JP2009239451A - Arrival check and relay processing check type network device and system, and frame transfer method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for transmitting an acknowledge frame at an early stage without interfering with frame transfer between reservation transfer sections since the frame of the reservation transfer zone is reserved for transmission between prescribed devices in cycle type transfer. <P>SOLUTION: A network device divides transmission data into frame units, transmits and receives a plurality of frames in a fixed cycle, and performs cycle type data transfer, where the cycle is divided into the reservation transfer section for transferring a reserved frame and a free transfer section for transferring a non-reserved frame. The network device has an acknowledge control section for giving the transmission of the reserved frame a higher priority as compared with that of the acknowledge frame, and giving the transmission of the acknowledge frame a higher priority as compared with that of the non-reserved frame. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a network device and system, and a frame transfer method.

  Currently, a communication technology such as IEEE 1394 is used in the real-time communication technology. In such a communication technique, a communication method (hereinafter referred to as cycle type transfer) that performs cycle type transfer in which real-time data and best effort data are mixed is used.

  In the communication method as described above, for example, one cycle has a predetermined period, for example, a time slot of 125 μsec, as shown in FIG. This time slot is repeated a plurality of cycles. Packet data (hereinafter referred to as a frame) is transferred between the network devices in a certain band within the time slot. Here, the first half of the time slot is the reserved transfer section, and the second half is the free transfer section.

  In the reserved transfer section, a certain band in this section, for example, bands 1 to 5 in FIG. 9, is reserved for frame transmission. The reserved bands 1 to 5 are used only between the set devices. For example, in a network composed of a plurality of network devices as shown in FIG. 10, band 1 in FIG. 9 is used only for transmission between devices 11 and 14, and band 2 is used only for transmission between devices 12 and 13. Because it is reserved.

  Then, by setting the frames A1 to A5 of the real-time data in the reserved fixed band such as the bands 1 to 5, a certain amount of frame transmission is guaranteed within a certain time, and AV data or the like Real-time data can be transmitted between devices. Hereinafter, a frame transmitted in the reserved transfer section is referred to as a reserved frame.

  In the free transfer section, it is used for communication of best effort data. Here, the bandwidth for frame transmission is not secured by reservation. Therefore, in this section, data that does not have real-time characteristics is transferred. For this reason, if there is a free band such as band 6 in this section at the time of data transfer, the frame B1 is arranged there and data communication between apparatuses is performed.

  Various forms are conceivable as the network configuration for realizing the cycle-type transfer communication method of FIG. For example, the network devices 11 to 14 in FIG. 10 are connected by daisy chain connection, and the network devices 11, 12, 13, and 15 are connected by star connection or the like.

  Here, each network device has a bridge function, and the network devices 12, 13, 15 and the like transfer the transmission frame from the network device on one side of the own device to the network device on the other side. Can do. As a result, communication can be performed between network devices that are not directly connected using the bridge function.

  There is a movement to apply the above-described cycle type transfer to Ethernet (registered trademark) which is a standard of LAN (Local Area Network). For this reason, high speed and high reliability of data communication by cycle type transfer are required in a LAN using Ethernet.

  Patent Document 1 discloses a technology such as a node device that can secure a reserved resource during communication.

  By the way, the network device exchanges various information in addition to transmission / reception data. The simplest is to send back a response message for notifying that the network device on the receiving side has received data, that is, an Acknowledges (hereinafter referred to as ACK) frame. The transmission-side network device can proceed to the next process after confirming that it has been received.

As another example, there is a message informing the occurrence (or prediction) of a failure. Patent Document 2 discloses a technology for notifying the occurrence of a failure to the opposite device side by forcibly transferring control information when it is determined that a buffer overflow occurs at a relay node between devices.
JP 2002-185491 A JP 2005-269507 A

  When the reply of the ACK frame or the technique disclosed in Patent Document 2 is applied to the above-described cycle type transfer, the following problem occurs. That is, there is a possibility that the transfer of the reservation frame in the reservation transfer section may be disturbed by the return of the ACK frame or the transmission of the control information notifying the failure.

  An ACK frame, failure information, and the like need to be returned to the transmission source network device as soon as possible for subsequent processing of the transmission source device, frame retransmission processing, and the like. However, in the cycle type transfer, in order to transfer real-time data or the like, a predetermined time zone in the reserved transfer section is reserved for transmission / reception between predetermined network devices. For this reason, there is a need for a technique for returning an ACK frame, failure information, and the like at an early stage without interfering with transmission of frames in the reserved transfer section.

