JP3156721B1 - Data transmission system - Google Patents

Abstract

A procedure related to acquisition of a band is simplified by expressing a propagation delay of a communication medium using an identifier. SOLUTION: Band acquisition means 6 of a second transmission device 614
09, after stopping the transmission of the first transmitting device 606,
Propagation delay identifier 1 read from first transmitting apparatus 606
05 and the maximum transmission data amount 605,
The band used by the first transmitting apparatus 606 is obtained, and transmission is started using this band. Necessary procedures are simplified because switching between transmission devices does not involve returning and reacquiring a band. Further, by using the propagation delay identifier, the band can be effectively used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission system for transmitting video and audio signals between digital video and audio equipment.

[0002]

2. Description of the Related Art A P1394 interface can be used as a means for transmitting digital video data and audio data. P1394 is a high-speed serial interface for next-generation multimedia that is being studied by the IEEE (Ref.
Serial bus P1394 Draft 7.1v1: High
Performance Serial Bus P1394 / Draft 7.1v1). P13
Reference numeral 94 denotes a serial bus type communication medium capable of guaranteeing the real-time property required for transmitting video data and audio data.

[0003] Devices (hereinafter referred to as nodes) connected to the P1394 are connected in a tree structure having branches, and a node having a plurality of terminals outputs a signal received from one terminal to another terminal to output a signal. Relay. Therefore, it is guaranteed that data output from any node reaches all connected nodes. For this reason, although P1394 has a tree structure in terms of structure, it theoretically operates as a bus. However, in P1394, since a bus is realized by relaying a plurality of nodes, a propagation delay depending on the number of relay nodes occurs in addition to a propagation delay determined by the length of the transmission path. In P1394, the arbitration of the bus by only one node guarantees that a plurality of nodes do not transmit at the same time.

As described above, each node configured as a bus has an identifier (hereinafter referred to as a node I) for identifying the node.
D) is added. The addition of this node ID is
This is automatically performed by initializing the bus (hereinafter, referred to as a bus reset) that occurs when a new node is added to the bus or when the node is disconnected. When a bus reset occurs, a node connected to the bus sends a packet indicating the connection status of the node (hereinafter referred to as a self-ID packet) to the bus in a predetermined order. The node ID is determined by the order of transmission of the self ID packet. The self ID packet includes the node ID determined at the time of transmission and information indicating whether or not another terminal is connected to each terminal. . The nodes on the bus can know the tree structure of the bus by receiving and analyzing all the self ID packets sent from each node.

Further, P1394 operates based on a cycle (hereinafter, referred to as a cycle) every 125 μsec, and performs a synchronous transfer performed in the first half of each cycle and an asynchronous transfer performed in a time remaining after the synchronous transfer is performed. Two types of transfer can be performed. Transfer of data that requires real-time properties such as video data and audio data is transferred using this synchronous transfer, while control information that does not require real-time properties is transferred using asynchronous transfer.

When performing synchronous transfer, it is necessary to obtain the time (band) to be used in one cycle from the node that manages the band before transmitting. In P1394, there is one node on the bus that manages the band used for synchronous transfer, and the band to be used is transmitted from this band management node after acquiring it. The node performing the synchronous transfer can transmit data within the range of the acquired band, and the data transmitted by the synchronous transfer is transmitted as a packet specified in P1394. In synchronous transfer, real-time data can be transferred by guaranteeing transfer of a predetermined amount of data for each cycle. Here, the bandwidth to be acquired prior to transmission is the bandwidth necessary for the actual data transfer and the overhead such as the propagation delay that occurs at the time of data transfer and the bandwidth required for the data transfer added for the purpose of error detection. It is a combination of

In P1394, a plurality of transmission rates can be used in combination, and a signal indicating the transmission rate is output before transmitting a packet to identify them.

Further, in P1394, all nodes connected to the bus have a virtual address space, and the transfer of asynchronous data between the nodes is performed as a read operation or a write operation of this address space. Also, a part of this address space includes a register used for controlling the operation of each node. A node connected to the bus can know the state of that node by reading the control register of another node, and can control the node by writing to the control register.

