JP2005348015A - Real time streaming data receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent data missing, frame omission by the data missing and a phenomenon such as sound break while suppressing an increase in a load to a network. <P>SOLUTION: Streaming data 101 transmitted from a server 100 is received by a packet receiving part 205 of a client 200 and sent to a buffer 202. The buffer 202 sequentially stores packets received in a time interval at which the packets are transmitted from a leading area of the buffer in a number order attached to the packets. When the received packets reach an end area of the buffer 202, the received packets are transferred to a streaming data processing part 201. When a missing determining part 206 determines data missing, a retransmission requesting part 204 requests the retransmission of the missing data in accordance with difference among the present time and a predetermined time when data is transmitted from the buffer 202 to the processing part 201 and a retransmission request time, and the server 100 executes retransmission of the missing data. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a real-time streaming data receiving apparatus that receives streaming data such as moving images and music in real time using a network, and relates to a real-time streaming data receiving apparatus that can be used for Internet television, for example.

Various systems for reproducing streaming data such as moving images and music in real time have been proposed.
For example, Patent Document 1 includes a reception unit that receives a real-time signal, a packet analysis unit, an error correction unit, a communication path evaluation unit, a buffer that stores data, a plurality of antennas, an antenna switching unit, A retransmission request control unit that instructs antenna switching based on the channel evaluation result, and generates a retransmission request packet when a packet or block for which retransmission is requested by the retransmission request control unit is selected. Thus, a wireless communication device that transmits to a transmitting device is disclosed.
In the case of the above-mentioned Patent Document 1, it is suppressed as much as possible that real-time transmission is interrupted due to retransmission even if the signal is deteriorated due to the transmission process. To choose the right antenna. Note that the information described in Patent Document 1 does not request retransmission by discarding information on blocks and packets in packets that have already been interrupted in real-time transmission.
Patent Document 2 describes a continuous media stream playback system in which a continuous media stream is received and then played back while adjusting the transmission speed and the playback speed using a circular buffer composed of a plurality of buffers. Has been.
In the apparatus described in Patent Document 2, since the reproduction data rate is adjusted and the data amount of the buffer is manipulated, it is possible to reduce deterioration of reproduction media quality due to instability of the transmission path.
JP 2002-223248 A JP 2002-330180 A

In a protocol such as TCP (Transmission Control Protocol) that guarantees that a client can normally receive a packet, when the data is normally received, the client notifies the server of the data to transmit the data.
On the other hand, in the case of transfer using a protocol that does not guarantee packets, such as UDP (UserDatagramProtocol), in order to cover data loss, the application prepares its own buffer, generates a retransmission request, and re-receives the lost packet. .
However, in real-time transmission, it takes time to accumulate data in the buffer, and when the network environment is bad, retransmission requests frequently occur.
Further, in the transfer using TCP, since the server is notified that the packet has been normally received, the load on the network increases as compared with UDP. In addition, when the network environment is unstable, retransmission requests are frequently generated, and the real-time property is impaired. In general, in the transfer of streaming data using a buffer, the streaming data is not reproduced until the data is accumulated in the buffer, and the user must wait for the reproduction.

In transmission of real-time streaming data, if transmission interruption occurs, frame dropping or sound interruption occurs, so it is desirable to minimize data loss. However, if retransmission requests occur frequently, the network load increases as described above, and real-time performance is impaired.
Therefore, in streaming data transmission where both the sending side and the receiving side have buffers, the retransmission request is controlled according to the state of the buffer on the receiving side, thereby reducing the network load while minimizing data loss. Is desirable.
The present invention has been made in view of the above circumstances, and an object of the present invention is to control a retransmission request according to the state of a buffer on the receiving side in a receiving device for real-time streaming data having a buffer, It is to be able to prevent phenomena such as data loss and resulting frame dropping and sound interruption while suppressing an increase in the load on the network.

