JP2004289544A - Network connection machine and time stamp processing method using therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a network connection machine capable of properly removing time information with a large error corresponding to an uncertain amount of jitters. <P>SOLUTION: A network connection machine 1B receives a time stamp (PCR) from a network connection machine 1A. A time stamp generation part 13B generates the time stamp (STC). The CPU 11B statistically calculates the jitter amount of the PCR by using difference between the PCR and the STC. The CPU 11B eliminates the PCR with the jitter amount exceeding a predetermined value and generates a correction value for correcting the STC. The time stamp generation part 13B generates the STC corrected based on the correction value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００２６】
【数２】

【００２７】
このようにして得た標準偏差値σの偏差Δｘを横軸、確率をｙとすると、図６に示すような放物線状の確率分布曲線を示す。ステップＳ２にて、偏差Δｘが±２σを越える差分値ｘ（ｉ）を示すＰＣＲを除外する。±２σ以内の範囲は発生確率が９５．４５％以上の範囲であり、±２σを越える範囲の発生確率は、４．５５％未満である。そして、ステップＳ３にて、総サンプル数ｎから除外するデータを差し引いたサンプル数ｍで、新たに平均値を算出する。この平均値Ａｖｇｘ′は、次の数３にて示す（４）式となる。
【００２８】
【数３】

【００２９】
次に、ステップＳ４にて、次の数４にて示す（５）式により、スムージング演算を施して、ＳＴＣの補正値Ｖを生成する。（５）式中、ｋはループゲインであり、１以下の値とする。この（５）式によるスムージング演算により、ジッタの変動に徐々に追従することができ、タイムスタンプ処理動作の急激な変動を回避することができる。
【００３０】
【数４】

