JP2008060658A - Buffer controller and control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a data transfer unit in which delay time of data transfer is minimized without increasing the data discard rate by performing buffer management for setting a minimum buffer length adaptively. <P>SOLUTION: The buffer controller comprises a means for monitoring the amount of data accumulated in a buffer for accumulating and outputting the input data, a timing generation means for generating a period for monitoring the amount of the data accumulated in the buffer, a means for calculating an effective buffer length based on the minimum amount of the data accumulated in the buffer monitored during the above-period, and a means for controlling the buffer based on the effective buffer length calculated by the buffer length calculation means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a buffer control device and a buffer control method.

  In conventional buffer control devices, the buffer is usually provided with a fixed length (fixed size), and a FIFO (First In First Out) method is adopted so that the amount of data in the buffer does not exceed the buffer length (buffer size). Data is being discarded. If the output data capacity is greater than or equal to the input data volume, the data is output with a low delay, but if the output data capacity continues to be smaller than the input data volume, the waiting time until the input data is output from the buffer When (delay time) increases and eventually the amount of data in the buffer reaches the buffer length, overflow, that is, data discard occurs.

  Therefore, as buffer control that operates adaptively according to the buffer and data transfer conditions, for example, real-time control that adaptively controls the buffer length according to the average jitter amount of the video frame interval as disclosed in Patent Document 1. There is buffer control.

  In the buffer control of an apparatus having an encoder, for example, as disclosed in Patent Document 2, the effective size of the buffer is changed together with the transmission bit rate, and the filling level is maintained within the limited range by changing the encoding rate. Then, transmission with a certain delay is performed.

Japanese Patent Laying-Open No. 2005-322995 (pages 5 to 7, FIG. 1) JP-T 8-510628 (pages 25 to 28, FIG. 4)

  In conventional buffer control, when data is transferred, the buffer is controlled so as not to overflow. When the buffer length is fixed, the amount of data in the buffer is large when the input data amount is larger than the output data capacity of the buffer. However, there is a problem in that it is impossible to suppress the delay time of data transfer because it takes a long time from when data is input to the buffer until it is output from the buffer.

  Even when the amount of input data is small relative to the output data capacity, control of intentionally retaining data in the buffer is performed as a countermeasure for jitter, so it is not possible to suppress the delay time of data transfer. There was a problem.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to suppress the data transfer delay time without increasing the data discard rate due to buffer overflow.

  The buffer control device and the buffer control method according to the present invention include a buffer state monitoring means for monitoring the amount of data stored in a buffer for storing and outputting input data, and a data storage amount of the buffer by the buffer state monitoring means. And a buffer for calculating an effective buffer length based on a minimum data storage amount in the data storage amount of the buffer monitored by the buffer state monitoring means during the period generated by the timing generation unit. Length calculating means and buffer control means for controlling the buffer based on the effective buffer length calculated by the buffer length calculating means are provided.

  According to the present invention, the buffer can be controlled with an adaptive effective buffer length corresponding to the buffer state, and the data transfer delay time can be suppressed without increasing the data discard rate due to buffer overflow. There is an effect that can be done.

  The buffer control device according to the present invention monitors the buffer state, that is, the data accumulation amount, and sets the effective buffer length of the buffer in the next period based on the minimum data accumulation amount observed in a certain period. The processing is performed. The effective buffer length indicates a maximum storage allowable amount used for data storage set for each period with a length not exceeding the storage capacity for a buffer having a physically sufficient storage capacity. Hereinafter, “buffer length” in the description refers to this effective buffer length.

  By appropriately setting the buffer length, a data output delay caused by setting a buffer length larger than necessary that is not suitable for the state of data input / output to the buffer is suppressed. Further, when the amount of data stored in the buffer exceeds the buffer length, buffer control is performed to discard a part of the stored data. Hereinafter, buffer control processing according to the buffer control device according to the present invention will be described using input / output data to / from the buffer as moving image data.

Embodiment 1 FIG.
In Embodiment 1 of the present invention, when moving image data (hereinafter referred to as data) is accumulated in the buffer and transfer delay increases, the data is discarded in units of image frames (hereinafter referred to as frames), and at the end of a certain period. A buffer control device that sets the buffer length calculated based on the buffer length and the minimum data accumulation amount in the completed period as the buffer length in the next period will be described.

  FIG. 1 is a block diagram showing an example of a buffer control apparatus according to Embodiment 1 of the present invention. Based on this block diagram, the function of each component will be described.

  In FIG. 1, a buffer state monitoring unit 110 monitors the amount of data stored in a buffer 101 that stores and outputs input data. The buffer state monitoring unit 110 includes a state detection unit 111 that detects the amount of data accumulated in the buffer 101, and a state storage unit 112 that stores the amount of data accumulated in the buffer 101 detected by the state detection unit 111. It consists of and.

  Next, the timing generation unit 121 generates a period during which the buffer state monitoring unit 110 monitors the data accumulation amount of the buffer 101. The accumulated data amount stored in the state storage unit 112 in the buffer state monitoring unit 110 is initialized at the timing at which the timing generation unit 121 is generated, that is, at a period boundary (break).

