WO2013145241A1

WO2013145241A1 - Terminal device, communication system and packet transmission system

Info

Publication number: WO2013145241A1
Application number: PCT/JP2012/058465
Authority: WO
Inventors: 中野　亮; 悠一五十嵐; 松井　進; 和也門田; 原田　諭
Original assignee: 株式会社日立製作所
Priority date: 2012-03-29
Filing date: 2012-03-29
Publication date: 2013-10-03

Abstract

In a communication system, when flooding packets are being transmitted in respect of a given destination, the number of relay terminals is cut, while maintaining the arrival rate when flooding is employed: thus efficient transmission can be achieved in a partial area by securing directionality in transmission. If a terminal receives flooding packets, this terminal stands by for a fixed time before transmitting the received packets. If, during this standby period, the first-mentioned terminal receives the same packets from another terminal in respect of which the number of hops to the destination is the same as or smaller than the number of hops in respect of the same packets received by the first-mentioned terminal, the first-mentioned terminal updates the received count value in relation to the packets in question. A threshold value is set for each number of hops to the destination. If the received count value reaches the threshold value, transmission of the packets in question is disabled. If, during transmission standby, transmission has been disabled but the packets in question have not been received even once from a terminal in respect of which the number of hops to the destination is smaller than this first-mentioned terminal, if these packets cannot be received from a terminal in respect of which the number of hops to the destination is smaller than this first-mentioned terminal during a fixed period after such disablement, the transmission disablement is cancelled and transmission is performed.

Description

Terminal apparatus, communication system, and packet transfer method

The present invention relates to a terminal device, a communication system, and a packet transfer method, and more particularly to packet transfer control in a communication system.

As the use and diversification of network progresses, there are many situations where networks with a form to collect data at specific management nodes are constructed in fields such as remote meter reading (AMI: Advanced Metering Infrastructure) and sensor networks. To do. In this network, when an abnormality such as a partial power failure occurs in a limited area, it is necessary to reliably send an abnormality notification packet to the management node. Further, when delivering a packet to the management node, it is necessary to transfer the packet so as not to disturb as much as possible communication of a terminal existing in an area where no abnormality has occurred.

If communication is performed using wireless or power line communication (PLC: Power 経路 Line Communication), whether or not the route to the management node that has been constructed in advance can be used at the time of transmission due to changes in radio wave conditions or noise. Indeterminate. Therefore, unicast is not sufficient for reliably delivering the abnormality occurrence notification packet to the management node.

When sending a packet by unicast, the arrival of the packet at the destination can be achieved by taking measures such as (1) checking the existence of the terminal on the route before transmission, or (2) performing retransmission several times. Achieve rate improvement. However, other problems such as the occurrence of delay also occur.

On the other hand, flooding improves the arrival rate to the destination by transferring packets using multiple routes. However, since the terminal that received the packet performs rebroadcast, the traffic volume increases rapidly. In addition, since packets are transferred to terminals that do not require relaying, communication with other terminals is hindered.

Therefore, Patent Document 1 sets the probability that the terminal that received the packet will execute the transfer, and sets the probability value individually based on the location information of each terminal. In the case of simple flooding, a terminal that receives a packet performs rebroadcast with a probability of 100%. However, in Patent Document 1, the number of relay terminals is reduced by setting the transfer probability to 80% or the like. Furthermore, by setting the transfer probability of the terminal that exists in the direction where packet transfer is not required based on the position information to 0%, it is possible to ensure directivity for packet transfer and realize transfer within a local area. You can also.

JP 2010-219572 A

However, when the terminal transfer probability is set and the number of relay terminals is reduced as in Patent Document 1, there is a probability that the transfer is interrupted before the packet reaches the destination. Therefore, when it is necessary to reliably deliver a packet to a destination, control based on probability is not suitable.

The present invention has been made in view of the above, and reduces the number of relay terminals while maintaining the arrival rate when flooding is used, and partially ensures efficient packet transfer to a destination by ensuring directivity for transfer. In a typical area.

In order to solve the above problems, the present invention has the following configuration. A terminal that receives a flooding packet from a source terminal or a relay terminal waits for a certain period of time until the received packet is transferred (rebroadcast) to a neighboring terminal. The same number of hops to the destination is called the same layer, a layer having a small number of hops is defined as an upper layer, and a layer having a large number of hops is defined as a lower layer. If the same packet is received from another terminal located in the same layer as the own terminal during the standby time, the reception counter is incremented by 1, and if received from another terminal located higher in the hierarchy than the own terminal, the reception counter is set to x It increases by (x: an integer value of 1 or more). The receiving terminal stops packet transfer when the value of the reception counter reaches a threshold value during the waiting time. This threshold is set for each hierarchy, and is set so that the value becomes smaller as the hierarchy is higher. In addition, if the reception counter reaches the threshold only by receiving from a terminal located in the same layer without receiving a packet from the upper layer terminal, the same packet from the upper layer even if a certain period of time elapses after transfer stop If the packet cannot be received, the transfer cancellation is canceled and the packet is transferred to the neighboring terminal. In this way, if it can be determined that a neighboring terminal in the same layer has sufficiently transferred to the upper layer, or if it can be confirmed that the transfer has been performed up to the upper layer, the transfer to the destination can be stopped by stopping the transfer. The number of relay terminals is reduced while maintaining the packet arrival rate, and the directivity is ensured for transfer.

The problem described above includes a reception counter for each flooding packet received from another terminal device, and the reception counter is counted every time the flooding packet is received from a terminal device whose hop count to the destination is the same as or smaller than that of the terminal device. Update the value and send the flooding packet based on the packet transfer control unit that determines whether the forwarding of the flooding packet is possible based on the counter value and the threshold value set for the number of hops to the destination. This can be achieved by a terminal device further comprising a communication processing unit.

Further, in a communication system including a plurality of terminal devices constituting a plurality of hierarchies and a management node that communicates with one of the terminal devices, the terminal device includes a reception counter for each flooding packet received from another terminal device. The reception counter updates the counter value every time the flooding packet is received from a terminal device having the same or smaller number of hops to the destination as its own terminal device, and the communication device determines whether the flooding packet can be transferred, This can be achieved by a communication system further including a packet transfer control unit that is determined based on a threshold value set for the number of hops to the destination, and a communication processing unit that transmits a flooding packet based on the determination of the packet transfer control unit.

A packet transfer control unit that determines a reception counter for each flooding packet received from another terminal device, and whether or not the forwarding of the flooding packet is based on a counter value and a threshold value set in the number of hops to the destination; A packet transfer method in a terminal device further comprising a communication processing unit for transmitting a flooding packet based on the determination of the control unit, wherein the flooding packet is received from a terminal device having the same or smaller hop count to the destination A step of updating the counter value of the reception counter, a step of comparing the counter value with a threshold value set for the number of hops to the destination in a predetermined period, and a predetermined period when the counter value is less than the threshold value The step that forwards the flooding packet when it expires. The packet transfer method comprising the bets can be achieved.

In a communication system, the number of relay terminals is reduced while maintaining the arrival rate when flooding is used, and efficient packet transfer to the destination is realized in a partial area by ensuring directivity for transfer.

It is a block diagram explaining the structure of a communication system. It is a hardware block diagram of a terminal. It is a hardware block diagram of a management node. Packet format. It is a flowchart of the process which a transmission origin terminal transmits a flooding packet. It is a flowchart of the process which a relay terminal transmits a flooding packet. It is a flowchart of the process which determines the transfer propriety of the terminal which received the flooding packet. It is a flowchart of the process which determines whether the cancellation | release cancellation | release cancellation of the terminal which stopped transfer is possible. It is a figure explaining the structure of a packet management table. It is a sequence diagram of packet transfer. It is a block diagram explaining the structure of another communication system. It is a flowchart of the other process which determines the propriety of transfer in the terminal which received the flooding packet. It is a flowchart of the other process which determines whether cancellation cancellation is possible in the terminal which canceled transfer. It is a figure explaining the structure of another packet management table.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings using examples. The same reference numerals are assigned to substantially the same parts, and the description will not be repeated.

The configuration of the communication system will be described with reference to FIG. In FIG. 1, the network system 100 includes a management node 300 and hierarchically configured terminals 200. A terminal 200-11 and a terminal 200-12 are connected to the management node 300. The terminal 200-11 is connected to a terminal 200-21 and a terminal 200-22 at a lower level. The terminal 200-21 is connected to a terminal 200-31 and a terminal 200-32 at a lower level. The connection relationship of the terminal 200 is as illustrated. Here, m of the terminal 200-mn is a hierarchy, and n is a serial number in the same hierarchy.

The communication system 100 in FIG. 1 has a tree structure topology in which the terminals 200 are connected in a manner that branches from the root management node 300. In the communication system 100, the number of terminals in each layer is larger in the lower layer.

Referring to FIG. 2, the hardware configuration of the terminal will be described. The terminal 200 is an embedded device having a communication function with the management node 300 or another terminal 200. In FIG. 2, the terminal 200 includes a microcomputer 201, a clock generation circuit 208, a power supply circuit 209, and a transmission / reception circuit 210. The microcomputer 201 is composed of a ROM 202 and a RAM 207. The microcomputer 201 is connected to the clock generation circuit 208, the power supply circuit 209, and the transmission / reception circuit 210.

The ROM 202 is a storage device including a read-only semiconductor memory. The ROM 202 includes a central control unit 203, a communication processing unit 204, a route management unit 205, and a packet transfer control unit 206. The ROM 202 is connected to the RAM 207. The central control unit 203 controls execution of programs in the ROM 202. The central control unit 203 is connected to the communication processing unit 204 and the route management unit 205.

The communication processing unit 204 realizes transmission / reception processing in communication. Specifically, the communication processing unit 204 performs packet assembly processing such as transmission destination designation at the time of transmission. The communication processing unit 204 performs packet analysis processing such as determination of whether or not the packet is addressed to the own terminal at the time of reception. The communication processing unit 204 is connected to the central control unit 203 and the packet transfer control unit 206. The route management unit 205 manages a route in communication between terminals in the network. The route management unit 205 is connected to the central control unit 203.

The RAM 207 is a storage device such as a rewritable semiconductor memory element. The RAM 207 is used as a transmission / reception buffer for communication. The RAM 207 is connected to the ROM 202. The clock generation circuit 208 generates a clock used by the microcomputer 201 and the transmission / reception circuit 210. The clock generation circuit 208 is connected to the power supply circuit 209, the microcomputer 201, and the transmission / reception circuit 210.

The power supply circuit 209 supplies power to the terminal itself. The power supply circuit 209 is connected to the clock generation circuit 208, the microcomputer 201, and the transmission / reception circuit 210. The transmission / reception circuit 210 transmits and receives signals. The transmission / reception circuit 210 is connected to the clock generation circuit 208, the power supply circuit 209, and the microcomputer 201. When performing wireless communication, the RF peripheral circuit corresponds to the transmission / reception circuit 210. The packet transfer control unit 206 determines whether or not to transfer a packet received from another terminal according to a process described later. Note that the terminal 200 may be an independent device instead of an embedded device.

The hardware configuration of the management node will be described with reference to FIG. The management node 300 communicates with the terminal 200 and collects data. In FIG. 3, the management node 300 includes a microcomputer 201, a clock generation circuit 208, a power supply circuit 209, and a transmission / reception circuit 210. The microcomputer 201 includes a ROM 202A and a RAM 207. The microcomputer 201 is connected to the clock generation circuit 208, the power supply circuit 209, and the transmission / reception circuit 210. The ROM 202 includes a central control unit 203, a communication processing unit 204, and a route management unit 205.

