JPH10313294A - Transmission controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a wait time till start of reproduction and an interruption time of reproduction and to realize reproduction with small interruption in the case of sending real time system data via a transmission line whose transmission quality is lower than that of a wired system transmission line and whose transmission quality is largely changed. SOLUTION: The controller is provided with a delay difference absorbing buffer 26 that buffers prescribed quantity of received data and provides an output of the data at a prescribed bit rate to a host layer device and two re- transmission control means 22, 24. The 1st re-transmission control means 22 makes a retransmission request of a frame to a transmitter side when a transmission error is in existence in the received data and gives the data without transmission error that are received again to the delay difference absorbing buffer 26. The 2nd re-transmission control means 24 monitors a buffering quantity of the data in the delay difference absorbing buffer 26 and gives the data where an error in the payload part is allowed to the delay difference absorbing buffer 26 without making a re-transmission request of a frame having the transmission error when the buffered quantity is smaller than a transition value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission line, such as a radio section, having a transmission quality lower than that of a wired transmission line, for example, a transmission line whose transmission quality greatly changes depending on a positional relationship between a base station and a mobile station. The present invention relates to a transmission control device for transmitting real-time data. Here, the real-time system data is different from ordinary computer data, and is data such as voice, music, and moving images that need to arrive at a receiving upper layer device such as a decoder while satisfying time constraints.

[0002]

2. Description of the Related Art When transmitting real-time data, it is necessary to correct a transmission error caused by an individual frame during transmission on the receiving side and reproduce the original frame or original image as close as possible. Also, when data is reproduced on the receiving side, even if the data is transmitted periodically from the transmitting side, the data does not arrive periodically due to variations in the transmission delay of individual frames due to transmission control. In some cases, there is no data to be reproduced next to the completed data on the receiving side.

When transmitting general data, GBN (Go-Back N), SR (Sequence) are used to correct transmission errors.
request (ARQ: Automat)
icRepeat reQuest) method is used. On the other hand, when transmitting real-time data, in order to absorb the above-described variation in the transmission delay time of each frame,
There is a method of starting reproduction after buffering data arriving at the receiving side in a delay difference absorbing buffer, thereby maintaining a state in which data to be reproduced next always exists at the receiving side.

FIG. 5 shows an example of operation according to the conventional SR-ARQ system. In the figure, 51 indicates a time series of a transmission frame, 52 indicates a time series of a reception frame, 53 indicates a time series of a buffering state of a delay difference absorbing buffer, and 54 indicates a time series of reproduction data. .. Indicate frame numbers, alphabets a, b, c,... Indicate payload data, “x” indicates data in which a transmission error has occurred, and a retransmission request Nak of the frame is transmitted. Will be returned to the side.

Here, the round-trip delay time in the transmission path is set to a constant value Tr, and the transmitting side detects that the frame transmitted at the time Tc-Tr is incorrect at the time Tc when the Nak returned from the receiving side is received. Shall be. In this case, as compared with the case where the round-trip delay time fluctuates, the number of times that frames are transmitted redundantly is reduced, so that the transmission delay time due to retransmission control of each frame is reduced.

The transmitting side transmits real-time data {a, b, c, d,...} From the time T0 by the SR-ARQ scheme. The receiving side starts reproduction from time T9 when buffering of data a, b, c, d, e, and f into the buffer for absorbing delay difference is completed. After time T9, the reproduction is continued while absorbing the transmission delay time difference by using the data buffered in the delay difference absorption buffer.

Although not explicitly shown in FIG. 5, a frame arriving after a retransmission request for frame 6 (data g) in which a transmission error has occurred is temporarily buffered in a retransmission control buffer. When the frame 6 (data g) arrives without transmission error (time T13), the frame 6 (data g) and the previously arrived frame 7 (data h) are buffered in the delay difference absorbing buffer. Is done. The same applies to frame 8 (data i) and thereafter.

[0008]

However, the conventional method using transmission control based on the SR-ARQ scheme has the following problems. Hereinafter, description will be made with reference to FIG. In FIG. 6, reference numeral 61 denotes a time series of a transmission frame, 62 denotes a time series of a reception frame, 63 denotes a time series of a buffering state of a delay difference absorbing buffer, and 64 denotes a time series of reproduced data.

Here, since a transmission error has occurred in frame 1 (data b) and frame 2 (data c), the receiving side requests retransmission of frames 1 and 2, and the retransmitted frame arrives at the receiving side. Reproduction starts at time T11 when the buffering of the data a, b, c, d, e, and f is completed. Thus, in the case of FIG. 6, the data a, b, c,
As compared with the case where no transmission error occurs during buffering of d, e, and f (FIG. 5), the waiting time until the start of reproduction becomes longer. That is, if a transmission error occurs during buffering, the time required for buffering a specified amount of frames increases. When the transmission delay is large, the increase in the buffering time due to the effect of the transmission error becomes even greater.

