JPH11298458A - Synchronization establishing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a synchronization establishing system where synchronization is established between storage servers and user terminals by reducing jitter. SOLUTION: An MPU 121 sets a transmission time, determined by a CPU 111, of a unit data stream to be sent at an STC timer 1222. When the current time of a storage sever denoted by an STC counter 1221 reaches the transmission time set by the STC timer 1222, an STC section 122 causes an interruption to the MPU 121. The MPU 121 outputs a data transmission request to a data assembly section 13 in response to this interruption. The data assembly section 13 assembles the unit data stream to be sent in response to the received data transmission request into ATM cells and sends them to a user terminal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synchronization establishing apparatus, and more particularly, to a communication system in which a receiving end receives from a transmitting end a data stream divided into unit data of a predetermined size. The present invention relates to an apparatus for establishing synchronous communication between the receiving end and the transmitting end.

[0002]

2. Description of the Related Art In a video-on-demand (hereinafter abbreviated as VOD) system, a stream of video information and / or audio information is stored in a storage server in advance, and this stream is transmitted to a user in response to a request from the user. Is sent to the terminal. The user terminal decodes the transmitted stream and reproduces and outputs video information and / or audio information. Generally, video information and audio information are compressed, and the leading standard used for the compression is MP
EG (Moving Picture Experts)
Group). In a VOD system, MPEG is generally adopted.

[0003] In the VOD system, there are a pull type and a push type as a method relating to a stream transfer from a storage server to a user terminal. In the pull system, the user terminal acquires an MPEG stream from the storage server in accordance with its own decoding speed. In this pull-type system, a program stream (hereinafter abbreviated as PS) is used for stream transfer from the storage server to the user terminal. On the other hand, in the push type system, the MPEG stream is transmitted in synchronization with the clock of the storage server, and the user terminal establishes synchronization with the transmitted MPEG stream and reproduces and outputs. In this push type system, a transport stream (hereinafter abbreviated as TS) is used for stream transfer.

When a TS is used for stream transfer, a storage server uses a PCR (Program Clock) so that clock synchronization is established by a decoder of a user terminal.
Reference) must be transmitted periodically (at an interval of 100 msec or less). The user terminal uses this P
STC (System Time Clock), which is a reference clock synchronized with the storage server based on the CR
Generate Since the user terminal uses this STC,
Streams can be decoded in synchronization with the storage server.
Japanese Unexamined Patent Publication No. 9-270994 discloses an apparatus proposed by the present applicant for establishing and synchronizing an MPEG stream stored in a storage server with a PCR packet and transmitting the PCR packet. In this device, when the STC timer matches the value of the STC counter, the read control device acquires the corresponding MPEG stream from the data storage device and sends it. At this time, by synchronizing the PCR packet and the MPEG stream with each other and transmitting them, synchronization between the PCR packet and the MPEG stream is established.

[0005]

By the way, in stream transfer by TS, a user terminal performs PCR so that an internal buffer does not overflow or underrun.
The STC must be generated correctly based on the packet. Therefore, the fluctuation (jitter) generated between the PCR packet and the MPEG stream sent from the storage server must be reduced. In particular, a PCR packet requires high accuracy with respect to jitter. If jitter occurs and the PCR packet arrives at the user terminal earlier or later than the time it should have arrived, the user terminal side cannot generate the STC accurately, and as a result, the internal buffer becomes There is a first problem of overflow or underrun.

[0006] Even when the storage server sends a stream to a plurality of user terminals, synchronization must be established between the storage server and each user terminal. However, in the conventional stream transfer, there is a second problem that synchronization is not considered at all between the storage server and the plurality of user terminals.

Therefore, an object of the present invention is to provide a synchronization establishing apparatus for establishing synchronization between a storage server and a user terminal by reducing jitter. It is another object of the present invention to provide a synchronization establishing device for establishing synchronization between a storage server and a plurality of user terminals.

[0008]

Means for Solving the Problems and Effects of the Invention The first invention is a communication system in which a receiving end receives a data stream divided into unit data of a predetermined size from a transmitting end. A time specifying unit for specifying a transmission time of each unit data to be transmitted to the receiving end, and a current time internally measured by the time specifying unit. A transmission unit for transmitting each corresponding unit data to the receiving end when each transmission time specified by the unit is reached, wherein the transmission time of each unit data guarantees a unique transmission speed of the data stream. It is characterized by being specified.

According to the first aspect, the transmission time of each unit data is specified so as to guarantee the transmission speed. Therefore, the data stream is generated without causing jitter.
Received by the receiving end. As a result, overflow or underrun of the buffer at the receiving end is reduced.

[0010] In a second aspect based on the first aspect, a plurality of receiving ends are connected to the transmitting end, and the time designating section transmits, for each of the plurality of receiving ends, each unit data to be transmitted. The transmission unit determines a transmission order of each unit data to be transmitted to the plurality of receiving ends based on the transmission times specified by the time specification unit. When the current time measured internally reaches each of the transmission times specified by the time specification unit while following the transmission order, the corresponding unit data is transmitted to the receiving end.

According to the second aspect, a transmission time is specified for each unit data to be transmitted for each receiving end, and the transmission unit follows the transmission order determined based on the transmission time. Accordingly, even when a plurality of receiving ends are connected to the transmitting end, that is, when transmitting data streams to a plurality of channels, each data stream can be received without jitter. Received by the end.

[0012] In a third aspect based on the first or second aspect, unlike the unit data, the non-priority data whose transmission time is not specified is configured to be transmittable. After the transmission of the unit data is completed, the non-priority data that can be transmitted is transmitted to the receiving end before the transmission time of the next unit data to be transmitted comes.

According to the third aspect of the present invention, after the transmission of each unit data is completed, the non-priority data that can be transmitted is transmitted using the idle time until the transmission time of the next unit data to be transmitted. Can be sent. Accordingly, data can be efficiently transmitted from the transmitting end to the receiving end.

According to a fourth aspect of the present invention, in any one of the first to third aspects, each of the unit data is encoded based on the MPEG standard, and the transmitting unit measures the current time internally. At each transmission time specified by the time specification unit, a PCR packet used by the receiving end to establish clock synchronization with the transmitting end before transmitting the corresponding unit data to the receiving end. Is transmitted to the receiving end.

[0015] According to the fourth aspect of the present invention, in the case of data stream transfer using a transport stream (TS), jitter that can occur in a PCR packet becomes smaller than in the past. Since such a PCR packet is received by the receiving end, the buffer of the receiving end is less likely to overflow or underrun.

In a fifth aspect based on the fourth aspect, the transmission unit includes a PCR timer for designating a transmission time at which the PCR packet is to be transmitted, and the current time measured internally is determined by the time specification. If the corresponding unit data cannot be transmitted to the receiving end even at the transmission time specified by the section, the current time is set to the transmission time specified by the PCR timer, and the PCR packet is It is characterized by transmitting to the receiving end.

According to the fifth aspect, even when the transmission interval of the PCR packet does not satisfy the MPEG standard due to the fluctuation of the processing load of the transmission unit or the like, the transmission interval of the PCR packet can be guaranteed.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A synchronization establishing apparatus according to each embodiment of the present invention is applied to a communication system in which a transmitting end and a receiving end need to communicate synchronously as in the above-mentioned VOD system. You. FIG. 1 is a block diagram showing a configuration of the synchronization establishing apparatus according to the first embodiment of the present invention. In FIG. 1, the synchronization establishing device is installed on the transmission end side of the communication system, more specifically, on the storage server side of the VOD system, and includes an upper layer and a lower layer. The upper layer includes a transmission control unit 11 and a data transmission unit 12. The transmission control unit 11 includes a CPU 111 and a main memory 112.
And typically comprises a personal computer (hereinafter referred to as
PC). The data transmission unit 12
U121, STC 122, control memory 123 and packet memory 124. The lower layer is a data transmission unit 12
And a data assembling unit 13. The data transmitting unit 12 and the data assembling unit 13 are typically mounted on an expansion board that can be inserted into the PC expansion slot.

A storage device 14 is communicably connected to an upper layer via an interface unit 15 outside the synchronization establishing device. The storage device 14 stores a plurality of data streams DS including complete video information and audio information. As shown in FIG. 2, one data stream DS is divided into, for example, 64 KB unit data streams and has a unique transmission rate. Each unit data stream is provided with a number (hereinafter, referred to as a RAP number) indicating a transmission order, as shown in parentheses in FIG. Further, in each unit data stream, a value (hereinafter, referred to as an NPT value) relating to a transmission time to be transmitted to a user terminal (not shown) located outside the storage server is defined. This NPT value is determined based on the NPT value of the unit data stream having the immediately preceding RAP number.

The storage device 14 further stores an auxiliary file RF as shown in FIG. This auxiliary file RF is created for each data stream DS. Further, for each unit data stream, RA
The P number, the NPT value, and the storage location in the storage device 14 are written. For example, the unit data stream with the RAP number “2” has the NPT value “t ₂ ”, and in the present embodiment, the time “t ₂ ” has elapsed since the one with the RAP number “1” was transmitted. Then it is sent. Also, R
The storage position of the unit data stream with the AP number “2” is “x0ab”.

Hereinafter, the detailed operation of the synchronization establishing apparatus of this embodiment will be described with reference to the flowchart shown in FIG. 4 and the sequence chart shown in FIG. First, the user terminal
The storage server is requested to reproduce a certain data stream DS from a predetermined RAP number (this description assumes "5"). The CPU 111 of the synchronization establishing device responds to the request from the user terminal by using the auxiliary file R in the storage device 14.
With reference to F, the storage position of the unit data stream to be transmitted to the user terminal in the storage device 14 is recognized. According to the above assumption, the requested data stream D
In S, the storage position “x0ae” of the unit data stream after the RAP number “5” is recognized. CPU1
11 reads the unit data stream to be transmitted to the user terminal with reference to the recognized storage position, and writes it to the main memory 112 (step S401). According to the above assumption, the unit data stream of the number “5” is read from the storage position “x0ae” and written to the main memory 112. Also, the unit data streams after the number “6” are similarly written.

Next, the CPU 111 executes DMA (Direct Me
mory Access) request command is written to the packet memory 124 (step S402). The MPU 121 reads the DMA request command written in the packet memory 124 (Step S403). As a result, the DMA request command is transferred from the transmission control unit 11 to the data transmission unit 12 (sequence SQ501 (see FIG. 5)). As a result, the unit data stream written in the main memory 112 in step S401 is DMA-transferred to the packet memory 124 (step S404, sequence SQ502). When the DMA transfer ends (step S405), the MPU 121 writes the DMA transfer end notification status into the packet memory 124 (step S406). The CPU 111 reads the DMA transfer end notification status from the packet memory 124 (step S407). As a result, the DMA transfer end status written in the packet memory 124 in step S406 is transferred from the data sending unit 12 to the sending control unit 11 (sequence SQ503), and the CPU 111 recognizes that the DMA transfer has been completed.

When recognizing the completion of the DMA transfer, the CPU 111 issues a current time acquisition request command to the packet memory 12.
4 (step S408). The MPU 121
The current time acquisition command written in the packet memory 124 is read (step S409). As a result, the current time acquisition request command written in the packet memory 124 in step S408 is transferred from the transmission control unit 11 to the data transmission unit 12 (sequence SQ504).
After step S409, the MPU 121
STC indicating the reference time on the storage server in 2
After reading the current time from the counter 1221 (step S410), the current time notification status including the current time is written to the packet memory 124 (step S41).
1). The CPU 111 reads the current time notification status written in the packet memory 124 (step S
412). As a result, the current time notification status written in the packet memory 123 in step S411 becomes
The data is transmitted from the data transmission unit 12 to the transmission control unit 11 (sequence SQ505). As a result, the CPU 111 is notified of the current time. Now, assume that the current time is 15:00.

The CPU 111 determines the transmission time of the unit data stream to be transmitted this time based on the notified current time (step S413). In this embodiment, the transmission time of the unit data stream transmitted first is determined to be one minute after the current time obtained in step S412. The transmission time of the other unit data streams is determined based on the NPT value and the transmission time of the unit data stream transmitted immediately before. According to the above assumption, the transmission time is determined to be 15:01 for the unit data stream of the RAP number “5” transmitted first. Further, for example, for the unit data stream with the RAP number “6”, the transmission time is determined to be “t ₆ ” after 15:01.

Next, the CPU 111 writes a data transmission request command into the packet memory 124 (step S).
414). The data transmission request command includes the transmission time determined by the CPU 111 for the unit data stream to be transmitted this time. According to the above assumption, the transmission time included in the current data transmission request command is “15:01”. The MPU 121 reads the data transmission request command written in the packet memory 124 (Step S415). As a result, the data transmission request command is transmitted from the transmission control unit 11 to the data transmission unit 12.
(Sequence SQ506). MPU12
1 sets the transmission time included in the read data transmission request command in the STC timer 1222 composed of a register in the STC unit 122 after step S415 (step S416). According to the above assumption, ST
15:01 is set in the C timer 1222 as the transmission time. Further, the MPU 121 writes information (ATM cell header information, a packet memory address of data to be transferred, and the like) necessary for the data assembling unit 13 to assemble the ATM cell into the control memory 123 (step S41).
7).

The STC unit 122 includes an STC counter 122
1 is equal to the time set in the STC timer 1222 (step S418), the MPU 12
An interrupt is generated for 1. The MPU 121 transmits a data transmission request in response to this interrupt (Step S419). Further, the MPU 121 writes the transmission start notification status in the packet memory 124 (Step S420).

The data transmission request is input to the data assembling unit 13 (sequence SQ507). Data assembler 1
3 reads information necessary for assembling an ATM cell from the control memory 14 in response to the data transmission request;
The unit data stream to be transmitted this time is read from the packet memory 124. After that, the data assembling unit 13
Constructs an ATM cell based on the read information and the unit data stream and outputs the assembled ATM cell to the user terminal. Further, the CPU 111 reads the transmission start status from the packet memory 124 (step S421).
As a result, the transmission start status is changed to the data transmission unit 12.
To the transmission control unit 11 (sequence SQ50).
8), the CPU 111 recognizes that the unit data stream is being transmitted to the user terminal.

If there is another unit data stream to be transmitted, the CPU 111 proceeds to step S40 in FIG.
Step 8 and subsequent steps are executed. As a result, when expressed on the time axis, each unit data stream may have a predetermined transmission interval with respect to the unit data stream transmitted immediately before. This transmission interval is within a predetermined time interval (100 msec in the case of MPEG) and is the maximum value that can transmit a unit data stream of a predetermined size (64 KB in this description). The transmission time is determined by the CPU 111 based on such a transmission interval in step S413 in FIG. For example, when one data stream DS has a specific transmission rate of 6 Mbps, it takes 87.4 msec to transmit a unit data stream of 64 KB. Therefore, the storage server sets the transmission interval to 87.4 m.
When transmitted in sec, each transmitted unit data stream is ideally transmitted without generating a no-signal section as shown in FIG. 6A, and as a result, is received by the user terminal without generating jitter. Is done. A conventional storage server may not be able to transmit each unit data stream at an accurate transmission rate, and as a result, jitter may occur and a buffer (not shown) of a user terminal may overflow or underrun. . However, the synchronization establishing apparatus according to the present embodiment transmits each unit data stream at the transmission time determined to have the above-described transmission interval. As a result, even if the storage server cannot transmit the data at the correct transmission rate, each transmitted unit data stream has a non-signal section as shown in FIG. 6B. Considering this non-signal section, each unit data stream is transmitted at a specific transmission rate. As a result, overflow or underrun of the buffer of the user terminal is reduced.

Next, a synchronization establishing apparatus according to a second embodiment of the present invention will be described. The present synchronization establishing apparatus has the same configuration as that of the first embodiment, and therefore, FIG. However, the present synchronization establishing apparatus is different from the first embodiment in the following points. First, the synchronization establishing unit, the user terminal of the N stage is communicatively connected via different N channels Ch ₁ to CH _N together. IDs (hereinafter, referred to as ChIDs) are assigned to channels of the plurality of user terminals in advance so that the CPU 111 can identify each of them. In this description, ChID ₁ -C
It is assumed that hID _N is added in advance. Furthermore, the synchronization establishing apparatus is characterized in that the transmission order control described below is performed to guarantee a unique transmission rate of each data stream transmitted to a plurality of user terminals.

The operation of the synchronization establishing apparatus will be described below. CPU 111 and MPU 121 of the synchronization establishing apparatus
Is basically the same as the first embodiment, executes its own process shown in the flowchart of FIG. 4 and the sequence chart of FIG. 5, and outputs a unit data stream to be transmitted for each ChID, and The corresponding data transmission request commands are written in the packet memory 124 (steps S401 to S414). Unlike the first embodiment, the packet memory 124 stores each C as shown in FIG.
Queues 71 _{1 to} 71 _{N for} each hID are prepared in advance. ChID ₁ ~ChID _N data transmission request command is stored in the corresponding queue 71 ₁ -71 _N. MP
The U121 sorts the stored data transmission request commands for each of the queues 71 _{1 to} 71 _{N in} ascending order of transmission time. Therefore, the transmission time included in the data transmission request command located at the head of each of the queues 71 _{1 to} 71 _N is that of the unit data stream to be transmitted first to the corresponding ChID _{1 to} ChID _N.

In this embodiment, the MPU 121 must select one queue storing a data transmission request command to be read from the packet memory 124 from the plurality of queues 71 _{1 to} 71 _{N in} step S 415 of FIG. Must. Therefore, the MPU 121
_1-71 compares the transmission time included in the data transmission request command located at the head of the _N, obtains the data transmission request command which contains the earliest transmission time. MPU121
Sets the transmission time of the obtained data transmission request command in the register 1222, as shown in FIG. After that, as described in the first embodiment, when the operations of steps S417 to S420 are performed, the data transmission unit 12 stores the data transmission request command to be read from the packet memory 124 again, as described above. 1
Select one queue.

As described above, the present synchronization establishing apparatus
The transmission order control as described above is executed to guarantee a specific transmission rate of each data stream transmitted to a plurality of user terminals, whereby each user terminal receives the unit data stream in synchronization with the storage server. It becomes possible.

Next, a synchronization establishing apparatus according to a third embodiment of the present invention will be described. The present synchronization establishing apparatus has the same configuration as that of the first embodiment, and therefore, FIG. However, the present synchronization establishing apparatus is different from the first embodiment in the following points. That is, FIG.
As is clear from (b), in the synchronization establishing apparatus according to the previous embodiment, a non-signal section (referred to as idle time) may occur between the transmitted unit data streams. The synchronization establishing apparatus according to the third embodiment uses this idle time to transmit data that does not require real-time processing (hereinafter referred to as non-priority data) unlike unit data streams that require real-time processing. It is characterized by the following. In addition, since the unit data stream is required to have real-time properties, in this embodiment, it is referred to as priority data for convenience.

To realize this feature, the data amount of the priority data (unit data stream) (6
4 KB) and a parameter for specifying the data amount of the non-priority data. In the present embodiment, not only the priority data but also the non-priority data are stored in the main memory 112.
Is transferred to the packet memory 124 by DMA. However, as described in the first embodiment, the transmission time is determined for the priority data, but the transmission time is not determined for the non-priority data.

As described in the first embodiment, the STC
When the unit 122 generates an interrupt in step S418 in FIG. 4, the MPU 121 transmits a data transmission request for priority data to the data assembling unit 13 in step S419. The data assembling section 13 reads out the priority data to be transmitted from the packet memory 124, assembles and transmits the ATM cells. When the transmission of the priority data is completed, the data assembling unit 13 generates an interrupt to the MPU 121. M
The PU 121 responds to this interrupt by responding to the STC unit 12.
The current time is acquired from the second counter 1221 and the amount of data that can be transmitted by the transmission time included in the next data transmission request command to be transmitted is calculated. And MPU121
Transmits to the data assembler 13 a data transmission request for non-priority data of a data amount that can be transmitted. The data assembling unit 13 assembles the non-priority data into ATM cells and transmits the ATM cells.

In this embodiment, the STC counter 1221
When the priority data is transmitted first when the interrupt occurs, the jitter of the priority data can be reduced, and the non-priority data can be transmitted using the idle time during which the priority data is not transmitted.

Next, a synchronization establishing apparatus according to a fourth embodiment of the present invention will be described. The configuration of the synchronization establishing apparatus of this embodiment is the same as that of the first embodiment except that the unit data stream to be transmitted is a TS packet of video information and / or audio information encoded based on the MPEG standard. , And TS packets are mapped to ATM cells and transmitted. The MPU 121 determines in step S4 in FIG.
When the data transmission request command is read from the packet memory 124 from the CPU 11 at 15, the transmission time included in the command is set in the register 1222 of the STC unit 13 (step S416). Immediately after this setting, the MPU 121 generates a PCR packet using the value set in the register 1222 as a PCR value, and writes the PCR packet in a predetermined area of the packet memory 124. The MPU 121 is shown in FIG.
In step S418, when the STC unit 122 generates an interrupt, a data transmission request for a PCR packet is transmitted to the data assembling unit 17 prior to the TS packet transferred from the main memory 122, and then a data transmission request for the TS packet is transmitted. Send Data assembler 13
Responds to the data transmission request from the MPU 121,
An ATM cell is assembled and transmitted in the order of the R packet and the TS packet. As a result, the PCR packet and the TS packet are transmitted to the user terminal as shown in FIG.

In this embodiment, the PCR packet is transmitted with the highest priority when the STC unit 122 interrupts. Therefore, the fluctuation (jitter) of the transmission time of the PCR packet can be reduced, whereby the user terminal can
The TS packet can be decoded in accurate synchronization with the storage server.

Next, a synchronization establishing apparatus according to a fifth embodiment of the present invention will be described with reference to FIG. In FIG. 9, the synchronization establishing apparatus according to the present embodiment is different from the fourth embodiment in that a PCR timer 91 is provided in the data transmission unit 12. Since there is no other difference, the same components are denoted by the same reference numerals.

The PCR timer 91 generates an interrupt to the MPU 12 when the STC counter becomes equal to the value set in the PCR timer, similarly to the STC timer.
When reading the data transmission request command from the CPU 111 from the packet memory 124 in step S415, the MPU 121 sets the transmission time included in the command to ST
The value is set in the STC timer 1222 of the C unit 122 (step S416). Immediately after this setting, the MPU 121
PC that uses the value set in TC timer 1222 as the PCR value
An R packet is generated and written to a predetermined area of the packet memory 124. In addition, the MPU 121
A value obtained by adding 100 msec to the value set in the C timer 1222 is set in the PCR timer 91.

The MPU 121 determines in step S418 in FIG.
Then, when the STC unit 122 generates an interrupt, the STC unit 122 generates an interrupt prior to the TS packet transferred from the main memory 122.
The data assembler 1 sends a data transmission request for a CR packet.
7, and then transmits a data transmission request for the TS packet. The data assembling unit 13 assembles and transmits the ATM cells in the order of the PCR packet and the TS packet in accordance with the data transmission request from the MPU 121. As a result, the PCR packet and the TS packet are transmitted to the user terminal as shown in FIG.

Here, designated by the CPU 111,
The difference between the current transmission time and the previous transmission time is 100 ms
If ec or more, the set value of the PCR timer 91 becomes equal to the current time indicated by the STC counter 1221 earlier than the set value of the STC timer 1222, so that the interrupt of the PCR timer 91 occurs earlier. At this time, MP
The U121 transmits a data transmission request of a PCR packet including the set value of the PCR timer 91 to the data assembling unit 17 when the interruption of the PCR timer 91 occurs.
As a result, only the PCR packet is transmitted to the user terminal.