  Further, the buffer length calculation unit 131 calculates an effective buffer length based on the minimum data accumulation amount in the data accumulation amount of the buffer 101 monitored by the buffer state monitoring unit 110 during the period generated by the timing generation unit 121. .

  Further, the buffer control unit 140 controls the buffer 101 based on the buffer length calculated by the buffer length calculation unit 131. The buffer control unit 140 resets the frame length calculated by the buffer length calculation unit 131 when the frame detection unit 141 detects a frame from the accumulated data of the buffer 101 and enters a new period, and resets the buffer length. When the data storage amount at that time overflows beyond the buffer length or when the data storage amount of the buffer 101 detected by the buffer monitoring unit 110 overflows beyond the buffer length even during the period, the frame detection unit 141 detects The data discarding unit 142 performs control so that a part of the accumulated data is discarded in units of frames and fits in the buffer length. Note that the buffer length is not reset even if it overflows during the period. Further, the buffer control unit 140 sets the buffer length in the buffer 101 so that the buffer 101 controls the data accumulation amount based on the buffer length. However, the buffer control unit 140 performs buffering based on the buffer length. The data storage amount may be controlled with respect to 101.

  In the following, the minimum data accumulation amount in the data accumulation amount of the buffer 101 within the period is the following between the state detection unit 111 and the state storage unit 112 and the buffer length calculation unit 131 in the buffer state monitoring unit 110 in FIG. Shall be managed as follows. The state detection unit 111 detects the amount of data stored in the buffer 101. When the state storage unit 112 is informed of the timing of the period start from the timing generation unit 121, the state storage unit 112 minimizes the data storage amount stored in the buffer 101 at that time, that is, the data storage amount detected by the state detection unit 111. When the data accumulation amount is initialized and the data accumulation amount detected by the state detection unit 111 within the period until the start of the next period falls below the minimum data accumulation amount, the data accumulation amount is reduced to the minimum data accumulation amount. Update and store as As a result, the buffer length calculation unit 131 can calculate the buffer length by obtaining the minimum data accumulation amount stored by the state storage unit 112 within the period.

  Next, the buffer control operation based on the data accumulation amount and the buffer length of the buffer 101 of the buffer control device according to the first embodiment of the present invention will be described. First, an outline of basic buffer control will be described.

  FIG. 2 is an explanatory diagram showing an example of the relationship between the amount of data stored in the buffer and the buffer length of the buffer control device according to the first embodiment of the present invention. The horizontal axis indicates time (time), and the vertical axis indicates the amount of data stored at that time. The period in which the timing generation unit 121 is generated may not be equally spaced, but here it is every time interval T. Hereinafter, based on the start time (n−2) T, (n−1) T, nT, and (n + 1) T of each period, the period (n−2), the period (n−1), the period n, and the period (n + 1) ) To distinguish.

  Here, BufferSize indicates the buffer length of the buffer 101, and BufferSize (n) is the buffer length in the period n calculated by the buffer length calculation unit 131. The buffer length BufferSize (n) is fixed to a constant value during the period n. DataSize indicates the data accumulation amount of the buffer 101, and DataSize (n) is the data accumulation amount that changes at each time of the period n monitored by the buffer state monitoring unit 110. DataSizeMin indicates the minimum data storage amount of the buffer 101, and DataSizeMin (n) is the minimum data storage amount taken by the data storage amount DataSize (n) in the period n monitored by the buffer state monitoring unit 110.

  For example, the buffer length calculation unit 131 sets the buffer length BufferSize (n) in the period n to the buffer length BufferSize (n-1) set in the previous period (n-1) and the end of the period (n-1). It is calculated based on the minimum data accumulation amount DataSizeMin (n-1) at the time (time nT). The minimum data accumulation amount DataSizeMin (n-1) is as indicated by a thick broken line on the lower side of FIG. 2, with the data accumulation amount at the start time (time (n-1) T) of the period (n-1) as an initial value. It changes with time. Formula 1 of the buffer length BufferSize (n) based on the buffer length BufferSize (n-1) and the minimum data accumulation amount DataSizeMin (n-1) is shown in the following formula 1.

  The temporary buffer length tmp calculated first is the size that can be reduced by reducing the buffer length from the buffer length BufferSize (n-1) of the period (n-1) to the minimum data storage amount DataSizeMin (n-1). , A constant K is given a margin for absorbing data fluctuations. This constant K functions to increase the buffer length buffer length BufferSize (n) when an underflow occurs in which the minimum data storage amount DataSizeMin (n−1), which is a size that can be reduced, occurs. It should be noted that the range of the value taken by the buffer length calculated by the buffer length calculation means 131 is set to be not less than the minimum buffer length BufferSizeMIN and not more than the maximum buffer length BufferSizeMAX. The constant K, the minimum buffer length BufferSizeMIN, and the maximum buffer length BufferSizeMAX used in Equation 1 may be set in advance or externally as indicated by the broken line arrow input signal lines shown in the buffer length calculation means 131 of FIG. It may be possible to set from the following.

  When the data accumulation amount DataSize (n) of the buffer 101 at each time in the period n illustrated in FIG. 2 is changed by the calculation method as described above, the buffer length calculation unit 131 sets the buffer length as follows. Calculate. Here, the constant K is 1.

