JP3228670B2 - Data transmission system and data transmission control method applied to the system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transmission system for transmitting a stream of, for example, video data from a transmitting node to a receiving node on a network.

[0002]

2. Description of the Related Art In recent years, with the development of computer network technology and digital information communication technology, for example, video on demand (video on demand) has been developed.
A system for achieving d) has been developed. In such a system, a requested video signal such as a movie is converted into digital information and transmitted from a transmission source (video server or the like) to a reception source (user terminal device or client) via a communication line on a network. Required data transmission processing.

[0003] Digital information such as a video signal is a series of data strings (hereinafter, referred to as a stream) which are sequentially generated in a number of data elements (data frames) called frames. Such a stream is transferred at a predetermined transfer rate from a transmitting node, which is a transmission source, to a receiving node, which is a reception source, via a communication line on a network. At this time, the transfer speed of the stream is determined depending on the reception processing speed on the receiving node side.

Therefore, in continuous data transmission such as a stream, a transmitting node transmits a requested stream at a high transfer rate, and shifts to a stream transmission process according to the next request. Processing is not possible.
That is, the transmission node is not released until the transmission processing of a series of streams is completed.

As a method for solving such a problem,
A method is conceivable in which a relay node is provided on a stream transmission system, and the relay node temporarily buffers a stream transmitted from a transmission node in a buffer memory.
With such a method, the transmitting node can transmit a stream at a high transfer rate regardless of the receiving processing speed of the receiving node. The relay node, after buffering the stream transferred from the transmitting node,
The data is transmitted at a transfer rate corresponding to the reception processing speed of the receiving node.

[0006]

As described above, for example, in a system for realizing video-on-demand,
It is necessary to construct a transmission system that transmits a stream, which is a series of video data strings, via a communication line on a network. At this time, in order to increase the transmission efficiency of the stream and efficiently distribute the stream to a large number of receiving nodes, the transfer speed of the transmitting node that transmits the stream is increased, and the transmitting node is set as fast as possible. It needs to be released.

As a method for realizing this, a method is conceivable in which a relay node is provided on a network, and the relay node temporarily buffers a stream from the transmission node. However, in this method, after the stream from the transmitting node is buffered, the relay node transmits the stream to the receiving node, so that the arrival start of stream transmission at the receiving node is delayed. When transmitting a video stream such as a movie to a user, it is necessary to continuously transmit the video stream without interruption without interruption. Therefore, in a method of simply arranging a relay node having a buffer function,
For example, it cannot be applied to a system that implements video-on-demand.

SUMMARY OF THE INVENTION An object of the present invention is to provide a system for transmitting a stream from a transmitting side to a receiving side without increasing the transmission speed of the stream without interrupting the transmission of the stream. The purpose is to improve processing efficiency.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a data transmission system for transmitting a stream, which is a series of continuous data streams, from a transmitting node to a receiving node, particularly using a communication line on a network. The node is a system having a plurality of transmission systems and a relay node having a function of selecting one of the streams transferred from the plurality of transmission systems and transferring the stream to a reception node.

[0010] When transmitting the first stream and the second stream having the same contents to the relay node, the transmitting node transfers the second stream at a relatively high speed. The relay node sends the first stream received from the transmitting node to the receiving node, and buffers the second stream in the buffer unit. Further, the relay node compares the phase (time difference from the head of the stream) of each frame of the first stream and the second stream, and switches the first stream to the second stream when the phases match. Is transmitted to the receiving node from the frame at the time of the coincidence.

With such a system, the transmitting node transmits the first stream and transmits the second stream to the relay node at a high transfer rate. The relay node includes a large-capacity buffer memory to buffer the second stream from the transmitting node, and
From the stream to the second stream. Accordingly, stream transmission is processed at a predetermined transfer rate without interruption from the start of stream transmission to the receiving node.