In the present invention, the above problem is solved as follows.
(1) In a streaming data receiving apparatus that receives streaming data transmitted from a server via a network in real time, a streaming data transmission / reception unit, a buffer that stores packets received by the transmission / reception unit, A retransmission request unit is provided for making a retransmission request to the server when a packet is lost.
The buffer includes a plurality of areas for storing received packets, and sequentially shifts at a scheduled time interval at which the packets are transmitted, while attaching the received packets or empty data to the packets when the packets are lost. The number is stored in order from the top of the buffer, and when the packet reaches the end of the buffer, the packet is transferred to the streaming data processing unit.
Further, there is provided a scheduled transmission time holding unit for holding a time at which a packet is transmitted to the streaming data processing unit in correspondence with each area of the buffer, and the transmission schedule time holding unit has a packet stored in each area of the buffer or Holds the time when empty data reaches the end of the buffer.
Then, the retransmission request unit checks whether there is empty data outside the predetermined number of packet reception waiting areas from the top of the buffer, and when there is empty data outside the area, the empty data The time held in the transmission time holding unit corresponding to a certain area is compared with the current time, and when the difference is equal to or longer than a predetermined time during which retransmission can be requested, a retransmission request for a packet to be stored in the empty area is issued. Do.
(2) A retransmission request time holding unit is provided corresponding to each area of the buffer, and the retransmission request time holding unit holds the retransmission request time when the retransmission request unit requests retransmission of a packet.
The retransmission request unit makes a packet retransmission request again when the difference between the current time and the retransmission request time is equal to or longer than a predetermined time during which the retransmission request can be made.
(3) In the above (1) and (2), the retransmission request unit determines the predetermined time during which the retransmission can be requested from the packet transmission / reception time.
(4) In the above (1), (2) and (3), means for setting the buffer capacity by the user is provided.

According to the present invention, data loss can be minimized in real-time transfer of various streaming data.
In particular, the following effects can be obtained.
(1) Check whether there is empty data outside the packet reception waiting area for a preset number from the top of the buffer, and if there is empty data outside the area, it corresponds to the area with the empty data When the current time is compared with the time held in the scheduled transmission time holding unit and the retransmission request time holding unit, and the difference is equal to or longer than a predetermined time during which retransmission can be requested, retransmission of the packet to be stored in the empty area Since a request is made, a retransmission request is made in consideration of the possibility of "packets arriving before and after" or "there is no possibility of complementing the packet until data is used even if a retransmission request is sent" It can be carried out. For this reason, retransmission requests can be reduced, and an increase in the amount of use of the network bandwidth can be suppressed.
(2) The network load changes with time. In addition, when a re-transmission request is generated, a phenomenon in which the network bandwidth is further pressed occurs.
In the present invention, the transmission delay time (packet transmission / reception time) of the network is obtained by using the reception of the retransmission request packet, the predetermined time that can be requested for retransmission is determined by the transmission delay time, and the retransmission is performed by using the transmission delay time. Since the request is controlled, even when the network load changes, an efficient retransmission request can be transmitted.
(3) In real-time streaming data transfer having a buffer, dropping frames and increasing delay time occur in principle as the buffer capacity is increased.
In the present invention, since the means for setting the buffer capacity by the user is provided, the user can adjust the data loss and the waiting time when using the buffer according to his / her environment.
For example, in the streaming distribution of a TV image, there are individual differences in how much frame dropping / delaying time can be tolerated, but according to the present invention, the user confirms the image when adjusting the frame dropping and the delay time. And can be adjusted according to the user.

FIG. 1 is a diagram showing the configuration of a streaming data transfer apparatus according to an embodiment of the present invention.
As shown in FIG. 1, the streaming data transfer apparatus according to the present embodiment includes a server 100 connected to a network 300 and a client 200 that receives streaming data transmitted from the server 100 and reproduces it.
Streaming data 101 transmitted from the server 100 is sent to the packet transmission / reception unit 105 and the buffer 102 of the server 100, and is sent from the packet transmission / reception unit 105 to the packet transmission / reception unit 205 of the client 200 via the network 300.
The client 200 that has received the streaming data once sends the streaming data to the buffer 202.
The buffer 202 that has received the data sends the data to the streaming data processing unit 201 (an appropriate processing application for processing the streaming data).
The buffer 202 includes a plurality of areas (hereinafter referred to as packet areas) for storing received data (packets), and sequentially adds received packets to the packets while sequentially shifting the packets at time intervals when the packets are transmitted from the server 100. The data is stored in each packet area in the order of the numbers in order from the top of the buffer. Further, when a packet cannot be received at the transmission time interval and a packet is lost, the packet area becomes empty (here, empty data is stored in this state).
When the received packet reaches the packet area at the end of the buffer 202, the packet stored in the packet area (if the area is empty, remains empty) is transferred to the streaming data processing unit 201. Played.

