JPH10126772A - Dynamic image data transfer system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dynamic image data transfer system which avoids the extreme drop of a reproduced image quality without making a system structure large nor making network resources waste even when dynamic image data that consists of image frames whose effect degree on reproduced image quality is different is transferred. SOLUTION: A server 1 is provided with an image frame identifying part 11 which identifies an image frame that has more effect degree than a frame type which has a prescribed effect degree to reproduced image quality that is registered in a resending frame designation table 12 among dynamic image data 5 which is read from a file system 4 and a resending buffer 14 which holds image frames that are identified by the part 11, and resends a lost packet from the buffer 14 when a resending request is notified from a client 2 in accordance with the packet loss that is caused by a transmission error.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moving image data transfer method, and more particularly to a method for transferring moving image data composed of a plurality of image frames having different influences on a reproduced image quality on a receiving side via a network. The present invention relates to a moving image data transfer method in such a case.

[0002]

2. Description of the Related Art Generally, as a moving image data transfer method for transferring moving image data from a server (transmitting terminal device) to a client (receiving terminal device) via a network, (1) no error correction is provided. A method that employs a simple communication protocol (such as UDP) and transfers packets according to the playback speed on the client side. (2) Prepares a frame buffer on the client side that performs playback, pre-reads the moving image data, and checks the moving image data. A method of recovering from a transmission error using a protocol (such as TCP) has been realized.

On the other hand, storage type moving image data stored in an arbitrary recording medium is compressed using various compression techniques in order to save a storage capacity required for storing the moving image data and a data transfer band. For example, a typical MPEG (Moving P
moving image data (hereinafter referred to as MPEG image data) by an image compression method, I (intra coded) picture, P (predic
tive coded) picture, B (bi-directionally predict)
ive coded) pictures are used and compressed.

In general, moving image data can be regarded as being composed of a plurality of temporally continuous still images (image frames). In the MPEG image compression method, encoding is performed between frames by extracting a difference from a still image that precedes and succeeds in time, thereby reducing the redundancy of moving image data in the time direction, that is, achieving data compression. I have. FIGS. 5A and 5B are explanatory diagrams showing the structure of MPEG image data. FIG. 5A shows a picture coding order, and FIG. 5B shows a data transfer order. FIG. 6 shows an identification code of each picture.

As shown in FIG. 6, a code is assigned to each picture, which identifies the type of the image frame. In FIG. 5B, first, an I picture 51 is intra-frame encoded image data. The screen # 1 indicated by the I picture 51 is used as a reference frame, motion compensation is performed by a P picture or a B picture, and an image is decoded. P picture 5
Reference numeral 4 denotes data indicating a difference between the screen # 1 of the I picture 51 and the subsequent screen # 4. The motion compensation prediction from the screen # 1 to the screen # 4, that is, the motion compensation prediction for an arbitrary area in the screen # 1. It is composed of a motion vector indicating the direction and the size, and serves as a reference frame of a B picture.

The B picture 52 shows the difference between the screen # 1 of the I picture 51 and the screen # 4 and the screen # 2 of the P picture 54, and the movement from the screen # 1 and the screen # 4 to the screen # 2. It is composed of motion vectors indicating compensation prediction. Similarly, the B picture 53 is composed of motion vectors indicating motion compensation prediction from the screen # 1 and the screen # 4 to the screen # 3. Therefore, screen # 4 is a P-picture 5 using screen # 1 of I-picture 51 as a reference frame.
4 to perform motion compensation and decoding. Also screen #
2 and # 3 are B pictures 52, using screen # 1 of I picture 51 and screen # 4 of P picture 54 as reference frames.
The motion is compensated by 53 and decoded.

