CN101536435A - Method for establishing bidirectional data transmission paths in a wireless meshed communication network - Google Patents

Abstract

The invention relates to a method for establishing a bidirectional data transmission path in a wireless mesh packet-switched communication network, wherein a logical topology structure in the form of at least one routing tree is proactively established, wherein the root network node ( R) sending a routing query message (RAN) at periodic time intervals to the network nodes (M1-M7) of the communication network, the routing query message specifying a first unidirectional data transmission path leading to the root network node (R), In the network nodes (M1-M7) of the routing tree, first flags that can be placed in two different states are respectively established, and only when the first flag is placed in the selectable first state (ON), the network nodes ( M5) Send a routing response message (RWN) to the root network node (R) when receiving the routing query message (RAN), and the routing response message specifies the second unidirectional data transmission path leading to the network node, thus in A bidirectional data transmission path is established between the root network node (R) and the network node (M5).

Description

Method for implementing a bidirectional data transmission path in a wireless mesh communication network

technical field

The present invention is in the technical field of message technology, and relates to a method for realizing a bidirectional data transmission path in a wireless mesh communication network. The invention also relates to a suitable wireless mesh communication network for carrying out the method.

Background technique

For wireless WLAN communication networks (WLAN=Wireless Local Area Network), a number of different standards have been published by the Institute of Electrical and Electronics Engineers (IEEE) within the framework of the standard series IEEE802.11 since the beginning of the nineties. Certain characteristics of communication networks, such as transmission rates, frequency ranges, modulation methods, number of channels, encryption, etc., are constrainedly prescribed based on rapidly advancing technological developments.

In current standards, the smallest unit of a WLAN communication system is a wireless cell, in which an access point can exchange data with multiple terminal devices. Several radio cells are connected to one another via cable connections between the access points.

A recent development within the series of standards IEEE 802.11, known as IEEE 802.11s and expected to become an effective standard in 2009, is a publicized development that standardizes wireless communication between network nodes. In IEEE802.11s, network nodes, so-called mesh points (abbreviated as MP (Mesh Point)) are used as routers for wireless data transmission, thus forming a wireless mesh Ad-hoc wireless network (mesh point network).

Proactive, reactive or hybrid routing protocols can generally be implemented in communication networks.

In a communication network using a proactive routing protocol, a data transmission path is prepared between a source network node and a destination network node for the transmission of data, which enables a fast data exchange, but in particular resources are reserved so that Potentially unusable disadvantage for data exchange. In the reactive routing protocol, the data transmission path between the source network node and the target network node is established when necessary, which is more beneficial in terms of resources, but it brings delay time for establishing the data transmission path.

In order to take advantage of the advantages of the proactive routing protocol and the reactive routing protocol, for a wireless communication network based on the standard IEEE802. WirelessMesh Protocol, hybrid wireless mesh protocol) hybrid routing protocol. In HWMP, one or more logical topologies in the form of routing trees are established on the physical topological structure of the network. In order to establish and update the routing tree, a root MP sends routing query messages to other MPs according to the broadcast method at periodic time intervals. =Path Request, path request). The MPs receive the PREQ, enter the corresponding path data into their routing tables, and in this way establish a unidirectional data transmission path from the MP to the sender root MP. Keep as little as possible for the quantity of the route message that is used to set up the local route tree, can clear the so-called pre-response PREP sign that is used for route response message PREP (PREP=Path Reply, path response) in the pre-response formula PREQ , that is, the MP receives the proactive PREQ, establishes a forward path for transmitting data from the MP to the root MP, but does not send a routing response message (PREP) to the root MP, and thus does not establish a forward path from the root MP to the MP The reverse path used to transfer data.

Since the data flow between the root MP of the routing tree and the MP is usually bidirectional, in HWMP there exists an Possibility to send a Routing Response message (PREP) to the root MP, thereby establishing in this way a unidirectional reverse path from the root MP to the MP sending the PREP.

The unidirectional data transmission path (forward path) from the MP to the root MP is periodically updated through the PREQ sent periodically from the root MP, so that the unidirectional forward path of the routing tree can be combined with the changing conditions in the mesh network match. In particular newly added MPs to the mesh network can be integrated into the routing tree, or for example alter data transmission paths which are no longer functioning due to a failure of a data link.

However, since the reverse path from the root MP to the MP cannot be updated and remains as established by sending a PREP from the MP before sending the first data packet of the data traffic, it may occur that the connectivity does not change while the link When the metric (Link-Metriken) changes, the forward and reverse paths between the root MP and the MP are different, so that the data packets take the (updated) more favorable route on the forward path, while on the reverse path to take the (not updated) less favorable route. If the data link in the data transmission path between the root MP and the MP fails, an alternate forward path between the root MP and the MP is established through periodically sent PREQs, and conversely, it is no longer possible to pass the unupdated reverse forward path. Data transfer to path. In this case, a standard mechanism based on AODV (Ad Hoc On Demand Distance Vector, Ad Hoc On Demand Distance Vector) is accessed in HWMP, which brings about a relatively long time before starting to transmit data packets from the root MP to this MP. delay.

Contents of the invention

Therefore, the technical problem to be solved by the present invention is to provide a method for establishing a bidirectional data transmission path in a wireless mesh communication network, by which the above-mentioned disadvantages can be avoided.

This technical problem is solved according to the invention by a method for setting up bidirectional data transmission paths in a wireless mesh communication network with the features of claim 1 . Advantageous embodiments of the invention are given by the features of the subclaims.

According to the present invention, a method for establishing a bidirectional data transmission path in a wireless mesh packet switching (Ad-hoc) communication network is established proactively on the physical topology of the communication network with at least one tree Logical topology of the structure (routing tree). For this reason, the network node of the communication network used as the root network node of the routing tree generates a routing query message at periodic time intervals, abbreviated as RAN (Routing AnfrageNachricht), and sends it to the network node of the communication network to set the routing query message. A first unidirectional data transmission path towards a root network node. For this purpose, upon receipt of the RAN by a network node, an entry can be stored or updated for the target network node (root network node) in the routing table (transmission table) of the network node receiving the RAN in the network, This entry contains the path metric (Pfadmetrik) and the next hop (Hop) to the target network node (that is, the next network node on the path to the target network node that has obtained the RAN network nodes). Furthermore, it is also possible, for example, to store the number of hops in a routing table. The method for establishing the routing tree can be based, in particular, on a procedure implemented in the hybrid routing protocol HWMP. In particular, the routing request message (RAN) can be a proactive route request (PREQ) according to the hybrid routing protocol HWMP.