It is conceivable to control transmission and reception of synchronous data using such a control register. In such a case, the state of transmission or reception can be known by reading the register for synchronous communication control.On the other hand, by writing a necessary value to this register, transmission or reception of synchronous data can be started, Conversely, control such as stopping can be performed.

[0010]

When transmission is performed after acquiring a part of the bandwidth of a communication medium prior to transmission as in P1394 or the like, the communication that has already been performed is stopped, and the stop is performed. It is possible that transmission of another device is started by using the band used in the communication that was performed.

An example is a case where the second device attempts to start sending data while the first device sends data to a communication medium. Here, the second communication medium
If there is a band left for the device to transmit data, the second device can start transmission after acquiring the band. However, if the required band is not left, transmission cannot be started. So the first
By stopping transmission of the second device, transmission can be started after the second device secures a band required for transmission.

In such a case, it is necessary to return the used band once to the band management node, obtain the band again, and then start transmission. Also, since the acquisition of the band must be performed after the return of the band, the device that acquires the band needs to check whether the return of the band has been completed and monitor the return operation. Furthermore, since it takes time from when the bandwidth is returned to when the bandwidth is acquired again, there is a risk that another node may acquire the bandwidth.

That is, there is a problem that a procedure for acquiring a band is complicated. On the other hand, when a propagation delay occurs depending on the connection form of the node connected to the communication medium as in P1394, in addition to the band required for actual transmission, the band including the overhead such as the time of the propagation delay is used. Must be obtained.

In such a case, the predetermined
It is possible to acquire a band based on the maximum propagation delay time. However, when the band to be acquired is determined based on the maximum propagation delay time assumed in this way, an unnecessary band is actually acquired, so that the communication medium cannot be used efficiently. For this reason, there is a danger that other communications that should be able to communicate should be prevented.

That is, if a band is acquired based on the maximum value of the propagation delay, there is a problem that the communication medium cannot be used efficiently.

[0016]

According to a first aspect of the present invention, there is provided a data transmission system capable of performing synchronous transfer, and determining the value of a propagation delay identifier when performing transmission by synchronous transfer. A system by a device connected to a communication medium that needs to be allocated a transmission band determined by adding a band required for transmission determined by the maximum transmission data amount, and a bandwidth of overhead,
By writing a value to the register of the transmitting device,
A transmission control device that controls transmission, a transmission delay identifier holding unit that holds a propagation delay identifier used to determine a bandwidth of an overhead when a band is allocated in advance before transmission when performing transmission, and Maximum transmission holding a maximum transmission data amount indicating a maximum amount of data that can be included in a packet transmitted to the communication medium and used for calculating a band required for packet transmission when a band is allocated in advance prior to the transmission. Data amount holding means;
A counter for controlling start and stop of transmission is provided in the register, and the contents of the propagation delay identifier holding unit and the maximum transmission data amount holding unit are transmitted from another device connected to the communication medium. By being readable via the medium, it is possible to know the band to be released when another device stops transmitting the transmission device, and furthermore, the propagation delay identifier holding unit is connected to the communication medium. A transmission device that is writable from the other device via the communication medium, the transmission device includes the propagation delay identifier holding unit and the maximum transmission data amount holding unit in a continuous area on the register, A management node that manages a synchronous transfer band in a communication medium, wherein the transmission control device starts transmission by the transmission device; Reading the maximum transmission data amount having the maximum packet size for synchronization data from the read maximum transmission data amount, and the first bandwidth required for the synchronous transfer of the packet from the data rate of the communication medium. Is determined from a value of the propagation delay identifier, a second band that is an overhead band is determined using a correspondence table of the propagation delay identifier and the overhead band, and a value obtained by adding the first band and the second band is determined. receiving a bandwidth allocation from the management node, the value of the propagation delay identifier used when receiving an allocation of bandwidth is set to the propagation delay identifier holding means of the transmitting device, the value in the counter of the register of the transmitting device The transmission is started by writing the following.