On the other hand, the transmitting node transmits the first stream and transmits the second stream to the relay node by high-speed transfer. Since the second stream is buffered by the buffer means of the relay node, the transmitting node unilaterally transmits, and stops transmitting the second stream when the transmission ends. At this time, the relay node
And the transmission process is switched from the first stream to the second stream when the frame phases match. That is, the relay node reads out the second stream from the buffer means and sends it out during the transmission of the first stream. Therefore, the sending node
When the transmission of the stream is completed at a high transfer rate, the stream is released from the transmission processing. Accordingly, the transmitting node starts, for example, a process of transmitting a stream to another receiving node.

In short, according to the present invention, the transmitting node transmits the stream at a high transfer rate independent of the receiving processing speed of the receiving node without interrupting the transmission of the stream to the receiving node. You will be released from processing. Therefore, it is possible to efficiently distribute a stream to a large number of receiving nodes.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating a system configuration related to the present embodiment, and FIG. 2 is a block diagram illustrating a configuration of a relay node related to the present embodiment. (System Configuration) As shown in FIG. 1, the system of the present embodiment includes a transmission node 2 arranged on a network,
The relay node 1 and the receiving node 3 are connected to the communication lines 20A and 20A.
Assume a stream transmission system connected via OB. The transmission node 2 corresponds to, for example, a video server that transmits a video signal such as a movie as a video stream converted into digital information in a system that implements video-on-demand. Further, the receiving node 3
This corresponds to a user terminal device or client on the user side that consumes the received stream.

The transmitting node 2 roughly divides a stream, sends a stream, sends a stream, controls a transfer rate of the stream, and exchanges stream control information and communication control information. And a control communication unit 12. On the other hand, the receiving node 3 is roughly divided into a stream receiving unit 13 for receiving and processing a stream.
And a stream decoding display unit 14. The stream decoding and display unit 14 is a component for restoring the received stream to the original video signal and reproducing it on the display screen of the display. The receiving node 3 is specifically a personal computer having a communication function and a color display.

The relay node 1 has the following components: a buffer unit 5 composed of a buffer memory, a stream receiving unit 6, a stream transmitting unit 7, a control communication unit 8, and a stream speed control unit 9. The buffer unit 5 buffers each of the first stream SA and the second stream SB transmitted from the plurality of transmission systems of the transmission node 2, as described later (see FIG. 2). Stream receiving unit 6
Is the first stream SA transmitted from the transmitting node 2.
And an element for receiving and processing each of the second stream SB.

As will be described later, the stream transmitting unit 7
A selection function (selector) for selecting one of the first stream SA and the second stream SB and transmitting the selected stream to the receiving node 3 is provided. The stream transmission unit 7 transmits the stream selected under the control of the stream speed control unit 9 at a predetermined transfer rate. The control communication unit 8 includes the transmitting node 2
And a component for exchanging stream control information and communication information with the receiving node 3.

Furthermore, a control node 4 is normally provided, and the transmission node 2 and the relay node 1 are controlled by the control node 4 to execute a stream transmission process.
The control node 4 has a transfer control unit 15 and a control communication unit 16 necessary for controlling the transmission processing of the stream. Further, the control node 4 receives an instruction (a forward reproduction instruction, a backward reproduction instruction, and the like, which will be described later) related to a stream transmission process with the receiving node 3, and transmits various guidance messages and the like. Note that the control node 4 is not an independent element,
It may be assumed as a control element included in the relay node 1. (Structure of Relay Node) As shown in FIG. 2, the relay node 1 of the present embodiment corresponds to a plurality of transmission systems of the transmission node 2 and a stream receiving unit 6A for receiving the first stream SA and its control unit. It has a communication section 8A, and has a stream receiving section 6B for receiving the second stream SB and a control communication section 8B thereof. Further, the buffer unit 5 stores the stream S
A buffer 5A for storing A and a buffer 5B for storing a stream SB. The buffer 5B is a buffer memory having a larger capacity than the buffer 5A,
For example, a stream SB for one movie is stored.