In the network nodes of the routing tree, a first flag is established which can be placed in two different states to control the sending of routing response messages. If the first sign of a network node of the routing tree is placed in an optional first state, then the network node generates a routing response message when receiving a routing query message (RAN) from the root network node, abbreviated as RWN (Routing AntwortNachricht ), and send the routing response message to the root network node through the network nodes included in the first unidirectional data transmission path. If the first flag of a network node of the routing tree is set to the second state, the network node does not generate the RWN when receiving the RAN from the root network node. Through the RWN, a second unidirectional data transmission path from the root network node to the network node generating the RWN is set. For this purpose, when a RWN is received by a network node, an entry can be stored or updated in the routing table (transmission table) for the network node originating the RWN, which entry contains the path metric and the The next hop (Hop) (that is, the next network node on the path leading to the network node that generates the RWN, the next network node is the network node that has obtained the RWN). Additionally, the number of hops can be stored in the routing table. In particular, the routing response message (RWN) may be a path response (PREP) according to the hybrid routing protocol HWMP. The root network node receives the routing response message (RWN), and establishes a second unidirectional data transmission path from the root network node to the network node generating the RWN, thereby establishing a bidirectional data transmission path between the root network node and the network node generating the RWN data transmission path.

Inside a communication network, data packets are transmitted from one network node to another network node in the same layer (OSI model). This is especially layer 2 or 3.

With the method according to the invention, a bidirectional data transmission path is advantageously established between the root network node and the network node of the routing tree only when data packets are actually transmitted on the data transmission path, so that the number of routing messages is relatively small. In addition, in addition to the forward path from the network node to the root network node, the reverse path from the root network node to the network node is also updated, so that the updated bidirectional data transmission path between the root network node and the network node Provided for the transmission of data packets, and can quickly respond to changes in data transmission paths that may be caused by changes in path metrics or failures in data links.

In the first state of the first flag, the first flag is, for example, "set", that is, is placed in the state "ON (open)" or "1", while in the second state the first flag is "cleared". ”, that is, be placed in the state “OFF (off)” or “0”. Likewise, the first flag may be placed in the state "OFF" in its first state and in the state "ON" in its second state.

In a preferred embodiment of the method of the present invention, if a network node of the routing tree is obtained as the first network node (source network node) of the communication network on the data transmission path leading to the root network node to be transmitted to the root network node ( target network node), then put the first flag of the network node in the first state. In this case, the network node receives the data packets from a layer (OSI model) which is higher than the layer in which the transmission of the data packets within the communication network takes place internally. As a result, a bidirectional data transmission path from the root network node to this network node can be set up as required with a particularly simple implementation.

In another preferred embodiment of the method according to the invention, the first identification of a network node is placed in the second state immediately after sending the routing response message (RWN) to the root network node, which has the advantage that this measure is specific to the routing protocol running. Furthermore no timer is required.

In a further preferred embodiment of the method according to the invention, the first flag of a network node is not set into the second state until after a selectable first time interval has elapsed, which will then follow to the target network node The root network node of the network node sends a data packet, which is the source network node of the data packet, (the data packet is the network node as the first network node on the data transmission path leading to the root network node in the communication network obtained), wherein the first time interval is reset to the initial value of the optional time interval each time a data packet in which the network node is the source network node and the root network node is the target network node is sent . This embodiment of the method according to the invention can be carried out particularly simply.

In another preferred embodiment of the method according to the invention, if the network node receives a data packet as a source network node (the data packet is received by the network node as the first network node of the communication network on the data transmission path leading to the root network node obtained for sending to the root network node), and the data packet is not obtained as the source network node within a certain second time interval immediately before receiving the data packet (that is to say, as the communication network is on the way to the root If the first network node on the data transmission path of the network node does not obtain the data packet to be sent to the root network node), the network node generates a routing response message (RWN) and sends it to the root network node. As a result, a bidirectional data transmission path can advantageously be established between the root network node and this network node at the start of each data communication.

Especially in the last-mentioned embodiment of the inventive method, if a second flag set in the network node, which can be placed in two different states, is placed in an optional second state, the network node can generate Routing Response Message (RWN) is sent to Root Network Node. This makes it possible to implement the method according to the invention particularly simply.

In the first state of the second flag, the second flag is for example "set", i.e. placed in the state "ON (open)" or "1", and in its second state it is "cleared", i.e. Set to state "OFF" or "0". Likewise, the second flag may be placed in the state "OFF" in its first state and in the state "ON" in its second state.

In a further embodiment of the method according to the invention, for the case where the data packet is the first data packet of a data communication, this can be recognized, for example, by placing the second flag in its second state, if the network node is in the data communication Sending a routing response message (RWN) to the root network node before the first data packet (D1), the first flag of the network node is placed in the first state. But this results in additional conditions having to be queried.

In a further embodiment of the method according to the invention, the routing response message (RWN) is sent to the root network node directly after receiving the routing request message (RAN). In an alternative embodiment of this embodiment, the routing response message (RWN) is sent to the root network node (R) after a certain time delay after receiving the routing inquiry message (RAN). The latter-mentioned alternative is preferred according to the invention, since it has the advantage that the number of routing messages can be reduced, since the probability of receiving further routing inquiry messages (RAN) with better path metrics after sending the RWN is reduced .

In another preferred embodiment of the method according to the invention, the lifetime parameter of the routing response message (RWN) encoding the lifetime of the second unidirectional data transmission path to the network node is set as contained in the received routing inquiry message (RAN A lifetime parameter encoding the lifetime of the first unidirectional data transmission path to the root network node (R) in ). In this way it can advantageously be achieved that the lifetimes of the forward path and the reverse path of the bidirectional data transmission path between the root network node and the network node are the same.

Furthermore, the present invention also relates to a method for establishing a bidirectional data transmission path in a wireless mesh packet-switched communication network as described above, which method can especially be combined with the above method. In this method, if the first flag is set to its selectable first state, when the first change of the first unidirectional data transmission path leading to the root network node is obtained, a designated path to the root network node is sent to the root network node. A routing response message (RWN) of the second unidirectional data transmission path of the network node, thereby establishing a bidirectional data transmission path between the root network node and the network node.

The invention also extends to a wireless mesh packet-switched (Ad-hoc) communication network as described above, which is constructed so as to implement the method as described above.

Furthermore, the invention also extends to a network node of a wireless mesh packet-switched (ad-hoc) communication network as described above, on which the above-mentioned machine-readable program code is implemented.

Furthermore, the invention also extends to a storage medium having stored thereon a program code which is machine-readable as described above.

Description of drawings

The invention will now be explained in detail with the aid of an exemplary embodiment, with reference to the accompanying drawings.

Fig. 1 shows the embodiment of the wireless mesh communication network of the present invention that has set up routing tree with schematic diagram;

Fig. 2 schematically shows the transmission of the data packet D1 as the source node and the transmission of the data packet D2 by the non-source network node in the communication network of Fig. 1;

FIG. 3 schematically shows an embodiment of the method according to the invention, which is implemented on a network node of the communication network of FIG. 1;

FIG. 4 shows a schematic diagram of a further exemplary embodiment of the method according to the invention, which is implemented on a network node of the communications network of FIG. 1 .

Detailed ways

An embodiment of a wireless mesh packet-switched ad-hoc communication network (mesh network) according to the invention is shown in FIG. 1 . The mesh network includes a plurality of network nodes (mesh points) R, M1, M2, ..., M7 (e.g. 8 here), which are connected via 14 wireless, physical point-to-point data links L1, L2 , . . . , L14 are connected to each other in a mesh. Thus, for example, the root network node R communicates with the third network node M3 via the first data link L1, with the second network node M2 via the third data link L3, and with the first network node M1 via the sixth data link L6. Wireless connections. Furthermore, for example, the second network node M2 is data-technically connected to the third network node M3 via an eighth data link L8. All other descriptions of data links and network nodes can be understood in a similar manner.

In the mesh network in Fig. 1, a proactive routing tree from the root network node R as the root node to all network nodes M1, M2, ..., M7 is established, wherein the data links belonging to the routing tree also That is, the first data link L1, the third data link L3, the sixth data link L6, the second data link L2, the fourth data link L4, the fifth data link L5 and the seventh data link L7, In FIG. 1, it is represented by a solid thick line, and the rest of the data links which do not belong to the routing tree are represented by broken thin lines.

The establishment of the routing tree is based on standard mechanisms using distance vector and link state protocols, as specified in the routing protocol HWMP of IEEE 802.11s. Therefore, the root network node R periodically sends routing query messages (RAN) to all network nodes M1, M2, ..., M7 of the communication network by means of broadcasting, and these routing query messages specify the data transmission path leading to the root network node And it is used to update the routing tables of the network nodes M1, M2, . . . , M7. A unidirectional data transmission path is thereby established in each case from the network nodes M1 , M2 , . . . , M7 to the root network node R for transmitting payload data packets. Thus, for example from the seventh network node M7 via the second data link L2 and the first data link L1, in the case of an intermediate connection of the third network node M3 to the root network node R proactively establishes a unidirectional data transmission path. Furthermore, a unidirectional data transmission is proactively established, for example from the fifth network node M5 via the fifth data link L5 and the third data link L3, in the case of an intermediate connection of the second network node M2 to the root network node R path. All other proactively established unidirectional data transmission paths from network nodes M1 , M2 , . . . , M7 to root network node R are interpreted in a corresponding manner.

In the network nodes M1, M2, .

In the network nodes M1, M2, .

If the RWN response flag is set in a network node M1, M2, ..., M7, and the network node obtains the RAN periodically sent from the root network node R, the network node sends a response message (RWN) to the root A network node R in order to establish a reverse path from the root network node R to this network node for the transmission of (useful) data packets. If the RWN response flag is set in a network node M1, M2, . has changed, the network node in this case also sends a response message RWN to the root network node R in order to establish a reverse path from the root network node R to the network node for the transmission of (useful) data packets. The RWN is a message of the (PREP) type given in the routing protocol HWMP of the standard IEEE 802.11s, but is sent in this standard only before the start of the data communication, ie before the first data packet is sent.

In order to set or clear the RWN response flag in a network node M1, M2, .., M7, it is important whether the network node M1, M2, .., M7 receives a data packet from a higher layer, which The layer is above the wireless mesh network layer arranged between network nodes for the purpose of transmitting data packets within a communication network, or whether a network node only receives data packets from another network node.

This is explained in detail below with reference to FIG. 2 . In FIG. 2 , data packets for which the network node is the source network node are denoted as data packets “D1” and those for which the network node is not the source network node are denoted as data packets “D2”. The data packet D1 comes from a higher layer (OSI model), such as the application layer, the Internet protocol layer or IEEE802.11D-Bridging, which are represented together by S2 in Figure 2, and the data packet D1 is as shown in Figure 2 by pointing downwards As indicated by the arrows , the data packets D1 are transmitted to the wireless mesh layer, which is used for data transmission within the mesh network and denoted by S1 in FIG. 2 , and then the data packets D1 are transmitted between network nodes. In contrast to this, the data packet D2 is transmitted from one network node to another within the wireless mesh layer S1. Thus, the same network node that is the source network node for data packet D1 is not the source network node for data packet D2. The destination network node forwards the data packet D2 into one of the higher layers S2, which is not shown in detail in FIG. 2 . Only the network nodes which received the data packet D1 from the higher layer S2 are source network nodes and these network nodes set and clear the RWN response flag. A network node that does not receive the data packet D1 from the higher layer S2 is not a source network node and thus does not set and clear the RWN response flag.

During the initialization of the wireless mesh communication network, all RWN response flags of the network nodes M1 , M2 , . . . , M7 are (preset) cleared (0). Likewise, during the initialization of the wireless mesh communication network, all RWN sent flags of the network nodes M1 , M2 , . . . , M7 are (preset) cleared (0).

The root network node R periodically injects RAN into the mesh network, so that each network node can enter the corresponding data transmission path leading to the root network node R into the routing table of the network node after receiving the RAN. If the network node receives the RAN, an entry is stored or updated for the target network node (root network node) in the routing table (push table) of the network node receiving the RAN, the entry containing the path metric and the The next hop of the network node, that is, the next network node on the path to the target network node. Additionally, the number of hops can be stored in the routing table. The method for building the routing tree is based on a procedure implemented in the hybrid routing protocol HWMP, wherein the routing request message (RAN) is a proactive route request (PREQ) according to the hybrid routing protocol HWMP. The method steps are carried out by all network nodes irrespective of whether these network nodes are source network nodes or not.

