JP3525861B2 - Data transmission device, data transmission control device, and data transmission method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission device 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 being studied by IEEE (references, high performance
Serial bus P1394 draft 7.1v1: High
Performance Serial Bus P1394 / Draft 7.1v1). P1
Reference numeral 394 is a serial bus type communication medium capable of guaranteeing real-time property required for transmission of video data and audio data.

Devices connected to P1394 (hereinafter referred to as nodes) 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 the data output by an arbitrary node reaches all the connected nodes. Therefore, although the P1394 is structurally a tree structure, it theoretically operates as a bus. However, in P1394, since the bus is realized by relaying a plurality of nodes, in addition to the propagation delay determined by the length of the transmission path, the propagation delay depends on the number of relaying nodes. Further, in P1394, only one node arbitrates the bus, so that it is guaranteed that a plurality of nodes do not transmit at the same time.

Each node configured as a bus as described above has an identifier (hereinafter referred to as a node I) for identifying the node.
(Referred to as D) is added. The addition of this node ID is
This is automatically performed by bus initialization (hereinafter referred to as bus reset) that occurs when a new node is added to the bus or conversely the node is disconnected. When a bus reset occurs, the 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 sending this self ID packet, and the self ID packet includes the node ID determined at the time of sending and information indicating whether or not another terminal is connected to each terminal. . A node on the bus can know the tree structure of the bus by receiving and analyzing all the self-ID packets sent by each node.

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

When performing synchronous transfer, it is necessary to acquire the time (bandwidth) used in one cycle prior to transmission from the node that manages the bandwidth. 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 after being acquired from this band management node. The node performing the synchronous transfer can transmit the data within the acquired band range, and the data transmitted by the synchronous transfer is sent out as a packet defined in P1394. In synchronous transfer, real-time data can be transferred by guaranteeing transfer of a predetermined data amount for each cycle. The bandwidth to be acquired prior to transmission here is the overhead required for the actual data transfer, the propagation delay that occurs during data transfer, and the bandwidth required for the data transfer added for error detection. Is a combination of.

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

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

It is conceivable to control transmission / reception of synchronous data by using such a control register. In such a case, the status of transmission or reception can be known by reading the synchronous communication control register, while the necessary value can be written to this register to start the transmission or reception of synchronous data, Conversely, it is possible to perform control such as stopping.

[0010]

When the transmission is performed after acquiring a part of the band of the communication medium prior to the transmission, such as P1394, the already performed communication is stopped and then stopped. It is possible that the transmission of another device is started using the band used in the caused communication.

An example thereof is a case where the second device tries to start transmitting data while the first device is transmitting data to the communication medium. Here, the second as a communication medium
If there is a band left for the device to send the data, the second device can start sending after acquiring the band. However, if the required bandwidth is not available, transmission cannot be started. So first
By stopping the transmission of the device of No. 2, the second device can start the transmission after securing the band necessary for the transmission.

In such a case, it is necessary to return the used band once to the band management node, acquire it again, and then start transmission. In addition, the band must be acquired after the band is returned, so the device that acquires the band needs to check whether the band has been returned or not, and monitor the return operation. Furthermore, since it takes time from when the band is returned to when the band is acquired again, there is a risk that another node may acquire the band.

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

In such a case, a predetermined value,
It is possible to acquire the band based on the maximum propagation delay time. However, if the band to be acquired is determined based on the maximum propagation delay time assumed in this way, an unnecessary band is actually acquired, and efficient use of the communication medium cannot be achieved. Also, because of this, there is a risk of interfering with other communications that should otherwise be able to communicate.