Further, the relay node 1 includes a buffer 5A,
Stream reading units 21A and 21B, reading position control units 22A and 22B, selector 23, stream transmission unit 24, selector control unit 25, and stream phase measurement unit 2 for reading streams SA and SB in frame units from 5B.
6A and 26B, and a phase comparison unit 27. The read position control units 22A and 22B instruct the stream read units 21A and 21B with pointers for reading frames from the buffers 5A and 5B. In the present embodiment, the reading position control unit 22B indicates the pointer designated at that time according to the phase coincidence signal PE from the phase comparing unit 27, as described later.

The selector 23 responds to a selection signal from the selector control section 25 by means of stream reading sections 21A, 21B.
, And outputs one of the stream SA and the stream SB output to the stream transmission unit 24. The stream transmitting unit 24 transmits the stream ST selected by the selector 23 to the receiving node 3 at a predetermined transfer rate under the control of the stream speed control unit 9 described above. (Stream Data Structure and Phase) As described above, the relay node 1 of the present embodiment measures the phases of the streams SA and SB by the stream phase measuring units 26A and 26B, and compares the phases by the phase comparing unit 27. It has the function to do. Here, the phase is the start (start) of the stream.
Means the time difference from

As shown in FIG. 3, the stream is composed of a number of frames (for example, data elements which are units of image information). Each frame is composed of a frame boundary at the beginning, a time stamp, and a data body (BODY).
The time stamp is time information indicating a time difference from the head of the stream.

The stream phase measuring units 26A and 26B
Each phase is measured based on the time stamp recorded in each frame of the streams SA and SB.
The phase comparing section 27 includes stream phase measuring sections 26A, 26
The respective phases from B are compared, and when they match, a phase match signal PE is output. When the phases are different, the phase comparing section 27 outputs an instruction signal for selecting the stream SA to the selector control section 25. (Operation of the present embodiment) Hereinafter, in particular, FIG. 2, FIG. 4, and FIG.
The operation of the present embodiment will be described with reference to the flowchart of FIG.

First, the control node 4 instructs the transmission node 2 to transmit a specified stream in response to a stream transfer request from the reception node 3. In the video-on-demand system, in response to a request from the receiving node 3, the transmitting node 2 starts transferring a video stream with the specified movie name.

In this embodiment, the transmitting node 2 uses two communication lines to transmit a stream SA having the same data content.
And the stream SB (steps S1 and S2).
Here, the stream SA is transmitted by a protocol that allows a certain amount of data loss and has a small data transfer delay. On the other hand, the stream SB has a relatively large data transfer delay due to, for example, a protocol including an error retransmission procedure, but is transmitted by a highly reliable transfer process. Therefore, as shown in FIG. 4, the stream SB is transmitted from the transmitting node to the stream SA at a delayed timing. Further, the transmitting node 2 transmits the stream SB to the stream SA at a high transfer rate. That is, the stream SA is transmitted at a transfer rate that depends on the reception processing speed of the receiving node 3.

In the relay node 1, the stream receiving unit 6A
Receives stream SA from transmitting node 2, buffer 5A, stream reading unit 21A, selector 2
3. The data is transmitted to the receiving node 3 via the stream transmitting unit 24 at a predetermined transfer rate. Here, the selector 23 normally operates to select transmission of the stream SA. On the other hand, when the stream SB is received by the stream receiving unit 6B, it is stored in the buffer 5B (step S3). Therefore, while the stream SB is transmitted with a delay and is stored in the buffer 5B, the stream SA is transmitted to the receiving node 3.

The phase comparing section 27 constantly compares the phases (time information of time stamps) of the respective frames of the streams SA and SB output from the stream phase measuring sections 26A and 26B, and monitors whether or not they match. (Step S
4). That is, since the stream SB stored in the buffer 5B is transferred at a high speed with respect to the stream SB, the stream SB catches up at a certain point and has the same phase. The frames with the same phase are the same frames in the stream. Specifically, as shown in FIG.
In this case, the phases of the frame F5 of the stream SA before being transmitted to the receiving node 3 and the frame F5 of the stream SB stored in the buffer 5B match (the position indicated by the arrow in FIG. 4).