  First, the buffer length BufferSize (n-2) in the period (n-2) is set to 8. The minimum data storage amount DataSizeMin (n-2) of the data storage amount DataSize (n-2) in this period is 0 at time (n-1) T, and the buffer in the next period (n-1). The length BufferSize (n-1) is 9 from (BufferSize (n-2) -DataSizeMin (n-2) + K). Next, the minimum data storage amount DataSizeMin (n-1) of the data storage amount DataSize (n-1) within the period (n-1) is 2.5 at time nT, and the buffer in the next period n The length BufferSize (n) is 7.5. Further, the minimum data storage amount DataSizeMin (n) of the data storage amount DataSize (n) within the period n is 1.5 at time (n + 1) T, and the buffer length BufferSize (n in the next period (n + 1) +1) becomes 7.

  Next, an example of the buffer control processing procedure and its operation in the buffer control device according to the first embodiment will be described based on the flowchart of FIG.

  In FIG. 3, the process surrounded by the broken line frame indicated by A indicates a portion related to data input. In general, the procedure may be configured to input the data that has arrived at the buffer 101 when the input data length is confirmed in advance from a header or the like and no overflow occurs. However, in this procedure, when overflow occurs, the input data cannot be received, and the data is discarded and the buffer 101 is made free by transmitting the stored data and waiting for reception. Therefore, in this data input procedure, the maximum buffer length BufferSizeMAX is set to be smaller than the physical storage capacity of the buffer 101 by, for example, about one frame of data, and a margin for receiving one frame of input data is set. The configuration is such that the input of the frame of data that has already been input to the buffer 101 is completed by discarding the already accumulated data even if it temporarily overflows. This configuration can also be realized by having a secondary buffer for one frame in the preceding stage on the receiving side of the buffer 101. Hereinafter, of the two configuration examples for realizing data input, the latter will be described.

  The buffer 101 determines whether data can be input to the buffer 101 based on the buffer length and the data accumulation amount (step ST101). When data can be input (Yes), the buffer 101 inputs data (step ST102). The buffer state monitoring means 110 confirms the occurrence of overflow due to data input in the buffer 101 (step ST103). When it is confirmed that an overflow has occurred (Yes), the buffer control means 140 discards data from the buffer 101 (step ST104). When it is confirmed in step ST103 that no overflow has occurred due to buffer input (No), data discard (step ST104) is not performed and skipped. Since the data storage amount stored in the buffer in step ST102 or step ST104 changes, the buffer state monitoring unit 110 updates the buffer state (data storage amount) associated with the decrease (step 105).

  On the other hand, when it is not possible to input data in step ST101 (No), neither data input (step ST102) nor data discard (steps ST103 to ST104) is performed, and the buffer status (data storage amount) (Step ST105) is also unnecessary, so these steps are skipped.

  When data is discarded when overflow occurs (step ST104 and step ST112 described later), the data discarding unit 142 in the buffer control unit 140 prioritizes the oldest frame detected by the frame detection unit 141. However, the newest frame may be prioritized. If the oldest frame is in the transmission process and is in an incomplete state, the complete frame scheduled to be transmitted immediately after that may be the target of data discard. Alternatively, if the latest frame is in an accumulation process and is in an incomplete state, a complete frame accumulated before that may be a target of data discard. Furthermore, for example, when discarding a plurality of consecutive frames at a time, if it is not preferable that the discontinuity is large, the accumulated frames may be thinned out at an appropriate interval and discarded to ease the discontinuity. .

  Next, in FIG. 3, processing surrounded by a broken line frame indicated by B indicates a portion related to data output. The buffer 101 determines whether data can be output from the buffer 101 (step ST106). When the data can be output (Yes), the data is output from the buffer 101 (step ST107). Since the amount of data stored in the buffer 101 decreases due to the output of data, the buffer state monitoring unit 110 updates the buffer state (data storage amount) associated with the decrease (step ST108). On the other hand, when data output is not possible in step ST106 (No), data output (step ST107) and buffer state (data accumulation amount) update (step ST108) are not performed, and these steps are skipped. To do.

  Further, in FIG. 3, processing surrounded by a broken line frame indicated by C indicates a part related to calculation and setting of a new buffer length. It is determined whether or not the period (monitoring period) during which the timing generation unit 121 monitors the buffer state (data accumulation amount) by the buffer state monitoring unit 110 has ended (step ST109). When the monitoring period ends (Yes), the buffer status monitoring unit 110 detects the buffer status (step ST110). The buffer length calculating unit 131 calculates the buffer length with reference to the buffer state (data accumulation amount) detected by the buffer state monitoring unit 110 (step ST111). Buffer control means 140 sets the buffer length calculated by buffer length calculation means 131 in buffer 101 (step ST112). At this time, if the buffer state (data storage amount) of the current buffer 101 detected by the buffer state monitoring unit 110 in step ST110 exceeds the set buffer length by setting the buffer length, the stored data is stored. A control for discarding a part and putting it in the buffer length (data discard corresponding to step ST104) is also performed. After the processing from step ST110 to step ST112, the timing generator 121 initializes the monitoring period and enters the next monitoring period (step ST113). On the other hand, when the monitoring period has not expired in step ST109 (No), detection of the buffer status (step ST110), calculation of the buffer length (step ST111), setting of the buffer length (step ST112) and The monitoring period is not initialized (step ST113), and these steps are skipped.

