WO2009146736A1

WO2009146736A1 - Method for transmitting data between network elements defining an anycast group within a mesh network

Info

Publication number: WO2009146736A1
Application number: PCT/EP2008/056826
Authority: WO
Inventors: Xue Jun Cai; Ling Chen
Original assignee: Nokia Siemens Networks Oy
Priority date: 2008-06-03
Filing date: 2008-06-03
Publication date: 2009-12-10

Abstract

It is described a method for transmitting data between network elements (A, B, C, D, E, F) defining an anycast group within a mesh network, in particular within a wireless mesh LAN. The method comprises transmitting data from a transmitting element (A) of the anycast group to an intermediate element (E) of the anycast group, sending an acknowledgement message from the intermediate element (E) to the transmitting element (A) indicating a receipt of the data, transmitting a confirmation message from the transmitting element (A) to the intermediate element (E) indicating that the intermediate element (E) is responsible for forwarding the data to a receiving element (D) of the anycast group, and forwarding the data from the intermediate element (E) to the receiving element (D). It is further described a transmitting element (A), an intermediate element (E) and a mesh network comprising at least the transmitting element (A) and the intermediate element (E), which are adapted for performing the above mentioned method.

Description

DESCRIPTION

Title

Method for transmitting data between network elements defining an anycast group within a mesh network

Field of invention

The present invention relates to the field of transmitting and forwarding data between network elements in a mesh network, in particular in a wireless mesh network. In particular, the present invention relates to a method for transmitting data between network elements defining an anycast group within a mesh network. Further, the present invention relates to a transmitting element, an intermediate element and a mesh network comprising at least the transmitting element and the intermediate element, which are adapted for performing the above mentioned method.

Art Background

A typical mesh or ad-hoc network consists of a number of network elements, so-called mesh nodes (MNs), which may be wireless routers. These MNs act as repeaters to relay packets from source MNs to target MNs via wireless links between them. Therefore a fundamental feature of the mesh network is the so-called multi-hop wireless transmission.

Unfortunately, unlike highly reliable wired media such as cable and optical fabric, wireless links shared by MNs are very sensitive to environment parameters, e.g., interference, channel fading, and surrounding buildings . Many ad-hoc routing protocols are deployed in MNs to address such fluctuations and to make maximum usage of wireless resources by using an opportunistic routing scheme. The essential idea of all opportunistic routing schemes is that, for each destination, a set of possible next-hops are selected in advance and one of them is chosen for forwarding on a per-packet basis according to its reachability at that instant.

Further, an Extremely Opportunistic Routing (ExOR) scheme may be used. When a MN relays a data packet, it chooses a candidate subset of all its neighboring MNs which could bring the packet closer to the destination. The sender MN lists a candidate receiver set in the header of the data packet header, prioritized by distance. After transmission, each node that receives the packet looks for its address in the candidate list in the header. Each recipient then waits for an amount of time determined by its position in the list before transmitting an acknowledgment message. Each node looks at the set of acknowledgment messages it receives to decide, whether it should forward the packet. The forwarding node rewrites the data packet header with a new set of candidates and transmits the packet. This process is repeated until the ultimate destination receives the packet.

The acknowledgement message period of ExOR is longer than that of the standard acknowledgement message defined in the standard IEEE 802.11. The ExOR routing therefore introduces a heavy latency even when the number of candidates is modest. This problem gets worse as the number of candidates increases. Another disadvantage of ExOR is that even if the transmitter receives the acknowledgement message from the recipient with the highest priority, it still has to wait until the whole acknowledgment period ends. Furthermore, the candidate list embedded in ExOR data frames brings extra computational cost .

The above two disadvantages prevent ExOR to support large number of neighbors e.g. in high density networks where nodes are located in close proximity to each other. Further, ExOR introduces a Node-ID to suppress the packet duplication, which is problematic when hidden nodes exist. Each node can receive data frames from the sender, but cannot receive ACK frames from other nodes. As a result, each node forwards packets based on their local policy. Therefore, packets are duplicated.

There may be a need for providing a reliable and computational inexpensive method for transmitting data between network elements defining an anycast group within a mesh network, which reduces the data traffic within the mesh network .

Summary of the Invention

This need may be met by the subject matter according to the independent claims. Advantageous embodiments of the present invention are described by the dependent claims.

l#According to a first aspect of the invention there is provided a method for transmitting data between network elements defining an anycast group within a mesh network, in particular within a wireless mesh LAN. The provided method comprises (a) transmitting data from a transmitting element of the anycast group to an intermediate element of the anycast group, (b) sending an acknowledgement message from the intermediate element to the transmitting element indicating a receipt of the data, (c) transmitting a confirmation message from the transmitting element to the intermediate element indicating that the intermediate element is responsible for forwarding the data to a receiving element of the anycast group, and (d) forwarding the data from the intermediate element to the receiving element.

This aspect of the invention is based on the idea that the packet duplication may be avoided by a further confirmation message. With this message, the intermediate element is chosen and informed about being responsible for further forwarding the data. Other elements which may have received the data from the transmitting element do not receive a confirmation message and are therefore not responsible for forwarding the data.

In the following there will be described exemplary embodiments of the present invention.

2#According to an embodiment of the invention forwarding the data may comprises (a) transmitting the data from the intermediate element to the receiving element, (b) sending a further acknowledgement message from the receiving element to the intermediate element indicating a receipt of the data by the receiving element, and (c) transmitting a further confirmation message from the intermediate element to the receiving element indicating that the receiving element is responsible for further forwarding the data to a further receiving element of the anycast group.

With this embodiment, a multi-hop method is provided. This may be continued until the network element representing the final destination of the anycast group within a mesh network receives the data. Due to the confirmation message, the data will only be forwarded from one intermediate element to the next network element. This may provide the advantage that the above mentioned packet duplication problem of the prior art, which problem typically get more and more relevant when the number of hops being involved in a data transmission from the transmitting element to the receiving element increases, gets solved in a highly effective and efficient manner.

3#According to a further embodiment of the invention the method further comprises sending the data from the transmitting element to at least one further intermediate element. This may provide the advantage that a large number of neighboring nodes may be supported without a significant performance deterioration. Thereby, due to the providing of redundant data transmission paths the reliability of data transmissions within the mesh network can be significantly increased while completely avoiding the above mentioned packet duplication problem.

4#According to a further embodiment of the invention, a priority value is assigned to the intermediate element and the further intermediate element, wherein the respective priority value is indicative for the respective intermediate element to forward the data to the receiving element.

An Expected Transmission Count (ETX) metric may be used for example to prioritize the group members. A forwarding set may be specified in priority order based on the cost of transmission to the destination. Ordering increases the performance by decreasing the number of transmissions procedures. Thereby, network elements may be prioritized, which are located close to a destination network element respectively to the receiving element. In other words, due to a high prioritization certain network elements may be used as intermediate network elements, which are more likely to participate in an overall data transmission, wherein the data reach the destination network element with a fewer number of individual transmissions.

The network elements of the anycast group may calculate the ETX metric by broadcasting test data packets of a fixed size. ETX test data packets are preferably broadcasted, so they are not acknowledged or retransmitted. Every network element remembers the test data packets it has been received during an elapsed time period. This time period may be for instance some seconds. Therefore, on the basis of the number of test data packet being received by a network element within the elapsed time period, the ETX being indicative for the network element's priority is calculated.

Each network element then may maintain a table with the ETX to all the other network elements in the meshed network based on its knowledge of the network topology including the links, i.e. connections, between the network elements.

The source network element, i.e. the transmitting element, then specifies the anycast group in priority order based on the ETX. The network element having the least ETX value will be assigned the highest priority. After the anycast group is formed, the ID of the anycast group, its members and their priorities may be sent in a routing table to all network elements by a regular unicast procedure to ensure all related network elements get the right information.

5#According to a further embodiment of the invention, the priority values of the intermediate Element and the further intermediate element are modified periodically according to their forwarding periodicity within a specified time interval .

In wireless networks, the delivery probability of each node changes dynamically because of environments, interference and other factors. The priority of each candidate therefore should reflect such dynamic conditions. Therefore, in the present embodiment, an adaptive prioritization for the anycast group may be additionally used.

6#According to a further embodiment of the invention modifying the priority values comprises (a) promoting the priority value of the intermediate element, which is forwarding more packets, and/or (b) demoting the priority values of those intermediate elements, which are forwarding fewer packets. With this embodiment, network elements which for example provide a better connection to the transmitting element with fewer failures may be favored. In this way, a more reliable and faster transmission may be provided.

7#According to a further embodiment of the invention, only the priority values of a predetermined number of intermediate elements having the highest priority value in the any cast group are modified.

This may be in particular useful in order to reduce the effort for keeping the priority values of the network elements of the anycast group up to date in case the topology of the mesh network changes. This can be caused for instance by a failure of a particular network element and/or a deterioration of one or more radio transmission links within the mesh network. For example, in the anycast group, the three network elements having the highest priorities are B, C, D and Pb, Pc, Pd denote their priorities in the group, respectively. If in a specified duration TD, the number ri of the received acknowledgement messages (ACK) of one network element is greater than the sum of another two network elements, e.g. rb > re + rd, then Pb increases by 1 except when network element B is already the network element having the highest priority and pc and pd decrease. Otherwise, if none of the priority values of the network elements is greater than the priority values of the other two network elements, the priorities of the network elements of the anycast group remain unchanged. The adaptive process may occur at a fixed interval TD. If the priorities are changed, the modified priorities may be sent to related network elements by a normal unicast data transmission procedure.

8#According to a further embodiment of the invention, the priority value is indicative for a waiting time between the receipt of the data and a reaction to the receipt. In other words, the intermediate elements having a higher priority than the other intermediate elements may react without any interference by a communication between the transmitting element and the other intermediate elements. The transmission may therefore be faster and more reliable performed.

9#According to a further embodiment of the invention, the intermediate element and the further intermediate elements determine during the waiting time the state of a radio channel link of the mesh network and discard the data if the radio channel link is at least partially occupied by other network elements until the end of the respective waiting time .

With this embodiment, the packet duplication is avoided as the intermediate network elements having lower priorities may discard the received packets. By determining the state of the radio channel link, the network elements may recognize if any communication between the transmitting node and any of the intermediate nodes has already been started and may assume that the data will therefore be forwarded by one of the other intermediate nodes .

10#According to a further embodiment of the invention, the method further comprises waiting for a predefined period of time after receipt of the acknowledgement message before transmitting the confirmation message by the transmitting element. With this embodiment, the risk of collisions may be decreased as there is always a short waiting time between transmissions .

ll#According to a further embodiment of the invention, the data is included in a data packet comprising a header with a Group ID field for a Group ID representing an ID of the anycast group .

The intermediate elements receiving the data may directly determine, if the data is relevant or not for them. Accordingly, irrelevant data may be handled as such, i.e. an intermediate element of another anycast group will for example not react to this data and thereby avoid unnecessary network traffic. Further, the data packet may comply with specifications being given by the standard 802.11 or other standards. In particular, it may be possible that fields being already defined in several standards, especially the standard 802.11, are used for the forwarding method described here . 12#According to a further embodiment of the invention the intermediate element discards a received data packet comprising a Group ID representing another anycast group as the anycast group the intermediate element is a member of.

Therefore, only the members of the relevant anycast group are involved in carrying out the described method. This may provide the advantage that needless communication within the mesh network may be effectively avoided.

13#According to a further embodiment of the invention, the confirmation message comprises a Group ID field value for the Group ID representing an ID of the anycast group. This may provide the advantage that the intermediate element receiving this message may ascertain that it is the correct receiver of this message and the Group ID may be used for further forwarding. Furthermore, the confirmation message may be extended from the standard acknowledgement (ACK) frame as used in the standard 802.11 or from an acknowledgement frame used in other standards.

14#According to a further embodiment of the invention, the confirmation message comprises an address field for an address of the intermediate element. Also this embodiment may provide the advantage that the intermediate element receiving this element may ascertain that it is the correct receiver of this message.

With these embodiments defining various frame structure suitable to be used for data packet for performing the described forwarding method, it may not be necessary to add any new fields into the standard data and ACK frame as the data frame and the confirmation message are extended from the usually used frames. Therefore, the method has a good efficiency.

15#According to a second aspect of the invention there is provided a transmitting element comprising a unit for transmitting a data packet to an intermediate element, a unit for receiving an acknowledgement message from the intermediate element indicating a receipt of the data packet and a unit for transmitting a confirmation message to the intermediate element indicating that the intermediate element is responsible for forwarding the data packet to a receiving element .

16#According to a further aspect of the invention there is provided an intermediate element comprising a unit for receiving a data packet from a transmitting element, a unit for sending an acknowledgement message to the transmitting element indicating a receipt of the data packet, a unit for receiving a confirmation message from the transmitting element indicating that the intermediate element is responsible for forwarding the data packet to a receiving element, and a unit for forwarding the data to the receiving element .

17#According to a further aspect of the invention there is provided a mesh network, in particular a wireless mesh LAN. The mesh network comprises a transmitting element as mentioned above and an intermediate element as mentioned above .

It has to be noted that the forwarding method and the relating apparatuses may be applied in a network according to standard 802.11, according to any other standard or in any other kind of network.

It has to be noted that embodiments of the invention have been described with reference to different subject matters. In particular, some embodiments have been described with reference to method type claims whereas other embodiments have been described with reference to apparatus type claims. However, a person skilled in the art will gather from the above and the following description that, unless other notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters, in particular between features of the apparatus type claims and features of the method type claims is considered as to be disclosed with this application.

The aspects defined above and further aspects of the present invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment. The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited.

Brief Description of the Drawings

Figure 1 shows an anycast group within a mesh network.

Figure 2 shows a data frame being used in an embodiment of the invention.

Figure 3 shows a frame being used for a confirmation message

Figure 4 shows a timing diagram illustrating a first embodiment of the described method.

Figure 5 shows a timing diagram illustrating a second embodiment of the described method.

Figure 6 shows a timing diagram illustrating a third embodiment of the described method.

Detailed Description

The illustration in the drawing is schematically. It is noted that in different figures, similar or identical elements are provided with reference signs, which are different from the corresponding reference signs only within the first digit.

Figure 1 shows an anycast group 100 within a mesh network. The anycast group comprises network elements A, B, C, D, E and F. In this case, network element A serves as transmitting or source element, network element D serves as destination element or node. The network elements B, C, E and F serve as intermediate or receiving elements.

Before any data transmission within a mesh network from the source node A to the destination node D may be performed, the anycast group 100 is formed. The anycast group 100 comprises all candidate nodes B, C, E and F for forwarding data between the source node A and the destination node D.

A priority value is assigned to each candidate B, C, E and F in the anycast group 100. The priority value is indicative for the candidate B, C, E and F to act as the node, which is selected for forwarding received data. Based on a plurality of priority values an order within the candidate nodes B, C, E and F can be established.

The anycast group 100 is formed by all nodes, which may be involved in data transmissions via all possible routes being defined by one or more next hops, which routes extend between the source node A and the destination node D. For small networks, the anycast group may include all network nodes. For larger networks, only the nodes which are most likely to be used for relaying packets should be used. The members of the anycast group 100 shown in Figure 1 represent a complete mesh network.

In the forwarding method described here, two specified frame formats are used. As can be seen from Figure 2, data are comprised in a data packet using a data frame 201, which can be obtained by a simple extension from a data frame specified in the standard 802.11. It may be also possible to use another data frame used in any kind of network traffic. The destination address field in the header of the standard data frame is replaced by a Group-ID (Group Identification) 202. In order to avoid confusion with the standard data frame, the "Subtype" field 204 in the frame control header 203 is set to a reserved value 0x1000. The Group-ID is a 6-Byte field being compatible with the IEEE 802.11 specification. It The Group ID represents the ID of the destination anycast group.

In order to carry out the forwarding method described in this application, a new frame is defined. This frame is called Forwarding Acknowledgment (FACK) frame 301. Figure 3 shows this FACK frame. It is extended from a standard acknowledgement (ACK) frame with a 6 Byte Group-ID field value 302.

In the following, the method for transmitting data between network elements defining the anycast group within a mesh network will be detailed described.

For the example as shown in Figure 4, the network comprises the network elements sender, candidate 1, candidate 2, candidate 3 and candidate 4. Except of candidate 4, all network elements are members of an anycast group 1. Candidate 2 has the highest priority. Candidate 3 has the lowest priority.

According to the embodiment described here a first step of the forwarding method is the forming of the anycast group 1 as described above. Of course, it is only necessary to carry out this step if the anycast group 1 does not already exist.

The transmitting element, which in the hereinafter is also called source node and/or sender, intends to send data comprising a data frame to a destination or receiving network element (not shown in Figure 4) via one or more intermediate elements (shown in Figure 4 as candidates 1, 2, 3) . First, the sender checks the routing table and obtains the Group-ID of the next hop. The Group-ID should be inserted in the data frame as the destination address as depicted in Figure 2. Each intermediate element, i.e. the candidates 1, 2 and 3 in Figure 4, receiving the data should compare the Group-ID and the sender address within the data frame with its local information to decide whether it should accept the frame. A network element, which is not part of the anycast group 1, i.e. candidate 4, discards this data. Therefore, the data is sent only to the members within the same anycast group. All the network elements, i.e. the intermediate elements, receiving the data successful perform the following process.

An intermediate element defer a (ni - 1) *timeslot period before reacting to the received data, for example by sending an acknowledgment message. Thereby, ni represents the priority of the network element in the anycast group and the timeslot is a pre-defined constant time interval. For example, in Figure 4 the network element 2 should defer (1 - 1) = 0 timeslots, i.e., it will react immediately by sending back an acknowledgment message. Network elements 1 and 3 should defer their reaction by 1 and 2 timeslots, respectively .

During the deferment or waiting time, the candidates 1 and 3, which have received data, invoke for example a carrier-sense mechanism to determine if a transmission medium, e.g. a radio channel link, used by the network elements of the anycast group 1 is occupied, i.e. the busy or idle state of the transmission medium.

Candidate 2 having the highest priority does not have a waiting time and therefore sends an acknowledgement message (ACK) immediately. After having received the ACK, the sender waits a predefined time (SIFS) period and transfers a communication message, i.e. a forwarding acknowledgement message (FACK) like that shown in Figure 3, to the responding candidate 2 to indicate that candidate 2 is now responsible for further forwarding the data. The address field of the FACK frame should be inserted with the address of candidate 2. This two-way handshake mechanism is used to eliminate the packet duplication since only the FACK receiver is responsible for a further forwarding of the data. After that, the described forwarding method may be started again with candidate 2 serving as the new transmitting element. This may be continued until the data receives the destination element .

The candidates 1 and 3 do not send an acknowledgement, as the transmission medium is occupied by the sender and the candidate 2 until the end of the respective waiting time. Therefore, the candidates 1 and 3 discard the data.

The data frame contains a duration field which allocates time for an acknowledgment message from the correct candidate in a shared Network Allocation Vector (NAV) and a backoff window. The 802.11 standard uses the NAV for collision avoidance, so other network elements within radio range will not contend for the transmission medium, while it is reserved. The NAV field of the ACK frame is obtained from the duration field of the immediately previous data frame, minus the time which is required to transmit the ACK frame and an SIFS interval. The NAV field of the FACK frame is obtained from the Duration field of the immediately previous ACK frame, minus the time which is required to transmit the FACK frame and an SIFS interval.

In Figure 5, a further example of the forwarding method is shown, in which some of the immediate elements fail to receive the data. In this case, all the intermediate elements except candidate 2 receive the data successfully. The network element candidate 4 discards the data since it does not belong to anycast group 1. Candidate 1 defers its transmission and listening to the transmission medium for one timeslot. Then it will find that the medium is no more occupied and starts to send an acknowledgment message. Intermediate element 3 defer its transmission and listening for two timeslots. Candidate 3 detects that the transmission medium is busy and will not send an ACK. The transmitting element (sender) receives the ACK from candidate 1 and sends a FACK to candidate 1. After candidate 1 receives the FACK, the forwarding procedure for this step is over and candidate 1 is the final receiver.

If none of the intermediate elements receive the data correctly, a recovery procedure may be performed as shown in Figure 6. After an ACK timeout, the sender, i.e. the transmitting element, will start the retransmission until an ACK is received.

This retransmission may also be started in several error cases, as for example when the transmitting element fails to receive the ACK message.

It should be noted that the term "comprising" does not exclude other elements or steps and "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

List of reference signs :

A transmitting element

B further intermediate element C network element

D receiving element

E intermediate element

F further intermediate element

100 anycast group 201 data packet frame

202 Group-ID field

203 Frame Control field

204 Subtype field

301 Forwarding Acknowledgment frame 302 Group-ID field 303 address field

Claims

CLAIMS :

1. A method for transmitting data between network elements (A, B, C, D, E, F) defining an anycast group within a mesh network, in particular within a wireless mesh LAN, the method comprising

• transmitting data from a transmitting element (A) of the anycast group to an intermediate element (E) of the anycast group, • sending an acknowledgement message from the intermediate element (E) to the transmitting element (A) indicating a receipt of the data,

• transmitting a confirmation message from the transmitting element (A) to the intermediate element (E) indicating that the intermediate element (E) is responsible for forwarding the data to a receiving element (D) of the anycast group, and

• forwarding the data from the intermediate element (E) to the receiving element (D) .

2. The method as set forth in claim 1, wherein forwarding the data comprises

• transmitting the data from the intermediate element (E) to the receiving element (D) , • sending a further acknowledgement message from the receiving element (D) to the intermediate element (E) indicating a receipt of the data by the receiving element (D),

• transmitting a further confirmation message from the intermediate element (E) to the receiving element (D) indicating that the receiving element (D) is responsible for further forwarding the data to a further receiving element of the anycast group.

3. The method as set forth in any one of the preceding claims, further comprising sending the data from the transmitting element (A) to at least one further intermediate element (B, F) .

4. The method as set forth in claim 3, wherein a priority value is assigned to the intermediate element (E) and the further intermediate element (B, F) , wherein the respective priority value is indicative for the respective intermediate element (E, B, F) to forward the data to the receiving element (D) .

5. The method as set forth in claim 4 further comprising modifying the priority values of the intermediate element (E) and the further intermediate element (B, F) periodically according to their forwarding periodicity within a specified time interval .

6. The method as set forth in claim 5, wherein modifying the priority values comprises

• promoting the priority value of the intermediate element

(E) , which is forwarding more packets, and/or

• demoting the priority values of those intermediate elements (B, F), which are forwarding fewer packets.

7. The method as set forth in claim 5 or 6, wherein only the priority values of a predetermined number of intermediate elements having the highest priority value in the any cast group are modified.

8. The method as set forth in claim 4, wherein the priority value is indicative for a waiting time between the receipt of the data and a reaction to the receipt.

9. The method as set forth in claim 8 wherein the intermediate element (E) and the further intermediate elements (B, F) determine during the waiting time the state of a radio channel link of the mesh network and discard the data if the radio channel link is at least partially occupied by other network elements (C, D) until the end of the respective waiting time.

10. The method as set forth in any one of the preceding claims, further comprising

• waiting for a predefined period of time after receipt of the acknowledgement message before transmitting the confirmation message by the transmitting element (A) .

11. The method as set forth in any one of the preceding claims, wherein the data is included in a data packet (201) comprising a header with a Group ID field (202) for a Group ID representing an ID of the anycast group.

12. The method as set forth in claim 11, wherein the intermediate element (E) discards a received data packet comprising a Group ID representing another anycast group as the anycast group the intermediate element (E) is a member of.

13. The method as set forth in any one of the preceding claims, wherein the confirmation message (301) comprises a Group ID field (302) value for the Group ID representing an ID of the anycast group .

14. The method as set forth in any one of the preceding claims wherein the confirmation message comprises an address field (303) for an address of the intermediate element (E) .

15. A transmitting element (A) comprising

• a unit for transmitting a data packet to an intermediate element (E) ,

• a unit for receiving an acknowledgement message from the intermediate element (E) indicating a receipt of the data packet,

• a unit for transmitting a confirmation message to the intermediate element (E) indicating that the intermediate element is responsible for forwarding the data packet to a receiving element (D) .

16. An intermediate element (E) comprising • a unit for receiving a data packet from a transmitting element (A) ,

• a unit for sending an acknowledgement message to the transmitting element (A) indicating a receipt of the data packet, • a unit for receiving a confirmation message from the transmitting element (A) indicating that the intermediate element is responsible for forwarding the data packet to a receiving element (D) , and

• a unit for forwarding the data to the receiving element (D) .

17. A mesh network, in particular a wireless mesh LAN, the mesh network comprising

• a transmitting element (A) as set forth in claim 15 and • an intermediate element (E) as set forth in claim 16.