In the following it is assumed by way of example that the fifth network node M5 receives the data packet D1 from the higher layer S2 and thus serves as the source network node.

If the fifth network node M5 receives the query message RAN periodically sent from the root network node R, the fifth network node M5 will enter the data transmission path specified by the RAN into the routing table of the fifth network node M5, or re- The current entry is written, whereby the unidirectional data transmission path of the fifth network node M5 to the root network node R is periodically updated.

When inquiring about sending data packet D1 to root network node R, ie before sending the first data packet of the data communication, fifth network node M5 generates a routing response message RWN and sends it to root network node R. The root network node R receives the RWN, and enters the corresponding data transmission path leading to the fifth network node M5 into the routing table of the root network node R, thereby establishing a one-way data transmission from the root network node to the fifth network node M5 A transmission path (reverse path), whereby a bidirectional data transmission path is established between the root network node R and the fifth network node M5.

All data packets sent by the fifth network node M5 after the last data packet D1 within a defined time interval are referred to as "other" data packets. If the fifth network node M5 has not sent a data packet D1 within said time interval, then each data packet sent after the end of this time interval is referred to as the "first" data packet. The different "data communications" are distinguished by this predeterminable time interval.

The fifth network node M5 can determine from the state of its RWN sent flag whether the data packet D1 is the "first" data packet or another data packet of the same data communication. If the RWN is sent before the first data packet D1, or in response to the obtained RAN if the RWN response flag is set, the RWN sent flag is set, that is, set to "ON/1" . Clear the RWN Sent flag, ie set to "OFF/0", by getting the RAN each time the RWN Response flag is set to cause the RWN to send.

In addition, this can also ensure that the RWN sent flag will not be cleared by mistake when the second RAN of the current Root-Announcement (Root-Announcement) is obtained, based on which the second RAN will not send the RWN to the root network node, because the second RAN The path metric of is worse than the path metric of the first RAN. The RWN sent flag must not now be reset, otherwise another RWN would be sent before the next data packet D1.

Advantageously, the RWN Sent flag is only cleared when the RWN Response flag is cleared. As a result, no additional RWN is sent if the data packet D1 is to be sent between the RWN and the associated RWN.

If the RWN sent flag is cleared in the fifth network node M5, then the data packet D1 is regarded as the first data packet, on the contrary, if the RWN sent flag is set in the fifth network node M5, the data packet D1 Think of it as other data packets.

In the first flag setting variant of the method of the present invention, if a response message RWN is sent to the root network node R based on the first data packet D1, the RWN response flag of the fifth network node M5 is set.

In the second flag setting variant of the method according to the invention, which is more advantageous than the first flag setting variant, the fifth network node M5 is only activated when the data packet D1 is sent from the fifth network node M5 to the root network node R. The RWN response flag is set. The second flag setting and deformation scheme is more advantageous than the first flag setting and deformation scheme, because no other conditions need to be checked, thereby reducing the difficulty of implementation.

If the fifth network node M5 receives the route query message RAN periodically sent from the root network node R, the fifth network node M5 will enter the data transmission path specified by the RAN into the routing table of the fifth network node M5 or rewrite The current entry, thereby updating the data transmission path from the fifth network node M5 to the root network node R. If the RWN response flag is set, the fifth network node M5 also sends a response message RWN to the root network node R. The root network node R receives the RWN, and enters the data transmission path leading to the fifth network node M5 designated by the RWN into the routing table of the root network node R or rewrites the current entry, thereby establishing or updating the route from the root network node to the fifth network node M5. A unidirectional data transmission path (reverse path) of the fifth network node M5 and in this way a bidirectional data transmission path is established between the root network node and the fifth network node M5.

The root network node R periodically sends query messages RAN to the network nodes M1, M2, . . . , M7 by means of broadcasting. This means that each network node M1, M2, . transfer path. By means of an identification or a serial number, each network node M1, M2, .

If the fifth network node M5 receives the routing query message RAN from the root network node R and the RWN response flag is set, the fifth network node M5 can immediately send the routing response message RWN according to the first RWN sending variant of the method of the present invention to the root network node R. If the fifth network node M5 receives other route query messages RAN with the same sequence number or identification from the root network node R, the fifth network node M5 immediately Send the routing response message RWN to the root network node R. This means that routing response messages RWN are sent from the fifth network node M5 to the root network node R until no routing query messages with better path metrics are obtained.

If the fifth network node M5 receives the route query message RAN periodically sent from the root network node R, and the RWN response flag is set, then the fifth network node M5 according to the preferred second RWN sending variant of the method of the present invention, in An optional waiting time elapses after receiving the RAN before sending the routing response message RWN to the root network node R. The path metrics are analyzed for all routing query messages RAN (with the same sequence number or ID) received by the fifth network node M5 during this waiting time, wherein the fifth network node M5 sends the root network node for the RAN with the best path metric R sends a routing response message RWN. This reduces the probability that the fifth network node M5 will also receive other RANs (with the same sequence number or ID) with better path metrics after sending the routing response message RWN, thereby advantageously reducing the sent Routing responds to the number of RWN messages and reduces the amount of data traffic.

Likewise, when the data transmission path from the fifth network node M5 to the root network node R is changed for reasons other than receiving the RAN and the RWN response flag is set, a routing response can also be generated by the fifth network node M5 The message RWN is sent to the root network node R. This is the case, for example, when the fifth network node M5 receives a failure message encoding a failure of a data link in the data transmission path or learns from a hardware detector that a failure of an adjacent data link has occurred.

To clear the RWN response flag, various reset variants exist.

According to the first flag reset variant, the RWN response flag is reset to 0 immediately after the RWN is sent by the fifth network node M5 as a reaction to the receiving RAN. If the fifth network node M5 does not send a data packet D1 within the time interval for the periodic transmission of the RAN by the root network node R, it no longer responds to the received RAN with an RWN. For each data packet D1 sent during this time interval, the RWN response flag is set again.

According to the second flag reset variant scheme, a selectable time interval elapses after sending the RWN as a response to the receiving RAN, and before the first data packet D1 or before a change in the data transmission path, the fifth network node M5 sends The RWN response flag is reset to 0. In this case, the timer for measuring the change in time of the selectable time interval is reset to the start value every time the fifth network node M5 sends a data packet D1 to the root network node R. In this case, the start value of the timeout is greater than the time interval for the periodic transmission of the RAN by the root network node R, whereby the RAN has reached the fifth network node M5 when the RWN response flag is set.

