JP2023046647A - MESH NETWORK SYSTEM AND COMMUNICATION CONTROL METHOD - Google Patents

Abstract

To perform control so that a loop is not formed between a wireless network and a wired network in a wired/wireless mesh network having mobile nodes and fixed nodes.SOLUTION: A wired/wireless mesh network system of this example includes a mobile node 401 and a plurality of fixed nodes 411, 412, 413, and 414, as wireless nodes forming a wireless network. Two or more fixed nodes 411, 413, and 414 among the plurality of fixed nodes are also connected to a wired network. The fixed nodes 411, 413, and 414 connected to both wireless network and wired network are configured to discard a received packet when the packet whose transmission source is a wireless network side is received from the wired network side, or the packet whose transmission source is the wired network side is received from the wireless network side.SELECTED DRAWING: Figure 5

Description

The present invention relates to a wired/wireless mesh network system in which both wireless and wired mesh networks are configured.

The progress of robot technology in recent years is truly remarkable, and robots are often used to solve various social problems. Many of such robots are unmanned mobile objects such as unmanned aerial vehicles and autonomous vehicles. An unmanned mobile body needs to be equipped with a communication system in order to transmit control instruction data for remote control and autonomous control, and video data captured by a camera or the like mounted on the unmanned mobile body. At this time, if the unmanned mobile object is not a machine that moves along a predetermined route along rails or the like, wireless communication suitable for movement is often used.

For example, in Patent Document 1, a mobile base station and a terminal station are equipped with a long-distance communication function for preparing short-distance communication and a short-distance communication function for data transmission. , an invention for scheduling the timing of short-range communication is disclosed. In addition, in Patent Document 2, in a relay system using an unmanned flying object, based on the communication quality of the relay, the scheduled relay time, and the state of the power supply of the unmanned flying object (amount of power that can be supplied), the relay of the unmanned flying object An invention for locating is disclosed.

WO2017/018021 JP 2019-169848 A

One type of communication network that can be used to communicate with unmanned vehicles is a mesh network. A mesh network is composed of a plurality of nodes, and by connecting adjacent communicable nodes, a net-like network is formed as a whole. In particular, when the connection between nodes is performed wirelessly, it is called a wireless mesh network, and data is wirelessly transferred across a plurality of nodes in a bucket brigade manner.

A mesh network usually has multiple routes, and even if communication is lost on one route, it can switch to an alternative route. However, the presence of multiple routes also means that there are looped routes in the network. When IP packets are broadcast in such a network, a spanning tree protocol is generally applied in order to avoid repeated broadcasts even after the IP packets have gone around a looped path, causing a broadcast storm.

The spanning tree protocol uses a spanning tree algorithm to automatically block communications between specific nodes, thereby preventing loops. Also, when a failure occurs, it is possible to continue communication through an alternative route by canceling the blocking state.

However, in such a mesh network, routes are not determined by centralized control by specific high-priority nodes, but all nodes determine routes in an equal relationship, which is more efficient than a centralized control method. decreases. In particular, in cases where high throughput and low latency are required, there is a risk that a highly fault-tolerant mesh network cannot be adopted.

As a use case that requires high throughput and low delay in addition to fault tolerance, a wireless communication system that performs video transmission related to remote control of an unmanned aerial vehicle (UAV) can be considered. FIG. 1 shows a configuration example of conventional example 1 regarding such a radio communication system. This system transfers images of the UAV's surroundings from the UAV to a server so that the operator can check the images in real time.

In the wireless mesh network of Conventional Example 1 shown in FIG. 1, a first fixed node 111, a second fixed node 112, a third fixed node 113, and an n-th fixed node are arranged along the flight path of the mobile node 101 including the UAV itself. 114 are placed on the ground. A server 121 is also connected to the first fixed node 111 by wire. In the following explanation, regardless of whether the node is a mobile node or a fixed node, the case where wireless communication is performed between two nodes is 1 hop, and the case where wireless communication is performed between three consecutive nodes is 2 hops. The number of hops is defined as a value obtained by subtracting 1 from the number of nodes with which communication is performed, such as hops.