  As described above, buffer control is performed according to the processing procedure including data input, data output, and buffer length calculation and setting in FIG. Further, FIG. 4 shown next is a flowchart for explaining in more detail an example of the operation of the buffer length calculation procedure in step ST111 and the buffer length setting procedure in step ST112 in FIG.

  In FIG. 4, the process enclosed by the broken line frame indicated by D indicates a portion related to the buffer length calculation shown in the above equation 1 performed by the buffer length calculation means 131 corresponding to step ST111 in FIG. 3. First, the buffer length calculation means 131 sets the temporary buffer length tmp as a difference between the buffer length BufferSize (n-1) set for the period (n-1) and the minimum data accumulation amount DataSizeMin (n-1). The added value is set (step ST201).

  Next, the temporary buffer length tmp is compared with the maximum buffer length BufferSizeMAX (step ST202). When the temporary buffer length tmp is larger than the maximum buffer length BufferSizeMAX (Yes), the temporary buffer length tmp is updated to the maximum buffer length BufferSizeMAX (step ST203).

  On the other hand, when the temporary buffer length tmp is less than the maximum buffer length BufferSizeMAX (No) in step ST202, the temporary buffer length tmp is compared with the minimum buffer length BufferSizeMIN (step ST204). When the temporary buffer length tmp is less than the minimum buffer length BufferSizeMIN (Yes), the temporary buffer length tmp is updated to the minimum buffer length BufferSizeMIN (step ST205). In step ST204, when the temporary buffer length tmp is equal to or larger than the minimum buffer length BufferSizeMIN (No), the temporary buffer length tmp is skipped in both step ST203 and step ST205 and remains the value calculated in step ST201. And

  Thus, the temporary buffer length tmp takes one of the value as calculated in step ST201, the value updated in step ST203, or the value updated in step ST205, and the buffer size BufferSize ( n) is set (step ST206).

  Next, in FIG. 4, the process enclosed by a broken line frame indicated by E indicates a part related to buffer control performed by the buffer control means 140 corresponding to step ST112 in FIG. 3. First, the buffer control means 140 compares the data accumulation amount DataSize (n), which is the buffer state at the time of processing from step ST201 to step ST206, with the new buffer size BufferSize (n) set in step ST206 ( Step ST207). This data accumulation amount DataSize (n) is an initial value of the data accumulation amount in the period n, and the buffer state at the end of the period (n−1) detected by the buffer state monitoring unit 110 in step ST110 of FIG. (Data accumulation amount). When this data accumulation amount DataSize (n) is larger than the buffer size BufferSize (n) (Yes), the data accumulation amount Cancel is subtracted from the data accumulation amount DataSize (n) to update the corresponding accumulated data portion. (Step ST208). The data accumulation amount Cancel to be discarded from the data accumulation amount DataSize (n) is set here based on the frame unit detected by the frame detection means 141, and the data discarding means 142 discards the corresponding frame. If the data accumulation amount DataSize (n) is equal to or smaller than the buffer size BufferSize (n) in step ST207, step ST208 is skipped and the data accumulation amount DataSize (n) is not updated and is left as it is.

  Then, the data accumulation amount DataSize (n) at this time is set as an initial value of the minimum data accumulation amount DataSizeMin (n) in the buffer state in the next period n (step ST209). Thereafter, when the data storage amount DataSize (n) of the buffer 101 falls below the minimum data storage amount DataSizeMin (n) within the period n, the minimum data storage amount DataSizeMin (n) becomes the data storage amount DataSize (n). Updated.

  With the above procedure, the calculation and setting of the buffer length and the control of the data accumulation amount of the buffer are performed by the buffer control device according to the first embodiment of the present invention.

  Note that if the state storage unit 112 only stores the buffer state within a single period, that is, the data storage amount, the state storage unit 112 may reset the stored data storage amount at the timing of the period indicating the buffer length update. Good. The data accumulation amount stored here may be only the minimum data accumulation amount.

  In the above description, the buffer state used for calculating the buffer length has been described as using the data storage amount stored in a single period. However, the buffer state used in the plurality of periods is used. It doesn't matter. In Embodiment 1 of the present invention, when storing data over a plurality of periods, the buffer length is stored together with the data accumulation amount for each period, and after calculating the buffer length for each period by the above equation 1, It is assumed that the buffer length to be set in the buffer is calculated based on the buffer length during the period. The data accumulation amount for the past period stored here may be only the minimum data accumulation amount.

  For example, when storing and referring to the buffer length and data accumulation amount for the past N periods as the period for calculating the buffer length, each period number corresponds to the buffer length and data accumulation amount for each stored period. In addition, the history may be stored, and the buffer length and the data accumulation amount of the period number that is not referred to may be deleted. When using the buffer length and data accumulation history for the past N periods, for example, the buffer length calculated in a newer period than the buffer length obtained from the buffer length and data accumulation history for each period. An update value of the buffer length reflecting the buffer lengths of a plurality of periods and the history of the data accumulation amount may be obtained by calculating with a weighted average or an arithmetic average that increases the weight. For the past, instead of storing the buffer length and data accumulation amount, only the buffer length history calculated for that single period that is not weighted average or arithmetic average is stored, and multiple periods are stored. Based on the buffer lengths of those single periods, the weighted average or arithmetic average code length may be set in the buffer.