The hardware configuration of the management node 300 is the same as that of the terminal 200 except that the packet transfer control unit 206 is not installed. The management node 300 may include an external network connection circuit when a function for using an external network such as Ethernet (registered trademark), WiFi (registered trademark), an optical line, or a telephone network is necessary.

Referring to FIG. 4, the packet configuration will be described. In FIG. 4, a packet 400 includes a header 401 and a payload 402. The header 401 includes a destination address 403, a final destination address 404, a transmission source address 405, a transmission source address 406, a flooding ID 407, and a transmission source terminal hierarchy number 408. However, if other fields such as packet length and TTL (Time To Live) are necessary, they may be added to the header as appropriate. That is, the header configuration is not particularly limited as long as it includes fields equivalent to the destination address 403 to the number of layers 408. The header configuration may be a header including a MAC header and an IP header.

The destination address 403 is a field that describes a destination address or ID in communication between links. The identifier of the terminal of the address or ID described in this field is made to conform to the method adopted in the communication system 100. If it is identified by an IP address, a MAC address or a unique ID, the ID may be described. At this time, when performing flooding, an address or ID indicating flooding is written in the destination address 403. When described in the MAC address, it corresponds to “FF: FF: FF: FF: FF: FF”.

The final destination address 404 is a field that describes the final destination address or ID of the packet. When transmitting a flooding packet addressed to the management node, the address or ID of the management node is described in the final destination address 404. The source address 405 is a field that describes the address or ID of the terminal that relayed the packet. When the terminal serving as the transmission source transmits, the address or ID of the transmission source terminal is described in the transmission source address 405. The source address 406 is a field that describes the address or ID of the source terminal of the packet. The packet ID 407 is a field that describes an ID used for packet identification. The packet ID 407 is described by the source terminal. The sequence number used in the IP header corresponds to the packet ID.

The transmission source terminal hierarchy number 409 describes the transmission source terminal hierarchy number when the transmission source terminal transmits a packet. When the relay terminal transfers a packet, the number of layers of the relay terminal is described in the number of layers 409 of the transmission source terminal. Specifically, when the terminal 200-22 relays a packet, the packet is transferred with a value of 2 written in the field of the number of layers 409 of the transmission source terminal. By doing in this way, the receiving terminal of a packet grasps | ascertains the hierarchy number of a transmission origin or a relay terminal using the hierarchy number 409 of a transmission source terminal. Specifically, the communication processing unit 204 analyzes the received packet and confirms the field of the number of layers 409 of the transmission source terminal. After the confirmation, whether or not the received packet can be transferred is determined by the process described later with reference to the hierarchy of the source of the received packet or the relay terminal. Further, when the number of layers in which the terminal is located changes due to a topology change, the number of layers is updated by referring to the corresponding field of the packet received from the adjacent terminal.
The payload 402 stores application data 409 to be transmitted. Specifically, the application data 409 is a message such as a battery exhaustion.

Referring to FIG. 5, the packet transmission procedure of the source terminal that transmits the flooding packet will be described. When the own terminal is the transmission source and a packet such as an abnormality notification is transmitted to the management node by flooding, the packet is transmitted according to the processing flow of FIG. In FIG. 5, step 501 is processing for storing application data to be transmitted in the payload 402. Specifically, when an abnormality occurrence notification packet is transmitted, the content of the abnormality that has occurred is described in the payload 402.

Step 502 is a process for assembling a packet by writing necessary information in each field of the header 401 and attaching the header 401 to the payload 402. Specifically, it is as follows.

In the destination address 403 field, an address or ID indicating flooding is entered. As described above, “FF: FF: FF: FF: FF: FF” is described when the MAC address is used. An address or ID indicating the final destination of the flooding packet is described in the final destination address 404 field. If the management node 300 is the final destination, the address or ID of the management node 300 is described.

In the field of source address 405, the address or ID of the terminal is entered. In the field of the source address 406, the address or ID of the own terminal is described. In the field of the packet ID 407, an ID unique to the packet is described so that it can be distinguished from other packets. The number of layers in which the terminal is located is described in the field of the number of layers 408 of the transmission source terminal. When a field such as TTL is provided, necessary information is described in the header before proceeding to step 503. The processing related to the packet assembly up to this point is performed by the communication processing unit 204.

Step 503 is a process for transmitting the packet assembled up to Step 502 by flooding. This transmission processing is performed by the transmission / reception circuit 210, and the flowchart of FIG.

Referring to FIG. 6, a transmission procedure when the relay terminal transfers the flooding packet will be described. When a terminal that receives a flooding packet from a source terminal or a relay terminal transfers the packet, the packet is transmitted according to the processing flow of FIG. In FIG. 6, step 601 is a process of copying the application data of the received packet to be transferred to the payload 402. Step 602 is a process for assembling the packet by copying the header of the received packet and overwriting the field that needs to be rewritten. Of the fields described in the header 401, the fields that need to be overwritten are as follows.

Rewrite the field of the source address 405 with the address or ID of the own terminal. The field of the layer number 408 of the transmission source terminal is rewritten to the number of layers where the own terminal is located. At this time, if a field such as TTL is provided as in the packet transmission procedure of the source terminal, necessary information is copied or overwritten in the header before proceeding to step 603. Specifically, if a TTL field is provided, the TTL value is updated by decrementing in this step 602. Processing related to packet assembly up to this point is performed by the communication processing unit 204.

Step 603 is a process of transmitting the packet assembled up to Step 602 by flooding. The transmission process is performed by the transmission / reception circuit 210, and the flowchart of FIG.

With reference to FIG. 7, a procedure for the terminal that has received the flooding packet to determine whether or not to forward the received packet will be described. After the source terminal transmits the flooding packet, when another terminal newly receives the packet from the source terminal or the relay terminal, the receiving terminal determines whether to transfer the packet according to the processing flow of FIG. To do. In FIG. 7, step 701 indicates that a flooding packet has been received from a source terminal or a relay terminal and reception processing has started.

Step 702 is processing for starting standby after receiving a packet until the received packet is transferred to a neighboring terminal. Thus, the terminal that has received the flooding packet waits for a certain period of time until the received packet is transferred to the neighboring terminal. The received terminal starts standby from step 702 and proceeds to step 703. Note that this standby time is not necessarily the same for all terminals, and the standby time may be changed according to the number of neighboring terminals. A specific operation in step 702 is to start a timer.

Step 703 is processing for determining whether or not a new packet has been received. If a packet has been received (YES), the process proceeds to step 704, and if not received (NO), the process proceeds to step 713.

Step 704 is a process for determining whether the packet received in Step 703 is the same packet received in Step 701. This determination is performed by determining whether both the source address 406 and the packet ID 407 have the same value as the packet received in step 701. If the values of both fields are the same as the packet received in step 701, it is determined that they are the same packet. If it is determined that the packets are the same (YES), the process proceeds to step 706. If they are not the same packet (NO), the process proceeds to step 705.

Step 705 is processing for storing the packet received in step 703 in the reception buffer. There is a possibility that the receiving terminal receives a plurality of different packets, and a plurality of processes in FIG. 7 or FIG. Therefore, it is necessary to store the received packet in a buffer and perform identity determination with other received packets in each process. In order to realize this, the received packet is stored in the buffer in this step.

Step 706 is a process for determining whether or not the packet received in step 703 is received from a terminal in the same hierarchy as the own terminal. Specifically, the determination is made with reference to the value described in the field of the number of layers 408 of the transmission source terminal. If received from a terminal in the same hierarchy (YES), the process proceeds to step 707; otherwise (NO), the process proceeds to step 708.

Step 707 is a process of incrementing the reception counter for the packet received in step 701 by one. Thus, each terminal holds a reception counter for each received packet and stores a reception counter value. Then, when the reception counter reaches a predetermined threshold, transfer of the received packet is stopped. Details will be described later in later steps.

Step 708 is a process for determining whether or not the packet received in step 703 is received from a terminal located higher in the hierarchy than the own terminal. This determination is also made by referring to the field of the number of layers 408 of the transmission source terminal as in step 706. If the packet is received from an upper layer terminal, the process proceeds to step 709; otherwise, the process proceeds to step 713.

Step 709 is a process of setting a flag indicating that the received packet has been received from a terminal higher than the own terminal. In this way, each terminal holds a flag indicating whether or not the received packet has been received from the upper layer terminal even once for each received packet.

Step 710 is a process for incrementing the reception counter for the same packet as that received in Step 701 by x. If the packet received in step 703 is received from a terminal in the same layer, the counter value is incremented by 1 in step 707, but the addition value x in this process is an arbitrary integer of 1 or more. It is a numerical value and can be set as a parameter. The smaller the value of x, the lower the probability that the reception counter will reach the threshold within the transfer waiting time, so the number of packet relay terminals will increase, but on the other hand, more packets will be transferred to the upper layer. become. Therefore, it is possible to improve the packet arrival rate to the management node 300. Specifically, in a network environment where the packet loss rate is extremely high, the value of x is set to be small when it is desired to reliably deliver a packet such as an abnormality notification to the management node.

On the other hand, when the same value as the threshold value set for the own terminal is set as the addition value x, the reception counter reaches the threshold value immediately after receiving the same packet as received at step 701 from the upper layer terminal. The transfer will be canceled. When such a setting is made, the arrival rate is somewhat lower than when the value of x is set to be smaller than the threshold value, but at least one of the terminals located in the upper layer receives the packet. When it is confirmed that the transfer is complete, the transfer is stopped. Therefore, the number of relay terminals can be reduced, and the influence on other terminals in flooding can be further reduced. In addition, since the lower layer terminal that receives the packet from the upper layer stops the packet transfer, the directivity from the lower layer to the upper layer can be ensured for the packet transfer. With this directivity, the flooding packet can be transferred to the management node without interfering with the communication of a terminal located in a lower layer that does not require relaying. In the case of a network environment with a low packet loss rate and high reliability, a larger effect can be obtained in terms of reducing the number of relay terminals and the like by setting the value of the addition value x large in this way.

Step 711 is processing for determining whether or not the reception counter updated in Step 707 or Step 710 has reached a predetermined threshold value. The threshold value of this reception counter is set for each hierarchy, and is set so that the value becomes smaller as the hierarchy is higher. That is, when a threshold value given to a terminal having a hop count of 1 from the management node is defined as a1 and a threshold value given to a terminal having a hop count of 2 is defined as a2..., The threshold value is set so that the relational expression a1 ≦ a2 ≦. To do. This threshold is determined based on the number of layers in which each terminal is located or topology information, and the determination method is not limited to one.

As shown in FIG. 1, in the case of a topology in which the number of terminals located in each layer increases as it goes down, it is more appropriate that the threshold increases linearly with the number of hops from the management node. In such a case, a method of giving the hop count from the management node as a threshold value can be considered. That is, when ai is a threshold given to a terminal having the number of hops i from the management node, the threshold is set so that ai = i. As described above, the threshold determination method is determined based on the topology structure or the like, and does not depend on a specific application. As a result of updating the reception counter in step 707 and step 710, if the counter value is equal to or greater than the threshold value (YES), the process proceeds to step 712. If the counter value is less than the threshold value (NO), the process proceeds to step 713.

Step 712 is a process for stopping the transfer of the packet received in Step 703. Thereafter, the flowchart of FIG. 7 ends. The description related to this transfer cancellation process will be described in detail with reference to FIG.

Step 713 is a process of determining whether or not a predetermined standby time has elapsed from step 702 as a starting point. If the standby time has timed out (YES), the process proceeds to step 714, and if the standby time still remains (NO), the process returns to step 703. Step 714 is a process of transferring the packet received in step 701 to the neighboring terminal according to the process of FIG. Step 715 is a process for setting a flag indicating that the packet has been transferred. Thus, each terminal holds a flag indicating whether or not the packet has been transferred for each received packet. After performing the flag processing, the flowchart of FIG.