When the mobile node 101 is flying over the first fixed node 111, one-hop communication is performed between the mobile node 101 and the first fixed node 111, and data is transferred to the server 121 by the shortest route. be done. Next, when mobile node 101 moves above second fixed node 112 and becomes unable to communicate directly with first fixed node 111, mobile node 101 travels from mobile node 101 to first fixed node 111 via second fixed node 112, and 2 Hop communication takes place. Similarly, when the mobile node 101 moves over the third fixed node 113, the communication becomes 3 hops, and when it moves over the nth fixed node 114, the communication becomes n hops. As the number of hops increases, throughput decreases and delay time increases.

FIG. 2 shows a configuration example of a wired and wireless mesh network (hereinafter referred to as a "wired/wireless mesh network") as a conventional example 2. As shown in FIG. In the system of FIG. 2, similarly to the system of FIG. 214 are located on the ground, and a server 221 is wired to all fixed nodes.

Therefore, at first glance, it seems that one-hop communication with the server 221 can be realized regardless of which fixed node the mobile node 201 is wirelessly connected to. However, since a loop is formed between the wired network and the wireless network, only one fixed node and the server 221 are allowed to communicate over the wired line, and all the remaining fixed nodes are permitted to communicate. Wired lines are blocked.

In other words, only the connection between the first fixed node 211 and the server 221 is not blocked. Therefore, when the mobile node 201 moves from above the first fixed node 211 to above the second fixed node 212 and becomes unable to directly communicate with the first fixed node 211, the mobile node 201 moves through the second fixed node 212. 2-hop communication is performed to the first fixed node 211, and the server 221 is connected.

In addition, since loop detection is generally performed by broadcasting a loop detection packet, it may take a long time to detect a loop if the scale of the network is large or the communication load is heavy. Furthermore, since the loop detection function itself increases the network load, a network should be constructed that does not form loops as much as possible.

FIG. 3 shows another configuration example of a wired/wireless mesh network as conventional example 3. In FIG. In the system of FIG. 3, similarly to the system of FIG. 314 are located on the ground, and a server 321 is wired to all fixed nodes. However, wireless communication between fixed nodes is prohibited.

Specifically, for the first fixed node 311, the MAC address of the second fixed node 312, the MAC address of the third fixed node 313, and the MAC address of the nth fixed node 314 are specified, and MAC address filtering is performed to Prohibit connection with fixed nodes. This allows first fixed node 311 to wirelessly connect only to mobile node 301 . Similar settings are made for other fixed nodes.

The system of FIG. 3 also differs from the conventional example 2 in that the maximum value of the number of hops is set to one. This can be achieved by setting TTL (Time To Live) in the IP header of the packet to be sent to 1. When a packet is transferred from a wireless node to a wireless node, 1 is subtracted from the TTL and immediately becomes 0. If the packet has not reached the destination node at this point, the packet is discarded. become a wireless network. In other words, since the route indicated by the dashed line in FIG. No blocking.

Thus, when the wireless network side exceeds a predetermined number of hops, the packet is forcibly discarded to prevent the formation of a loop, thereby preventing blocking on the wired network side. Furthermore, by setting a route so that the wired network can always be reached within a predetermined number of hops from the wireless network, communication can always be performed using the shortest route regardless of which fixed node the mobile node 301 is connected to. do. This makes it possible to build a network with high throughput and low delay.

However, such a mesh network has a problem that it is difficult to expand the communication area to a place far from the wired network as the allowable number of hops becomes smaller due to restrictions on the number of hops on the wireless network side. Moreover, as the allowable number of hops increases, there is a problem that it becomes more difficult to arrange fixed nodes while considering the number of hops so as not to form a loop. Also, for example, when the mobile node 301 can communicate only with the second fixed node 312, if a failure occurs between the second fixed node 312 and the server 321, the mobile node 301 accesses the server 321. There was also an aspect that the high fault tolerance inherent in the mesh network was sacrificed, such as being unable to do so.