  In this way, the buffer control device according to the first embodiment of the present invention controls the buffer length for each period based on the latest buffer state, thereby adaptively buffering the buffer with the optimal buffer length. It is possible to operate, and it is no longer necessary to set an excessively large buffer length or an excessively small buffer length, the data discard rate is not increased more than necessary, and the data transfer delay time can be suppressed.

  Further, by adding a constant K when calculating the buffer length, it is possible to absorb a temporary increase in the amount of accumulation due to fluctuations in data transfer and to reduce data discard. Further, by adding the constant K, when underflow occurs in the accumulated data in the buffer, the buffer length in the next period can be expanded so that a large amount of data can be retained.

Embodiment 2. FIG.
In Embodiment 2 of the present invention, when moving image data (hereinafter referred to as data) is accumulated in the buffer and transfer delay increases, the data is discarded in units of image frames (hereinafter referred to as frames), and at the end of a certain period. A buffer control device that sets the buffer length calculated based on the maximum data storage amount and the minimum data storage amount of the data storage amount during the ended period as the buffer length of the next period will be described. The second embodiment of the present invention differs from the first embodiment of the present invention in the part relating to the calculation of the buffer length, and other basic functions and operations are the same as the functions and operations of the first embodiment of the present invention. It is the same. In the following, a method for calculating the buffer length in the second embodiment of the present invention will be described in particular.

  A block configuration diagram showing an example of a buffer control apparatus according to Embodiment 2 of the present invention, and an example of a detailed internal configuration of buffer state monitoring means 110, are shown in Embodiment 1 of the present invention with reference to FIG. It can be explained in the same way. Therefore, descriptions of the buffer status monitoring unit 110, the timing generation unit 121, the buffer length calculation unit 131, and the buffer control unit 140 are omitted. However, in the buffer control device according to the second embodiment of the present invention, the maximum data accumulation in addition to the minimum data accumulation amount in the data accumulation amount of the buffer 101 required in the buffer control device according to the first embodiment of the present invention. The amount is also necessary for calculating the buffer length.

  When an overflow occurs during the monitoring period of the data storage amount of the buffer 101, the maximum data storage amount used in the buffer length calculation by the buffer length calculation means 131 is handled as the buffer length. When the overflow occurs, the state detection unit 111 may notify the state storage unit 112 of the accumulated data amount exceeding the buffer length of the buffer 101 or store it as the buffer length, or the state storage unit 112 may store the state. When the detection unit 111 notifies the data accumulation amount exceeding the buffer length, it may be stored as the buffer length, and the buffer length calculation unit 131 uses the buffer length at that time as the maximum data accumulation amount. Further, the state detection unit 111 detects the data accumulation amount exceeding the buffer length, the state storage unit 112 stores the data accumulation amount, and the buffer length calculation unit 131 stores the data exceeding the buffer length stored in the state storage unit 112. When the accumulated amount is detected, the buffer length at that time may be used for calculating a new buffer length.

  Hereinafter, the maximum data storage amount and the minimum data storage amount in the data storage amount of the buffer 101 within the period are the values of the state detection unit 111, the state storage unit 112, and the buffer length calculation unit 131 inside the buffer state monitoring unit 110 in FIG. It shall be managed as follows. The state detection unit 111 detects the amount of data stored in the buffer 101. When the state storage unit 112 is informed of the timing of the period start from the timing generation unit 121, the state storage unit 112 maximizes the data storage amount stored in the buffer 101 at that time, that is, the data storage amount detected by the state detection unit 111. When the data storage amount and the minimum data storage amount are initialized, and the data storage amount detected by the state detection unit 111 within the period up to the start timing of the next period exceeds the maximum data storage amount, the data storage amount Is updated and stored as the maximum data accumulation amount, and when the data accumulation amount detected by the state detection means 111 falls below the minimum data accumulation amount, the data accumulation amount is updated and stored as the minimum data accumulation amount. As a result, the buffer length calculation unit 131 can calculate the buffer length by obtaining the maximum data accumulation amount and the minimum data accumulation amount stored by the state storage unit 112 within the period.

  Next, the buffer control operation based on the data accumulation amount and the buffer length of the buffer 101 of the buffer control device according to the second embodiment of the present invention will be described. First, an outline of basic buffer control will be described.

  FIG. 5 is an explanatory diagram showing an example of the relationship between the amount of data stored in the buffer and the buffer length of the buffer control device according to the second embodiment of the present invention. Here, the buffer length BufferSize, the data accumulation amount DataSize, and the minimum data accumulation amount DataSizeMin are as described in the first embodiment of the present invention. DataSizeMax indicates the maximum data storage amount of the buffer 101, and DataSizeMax (n) is the maximum data storage amount taken by the data storage amount DataSize (n) in the period n monitored by the buffer state monitoring unit 110.

  For example, the buffer length calculation unit 131 sets the buffer length BufferSize (n) in the period n to the minimum data accumulation amount DataSizeMin (n-1) and the maximum data at the end time (time nT) of the previous period (n-1). Calculation is based on the accumulation amount DataSizeMax (n-1). The maximum data accumulation amount DataSizeMax (n-1) is equal to the start time (time (n-1) T of the period (n-1), similarly to the minimum data accumulation amount DataSizeMin (n-1) described in FIG. ) With the initial value of the data storage amount of), and changes with time as indicated by a thick broken line on the upper side of FIG. The formula of the buffer length BufferSize (n) based on the minimum data accumulation amount DataSizeMin (n-1) and the maximum data accumulation amount DataSizeMax (n-1) is shown in the following equation 2.

  The temporary buffer length tmp calculated first is the data of the maximum data accumulation amount DataSizeMax (n-1) and the minimum data accumulation amount DataSizeMin (n-1) from the buffer length BufferSize (n-1) of the period (n-1). The difference corresponding to the accumulated amount is set to a reducible size of the buffer length, and a constant K is given a margin for absorbing data fluctuations. It should be noted that the range of the value taken by the buffer length calculated by the buffer length calculation means 131 is set to be not less than the minimum buffer length BufferSizeMIN and not more than the maximum buffer length BufferSizeMAX. The constant K, the minimum buffer length BufferSizeMIN, and the maximum buffer length BufferSizeMAX used in Equation 2 may be set in advance or externally as indicated by the broken arrow input signal lines shown in the buffer length calculation means 131 of FIG. It may be possible to set from the following.

  When the data accumulation amount DataSize (n) of the buffer 101 at each time in the period n illustrated in FIG. 5 is changed by the calculation method as described above, the buffer length calculation unit 131 sets the buffer length as follows. Calculate. Here, the constant K is 1.

  First, the buffer length BufferSize (n-2) in the period (n-2) is set to 8. The maximum data storage amount DataSizeMax (n-2) and the minimum data storage amount DataSizeMin (n-2) of the data storage amount DataSize (n-2) in this period are 6 and 0 at time (n-1) T, respectively. The buffer length BufferSize (n−1) in the next period (n−1) is 7 from (DataSizeMax (n−2) −DataSizeMin (n−2) + K). Next, the maximum data storage amount DataSizeMax (n-1) and the minimum data storage amount DataSizeMin (n-1) of the data storage amount DataSize (n-1) within the period (n-1) are each 6. 5 and 2.5, and the buffer length BufferSize (n) in the next period n is 5. Further, the maximum data storage amount DataSizeMax (n) and the minimum data storage amount DataSizeMin (n) of the data storage amount DataSize (n) within the period n are 4.5 and 1.5 at time (n + 1) T, respectively. Thus, the buffer length BufferSize (n + 1) in the next period (n + 1) is 4.

  Next, an example of the buffer control processing procedure and its operation in the buffer control device according to the second embodiment is shown in the flowchart of FIG. 3 showing the buffer control processing procedure and its operation in the buffer control device according to the first embodiment. FIG. 6 shown next is an example of the operation of the buffer length calculation procedure in step ST111 and the buffer length setting procedure in step ST112 in FIG. 10 is a flowchart for explaining the buffer control device according to the second embodiment in more detail.

  In FIG. 6, the process enclosed by a broken line frame indicated by F indicates a portion related to the buffer length calculation shown in the above equation 2 performed by the buffer length calculation means 131 corresponding to step ST111 in FIG. 3. Further, the process surrounded by a broken line frame indicated by G indicates a part related to buffer control performed by the buffer control means 140 corresponding to step ST112 in FIG.

  First, the buffer length calculation unit 131 sets the temporary buffer length tmp to a difference between the maximum data accumulation amount DataSizeMax (n-1) and the minimum data accumulation amount DataSizeMin (n-1) taken in the period (n-1). A value obtained by adding K (step ST301). Since steps ST302 to ST308 perform the same processing as steps ST202 to ST208 in the flowchart of FIG. 4, their descriptions are omitted.

  Then, after the buffer length is calculated (steps ST301 to ST306) and the buffer control is performed (steps ST307 to ST308), the data storage amount DataSize (n) at this time is set to the maximum data in the buffer state in the next period n. Set as initial values of the accumulation amount DataSizeMAX (n) and the minimum data accumulation amount DataSizeMin (n) (steps ST309 and ST310). After this, if the data storage amount DataSize (n) of the buffer 101 exceeds the maximum data storage amount DataSizeMax (n) within the period n, the maximum data storage amount DataSizeMax (n) becomes the data storage amount DataSize (n). When it is updated and falls below the minimum data storage amount DataSizeMin (n), the minimum data storage amount DataSizeMin (n) is updated to the data storage amount DataSize (n).

  By the above procedure, the calculation and setting of the buffer length and the control of the data accumulation amount of the buffer are performed by the buffer control device according to the second embodiment of the present invention.

  In the buffer control apparatus according to the second embodiment of the present invention as well, the buffer length calculation means 131 is within the single period stored in the state storage means 112, as described in the first embodiment of the present invention. Even if the buffer length is calculated based on the buffer state, or based on the buffer length calculated from the buffer state of each period reflecting the history of the buffer state over a plurality of periods (N periods) stored in the state storage unit 112. The buffer length to be set may be calculated.

  Thus, the buffer control device according to the second embodiment of the present invention can obtain the same effects as the buffer control device according to the first embodiment of the present invention.

  In addition, the buffer control device according to the second embodiment of the present invention calculates the buffer length based on the difference between the maximum data accumulation amount and the minimum data accumulation amount, and in particular, based on the difference between the buffer length and the minimum data accumulation amount. Since the buffer length is calculated to be smaller than that of the buffer control device according to the first embodiment of the present invention that calculates the buffer length, the delay time of data transfer can be further suppressed.

  In the process from the monitoring of the data accumulation amount of the buffer 101 to the calculation of the buffer length of the buffer length calculation unit 131, the buffer control device according to the first embodiment of the present invention stores the state storage inside the buffer state monitoring unit 110. The means 112 stores the data after determining that the data storage amount of the buffer 101 detected by the state detection means 111 is the minimum data storage amount, and the buffer length calculation means 131 stores the minimum data storage stored by the state storage means 112. An example of calculating the buffer length based on the amount has been described. Further, in the buffer control device according to the second embodiment of the present invention, the state storage unit 112 inside the buffer state monitoring unit 110 is configured such that the data storage amount of the buffer 101 detected by the state detection unit 111 is the maximum data storage amount or the minimum data storage amount. The buffer length calculation unit 131 determines the buffer amount based on the maximum data storage amount and the minimum data storage amount stored by the state storage unit 112 after determining that it is the storage amount. .

  Therefore, here, a description will be given of a modified example in which the means for determining that this data accumulation amount is the minimum data accumulation amount or the timing is different. The maximum data storage amount required in the buffer control device according to the second embodiment of the present invention can be obtained by performing the maximum determination at the same location as in the minimum determination of the minimum data storage amount. A mode in which only the minimum data accumulation amount of the buffer control device according to the first embodiment is determined and stored will be described.

  In the first modified example, the state storage unit 112 sequentially stores the data accumulation amount of the buffer 101 detected by the state detection unit 111 while maintaining the configuration of the block configuration diagram illustrated in FIG. In this embodiment, the minimum data accumulation amount is selected from the data accumulation amounts stored in the state storage unit 112 at the length calculation stage.

  In this form, the state detection unit 111 detects the amount of data stored in the buffer 101. When the state storage unit 112 is informed of the timing of the period start from the timing generation unit 121, the state storage unit 112 initializes the data storage amount stored at that time and sequentially stores the data storage amount detected by the state detection unit 111. To do. The buffer length calculation means 131 is obtained by selecting the minimum data accumulation amount from the data accumulation amounts stored by the state storage means 112 within the period, and can calculate the buffer length. The minimum data accumulation amount may be selected by either the state storage unit 112 or the buffer length calculation unit 131, but selected from the data accumulation amount stored in the state storage unit 112 at the buffer length calculation stage. To do.

  Further, the second modification is configured as shown in the block configuration diagram of FIG. 7 so that the state detection unit 111 determines whether the data storage amount of the buffer 101 detected by the state detection unit 111 is the minimum data storage amount. Is determined and stored in the state storage unit 112.

  In this form, when the state storage unit 112 is informed of the timing of the period start from the timing generation unit 121, the amount of data stored in the buffer 101 at that time, that is, the data detected by the state detection unit 111 Initialize the accumulation amount as the minimum data accumulation amount. The state detection unit 111 detects the data accumulation amount accumulated in the buffer 101, and updates the data accumulation amount as the minimum data accumulation amount when the data accumulation amount falls below the minimum data accumulation amount stored in the state storage unit 112. And stored in the state storage means 112. As a result, the buffer length calculation unit 131 can calculate the buffer length by obtaining the minimum data accumulation amount stored by the state storage unit 112 within the period.

  In the embodiments of the present invention described so far, the example in which data is discarded in units of frames has been shown. However, data may be discarded in units other than frames. In other words, instead of a frame that is a unit to be detected by the frame detection unit 131, a data unit such as a byte or a word, a transmission unit such as a packet, or the like may be detected. In selecting the unit to be detected, any unit can be used as long as it can re-synchronize even if the data to be transferred is discarded. With such a configuration change, the unit of the buffer state handled by the state detection unit 112 and the state storage unit 121 is also changed.

  In the embodiment of the present invention, as an example of the buffer state to be monitored, it has been described that data in units of frames is stored as the maximum data accumulation amount or the minimum data accumulation amount. However, the accumulated data accumulation amount is The maximum number of stored frames and the minimum number of stored frames may be managed as the number of stored frames. At this time, the designated unit of the constant K is also the number of frames.

  Note that the data input to the buffer is usually in units of packets (for example, RTP packets), and a frame is formed by gathering all the data having the same time stamp when a plurality of packets arrive. On the other hand, since the data output from the buffer is transferred by TCP and handled in units of bytes, the frame data is not always output at a time. Therefore, in the form in which the data storage amount is managed as the number of frames, the number of frames in a complete state is managed in the buffer without including the frame in the middle of transfer. These data input / output format conversions are assumed to be provided as part of the function of the buffer.