As described above, in the first embodiment, the terminal that has received the flooding packet waits for a certain period of time until transfer is performed. As a result of receiving the same packet from the terminal located in the same hierarchy or higher hierarchy as the own terminal and updating the reception counter during this waiting time, the transfer is stopped when the reception counter value reaches the threshold value.

If it can be determined that a neighboring terminal in the same layer as the local terminal has sufficiently transferred to the upper layer terminal, or if it has been confirmed that the transfer has been performed up to the upper layer, the transfer is stopped to the management node. The number of relay terminals is reduced while maintaining a high packet arrival rate, and directivity in packet transfer is ensured by adjusting the added value x.

Referring to FIG. 8, a description will be given of a process for determining whether or not to cancel the transfer cancellation in the terminal that performed the transfer cancellation process in step 712 of FIG. The terminal cancels the transfer cancellation and determines whether or not to transfer the received packet to the neighboring terminal according to the flowchart of FIG. However, in this case, a terminal in which the flag described in step 709 in FIG. 7 indicating that it has been received from a higher-layer terminal is not set. That is, a terminal whose reception counter reaches a threshold value only by receiving from the same layer without receiving a packet from a terminal of higher layer is targeted. This is because, when a packet is received from an upper layer terminal and the transfer is stopped, it is obvious that the packet has already been transferred to the upper layer.

In FIG. 8, step 802 is processing for determining whether or not a flag indicating that the packet has been received from the upper layer is down. If the flag is down (YES), the process proceeds to step 803, and if the flag is set (NO), the process returns. Step 803 is processing to start waiting until transfer cancellation cancellation is rejected. Step 803 is specifically a timer start. Similar to the transfer waiting time described with reference to FIG. 7, each terminal waits for a certain period of time before deciding to cancel the transfer cancellation. This waiting time is not necessarily the same in all terminals. The terminal starts standby from step 803 and proceeds to step 804.

Step 804 is processing for determining whether or not a new packet has been received. If a packet has been received (YES), the process proceeds to step 805, and if not received (NO), the process proceeds to step 808.

Step 805 is processing for determining whether the packet received in Step 804 is the same packet as the packet received in Step 701 of FIG. This determination is made by referring to the values of the source address 406 and the packet ID 407. If it is determined that the packet is the same (YES), the process proceeds to step 807. If the packet is not the same (NO), the process proceeds to step 806. Step 806 is processing to store the packet received in step 804 in the reception buffer. Step 807 is processing for determining whether or not the packet received in step 804 is received from a higher-layer terminal than the own terminal. Whether or not the packet is received from an upper layer terminal is determined by referring to the field of the layer number 408 of the transmission source terminal in the received packet. If it is received from an upper layer terminal (YES), the process returns; otherwise (NO), the process proceeds to step 808.

Step 808 is a process of determining whether or not a predetermined standby time has elapsed from Step 803 as a starting point. If the waiting time has timed out (YES), the process proceeds to step 809. If the waiting time still remains (NO), the process returns to step 804.

Step 809 is a process of canceling the transfer stop in step 801 and transferring the packet for which transfer was stopped. Step 810 is a process for setting a flag indicating that the packet has been transferred. It returns after this flag processing.

In other words, if the same packet cannot be received from the upper layer terminal after a certain period of time after the terminal has stopped the transfer, it is determined that the transfer to the upper layer has not been successful and the transfer stop is canceled. Forward the packet to the neighboring terminal. In this way, even if the transfer by the neighboring terminal fails due to packet loss or the like, the terminal that has stopped the transfer detects the transfer failure to the upper layer and performs the transfer. Improve packet arrival rate.

The configuration of the packet management table will be described with reference to FIG. Each terminal holds the packet management table 900 shown in FIG. 9, and performs control while referring to and updating information in the packet management table 900. In FIG. 9, the packet management table 900 includes a packet ID 901, a reception counter 902, a reception flag 903 from an upper layer terminal, and a transfer completed flag 904.

The packet ID 901 is a field that describes an ID for identifying the packet. Specifically, the ID described in the packet ID 407 is copied from the header of the received packet. The reception counter 902 is a field for recording a reception counter value for the received packet. In step 707 and step 710 of FIG. 7, the value of the field is updated. A reception flag 903 from a higher layer terminal is a field that describes a flag indicating whether or not the packet has been received at least once from a higher layer terminal than the own terminal. The flag processing in step 709 in FIG. 7 and the flag reference processing in step 802 in FIG. 8 are realized by updating and referring to the value of this field. The transfer completed flag 904 is a field that describes a flag indicating whether or not the packet has been transferred. The flag processing in step 715 in FIG. 7 and step 810 in FIG. 8 is realized by updating the value of this field. If the same packet as the packet for which the flag of this field is set is received, it can be seen that the packet has been transferred in the past, and thus processing such as discarding the packet is realized.
Note that the configuration of the packet management table is not limited to the configuration of FIG. 9, and if there is other information to be stored by the terminal, fields may be added as appropriate.

The packet transfer control will be described with reference to FIG. Here, packet transfer in terminal 200-21, terminal 200-22, and terminal 200-23 with the number of hierarchies 2, and terminal 200-11 and management node 300 with the number of hierarchies of 1 will be described. Here, the case where the threshold value of the reception counter is set to the same value as the number of layers will be described. Specifically, the threshold value of the terminal 200-21, the terminal 200-22, and the terminal 200-23 having the number of layers of 2 is 2. Further, the threshold value of the terminal 200-11 having the number of layers of 1 is 1.

First, the same flood packet is received from the lower layer terminals in the order of the terminal 200-23, the terminal 200-22, and the terminal 200-21. At this time, each terminal 200 performs packet reception processing (S1001, S1003, S1005), and then starts waiting for a certain period of time (S1002, S1004, S1006).

Since the terminal 200-23 has not received the same packet and the transfer standby time has elapsed, the terminal 200-23 performs packet transmission processing after the standby time has timed out (S1007), and transfers the packet. Then, this packet reaches terminal 200-11, terminal 200-22, and terminal 200-21, and each terminal performs packet reception processing (S1008, S1010, S1011). At this time, since the terminal 200-11 has received the packet for the first time, the terminal 200-11 starts waiting for transfer for a certain time after the packet reception process (S1009). For the terminals 200-21 and 200-22, the same packet is received from the terminal 200-23 of the same layer during the transfer standby, so that the reception counter is incremented by 1, respectively.

The terminal 200-22 received the same packet once from the terminal 200-23 of the same number of layers during the transfer standby time, but the reception counter has not reached the threshold value, so that the packet transmission processing is performed after the standby time has timed out. (S1012), the packet is transferred. This packet reaches terminal 200-11, terminal 200-23, and terminal 200-21, and each terminal performs packet reception processing (S1013, S1014, S1015). Terminal 200-11 does not update the reception counter because it has received a packet from terminal 200-22 located at a lower hierarchy than the terminal 200-11. However, since the terminal 200-21 is receiving from the same layer, the reception counter is incremented by 1 again. Also, since the terminal 200-23 has already transferred the packet, no particular control is performed.

At this time, the terminal 200-21 receives the same packet from the two terminals 200-22 and 200-23 already located in the same layer during the transfer waiting time, and the reception counter reaches 2 which is a threshold value. Therefore, the transfer cancellation process is performed (S1016). Since the terminal 200-21 has stopped the transfer without receiving the packet even from the upper layer terminal, the terminal 200-21 starts waiting for the transfer cancellation to be determined in order to determine whether or not the transfer cancellation can be canceled (S1017).

After that, the terminal 200-11 performs the packet transmission process (S1018) and transfers the packet because the transfer waiting time has timed out without the reception counter reaching the threshold value. As a result, the packet reaches the neighboring terminal 200-23, terminal 200-22, and terminal 200-21 including the destination management node 300, and each terminal performs reception processing (S1019, S1020, S1021, and S1022). Here, since the terminal 200-21 received the packet from the terminal 200-11 located at a higher layer than the own terminal during the waiting time for canceling the transfer cancellation, the terminal 200-21 makes a transfer cancellation cancellation rejection (S1022). The process for determining whether or not to cancel is terminated.

Here, although not shown, in both the packet transmission process (S1007) of the terminal 200-23 and the packet transmission process (S1012) of the terminal 200-22, the terminal 200-21 may receive the packet. However, consider a case where a packet loss occurs for the terminal 200-11 and the packet transfer to the terminal 200-11 fails. In this case, since the terminal 200-21 does not receive the packet from the terminal 200-11 and the waiting time for canceling the transfer cancellation times out, the terminal 200-21 transfers the packet after the transfer cancellation canceling process. Packet transfer to.

In the present embodiment, the tree structure topology as shown in FIG. 1 has been described as an example. However, the topology assumed in the present embodiment is not limited to the tree structure. In this embodiment, the description has been made assuming flooding addressed to the management node. However, if each terminal knows the number of hops to a certain destination, the number of hops to the destination can be regarded as a hierarchy. Thus, even if a terminal other than the management node is selected as the destination of the flooding packet, this embodiment can be applied.

Example 1 is an example that assumes a topology in which the number of terminals located in each layer increases as it goes down as shown in FIG. On the other hand, in the second embodiment, an embodiment assuming a topology in which the number of terminals located in each layer is almost the same will be described. Specifically, when one terminal is installed in each room of an apartment for the purpose of AMI or the like, it is possible to form the topology assumed in the second embodiment.

First, a communication system configuration, a packet configuration, a transmission procedure of a flooding packet of a transmission source terminal and a relay terminal, and an outline of an operation when a terminal receives a flooding packet addressed to a management node will be described.

The configuration of the communication system will be described with reference to FIG. In FIG. 11, the communication system 100 </ b> A includes a management node 300 and a plurality of terminals 200. The terminal 200-1n (n = 1 to 4) connects the terminal 200-2n to the lower level. The terminal 200-2n connects the terminal 200-3n to the lower level. The terminal 200-3n connects the terminal 200-4n to the lower level. Unlike the communication system 100 of FIG. 1 shown in the first embodiment, the communication system 100A has a topology configuration in which the number of terminals located in each layer is almost the same regardless of the number of layers.

Hardware configuration of the terminal 200 and the management node 300 according to the second embodiment (FIGS. 2 and 3), a packet configuration (FIG. 4), a transmission procedure of flooding packets between the source terminal and the relay terminal (FIGS. 5 and 6), The procedure for determining whether to cancel transfer cancellation (FIG. 8) and the table structure (FIG. 9) relating to packets are the same as in the first embodiment.

The contents of the process for determining whether or not to allow packet transfer (FIG. 7) are the same as those in the first embodiment. However, since the topology structure is different from that of the first embodiment, the threshold value of the reception counter used in step 711 in FIG. 7 is preferably determined by a method different from that of the first embodiment. In the first embodiment, a topology is assumed in which the number of terminals located in each layer increases as it goes to the lower layer as shown in FIG. 1, so that the threshold value increases linearly with the number of hops from the management node. showed that.

However, in the topology of FIG. 11 assumed in the second embodiment, the number of terminals located in each layer is almost the same regardless of the layer, so that the threshold does not change greatly until the upper layer near the management node 300 is reached. It is more suitable that the threshold value increases logarithmically with respect to the number of hops from the management node 300. When the number of neighboring terminals existing on the same layer as the own terminal is y, the number of hops from the management node is i, and an arbitrary integer value of 1 or more is n, the threshold ai is set to the number 1 for the hop number i. The method etc. are mentioned.

Here, the bracket-like symbols included in Equation 1 are ceiling functions, which are functions that round up the decimal point. When y = 2 and n = 1, the threshold values for the number of hops i are summarized in Table 1 as compared with the first embodiment. According to Table 1, as the number of hops increases, the threshold value of Example 2 increases logarithmically. The values in parentheses in Example 2 in Table 1 are values before sealing.

Table 1 Threshold for each hop ---------------------------------
Number of hops (i) Example 1 (i) Example 2 (ceiling (2√i))
---------------------------------
1 1 (2 × 1) → 2
---------------------------------
2 2 (2 × 1.41) → 3
---------------------------------
3 3 (2 × 1.73) → 4
---------------------------------
4 4 (2 × 2) → 4
---------------------------------
5 5 (2 × 2.23) → 5
---------------------------------

However, the threshold value setting method is not limited to the above, and the threshold value may be determined using other setting methods.

Example 1 and Example 2 are examples that assume transfer of application data packets such as notification of occurrence of abnormality. The third embodiment will be described with respect to an embodiment in which it is assumed that the route construction packet is delivered to the management node. When a route is constructed using AODV (Ad hoc On-Demand Distance Vector) stipulated in RFC3561, a terminal newly entering the network transmits a packet called RREQ (Route REQuest) by flooding and sends it to the management node. Route construction is implemented by delivering. The third embodiment describes a transfer control method when a RREQ packet is transmitted to the management node 300 by flooding when a route is constructed by AODV.

First, a communication system configuration, a packet configuration, a transmission procedure of an RREQ packet between a transmission source terminal and a relay terminal, and an operation outline when the terminal receives an RREQ packet addressed to a management node will be described.

Note that the communication system according to the third embodiment (FIG. 1 or FIG. 11), the hardware configuration of the terminal and the management node (FIGS. 2 and 3), the procedure for determining whether transfer cancellation can be canceled (FIG. 8), and the configuration of the packet management table (FIG. 9) is the same as that of Example 1 and Example 2. FIG.

The RREQ packet configuration is the same as the packet configuration in FIG. 4 except that information is described in the payload 402 portion in FIG. 4 according to the RREQ message format defined in RFC3561. However, since the terminal newly entering the network does not belong to any layer at the time of assembling the RREQ packet, the number of layers of the own terminal cannot be described in the field of the number of layers 408 of the transmission source terminal in FIG. . Therefore, for the RREQ source terminal, the maximum value that can be described in this field is described. This maximum value depends on the bit length assigned to the field of the layer number 408 of the transmission source terminal.

Also, the transmission flow and contents of the RREQ packet between the source terminal and the relay terminal are the same as those shown in FIGS. However, in the third embodiment, information according to the format of the RREQ message defined in RFC3561 is described in the payload 402 in step 501 in FIG. 5 or step 601 in FIG. In step 601, the relay terminal not only copies the RREQ message part of the payload 402, but also updates the hop number field in a form that conforms to the AODV operation. Further, as described above, the source terminal stores the maximum value that can be described in the field of the number of layers 408 of the source terminal in step 502 of FIG.

Regarding the procedure for determining whether or not packet transfer is possible, the contents of the processing are all the same as in FIG. However, when establishing a route, it is necessary to select a stable communication route with good communication quality. Therefore, it is more efficient to transfer more RREQ packets around a good communication route. Therefore, in the third embodiment, the threshold value of the reception counter used in step 711 in FIG. 7 is added to the link cost obtained by quantifying the link quality between terminals or the path cost obtained by quantifying the route quality from the terminal to the management node. decide.

Specifically, a method of calculating the threshold value ai according to Equation 2 with i being the number of hops from the terminal that received the RREQ packet to the management node, Pcost being Pcost, and any integer value of 1 or more being n is conceivable.

According to Equation 2, the lower the path cost (in other words, the better the quality, the lower the Pcost), that is, the higher the value of the threshold value, the higher the value of the threshold value becomes. It is possible to transfer more RREQ packets. Here, the link cost and the path cost are calculated based on an RSSI (Received Signal Strength Indication) value of the received radio wave. The link cost has a value greater than 0 and less than 1. The path cost is calculated as the sum of the link costs from the terminal to the management node. However, the link cost or path cost is not limited to this calculation method, but may be calculated by another method.

Embodiments 1 to 3 are embodiments having only one reception counter and one threshold for each received packet. On the other hand, in the fourth embodiment, a reception counter A that counts the number of times the same packet is received from a terminal in the same layer as the own terminal, and a reception counter B that counts the number of times the same packet is received from a terminal in the upper layer. This is an embodiment having two counters.

First, a communication system configuration, a packet configuration, a transmission procedure of a flooding packet between a transmission source terminal and a relay terminal, and an outline of an operation when the terminal receives a flooding packet addressed to a management node will be described.

Example 4 Communication System (FIG. 1 or FIG. 11), Terminal and Management Node Hardware Configuration (FIGS. 2 and 3), Packet Configuration (FIG. 4), Transmission Procedure of Flooding Packets of Originating Terminal and Relay Terminal (FIG. 5 and FIG. 6) is the same as that of Example 1 thru | or Example 3. FIG.

Referring to FIG. 12, a procedure in which a terminal that receives a flooding packet determines whether or not to transfer the received packet is described. However, the difference from the flowchart of FIG. 7 described in the first embodiment is that processing (steps 1201 and 1202) after determining that the same packet is received from the terminal of the same layer in step 706 during the transfer waiting time, This is only processing after determining that the same packet is received from the upper layer terminal in step 708 (steps 1203 and 1204). In the fourth embodiment, two reception counters, a reception counter A that counts the number of times the same packet is received from a terminal in the same layer and a reception counter B that counts the number of times that the same packet is received from a terminal in an upper layer, are received packets. Hold every time. For this reason, in the fourth embodiment, a threshold value for determining whether to stop packet transfer is separately given to each reception counter. That is, the threshold value ai of the reception counter A and the threshold value bi of the reception counter B are set for the terminal having the number of layers i. If it is determined in step 706 that the packet received in step 703 is received from the terminal of the same layer under the reception counters A and B and the threshold values ai and bi, step 1201 is performed. The reception counter A is incremented by 1. Thereafter, it is determined in step 1202 whether the value of the reception counter A is equal to or greater than the threshold value ai. If the threshold value ai has been reached, the process proceeds to step 712A, and if it is less than the threshold value ai, the process proceeds to step 713.