[0010] Therefore, if the transmission quality is poor, the waiting time until the start of reproduction becomes long. Also, if operations such as fast forward, rewind, and skip are performed during playback on the receiving side, and the order of the playback frames is changed,
The playback interruption time becomes longer. Data a,
The reproduction is started after b, c, d, e, and f are buffered, and while the frame 6 (data g) to be reproduced next is retransmitted a plurality of times as at times T17 to T19. Data in the delay difference absorption buffer may be consumed, and reproduction may be interrupted. If the same frame is retransmitted a plurality of times due to the deterioration of the transmission quality in this way, the transmission delay time of the frame exceeds the reproduction time according to the data amount buffered in the delay difference absorption buffer, Playback is interrupted. As shown at time T23 in FIG. 5, the reproduction may be interrupted even if only one retransmission occurs in the frame 14 (data o).

Conventionally, to solve the above problem, a method of increasing the buffering amount of the delay difference absorbing buffer on the receiving side has been adopted. However, this method increases the buffering time and increases the probability of occurrence of transmission errors during buffering, so that the waiting time until the start of reproduction may be extremely long as described above.

According to the present invention, when transmitting real-time data through a transmission line whose transmission quality is lower than that of a wired transmission line and where the transmission quality changes greatly, there is a waiting time until reproduction starts or interruption of reproduction. It is an object of the present invention to provide a transmission control device capable of shortening the time and realizing reproduction with less interruption.

[0013]

SUMMARY OF THE INVENTION A transmission control apparatus according to the present invention comprises: a buffer for absorbing a delay difference which buffers a fixed amount of received data and outputs the buffered data to an upper layer device at a constant bit rate; Is provided. When there is a transmission error in the received data, the first retransmission control unit requests the transmission side to retransmit the frame, and sends the retransmitted data without transmission error to the delay difference absorbing buffer.

The second retransmission control means monitors the buffering amount of the data in the delay difference absorbing buffer, and if the buffering amount of the delay difference absorbing buffer becomes smaller than the transition value, a transmission error is detected. A request for retransmission of the generated frame is not sent, and data allowing an error in the payload portion is sent to the delay difference absorbing buffer. This makes it possible to shorten the buffering time at the start of reception, secure a buffering amount equal to or greater than the transition value in the delay difference absorption buffer, and supply data at a constant bit rate to the host device on the receiving side. it can.

Further, the transmission control device of the present invention selects the first retransmission control means when the buffering amount of the data in the delay difference absorbing buffer is larger than the transition value, and the buffering amount is smaller than the transition value. If the number is small, a retransmission control method change control means for selecting retransmission control by the second retransmission control means may be provided. Further, the transmission control apparatus of the present invention further comprises means for adding an error correction detection code to a header portion and generating a frame to which an error detection code is added to a payload portion on the transmission side, and wherein the second retransmission control means The header information restored by the error correction detection code added to the header part of the above may be used to send data allowing an error in the payload part to the delay difference absorption buffer.

[0016]

FIG. 1 shows a configuration example of a transmission control device according to the present invention. In the figure, the transmitting side includes a transmitting side retransmission control unit 11, a transmission waiting buffer 12, and a transmitting side retransmission control buffer 13. The receiving side includes retransmission control method change control means 21, reception side retransmission control means A22, reception side retransmission control buffer A23, reception side retransmission control means B24, reception side retransmission control buffer B25, delay difference absorption buffer 2.
6. Here, a solid arrow indicates a data flow, and a broken line indicates a control relationship.

The data sent from the upper layer device on the transmission side is input to the transmission side retransmission control means 11 via the transmission waiting buffer 12 and the transmission side retransmission control buffer 13,
It is framed by the frame configuration as shown in FIG. 2, and is sequentially transmitted to the transmission path. In the frame configuration, an error correction detection code is added to a header part (control bits), and an error detection code is added to a payload part (data). The transmission-side retransmission control unit 11 reads out the frame for which the retransmission request is received from the reception side from the transmission-side retransmission control buffer 13 and performs retransmission.

On the receiving side, the received frame is buffered in the receiving side retransmission control buffer A23 and the receiving side retransmission control buffer B25 via the receiving side retransmission control means A22 and the receiving side retransmission control means B24, respectively. A fixed amount of the data buffered in the reception-side retransmission control buffer A23 and the reception-side retransmission control buffer B25 is buffered in the delay difference absorption buffer 26, and is output to the reception-side upper layer device at a constant bit rate. . When the buffering amount of the data in the delay difference absorption buffer 26 is larger than the transition value, the retransmission control method change control unit 21 selects the retransmission control by the receiving side retransmission control unit A22, and the buffering amount becomes smaller than the transition value. If the number is small, retransmission control by the receiving side retransmission control means B24 is selected.