The present invention has been made in view of the conventional circumstances as described above. intended to

In order to achieve the above object, a mesh network system that is one aspect of the present invention is configured as follows. That is, a mesh network system according to the present invention is a mesh network system having a mobile node and a plurality of fixed nodes as wireless nodes forming a wireless network, wherein two or more of the plurality of fixed nodes are It is also connected to a wired network, and a fixed node connected to both a wireless network and a wired network receives a packet whose source is the wireless network side from the wired network side, or receives a packet whose source is the wired network side When a packet is received from the wireless network side, the received packet is discarded.

Here, in the mesh network system according to the present invention, a fixed node connected to both a wireless network and a wired network performs address resolution with a network device connected to the wired network, and transfers the address resolution result. It can be configured to notify the node.

Further, in the mesh network system according to the present invention, the mobile node is configured to designate the fixed node with the lowest communication cost as the final node in the wireless network when receiving address resolution results from a plurality of fixed nodes. obtain.

A communication control method, which is another aspect of the present invention, is configured as follows. That is, in a communication control method in a mesh network system having a mobile node and a plurality of fixed nodes as wireless nodes forming a wireless network, two or more of the plurality of fixed nodes are also connected to a wired network. A fixed node connected to both a wireless network and a wired network receives a packet whose source is the wireless network side from the wired network side, or receives a packet whose source is the wired network side and sends it to the wireless network side. characterized in that the received packet is discarded when it is received from

According to the present invention, it is possible to control a wired/wireless mesh network having mobile nodes and fixed nodes so that a loop is not formed between the wireless network and the wired network.

1 is a diagram showing a configuration example of a wireless mesh network according to Conventional Example 1; FIG. FIG. 10 is a diagram showing a configuration example of a wired/wireless mesh network according to Conventional Example 2; FIG. 11 is a diagram showing a configuration example of a wired/wireless mesh network according to Conventional Example 3; 1 is a diagram showing a configuration example of a wired/wireless mesh network according to an embodiment of the present invention; FIG. FIG. 5 is a diagram showing an example route in the wired/wireless mesh network of FIG. 4;

One embodiment of the present invention will be described below with reference to the drawings.
FIG. 4 shows a configuration example of a wired/wireless mesh network according to an embodiment of the present invention. The wired/wireless mesh network of this example comprises a mobile node 401, a first fixed node 411, a second fixed node 412, a third fixed node 413, an nth fixed node 414, and a server 421. . The server 421 is connected by wires to a plurality of fixed nodes other than the second fixed node 412, that is, the first fixed node 411, the third fixed node 413, and the nth fixed node 414. FIG. In this example, a UAV is assumed as the mobile node 401, but any mobile radio device such as a radio device mounted on a train or automobile, or a radio device that can be carried by a person can be applied.

Here, the routes between mobile node 401 and all fixed nodes 411-414 are determined by spanning tree protocol. Also, the first fixed node 411, the third fixed node 413, and the n-th fixed node 414 connected to the wired network have a MAC address filtering function so as not to form a loop between the wireless network and the wired network. there is

Specifically, when a packet having a source address belonging to the wireless network is received from the wired network side, the packet is discarded. Similarly, when a packet having a source address belonging to the wired network is received from the wireless network side, the packet is discarded. This makes it possible to avoid broadcast storms without blocking the route on the wired network side. A fixed node connected to a wired network has a different MAC address on the wired side and on the wireless side, that is, a source address.

Also, the first fixed node 411, the third fixed node 413, and the n-th fixed node 414 connected to the wired network directly communicate with the server 421 on a regular basis. It also has a function of monitoring the state of address resolution and reporting the result to the mobile node 401 by sending it.

Next, the operation of the wired/wireless mesh network of this example will be described using FIG. FIG. 5 has the same basic configuration as FIG. 4, and shows that fixed nodes that can be wirelessly connected to the mobile node are limited depending on the position of the mobile node. In addition, in FIG. 5, the metric values between nodes are represented by numerical values in parentheses. For example, the metric value between the first fixed node 411 and the second fixed node 412 is 4 as indicated by (4) in the figure.