Further, the buffer 202 is provided with a scheduled transmission time holding unit that holds time corresponding to each packet area of the buffer 202 and a retransmission request time holding unit as will be described later. Then, time information timed by the clock 209 is given to the buffer 202, and a packet or empty data stored in each packet area of the buffer 202 is stored in the end of the buffer 202 in the scheduled transmission time holding unit, as will be described later. The time to reach is held. Here, the “scheduled transmission time” refers to a time at which data is transmitted to the streaming data processing unit 201.
The retransmission request time holding unit holds the retransmission request time when the retransmission request unit 204 requests retransmission of a packet, as will be described later.
The retransmission request unit 204 makes a packet retransmission request according to the difference between the current time, the scheduled transmission time, and the retransmission request time.

The user can change the capacity of the buffer 202 by the buffer capacity control unit 203 via the user input 208. Increasing the capacity of the buffer 202 increases the possibility of supplementing data loss as will be described later, but increases the delay time. The user adjusts the buffer capacity in consideration of frame dropping due to data loss, sound interruption, and the like. Here, the size of the buffer 102 of the server 100 is the maximum size of the buffer 202 of the client 200.
When the missing determination unit 206 determines that the streaming data is missing, the retransmission request unit 204 requests the server 100 to retransmit the missing data according to the state of the data in the buffer 202 as described above. . In the server 100 that receives the request, the retransmission request receiving unit 104 causes the buffer 102 to retransmit the missing data.

FIG. 2 is a diagram showing a configuration of the buffer 202 shown in FIG. Hereinafter, the retransmission request processing by the retransmission request unit 204 of this embodiment will be described with reference to FIGS.
First, the packet transmission / reception unit 105 on the server 100 side and the packet transmission / reception unit 205 on the client side shown in FIG. 1 notify the client 200 of the packet transmission time interval prior to transmission of streaming data.
Each packet transmitted from the server 100 includes a continuous sequence number. For the sequence number, a sequential number is assigned to each packet, and when the value becomes the maximum, the next packet returns to the first number again (for example, the sequence number is “0, 1, 2 ... 104875, 0”). , 1 ").
The client 200 side stores the received packet in the buffer 202. As shown in FIG. 2, the buffer 202 has a plurality of packet areas b1 to bn that hold received packets, and sequentially stores the received packets in the areas b1 to bn.
The packet stored in each packet area is sequentially shifted to the next area at the transmission time interval notified from the server 100, and the packet that reaches the last area bn of the buffer 202 is sent to the streaming data processing unit 201. Is done.

The received packet is stored in each packet area of the buffer 202 in the order of the sequence numbers attached to the packet. However, depending on the state of the network 300, it may be lost without being received at the scheduled transmission interval, or the order of receiving packets may be reversed. When a packet is not received at the scheduled transmission interval, the packet area in which the packet is to be stored becomes empty as indicated by 403 in FIG. For example, when a packet to be stored in the empty packet area is received with a delay, the packet is stored in an empty packet area in which the packet is to be stored. When the packet is lost, the retransmission request unit 204 makes a retransmission request when an empty packet area is in an area in the buffer 202 within a range where retransmission can be requested.
The capacity of the buffer 202 can be arbitrarily changed by the buffer capacity control unit 208 as described above.

Further, as described above, the scheduled transmission time holding unit 202a and the retransmission request time holding unit 202b that hold the scheduled transmission time and the retransmission request time are provided corresponding to each packet area of the buffer 202.
When a packet is received for the first time, a value obtained by adding the current time and the waiting time calculated from the buffer size is set in the scheduled transmission time holding unit 202a. This waiting time is the time from when the received packet is stored in the packet area b1 of the buffer 202 until the data reaches the last packet area bn of the buffer 202 and is sent to the streaming data processing unit 201. It is. Thereafter, a value calculated by [current time] + [time calculated from sequence number and transmission time interval] + [waiting time] is set.
That is, each packet received and held in the packet area of the buffer 202 is sent to the streaming data processing unit 201 at the time held in the scheduled sending time holding unit 202a.