Here, the retransmission control operation by the receiving side retransmission control unit A22 or the receiving side retransmission control unit B24 will be described with reference to FIG. FIG. 3 shows a frame X (data g), a frame X + 1 (data h), a frame X + 2
(Data i) and a frame X + 3 (Data j) are sequentially received, and the frame X includes an error. Upon detecting an error in the frame X (data g), the receiving-side retransmission control unit A22 controls retransmission of the frame X. Upon detecting an error in the frame X (data g), the receiving side retransmission control means B24 restores the header information by using the error correction code added to the header part, and controls the data g 'having the error in the payload part to the receiving side retransmission control. Buffer in buffer B25.

If the buffering amount of data in the delay difference absorbing buffer 26 is larger than the transition value and the frame X (data g) retransmitted by the transmitting side is received without error by the receiving side, the frame X (Data g) and frames X + 1 (data h) to frame X + 3 (data j) buffered in the receiving-side reproduction control buffer A23
Is sent to the delay difference absorbing buffer 26. As described above, when the buffering amount of the data in the delay difference absorption buffer 26 is large and the data can be continuously supplied to the upper layer device at a constant bit rate, the receiving side retransmission control unit A22 uses the existing SR- Retransmission control equal to ARQ is performed, and error-free transmission can be performed.

On the other hand, if the buffering amount of data in the delay difference absorbing buffer 26 is smaller than the transition value, retransmission control by the receiving-side reproduction control means B24 is selected and buffered in the receiving-side reproduction control buffer B25. Frame X (data g ') containing the error
+1 (data h) to frame X + 3 (data j) are sent to the delay difference absorbing buffer 26. As described above, when the amount of data buffering in the delay difference absorption buffer 26 is small and it becomes impossible to supply data to the upper layer device at a constant bit rate, the error-allowed data is absorbed by the delay difference absorption buffer 26. To the data buffer 26. further,
By prompting the transmission of the next frame without performing retransmission,
The buffering amount of the data in the delay difference absorbing buffer 26 can be recovered, and the data supply at a constant bit rate to the upper layer device can be continued.

FIG. 4 shows an operation example of the transmission control device of the present invention. In the figure, 41 is a time series of a transmission frame, 42
Denotes a time series of the received frame, 43 denotes a time series of the buffering state of the delay difference absorbing buffer, and 44 denotes a time series of the reproduced data. .. Indicate frame numbers, alphabets a, b, c,... Indicate payload data, “x” indicates data in which a transmission error has occurred, and a retransmission request Nak of the frame is transmitted. Will be returned to the side.

Here, the round-trip delay time in the transmission path is set to a constant value Tr, and the transmitting side detects that the frame transmitted at time Tc-Tr is erroneous at time Tc when receiving Nak returned from the receiving side. Shall be. Also,
Even when an error occurs in the frame, the header information is restored by the error correction code added to the header part.

On the receiving side, between the time T2 when the frame 0 (data a) arrives and the time T5, the buffering amount of the data in the delay difference absorbing buffer 26 is equal to or less than the transition value. The retransmission control B is performed by the control means B24. At this time, frame 1 (data b) and frame 2 (data c) receive an error during transmission, but the header information is restored by using the error correction code, the frame number is confirmed, and the error is received in the payload portion while receiving. The data is buffered in the side retransmission control buffer B 25 and sent to the delay difference absorbing buffer 26. In the figure, data in which an error is permitted are indicated as b 'and c'.

As a result, although the reproduced data b 'and c' contain errors, the data a to f are stored in the delay difference absorbing buffer 26.
Can be shortened compared to the case where frames 1 and 2 are retransmitted (FIG. 6). That is, the reproduction can be started from time T9 as in the case of FIG. From time T5 to time T12, the buffering amount of data in the delay difference absorption buffer 26 exceeds the transition value, so that the retransmission control A by the receiving side retransmission control means A22 is performed. At this time, frame 6 (data g)
And frame 8 (data i) suffers an error during transmission,
Nak by the retransmission control is returned to the transmission side, and the data after g is not buffered in the delay difference absorbing buffer 26. However, the data g ', h, i', j are buffered in the receiving side retransmission control buffer B25.

When the buffering amount of the data in the delay difference absorbing buffer 26 becomes equal to or less than the transition value at the time T12, the processing shifts to the retransmission control B by the receiving side retransmission control means B24. At this time, the retransmitted frame 6 (data g) contains an error again, but the retransmission request is not returned and is buffered as data g 'in the receiving side retransmission control buffer B25.
By the retransmission control B, the data g ', h buffered in the reception side retransmission control buffer B25 at the time T13.
Is sent to the delay difference absorbing buffer 26, and the buffering amount in the delay difference absorbing buffer 26 is recovered.

When the buffering amount of the data in the delay difference absorbing buffer 26 exceeds the transition value at time T13, the process returns to the retransmission control A by the receiving side retransmission control means A22. Next, when the buffering amount of the data in the delay difference absorbing buffer 26 becomes equal to or less than the transition value at time T14, the process shifts to retransmission control B by the receiving side retransmission control means B24. At this time, the retransmitted frame 8 (data i) is transmitted to the receiving side retransmission control buffer B2.
5 is buffered as data i. By this retransmission control B, the reception side retransmission control buffer B25 at time T15
Are sent to the delay difference absorption buffer 26, and the delay difference absorption buffer 2
The buffering amount in 6 recovers.

The same applies to the following, except that the frame 14 (data o) retransmitted at time T22 is received without error, but is discarded because it overlaps with the timing at which the error data o 'is reproduced. As described above, when the buffering amount of the data in the delay difference absorbing buffer 26 becomes equal to or less than the transition value, the retransmission control B by the receiving-side reproduction control means B24 is caused to function, and the error-allowed data is transferred to the receiving side. By sending the buffer from the retransmission control buffer B25 to the delay difference absorbing buffer 26, the buffering amount is recovered.
As a result, although the reproduction quality is degraded due to the influence of the data including the transmission error, the state in which the data buffered in the delay difference absorbing buffer 26 is lost and the reproduction is interrupted can be avoided.

In the above description, it is assumed that the system has a known round-trip delay time of the transmission path, and the receiving side returns Nak to request retransmission of a frame transmitted one round-trip delay time earlier. Is shown as an example, on the transmitting side, among the frames not received by the receiving side returned from the receiving side, RN which is the smallest frame number
Even when retransmission is performed based on (Request Number), the transmission control device of the present invention can be used similarly.

[0030]

As described above, when the buffering amount of the delay difference absorbing buffer is small, the transmission control device of the present invention accepts a frame in which a transmission error has been permitted on the receiving side and makes a retransmission request. Dynamically switch to no transmission control. As a result, the buffering amount of the delay difference absorption buffer can be reduced, and real-time data
Even if the transmission is controlled by the method, it is possible to reduce the waiting time until the reproduction starts and the reproduction interruption time due to the buffering of the delay difference absorption buffer.

Further, even if the transmission quality is deteriorated and the transmission delay time of an arbitrary frame is increased due to the effect of retransmission, the buffer for delay difference absorption is suppressed from being emptied. Can be avoided. However, since the data to which the transmission error is allowed is temporarily buffered in the delay difference absorption buffer, a decrease in reproduction quality is inevitable. In that case, the encoding method in which the deterioration of the reproduction quality due to the mixing of errors is relatively small,
What is necessary is just to transmit the compressed real-time data.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of a transmission control device according to the present invention.

FIG. 2 is a diagram showing a configuration of a frame to be transmitted.

FIG. 3 is a diagram illustrating a retransmission control operation in the transmission control device of the present invention.

FIG. 4 is a timing chart showing an operation example of the transmission control device of the present invention.

FIG. 5 is a timing chart showing an operation example according to the conventional SR-ARQ scheme.

FIG. 6 is a timing chart showing an operation example according to a conventional SR-ARQ scheme.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 transmission side retransmission control means 12 transmission wait buffer 13 transmission side retransmission control buffer 21 retransmission control method change control means 22 reception side retransmission control means A 23 reception side retransmission control buffer A 24 reception side retransmission control means B 25 reception side retransmission control buffer B26 Delay difference absorption buffer

Claims (3)

[Claims] 1. A buffer for delay difference absorption that outputs a fixed amount of data to a higher-layer device after buffering a certain amount of received data, and a frame that is transmitted to a transmission side when there is a transmission error in the received data. A first retransmission control unit for performing a retransmission request of the above, and transmitting retransmitted data without transmission errors to the delay difference absorption buffer; and monitoring a buffering amount of data in the delay difference absorption buffer, If the buffering amount of the difference absorption buffer becomes smaller than a certain value (hereinafter referred to as “transition value”), the retransmission request of the frame in which the transmission error has occurred is not performed, and the data allowing the error of the payload portion is transmitted. A second retransmission control unit for transmitting the data to the delay difference absorption buffer. 2. The transmission control device according to claim 1, wherein the first retransmission control unit is selected when a buffering amount of data in the delay difference absorption buffer is larger than a transition value.
A transmission control device comprising retransmission control method change control means for selecting retransmission control by a second retransmission control means when the buffering amount is smaller than a transition value. 3. The transmission control device according to claim 1, wherein the transmission side includes means for generating a frame in which an error correction detection code is added to a header portion and an error detection code is added to a payload portion. The second retransmission control means uses the header information restored by the error correction detection code added to the header portion of the frame, and sends data allowing an error in the payload portion to the delay difference absorption buffer. A transmission control device, comprising: