JP2002064506A - Data transfer system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a data transfer system that warrants transfer of data in a band secured in advance within a prescribed time at a high transfer success rate. SOLUTION: A coder 15 codes original data 13 to be transferred into redundant data 14 used as backup data on the occurrence of a transfer error, a multiplexer 16 copies the received data or demultiplexes the data and transfers the copied or demultiplexed data. A demultiplexer 17 multiplexes the transferred redundant data 14 into one set of redundant data 14, and a decoder 18 decodes the redundant data 14 into the original data 13. As the redundant data 14, the original data 13 including check sum data subjected to time division or the transferred copied original data 13 delayed for each prescribed cycle or the like are generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transfer system to which an isochronous transfer mode, which is a data transfer mode in which data transfer within a band secured in advance within a predetermined time, is guaranteed.

[0002]

2. Description of the Related Art With the development of communication technology, data transfer modes corresponding to various uses have been developed. The isochronous transfer mode is one of them, in which data transfer within a band secured in advance within a predetermined time is guaranteed, and real-time data that is required to be transferred at a certain timing, such as video or audio, is required. It is mainly used for transferring multimedia data.

The isochronous transfer mode is actually used in a device requiring a large amount of information transmission, such as a digital VCR (Video Cassette Recorder), a digital camcorder, and a hard disk.

The transfer in the isochronous transfer mode (hereinafter, isochronous transfer) is a kind of synchronization signal.
This is performed in synchronization with a cycle start packet transmitted by a single cycle master existing on the bus at regular intervals.
In addition, in the isochronous transfer, a higher throughput can be easily obtained than in the asynchronous transfer (asynchronous transfer).
In addition to the above-described transfer of multimedia data, it is also used for data transfer of an image forming apparatus such as a printing apparatus or a scanner.

Further, a serial bus (hereinafter, IEEE 1394 bus) defined by IEEE Std 1394 and a serial bus (hereinafter, USB: Universal Serial Bus) defined by Universal Serial Bus Specification are used.
The serial bus interface has an isochronous transfer mode as one of the transfer methods.

The prior art using the isochronous transfer as described above includes a printer system and an operation control method thereof (hereinafter referred to as Conventional Example 1) disclosed in Japanese Patent Application Laid-Open No. H10-111773, 10-30
No. 7691 discloses a data transfer method and apparatus, a printing apparatus, and a printing system including the apparatus (hereinafter, referred to as “printing apparatus”).
Conventional example 2).

In the isochronous transfer mode, data reception is not confirmed instead of guaranteeing the bandwidth. Therefore, even if data is lost for some reason, data recovery processing such as retransmission is not performed. Although this characteristic hardly causes a problem when transferring data such as moving images and audio, it is a fatal problem in still image data used for printing, and requires some measures.

In Conventional Example 1, when a large amount of data such as a full-color image is transferred to a printing apparatus within a predetermined time,
The IEEE 1394 bus and its isochronous transfer mode are used. Further, the problem of data loss is solved by performing bidirectional communication by time-sharing a single isochronous channel and performing retransmission control in the isochronous transfer mode for the purpose of recovering data transfer errors.

In the second conventional example, when a large amount of data is transferred to a printing apparatus within a predetermined time, the IEEE 1394 bus and its isochronous transfer mode are used only for data transfer, and retransmission control is asynchronous transfer (asynchronous transfer) of the IEEE 1394 bus. ) Is used.

[0010]

However, in the conventional example 1, two-way communication is performed by time-dividing a single isochronous channel.
In the Std 1394 standard, a plurality of nodes (conventional example 1
In the invention of the prior art, the printer controller side node and the printer side node) do not permit sending data to a single channel, and the invention described in the prior art 1 requires operation outside the standard. Problem.

In the second conventional example, a method is used in which the isochronous transfer mode is applied only to data transfer, and the asynchronous transfer mode of the IEEE 1394 bus is applied to retransmission control. However, IE
The asynchronous transfer mode of the EE1394 bus does not guarantee the latency of data transmission and reception, and therefore does not guarantee the time until the requested retransmission data is received. There was a problem that the data buffer overflowed because the processing could not be completed in time.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has been made in view of the above, and in an apparatus having an interface such as an IEEE 1394 bus or a USB, transferring redundant data that can serve as backup data when data to be transferred is lost. Based on the raw data to be
An object of the present invention is to provide an image forming apparatus having a highly reliable high-speed data transfer method without transmitting a retransmission request from a data receiving side by transferring.

[0013]

To achieve the above object, according to the first aspect of the present invention, a plurality of image forming apparatuses existing on the same network are interconnected at a predetermined cycle via a plurality of communication paths. A data transfer method having an isochronous transfer mode for transferring a predetermined amount of data in synchronization with a signal of the data, wherein redundant data creating means for creating redundant data as backup data when image data is lost based on image data; And redundant data transfer means for transferring redundant data.

Therefore, according to the first aspect of the present invention, by transferring redundant data, which is backup data when image data is lost, in the isochronous transfer mode,
It is possible to secure a constant transfer rate of image data. Further, it is possible to guarantee the time for restoring when image data is lost during transfer.

According to a second aspect of the present invention, in the data transfer method according to the first aspect, data dividing means for dividing image data having a plurality of packets into divided data which is binary data for each predetermined packet. A divided data transfer unit that transfers the divided data via a plurality of communication paths, and a binary sequence in which the sum of the divided data before transfer is added for each packet with the same digit of the plurality of divided data. A first checksum generating means for generating a checksum of 1 and a second checksum which is a binary string obtained by adding the total sum of the divided data after transfer for each packet to the same digit of the plurality of divided data. A second checksum creating unit to be created; a missing data detecting unit that compares the first checksum with the second checksum and detects a missing portion of the divided data; A data restoring means for restoring the missing part of the divided data detected by the missing data detecting unit,
It is characterized by having.

Therefore, according to the second aspect of the present invention, a checksum is created based on the divided data before and after the transfer, and the two are compared to identify and restore the missing portion of the image data. As a result, highly reliable transfer of image data can be realized.

According to a third aspect of the present invention, in the data transfer method of the second aspect, a plurality of divided data and the first checksum are used as redundant data.

Therefore, according to the third aspect of the present invention, by transferring the plurality of divided data and the first checksum created based on the plurality of divided data as redundant data, By identifying and restoring the missing portion of the image, it is possible to realize highly reliable transfer of image data.

According to a fourth aspect of the present invention, in the data transfer method according to the first aspect, a data duplicating means for duplicating the image data and a plurality of duplicated image data delayed by a predetermined packet are transmitted. And a predetermined interval transfer unit.

Therefore, according to the fourth aspect of the present invention, by transferring a plurality of copied image data with a delay of a predetermined packet each time, the transfer of even one of the plurality of image data is normally completed. Thus, it can be considered that the data transfer process has succeeded, and highly reliable image data transfer can be realized.

According to a fifth aspect of the present invention, in the data transfer method of the fourth aspect, a plurality of image data transferred with a delay by a predetermined packet are used as redundant data.

Therefore, according to the fifth aspect of the present invention, by using a plurality of image data transferred with a delay of a predetermined packet at a time as redundant data, even if one image data is lost at the time of transfer, the other image data can be used. Complemented by the normally transferred image data, it is possible to realize highly reliable transfer of image data.

According to a sixth aspect of the present invention, in the data transfer method according to the second or third aspect, every time the first checksum is transferred by a predetermined number of packets, the first checksum is transferred. It is characterized in that the assigned communication path is changed.

Therefore, according to the present invention, the first checksum is transferred every predetermined number of packets.
Transfer the first checksum by changing the communication path assigned when the checksum is transferred and distributing the first checksum to a plurality of communication paths instead of fixing the communication path to one. Even when a failure occurs in one of the communication paths, the failure detection using the checksum can be executed.

According to a seventh aspect of the present invention, in the data transfer method according to any one of the first to sixth aspects, the number of communication paths for transferring redundant data is changed. .

Therefore, according to the present invention, the transfer efficiency or the transfer success rate can be improved by changing the number of communication paths for transferring redundant data in consideration of the error occurrence rate at the time of transfer. It is possible to realize.

According to an eighth aspect of the present invention, in the data transfer method according to any one of the first to seventh aspects, a bandwidth which is a transfer amount of redundant data within a predetermined time is changed. It is characterized by.

Therefore, according to the present invention, it is possible to improve the transfer efficiency or the transfer success rate by changing the bandwidth which is the transfer amount of the redundant data within a predetermined time. .

According to a ninth aspect of the present invention, in the data transfer method according to any one of the first to eighth aspects, an IE is used as a transmission path connecting a plurality of image forming apparatuses.
It is characterized by using an IEEE 1394 bus, which is a serial bus specified by EEStd 1394.

According to the ninth aspect of the present invention, the transmission path connecting the plurality of image forming apparatuses is IEEE 139.
By using an IEEE 1394 bus that fully conforms to the four standards, it is possible to connect a plurality of devices to one bus, and further synchronize the bus with a cycle time at a fixed time interval, and control the cycle. It is possible to do.

According to the ninth aspect of the present invention, it is possible to adopt a configuration that does not need to support an additional circuit or a special protocol. Furthermore, it is possible to coexist with other protocols, and it is possible to minimize the influence on other devices connected on the same bus.

According to a tenth aspect of the present invention, in the data transfer method according to any one of the first to eighth aspects, a transmission line connecting a plurality of image forming apparatuses is provided with a U.
universal Serial Bus Speci
The present invention is characterized in that a USB, which is a serial bus specified in the FICATION, is used.

According to the tenth aspect of the present invention, a plurality of devices are connected to one bus by using a USB as a transmission path for connecting a plurality of image forming apparatuses.
It is possible to adopt a configuration that does not require special support of additional circuits, and furthermore, it is possible to synchronize the bus with a cycle time at a fixed time interval, and control the cycle.

[0034]

FIG. 2 is a block diagram showing an operation mode in which a plurality of nodes are connected by an IEEE 1394 bus according to an embodiment of the present invention. In FIG.
IEs of the data source device 1, data sink device 2, and other devices (other nodes) 3
The EE1394 ports 4 are interconnected by a connection cable 5.

Since the isochronous transfer on the IEEE 1394 bus employs a multicast format capable of distributing the same data to a plurality of nodes, a plurality of nodes are transmitted to one data transfer source (data source device 1). It can function satisfactorily even in a configuration where the data transfer destination (data sink device 2) is connected.

For example, when the data source device 1 is a personal computer (hereinafter, PC) or a printer controller and the data sink device 2 is a printer,
One or more printers receive the print data transferred from the printer controller C or the printer controller using the isochronous transfer, and the printing process is performed (simultaneously when a plurality of printers are connected).

FIG. 3 shows an embodiment of the present invention.
6 is a block diagram illustrating an operation mode in which a plurality of nodes are connected by B. FIG. In FIG. 3, the data source device 12,
Each US included in the data sink device 7, the hub 10, and the other device (other functions) 8
The B ports 11 are interconnected by a connection cable 5. The data source device 12 has a host 6 and a root hub 9, and is similarly interconnected by a connection cable 5.

In the configuration using USB, the function having the host 6 does not necessarily have to be the data source device, and the other function 8 can be selected as the data source device. The function having the host 6 is applied as a data sink device.

For example, when the data source device 12 is a PC,
If the data sink device 7 is a printer, the printer receives print data transferred from the PC using isochronous transfer, and performs print processing.

FIG. 1 is a conceptual diagram of a communication path established between a data source device 1 and a data sink device 2 according to an embodiment of the present invention. Hereinafter, the IEEE will be described with reference to FIG.
The configuration when the 1394 bus is used will be described.

In FIG. 1, a data source device 1 and a data sink device 2 are connected by n + 1 communication paths. Each communication path corresponds to an isochronous channel to which a band and a channel number are assigned in advance according to a predetermined protocol.
Assigned to. In the present embodiment, two or more channels are reserved. Physically, it can be sufficiently considered that another node exists between the data source device 1 and the data sink device 2.

On the data source device 1 side, data requested to be transferred (hereinafter referred to as original data 13)
Is encoded by Thereafter, the encoded data (hereinafter, redundant data 14) is distributed to each channel by the multiplexer 16. The number of channels is appropriately selected depending on the size of the original data 13 and the redundant data 14 and the process of generating the redundant data 14, and may be dynamically changed.

Redundant data is created so that even if data is lost during data transfer in some channels, the original data can be restored by using the data of the successfully transferred channel. Is done. One of the simplest methods of creating redundant data is to duplicate the original data for the number of channels reserved.

On the data sink device 2 side, a plurality of data received through each channel are demultiplexed by the demultiplexer 17.
Are combined into one redundant data 14, and the decoder 1
8 to be decoded into original data.

A configuration using a USB will be described similarly with reference to FIG. In FIG. 1, a data source device 1 and a data sink device 2 are connected by n + 1 communication paths.

Each communication path corresponds to an isochronous pipe in which endpoints are connected through a predetermined procedure in advance, and is assigned to each of pipes C0 to Cn. In this embodiment, two or more pipes are secured. Physically, it can be sufficiently considered that another hub exists between the data source device 1 and the data sink device 2.

On the data source device 1 side, data requested to be transferred (hereinafter referred to as original data 13)
Is encoded by Thereafter, the encoded data (hereinafter, redundant data 14) is distributed to each pipe by the multiplexer 16. The number of pipes is appropriately selected depending on the size of the original data 13 and the redundant data 14 and the process of generating the redundant data 14, and may be dynamically changed.

The redundant data 14 can be used even if data loss occurs during data transfer in some pipes.
It is created for the purpose of restoring the original data by using the data of the pipe that has been successfully transferred. One of the simplest methods of creating the redundant data 14 is to duplicate the original data 13 by the number of secured pipes.

On the data sink device 2 side, a plurality of data received through each pipe are combined into one redundant data 14 by a demultiplexer 17 and
To decrypt the original data 13.

FIG. 4 shows an embodiment of the present invention in which original data is divided into n pieces of data, and each piece of data is divided into n pieces of data.
FIG. 3 is a diagram illustrating a data transfer method of distributing and transferring data to a plurality of communication paths and using a checksum to compensate for a data transfer error. Hereinafter, the data transfer method will be described with reference to FIG. The “communication path” described below is IEEE139
When four buses are used, channels are shown, and when USB is used, pipes are shown.

The checksum is a total value for detecting whether an error has occurred when a plurality of binary numbers have been transferred. For example, considering the binary numbers “01101110” and “11100101”,
The checksum is the sum "10001011" obtained by ignoring carryover for each digit of these two numbers.

In FIG. 4, each row represents each communication path, and the horizontal axis corresponds to time. Of the n + 1 communication paths secured, n from the communication path C0 to the communication path Cn-1
Each of the communication paths is used for transferring data obtained by dividing original data into a plurality of packets for each cycle. In the remaining communication channel Cn, the checksum calculated in advance from the original data is transferred from the data source device to the data sink device.

Even if a transfer error occurs in a certain cycle of one communication path (cycle x of communication path C1 in FIG. 4), the checksum received on communication path Cn and the communication paths C0 to Cn in the data sink device. It is possible to detect an error by comparing the checksum calculated from the data received at -1, and restore the original data,
The above operation is based on RAID (redundant array of inexpensi
ve disk) Similar to the operation of a 5-disk device or stripe set with parity.

The number of communication paths for transferring redundant data is appropriately determined according to the redundant data generation method. Further, the number of data transfer errors that can be detected in a single cycle also depends on the redundant data generation method, and it is impossible to detect a plurality of errors in the configuration of FIG.

FIG. 5 is a diagram showing a transfer operation when a plurality of original data to be transferred with a delay of a predetermined packet are used as redundant data. Hereinafter, transfer is performed with a delay of a predetermined packet with reference to FIG. A transfer format for correcting an error during transfer using a plurality of original data will be described. The "communication path" described below indicates a channel when an IEEE 1394 bus is used, and a pipe when a USB is used.

In FIG. 5, each row represents each communication path, and the horizontal axis corresponds to time. In the n + 1 communication paths secured, the original data is transferred via the communication path C0, and the communication path C1
In this case, data delayed by t cycles from the communication path C0 is transferred. Further, data delayed by t × 2 from the communication path C0 is transferred on the communication path C2, and data transmitted by t ×
The data delayed by n are respectively transferred. That is, the original data is transferred through each communication path.

The original data received on the communication path C0 of the data sink device is stored in an intermediate buffer or the like. If a transfer error occurs in the cycle x of the communication channel C0, that is, if the reception of the packet x fails, the data sink device stores the data received on the communication channel C1 after t cycles in the intermediate buffer instead.

If an error has also occurred in the data received on the communication channel C1, the data on the communication channel C2 which is received with a delay of t cycles after the communication channel C1 is similarly stored in the intermediate buffer. Hereinafter, this operation is repeated until the reception is successful. If reception on the communication channel Cn fails,
Alternatively, if the intermediate buffer overflows due to a delay in data reception, the transfer of the packet x is finally regarded as a failure.

FIG. 6 shows that, in one embodiment of the present invention, original data is divided into n pieces of data, and each piece of data is divided into n pieces of data.
FIG. 3 is a diagram illustrating a data transfer method of distributing and transferring data to a plurality of communication paths and using a checksum to compensate for a data transfer error.

The configuration in FIG. 6 differs from the configuration in FIG. 4 in that the checksum is not transferred by one communication path but is dynamically changed and transferred by a plurality of communication paths. Hereinafter, the data transfer method will be described with reference to FIG. The "communication path" described below indicates a channel when an IEEE 1394 bus is used, and a pipe when a USB is used.

In FIG. 6, each row represents each communication path, and the horizontal axis corresponds to time. Communication channel C0 secured
The n + 1 communication paths from to the communication path Cn are used for transferring data obtained by dividing original data into a plurality of packets for each cycle. As shown in FIG. 6, the communication path through which the checksum is transferred is dynamically changed for each packet.

In FIG. 6, as in FIG.
The presence or absence of an error is detected based on the comparison between the sum of the radix and the checksum, and when an error occurs, the original data is restored. Also, in the configuration of FIG. 6, it is possible to detect one error in a single cycle as in the configuration of FIG.

It is also possible to monitor the occurrence status of the transfer failure and adjust the information amount of redundant data called redundancy to set an optimum transfer environment based on the rate of occurrence of errors.

When the error occurrence rate is equal to or higher than a predetermined rate, the redundancy is increased to emphasize transfer reliability. When the error occurrence rate is equal to or lower than a predetermined rate, the redundancy is reduced to improve the transfer efficiency of the entire bus.

For example, in the configuration in FIG. 6, the communication path to which the checksum is transferred is dynamically changed by a predetermined method. However, if the error occurrence rate is equal to or higher than a predetermined rate, the number of communication paths is reduced. By doing so, the amount of checksum information transferred in each communication path is increased, and transfer reliability is improved.

On the other hand, when the error occurrence rate is equal to or less than the predetermined ratio, it is determined that the reliability of the transfer is not impaired even if the information amount of the checksum transferred in each communication path is reduced. To increase the transfer efficiency of the entire bus.

Further, in the configuration shown in FIG. 5, the reliability of transfer is improved by transferring redundant data composed of a plurality of original data to the respective communication paths by delaying by a predetermined cycle, but the error occurrence rate is increased by a predetermined value. If the ratio is equal to or more than the ratio, the transfer reliability is improved by increasing the number of communication paths and the number of redundant data to be transferred.

On the other hand, if the error occurrence rate is equal to or less than the predetermined ratio, it is determined that the transfer reliability is not impaired even if the number of communication paths and the number of redundant data to be transferred are reduced. It is possible to reduce the number to a minimum of two.

As described above, when the transfer conditions such as the number of communication paths are changed, another communication path (for example, asynchronous communication) is used before the change, so that the data source device and the data sink device can be used. Negotiation etc. is performed between.

[0070]

As described above, according to the first aspect of the present invention, by transferring redundant data, which is backup data when image data is lost, in the isochronous transfer mode, a constant transfer rate of image data can be obtained. Can be secured. Further, it is possible to guarantee the time for restoring when image data is lost during transfer.

According to the second aspect of the present invention, a checksum is created based on the divided data before and after the transfer, and the two are compared to identify and restore the missing portion of the image data. As a result, highly reliable transfer of image data can be realized.

According to the third aspect of the present invention, a plurality of divided data and a first checksum created based on the plurality of divided data are transferred as redundant data, so that data at the time of transfer is transferred. By identifying and restoring the missing portion of the image, it is possible to realize highly reliable transfer of image data.

According to the fourth aspect of the present invention, by transferring a plurality of copied image data with a delay of a predetermined packet each time, the transfer of even one of the plurality of image data is normally completed. Thus, it can be considered that the data transfer process has succeeded, and highly reliable image data transfer can be realized.

According to the fifth aspect of the present invention, by using, as redundant data, a plurality of image data transferred with a delay of a predetermined packet each time, even if one image data is lost at the time of transfer, the other image data is transferred. Complemented by the normally transferred image data, it is possible to realize highly reliable transfer of image data.

According to the sixth aspect of the present invention, the first
Each time a predetermined number of checksums are transferred, the communication path assigned at the time of transferring the first checksum is changed, and the communication path for transferring the first checksum is distributed to a plurality of paths instead of being fixed to one. By doing so, even if a failure occurs in one communication path for transferring the first checksum, failure detection using the checksum can be executed.

According to the present invention, the number of communication paths for transferring redundant data is changed in consideration of the error occurrence rate at the time of transfer, thereby improving the transfer efficiency or the transfer success rate. It is possible to realize.

According to the eighth aspect of the present invention, it is possible to improve the transfer efficiency or the transfer success rate by changing the bandwidth which is the transfer amount of the redundant data within a predetermined time. .

According to the ninth aspect of the present invention, the transmission path for connecting a plurality of image forming apparatuses is IEEE 139.
By using an IEEE 1394 bus that fully conforms to the four standards, it is possible to connect a plurality of devices to one bus, and further synchronize the bus with a cycle time at a fixed time interval, and control the cycle. It is possible to do.

According to the ninth aspect of the present invention, it is possible to adopt a configuration that does not need to support an additional circuit or a special protocol. Furthermore, it is possible to coexist with other protocols, and it is possible to minimize the influence on other devices connected on the same bus.

According to the tenth aspect of the present invention, a plurality of devices are connected to one bus by using a USB as a transmission path connecting a plurality of image forming apparatuses.
It is possible to adopt a configuration that does not require special support of additional circuits, and furthermore, it is possible to synchronize the bus with a cycle time at a fixed time interval, and control the cycle.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a communication path established between a data source device and a data sink device according to an embodiment of the present invention.

FIG. 2 shows an IEEE1394 according to an embodiment of the present invention.
FIG. 3 is a block diagram illustrating an operation mode in which a plurality of nodes are connected by a bus.

FIG. 3 is a block diagram showing an operation mode in which a plurality of functions are connected by USB according to an embodiment of the present invention.

FIG. 4 is a diagram showing a data transfer system in which original data is divided, each data is distributed and transferred for each communication channel, and a data transfer error is compensated for using a checksum in one embodiment of the present invention. .

FIG. 5 is a diagram showing a data transfer method for compensating for a data transfer error by transferring original data over a plurality of communication paths at predetermined time intervals in one embodiment of the present invention.

FIG. 6 is a diagram showing a data transfer method for compensating for a data transfer error by dynamically transferring a checksum over a plurality of communication paths in one embodiment of the present invention.

[Explanation of symbols]

 1, 12 Data source device 2, 7 Data sink device 3 Other nodes 4 IEEE 1394 port 5 Connection cable 6 Host 8 Other functions 9 Root hub 10 Hub 11 USB port 13 Raw data 14 Redundant data 15 Coder 16 Multiplexer 17 Demultiplexer 18 Decoder

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04L 1/22 H04L 11/00 310D 5K033 29/02 13/00 301B 5K034 F term (Reference) 5B014 EB03 GA09 GA15 GA46 GC02 GC14 GE05 5B021 AA01 BB02 BB09 EE02 NN07 5B077 AA04 AA23 AA24 BA05 BA06 NN02 NN08 5B083 AA05 BB03 CC01 CC02 EE05 EE06 EE11 EF05 GG04 5K014 AA01 BA03 DA06 EA01 A03 A01 A03 A03 A01 A03 A03 A03 A03 A03 HH16 MM01

Claims (10)

[Claims] A data having an isochronous transfer mode for transferring a predetermined amount of data in synchronization with a signal of a predetermined cycle via a plurality of communication paths interconnecting a plurality of image forming apparatuses existing on the same network. A transfer method, comprising: redundant data creating means for creating redundant data, which is backup data when the image data is lost, based on image data; and redundant data transferring means for transferring the redundant data. Data transfer method. 2. A data dividing means for dividing the image data having a plurality of packets into divided data which is binary data for each predetermined packet, and divided data for transferring the divided data via a plurality of the communication paths, respectively. Transfer means; and first checksum creation means for creating a first checksum, which is a binary sequence obtained by adding the sum of the divided data for each packet before transfer by the same digit of the plurality of divided data. A second checksum creating means for creating a second checksum which is a binary sequence obtained by adding the total sum of the divided data for each packet after transfer at the same digit of the plurality of divided data; A missing data detecting means for comparing the checksum of No. 1 with the second checksum and detecting a missing part of the divided data; Data transfer method according to claim 1, characterized in that it has a data restoring means for restoring the missing portion of the divided data issued, the. 3. The method according to claim 1, wherein the plurality of divided data and the first
3. The data transfer method according to claim 2, wherein the checksum is used as the redundant data. 4. The apparatus according to claim 1, further comprising: data duplicating means for duplicating the image data; and a predetermined interval transferring means for transferring a plurality of duplicated image data with a delay of a predetermined packet. Data transfer method. 5. The data transfer method according to claim 4, wherein a plurality of said image data transferred with a delay by said predetermined packet are used as said redundant data. 6. The communication path according to claim 2, wherein the communication path assigned at the time of transferring the first checksum is changed every time the first checksum is transferred by a predetermined number of packets. Data transfer method. 7. The data transfer method according to claim 1, wherein the number of the communication paths for transferring the redundant data is changed. 8. The data transfer method according to claim 1, wherein a bandwidth, which is a transfer amount of the redundant data within a predetermined time, is changed. 9. The apparatus according to claim 1, wherein an IEEE 1394 bus, which is a serial bus specified by IEEE Std 1394, is used as a transmission path connecting the plurality of image forming apparatuses. Data transfer method. 10. A universal serial bus as a transmission line connecting the plurality of image forming apparatuses.
The data transfer method according to any one of claims 1 to 8, wherein a USB which is a serial bus specified by Specification is used.