In the present embodiment, even when the transmission control unit 11 encounters a state where the transmission interval of the PCR packet cannot satisfy the MPEG standard due to some factor such as fluctuation of the processing load, the processing of the data transmission unit 12 is performed. P
The transmission interval of the CR packet can be guaranteed.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a synchronization establishing apparatus according to a first embodiment.

FIG. 2 is a diagram for explaining each data stream DS stored in a storage device 14 shown in FIG.

FIG. 3 is a diagram for explaining an auxiliary file RF stored in a storage device 14 shown in FIG.

FIG. 4 is a flowchart showing an operation of the synchronization establishing apparatus shown in FIG. 1;

FIG. 5 is a sequence chart showing an operation of the synchronization establishing apparatus shown in FIG. 1;

FIG. 6 is a diagram for explaining features of the synchronization establishing apparatus shown in FIG. 1;

FIG. 7 is a diagram for explaining a synchronization establishing apparatus according to a second embodiment.

FIG. 8 is a diagram for explaining features of a synchronization establishing apparatus according to a fourth embodiment.

FIG. 9 is a block diagram illustrating a configuration of a synchronization establishing apparatus according to a fifth embodiment of the present invention.

[Explanation of symbols]

 11: Transmission control unit 111: CPU 112: Main memory 12: Data transmission unit 121: MPU 122: STC unit 123: Control memory 124: Packet memory 13: Data assembly unit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H04N 7/14 H04N 7/13 Z (72) Inventor Reiko Yasue 2-6-1 Sakae, Naka-ku, Nagoya City, Aichi Prefecture Shirakawa Building Annex 5F Matsushita Electric Information System Nagoya Research Laboratories Co., Ltd. (72) Inventor Tsutomu 1006 Kazuma Odoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] An apparatus for establishing synchronization between a receiving end and a transmitting end in a communication system in which a receiving end receives a data stream divided into unit data of a predetermined size from a transmitting end. A time designating unit that designates a sending time of each unit data to be transmitted to the receiving end; and when the current time measured internally becomes each sending time designated by the time designating unit, A synchronization unit for transmitting unit data to the receiving end, wherein a transmission time of each unit data is specified so as to guarantee a specific transmission speed of the data stream. 2. A transmission terminal, wherein a plurality of reception terminals are connected to the transmission terminal, wherein the time designation unit designates, for each of the plurality of reception terminals, a transmission time of each unit data to be transmitted, Determines the transmission order of each unit data to be transmitted to the plurality of receiving ends based on each transmission time specified by the time specification unit, and internally measures while following the determined transmission order. 2. The synchronization establishing apparatus according to claim 1, wherein when the current time reaches each transmission time designated by the time designation unit, the corresponding unit data is transmitted to the receiving end. 3. The apparatus according to claim 2, wherein, unlike each of the unit data, the non-priority data whose transmission time is not specified is configured to be transmitted, and the transmission unit transmits the next unit data after completing the transmission of each unit data. 3. The synchronization establishing apparatus according to claim 1, wherein the transmittable non-priority data is transmitted to the receiving end before a transmission time of power unit data comes. 4. 4. The unit data is encoded based on the MPEG standard, and the transmitting unit responds when a current time measured internally becomes each transmission time specified by the time specifying unit. 2. The method according to claim 1, wherein prior to transmitting each unit data to the receiving end, the receiving end transmits to the receiving end a PCR packet used for establishing clock synchronization with the transmitting end. 4. The synchronization establishing device according to any one of claims 3 to 3. 5. The transmission unit includes a PCR timer for designating a transmission time at which the PCR packet is to be transmitted, and a current time measured internally becomes a transmission time designated by the time specification unit. Also, if the corresponding unit data could not be transmitted to the receiving end, the PCR packet is transmitted to the receiving end at the current transmission time specified by the PCR timer. The synchronization establishing apparatus according to claim 4.