The first logo reset modification scheme is oriented to the operation of the routing protocol, while the second logo reset modification scheme is designed according to the data traffic. The advantage of the first flag reset variant is that no additional timer is required. The advantage of the second logo reset variant is that it can be implemented very simply.

If the fifth network node M5 does not send a data packet D1 within the time interval for the periodic transmission of the RAN by the root network node R, it no longer responds to the received RAN with an RWN. For each data packet D1 sent during this time interval, the RWN response flag is set again.

The RWN parameter sent by the fifth network node M5 to the root network node R is set according to the rules of HWMP or RM-AODV/AODV based on HWMP. The lifetime in RWN is set to the lifetime contained in RAN or proactive PREQ.

Referring now to FIG. 3 , therein is schematically explained an embodiment of the method according to the invention in the communication network of FIG. 1 , wherein a first flag reset variant is implemented for resetting (clearing) the RWN response flag.

In the diagram of FIG. 3, line segment "FL" represents the state of the RWN response flag, which can be cleared (0) or set (1). The line segment M5 represents the fifth network node M5 as source network node. The arrow pointing to the line segment M5 represents the data packets received by the fifth network node M5. Arrows from line segment M5 represent data packets sent by fifth network node M5. In FIG. 3 , the line segments FL and M5 respectively distribute from top to bottom, thus showing the time course. Various situations during the method for establishing a bidirectional data transmission path between the fifth network node M5 and the root network node R are indicated by letters A-L.

The RWN sent flag of the fifth network node M5 is not shown in FIG. 3 . The RWN response flag and the RWN sent flag of the fifth network node M5 are set to clear in advance.

In situation "A", the fifth network node M5 receives a routing query message RAN from the root network node R, and enters the data transmission path specified in the routing query message into the routing table of the fifth network node M5, or updates the routing table of the fifth network node M5. Corresponding entries in the routing table of the fifth network node M5 in order thereby to establish a unidirectional data transmission path from the fifth network node M5 to the root network node R, update the RAN and send the modified RAN to the the next network node. The RWN response flag of the fifth network node M5 remains clear. The RWN sent flag of the fifth network node M5 remains cleared.

In situation "B", the fifth network node M5 receives a data packet D2 from another network node, such as the second network node M2, and passes this data packet D2 on to the other network node. The RWN response flag of the fifth network node M5 remains clear. The RWN sent flag of the fifth network node M5 remains cleared.

In situation "C", the fifth network node M5 in turn receives a data packet D2 from another network node, such as the second network node M2, and forwards this data packet D2 to the other network node. The RWN response flag of the fifth network node M5 remains clear. The RWN sent flag of the fifth network node M5 remains cleared.

In situation "D", the fifth network node M5 receives from the root network node R another (regenerated) query message RAN with a different sequence number than the previous RAN, updating the corresponding entry, so as to thereby establish an updated unidirectional data transmission path from the fifth network node M5 to the root network node R, update the RAN, and send the modified RAN to the next network node with a small time delay. The RWN response flag of the fifth network node M5 remains clear. The RWN sent flag of the fifth network node M5 remains cleared.

In situation "E", the fifth network node M5 receives the data packet D1 from a higher layer (S2), that is, from a layer above the wireless mesh layer of the mesh network in which the network nodes exchange data packets , the data packet D1 should be transmitted to the root network node R by the fifth network node M5. This is not shown in detail in FIG. 3 .

Before sending the data packet D1 to the root network node R, ie before sending the first data packet D1, the fifth network node M5 generates a response message RWN and sends it to the root network node R. The root network node R receives the RWN and enters the corresponding data transmission path leading to the fifth network node M5 into the routing table of the root network node R to thereby establish a one-way data transmission from the root network node to the fifth network node M5 transmission path (reverse path), and in this way a bidirectional data transmission path is established between the fifth network node M5 and the root network node R. At the same time, the fifth network node M5 sets its RWN sent flag. Next, the fifth network node M5 sends the data packet D1 to the root network node R. At the same time, the fifth network node M5 sets its RWN response flag.

In situation "F", the fifth network node M5 receives a further data packet D1 , which is not shown in detail in FIG. 3 , and sends this data packet D1 to the root network node R. The RWN response flag of the fifth network node M5 remains set. The RWN sent flag of the fifth network node M5 remains set.

In situation "G", the fifth network node M5 receives a further data packet D1 , which is not shown in detail in FIG. 3 , and sends this data packet D1 to the root network node R. The RWN response flag of the fifth network node M5 remains set. The RWN sent flag of the fifth network node M5 remains set.

In situation "H", the fifth network node M5 receives a further data packet D1 , which is not shown in detail in FIG. 3 , and sends this data packet D1 to the root network node R. The RWN response flag of the fifth network node M5 remains set. The RWN sent flag of the fifth network node M5 remains set.

Next, the fifth network node M5 receives another (regenerated) routing query message RAN from the root network node R in state "H" with a different sequence number than the previous RAN, updating the routing table of the fifth network node M5 in order to thereby establish an updated unidirectional data transmission path from the fifth network node M5 to the root network node R, update the RAN, and send the modified RAN to the next network node with a small time delay . Furthermore, the fifth network node M5 clears its RWN sent flag or allows it to be set since its RWN response flag is set.

Since the fifth network node M5 has received the query message RAN periodically sent from the root network node R, and since the RWN response flag is set, the fifth network node M5 generates a response message RWN and sends the response message, for example, in a small The time delay of is sent to the root network node R. The fifth network node M5 sets its RWN sent flag. The root network node R receives this RWN and rewrites the corresponding data transmission path to the fifth network node M5 in the routing table of the root network node R, in order thereby to update the single route from the root network node R to the fifth network node M5. To the data transfer path (reverse path).

By the time delay after receiving the RAN and until sending the RWN to the root network node R, it is reduced that the fifth network node M5 also receives other paths with better path metrics (and with the same sequence) after sending the routing response message RWN number) of the RAN, thereby reducing the number of RWNs sent to the root network node R in this way.

According to the first flag reset variant scheme for the RWN response flag, the RWN response flag is cleared with the sending of the response message RWN.

In situation "I", the fifth network node M5 receives another data packet D1 intended for the root network node R, which is not shown in detail in FIG. 3 , and sends this data packet D1 to the root network node R. The RWN response flag of the fifth network node M5 is set. The RWN sent flag of the fifth network node M5 remains set.

In situation "J", the fifth network node M5 receives a further data packet D1, which is not shown in detail in FIG. 3, and sends this data packet D1 to the root network node R. The RWN response flag of the fifth network node M5 remains set. The RWN sent flag of the fifth network node M5 remains set.

In situation "K", the fifth network node M5 receives from the root network node R another (regenerated) route inquiry message RAN with a sequence number changed relative to the previous RAN, updating the route of the fifth network node M5 corresponding entry in the table, so as to thereby establish an updated unidirectional data transmission path from the fifth network node M5 to the root network node R, update this RAN, and send the modified RAN to the next network node. Furthermore, the fifth network node M5 clears its RWN sent flag or allows it to be set since its RWN response flag is set. Since the fifth network node M5 receives the routing query message RAN periodically sent from the root network node R, and since the RWN response flag is set, the fifth network node M5 generates a routing response message RWN and sends the RWN, for example, in a small The time delay of is sent to the root network node R. The root network node R receives this RWN and rewrites the corresponding data transmission path to the fifth network node M5 in the routing table of the root network node R, in order thereby to update the single route from the root network node R to the fifth network node M5. To the data transfer path (reverse path). In addition, according to the first flag reset variant solution for the RWN response flag, the RWN response flag is cleared as the response message RWN is sent. The RWN sent flag is set as the RWN is sent.

In situation "L", the fifth network node M5 receives from the root network node R another (regenerated) routing query message RAN with a different sequence number than the previous RAN, updating the routing table of the fifth network node M5 with Corresponding entries in order to thereby establish an updated unidirectional data transmission path from the fifth network node M5 to the root network node R, update the RAN, and send the modified RAN to the next network node with a small time delay. Although the fifth network node M5 receives the query message RAN periodically sent from the root network node R, since the RWN response flag is cleared, the fifth network node M5 does not generate a response message RWN, and does not send a corresponding RWN. The RWN sent flag is cleared with RAN reception.

Referring now to FIG. 4 , therein is schematically explained another embodiment of the method according to the invention in the communication network of FIG. 1 , wherein a second flag reset variant is implemented for resetting the RWN response flag.

In the diagram of FIG. 4 , similar to FIG. 3 , the line segment "FL" represents the state of the RWN response flag, and the line segment M5 represents the fifth network node M5. In addition, the time course of the timer TI counting down, which is used to reset the RWN response flag of the fifth network node M5, is shown, and the timer TI counts from the starting value t to the preset time interval t. End time 0. The initial value of the timeout is greater than the time interval for periodically sending the RAN via the root network node R, so that the RAN can reach the fifth network node M5 when the RWN response flag is set. Various situations during the method for establishing a bidirectional data transmission path between the fifth network node M5 and the root network node R are indicated by letters A-L.

The RWN sent flag of the fifth network node M5 is not shown in FIG. 4 . In the second flag reset variant scheme for resetting the RWN response flag, the RWN response flag can also be used instead of the RWN sent flag to determine whether the data packet D1 is the first data packet (the RWN response flag is cleared) or other data packet (RWN response flag is set). The RWN response flag of the fifth network node M5 is set to clear in advance. The RWN sent flag of the fifth network node M5 is set to clear in advance.

In situation "A", the fifth network node M5 receives a query message RAN from the root network node R, enters the data transmission path specified in the query message into the routing table of the fifth network node M5, or updates the fifth network corresponding entry in the routing table of node M5 in order thereby to establish a unidirectional data transmission path from the fifth network node M5 to the root network node R, to update the RAN and to send the modified RAN to the next network node. The RWN response flag of the fifth network node M5 remains clear. The RWN sent flag of the fifth network node M5 remains cleared.

In situation "B", the fifth network node M5 receives a data packet D2 from another network node, such as the second network node M2, and passes this data packet D2 on to the other network node. The RWN response flag of the fifth network node M5 remains clear. The RWN sent flag of the fifth network node M5 remains cleared.

In situation "C", the fifth network node M5 in turn receives a data packet D2 from another network node, such as the second network node M2, and forwards this data packet D2 to the other network node. The RWN response flag of the fifth network node M5 remains clear. The RWN sent flag of the fifth network node M5 remains cleared.

In situation "D", the fifth network node M5 receives from the root network node R another (regenerated) query message RAN with a different sequence number than the previous RAN, updating the corresponding entry in order to thereby establish an updated unidirectional data transmission path from the fifth network node M5 to the root network node R, update the RAN, and send the modified RAN to the next network node, for example with a small time delay. The RWN response flag of the fifth network node M5 remains clear. The RWN sent flag of the fifth network node M5 remains cleared.

In situation "E", the fifth network node M5 receives the data packet D1 from a higher layer (S2), that is, from a layer above the wireless mesh layer of the mesh network in which the network nodes exchange data packets , the data packet D1 should be transmitted to the root network node R by the fifth network node M5. This is not shown in detail in FIG. 4 .

Before sending the data packet D1 to the root network node R, ie before sending the first data packet D1, the fifth network node M5 generates a response message RWN and sends it to the root network node R. The root network node R receives the RWN and enters the corresponding data transmission path leading to the fifth network node M5 into the routing table of the root network node R to thereby establish a one-way data transmission from the root network node to the fifth network node M5 transmission path (reverse path), and in this way a bidirectional data transmission path is established between the fifth network node M5 and the root network node R. At the same time, the fifth network node M5 sets its RWN sent flag. Next, the fifth network node M5 sends the data packet D1 to the root network node R, sets its RWN response flag and starts a timer TI with an initial value t.

In situation "F", the fifth network node M5 receives a further data packet D1 , which is not shown in detail in FIG. 4 , and sends this data packet D1 to the root network node R. The RWN response flag of the fifth network node M5 remains set. The RWN sent flag of the fifth network node M5 remains set. The timer TI is reset to the start value t and started again.

In situation "G", the fifth network node M5 receives a further data packet D1 , which is not shown in detail in FIG. 4 , and sends this data packet D1 to the root network node R. The RWN response flag of the fifth network node M5 remains set. The RWN sent flag of the fifth network node M5 remains set. The timer TI is reset to the start value t and started again.

In situation "H", the fifth network node M5 receives a further data packet D1 , which is not shown in detail in FIG. 4 , and sends this data packet D1 to the root network node R. The RWN response flag of the fifth network node M5 remains set. The RWN sent flag of the fifth network node M5 remains set. The timer TI is reset to the start value t and started again.

Next, the fifth network node M5 receives another (regenerated) routing query message RAN from the root network node R with a different sequence number than the previous RAN, updates the corresponding entry in the routing table of the fifth network node M5 so that the This establishes an updated unidirectional data transmission path from the fifth network node M5 to the root network node R, updates the RAN, and sends the modified RAN to the next network node with a small time delay. The fifth network node M5 clears its RWN sent flag or allows it to be set since its RWN response flag is set.

Since the fifth network node M5 has received the query message RAN periodically sent from the root network node R, and since the RWN response flag is set, the fifth network node M5 generates a routing response message RWN and sends the response message, for example, in A small time delay is sent to the root network node R. The fifth network node M5 sets its RWN sent flag. The root network node R receives this RWN and rewrites the corresponding data transmission path to the fifth network node M5 in its routing table, in order thereby to update the unidirectional data transmission path from the root network node R to the fifth network node M5 (reverse path). According to the second flag reset variant solution for the RWN response flag, the RWN response flag remains set.

In situation "I", the fifth network node M5 receives a further data packet D1 , which is not shown in detail in FIG. 4 , and sends this data packet D1 to the root network node R. The RWN response flag of the fifth network node M5 remains set. The RWN sent flag of the fifth network node M5 remains set. The timer TI is reset to the start value t and started again.

In situation "J", the fifth network node M5 receives a further data packet D1, which is not shown in detail in FIG. 4, and sends this data packet D1 to the root network node R. The RWN response flag of the fifth network node M5 remains set. The RWN sent flag of the fifth network node M5 remains set. The timer TI is reset to the start value t and started again.

In situation "K", the fifth network node M5 receives from the root network node R another (regenerated) routing query message RAN with a different sequence number than the previous RAN, updating the routing table of the fifth network node M5 with Corresponding entry in order thereby to establish an updated unidirectional data transmission path from the fifth network node M5 to the root network node R, update the RAN and send the modified RAN to the next network node with e.g. a small time delay . Furthermore, the fifth network node M5 clears its RWN sent flag or allows it to be set since its RWN response flag is set. Since the fifth network node M5 receives the routing query message RAN periodically sent from the root network node R, and because the RWN response flag is set to "1", the fifth network node M5 generates a routing response message RWN and sends the RWN For example, it is sent to the root network node R with a small time delay. The root network node R receives this RWN and rewrites the corresponding data transmission path to the fifth network node M5 in its routing table, in order thereby to update the unidirectional data transmission path from the root network node R to the fifth network node M5 (reverse path). According to the second flag reset variant solution for the RWN response flag, the RWN response flag remains set. The RWN sent flag is set.

In state "L", the time interval of the timer TI has run out and the RWN response flag of the fifth network node M5 is cleared. The fifth network node M5 then receives another (regenerated) routing query message RAN from the root network node R with a different sequence number than the preceding RAN, updating the corresponding entry in the routing table of the fifth network node M5 so that thereby An updated unidirectional data transmission path is established from the fifth network node M5 to the root network node R, the RAN is updated, and the modified RAN is sent to the next network node eg with a small time delay. Although the fifth network node M5 receives the routing query message RAN periodically sent from the root network node R, since the RWN response flag is cleared, the fifth network node M5 does not generate a response message RWN, and does not send a corresponding message to the root network node R. RWN. The RWN sent flag is cleared.

The advantages of the inventive method (example 1) over the conventional method are shown below by means of a calculation example. In the conventional method, a routing response message is sent to the root network node only once before the first data packet D1 (comparative example 1) , and an advantage over another possible method in which a routing response message is always sent to the root network node after obtaining a routing inquiry message (RAN) (compare example 2).

The following abbreviations are used:

N = number of network nodes

H = path length between network node and root network node

dH = the average path length from all network nodes to the root network node; dH≥1

t_g=t_gesamt: the time period under investigation

t_d=t_daten: the time when the network node sends data to the root network node as the source network node

RAI = Duration of Routing Inquiry Message (RAN) Interval

ara = number of routing query messages (RAN) initiated by the root network node during the time period considered ara = ((t_g/RAI) + 1)

Example 1

For example 1, ie proactive RAN with reactive (on-demand) RWN, the number of RANs is given as: ara*N.

The number of RWNs: ((t_d/RAI+1)*H.

The total number of routing messages: ara*N+((t_d/RAI)+1)*H.

Comparative example 1

Number of RANs: ara*N.

Number of RWNs: H (before the first data packet D1).

Total number of routing messages: ara*N+H.

Comparative example 2

Number of RANs: ara*N.

Number of RWNs: ara*N*dH.

The total number of routing messages: ara*N*(1+dH).

Typical values are for example:

N=30

H=4

dH=3

t_g=900s

t_d=300s

RAI=5s

The following costs arise here (total number of routing messages sent):

(ara=181)

Example 1: 5674 routed messages

Comparison example 1: 5431 routing messages

Comparison example 2: 21720 routing messages

As this calculation example shows, the number of routing messages can be significantly reduced by example 1 (the method of the invention), here by 73.9%.

Other features of the invention are given by the following description:

The general idea of the present invention to improve the non-logging mode includes:

- the network node always responds to the RAN with a RWN only if the network node sends a data packet D1 to the root network node and the network node is the source network node of the data packet D1;

- RWN Response Flag, which determines whether a RWN should be sent as a response to the RAN. OFF/0 means that RWN is not sent, ON/1 means that RWN is sent to the root network node as a response when RAN is obtained;

- Different mechanisms for setting and clearing the above flags.

The principle rules are as follows: when the following conditions are met, the RWN is sent by the network node to the root network node:

[RWN Response Flag=ON/1] and [[the network node has obtained RAN] or [the path to the root network node has changed]].

The mechanism of the inventive method is only executed by the network node which is the source network node of the data packet D1 and which data packet D1 is sent to the root network node R. This means that the data packets come from higher layers to the network nodes and these network nodes are the first nodes of the mesh connection. The intermediate nodes that receive the data packets D2 and pass them on to other network nodes according to their routing table do not need to pay attention to the mechanisms described in the method according to the invention for these data packets D2. In particular, due to these data packets D2, no RWN is sent to the root network node, nor is the RWN response flag set. By means of the method of the invention, when data is exchanged between the network node and the root network node, the forward path and the reverse path for transmitting data packets between the network node and the root network node pass through the same network node. The forward path and the reverse path go through the best path. Data link failures (link gaps) can be overcome by the method of the invention both for the forward path and for the reverse path. Failure of the data link on the reverse path from the root network node to the network node no longer needs to be overcome with complex AODV route restoration mechanisms.