【００３１】
ＣＰＵ１１Ｂは、以上のようにして生成した補正値Ｖを用いて、タイムスタンプ発生部１３Ｂにより生成するＳＴＣを調整する。図４に示すように、タイムスタンプ発生部１３Ｂは、ＶＣＸＯ制御パルスカウンタ１３１、ＶＣＸＯ（電圧制御水晶発振器）１３２、分周器１３３、ＳＴＣカウンタ１３４とを備える。補正値Ｖは、ＶＣＸＯ制御パルスカウンタ１３１に入力される。ＶＣＸＯ制御パルスカウンタ１３１は、補正値Ｖに応じて、ＶＣＸＯ１３２の発振を制御するための制御パルスを発生する。
【００３２】
ＶＣＸＯ１３２の発振出力は、分周器１３３に入力されて分周される。分周器１３３の分周出力は、ＳＴＣカウンタ１３４に入力される。ＳＴＣカウンタ１３４は、入力された分周器１３３の分周出力をカウントして、ＳＴＣを生成する。ＳＴＣカウンタ１３４は、時計１２Ｂと同一であってもよい。
【００３３】
なお、本実施形態では、統計的な演算方法として、標準偏差値σを用いたが、σの２乗である分散値を用いてもよい。本発明は以上説明した本実施形態に限定されることなく、本発明の要旨を逸脱しない範囲において種々変更可能である。
【００３４】
【発明の効果】
以上詳細に説明したように、本発明のネットワーク接続機器及びこれに用いるタイムスタンプ処理方法によれば、不確定なジッタ量に対応して誤差の大きい時間情報を的確に除去することができる。よって、複数のネットワーク接続機器を的確に同期させることが可能となる。
【図面の簡単な説明】
【図１】ネットワーク接続機器の使用例を示すブロック図である。
【図２】本発明のネットワーク接続機器の一実施形態を示すブロック図である。
【図３】ネットワーク上を流れるデータを説明するための図である。
【図４】図２中のタイムスタンプ発生部１３Ｂの具体的構成例を示すブロック図である。
【図５】本発明のタイムスタンプ処理方法の一実施形態を説明するためのフローチャートである。
【図６】本発明のタイムスタンプ処理方法を説明するための特性図である。
【符号の説明】
１Ａ，１Ｂ ネットワーク接続機器
２ ネットワーク
１１Ａ，１１Ｂ 中央処理装置（ＣＰＵ）（演算手段，除外手段，補正手段）
１２Ａ，１２Ｂ 時計（カウンタ）
１３Ａ タイムスタンプ発生部
１３Ｂ タイムスタンプ発生部（生成手段）
１４Ａ，１４Ｂ デジタル・シグナル・プロセッサ（ＤＳＰ）
１５Ａ データ送信部
１５Ｂ データ受信部（取り込み手段）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a network connection device used by being connected to a network, and particularly to a network connection device capable of avoiding a problem due to jitter of information flowing on a network when synchronously operating a plurality of network connection devices. And a time stamp processing method used therefor.
[0002]
[Prior art]
For example, when a video conference system is connected to a network at a plurality of different locations to conduct a video conference, network-connected devices have been widely used. When transmitting and receiving video data and audio data for a long time by connecting a plurality of network-connected devices to a network, it is necessary to synchronize the plurality of network-connected devices. If synchronization is not achieved between a plurality of network-connected devices, problems such as interruption of video may occur.
[0003]
Therefore, the network-connected device (transmitting device) that transmits data transmits the first time stamp, and the network-connected device (receiving device) that receives data receives the first time stamp based on the received first time stamp. The progress speed of the second time stamp generated in step (1) is adjusted. Thereby, the transmitting device and the receiving device can be synchronized.
[0004]
A method of synchronizing between a plurality of network connection devices is described in Patent Document 1 as an example. In this type of network connection device, the jitter of information flowing on the network adversely affects synchronization between the network connection devices. Performing jitter removal with a network connection device is described in Patent Document 2. Note that Patent Literature 2 does not describe a specific configuration (method) of jitter removal.
[0005]
[Patent Document 1]
JP-A-9-55754 [Patent Document 2]
JP 2000-92130 A
[Problems to be solved by the invention]
The amount of jitter of information flowing on a network is not constant, and the amount of jitter greatly varies depending on the situation. When operating a plurality of network-connected devices while maintaining synchronization between the plurality of network-connected devices, the operation of the network-connected devices is adversely affected unless time information having a large error due to jitter is accurately removed. The conventional network connection device and the time stamp processing method have a problem that time information having a large error cannot be accurately removed in response to an uncertain jitter amount.
[0007]
The present invention has been made in view of such a problem, and has disclosed a network connection device capable of accurately removing time information having a large error corresponding to an uncertain jitter amount, and a time stamp processing method used therefor. The purpose is to provide.
[0008]
[Means for Solving the Problems]
The present invention has been made to solve the above-mentioned problems of the related art.
(A) In a network connection device used by being connected to a network, a capturing means (15B) for capturing a first time stamp sequentially input via the network, a counter (12B) operating as a clock, Generating means (13B) for generating a second time stamp based on the count value of the counter; and using the difference between the first time stamp and the second time stamp to generate the first time stamp. Calculating means (11B) for statistically calculating the amount of jitter, and excluding, from the sequentially input first time stamps, the first time stamp in which the amount of jitter calculated by the calculating means exceeds a predetermined value. Exclusion means (11B), the first time stamp and the second time stamp not excluded by the exclusion means. By using the pump, to provide a network connection device, characterized by being configured and a correcting means for correcting (11B) of said second time stamp generated by said generating means,
(B) In a time stamp processing method used for a network connection device, a capturing step of capturing a first time stamp sequentially input through the network, and a second time based on a count value of a counter operating as a clock. A generating step of generating a stamp; a calculating step of statistically calculating a jitter amount of the first time stamp using a difference between the first time stamp and the second time stamp; An exclusion step of excluding the first time stamp whose jitter amount calculated in the operation step exceeds a predetermined value, among the first time stamps, and the first time stamp not excluded in the exclusion step. The second time stamp generated in the generation step using the time stamp of There is provided a time stamping method characterized by comprising the step of correcting the time stamp.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a network connection device of the present invention and a time stamp processing method used for the same will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing an example of use of a network connection device, FIG. 2 is a block diagram showing an embodiment of the network connection device of the present invention, FIG. 3 is a diagram for explaining data flowing on a network, and FIG. FIG. 5 is a block diagram showing a specific configuration example of the time stamp generating unit 13B in FIG. 2, FIG. 5 is a flowchart for explaining one embodiment of the time stamp processing method of the present invention, and FIG. FIG. 4 is a characteristic diagram for explaining
[0010]
First, a usage example of a network connection device will be described with reference to FIG. In FIG. 1, network connection devices 1A and 1B are connected to a network 2. A monitor 3A, a speaker 4A, a camera 5A, and a microphone 6A are connected to the network connection device 1A. A monitor 3B, a speaker 4B, a camera 5B, and a microphone 6B are connected to the network connection device 1B. The network connection devices 1A and 1B are codec devices as an example, and both have the same configuration.