In addition, when the sequence number is not a sequential number as when the packet 402 shown in FIG. 2 is received, when the scheduled transmission time of the packet 402 is set, the scheduled transmission time of the empty packet 403 is set as the scheduled transmission time. Set in the holding unit 202a.
The retransmission request unit 204 checks whether there is empty data outside the predetermined number of “packet reception waiting areas” from the top of the buffer 202 shown in FIG. 2, and when there is empty data outside the area, The current time is compared with the time held in the scheduled transmission time holding unit corresponding to the packet area with the empty data. When the difference is equal to or longer than a predetermined time during which retransmission can be requested (in the “retransmission requestable area” in FIG. 2), a retransmission request for a packet to be stored in the empty packet area is made.
The retransmission request time is held in the retransmission request time holding unit 202b, and the retransmission request unit 204 determines that the difference between the current time and the retransmission request time held in the retransmission request time holding unit 202b is the retransmission request time. When a predetermined time is exceeded, a packet retransmission request is made again.

FIG. 3 is a flow of processing performed by the loss determination unit 206 for each of the packet storage areas b1 to bn of the buffer. The loss determination unit 206 performs the following processing for each packet region of the buffer 202.
(1) It is checked whether the current time is the scheduled transmission time of the packet area of interest (step S1). If the current time is the scheduled transmission time, the packet is transmitted as streaming data to the streaming data processing unit 201 (step S2).
When no packet is stored in the packet area (packet is empty), streaming data is transmitted as an empty packet. In that case, the streaming data is missing.
(2) If the current time is not the scheduled transmission time of the packet area of interest, it is checked whether a packet is stored in the packet area (step S3), and nothing is stored if a packet is stored. do not do. Then, the processing from step S1 is performed for the next packet area.

(3) If the packet region of interest is empty, it is confirmed whether the arrival of the packet is around. As this confirmation, the number of packets whose scheduled transmission time is set later than the packet region of interest is received to check whether X or more packets have been received (step S4). That is, as shown in FIG. 2, the number of packet areas whose scheduled transmission time is set after the packet area of interest is X or more (the packet area of interest is “the packet reception waiting area”). To see if it is “outside”.
If more than a certain number of packets (X or more) have been received, it is determined that the packets may have been lost during transmission.
Here, X can be set to an arbitrary number, and is determined according to variations in packet reception intervals. It is desirable to increase X as the packet reception interval variation increases.
Also, if X or more packets have not been received, there is a possibility that the packet to be stored in the packet area may still be received, so the processing of the packet area is terminated without doing anything, and the next packet For the area, the processing from step S1 is performed.

(4) If more than a certain number of packets (X or more) have been received, next, take the difference between the scheduled transmission time and the current time, and process the streaming data using the packet of interest in the remaining seconds as streaming data See if it must be sent to part 201. That is, it is checked whether [scheduled transmission time]-[current time] is equal to or greater than Y seconds ("predetermined time" shown in FIG. 2) (step S5).
If this time is short, even if a packet re-transmission is requested, the re-transmission request processing is not performed because the transmission time will be exhausted before the packet is received.
That is, if [scheduled transmission time]-[current time] is short, before receiving the packet requested for retransmission, the empty packet area of interest reaches the area bn at the end of the buffer 202, and the retransmission request is made. This is because even if a packet is received, it is not used.
Here, the time corresponding to the Y seconds can be arbitrarily set. However, when the time from the retransmission request to the retransmission is long, it is desirable to increase the value of Y. As will be described later, the time from the retransmission request to the retransmission may be recorded, and Y seconds may be automatically obtained from this time.
If [scheduled transmission time]-[current time] is not equal to or greater than Y seconds, as described above, the processing of the packet region is terminated without doing anything, and the processing from step S1 is performed on the next packet region. Do.

(5) Finally, it is checked whether the packet area has already been requested for retransmission. If a re-transmission request has already been made, the difference between the re-transmission request time and the current time is taken to check whether it is Y seconds or longer (step S6).
If it is a packet area where a retransmission request has already been made and the difference between the retransmission request time and the current time is not more than Y seconds, the processing of the packet area is terminated without doing anything as described above, and the next The process from step S1 is performed on the packet area.
On the other hand, when there is no retransmission request time, a retransmission request is made. If the difference between the retransmission request time and the current time is equal to or greater than Y seconds, it is determined that a packet that has been retransmitted and retransmitted has been lost, and a retransmission request is made again.