The RWN Response Flag provides an easy way to determine whether a RWN should be sent in response to the RAN. Different methods for resetting the RWN response flag provide flexible implementation, e.g. with a safe time after the last data packet during which the RWN is still sent and thus still maintained from the root network node to the network The node's reverse path. By responding to the RAN with the RWN, it is also possible to update the change of the data transmission path in the intermediate node for the opposite direction. With the additional improvement that the RWN is also sent to the root network node with the RWN response flag set when the data transmission path from the network node to the root network node changes for reasons other than obtaining the RAN, then the Changes to the path can be propagated to the reverse path, which updates the reverse path accordingly. Using the lifetime from the RAN or the lifetime from the proactive PREQ as the lifetime in the sent RWN may result in the availability of the same length for the forward and reverse paths.

Claims (18)

1. method of in wireless netted packet-switched communication networks network, setting up bidirectional data transmission paths, this communication network has a plurality of network nodes, and a network node is as the root network node, wherein in this communication network in these network nodes:

-answer formula ground to set up logical topology structure earlier with at least one routing tree form, wherein the root network node (R) of this routing tree sends to routing inquiry message (RAN) with the periodic time interval network node (M1-M7) of communication network, wherein this routing inquiry message is specified the first one-way data transmission path that leads to root network node (R)

-in the network node (M1-M7) of routing tree, set up the transmission that first sign that can be placed in two different conditions is controlled route response message (RWN) respectively,

If-the first sign is placed in selectable first state (ON), then network node (M5) sends to root network node (R) with route response message (RWN) when receiving routing inquiry message (RAN), wherein this route response message is specified the second one-way data transmission path that leads to this network node, between root network node (R) and this network node (M5), set up two-way data transfer path thus

If-the first sign is placed in second state, then network node does not send route response message.

2. method according to claim 1, if wherein a network node (M5) as communication network on the data transfer path that leads to root network node (R) first network node and obtain to send to the packet (D1) of root network node (R), then first sign with this network node (M5) places first state (ON).

3. method according to claim 1 and 2 wherein is right after first sign of a network node (M5) having sent route response message (RWN) to root network node (R) and places second state (OFF) afterwards.

4. according to each described method in the claim 1 to 3, wherein first sign with a network node (M5) just places second state (OFF) after selectable very first time interval elapses, this very first time at interval will be along with sending packet (D1) to the root network node and starting, this packet (D1) is that this network node (M5) obtains as first network node of communication network on the data transfer path that leads to the root network node, and the wherein said very first time all is reset to this initial value at interval of selectable very first time at interval when each this packet of transmission (D1).

5. according to each described method in the claim 1 to 4, if wherein network node (M5) obtains to be used to send to the packet (D1) of root network node as first network node of communication network on the data transfer path that leads to the root network node, and first network node on the data transfer path that is leading to root network node (R) in second time interval that is right after before receiving this packet as communication network does not obtain packet (D1) and will send to the root network node, and then this network node (M5) sends to root network node (R) with route response message (RWN).

6. method according to claim 5, if wherein be arranged on the transmission that is used to control route response message in the network node (M5), and can place second sign of two kinds of different conditions (ON/OFF) to be placed in selectable first state (O), then this network node (M5) sends route response message (RWN) to root network node (R).

7. method according to claim 6 wherein indicates that with second of network node (M1-M7) setting in advance is second state (OFF) when beginning the communication network initialization.

8. according to each described method in the claim 1 to 7, if wherein a network node (M5) sends route response message (RWN) to root network node (R) before in first packet (D1) that sends data communication to root network node (R), then first sign with this network node (M5) places first state (ON).

9. according to each described method in the claim 1 to 8, wherein directly receiving routing inquiry message (RAN) afterwards to root network node (R) transmission route response message (RWN).

10. according to each described method in the claim 1 to 8, wherein after receiving routing inquiry message (RAN), postpone to send route response message (RWN) to root network node (R) through the regular hour.

11., wherein when beginning, first of network node (M1-M7) is indicated that setting in advance is second state (OFF) to the communication network initialization according to each described method in the claim 1 to 10.

12. according to each described method in the claim 1 to 11, wherein to the life parameter of the route response message (RWN) of the life-span coding of the second one-way data transmission path of leading to network node be set to be included in the routing inquiry message (RAN) of reception, to the life parameter of the life-span coding of the first one-way data transmission path that leads to root network node (R).

13. according to each described method in the claim 1 to 12, this method is based on mixing Routing Protocol HWMP.

14. one kind especially according to each described method of setting up bidirectional data transmission paths in wireless mesh packet-switched communication networks network in the claim 1 to 13, this communication network has a plurality of network nodes, one of them network node is as the root network node, wherein in this communication network:

-answer formula ground to set up logical topology structure earlier with at least one routing tree form, wherein the root network node of this routing tree sends to routing inquiry message (RAN) with the periodic time interval network node (M1-M7) of communication network, wherein this routing inquiry message is specified the first one-way data transmission path that leads to root network node (R)

-in the network node (M1-M7) of routing tree, set up the transmission that first sign that can be placed in two different conditions is controlled route response message (RWN) respectively,

If-the first sign is placed in selectable first state (ON), then network node (M5) sends to root network node (R) with route response message (RWN) when detecting the first one-way data transmission path variation of leading to root network node (R), wherein this route response message is specified the second one-way data transmission path that leads to this network node, between root network node (R) and this network node (M5), set up two-way data transfer path thus

If-the first sign is placed in second state, then network node does not send route response message.

15. a wireless mesh packet-switched communication networks network is provided for carrying out the network node (M1-M7) according to each described method in the claim 1 to 14 in this communication network.

16. be used for computer-readable program code according to the network node (M1-M7) of the described communication network of claim 15, this computer-readable program code comprises control command, and this control command impels this network node to carry out according to each described method in the claim 1 to 14.

17. the network node according to the described communication network of claim 15 (M1-M7) is implemented computer-readable program code according to claim 16 on this network node.

18. a storage medium has the computer-readable program code according to claim 16 that is stored on this storage medium.

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