[0017]

Embodiments of the present invention will be described with reference to the drawings.

In this embodiment, the communication medium 1 shown in FIG.
Data transmitter 107 that transmits synchronization data 08 receives propagation delay identifier holding unit 1 that holds propagation delay identifier 105.
01, a maximum transmission data amount holding unit 102 for holding the maximum transmission data amount 106, a band acquisition unit 103, and a transmission / reception unit 104. When transmitting synchronous data to P1394, it is necessary to acquire a bandwidth from a node that manages the bandwidth before transmitting the data.

FIG. 2 shows a band required to be acquired when synchronous data is transmitted to P1394. The bandwidth of the synchronous data includes a time T1 from the detection that the bus is unused to a request for the right to use, a propagation time T2 required for the request for the right to use the bus to reach the management node, Determination time T3 at the usage right management node, propagation time T required to receive the determination result output from the usage right management node
4. Bus occupation period T5 before data transmission, time T6 for outputting a signal indicating the data transmission rate, time T7 for transmitting the packet itself, time T8 for outputting a signal indicating the end of transfer, and packet The bandwidth corresponds to the time determined by the total propagation delay T9 before reaching the use right management node.

In this band, the value other than T7, which is the time required for transferring the packet itself, is irrelevant to the transmission rate and the amount of transmission data, and is a value between the transmitting node and the node managing the right to use the bus. Is determined by the number of relay nodes existing in However, in P1394, the node that manages the right to use the bus does not need to be at the center of the connection, so the time taken other than the packet transfer time differs depending on each node. In order to obtain a value for each node, the position on the bus of the node that manages the right to use the bus must be considered.

However, when this value is obtained as a value irrelevant to the position of the use right management node, and when the same value is used for the entire bus, the maximum number of relay nodes existing on the bus is determined by the transmission node and the bus. May be used as the maximum number of relay nodes between the nodes that manage the usage rights of.

Therefore, as shown in FIG. 3, it is considered that a transmission node 303 which is N (N-1) relay nodes 302 apart from a node 301 that manages the right to use a bus outputs a packet. In this case, when the calculation is performed using the value specified in the P1394 standard, the time Toh used for other than packet transfer becomes the value shown in (Equation 1).

[0023]

(Equation 1)

Further, when this value is expressed using a unit used for band management in P1394, a necessary band (hereinafter referred to as an overhead band) BWoh other than the packet transfer band is expressed as (Equation 2). Can be done.

[0025]

(Equation 2)

The unit of the band used in P1394 is 1
This is a value where the band required for 2-bit transfer at the time of transmission at 00 Mbps is 1.

The propagation delay identifier 105 is used for the communication medium 108
The overhead band can be uniquely determined based on the value of this identifier. In the initial state, the propagation delay identifier 105 held in the propagation delay identifier holding means 101 is P13
A value corresponding to the overhead band when there are 15 relay nodes in 16 connections, which is the maximum connection form allowed in 94, is set. On the other hand, the maximum transmission data amount 106 held by the maximum transmission data amount holding means 102 is P13
It shows the maximum data amount that can be included in the payload portion, which is the data portion of the synchronous communication packet used in 94. FIG. 4 shows a format of a packet used for transmitting synchronous data. Packets for synchronous data transfer are:
4-byte packet header 40 specified in P1394
1, 4-byte CRC 402 for packet header, 8-byte C used to indicate the type of synchronization data, etc.
It comprises an IP header 403, synchronous data 404, and a 4-byte data CRC 405. Of these, the portion where the CIP header 403 and the synchronization data 404 are combined is the payload, and the size of the synchronization data is variable depending on the type of data and the rate required for transmitting the data.

To this packet, in addition to the synchronization data, 20 bytes of data including the header of the packet and the like are added. Among these, the value stored in the maximum transmission data amount holding means is the sum of 8 bytes of the CIP header 403 and the data amount of the synchronous data. Therefore, the bandwidth required to be acquired prior to transmission is the bandwidth required when a packet having a size obtained by adding 12 bytes to the value indicated in the maximum transmission data amount is transmitted at the rate used for transmission. , A band obtained by combining the above-mentioned overhead band.