  The network device according to the present invention divides transmission data into frames, transmits and receives a plurality of frames in a fixed cycle, and the cycle includes a reserved transfer section for transferring a reserved frame, and a non-reserved frame. A network device that performs cycle-type data transfer divided by a free transfer section to transfer, giving priority to transmission of a reserved frame over transmission of an acknowledge frame, and transmission of a frame that is not reserved for transmission of the acknowledge frame A higher-priority acknowledge (ACK) control unit is included.

  The network system according to the present invention divides transmission data into frames, transmits and receives a plurality of frames in a fixed cycle, and the cycle includes a reserved transfer section for transferring a reserved frame, and a non-reserved frame. A network system having a network device that performs cycle-type data transfer divided by a free transfer section to transfer, wherein the network device gives priority to transmission of a reserved frame over transmission of an acknowledge frame, and Prioritizes transmission of unreserved frames.

  In the frame transfer method according to the present invention, transmission data is divided into frame units, a plurality of frames are transmitted and received in a fixed cycle, and the cycle includes a reserved transfer section for transferring a reserved frame and an unreserved frame. Is a frame transfer method for performing cycle-type data transfer divided by a free transfer section for transferring a frame, wherein the transmission of the reserved frame is given priority over the transmission of the acknowledge frame, and the transmission of the acknowledge frame is not reserved Has priority over sending.

  According to such an invention, the ACK frame is transferred without infringing the frame in the reserved transfer section, and is transferred with priority over the frame in the free transfer section.

  In the network device according to the present invention, in the cycle type transfer, the ACK frame is quickly returned to the transmission source device without infringing the frame in the reserved transfer section.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiment. In addition, for clarity of explanation, the following description and drawings are simplified as appropriate.

  FIG. 1 shows an outline of a network configuration and a network apparatus according to this embodiment. As illustrated in FIG. 1, the network 100 includes network devices 101 to 106. The network devices 101 to 106 perform frame transmission / reception by the cycle-type transfer described above. Since the network devices 101 to 106 have the same configuration, the network device 101 will be described as an example here. The network device 101 includes an application 121, communication logic 122, and ports 123 to 125.

  The application 121 uses data generated by other network devices in the network and data generated by other network devices. For example, there are applications such as creating video data using a peripheral device such as a camera, transmitting the video data to another network device, and displaying the video data transmitted from another network device on a display. .

  The communication logic 122 includes, for example, a MAC bridge (including a switch and a routing table for realizing bridge communication between a plurality of ports in its own device), a spanning tree protocol (STP: Spanning Tree) defined by IEEE802.1 It consists of circuits that perform operations and controls specified by protocols such as Protocol. In addition, the data generated by the application 121 is divided into predetermined lengths and control information is added to form a frame.

  Ports 123 to 125 transmit and receive frames between network devices. For example, a connector or cable defined by IEEE 802.3, hardware conforming to a transmission / reception protocol such as MAC (Media Access Control), or the like is used.

  The network 100 is configured by connecting the communication logic 122 and the application 121 to adjacent network devices via the ports 123 to 125. The connection of each network device may be a daisy chain connection made up of network devices 101 to 104 or a star connection made up of network devices 101, 102, 103, 105.

  Each network device holds information about which port of its own device is connected to which port of other network device in a routing table (not shown) in its own device. For this reason, even when a plurality of ports are used like the network devices 102 and 103, communication between ports of appropriate network devices is performed based on the information.

  FIG. 2 is a detailed block diagram of the network devices 101 to 106 in FIG. Since the network devices 101 to 106 have the same configuration, the network device 101 will be described here as an example. In FIG. 2, the same reference numerals as those in FIG. Further, the ports 123 to 125 have the same configuration and only the port 123 is described for simplification.

  The port 123 has a reception port 131 and a transmission port 132. The reception port 131 sends a frame coming from another network device to a CRC check unit 141 and a reception buffer 142 described later. The transmission port 132 transmits a frame transmitted from an ACK control unit 143 described later to another network device.

  The communication logic 122 includes a CRC check unit 141, a reception buffer 142, an ACK control unit 143, a reservation table 144, and a cycle timer 145.