Similarly, if it is determined in step 708 that the packet received in step 703 is received from a higher layer terminal, the reception counter B is incremented by 1 in step 1203. Here, in the fourth embodiment, a flag indicating that it has been received from an upper layer as in step 709 of FIG. 7 is not held. Thereafter, in step 1204, it is determined whether or not the value of the reception counter B is greater than or equal to the threshold value bi. If the threshold value bi has been reached, the process proceeds to step 712A, and if it is less than the threshold value ai, the process proceeds to step 713.

In this embodiment, the spread of flooding packets relayed on the topology changes by adjusting the magnitudes of the threshold values ai and bi. For this reason, desired directivity can be secured for packet transfer. The values of the threshold values ai and bi are determined based on the topology structure or the desired directivity. However, the setting method is not limited to a specific method.

Referring to FIG. 13, the transfer stop process in step 712A of FIG. 12 will be described in detail. In FIG. 13, only the step 1301 is different from the flowchart of FIG. In the process of FIG. 8, the flag indicating that it has been received from the upper layer terminal is determined in step 802, but in step 1301 of FIG. 13, it is determined whether the value of the reception counter B is 0, and the counter If the value is 0, the process proceeds to step 803; otherwise, the flowchart of FIG. 13 is terminated. If the value of the reception counter B is greater than 0, it is obvious that at least once the packet has been received from the upper layer terminal and the transfer has been canceled. The flowchart of FIG. 13 ends. This is the reason why the flag used in step 709 in FIG.

The configuration of the packet management table of the fourth embodiment will be described with reference to FIG. In FIG. 14, the packet management table 900A includes a packet ID 901, a reception counter A1401, a reception counter B1402, and a transferred flag 904. The packet ID 901 and the transferred flag 904 are fields similar to those used in the first to third embodiments. In the fourth embodiment, since each terminal holds two reception counters, fields of reception counter A 1401 and reception counter B 1402 are provided in the table. On the other hand, in the fourth embodiment, since the reception flag 903 from the upper layer terminal in FIG. 9 is not necessary, it is not necessary to provide the field in the packet management table 900A in FIG.

DESCRIPTION OF SYMBOLS 100 ... Communication system, 200 ... Terminal, 201 ... Microcomputer, 202 ... ROM, 203 ... Central control part, 204 ... Communication processing part, 205 ... Path management part, 206 ... Packet transfer control part, 207 ... RAM, 208 ... Clock generation Circuit 209 power supply circuit 210 transmission / reception circuit 300 management node 401 header header 402 403 destination address 404 destination address 405 source address 406 source address 407 source address 407 Packet ID, 408 ... Number of layers of transmission source terminal, 409 ... Application data, 900 ... Packet management table, 901 ... Packet ID, 902 ... Reception counter, 903 ... Reception flag from upper layer terminal, 904 ... Transfer completed flag, 1401... Reception counter A, 1402.

Claims

A reception counter is provided for each flooding packet received from another terminal device,
The reception counter updates the counter value every time the flooding packet is received from a terminal device in which the number of hops to the destination is the same as or smaller than the own terminal device,
A packet transfer control unit that determines whether or not to transfer the flooding packet based on the counter value and a threshold value set in the number of hops to the destination;
A terminal device further comprising: a communication processing unit that transmits the flooding packet based on the determination of the packet transfer control unit.
The terminal device according to claim 1,
The packet transfer control unit stops the transfer of the flooding packet when the counter value reaches the threshold value.
The terminal device according to claim 1,
A timer that starts upon initial reception of the flooding packet;
The packet transfer control unit determines transfer of the flooding packet before the counter value reaches the threshold and when the timer expires.
The terminal device according to claim 1,
The reception counter includes a first reception counter and a second reception counter,
The first reception counter updates a counter value every time the flooding packet is received from a terminal device having the same number of hops to the destination as the terminal device itself,
The second reception counter updates the counter value every time the flooding packet is received from a terminal device whose number of hops to the destination is smaller than the terminal device.
The terminal device according to claim 2,
The packet transfer control unit stops the forwarding of the flooding packet when the packet cannot be received after a certain period of time elapses from a terminal device having a smaller number of hops to the destination after stopping the forwarding of the flooding packet. A terminal device for canceling and performing transfer.
In a communication system comprising a plurality of terminal devices constituting a plurality of hierarchies and a management node that communicates with one of the terminal devices,
The terminal device includes a reception counter for each flooding packet received from another terminal device,
The reception counter updates the counter value every time the flooding packet is received from a terminal device in which the number of hops to the destination is the same as or smaller than the own terminal device,
The communication device determines whether or not the flooding packet can be transferred based on the counter value and a threshold value set for the number of hops to the destination, and based on the determination of the packet transfer control unit, The communication system further comprising: a communication processing unit that transmits the flooding packet.
A packet transfer control unit that determines a reception counter for each flooding packet received from another terminal device and whether or not the flooding packet can be forwarded based on a counter value and a threshold value set in the number of hops to the destination; and the packet forwarding A packet transfer method in a terminal device further comprising a communication processing unit for transmitting the flooding packet based on the determination of the control unit,
A step of updating the counter value of the reception counter when a flooding packet is received from a terminal device having the same or smaller number of hops to the destination as the terminal device;
Comparing the counter value with a threshold value set for the number of hops to the destination in a predetermined period;
Transferring the flooding packet when the counter value is less than the threshold and the predetermined period has expired.