The phase comparator 27 outputs the phase coincidence signal PE at the time of coincidence, that is, at the time when the stream SB catches up with the stream SA, and controls the switching operation of the selector 23 via the selector control 25 (step S5). Of Y
ES, S7). That is, the selector 23 sends out the stream SA until the phases match, but stops sending the stream SA when the phases match (Step S
5, S6).

The stream reading unit 21B specifies the frame at the time of the coincidence with the pointer from the reading position control unit 22B to which the phase coincidence signal PE has been input (step S8). The stream reading unit 21B
From B, a specified frame of the stream SB (frame F5 shown in FIG. 4) is read and output to the selector 23 (step S9). The stream transmission unit 24 sends the stream SB from the selector 23 to the receiving node 3 as a stream ST.

Therefore, as shown in FIG.
Include frames F1 (A) to F1 of the first stream SA.
4 (A) is transferred and further continuously stream SB
From the frame F5 (B). That is, the frame F5 (B) of the stream SA having the same phase is not transferred to the receiving node 3. When all the streams SB stored in the buffer 5B are read out and sent to the receiving node 3, the stream transfer ends (step S10,
S11).

As described above, according to the present embodiment, the relay node 1 sends out the stream SA to which the data loss is allowed to some extent to the receiving node 3 at first, and the highly reliable stream SB stored in the buffer 5B is transmitted. Upon catching up, the stream SB is sent to the receiving node 3. Therefore, at the time of starting the stream transfer, the stream SA can be transmitted without causing a data delay, and the highly reliable stream SB can be transmitted in the middle.

Further, the transmitting node 2 can transmit the requested stream SB to the relay node 1 at a high transfer rate independent of the receiving processing speed of the receiving node 3. When the transmission node 2 finishes transmitting the stream SB, it shifts to a process of transmitting a stream to another reception node. Therefore, before the reception processing of the reception node 3 ends, the transmission node 2 is released from the transmission processing. As a result, it is possible to release the transmitting node earlier, so that the stream can be efficiently distributed to many receiving nodes. Also, the relay node 1 buffers the stream SB, but sends the stream SA to the receiving node 3 during the buffering.
The stream to be supplied to the receiving node 3 can be transferred without interruption. (Application Example 1 of the Present Embodiment) As shown in FIG. 1, the transmission node 2 can adjust the transfer speed of the stream SA and the stream SB by the function of the stream speed control unit 11. Now, suppose that the transfer speed of the stream SA is RA
And when the transfer rate of the stream SB is RB,
Set the transfer rate of the stream SA to “RA1 ≦ RA ≦ RA2”
It can be adjusted within the range. Further, the transfer speed of the stream SB can be adjusted in the range of “RB1 ≦ RB ≦ RB2”. In the case of the above-described embodiment, RA is a fixed value, and “RA1 = RA2”.

Here, "RA1 <RB2" and "RB
It is assumed that the transfer rates of the streams SA and SB are set to 1 <RA2. That is, the transfer rate RB1 is the minimum value, and the transfer rate RB2 is the maximum value.
Further, the phases of the streams SA and SB are set to φA,
φB. That is, φA and φB are the time stamp values of the latest frame received by the relay node 1.

When switching the stream SA to the stream SB, if the phase of the stream SB is advanced (φA <φB) based on the comparison result of the phase comparison section 27 when switching the stream SA to the stream SB, the relay node 1 Transfer rate RA
Is changed to a value larger than the minimum value RB1, and the stream S
The transmission node 2 is instructed to change the transfer rate RB of B to the minimum value RB1 (via the control communication units 8A and 8B).

Thus, the transfer rate R of the stream SB
B is smaller than the transfer rate RA of the stream SA (RB <RA), so that each phase φ of the streams SA and SB
The difference between A and φB approaches 0 quickly. When the difference between the phases φA and φB becomes 0, the relay node 1
To the stream SB.