The retransmission request unit performs the following processing.
(1) When a retransmission request is made, the retransmission request unit 204 first writes the current time in the retransmission request time holding unit 202b of the packet area in the buffer 202.
(2) A retransmission request is transmitted to the network 300 through the packet transmission / reception unit 205.
(3) The packet transmitting / receiving unit 105 on the server 100 side that has received the retransmission request determines that the received packet is a retransmission request, and sends the retransmission request to the retransmission request receiving unit 104.
(4) The retransmission request receiving unit 104 notifies the buffer 102 of the packet requested for retransmission. (5) The buffer 102 transmits the packet requested for retransmission to the network 300 through the packet transmitting / receiving unit 105.
(6) On the client 200 side, the packet is received by a normal procedure, and the packet is stored in the corresponding packet area of the buffer 202.

Next, setting of X parameters that define the “packet reception waiting area” and Y seconds that are a parameter that defines the “retransmission request possible time” will be described.
The retransmission request unit 204 takes and records the difference between the time when the packet for which the retransmission request has been made and the retransmission request time are received. This time is the time required for the packet to reciprocate through the network 300, and the time with an appropriate margin added thereto can be used as the above-mentioned Y seconds. Further, by taking statistics on the time required for the packet to reciprocate, the time variation can be obtained, and the variation / average time can be used as X.
FIG. 4 shows a processing flow for obtaining the time required for the packet to reciprocate.
Arbitrary initial parameters are set in advance, a retransmission request is made, and a retransmission request time is recorded (steps S1-S3). When a packet for which retransmission is requested is received, the time when the packet is received is recorded (steps S4 and S5). Then, the difference between the packet reception time and the retransmission request time is obtained and recorded as a round trip time (step S6).

Further, by recording a plurality of times required for the packet to reciprocate and taking the average / variation, it is possible to avoid an extreme change in parameters.
FIG. 5 shows a process of recording a plurality of times required for a packet to make a round trip as described above and determining X and Y parameters.
As shown in the figure, the processing of FIG. 4 is performed to obtain a plurality of packet round trip times, and the average is calculated (for example, 22.1 ms). Then, Y (for example, 27.1 ms) is obtained by adding a margin (for example, +5 ms) to this average.
Also, a standard deviation of a plurality of packet round-trip times is calculated (for example, 19.5 ms), and x that is [average × x]> [standard deviation] that is x times the average obtained when Y is determined is calculated. Then, a margin (for example, +1) is added and X is determined.
By determining X and Y as described above, it is possible to maintain optimum parameters regarding the retransmission request even in an environment where the line status changes.

By the way, the main point in the present invention is that, in streaming data that is transmitted in real time, a certain delay is added until it is reproduced, and when the lack of data is detected using the time difference, a retransmission request is made. is there.
That is, if the capacity of the buffer 202 is increased, the possibility that the omission can be complemented increases, but the delay time becomes longer.
In addition, since the permissible range for frame dropping differs for each user, the optimum buffer capacity for the user differs for each user. In view of this, a mechanism for reducing frame dropping is provided by the user watching the frame dropout when the omission cannot be complemented and performing an operation to increase the packet area of the buffer 202 when the user wants to reduce the frame dropout. The relationship between missing completion and delay time can be adjusted to any balance of the user.
That is, as shown in FIG. 6, the user views a video (or sound) based on the reproduced streaming data, and recognizes a frame drop. If it is recognized that there are many dropped frames, the buffer capacity control unit 203 increases the buffer capacity.
At this time, the size of X may be changed in accordance with the size of the buffer. If X is increased, even if there is a variation in packet transfer, this variation can be absorbed.