A mesh network is generally controlled to calculate the communication cost for each route and select the route with the lowest communication cost. For example, in IEEE 802.11s, which is a standard for wireless LAN mesh networks, the following metric value Ca is calculated as the communication cost.
Ca=[0+Bt/r]/(1-ef)
Here, 0 is the channel access overhead, Bt is 8192 (test frame bit size), r is the data rate (Mbit/sec), and ef is the frame error rate. A smaller metric value indicates better radio quality of the route.

This metric value can be regarded as airtime, that is, the time required to wirelessly transmit a predetermined amount of data. Also, in a route with multiple hops, the sum of the metric values between each node can be regarded as the metric value of the entire route. For example, when the mobile node 401 communicates with the first fixed node 411, there are a 1-hop route and a 2-hop route via the second fixed node 412, and the metric values of the 1-hop route are 7, 2 The metric value of the route of hops is 5+4=9. In this case, a one-hop route with a small metric value is selected. In addition, in FIG. 5, the metric value is assumed to be a single digit value for the sake of simplicity of explanation.

Furthermore, FIG. 5 clearly shows that the route starting from the mobile node 401 in the wired/wireless mesh network is constructed by the spanning tree protocol, and some routes are blocked. Specifically, the first fixed node 411 and the second fixed node 412 are blocked so that the mobile node 401 does not form a loop when communicating with other fixed nodes in the wired/wireless mesh network. A path of type topology has been determined.

Here, as shown in FIG. 5, the mobile node 401 flies between the first fixed node 411 and the second fixed node 412, and the mobile node 401 flies between the first fixed node 411 and the second fixed node 412. It is assumed that direct communication (one hop) is possible only for Also, the first fixed node 411 and the second fixed node 412 are blocked by the spanning tree protocol, and the second fixed node 412, the third fixed node 413 and the nth fixed node 414 are connected by one path. shall be

In this state, when a broadcast packet is transmitted from mobile node 401 , the broadcast packet reaches first fixed node 411 and second fixed node 412 . The broadcast packet that reaches the first fixed node 411 reaches the server 421, the third fixed node 413, and the nth fixed node 414 via the wired network. However, in the third fixed node 413 and the n-th fixed node 414, packets received from the wired network side and having the source address of the mobile node 401 are discarded by MAC address filtering, thereby preventing the broadcast storm.

On the other hand, a broadcast packet arriving from mobile node 401 to second fixed node 412 reaches third fixed node 413 . The broadcast packet reaching the third fixed node 413 reaches the server 421, the first fixed node 411, and the nth fixed node 414 via the wired network. However, in the first fixed node 411 and the n-th fixed node 414, packets received from the wired network side and having the source address of the mobile node 401 are discarded by MAC address filtering, thereby preventing the broadcast storm.

Also, the broadcast packet reaching the third fixed node 413 passes through the n-th fixed node 414 and then reaches the server 421, the first fixed node 411, and the third fixed node 413 via the wired network. However, in the first fixed node 411 and the third fixed node 413, packets received from the wired network side and having the source address of the mobile node 401 are discarded by MAC address filtering, thereby preventing the broadcast storm.

When a broadcast packet is transmitted from the server 421, it works similarly. For example, assume that a broadcast packet that has reached the third fixed node 413 from the server 421 reaches the nth fixed node 414 on the route on the wireless network side. In this case, the n-th fixed node 414 discards the packets with the source address of the server 421 received from the wireless network side by MAC address filtering, thereby preventing the broadcast storm.

Thus, the wired/wireless mesh network system of this example is configured to perform separate MAC address filtering on the wireless network side and the wired network side. As a result, even if a wireless network and a wired network are connected by a plurality of nodes to form a loop, no blocking occurs between the plurality of fixed nodes and the server 421. / A wireless mesh network can be constructed.