Conversely, if the phase of the stream SB is behind (φA> φB), the transfer rate RA of the stream SA is changed to a value smaller than RB2,
The transfer rate RB of B is changed to the maximum value RB2.

Thus, the transfer rate R of the stream SB
B is larger than the transfer rate RA of the stream SA (RB> RA), so that each phase φ of the streams SA and SB
The difference between A and φB approaches 0 quickly. When the difference between the phases φA and φB becomes 0, the relay node 1
To the stream SB.

With such a transfer rate adjusting method, for example, when switching to a stream SB from a transmission node having a relatively low cost, switching can be easily performed without slipping. Therefore, the cost of the entire stream distribution can be reduced. (Application Example 2 of this Embodiment) Next, with reference to the flowcharts of FIGS. 6 and 7, during the stream transfer of this embodiment,
The operation when a transfer rate change command is given will be described. Here, the transfer speed change command is assumed to be a fast-forward playback mode (forward playback command) and a backward playback mode (reverse playback command) in the video playback mode. Normally, when such an instruction is issued, a process of sampling and transmitting a series of frames constituting a stream while skipping them in the forward or backward direction at appropriate intervals is executed.

First, in the relay node 1, the stream SA
Is selected by the selector 23 and transmitted to the receiving node 3, it is assumed that a reverse reproduction command is issued from the receiving node 3 via the control node 4 (YES in steps S20 to S23). Here, the output stream S when changed by the command (the transfer speed change command)
T (stream transferred to receiving node 3)
Is φ0.

The relay node 1 has a phase φ 0
While the phase φB of the stream SB is delayed (φ0>
φB), accesses the buffer 5A of the stream SA, and reads the frame retrospectively (steps S24 and S2).
5, S26). Then, as described above, the stream S
When B catches up and phase φB of stream SB advances (φ0 <φB), selector 23 is switched (YES in step S25, S29). That is, the buffer 5B
To read the frame of the stream SB retroactively and send it to the receiving node 3.

On the other hand, when the stream SB is selected by the selector 23, the switching operation of the selector 23 is not executed, the buffer 5B is accessed, and the frame of the stream SB is read back and read. (NO in step S21, S30, S31).

Further, it is assumed that a forward reproduction command is issued in a state where the stream SA is selected by the selector 23 and transmitted to the receiving node 3 (NO in step S23, YES in S27). In this case, the relay node 1 sends the forward reproduction command to the transmitting node 2 (step S28). As a result, the transmission node 2 executes the process of sampling and transmitting a series of frames constituting the stream SA while skipping them at appropriate intervals in the forward direction, as described above.

On the other hand, when the stream SB is selected by the selector 23, it is assumed that the forward reproduction command has been issued (NO in step S21, NO in S30, S
32 YES). While the phase φB of the stream SB is advanced (φ0 <φB), the relay node 1
The buffer 5B of B is accessed and transmitted to the receiving node 3, and the forward reproduction command is transmitted to the transmitting node 2 (steps S33 to S36). This allows
A series of frames of the stream SB stored in the buffer 5B are sampled and transmitted at appropriate intervals while skipping in the forward direction, and the transmission node 2 receives the sampled and transmitted frames while skipping in the forward direction. And accumulates in the buffer 5A. Then, when the phase φ0 of the output stream has advanced (φ0> φB), the selector 23 is switched (NO in step S34, S3).
7). That is, the buffer 5A is accessed, the frame of the stream SA is read, and transmitted to the receiving node 3.

As described above, when the fast forward playback command (forward playback command) or the backward playback command (reverse playback command) is issued during the stream transfer, the relay node 1
Corresponds to the maximum within the range of the streams stored in the buffers 5A and 5B, and if it exceeds this range, the command is transmitted to the original transmitting node 2. When a stream corresponding to the instruction is transmitted from the transmission node 2, the relay node 1 switches from the stream from the buffer to the transmission of the stream from the transmission node. Here, as a matter of course, when the entire stream is stored in the buffers 5A and 5B, the process of switching to the stream from the original transmission node 2 is unnecessary.

[0044]

As described above in detail, according to the present invention, first, the transfer speed of the stream from the transmission side is increased,
The sender can be released earlier and the requested stream can be transmitted continuously to the receiving node without delaying the arrival of the stream. Therefore, if the present invention is applied to a system that implements video-on-demand, for example, it is possible to efficiently transmit a required video stream and efficiently distribute the video stream to a large number of receivers. Second, since the transfer rate of the stream from the transmitting side can be flexibly adjusted, it is possible to easily switch to a stream from a relatively low-cost transmitting node without slipping. Therefore, the cost of the entire stream distribution can be reduced. Third,
It is possible to cope with the stream transfer speed change instruction within the buffer accumulation range, so that the load on the transmission side can be reduced. Therefore, as a result, stream distribution processing can be made more efficient.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a system configuration related to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a relay node according to the embodiment.

FIG. 3 is a conceptual diagram illustrating the configuration of a stream related to the embodiment.

FIG. 4 is a timing chart for explaining the operation of the embodiment.

FIG. 5 is a flowchart for explaining the operation of the embodiment.

FIG. 6 is a flowchart for explaining an application example of the embodiment.

FIG. 7 is a flowchart for explaining an application example of the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Relay node 2 ... Transmission node 3 ... Reception node 4 ... Control node 5, 5A, 5B ... Buffer part 6, 6A, 6B ... Stream reception part 7 ... Stream transmission part 8, 8A, 8B ... Control communication part 9 ... Stream Speed control unit 10 Stream transmission unit 11 Stream speed control unit 12 Control communication unit 13 Stream reception unit 14 Stream decoding display unit 15 Transfer control unit 16 Control communication unit 20A, 20B Communication lines 21A, 21B Stream readout units 22A, 22B ... readout position control unit 23 ... selector 24 ... stream transmission unit 25 ... selector control unit 26A, 26B ... stream phase measurement unit 27 ... phase comparison unit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04L 13/00 H04L 29/00 H04L 12/00

Claims (6)