FIG. 7 is a diagram showing a configuration example when the present invention is applied to a system for reproducing content received by a TV receiving device on a personal computer through a network.
As shown in the figure, TV video, audio, etc. are received by a TV receiver 10, and streaming data is generated by a streaming data generator 11. The generated streaming data is transmitted from the streaming data transmission unit 12 having the configuration shown in FIG. 1 to the personal computer 20 via the network 30 such as a wireless LAN.
In the personal computer 20, the streaming data is received by the streaming data receiving unit 21 having the configuration shown in FIG. Then, the streaming data received by the receiving unit 21 is sent to the application 22 that processes the streaming data, and video, audio, and the like are reproduced.
As shown in FIG. 6, the present invention is applied to a system that plays back content received by a TV receiver 10 on a personal computer 20 through a network, thereby reducing “frame drop” and “sound skip” during viewing. Can do.
In addition, as described above, the viewer can adjust the relationship between the missing complement and the delay time by increasing / decreasing the buffer capacity.

It is a figure which shows the structure of the streaming data transfer apparatus of the Example of this invention. It is a figure which shows the structure of the buffer of the Example of this invention. It is a processing flow which a missing judgment part performs. It is a processing flow which calculates | requires the time required for the packet to go back and forth. It is a figure which shows the process which determines the parameter of X and Y from the time which a packet requires for a round trip. It is a figure explaining adjustment of the buffer capacity by a user. It is a figure which shows the structural example at the time of applying this invention to the system which reproduces | regenerates the content received with TV receiving apparatus with a personal computer through a network.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Server 300 Network 101 Streaming data generation part 102 Buffer 104 Retransmission request receiving part 105 Packet transmission / reception part 200 Client 201 Streaming data processing part 202 Buffer 203 Buffer capacity control part 204 Retransmission request part 205 Packet transmission / reception part 206 Missing judgment part 208 User input 209 clock

Claims (5)

A streaming data receiving device for receiving streaming data transmitted from a server connected via a network in real time,
The receiving apparatus includes a streaming data transmission / reception unit, a buffer for storing a packet received by the transmission / reception unit, and a retransmission request unit that makes a retransmission request to the server when a packet is lost,
The buffer includes a plurality of areas for storing received packets, and sequentially shifts at a scheduled time interval at which the packets are transmitted, while attaching the received packets or empty data to the packets when the packets are lost. Stored in order from the top of the buffer in the order of the number, when the packet reaches the end of the buffer, the packet is transferred to the streaming data processing unit,
Corresponding to each area of the buffer, there is provided a scheduled transmission time holding section that holds the time at which the packet is sent from the buffer to the streaming data processing section. The time when the packet or empty data reaches the end of the buffer is held,
The retransmission request unit checks whether there is empty data outside a predetermined number of packet reception waiting areas from the beginning of the buffer, and when there is empty data outside the area, the area where the empty data exists When the difference between the time held in the scheduled transmission time holding unit corresponding to the current time and the current time is equal to or longer than a predetermined time during which retransmission can be requested, a retransmission request for the packet to be stored in the empty area is made. A receiver for receiving real-time streaming data. A retransmission request time holding unit is provided corresponding to each area of the buffer, and the retransmission request time holding unit holds a retransmission request time when the retransmission request unit requests retransmission of a packet,
2. The real-time streaming according to claim 1, wherein the retransmission request unit makes a packet retransmission request again when a difference between a current time and the retransmission request time is equal to or longer than a predetermined time during which the retransmission request is possible. Data receiving device. 3. The real-time streaming data receiving apparatus according to claim 1, wherein the retransmission request unit determines a predetermined time during which retransmission can be requested from a packet transmission / reception time. 4. The apparatus for receiving real-time streaming data according to claim 1, further comprising means for a user to set a capacity of the buffer. Streaming data transmitted from a server connected via the network is received in real time, and the received packet or empty data is lost when the packet is lost while sequentially shifting the time interval at which the packet is transmitted. This is a program for storing a plurality of packets in a buffer having an area for storing a plurality of packets in order of the numbers attached to the packets, and transferring the packets to the streaming data processing unit when the packet reaches the end of the buffer. And
The program calculates a time when a packet or empty data stored in each area reaches the end of the buffer, and holds the time in a scheduled transmission time holding unit provided corresponding to each area of the buffer; ,
Check whether there is empty data outside the predetermined number of packet reception waiting areas from the beginning of the buffer, and when there is empty data in the area, the time held in the scheduled transmission time holding unit in the area And the current time is compared, and if the difference is equal to or longer than a predetermined time that can be requested for retransmission, the computer is caused to execute processing for requesting retransmission of the packet to be stored in the empty area. A real-time streaming data reception program.

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