By the way, when the mobile node 401 communicates with the server 421 for the first time and broadcasts an ARP request packet from the mobile node 401 to the server 421, the ARP request packet reaches the server 421 through a plurality of communicable routes. Then, server 421 unicasts an ARP response packet to mobile node 401 to resolve the address, and communication between mobile node 401 and server 421 becomes possible. However, since the address resolution information is overwritten by the last received ARP response packet among the plurality of ARP response packets, the shortest path is not necessarily selected. Further, when communication between the mobile node 401 and the server 421 becomes impossible, an ARP request packet is retransmitted, resulting in a processing delay associated with address resolution.

Therefore, it is desirable to perform address resolution by a method that does not broadcast an ARP request packet from mobile node 401 in order to suppress processing delay while selecting the best route. Therefore, in the wired/wireless mesh network of this example, address resolution between the mobile node 401 and the server 421 is performed by the method described below.

First, the first fixed node 411, the third fixed node 413, and the n-th fixed node 414 connected to the wired network periodically send pings to the server 421. FIG. If the address is not resolved, these fixed nodes broadcast an ARP request packet from the wired network side, that is, with the MAC address of the wired side set as the source address.

Here, when the first fixed node 411 broadcasts an ARP request packet to the wired network, the ARP request packet reaches the server 421 , the third fixed node 413 and the nth fixed node 414 . Server 421 then returns an ARP response packet to first fixed node 411 for address resolution. On the other hand, for example, assume that an ARP request packet that has reached the third fixed node 413 reaches the nth fixed node 414 via the wireless network. In this case, the n-th fixed node 414 discards packets received from the wireless network whose source address belongs to the wired network through MAC address filtering, thereby preventing broadcast storms.

Thus, even when a fixed node connected to a wired network broadcasts, MAC address filtering prevents the formation of a loop. Therefore, it is possible to maintain a non-blocking state between the fixed nodes 411 to 414 and the server 421 . Further, except for the case where communication with the server 421 becomes impossible due to a failure in the wired network, arrival confirmation is performed only by periodic ping without accompanying broadcasting of the ARP request packet thereafter.

If there is no particular failure in the wired network, the server 421 returns ping responses to the first fixed node 411, the third fixed node 413, and the nth fixed node 414, respectively. The first fixed node 411, the third fixed node 413, and the n-th fixed node 414 that have received the ping response transmit a control packet to which the MAC address of the server 421 is added to the mobile node 401 so that they themselves can communicate with the server 421. notify you that there is Conversely, if a failure or the like occurs in the wired network and a ping response cannot be obtained from the server 421, no control packet is transmitted to the mobile node 401. FIG.

Mobile node 401, which has received the control packet, obtains the MAC address of server 421 added to the control packet to perform address resolution, and determines a fixed node capable of communicating with server 421 from the transmission source address of the control packet. recognize.

On the other hand, the mobile node 401 grasps the metric value when communicating with each node during route search within the wired/wireless mesh network. For example, when calculated in association with the metric values for each route shown in FIG. The metric value is 5+3=8, and the metric value with the n-th fixed node 414 is 5+3+6=14. In other words, it can be determined that the first fixed node 411 is the fixed node with the best wireless quality among the fixed nodes connected to the server 421 by wire.

Therefore, when communicating with the server 421, the mobile node 401 can select the best route by making the first fixed node 411 the last node in the wired/wireless mesh network. Also, if the route becomes unusable, it is possible to instantly switch to the best route by selecting the third fixed node 413 with the second lowest metric value as the final node in the wired/wireless mesh network. is.

Here, in this example, the second fixed node 412 is the only fixed node that is not connected to the wired network, but generality is lost as long as a plurality of fixed nodes are connected to the wired network. can't break Also, in this example, ping is transmitted from the fixed node to the server, but it is not particularly limited to ping. Alternatively, the server may individually confirm whether or not communication with a plurality of fixed nodes connected to the wired network is possible. Also, in this example, a loop is avoided by a MAC address filtering function provided in a fixed node connected to a wired network, but a network switch having a loop avoidance function may be added.