On the other hand, FIG. 5 shows the configuration of a transmission PCR (plug control register) which is a register for controlling transmission of synchronous data, which is placed in the address space of each node of P1394. PCR is 32 bits
A 1-bit valid flag 501 indicating whether the PCR is usable or not, indicating that transmission controlled by the transmission PCR can be stopped during transmission.
Bit unknown connection counter 50
2. 6-bit connection counter 503 indicating the number of devices that have instructed the PCR, 2-bit unused field 504, channel 505 indicating the channel number used for transmitting 6-bit synchronous data, used for transmission A 2-bit data rate 506 indicating the rate at which data is transmitted, a 4-bit overhead ID 507 corresponding to the propagation delay identifier holding means, and a payload size corresponding to the maximum transmission data amount holding means, expressed in units of 4 bytes. It consists of a payload size 508 of bits.

The transmission control device that controls transmission can control transmission by writing a value to this register, while reading the value of this register allows the transmission state at that time to be known. The transmission device performs transmission when a value other than 0 is written to the unowned connection counter 502 or the connection counter 503 while the valid flag 501 of the transmission PCR is 1. Conversely, when both of them become 0, the output is stopped. Note that the connection counter 5
03 is 0, unowned connection counter 5
Only when 02 is 1, a device other than the device that has instructed the start of transmission can clear the unknown connection counter 502 and stop the transmission.

When the band acquisition means 103 performs this band acquisition, the propagation delay identifier 105 may be rewritten for the reason described later. The bandwidth is acquired based on the maximum transmission data amount 106 held in the transmission data amount holding unit 102. When performing bandwidth acquisition, the bandwidth acquisition unit 103 reads the maximum transmission data amount 106 from the maximum transmission data amount holding unit 102, and obtains the maximum transmission data amount from the payload size for the above-described reason. By adding 12 bytes to the quantity 106, the bandwidth required for transmitting a packet of this size at the data rate 506 included in the PCR is determined. Further, the band acquisition unit 103 reads the propagation delay identifier 105 from the propagation delay identifier holding unit 101,
The overhead band determined by the propagation delay identifier 105 is added to the packet transmission band.

The band acquisition unit 103 outputs the band obtained as a result to the transmission / reception unit 104 as a band allocation request. The transmission / reception unit 104 transmits the received band allocation request to the band management node as an asynchronous communication packet. The data is transmitted to the communication medium 108. Then, it outputs the packet received as a result of the request to band acquisition means 103. The bandwidth acquisition unit 103 determines whether or not a bandwidth has been acquired from the result of the bandwidth allocation request. Further, based on the result of the band acquisition, an instruction to start transmission can be given by writing the PCR to the unknown connection counter 502 or the connection counter 503.

The following describes an example of the above procedure in which band allocation is performed for the purpose of transmitting data of a digital VTR currently under development.

Using P1394, this digital VT
When transmitting data of R, the data is divided every 480 bytes and transferred as a synchronization packet. Therefore, in the maximum transmission data amount holding means, the 480 bytes have C
A value of 122, which represents 488 bytes obtained by adding 8 bytes of the IP header in units of 4 bytes, is written as the maximum transmission data amount.

The band acquisition means 103 is a means for holding the maximum transmission data amount included in the PCR (payload size 50).
The value of 122 which is the maximum transmission data amount is read from 8), and the value is multiplied by 4 to know that the size of the payload is 488 bytes. Further, it can be understood that 500 bytes obtained by adding 12 bytes to the 488 bytes is the size of the packet for synchronous data. Further, based on the value of the data rate 506 included in the PCR, the bandwidth required for packet transmission is determined. Here, when the data rate 506 indicates the transfer at 100 Mbps, this band is set to 200 using the unit of the band used in P1394.
It becomes 0. On the other hand, when the data rate 506 is 200 Mbp
In the case where s is indicated, the value is 1000, which is a half of this value.