[0011]
When the network connection device 1A is used as a transmission device and the network connection device 1B is used as a reception device, video data from the camera 5A and audio data from the microphone 6A are transmitted to the network 2 by the network connection device 1A. The video data and the audio data are received by the network connection device 1B, the video based on the video data is displayed on the monitor 3B, and the audio based on the audio data is reproduced by the speaker 4B. When the network connecting device 1B is used as a transmitting device and the network connecting device 1A is used as a receiving device, the reverse is true.
[0012]
Here, a specific configuration of the network connection devices 1A and 1B will be described with reference to FIG. As described above, the network connection devices 1A and 1B have the same configuration, and both can be a transmission device and a reception device. However, FIG. 2 shows a case where the network connection device 1A is used as a transmission device and the network connection device 1B is used as a reception device for simplification, and the operation as a transmission device and the operation as a reception device will be described respectively. I do.
[0013]
In FIG. 2, the network connection device 1A includes a central processing unit (CPU) 11A, a clock 12A, a time stamp generator 13A, a digital signal processor (DSP) 14A, and a data transmitter 15A. The DSP 14A performs a function as an MPEG encoder or a function as an MPEG decoder under the control of the CPU 11A. Whether the DSP 14A operates as an MPEG encoder or an MPEG decoder can be switched by software (program) built in the CPU 11A. In the network connection device 1A as a transmission device, the DSP 14A operates as an encoder.
[0014]
The clock 12A is, for example, a 32-bit counter that oscillates at 90 kHz. The counter value from the clock 12A is input to the CPU 11A. The CPU 11A controls the time stamp generator 13A to generate a time stamp based on the input counter value. The time stamp generated by the transmitting device is called a PCR (Program Clock Reference). Hereinafter, the time stamp generated by the time stamp generating unit 13A is referred to as PCR.
[0015]
The PCR generated by the time stamp generator 13A is input to the CPU 11A. The network connection device 1A operates based on the PCR. Data from the camera 5A and the microphone 6A, not shown in FIG. 2, are MPEG-encoded by the DSP 14A and input to the CPU 11A as compressed data. The CPU 11A combines the PCR with the compressed video or audio data and supplies the combined data to the data transmission unit 15A. The data transmission unit 15A includes a memory and a transmission driver, and transmits data once stored in the memory to the network 2.
[0016]
On the other hand, the network connection device 1B includes a central processing unit (CPU) 11B, a clock 12B, a time stamp generator 13B, a digital signal processor (DSP) 14B, and a data receiver 15B. The DSP 14B performs a function as an MPEG encoder or a function as an MPEG decoder under the control of the CPU 11B. Whether the DSP 14B operates as an MPEG encoder or an MPEG decoder can be switched by software (program) built in the CPU 11B. In the network connection device 1B as the receiving device, the DSP 14B operates as a decoder.
[0017]
The clock 12B is, for example, a 32-bit counter that oscillates at 90 kHz. The counter value from the clock 12B is input to the CPU 11B. The CPU 11B controls the time stamp generator 13B to generate a time stamp based on the input counter value. The time stamp generated by the receiving device is called STC (System Time Clock). Hereinafter, the time stamp generated by the time stamp generating unit 13B is referred to as STC. The STC generated by the time stamp generator 13B is input to the CPU 11B.
[0018]
The data receiving unit 15B includes a receiving driver and a memory, and the received data once stored in the memory is input to the CPU 11B. The CPU 11B separates the PCR contained in the input data from the video or audio compressed data, and supplies the compressed data to the DSP 14B. The DSP 14B performs MPEG decoding on the input compressed data, and supplies the decoded data to the monitor 3B and the speaker 4B, which are not shown in FIG.
[0019]
Further, the CPU 11B controls the time stamp generating unit 13B based on the PCR so as to adjust the speed of the STC generated by the time stamp generating unit 13B (such as the oscillation frequency of the system clock). The STC generated while adjusting based on the input PCR is input to the CPU 11B. The network connection device 1B operates based on the STC.
[0020]
FIG. 3 shows data flowing on the network 2. Data flowing on the network 2 is a data stream in which D1, D2, D3,... Are one unit of data. Each of the unit data D1, D2, D3... Is a packet group formed by collecting a plurality of pieces of information including PCR.
[0021]
As shown in FIG. 3, the intervals of the unit data are not constant, and the data intervals vary. As described above, the amount of jitter of data flowing on the network 2 is not constant but is uncertain. In the example of FIG. 3, the interval between the unit data D1 and D2 is slightly narrow, and the interval between the unit data D8 and D9 is very wide. The difference between the intervals is called jitter, and the jitter causes an error in the shift of the arrival time of the time information.
[0022]
As a method of removing time information having a very large error, it is considered to exclude the PCR when the absolute value of the error amount exceeds a predetermined value, that is, when the interval is extremely narrow or extremely wide. Can be However, if the PCR is excluded with a simple absolute value, all the PCRs are excluded, and it may be impossible to synchronize the network-connected devices.
[0023]
Therefore, in the present invention, the CPU 11B removes time information having a large error due to jitter by the following procedure. As shown in FIG. 5, in step S1, a standard deviation value σ of jitter is calculated. Specifically, it is based on the following formula.
x (i) = PCR (i) -STC (i) (1)
First, the difference between the PCR input from the network connection device 1A and the STC generated in the network connection device 1B is calculated by equation (1). i is a chronological order.
[0024]
Then, the average value Avgx of x obtained by the equation (1) is calculated by the following equation (2), and the standard deviation value σ is calculated by the following equation (3). . In the equations (2) and (3), n is a predetermined total number of samples, and i is a time series order.
[0025]
(Equation 1)

