission and a receiving station for receiving data from the transmitting station are connected on a communication network,
In an asynchronous information communication system in which the transmitting station and the receiving station communicate without using a synchronous clock of the communication network, the transmitting station generates a clock of a predetermined frequency, and a clock generated by the clock generating source. A transmission-side clock counter that constantly counts the received clock at a predetermined cycle; and a first transmission count value storage unit that stores a count value of the transmission-side clock counter when the transmission unit transmits data over the communication network. A second transmission count value storage unit that stores a count value of the transmission side clock counter when new data is transmitted by the transmission unit; and a second transmission count value storage unit that transmits new data by the transmission unit. The difference between the count value of the transmission side clock counter and the count value at the time of previous data transmission stored in the transmission count value storage means is calculated. Information for adding difference information of the transmission clock calculated by the difference calculation means and the count value of the transmission side clock counter stored by the second transmission count value storage means to the new data An addition unit, wherein the reception station receives data from the communication network, and the transmission side based on a count value of the transmission side clock counter included in the data received by the reception unit. A clock recovery unit for recovering a clock controlling a clock counter; a receiving clock counter for constantly counting a clock recovered by the clock recovery unit at a predetermined cycle; and a receiving unit receiving data from the communication network. Receiving count value storing means for storing the count value of the receiving side clock counter when the Adding means for adding the difference information of the transmission clock included in the received data and the count value at the time of previous data reception stored in the reception count value storage means, and addition performed by the addition means. An asynchronous information communication system comprising: jitter detection means for obtaining a difference between a value and a count value of the reception side clock counter when data is received this time to detect jitter. 4. A transmitting station for performing data transmission and a receiving station for receiving data from the transmitting station are connected on a communication network,
In an asynchronous information communication system in which the transmitting station and the receiving station communicate without using a synchronous clock of the communication network, the transmitting station generates a clock of a predetermined frequency, and a clock generated by the clock generating source. A transmission-side clock counter that constantly counts the received clock at a predetermined cycle; and a first transmission count value storage unit that stores a count value of the transmission-side clock counter when the transmission unit transmits data over the communication network. A second transmission count value storage unit that stores a count value of the transmission side clock counter when new data is transmitted by the transmission unit; and a second transmission count value storage unit that transmits new data by the transmission unit. The difference between the count value of the transmission side clock counter and the count value at the time of previous data transmission stored in the transmission count value storage means is calculated. Information for adding difference information of the transmission clock calculated by the difference calculation means and the count value of the transmission side clock counter stored by the second transmission count value storage means to the new data. An adding unit, wherein the receiving station receives data from the communication network; and the transmitting side, based on a count value of the transmitting side clock counter included in the data received by the receiving unit. A clock recovery unit for recovering a clock controlling the clock counter; a receiving clock counter for constantly counting the clock recovered by the clock recovery unit at a predetermined cycle; and a receiving unit receiving data from the communication network. Receiving count value storing means for storing the count value of the receiving side clock counter when the Adding means for adding the difference information of the transmission clock contained in the received data and the count value at the time of previous data reception stored in the reception count value storage means; and the addition performed by the addition means. Jitter detection means for calculating a difference between the value and the count value of the receiving side clock counter at the time when the data is received this time, and detecting the jitter; and discarding the received data according to the amount of jitter detected by the jitter detection means. An asynchronous information communication system, comprising: 5. The asynchronous information communication system according to claim 3, wherein a receiving-side clock counter for clock recovery provided in the receiving station is shared as a counter for jitter detection. 6. A comparing means for comparing the value of the jitter detected by the jitter detecting means with a predetermined allowable value, wherein the comparison result obtained by the comparing means indicates that the jitter value is acceptable. 5. The asynchronous information communication system according to claim 2, further comprising a received data discarding unit for discarding the received data when the value exceeds the value.