Further, the band acquiring means 103 is provided with a propagation delay identifier holding means (overhead ID 50) included in the PCR.
Read the propagation delay identifier from 7). Band acquisition means 10
Reference numeral 3 has a correspondence table between the bit pattern of the 4-bit propagation delay identifier and the overhead band shown in (Table 1), and obtains the overhead band from the read propagation delay identifier.

[0037]

[Table 1]

The sum of the resulting overhead bandwidth and the packet bandwidth of 2000 is the bandwidth to be acquired.

On the other hand, the PCR connection counter 5
03 is 0, unowned connection counter 5
When 02 is 1, transmission can be stopped by clearing the unowned connection counter 502 except for the node that has instructed the start of transmission, so that the band used in the stopped transmission is used. Other transmissions can be performed. At this time, the used band can be known from the propagation delay identifier and the maximum transmission data amount included in the PCR.

FIG. 6 shows a configuration of a transmitting apparatus when such a transmitter switching is performed. In FIG. 6, a first transmitting apparatus 606 that has already performed transmission includes a propagation delay identifier holding unit 601 that holds a propagation delay identifier 604, a maximum transmission data amount holding unit 602 that holds a maximum transmission data amount 605, and a communication medium. The second transmission device 614, which includes transmission / reception means 603 for transmitting / receiving a packet to / from the communication medium 607 and newly starting transmission, includes a communication medium 607.
Transmission / reception means 608 for transmitting / receiving packets to / from the terminal, band acquisition means 609, propagation delay identifier holding means 610 for holding propagation delay identifier 612, maximum transmission data amount 613
Is stored in a maximum transmission data amount holding unit 611 for holding the transmission data amount.

The second transmitting device 614 is connected to the first transmitting device 6
When the transmission of the 06 is stopped and the transmission is performed using the band used by the first transmission device 606, the unknown connection counter of the PCR of the first transmission device is cleared. At this time, the band acquisition unit 609 of the second transmission device is configured to transmit the propagation delay identifier 604 and the maximum transmission data amount stored in the propagation delay identifier holding unit 601 that is configured as a part of the PCR of the first transmission device 606. The maximum transmission data amount 605 held in the holding unit 602 is read.

In this case, since the node ID of the first transmitting device 606 is included in the CIP header of the synchronous data packet having the structure shown in FIG. 3 transmitted by the first transmitting device, , The second transmitting device 614 receives the data being transmitted once and checks the CIP header, and thereby the first transmitting device 60 transmitting the data.
6 can be specified.

Therefore, based on the propagation delay identifier 604 read from the first transmitting device 606 and the maximum transmission data amount 605, the band acquiring means 609 of the second transmitting device 614 performs In the method described above, the band acquired and used by the first transmitting apparatus is obtained. The band obtained by the first transmitting apparatus 606 obtained here is the first band.
After the transmission of the transmitting device 606 stops, the second transmitting device 614 can be used.

The data rate used to determine the band used by the first transmitting device 606 is usually
The data rate 506 included in the PCR is read out and used. However, since the data rate 506 can be known from the reception rate when the synchronous data packet is received in order to know the node ID of the first transmitting device 606, the PCR is not necessarily used. There is no need to read the included data rate 506.

Further, the band acquiring means 609 determines the acquired band obtained in the above procedure and the second transmitting device 614.
From the propagation delay identifier 612 held in the propagation delay identifier holding means 610 and the maximum transmission data amount 613 held in the maximum transmission data amount holding means 611 in the same manner.
It is necessary to compare the band to be used and, if there is a difference between the two, return an extra band to the band management node, or obtain a deficient band.

At this time, however, the propagation delay identifier 604 read from the first transmitting device 606 is
10 is smaller than the propagation delay identifier 612 held in the second transmission device 614,
12 can be set to the same value as the propagation delay identifier 604 read from the first transmitting device 606. This is because the propagation delay identifier is obtained only by the connection form of the bus, and depending on the calculation method used to calculate the outgoing propagation delay identifier described later, there is a possibility that a different value is written for each node. However, if the nodes are connected to the same bus, the smallest propagation delay identifier among them can be used.