Conventionally, when transferring these MPEG image data, based on one of the moving image data transfer methods described above, as shown in FIG. From I picture 51, B pictures 52, 53, P picture 54, B pictures 55, 5
6, transferred as P picture 57. Therefore, on the receiving side, these pictures are sequentially received, the screens of P pictures 54 and 57 are decoded from the immediately preceding I picture 51 or P picture 54, and B pictures 52, 53 and 5 are decoded.
The screens 5 and 56 include the I picture 51 and the P picture 54 immediately before and immediately after, or the P picture 54,
57, and these decoded images are reproduced according to the reception order and reproduction time of each picture.

[0008]

However, in such a conventional moving image data transfer method, the moving image data to be transferred is, for example, an MPEG image data encoding method for reducing redundancy in the time direction. However, if the receiving side has a different influence on the reproduction quality of the image reproduced, the image may be reproduced correctly depending on the degree of the moving image data in which the transmission error has occurred due to packet loss or the like. In some cases, the retransmission of the lost packet may not be in time for the reproduction timing, and in any case, the quality of the reproduced image is extremely reduced.

For example, in the above-described MPEG image data,
From the coding method, a B picture cannot be decoded unless there is a reference frame composed of preceding and succeeding I or P pictures, and a P picture also has no reference frame composed of past I or P pictures. Cannot be decrypted. Therefore, when a packet constituting a B picture is lost, there is no effect on other frames, but when a frame constituting an I picture or a P picture is lost, a subsequent P or B picture can be decoded. No, the effect on other frames is large.

According to the former method (1) of the conventional moving image data transfer methods described above, when a packet is lost due to a transmission error, recovery by retransmission is not performed. In particular, when a packet constituting an I picture is lost, other P and B pictures that have been normally transferred cannot be decoded, so that there is a problem that the substantial reproduced image quality is extremely reduced. According to the latter method (2), the lost packet is recovered from the error by retransmission. However, since all the lost packets are retransmitted regardless of the importance of the data, a transfer delay occurs, and the retransmission packet of the I picture is In the case where the probability that the retransmission packet is not in time for the screen reproduction timing is high and the decoding using the retransmitted packet is not in time for the screen reproduction timing, the substantial reproduced image quality is similar to the case where the packet is lost in the former method (1). Extremely low.

As a countermeasure, it is necessary to increase the amount of frame buffer for prefetching or to increase the transfer bandwidth in anticipation of retransmission, which causes problems such as an increase in system configuration and waste of network resources. The present invention is intended to solve such a problem, and when moving image data including image frames having different degrees of influence on reproduced image quality is transferred, the system configuration becomes large and network resources are wasted. It is an object of the present invention to provide a moving image data transfer method capable of avoiding an extreme decrease in the quality of a reproduced image without any problem.

[0012]

In order to achieve the above object, a moving image data transfer method according to the present invention provides a method for transmitting, on a transmitting side, each image frame constituting moving image data to be transferred into a predetermined packet. The image data is converted and sequentially transferred to the receiving side, and when a retransmission request for a predetermined packet is notified from the receiving side, only packets of image frames having a degree of influence equal to or more than a predetermined level are retransmitted to the receiving side.
Therefore, each image frame constituting moving image data to be transferred is converted into a predetermined packet and sequentially transferred to the receiving side, and when a retransmission request for the predetermined packet is notified from the receiving side, an image having a predetermined degree of influence or more is received. Only the packet of the frame is retransmitted to the receiving side.

The transmitting side converts each image frame constituting the moving image data to be transferred into a predetermined packet and sequentially transfers the packet to the receiving side. When a retransmission request for a predetermined packet is notified from the receiving side, the packet is retransmitted to the receiving side only when the packet is held. is there. Therefore, each image frame that constitutes the moving image data to be transferred is converted into a predetermined packet and sequentially transferred to the receiving side, and among the image frames, an image frame having a predetermined degree of influence on the reproduced image quality Is held, and when a retransmission request for a predetermined packet is notified from the receiving side, the packet is retransmitted to the receiving side only when the packet is held.

Further, the transmitting side discards the packets held continuously for a predetermined period or more among the held packets. Therefore, the packets held for a predetermined period or more among the packets held on the transmitting side are discarded. If the transmitting side does not hold the packet requested to be retransmitted by the receiving side, the transmitting side notifies the receiving side of a discard indicating that the packet has already been discarded. According to the notification, the packet is regarded as already received, and the retransmission request for the packet is stopped. Therefore, if the transmitting side does not hold the packet requested to be retransmitted by the receiving side, the receiving side is notified of the discard of the packet, and the receiving side has received the discarded packet. And the retransmission request for the packet is stopped.

[0015]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a moving image data transfer system according to an embodiment of the present invention, in which a server (transmitting terminal device) 1 and a client (receiving terminal device).
2 and a network 3 connecting the server 1 and the client 2. The server 1 is a transmitting terminal device that reads out moving image data 5 stored in a fixed storage device (hard disk device) or the like of the file system 4 and transfers the moving image data 5 to the client 2 via the network 3. The client 2 is a receiving terminal device that receives moving image data transferred from the server 1 via the network 3 and performs predetermined decoding processing to reproduce and output an image.

In the server 1, 1a is a file control unit for reading predetermined moving image data 5 stored as a file in the file system 4, and 1b is each of the moving image data 5 read by the file control unit 1a. The type of the image frame is identified by the image frame identification unit 11, and a retransmission designation flag indicating a retransmission target is set for an image frame of a predetermined frame type registered in the retransmission frame designation table 12 by the user. This is a moving image transfer control unit.

1c packetizes each image frame output from the moving image transfer control unit 1b by the packet generation unit 13 and converts the packet into a network 3 based on a predetermined MAC (Media Access Control) protocol.
Is a data transfer unit that transfers the data to the client 2 via the MAC unit 1d that controls the data transfer. In the data transfer unit 1c,
Reference numeral 14 denotes a retransmission buffer for holding a packet of a frame to which a retransmission designation flag is added among the packets generated by the packet generation unit 13, and holds the packet in the retransmission buffer 14 in response to a retransmission request from the client 2 described later. The packet corresponding to the given frame is retransmitted to the client 2.

A retransmission request processing unit 15 analyzes an acknowledgment packet and a retransmission request packet from the client 2. A retransmission request processing unit 16 has a retransmission timer T1 and a discard timer T2. The retransmission buffer management unit manages retransmission and discard of each packet held in the buffer 14. Reference numeral 17 denotes a discard notification packet generation unit that generates a predetermined discard notification packet for notifying the client 2 that the packet requested to be retransmitted has already been discarded based on an instruction from the retransmission buffer management unit 16.

On the other hand, in the client 2, 2c holds a packet received from the server 1 via the MAC unit 2d for controlling the network 3 based on a predetermined MAC protocol in the reception buffer 21, and
2, a data transfer unit for inspecting the loss of these packets and reconstructing and outputting an original image frame from these packets;
A retransmission request transfer unit that generates a predetermined acknowledgment packet indicating normal reception or a predetermined retransmission request packet indicating a retransmission request of a transmission packet based on the inspection result from the server and transmits the generated packet to the server 1. Reference numeral 2b denotes a moving image transfer control unit that stores the image frame from the data transfer unit 2c in the frame buffer 23, decodes each screen based on a predetermined decoding method, and outputs the decoded image. Thus, the image is displayed and output on the image display unit 2a at a predetermined screen reproduction timing.

Next, the operation of the present invention when transferring MPEG image data from a server to a client will be described with reference to FIG. The file system 4 stores a plurality of moving image data compressed in the MPEG format in a storage medium such as a hard disk. The file control unit 1a of the server 1 transmits the designated moving image data 5
Are sequentially read from the file system 4 and output to the moving image transfer control unit 1b.

The image frame identification unit 11 of the moving image transfer control unit 1b converts a sequentially input moving image data 5 into a picture start code (Picture Start Code pattern: 000001).
00 (H)) to identify the boundaries of individual image frames. In addition, the picture identifier (Picture Codeing
Type), the frame type as shown in FIG. 5 is identified. Subsequently, with reference to the retransmission frame designation table 12, it is determined whether or not the image frame being processed is of the same type as the retransmission designated frame.

Note that, between the server 1 and the client 2, two confirmation-type connections as shown in FIG. 2 are set in advance. FIG. 2 is an explanatory diagram showing a connection form between the server and the client. 3a is a moving image data transfer connection for transferring moving image data from the server 1 to the client 2, and 3b is a connection between the client 2 and the server 1. A moving image transfer control connection for transferring various control commands, and is set via the network 3.

The moving image data transfer connection 3a transmits a flow control packet indicating transfer of moving image data from the server 1 to the client 2 and a confirmation response to the received moving image data, a retransmission request, a discard notification, and the like. , Is used for transfer between the servers 1. The control connection 3b for moving image transfer transmits a control packet relating to designation of desired moving image data and image reproduction operation (for example, image reproduction, fast forward, rewind, stop, pause) between the client 2 and the server 1. In addition, the method is used when the frame type to be retransmitted when a packet loss occurs due to a transmission error is registered from the client 2 to the server 1.

The moving image transfer control unit 2b of the client 2
Transfers a predetermined control command indicating the frame type from the command transfer unit 27 to the server 1 via the moving image transfer control connection 3b when a frame type designating a retransmission frame is input by a user request input.
The moving image transfer control unit 1b of the server 1 receives and analyzes the control command from the client 2 by the command analysis unit 18, and registers the frame type specified according to the command specifying the retransmission frame in the retransmission frame specification table 12. I do.

The retransmission frame designation table 12
, A predetermined frame type may be registered in response to a user request input to the server 1. In this case, when the command analysis unit 18 in the moving image transfer control unit 1b of the server 1 receives a user request input and inputs a frame type that specifies a retransmission frame, the frame type is stored in the retransmission frame specification table 12. be registered.

Using the frame type registered in the retransmission frame designation table 12 as described above, the image frame identification unit 11 in the moving image transfer control unit 1b of the server 1 performs file control as shown in FIG. Each image frame 31 of the moving image data 5 read from the file system 4 via the unit 1a is compared. Here, as for the image frame 31 of the frame type having the same degree as the frame type registered in the retransmission frame specification table 12 or having a greater influence on the reproduced image quality than this frame type, the retransmission flag in which the retransmission specification flag is set A header (on) 32 is added, and in other cases, a retransmission flag header (off) 33 for which no retransmission designation flag is set.
, And output to the data transfer unit 1c.

Therefore, in the case of MPEG image data, each of the I, P, and B pictures has an influence on the reproduced image quality, and the order of the influence can be set as shown in FIG. For example, in the retransmission frame designation table 12, the frame type "01" indicating a P picture
In the case where “0” (influence rank = 2) is registered, among the image frames 31 input to the image frame identification unit 11, P pictures and I pictures having a greater influence than the P pictures
A retransmission flag header (ON) 32 in which a retransmission designation flag is set is added to a picture (influence rank = 1), and retransmission is performed for a B picture (influence rank = 3) having less influence than a P picture. A retransmission flag header (off) 33 in which the designation flag is not set is added.

In the MPEG image compression method, a frame including MPEG data information of a layer higher than a picture layer such as I, P, and B pictures, for example, a frame including information such as a sequence layer and a GOP layer,
Since the degree of influence on the reproduced image quality is greater than that of the I-picture, which has the greatest influence in the picture layer, the retransmission flag in which the retransmission designation flag is set is always set for the image frame in which the MPEG data information of the upper layer is stored. A header (ON) 32 is added.

As described above, the retransmission flag headers 32 and 33 are added to each image frame, and are input to the data transfer unit 1c. The packet generation unit 13 of the data transfer unit 1c separates and analyzes the retransmission designation flag from the input image frame, and generates a packet to which header information such as a sequence number and an error check code used for flow control described later is added. , To the MAC unit 14. Also, among the generated packets, packets constituting a frame whose retransmission is specified by the retransmission flag header are MAC
Output to the unit 14 and stored in the retransmission buffer 14.