  The CRC check unit 141 performs a CRC error check on the received frame, and then sends it to the reception buffer 142. At this time, if a CRC error occurs, this error information (hereinafter referred to as CRC error information), the header information of the received frame, and information on whether or not the received frame is a reserved frame are ACK controlled. Send to part 143.

  The reception buffer 142 buffers the frame sent from the CRC check unit 141. At this time, if a buffer overflow occurs in the reception buffer 142, this error information (hereinafter referred to as overflow error information), header information of the received frame, and whether or not the received frame is a reserved frame. Information is sent to the ACK control unit 143.

  Here, FIG. 3 shows an example of the received frame. It is assumed that the received frame is generated in conformity with IEEE 802.3. In the IEEE 802.3 MAC frame, a 7-byte preamble (Preamble), a 1-byte SFD (Start of Frame Delimiter), a 6-byte destination MAC address (Destination Address), a 6-byte source MAC address (Source Address), A 2-byte type (Type) is arranged. This is followed by data (DATA), and finally an FCS (Frame Check Sequence) is arranged. In this embodiment, 4-byte control information is arranged at the end of the header, that is, at the beginning of the data. In the control information, information about whether or not it is a reserved frame is written.

  The reservation table 144 has a time table of one time slot (for example, 0 to 125 μsec) for each port included in the apparatus. In this time table, information indicating which time zone in the time slot is reserved is registered. By referring to the registration information of this time table, for example, information such as that the time zones 1 and 3 of the reserved transfer section in FIG. This registration information is sent to the ACK control unit 143.

  The cycle timer 145 measures the time in one cycle time slot. For example, if the time slot period is 125 μsec, 0 to 125 μsec is measured. The measured time information is sent to the ACK control unit 143.

  The ACK control unit 143 includes a header information reception unit 151 and an ACK frame generation unit 152. The header information reception unit 151 receives the header information sent from the CRC check unit 141 or the reception buffer 142 and sends it to the ACK frame generation unit 152.

  The ACK frame generation unit 152 receives the header information from the header information reception unit 151, and generates an ACK frame based on the header information. Here, FIG. 4 shows an example of the ACK frame. The ACK frame is also created based on IEEE802.3. Therefore, a 7-byte preamble (Preamble), a 1-byte SFD (Start of Frame Delimiter), a 6-byte destination address (Destination Address), a 6-byte source address (Source Address), and a 2-byte type (Type) are arranged at the head of the frame. Is done. This is followed by 46-byte data (DATA), and finally an FCS (Frame Check Sequence) is arranged. Here, the MAC address of the transmission source of the header information from the header information receiving unit 151, that is, the information of A in FIG. 3 is written as the destination address of this ACK frame. In the source address of the ACK frame, the MAC address of the own device, that is, the MAC address of the device in which the CRC error or the like has occurred is written.

  In addition, control information of 4 bytes is arranged at the head of the data of 46 bytes. In this control information, information indicating an ACK frame, CRC error information, buffer overflow error information, and the like are written. Further, additional information may be written in a 46-byte data area. For example, the destination address (B in FIG. 3) of the received frame is written. By writing such an address, the network device that is the transmission destination of this ACK frame can refer to this additional information and determine whether or not the frame in error has been transmitted by itself. This is effective when a CRC error occurs and the source address of the received frame is destroyed.

  Similarly, as a countermeasure against CRC error, each device stores the MAC address of the network device connected to the network in advance, and when the destination address and the transmission source address of the received frame are not the stored address, the header It may be determined that a failure has occurred in the part.

  The ACK control unit 143 determines whether the received frame in which the error has occurred is a reserved frame based on information from the CRC check unit 141 or the reception buffer 142.

  First, consider a case where a received frame in which an error has occurred is not a reserved frame (hereinafter referred to as a normal frame). In this case, the ACK control unit 143 transmits the ACK frame generated by the ACK frame generation unit 152 to the transmission source of the received frame in a time zone having a free transfer interval.

  Next, consider a case where the received frame in which an error has occurred is a reserved frame. In this case, the ACK control unit 143 refers to the registration information of the reservation table 144 and the time information of the cycle timer 145, and waits for the shortest free transfer section from the present time. When the free transfer period is reached, the ACK frame generated by the ACK frame generation unit 152 is returned to the transmission source of the received frame in which the error has occurred with priority over other frames. As a result, the network device that is the transmission source of the frame in which the error has occurred can receive the ACK frame in a short time after the error has occurred. Also, if the ACK control unit 143 determines from the registration information of the reservation table 144 that there is a time slot in which there is no reservation frame transfer and no ACK frame transfer in the reservation transfer section, the ACK frame is returned to the reservation transfer section. Also good.

  Even if the received frame in which an error has occurred is a normal frame, the priority of transmission of an ACK frame may be increased as in the case of a reserved frame. However, the priority is lower than that in the case of the reserved frame.

  As described above, when a CRC error or a buffer overflow occurs in the received frame, the network device according to the present embodiment avoids the reserved time zone based on the information in the cycle timer 145 and the reservation table 144. Thus, the ACK frame can be preferentially returned to the transmission source of the frame. Further, this ACK frame includes CRC error information and buffer overflow error information, so that it is possible to confirm which error has caused the malfunction of the transmission source network device. Although the ACK frame includes error information regarding a CRC error and buffer overflow, and the transmission of the ACK frame is performed when a CRC error or a buffer overflow occurs, the present invention is not limited to this. The present invention can also be applied to a case where an ACK frame is transmitted simply for confirmation of reception of a transmitted frame.

  Further, in a network composed of such network devices, the network device of the relay device stops the transfer before the frame arrives at the destination network device. Then, the network device that is the relay device returns an ACK frame indicating the occurrence of an error such as a CRC error to the network device that is the transmission source. As a result, in the cycle-type transfer network, the network device that is the transmission source of the frame can grasp the occurrence of an error in the transmitted frame at high speed while protecting the frame in the reserved time zone.

  The processing flow of ACK frame transmission of the communication logic 122 of this embodiment is shown using the flowcharts shown in FIGS. The processing flow of FIG. 5 is a case where a CRC error has occurred in the received frame in the CRC check unit 141. The processing flow of FIG. 6 is a case where a buffer overflow has occurred in the reception buffer 142.

  In FIG. 5, a case where a CRC error occurs in the received frame in the CRC check unit 141 will be described. First, when a CRC error occurs in the received frame (S101), the frame is discarded and the header of the received frame is sent to the ACK control unit 143 (S102). The ACK control unit 143 generates an ACK frame including CRC error information (S103). Next, it is determined whether or not the current time is a reserved time zone (S104).

  If it is not the reserved time zone (No in S104), it is determined whether or not the transmission port of the port receiving the received frame is transmitting (S105). On the other hand, if it is the reserved time zone (Yes in S104), the process returns to S104. That is, this process is repeated until the reserved time period ends.

  When it is determined that the transmission is not being performed in the process of S105 (No in S105), it is determined whether the transmission of the generated ACK frame is completed before the start of the transfer of the next reserved frame (S107). This determination is made by referring to the cycle timer 145 and determining whether or not the ACK frame to be transmitted can be transmitted before the start of the transfer of the next reserved frame. The transfer time of the ACK frame is determined by the byte width of the ACK frame and the transfer rate of the network. For example, if the transfer rate is 1 Gbps with the 72-byte width ACK frame, the theoretical value takes 72 nsec. This can be determined by considering a predetermined margin such as a delay. On the other hand, if it is determined that the transmission is being performed by the process of S105 (S105 Yes), the transmission priority of the ACK frame is increased so that the next transmission can be transmitted with the highest priority, and the transmission of the frame being transmitted is completed. The process waits (S106) and proceeds to the process of S107.

  If transmission of the generated ACK frame is not completed by the start of transfer of the reserved frame (No in S107), the process returns to S104. On the other hand, when the transmission of the generated ACK frame is completed by the start of the transfer of the reserved frame (S107 Yes), the ACK frame is transmitted from the transmission port of the port that received the reception frame (S108).

  Next, a case where a buffer overflow occurs in the reception buffer 142 will be described with reference to FIG. First, when a buffer overflow occurs in the reception buffer 142 (S201), the header of the reception frame is sent to the ACK control unit 143 (S202). The ACK control unit 143 generates an ACK frame including the buffer overflow error information (S203). It is determined whether or not the current time is a reserved time zone (S204).

  If it is not the reserved time zone (No in S204), it is determined whether or not the transmission port of the port receiving the received frame is transmitting (S205). On the other hand, if it is the reserved time zone (S204 Yes), the process returns to S204. That is, this process is repeated until the reserved time period ends.

  When it is determined that the transmission is not being performed by the process of S205 (No in S205), it is determined whether the transmission of the generated ACK frame is completed by the start of the transfer of the next reserved frame (S207). This determination is made by referring to the cycle timer 145 and determining whether or not the ACK frame to be transmitted can be transmitted before the start of the transfer of the next reserved frame. The transfer time of the ACK frame is determined by the byte width of the ACK frame and the transfer rate of the network. For example, if the transfer rate is 1 Gbps with the 72-byte width ACK frame, the theoretical value takes 72 nsec. This can be determined by considering a predetermined margin such as a delay. On the other hand, if it is determined that the transmission is being performed by the processing of S205 (S205 Yes), the transmission priority of the ACK frame is increased so that the next transmission can be transmitted with the highest priority, and the transmission of the frame being transmitted is completed. It waits (S206) and progresses to the process of S207.

  If transmission of the generated ACK frame is not completed by the start of transfer of the reserved frame (No in S207), the process returns to S204. On the other hand, when the transmission of the generated ACK frame is completed by the start of the transfer of the reserved frame (S207 Yes), the ACK frame is transmitted from the transmission port of the port that received the reception frame (S208).

  Here, the network apparatus 101 according to the present embodiment may further include a cycle counter 161 as shown in FIG. This cycle counter 161 counts the cycle of cycle type transfer a predetermined number of times, and sends information on the count number to the ACK frame generation unit 152. The ACK frame generation unit 152 generates an ACK frame in which the count number information is written. For example, the count number information is written in the additional information of the ACK frame in FIG. Then, the ACK control unit 143 returns an ACK frame in which information on the count number is written to the transmission source device of the frame in which the CRC error or the like has occurred. As described above, this ACK frame is returned with priority over the normal frame while avoiding the time frame of the reserved frame.

  FIG. 8 shows a conceptual diagram of information of count numbers counted by the cycle counter 161. As shown in FIG. 8, the cycle counter 161 counts the 1st to nth cycles, and associates each cycle with a count number. The nth and subsequent cycles are again from the first. The count number corresponding to each cycle is set at the network design stage so as to be common to all network devices in the network.

  Here, consider a case where a CRC error or the like occurs in a frame of the second cycle in a certain network device. The information of the second count number is sent from the cycle counter 161 to the ACK frame generation unit 152 and written in the additional information of the ACK frame in FIG. Then, the ACK control unit 143 sends back the ACK frame to which the information of the count number is added to the transmission source network device while avoiding the reserved frame time zone and giving priority to the normal frame.

  If such an ACK frame is returned to the transmission source network device, the transmission source network device can immediately determine that an error has occurred in the frame of the second cycle transmitted by itself. As a result, the transmission source network device can retransmit the frame of the second cycle to the destination device at an early stage.

  This is effective, for example, in the case of transferring a frame including continuous stream data that requires real-time properties such as video data. Even if an error occurs in a frame including a part of the stream data, an ACK frame including information on the count number of the frame in which the error has occurred is returned to the transmission source. The transmission source device immediately identifies and retransmits the frame in which the error has occurred. As a result, the delay of the video data to be transferred can be minimized, and the occurrence of video block noise or the like can be prevented.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention.

1 is a schematic diagram of a network according to an embodiment. It is a block diagram of the network device concerning an embodiment. It is a conceptual diagram of the frame transferred by the network device according to the embodiment. It is a conceptual diagram of the ACK frame which the network apparatus which concerns on embodiment produces | generates. It is a flowchart which shows the process of the network device concerning embodiment. It is a flowchart which shows the process of the network device concerning embodiment. It is another example of the block diagram of the network device concerning an embodiment. It is a conceptual diagram for demonstrating the count number which the network device concerning embodiment counts. It is a figure which shows an example of a cycle pattern. 1 is a schematic diagram of a network.

Explanation of symbols

101 to 106 Network device 121 Application 122 Communication logic 123, 124, 125 Port 131 Reception port 132 Transmission port 141 CRC check unit 142 Reception buffer 143 ACK control unit 144 Reservation table 145 Cycle timer 151 Header information reception unit 152 ACK frame generation unit 161 Cycle counter

Claims (21)

Transmit data is divided into frame units, and multiple frames are sent and received in a fixed cycle.
A network device for performing cycle-type data transfer in which the cycle is divided into a reserved transfer section for transferring a reserved frame and a free transfer section for transferring a non-reserved frame;
Prioritize sending reserved frames over sending acknowledge frames,
A network device comprising an acknowledge control unit that prioritizes transmission of a frame not reserved for transmission of the acknowledge frame.   The network device according to claim 1, wherein the acknowledge frame includes information indicating a CRC error or a buffer over error of the received frame.   The network device according to claim 2, wherein the received frame is a reserved frame.   4. The network according to claim 2, further comprising a cycle timer for measuring time, wherein the transmission of the acknowledge frame is performed in a free transfer section closest to the time when the error occurs with reference to the cycle timer. apparatus.   Further, a cycle timer for measuring time and a reservation table having information on a time zone in which a reservation frame is reserved are provided, and the transmission of the acknowledge is performed by referring to the cycle timer and the reservation table. The network device according to claim 2 or 3, wherein the network device is performed in a time zone in which a reservation frame is not reserved in the most recent reservation transfer section from the time when the occurrence of the error occurs.   The network device according to claim 2, wherein the acknowledge frame includes transmission destination address information in the received frame. A cycle counter for counting the cycles and assigning a count number corresponding to each cycle;
The network device according to claim 1, wherein the count number is written in the acknowledge frame. Transmit data is divided into frame units, and multiple frames are sent and received in a fixed cycle.
A network system having a network device for performing cycle-type data transfer in which the cycle is divided into a reserved transfer section for transferring a reserved frame and a free transfer section for transferring a non-reserved frame;
The network device is:
Prioritize sending reserved frames over sending acknowledge frames,
A network system in which transmission of the acknowledge frame is prioritized over transmission of a frame not reserved.   The network system according to claim 8, wherein the acknowledge frame includes information indicating a CRC error or a buffer over error of the received frame.   The network system according to claim 9, wherein the received frame is a reserved frame.   The network device further includes a cycle timer for measuring time, and a reservation table having information on a time zone in which a reservation frame is reserved. For transmission of the acknowledge, refer to the cycle timer and the reservation table. The network system according to claim 9 or 10, wherein the network system is performed in a time zone in which a reservation frame is not reserved in the most recent reservation transfer section from the time of occurrence of the error.   The network device further includes a cycle timer for measuring time, and a reservation table having information on a time zone in which a reservation frame is reserved. For transmission of the acknowledge, refer to the cycle timer and the reservation table. The network system according to claim 9 or 10, wherein the network system is performed in a time zone in which a reservation frame is not reserved in the most recent reservation transfer section from the time of occurrence of the error.   The network system according to claim 9, wherein the acknowledge frame includes transmission destination address information in the received frame. A cycle counter for counting the cycles and assigning a count number corresponding to each cycle;
The network system according to claim 8, wherein the count number is written in the acknowledge frame. Transmit data is divided into frame units, and multiple frames are sent and received in a fixed cycle.
A frame transfer method in which the cycle is divided between a reserved transfer section for transferring a reserved frame and a free transfer section for transferring a non-reserved frame, and the cycle type data transfer is performed between network devices.
Prioritize sending reserved frames over sending acknowledge frames,
A frame transfer method in which transmission of the acknowledge frame is prioritized over transmission of a frame not reserved.   The frame transfer method according to claim 15, wherein the acknowledge frame includes information indicating a CRC error or a buffer over error of the received frame.   The frame transfer method according to claim 16, wherein the received frame is a reserved frame.   The network device includes a cycle timer for measuring time, and a reservation table having information on a time zone in which a reservation frame is reserved. For transmission of the acknowledge, refer to the cycle timer and the reservation table. The frame transfer method according to claim 16 or 17, wherein the frame transfer method is performed in a time slot in which a reserved frame is not reserved in a reservation transfer section nearest from the time when the error occurs.   The network device includes a cycle timer for measuring time, and a reservation table having information on a time zone in which a reservation frame is reserved. For transmission of the acknowledge, refer to the cycle timer and the reservation table. The frame transfer method according to claim 16 or 17, wherein the frame transfer method is performed in a time slot in which a reserved frame is not reserved in the most recent reserved transfer section from the time of occurrence of the error.   The frame transfer method according to any one of claims 16 to 19, wherein the acknowledge frame includes transmission destination address information in the received frame. The network device further includes a cycle counter that counts the cycles and assigns a count number corresponding to each cycle;
The frame transfer method according to any one of claims 15 to 20, wherein the count number is written in the acknowledge frame.

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