That is, if the 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]

In order to solve the above-mentioned problems, the method according to claim 1 is capable of performing synchronous transfer, and it is necessary to allocate bandwidth in advance when transmitting by synchronous transfer. A bandwidth allocation method for a medium, comprising: an analysis step of analyzing a connection form of devices connected to a communication medium; a propagation delay identifier determination step of determining a propagation delay identifier based on the analysis result; and a maximum transmission data amount. A first bandwidth determining step of determining a maximum packet size for synchronous data and determining a bandwidth necessary for transmitting the packet from this and the data rate of the communication medium, and an overhead from a value of the propagation delay identifier A second band deciding step for deciding a band, the band decided in the first band deciding step and the second band deciding A second band determined by the step, and a band allocation step of receiving a band corresponding to the value added by the addition step, the second band determination step comprising: It is characterized in that the band is determined using a correspondence table of the propagation delay identifier and the overhead band.

The apparatus according to claim 3 is capable of performing the synchronous transfer, is connected to a communication medium which needs to be allocated a band in advance when transmitting by the synchronous transfer, and allocates the band requiring the allocation. A determining device,
Analyzing means for analyzing the connection form of the equipment connected to the communication medium, propagation delay identifier determining means for determining the propagation delay identifier based on the analysis result, and the maximum packet size for synchronous data from the maximum transmission data amount. First bandwidth determining means for determining the bandwidth required for transmission of the packet from this and the data rate of the communication medium, and a second bandwidth determining means for determining the overhead bandwidth from the value of the propagation delay identifier.
Band determining means, an adding step of adding the band determined by the first band determining means and the second band determined by the second band determining means, and an adding step performed by the adding means. Band allocation means for receiving the allocation of a band corresponding to the value, and the second band determination means determines the band using a correspondence table of the propagation delay identifier and the overhead band.

[0018]

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

In this embodiment, the communication medium 1 shown in FIG.
The data transmitter 107 that transmits the synchronous data to the communication terminal 08 stores the propagation delay identifier 105.
01, maximum transmission data amount holding means 102 for holding the maximum transmission data amount 106, band acquisition means 103, and transmission / reception means 104. When transmitting the synchronous data to P1394, the band must be acquired from the node that manages the band prior to transmission.

FIG. 2 shows a band required to be acquired when the synchronous data is transmitted to P1394. The bandwidth of the synchronous data is the time T1 from the detection that the bus is unused to the request for the right of use, the propagation time T2 required for the request for the right of use of the bus to reach the management node, and the time of the bus. Judgment time T3 in the usage right management node, propagation time T required to receive the judgment result output from the usage right management node
4. Bus occupancy 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 transmission for the bus The bandwidth corresponds to the time determined by the total of the propagation delays T9 before reaching the management node of the usage right.

In this band, values other than T7, which is the time required to transfer the packet itself, are irrelevant to the transmission rate and the amount of transmission data, and are between the transmitting node and the node managing the right to use the bus. It depends on the number of relay nodes that exist in. However, in P1394, the node that manages the bus usage right does not have to be at the center of the connection, so the time other than the packet transfer time differs depending on each node. In order to obtain the value for each node, the position on the bus of the node that manages the bus usage right must be taken into consideration.

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

Therefore, as shown in FIG. 3, it is considered that the transmission node 303, which is separated by (N-1) relay nodes 302, outputs a packet by connecting N times from the node 301 managing the bus usage right. In this case, when 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).

[0024]

[Equation 1]

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

[0026]

[Equation 2]

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

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

In addition to the synchronization data, 20 bytes of data including the header of the packet are added to this packet. Of these, the maximum transmission data amount holding means holds a value obtained by combining the 8 bytes of the CIP header 403 and the data amount of synchronous data. Therefore, the bandwidth that needs 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. And the above-mentioned overhead band.

On the other hand, FIG. 5 shows the structure of a transmission PCR (plug control register) which is a register for controlling the transmission of synchronous data and is placed in the address space of each P1394 node. PCR is 32 bits
1-bit valid flag 501 indicating whether the PCR can be used, or 1 indicating that the transmission controlled by the transmission PCR can be stopped during transmission.
Bit unowned connection counter 50
2, a 6-bit connection counter 503 indicating the number of devices that have instructed the PCR, a 2-bit unused field 504, a channel 505 indicating a channel number used for transmitting 6-bit synchronous data, and used for transmission A 2-bit data rate 506 indicating the transmission rate, a 4-bit overhead ID 507 corresponding to the propagation delay identifier holding means, and a maximum transmission data amount holding means corresponding to the payload size in units of 4 bytes 10 It is composed 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 can know the state of transmission at that time. The transmitting device transmits 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. On the contrary, when both of them become 0, the output is stopped. In addition, connection counter 5
03 is 0, unowned connection counter 5
Only when 02 is 1, a device other than the device that has instructed to start the transmission can clear the unowned connection counter 502 and stop the transmission.

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

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

With respect to the above procedure, an example in which band allocation is performed for the purpose of transmitting data of a digital VTR which is currently being developed is shown below.

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

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

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

[0038]

[Table 1]

The value obtained by combining the resulting overhead bandwidth and 2000, which is the bandwidth of the packet, 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 by a node other than the node that has instructed to start transmission. Therefore, the band used in this stopped transmission is used. Other transmissions can be made. Further, at this time, it is possible to know the band used by the propagation delay identifier included in the PCR and the maximum transmission data amount.

FIG. 6 shows the structure of the transmitting device when the transmitter is switched as described above. In FIG. 6, the first transmitting device 606 that has already transmitted is 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 is composed of a transmission / reception unit 603 for transmitting / receiving a packet to / from the communication unit 607 and starts a new transmission, is a communication medium 607.
A transmission / reception unit 608 for transmitting / receiving a packet to / from, a band acquisition unit 609, a propagation delay identifier holding unit 610 holding a propagation delay identifier 612, a maximum transmission data amount 613.
The maximum transmission data amount holding means 611 for holding

The second transmitting device 614 is the first transmitting device 6
When the transmission of No. 06 is stopped and the transmission is performed using the band used by the first transmission device 606, the unowned connection counter of the PCR of the first transmission device is cleared. Further, at this time, the band acquisition unit 609 of the second transmission device has the propagation delay identifier 604 and the maximum transmission data amount held by the propagation delay identifier holding unit 601 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, 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 which is transmitted by the first transmitting device. , The second transmitting device 614 receives the transmitted data once and examines the CIP header, so that the first transmitting device 60 transmitting the data.
6 node IDs can be specified.

Therefore, the band acquisition means 609 of the second transmission device 614 is similar to the above-mentioned normal band acquisition based on the propagation delay identifier 604 and the maximum transmission data amount 605 read from the first transmission device 606. The bandwidth acquired and used by the first transmitter is obtained by the method. The band obtained by the first transmission device 606 obtained here is the first band.
After the transmission of the second transmission device 606 is stopped, the second transmission device 614 can be used.

The data rate used when obtaining the band used by the first transmitter 606 is usually
The data rate 506 included in the PCR is read and used. However, since it can be known by the reception rate at the time of receiving the synchronous data packet in order to know the node ID of the first transmission device 606, the PCR is not necessarily used. There is no need to read the included data rate 506.

Further, the band acquisition means 609 is configured to detect the band acquired in the above procedure and the second transmitter 614.
In the same manner, it is obtained 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.
It is necessary to compare the band to be used and return the extra band to the band management node if there is a difference between the two, or conversely acquire the insufficient band.

At this time, however, the propagation delay identifier 604 read from the first transmitting device 606 is the second transmitting device 6
If it is smaller than the propagation delay identifier 612 held in No. 10, the propagation delay identifier 6 of the second transmitting device 614.
12 can be set to the same value as the propagation delay identifier 604 read from the first transmission device 606. This is because the propagation delay identifier is obtained only by the connection form of the bus, and it is possible that different values are written for each node depending on the calculation method used when calculating the outgoing propagation delay identifier described later. This is because, if the nodes are connected to the same bus, the smallest propagation delay identifier can be used among them.

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 permitted by the P1394 standard. Therefore, the second transmission device 614 that takes over the band has an initial value as the propagation delay identifier 612, while the propagation delay identifier 604 of the first transmission device 606 is more than the initial value by checking the bus connection form. When a small value is written, it is possible to effectively use the bandwidth of the communication medium by comparing the sizes of the propagation delay identifiers when handing over the bandwidth and using the smaller value. Becomes

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

The analyzing means 701 receives all the self-ID packets sent by each node connected to the bus at the time of P1394 bus reset, and analyzes the tree structure of the bus using the information contained in this self-ID packet. To 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 propagation delay that may occur from the maximum number of relay nodes on the bus input from the analyzing unit 701, and obtains it when transmitting synchronous data based on this value. Determine the required overhead bandwidth. Further, the identifier determining means 702 determines and outputs the most appropriate propagation delay identifier from this overhead band.

As a 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.

[0052]

[Table 2]

The values shown in Table 2 are maximum values that are determined irrespective of the position of the node that manages the bus use right, and are obtained by calculation using the formula shown in (Equation 2). 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, and in this case, even if the maximum number of relays existing in 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 obtains the overhead band based on the number of maximum relay nodes input from the analyzing means 701, and further determines and outputs the propagation delay identifier from this overhead band. Further, by determining such correspondence, the overhead band can be uniquely determined from the propagation delay identifier.

The identifier setting means 703 inputs the propagation delay identifier determined by the identifier determining means 702 and writes it in the propagation identifier holding means 709 of the transmitting device 710. This writing uses an asynchronous communication packet to
A write operation to R is performed.

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

Therefore, the transmission control device 705 is connected to the communication medium, the connection form of the equipment connected to the bus is analyzed to obtain the propagation delay identifier, and the propagation delay identifier holding means of the transmission device connected to the bus is used. By setting an appropriate propagation delay identifier, the bandwidth of the communication medium can be used efficiently. Since the propagation delay identifier holding means can write through the bus, it is possible to set a propagation delay identifier smaller than the initial value if there is at least one transmission controller on the bus, and as a result, , It is not necessary for all the transmitting devices to have the connection mode analysis means 701, the identifier determination means 702, etc., and since the transmission delay identifier and the overhead band correspondence table shown in (Table 1) are held, the communication medium is It is possible to effectively use the bandwidth that the user has.

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 more appropriate than the already set value. Therefore, as described above, when the band acquisition unit acquires the band, it is necessary to read the value of the propagation delay identifier holding unit and obtain the overhead band based on the read value.

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

For the propagation delay identifier, if the connection form of the bus is originally determined, one most appropriate value is determined. However, in order to obtain the most appropriate value, the bus topology is analyzed to accurately determine the number of relay nodes between all nodes and, in some cases, the position of the bus right management node on the bus. Must-have. In order to perform such processing, complicated analysis processing is required. On the other hand, when 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 it is not optimal based on only the number of devices.

In P1394, the standard stipulates that the number of relay nodes between the most distant nodes is 15, and the connection must be made 16 times. When the number M of nodes connected to the bus is smaller than 17, the number of relay nodes between the most distant nodes exceeds (M-2), regardless of the connection form. There is no such thing. Therefore, in such a case, without analyzing the connection form, the propagation delay identifier is determined with (M-2), which is the maximum number of relay nodes considered in the number of nodes connected to the bus, as the number of relay nodes. be able to. On the other hand, when M is a value larger than 17, the number of relay nodes is P
Use 15 which is the maximum value allowed in 1394. 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,
The band can be effectively used as compared with the case where the propagation delay identifier is not set at all without performing complicated processing.

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

[0063]

As described above, according to the first aspect of the invention, since the propagation delay identifier and the maximum transmission data amount used when the band is acquired can be read from the outside through the communication medium, the same communication medium is used. It becomes possible for another connected device to obtain this acquired band, and as a result, the band acquisition procedure that involves band transfer when another transmitting device transmits using the band already acquired is performed. It is possible to simplify.

In the second aspect of the invention, the transmission controller analyzes the connection form of the equipment connected to the communication medium and sets the propagation delay identifier based on the analysis result, thereby effectively utilizing the band of the communication medium. It becomes possible. Furthermore, since this propagation delay identifier can be set from the outside of the device through the communication medium, even if all the transmitting devices do not have an analyzing means for analyzing the connection form of the device connected to the communication medium, By having at least one transmission control device on the medium, it is possible to effectively use the bandwidth of the communication medium.

In the third aspect of the present invention, when analyzing the connection form of the devices connected to the communication medium, the judgment is made based on the number of devices connected to the communication medium, thereby eliminating the need for complicated processing. In addition, it becomes possible to effectively use the band.

[Brief description of drawings]

FIG. 1 is a block diagram showing 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 is a diagram illustrating an embodiment of the present invention with (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 by P1394 in the embodiment of the present invention.

FIG. 5 is a diagram showing the configuration of a PCR that is a register that controls transmission of synchronous data in the embodiment of the present invention.

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

FIG. 7 is a block diagram showing a configuration of a transmission control device that determines and sets a propagation delay identifier and a main part of a transmission device to which a propagation delay identifier is set according to 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 Bandwidth 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 Synchronization data 405 Data CRC 501 Valid flag 502 Unowned connection counter 503 Connection counter 504 Unused field 505 Channel number 506 Data rate 507 Overhead ID 508 Payload size 701 Analysis means 702 Identifier determination means 703 Identifier setting means 705 Transmission control device

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-76434 (JP, A) JP-A-4-139934 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04L 12/28

Claims (4)

(57) [Claims] 1. A band allocation method for a communication medium capable of performing a synchronous transfer and requiring a band to be allocated in advance when transmitting by the synchronous transfer, and a connection form of a device connected to the communication medium. Analyzing step, a propagation delay identifier determining step for determining a propagation delay identifier based on the analysis result, a maximum packet size for synchronous data is obtained from the maximum transmission data amount, and this and the communication medium A first band determining step of determining a band required for transmitting the packet from a data rate; a second band determining step of determining an overhead band from a value of the propagation delay identifier; and the first band determining step. And a second band determined in the second band determination step. And a band allocation step of receiving a band allocation corresponding to the value added by the adding step, wherein the second band determining step determines the band using a correspondence table of a propagation delay identifier and an overhead band. how to. 2. The analyzing step analyzes the number of devices connected to a communication medium, and in the propagation delay identifier determining step, when the number is (M), the number of relay devices is (M-2 The method according to claim 1, characterized in that the propagation delay identifier corresponding to (1) is determined. 3. A device which is capable of performing a synchronous transfer and which is connected to a communication medium which needs to be allocated a band in advance when transmitting by the synchronous transfer and which determines a band to be allocated, the communication comprising: Analyzing means for analyzing the connection form of the device connected to the medium, propagation delay identifier determining means for determining the propagation delay identifier based on the analysis result, and the maximum packet size for the synchronous data from the maximum transmission data amount. And a second bandwidth determining means for determining an overhead bandwidth from the value of the propagation delay identifier, the first bandwidth determining means determining the bandwidth required for transmitting the packet from the data and the data rate of the communication medium. And an addition step for adding the band determined by the first band determination unit and the second band determined by the second band determination unit. And a band allocating unit for allocating a band corresponding to the value added by the adding unit, wherein the second band deciding unit decides the band using a correspondence table of a propagation delay identifier and an overhead band. Device to do. 4. The analyzing means analyzes the number of devices connected to a communication medium, and the propagation delay identifier determining means, when the number is (M), the number of relay devices is (M−2). 4. The apparatus according to claim 3, wherein the propagation delay identifier corresponding to (4) is determined.