  In the embodiment of the present invention, the constant K added at the time of calculating the code length based on the stored buffer state is not used, for example, the difference between the buffer length and the minimum data accumulation amount as in the above equation 1, or For example, the difference between the maximum data accumulation amount and the minimum data accumulation amount as expressed by the above equation 2 may be substituted by adding a constant rate such as 5% or 10% of the difference. Moreover, it is not limited to a constant rate, and for example, a random value within 10% of the difference may be added and substituted. Alternatively, the difference between the buffer length and the minimum data storage amount or the difference between the maximum data storage amount and the minimum data storage amount may be adjusted by a random size within a certain positive / negative rate.

  In the embodiment of the present invention, buffer control with moving image (video) data as a transfer target has been described. However, audio data and a wide range of other data can be transferred.

  As described above, the buffer control device according to the embodiment of the present invention adaptively operates the buffer with the optimum buffer length by controlling the buffer length for each period based on the latest buffer state. Thus, the buffer length that is too large or too small is not set, the data discard rate is not increased more than necessary, and the data transfer delay time can be suppressed.

  In addition, the buffer control device according to the embodiment of the present invention can add a constant K when calculating the buffer length to absorb a temporary increase in the amount of accumulation due to fluctuations in data transfer and reduce data discard. it can. Further, by adding the constant K, when underflow occurs in the accumulated data in the buffer, the buffer length in the next period can be expanded so that a large amount of data can be retained.

  The buffer control device according to the embodiment of the present invention calculates the buffer length based on the difference between the maximum data accumulation amount and the minimum data accumulation amount in the buffer control device according to the second embodiment of the present invention. Since the buffer length is calculated to be smaller than the buffer length based on the difference between the buffer length and the minimum data accumulation amount in the buffer control device according to the first embodiment of the invention, the data transfer delay time is further suppressed. Can do.

It is a block block diagram which shows an example of the buffer control apparatus which concerns on Embodiment 1 of this invention and Embodiment 2 of this invention. It is explanatory drawing which shows an example of the relationship between the data accumulation amount to the buffer of the buffer control apparatus which concerns on Embodiment 1 of this invention, and buffer length. It is a flowchart which shows an example of the buffer control processing procedure of the buffer control apparatus which concerns on Embodiment 1 of this invention. It is a flowchart which shows an example of the buffer length calculation processing procedure of the buffer control apparatus which concerns on Embodiment 1 of this invention. It is explanatory drawing which shows an example of the relationship between the data accumulation amount to the buffer of the buffer control apparatus concerning Embodiment 2 of this invention, and buffer length. It is a flowchart which shows an example of the buffer length calculation processing procedure of the buffer control apparatus which concerns on Embodiment 2 of this invention. It is a block block diagram which shows an example of the buffer control apparatus which concerns on Embodiment 1 of this invention and Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Buffer 110 Buffer state monitoring means 111 State detection means 112 State storage means 121 Timing generation means 131 Buffer length calculation means 140 Buffer length control means 141 Frame detection means 142 Frame discarding means 142

Claims (8)

Buffer status monitoring means for monitoring the amount of data stored in a buffer for storing and outputting input data; and
Timing generating means for generating a period for monitoring the amount of data stored in the buffer by the buffer status monitoring means;
A buffer length calculating unit that calculates an effective buffer length based on a minimum data accumulation amount in the data accumulation amount of the buffer monitored by the buffer state monitoring unit in the period generated by the timing generation unit;
A buffer control device comprising: buffer control means for controlling the buffer based on the effective buffer length calculated by the buffer length calculation means. The buffer control means detects a frame of data stored in the buffer, and discards data stored in the buffer that exceeds the effective buffer length set in the buffer for each detected frame. The buffer control device according to claim 1. The buffer length calculation means is an effective buffer obtained by adding a predetermined number to the difference between the effective buffer length set in the buffer and the minimum data accumulation amount based on the data accumulation amount of the buffer monitored by the buffer status monitoring means. The buffer control device according to claim 1, wherein the length is calculated. The buffer length calculating unit calculates an effective buffer length obtained by adding a predetermined number to a difference between the maximum data storage amount and the minimum data storage amount based on the data storage amount of the buffer monitored by the buffer state monitoring unit. The buffer control device according to claim 1, wherein: A buffer status monitoring step for monitoring the amount of data stored in a buffer that stores and outputs input data; and
A timing generation step for generating a period for monitoring the data accumulation amount of the buffer by the buffer state monitoring step;
A buffer length calculating step for calculating an effective buffer length based on a minimum data accumulation amount in the buffer data accumulation amount monitored by the buffer state monitoring step in the period generated by the timing generation step;
And a buffer control step for controlling the buffer based on the effective buffer length calculated by the buffer length calculation step. The buffer control step detects a frame of data accumulated in the buffer, and discards data accumulated in the buffer exceeding the effective buffer length set in the buffer in units of detected frames. The buffer control method according to claim 5. The buffer length calculation step includes an effective buffer obtained by adding a predetermined number to a difference between an effective buffer length set in the buffer and a minimum data accumulation amount based on the data accumulation amount of the buffer monitored by the buffer state monitoring step. The buffer control method according to claim 5 or 6, wherein the length is calculated. The buffer length calculating step calculates an effective buffer length obtained by adding a predetermined number to a difference between the maximum data accumulation amount and the minimum data accumulation amount based on the data accumulation amount of the buffer monitored by the buffer state monitoring step. The buffer control method according to claim 5, wherein:

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