On the other hand, in response to storing the packet in the retransmission buffer 14, the retransmission buffer management unit 16 of the data transfer unit 1c starts the retransmission timer T1 and the discard timer T2 corresponding to the packet. The retransmission timer T1 is the retransmission buffer 1
4 is a timer for judging the necessity of forced retransmission of the packet stored in the retransmission buffer 14. If no acknowledgment is received from the client 2 before the retransmission timer T1 times out, the packet is read from the retransmission buffer 14. Will be forcibly resent.

The discard timer T2 is set in the retransmission buffer 14
Is a timer for judging whether or not the packet stored in the client 2 is to be discarded. If an acknowledgment is not notified from the client 2 before the discard timer T2 times out, the packet is discarded from the retransmission buffer 14.
The timeout period of the discard timer T2 is set according to the frame buffer capacity for prefetching in the client 2. Note that the retransmission timer T1 has a time-out period set so as to time out earlier than the discard timer T2, and after completion of the forced retransmission necessity determination, the necessity of discard is determined.

As described above, the packet generated by the data transfer section 1c of the server 1 is sent out via the MAC section 1d and transferred to the client 2 via the video data transfer connection 3a of the network 3. The data transfer unit 2c of the client 2 receives these packets via the MAC unit 2d, and sequentially stores them in the reception buffer 21. The received packet inspection unit 22 reads a packet from the reception buffer 21 and performs an error check and a sequence check with reference to the header.

Here, the packets received in the normal sequence are reconstructed into image frames by the packets and output to the moving image transfer control unit 2b, and the retransmission request transfer unit 24 is notified of the normal packet reception. . On the other hand, error check and sequence check
When packet loss is detected, the retransmission request transfer unit 2
4 is notified of the occurrence of packet loss.

The retransmission request transfer unit 24 responds to the notification from the received packet inspection unit 22 to
5 or a retransmission request packet generator 26 generates an acknowledgment packet or a retransmission request packet, respectively,
The server 1 is notified via the C section 2d and the moving image data transfer connection 3a. Also, the received packet inspection unit 2
The image frame output from 2 is a moving image transfer control unit 1
b are sequentially stored in the frame buffer 23, each screen is decoded based on a predetermined decoding method, and displayed and output on the image display unit 2a at a predetermined screen reproduction timing.

The retransmission request processing unit 15 in the data transfer unit 1c of the server 1 analyzes the acknowledgment packet and the retransmission request packet notified from the client 2. Here, when the packet normal reception notification is detected by the acknowledgment packet, the retransmission request processing unit 15 notifies the retransmission buffer management unit 16 of the normal reception packet sequence number notified by the acknowledgment packet. In response to this, when the packet corresponding to the notified sequence number is stored in the retransmission buffer 14, the retransmission buffer management unit 16 discards the packet to release the buffer area, and sets the corresponding retransmission timer. T
1. Delete the discard timer T2.

On the other hand, when the retransmission request processing unit 15 detects a packet retransmission request notification, the retransmission request processing unit 15
The notified retransmission request packet sequence number is notified to the retransmission buffer management unit 16. In response to this, in the retransmission buffer management unit 16, when the packet corresponding to the notified sequence number is stored in the retransmission buffer 14,
The packet is retransmitted and the corresponding retransmission timer T
Reset 1 and restart.

If the packet corresponding to the notified sequence number is not stored in the retransmission buffer 14, the discard notification packet generator 17 generates a predetermined packet discard notification packet, and the MAC Transfer to 2. In response to the detection of the packet discard notification packet, the received packet inspection unit 22 of the client 2
Notifies the retransmission request transfer unit 24 of the normal reception of the packet assuming that the lost packet has been received.

The retransmission buffer management unit 16 determines whether each packet stored in the retransmission buffer 14 needs to be retransmitted and discarded by an individual retransmission timer T1 and discard timer T2.
It is managed by. In particular, when the retransmission timer T1 times out, the corresponding packet is forcibly retransmitted,
The retransmission timer T1 is started again. Further, when the discard timer T2 times out, the retransmission buffer 1
4 to discard the corresponding packet.

As described above, according to the present invention, of the moving image data 5 read out from the file system 4, the degree of influence of a frame type having a predetermined degree of influence on the reproduced image quality registered in the retransmission frame designation table 12 or more is considered. The server 1 is provided with an image frame identifying unit 11 for identifying an image frame having a frame and a retransmission buffer 14 for holding the image frame identified by the image frame identifying unit 11, and the client 2 responds to a packet loss due to a transmission error. When the retransmission request is notified from the retransmission buffer 14, the lost packet is retransmitted from the retransmission buffer 14.

Therefore, a packet having a relatively large influence on the reproduced image quality can be retransmitted as needed, and the reproduced image quality is extremely reduced as compared with the conventional case where no packet retransmission is performed. Can be avoided. Also,
Compared with the conventional one that enables retransmission of all packets, it is possible to suppress the occurrence of image frame transfer delay due to retransmission, and to solve these transfer delays, such as a frame buffer amount for pre-reading and It is not necessary to implement a solution such as increasing the transfer band, and it is possible to suppress waste of network resources.

The retransmission buffer management unit 16 for managing the packets held in the retransmission buffer 14 is provided with a retransmission timer T1 for each packet.
Activate the retransmission timer T1 in response to storing the packet in
When the acknowledgment of the corresponding packet is not notified from the client 2 before the retransmission timer T1 times out, the corresponding packet is forcibly retransmitted from the retransmission buffer 14, so that the packet retransmission from the client 2 is performed. Even if the request packet is lost,
It is possible to retransmit packets required for reproducing moving image data.

Also, the retransmission buffer management unit 16 is provided with a discard timer T2 for each packet, starts the discard timer T2 in accordance with the storage of the packet in the retransmission buffer 14, and waits until the discard timer T2 times out. When the acknowledgment of the corresponding packet is not notified from the client 2, the corresponding packet is discarded from the retransmission buffer 14, so that each packet held as a timeout period of the discard timer T2 is received. By eliminating the unnecessary time on the transmitting side, for example, until the image frame composed of individual packets is completely reproduced on the receiving side, unnecessary packets do not remain on the transmitting side and each packet is retained. It is possible to make effective use of the buffer capacity for performing the operation.

Further, when the packet requested to be retransmitted by the client 2 is not held in the retransmission buffer 14, the retransmission buffer management unit 16 transfers the discard notification packet from the discard notification packet generation unit 17 to the client 2, and The client 2 is notified that the retransmission-requested packet has already been discarded, and the retransmission request transfer unit 24 of the client 2 stops the retransmission request for the lost packet and receives the lost packet. As a result, the flow control for the subsequent packet is continued, so that the stagnation of the flow control performed between the server 1 and the client 2 can be avoided, and the transfer of the subsequent packet that should be transferred can be started. A transfer delay of moving image data due to stagnation of control can be suppressed.

Next, the flow control performed between the server and the client will be described with reference to FIG. FIG. 4 is a sequence diagram showing the flow control between the server and the client. Reference numeral 41 denotes a sequence number sequentially added to each packet by the data transfer unit 1c of the server 1.
It is initialized each time the moving image data transfer connection 3a is opened. Reference numeral 42 denotes a window number indicating the number of packets that can be received according to the capacity of the free area of the reception buffer 21 by a sequence number, and reference numeral 43 denotes an ACK (acknowledgement) number indicating the sequence number of a packet to be received next. is there.

Reference numeral 44 denotes a retransmission request number indicating a sequence number of a packet requested to be retransmitted in response to packet loss, and reference numeral 45 denotes a packet list indicating a sequence number of a packet received without error. In particular, window number 4
2 and the ACK number 43 are stored in the confirmation notification packet generated by the acknowledgment packet generation unit 25 of the client 2 and notified to the retransmission request processing unit 15 of the server 1. The retransmission request number 44 is also the retransmission request packet generation unit 2
It is stored in the retransmission request packet generated in step 6 and notified to the retransmission request processing unit 15 of the server 1.

First, the server 1 notifies the client 2 of the first sequence number, for example, “O (zero)”, and the sequence number is initialized between the two. In response, the client 2 notifies the server 1 of the window number. For example, when the buffer size of the reception buffer 21 of the client 2 is six packets, six windows from the first sequence number “0” to “5” can be received, so “5” is set as the window number. Notified.

In response, the server 1 adds a sequence number to each packet in order from “0” and transfers packets up to a sequence number “5” equal to the notified window number to the client 2. The client 2 receives each packet sequentially, and if the packets are received without error,
Based on the sequence number of the received packet, the window number and ACK number are updated and notified to the server 1 as an acknowledgment, and the packet list is updated to release the area of the reception buffer 21 holding the packet. I do. Further, in response to the confirmation response, the retransmission request processing unit 15 of the server 1 discards the packet received by the client 2 without error if the packet is held in the retransmission buffer 14 and retransmits the new packet. Forwarding a special packet.

Here, if the packet of sequence number "2" is lost and the next packet of sequence number "3" is received, or if there is an error in the packet data, client 2 determines that packet loss has occurred. do it,
A retransmission request is made to the server 1 with the sequence number “2” of the lost packet as the retransmission request number. Server 1 accordingly
The retransmission request processing unit 15 instructs the retransmission buffer management unit 16 to retransmit the packet, and the retransmission buffer management unit 16 reads the corresponding packet from the retransmission buffer 14 and transfers the packet to the client 2.

Therefore, the received packet inspection unit 22 of the client 2 confirms the retransmitted packet, and notifies the retransmission request transfer unit 24 of the normal reception of the packet of the packet number “2”. The retransmission request transfer unit 24 updates the packet list 45 to check for a missing packet (gap) in the received packet, and performs the above-described retransmission request or acknowledgment response process depending on whether or not there is a missing packet. On the other hand, if the packet requested to be retransmitted by the client 2, for example, the packet with the sequence number “10”, is determined to be unnecessary for retransmission from the influence on the reproduced image quality of the image frame and is not held in the retransmission buffer 14, the retransmission buffer management is performed. The unit 16 transfers a predetermined discard notification regarding the packet with the sequence number “10” from the discard notification packet generator 17 to the client 2.

Therefore, the received packet inspecting unit 22 of the client 2 confirms a predetermined discard notice regarding the packet of the sequence number “10”, and considers that this packet has been received, and sends the packet to the retransmission request transfer unit 24. A packet normal reception notification of the number “10” is performed. The retransmission request transfer unit 24 updates the packet list 45 to check for a missing packet (gap) in the received packet, and performs the above-described retransmission request or acknowledgment response process depending on whether or not there is a missing packet. Accordingly, it is possible to avoid the stagnation of the flow control performed between the server 1 and the client 2 and start the transfer of the succeeding packet that should be transferred, thereby suppressing the transfer delay of the moving image data due to the stagnation of the flow control. be able to.

[0051]

As described above, according to the present invention, on the transmitting side, each image frame constituting moving image data to be transferred is converted into a predetermined packet and sequentially transferred to the receiving side. When a retransmission request for a packet is notified, only a packet of an image frame having a predetermined degree of influence is retransmitted to the receiving side.
Further, the transmitting side holds a packet of an image frame having a degree of influence on the reproduced image quality of the image frame to be transferred among the image frames to be transferred, and when a retransmission request for the predetermined packet is notified from the receiving side, Only when a packet is held, it is retransmitted to the receiving side. Therefore, a packet having a relatively large degree of influence on the reproduced image quality can be retransmitted as needed, and an extreme decrease in the reproduced image quality can be avoided as compared with the conventional case where packet retransmission is not performed. . In addition, compared to the conventional case in which all packets can be retransmitted, the occurrence of image frame transfer delay due to retransmission can be suppressed, and a configuration for solving these transfer delays, for example, a frame buffer for prefetching It is not necessary to implement a solution such as increasing the amount and transfer bandwidth, and it is possible to suppress waste of network resources.

Since the transmitting side discards the packets held for a predetermined period or more among the held packets, the individual packets held for the predetermined period are received. By eliminating the unnecessary time on the transmitting side, for example, until the image frame composed of individual packets is completely reproduced on the receiving side, unnecessary packets do not remain on the transmitting side and each packet is retained. It is possible to make effective use of the buffer capacity for performing the operation. If the transmitting side does not hold the packet requested to be retransmitted by the receiving side, the transmitting side notifies the receiving side of a discard indicating that the packet has already been discarded. In response to the notification, the packet is regarded as already received, and the retransmission request for the packet is stopped, so that the stagnation of flow control of each bucket performed between the transmitting side and the receiving side can be avoided. Transfer of a subsequent packet to be transferred can be started, and transfer delay of moving image data due to stagnation of flow control can be suppressed.

[Brief description of the drawings]

FIG. 1 is a block diagram of a moving image data transfer system according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a connection form between a server and a client.

FIG. 3 is an explanatory diagram illustrating an image frame identification process.

FIG. 4 is a sequence diagram showing flow control between a server and a client.

FIG. 5 is an explanatory diagram showing a configuration of MPEG image data.

FIG. 6 is an explanatory diagram showing an identification code of each picture.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Server (transmission side terminal device), 2 ... Client (reception side terminal device), 1a ... File control part, 2a ... Image display part, 1b, 2b ... Moving image transfer control part, 1c, 2c ... Data transfer part, 1d , 2d MAC section, 11 image frame identification section, 12 retransmission frame designation table, 13 packet generation section, 14 retransmission buffer, 15 retransmission request processing section, 16 retransmission buffer management section, 17 discard notification packet Generating unit, 18 command analyzing unit, 21 receiving buffer, 22 receiving packet inspecting unit, 23 frame buffer, 24 retransmission request transfer unit, 25 acknowledgment packet generating unit, 26 retransmission request packet generating unit, 27 ... Command transfer unit, 3 ... Network, 3a ... Moving image data transfer connection, 3b ... Moving image transfer control connection, 4
... file system, 5 ... moving image data.

Claims (4)

[Claims] 1. A moving image data transfer method in which moving image data composed of a plurality of image frames having different degrees of influence on reproduced image quality on a receiving side is transferred from a transmitting side to a receiving side via a network. In the above, the transmitting side converts each image frame constituting the moving image data to be transferred into a predetermined packet, sequentially transfers the packet to the receiving side, and when a retransmission request for the predetermined packet is notified from the receiving side, the influence of the predetermined A moving image data transfer method comprising retransmitting only a packet of an image frame having a degree to a receiving side. 2. A moving image data transfer method in which moving image data composed of a plurality of image frames having different degrees of influence on reproduced image quality on a receiving side is transferred from a transmitting side to a receiving side via a network. The transmitting side converts each image frame constituting the moving image data to be transferred into a predetermined packet and sequentially transfers the packet to the receiving side. Moving image data transfer, wherein a packet of an image frame having the packet is held, and when a retransmission request for a predetermined packet is notified from the receiving side, the packet is retransmitted to the receiving side only when the packet is held. Method. 3. The moving image data transfer method according to claim 2, wherein the transmitting side discards packets held continuously for a predetermined period or more among the held packets. Data transfer method. 4. The moving image data transfer method according to claim 2, wherein when the transmitting side does not hold the packet requested to be retransmitted by the receiving side, the transmitting side determines that the packet has already been discarded to the receiving side. A moving image data transfer method, comprising: performing a discard notification indicating that the packet has been received; and determining that the packet has been received in response to the discard notification, and stopping a retransmission request for the packet.