As described above, the initial value of the propagation delay identifier holding means is a value corresponding to the case where the bus has the maximum configuration allowed by the P1394 standard. Therefore, the second transmitting device 614 that has the band has the initial value as the propagation delay identifier 612, while the propagation delay identifier 604 of the first transmitting device 606 has a lower value than the initial value by checking the bus connection form. If a small value has been written, the size of the propagation delay identifier is compared when the band is transferred, and the smaller value can be used to effectively use the bandwidth of the communication medium. Becomes

FIG. 7 is a block diagram showing an operation when the transmission control device obtains a propagation delay identifier. In this embodiment, the transmission device 710 includes a transmission / reception unit 707 for transmitting / receiving a packet to / from the communication medium 706, and a propagation delay identifier holding unit 708 for holding a propagation delay identifier 709, and the transmission control device 705 Analysis means 701 for analyzing the connection form of the device connected to the medium, identifier determination means 70 for determining a propagation extension identifier based on the analysis result
2. An identifier setting unit 703 for setting the propagation delay identifier 709 in the propagation identifier holding unit 708 of the transmission device 710, and a transmission / reception unit 704 for transmitting / receiving packets to / from the communication medium 706.

The analysis means 701 receives all the self ID packets transmitted from each node connected to the bus at the time of the bus reset of P1394, and analyzes the tree structure of the bus using the information contained in the self ID packets. I do. By analyzing this tree structure, the number of relay nodes at the time of communication between each node is obtained, and this maximum value is output. on the other hand,
The identifier determining unit 702 calculates the maximum possible propagation delay from the maximum number of relay nodes on the bus input from the analyzing unit 701, and obtains the maximum transmission delay based on this value when transmitting the synchronization data. The required overhead bandwidth is determined. Further, the identifier determining means 702 determines and outputs the most appropriate propagation delay identifier from the overhead band.

As the correspondence between the number of relay nodes used at this time and the overhead band, for example, the values shown in Table 2 can be used.

[0051]

[Table 2]

The values shown in Table 2 are maximum values determined irrespective of the position of the node that manages the right to use the bus, and are obtained by calculation using the equation shown in (Equation 2). In addition, it is also possible to calculate the propagation delay in consideration of the position on the bus of the node that manages the right to use the bus. In this case, even if the maximum number of relays existing on the bus is the same ( The value may be smaller than the overhead band shown in Table 1). The correspondence between the overhead band and the bit pattern of the 4-bit propagation delay identifier uses the values shown in (Table 1). Therefore, the propagation delay identifier can be determined.

In this way, the identifier determining means 702 determines the overhead band based on the maximum number of relay nodes input from the analyzing means 701, and further determines and outputs the propagation delay identifier from the overhead band. Further, by determining such a correspondence, the overhead band can be uniquely determined from the propagation delay identifier.

The identifier setting unit 703 receives the propagation delay identifier determined by the identifier determining unit 702 and writes it into the propagation identifier holding unit 709 of the transmitting device 710. This writing uses an asynchronous communication packet and the PC
This is performed by a write operation to R.

As described above, as the initial value of the propagation delay identifier holding means 708 of the transmitting device 710, an identifier determined by the maximum connection form permitted by P1394 is written. In order to change this value, it is necessary to analyze the bus connection form to know the maximum number of relay nodes. But,
Even if the propagation delay identifier is used as it is without analyzing the bus connection form, synchronous data communication is possible,
It is not necessary for all the transmission devices to have the connection form analyzing unit 701, the identifier determining unit 702, and the identifier setting unit 703. However, in this case, a band larger than the originally required band is acquired, so that the band of the communication medium cannot be used effectively.

Therefore, the transmission control device 705 is connected to the communication medium, the connection form of the device connected to the bus is analyzed to determine a propagation delay identifier, and the transmission delay identifier is stored in the propagation delay identifier holding means of the transmission device connected to the bus. By setting an appropriate propagation delay identifier, the band of the communication medium can be used efficiently. Since the propagation delay identifier holding means can write data through the bus, if there is at least one transmission control device on the bus, it is possible to set a propagation delay identifier smaller than the initial value. However, it is not necessary for all the transmission devices to have the connection form analyzing means 701 and the identifier determining means 702, etc., and since the transmission medium has the correspondence table of the propagation delay identifier and the overhead band shown in (Table 1), the communication medium can be used. It is possible to make effective use of the bandwidth possessed.

On the other hand, there is a possibility that a transmission control device other than the transmission device having the propagation delay identifier holding means writes a propagation delay identifier that is more appropriate than the value already set. Therefore, as described above, when the band acquisition unit acquires a band, it is necessary to read the value of the propagation delay identifier holding unit and determine the overhead band based on the read value.

Further, the propagation delay identifier held in the propagation delay identifier holding means needs to be the value used when acquiring the band, because it is used when switching the transmission apparatus. Therefore, the transmission control device sets the propagation delay identifier only for the transmission device that is not transmitting at that time. That is, the unowned connection counter 502 and the connection counter 503 of the PCR
Only when both are 0, the propagation delay identifier can be set.

As for the propagation delay identifier, if the connection form of the bus is originally determined, one of the most appropriate values is determined. However, in order to determine the most appropriate value, it is necessary to analyze the bus connection configuration and accurately determine the number of relay nodes between all nodes and, in some cases, the position of the right-of-use management node on the bus. Must-have. To perform such a process, a complicated analysis process is required. On the other hand, if the number of devices connected to the bus is small, the propagation delay identifier can be set to a value smaller than the initial value, although not optimal, based on only the number of devices.

In P1394, the standard specifies that the number of relay nodes between the farthest nodes is 15, and the connection must be made 16 times. If the number M of nodes connected to the bus is smaller than 17, the number of relay nodes between the farthest nodes exceeds (M−2) regardless of the connection form. Never. Therefore, in such a case, the connection form is not analyzed, and the propagation delay identifier is determined using (M−2), which is the maximum number of relay nodes that can be considered as the number of nodes connected to the bus, as the number of relay nodes. be able to. On the other hand, if M is greater than 17, P
The maximum value 15 allowed in 1394 is used. By setting the propagation delay identifier obtained in this way, when the number of devices connected to the bus is small, the bandwidth of the communication medium cannot be used to the maximum,
Bandwidth can be used more efficiently than when no propagation delay identifier is set without performing complicated processing.

As described above, there are a plurality of methods by which the transmission control device can obtain the propagation delay identifier. Further, there may be a plurality of transmission control devices for setting the propagation delay identifier on the same bus. Therefore, a propagation delay identifier larger than that may be written to the propagation delay identifier holding unit in which the propagation delay identifier that is already considered optimal is written. If this occurs, there is a risk that the bandwidth of the communication medium cannot be used effectively.
Therefore, when setting the propagation delay identifier, the value is compared with the value already set and the value to be set, and only when the value is smaller than the value already set, the setting is performed. Danger can be avoided.

[0062]

As described above, in the transmission system according to the present invention, the synchronous transfer can be performed by calculating the bandwidth of the overhead using the propagation delay identifier. It is possible to prevent an extra band from being acquired when a band is reserved in a communication medium that needs to be allocated a band in advance.

Further, since the transmission delay identifier and the maximum amount of transmission data used when the transmission device obtains the band when transmitting data can be read from the outside through the communication medium, the transmission delay identifier and the maximum transmission data amount can be connected to the same communication medium. Another device that has obtained the acquired bandwidth can obtain the acquired bandwidth, and as a result, the bandwidth acquisition procedure involving a shift of the bandwidth when another transmitting apparatus performs transmission using the already acquired bandwidth can be simplified. Can be

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a main part of a transmission device that transmits synchronous data according to an embodiment of the present invention.

FIG. 2 is a diagram showing a band required to be acquired when transmitting P1394 synchronous data in the embodiment of the present invention.

FIG. 3 shows an example of the present invention in which N connections are performed (N−
1) Diagram showing connection of nodes separated by relay nodes

FIG. 4 is a diagram showing a configuration of a packet used when transmitting synchronous data in P1394 in the embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of a PCR which is a register for controlling transmission of synchronous data in the embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of a main part of two transmission devices when switching a synchronous data transmission node in the embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration of a transmission control device for determining and setting a propagation delay identifier and a main part of a transmission device for setting a propagation delay identifier in an embodiment of the present invention.

[Explanation of symbols]

101, 601, 610, 708 Propagation delay identifier holding means 102, 602, 611 Maximum transmission data amount holding means 103, 609 Band acquisition means 104, 603, 608, 704, 707 Transmission / reception means 105, 604, 612, 709 Propagation delay identifier 106, 605, 613 Maximum transmission data amount 107, 606, 614, 710 Transmission device 108, 607, 706 Communication medium 201 Packet 202 Bus usage right request 203 Bus usage permission 301 Bus usage right management node 302 Relay node 303 Transmission Node 401 Packet header 402 Header CRC 403 CIP header 404 Synchronous data 405 Data CRC 501 Valid flag 502 Unowned connection counter 503 Connection counter 504 Unused file Rudo 505 channel number 506 data rate 507 overhead ID 508 payload size 701 analyzer 702 identifier determining means 703 identifier setting means 705 transmission control unit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-139934 (JP, A) JP-A-8-8913 (JP, A) JP-A-8-23584 (JP, A) JP-A-8- 307453 (JP, A) Tokuyo 9-507628 (JP, A) Tokuyo 11-505988 (JP, A) Tokuyo 11-506879 (JP, A) International Publication 96/34477 (WO, A1) IEEE TRANSACTIONS ON CONSUMER ELECT RONICS, Vol. 41 No. 3, AUGUST 1995, KUNZMAN A. J. , "1394 HIGH PERF ORMANCE SERIAL BUS: THE DIGITAL INTER FACE FOR ATV", pages. 893-900 (58) Field surveyed (Int. Cl. ⁷ , DB name) H04L 12/28-12/56 INSPEC (DIALOG)

Claims (1)

(57) [Claims] 1. A synchronous transfer can be performed. When performing transmission by synchronous transfer, an overhead band determined by a value of a propagation delay identifier and a band required for transmission determined by a maximum transmission data amount are added. A system by a device connected to a communication medium that needs to be assigned a determined transmission band, by writing a value to a register of the transmission device,
A transmission control device that controls transmission, a transmission delay identifier holding unit that holds a propagation delay identifier used to determine a bandwidth of an overhead when a band is allocated in advance before transmission when performing transmission, and Maximum transmission holding a maximum transmission data amount indicating a maximum amount of data that can be included in a packet transmitted to the communication medium and used for calculating a band required for packet transmission when a band is allocated in advance prior to the transmission. A data amount holding unit and a counter for controlling start and stop of transmission are provided in the register, and the contents of the propagation delay identifier holding unit and the maximum transmission data amount holding unit are connected to the communication medium. By making it readable from other devices via the communication medium, it can be released when other devices stop transmitting the transmission device. The transmission delay identifier holding means is writable from another device connected to the communication medium via the communication medium, and the transmission device is capable of storing the propagation delay identifier holding means. And a management node that manages a synchronous transfer band in the communication medium, wherein the transmission control device includes: When starting, read the maximum transmission data amount that the transmitting device has in the register, determine the maximum packet size for synchronization data from the read maximum transmission data amount, from this and the data rate of the communication medium A first band necessary for the synchronous transfer of the packet is determined, and a correspondence table of the propagation delay identifier and the overhead band is determined from the value of the propagation delay identifier. A second band, which is an overhead band, is used to receive, from the management node, a band assigned a value obtained by adding the first band and the second band, and a propagation used when receiving the band assignment. A system wherein a value of a delay identifier is set in the propagation delay identifier holding means of the transmitting device, and transmission is started by writing a value to the counter of the register of the transmitting device.