As described above, the wired/wireless mesh network system of this example has a mobile node 401 and a plurality of fixed nodes 411, 412, 413, and 414 as wireless nodes forming a wireless network. Two or more of the fixed nodes 411, 413, 414 are also connected to the wired network, and the fixed nodes 411, 413, 414 connected to both the wireless network and the wired network transmit packets whose source is the wireless network side. is received from the wired network side, or when the transmission source receives a packet from the wired network side from the wireless network side, the received packet is discarded. In this way, by performing address filtering separately on the wireless network side and the wired network side, it is possible to control so that a loop is not formed between the wireless network and the wired network.

In the wired/wireless mesh network system of this example, the fixed nodes 411, 413, and 414 connected to both the wireless network and the wired network perform address resolution with the server 421 connected to the wired network. , to notify the mobile node 401 of the address resolution result. Therefore, without broadcasting an ARP request packet from the mobile node 401, the address can be resolved, and communication between the mobile node 401 and the server 421 can be established. In this example, the server 421 is used as an example of the network device according to the present invention, but the address resolution method according to the present invention can be applied to address resolution with any other network device connected to a wired network. It is possible.

Also, in the wired/wireless mesh network system of this example, when the mobile node 401 receives address resolution results from a plurality of fixed nodes 411, 413, and 414, the fixed node with the lowest communication cost is selected as the final node in the wireless network. configured to point to a node. Therefore, mobile node 401 can select the best route when communicating with server 421 .

As described above, both wireless and wired mesh networks are configured, the wireless network side constructs routes using a normal spanning tree protocol, and the wired network side performs different address filtering on the wireless and wired sides to prevent loops. Build a high-throughput, low-delay, fast-switching, fault-tolerant network by determining the final node of a wireless mesh network according to the best path while preventing formation (i.e., not causing blocking) It is possible to

Although the embodiments of the present invention have been described above, these embodiments are merely examples and do not limit the technical scope of the present invention. The present invention can take various other embodiments, and various modifications such as omission and replacement can be made without departing from the gist of the present invention. These embodiments and their modifications are included in the scope and gist of the invention described in this specification and the like, and are included in the scope of the invention described in the claims and equivalents thereof.

In addition, the present invention can be provided not only as devices such as those mentioned in the above description and systems configured with these devices, but also as methods executed by these devices and functions of these devices by a processor. It is also possible to provide a program for implementation, a storage medium storing such a program in a computer-readable manner, and the like.

INDUSTRIAL APPLICABILITY The present invention can be used in a wired/wireless mesh network system in which mesh networks are configured both wirelessly and wiredly.

101, 201, 301, 401: mobile node, 111, 211, 311, 411: first fixed node, 112, 212, 312, 412: second fixed node, 113, 213, 313, 413: third fixed node, 114, 214, 314, 414: nth fixed node, 121, 221, 321, 421: server

Claims (4)

In a mesh network system having a mobile node and a plurality of fixed nodes as wireless nodes forming a wireless network,
two or more fixed nodes of the plurality of fixed nodes are also connected to a wired network;
A fixed node connected to both the wireless network and the wired network receives a packet whose transmission source is the wireless network side from the wired network side, or receives a packet whose transmission source is the wired network side from the wireless network side. A mesh network system characterized by discarding a received packet when a packet is received. The mesh network system of claim 1, wherein
A fixed node connected to both the wireless network and the wired network performs address resolution with a network device connected to the wired network, and notifies the mobile node of the address resolution result. mesh network system. In the mesh network system of claim 2,
A mesh network system, wherein said mobile node designates a fixed node with the lowest communication cost as a final node in said wireless network when receiving address resolution results from a plurality of fixed nodes. In a communication control method in a mesh network system having a mobile node and a plurality of fixed nodes as wireless nodes forming a wireless network,
two or more fixed nodes of the plurality of fixed nodes are also connected to a wired network;
A fixed node connected to both the wireless network and the wired network receives a packet whose transmission source is the wireless network side from the wired network side, or receives a packet whose transmission source is the wired network side from the wireless network side. A communication control method, characterized in that the received packet is discarded when the

Images