[0026]
(Equation 2)

[0027]
Assuming that the deviation Δx of the standard deviation σ thus obtained is the horizontal axis and the probability is y, a parabola-shaped probability distribution curve as shown in FIG. 6 is shown. In step S2, the PCR indicating the difference value x (i) in which the deviation Δx exceeds ± 2σ is excluded. The range of occurrence within ± 2σ is a range where the occurrence probability is 95.45% or more, and the range of occurrence exceeding ± 2σ is less than 4.55%. Then, in step S3, an average value is newly calculated with the sample number m obtained by subtracting the data to be excluded from the total sample number n. The average value Avgx 'is expressed by the following equation (4).
[0028]
[Equation 3]

[0029]
Next, in step S4, a smoothing operation is performed by the following equation (5) to generate a STC correction value V. In the equation (5), k is a loop gain, which is set to a value of 1 or less. By the smoothing calculation using the equation (5), it is possible to gradually follow the fluctuation of the jitter, and it is possible to avoid a rapid fluctuation of the time stamp processing operation.
[0030]
(Equation 4)

[0031]
The CPU 11B adjusts the STC generated by the time stamp generator 13B using the correction value V generated as described above. As shown in FIG. 4, the time stamp generating unit 13B includes a VCXO control pulse counter 131, a VCXO (voltage controlled crystal oscillator) 132, a frequency divider 133, and an STC counter 134. The correction value V is input to the VCXO control pulse counter 131. The VCXO control pulse counter 131 generates a control pulse for controlling the oscillation of the VCXO 132 according to the correction value V.
[0032]
The oscillation output of the VCXO 132 is input to the frequency divider 133 and divided. The frequency-divided output of the frequency divider 133 is input to the STC counter 134. The STC counter 134 counts the frequency-divided output of the frequency divider 133 and generates an STC. The STC counter 134 may be the same as the clock 12B.
[0033]
In the present embodiment, the standard deviation value σ is used as a statistical calculation method, but a variance value that is the square of σ may be used. The present invention is not limited to the embodiment described above, and can be variously modified without departing from the gist of the present invention.
[0034]
【The invention's effect】
As described above in detail, according to the network connection device of the present invention and the time stamp processing method used for the same, it is possible to accurately remove time information having a large error corresponding to an uncertain jitter amount. Therefore, it is possible to accurately synchronize a plurality of network connection devices.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a usage example of a network connection device.
FIG. 2 is a block diagram showing one embodiment of a network connection device of the present invention.
FIG. 3 is a diagram for explaining data flowing on a network.
FIG. 4 is a block diagram illustrating a specific configuration example of a time stamp generating unit 13B in FIG. 2;
FIG. 5 is a flowchart illustrating an embodiment of a time stamp processing method according to the present invention.
FIG. 6 is a characteristic diagram for explaining the time stamp processing method of the present invention.
[Explanation of symbols]
1A, 1B Network connection equipment 2 Network 11A, 11B Central processing unit (CPU) (calculation means, exclusion means, correction means)
12A, 12B clock (counter)
13A Time stamp generator 13B Time stamp generator (generation means)
14A, 14B Digital Signal Processor (DSP)
15A Data transmission unit 15B Data reception unit (acquisition means)

Claims (2)

In network connection equipment used by being connected to the network,
Capturing means for capturing a first time stamp sequentially input through the network;
A counter that operates as a clock,
Generating means for generating a second time stamp based on the count value of the counter;
Calculating means for statistically calculating the jitter amount of the first time stamp using a difference between the first time stamp and the second time stamp;
Excluding means for excluding, from the sequentially input first time stamps, the first time stamps whose jitter amount calculated by the calculating means exceeds a predetermined value;
Correction means for correcting the second time stamp generated by the generation means using the first time stamp and the second time stamp not excluded by the exclusion means. Network connection equipment characterized by the above-mentioned. In the time stamp processing method used for the network connection device,
Capturing a first time stamp sequentially input through the network;
A generation step of generating a second time stamp based on a count value of a counter operating as a clock;
A calculating step of statistically calculating a jitter amount of the first time stamp using a difference between the first time stamp and the second time stamp;
An exclusion step of excluding, from the sequentially input first time stamps, the first time stamps whose jitter amount calculated in the calculation step exceeds a predetermined value;
A correcting step of correcting the second time stamp generated in the generating step by using the first time stamp and the second time stamp that are not excluded in the removing step. Time stamp processing method.

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