(57) [Claims] 1. A data transmission system for continuously transmitting a data string composed of a series of data elements from a transmission side to a reception side, the data transmission system being provided on the transmission side and including a series of data elements. One data string is transmitted at a predetermined transfer rate, and a second data string composed of the same data elements as the first data string is transmitted at a transfer rate higher than the transfer rate of the first data string. Transmitting means; and buffer means for sequentially holding the second data string transferred from the transmitting means, wherein the first data string or the first data string transferred by the transmitting means in response to occurrence of a predetermined condition. Selecting the second data string read from the buffer means, and selecting from the series of data elements including a data element included in the first data string and a data element included in the second data string; Data transmission system, characterized in that it comprises a relay unit having a sending means for sending a data string continuously to the receiving side at a predetermined transfer rate that. 2. A data transmission system for continuously transmitting a data string composed of a series of data elements from a transmission side to a reception side, wherein the data transmission system is provided on the transmission side and includes a series of data elements composed of the series of data elements. One data string is transmitted at a predetermined transfer rate, and a second data string composed of the same data elements as the first data string is transmitted at a transfer rate higher than the transfer rate of the first data string. Transmitting means, and relay means for selectively transmitting the first data sequence or the second data sequence transferred from the transmitting means to the receiving side, wherein the relay means Said second transferred
Buffer means for sequentially holding the data strings of the first data string, and compares the data elements of the first data string sent to the receiving side with the data elements of the second data string read from the buffer means. When the predetermined condition of each data element is matched, the transmission is switched from the first data string to the transmission of the second data string, and the second data string starting from the data element at the time of matching is changed. A data transmission system comprising control means for controlling the data to be read from the buffer means and transmitted to the receiving side. 3. A relay device of a data transmission system for receiving a data string continuously transmitted from a transmission side and transmitting the data stream to a reception side at a predetermined transmission rate, wherein the transmission is performed at a predetermined transmission rate from the transmission side. First receiving means for receiving the first data string to be transmitted, and a data string having the same content as the first data string from the transmitting side, wherein the data stream is higher in speed than the transfer rate of the first data string. Second receiving means for receiving a second data string transferred at a speed, buffer means for sequentially storing the second data string received by the second receiving means in predetermined data element units, A data element constituting the first data string received by the first receiving means is compared with a data element constituting the second data string read from the buffer means, and a time series of the data string is compared. In the upper position Phase comparing means for determining whether or not the data elements match; and transmitting means for transmitting one of the first data sequence or the second data sequence to the receiving side, wherein the phase The first data sequence is sent to the receiving side until the comparison result matches according to the comparison result of the comparing means, and when the comparison result matches, the first data sequence is sent from the buffer to the buffer. Transmitting means for switching to the second data string read from the means and transmitting the second data string to the receiving side with the data element corresponding to the coincidence point as the head. Relay device. 4. A data transmission control method applied to a data transmission system for continuously transmitting a stream composed of a plurality of data frames from a transmitting node to a receiving node via a relay node, wherein the relay node comprises: A first stream transferred from a node at a predetermined transfer rate and a second stream transferred at a transfer rate higher than the transfer rate of the first stream, the stream having the same content as the first stream. Receiving the first stream and the second stream read from the buffer memory, sequentially accumulating the second stream transferred from the transmitting node in a buffer memory in data frame units. Are compared in units of data frames, and based on time information contained in each data frame, Performing a phase comparison of the data frame for position when the series of streams a determination is made as to whether or not to match, until the result of the phase comparison is determined to match, the first
Sending the stream to the receiving node at a predetermined transfer rate, and sending the stream to the second stream read from the buffer memory from the first stream when the result of the phase comparison is determined to match. And transmitting the second stream starting with the data frame corresponding to the determined time point to the receiving node. Executing a stream to the receiving node at a predetermined transfer rate. A data transmission control method comprising: storing a stream transferred at a high speed from the transmitting node in a state where the data is being transmitted. 5. The transmission means has a transfer adjustment means for adjusting a transfer rate of the first data string and a transfer rate of the second data string, and the relay means has a function of the first data string. When switching the transmission to the receiving side from the second data string to the second data string, the transmission means outputs an instruction for adjusting the transfer rate of each of the first data string and the second data string to the transmitting means, The control means determines whether or not each data element of the first data string matches the data element of the second data string at a time-sequential position of the data string. A first data string is sent to the receiving side, and when the result of the determination is a match, the first data string is switched to the second data string read from the buffer means and sent to the receiving side. 3. The method according to claim 2, wherein
Data transmission system as described. 6. A data transmission system for continuously transmitting a stream composed of a plurality of data frames from a transmission node to a reception node, wherein the data transmission system is provided in the transmission node and transmits a first stream at a predetermined transfer rate. Transmitting means for transmitting a second stream having the same content as the first stream at a transfer rate higher than the transfer rate of the first stream; and the first stream and the first stream transferred from the transmitting means. Receiving the second stream and the first and second
And a relay node having a function of selectively transmitting the first stream or the second stream to the reception node, wherein the relay node stores the first stream in the buffer memory means. When transmitting to the receiving node, a phase corresponding to a time-series data frame position of the second stream is being transmitted to the receiving node in response to a backward transmission command from the receiving node. Looking back the first stream from the first buffer memory means when lagging behind the stream phase,
When the phase of the second stream advances, the second stream is traced back from the second buffer memory means. When the second stream is sent to the receiving node, In response to the forward transmission command of the second stream, when the phase corresponding to the data frame position on the time series of the second stream is advanced with respect to the phase of the stream transmitted to the receiving node, Means for reading and transmitting the second stream from the buffer memory means, and for reading and transmitting the first stream from the first buffer memory means when the phase of the second stream is delayed. A data transmission system, characterized in that: