Patent Publication Number: US-2020305060-A1

Title: Beacon and method for setting up and for maintaining a network

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is continuation of U.S. patent application Ser. No. 15/742,911, filed Jan. 9, 2018, which was a 371 application of International Patent Application No. PCT/EP2016/066605 filed on Jul. 13, 2016, and further claims benefit of German Patent Application No. 102015111405.4, filed Jul. 14, 2015, each which is hereby incorporated by reference in its entirety. 
    
    
     A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the reproduction of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 
     BACKGROUND 
     The invention relates to a method for establishing and maintaining a network having two or more subscribers, based on radio connections between the subscribers in accordance with a Bluetooth Low Energy (BLE) standard, each subscriber being uniquely characterized by way of a subscriber identifier (node ID). 
     The invention further relates to a beacon, in particular a battery- or rechargeable battery-operated beacon, having a microprocessor and a radio interface, the radio interface being designed to establish, in accordance with a Bluetooth Low Energy (BLE) standard, a data connection to a further subscriber having such an interface, the beacon being designed to send out connection data and to search for transmitted connection data of further subscribers. 
     Bluetooth Low Energy (Bluetooth LE or BLE) creates a standard for radio-based data transfer between electronic devices in which low energy consumption is particularly emphasized. It is thus suitable for battery- or rechargeable battery-operated devices. Transfer occurs on 40 channels at 2.4 GHz in the ISM band. The channels are divided into advertising channels and data channels. The advertising channels are used to establish a BLE connection between two subscribers and to transmit broadcasts, while larger quantities of data are transferred via the data channels. In order to establish a connection, advertising packets are constantly being sent or constantly searched for, which results in comparatively high energy consumption. 
     Devices having BLE interfaces can be interconnected into piconets in which one subscriber, as master, is connected to one or more subscribers functioning as slaves. It is disadvantageous in this context that the master must possess greater resources. This refers to hardware but also to the energy supply for establishing and maintaining the connections to the piconet subscribers. 
     “Beacons” are small, usually battery- or rechargeable battery-operated electronic devices for transferring data, preferably using the Bluetooth LE standard. Beacons supplied with energy in other ways, for example beacons connected to the power grid, are nevertheless also known. Beacons can be designed for a variety of applications. They are used in sensors, for example temperature sensors, in order to transfer measurement signals, as signal transducers for localization functions (e.g. iBeacon of the Apple company), as transmitters of data, for example advertising, for directing large flows of visitors, for example in stadiums, for information transfer, e.g. in museums and exhibitions, and much more. The Bluetooth LE standard enables bidirectional data exchange in this context. It is disadvantageous that beacons usually possess only very small inventories of energy and other resources (transmission power, range, computing power, memory capacity, etc.). They are therefore not suitable as connection coordinators in a network. 
     BRIEF SUMMARY 
     An object of the invention is therefore to furnish a method that makes it possible to establish and maintain, on the basis of BLE connections, a network having subscribers with few energy resources. 
     A further object of the invention is to create a beacon that is suitable as a subscriber for such a network. 
     That object of the invention which relates to the method is achieved by the fact that clusters having one subscriber, or several subscribers connected by means of BLE network connections, are formed; that a unique cluster identifier (cluster ID) is allocated to each cluster; that a first subscriber of a first cluster selects a second subscriber, located within range of a BLE connection, from a second cluster that is smaller or of the same size, and causes it to be detached from the second cluster and integrated into the first cluster by way of a BLE network connection to the first subscriber. Thanks to the method it becomes possible to establish a mesh network without a centrally arranged connection coordinator. The network can thus be formed with subscribers that possess only very few resources. The method makes it possible in particular to establish a network with battery- or rechargeable battery-operated subscribers having little battery or rechargeable-battery capacity, and to operate it over long periods of time. Thanks to the method according to the present invention, smaller clusters become dissolved while larger clusters grow, until all the subscribers are connected in one cluster and thus in one network. Current implementations of a Bluetooth Low Energy standard permit only one input and several, for example three, outputs for the establishment of BLE connections (Bluetooth Low Energy standard 4.1, version 1.0). The limitation to one input is advantageous because a subscriber connected via the input, and thus operated as a slave, must conform to the connection parameters of the master connected to the input, which ultimately is efficiently possible only for one master. The method makes it possible to establish a BLE network connection between two subscribers whose inputs are already occupied. For this, the selected subscriber firstly severs its connections to its cluster and then connects itself to the subscriber that has selected it for establishment of a BLE network connection. Provision can advantageously be made that each cluster is uniquely characterized via a cluster identifier (cluster ID); and that a new BLE network connection can be established only between two subscribers of different clusters. Ring interconnections can thereby be avoided, and a simple tree structure is obtained for the resulting network. The cluster identifier of the subscriber that established the first BLE network connection of the existing cluster can preferably be used as a cluster identifier (cluster ID). 
     In accordance with a preferred variant embodiment of the invention, provision can be made that before a BLE network connection is established, identifier data (“join-me” packet) are delivered between subscribers of existing clusters; that the identifier data contain at least the subscriber identifier (node ID) and/or the number of unoccupied inputs and/or the number of unoccupied outputs of a respective subscriber, and/or the cluster identifier (cluster ID) and/or a cluster size of the cluster to which the respective subscriber belongs; that receiving subscribers determine, from the identifier data sent from various subscribers, an evaluation number (connection score) for each of those subscribers; and that a subscriber of a larger cluster selects, on the basis of the evaluation number (connection score), a subscriber of a smaller cluster for establishment of a BLE network connection; or that, for clusters of the same size, a subscriber is defined as a function of the respective cluster identifier (cluster ID) and/or the respective subscriber identifier (node ID) and selects, on the basis of the evaluation number (connection score), a second subscriber for establishing the network connection. The identifier data can be delivered by means of advertising packets provided in the context of Bluetooth Low Energy applications. The connection score can then be determined from the identifier data, for example by means of a function (cluster score function). The subscriber of the larger cluster is responsible for selecting the connection partner. With the aid of the connection score, the subscribers can select the most suitable connection partner and enter into a BLE network connection to it. If the two clusters are of the same size, provision can be made that a decision is made, based on the cluster identifier (cluster ID), as to which subscribers can decide regarding the establishment of a BLE network connection. A knowledge of the cluster size is essential for establishment of the network. That knowledge is preferably stored in each subscriber of a cluster. When a new subscriber is connected to the cluster, the cluster size can be incremented by one and the new cluster size can be transmitted to the other subscribers of the cluster. In accordance with a farther-reaching embodiment of the invention, provision can be made that the evaluation number (connection score) assumes a value that prevents a BLE network connection if the subscriber transmitting the identifier data (join-me packet) belongs to the same cluster as the subscriber that is receiving and evaluating the identifier data, and/or if the transmitting subscriber belongs to a larger cluster than the receiving and evaluating subscriber. Provision can correspondingly be made that the evaluation number (connection score) assumes a value that corresponds to a higher score for a possible BLE network connection if the transmitting subscriber has an unoccupied input and if the transmitting subscriber does not belong to the same cluster or to a larger cluster. A connection in which the selecting subscriber is connected as master, and the selected subscriber as slave, is then enabled. It is likewise possible take into consideration, in ascertaining the connection score, a signal strength of the signal received from a subscriber that is to be evaluated. This can occur, for example, in the form of a received signal strength index (RSSI). BLE network connections are then preferentially set up to subscribers from which a high signal strength is available. It is furthermore possible for a battery run time and/or the device type to be conveyed in the context of ascertaining the connection score, and to be used to determine the connection score. What can thereby be achieved is that connections are preferentially set up to subscribers that possess good battery resources and/or that belong to a specific device class. 
     Before a BLE network connection is established, subscribers must first recognize one another and evaluate a possible connection establishment. Provision can therefore be made that during a discovery phase of network establishment, the subscribers continuously transmit connection data having their identifier data (join-me packet) and receive connection data having identifier data from transmitting subscribers; that receiving subscribers store the respectively most recently received identifier data of the transmitting subscribers; and that the frequency with which connection data are sent out, and/or with which connection data for reception are searched for, is reduced or terminated if the received identifier data all have the same cluster identifier (cluster ID). The transmission of and scanning for data result in high energy consumption. It is necessary during the discovery phase to transmit and scan frequently, however, so that subscribers within range can quickly be detected and connections established. Once all the reachable subscribers have been connected, they all have the same cluster identifier (cluster ID). Advantageously, the frequency with which connection data are sent out, and connection data for reception are searched for, can be reduced. Energy can thereby be saved, and the operating time of battery- or rechargeable battery-operated subscribers can be appreciably extended. With a reduced frequency of transmission and reception, new subscribers can be found, if applicable with an accepted delay, and integrated into the network. Energy consumption can be further reduced if the transmission of and search for connection data is completely halted, but new subscribers cannot be recognized and accepted. According to a further embodiment of the invention, provision can be made that after an interruption of a BLE network connection has occurred, the frequency with which connection data are transmitted and received is increased again in order to enable reconnection to the lost subscriber. 
     According to a particularly preferred embodiment of the invention, provision can be made that at least one beacon is used as a subscriber. Beacons are small, usually battery- or rechargeable battery-operated and Bluetooth-capable, devices having a wide variety of possible applications, for example as sensors, as data transmitters for targeted advertising, for navigation, and much more. The mesh network that is formed is particularly suitable for this type of subscriber, which possesses only a low level of resources in terms of energy and hardware. 
     In order to allow the correct cluster size to be determined even in the event of an interruption of a BLE network connection, provision can be made in a further embodiment of the invention that for each input and output of a subscriber, the number of subscribers in a branch of the network that is connected to the respective input or output is stored by the subscriber (“connected cluster size”); that the counter (“cluster size”) is reduced by an amount equal to the number of subscribers in the branch (connected cluster size) if a BLE network connection to the branch is interrupted; and that the new value of the counter (cluster size) is transmitted to the other subscribers of the cluster. Advantageously, in order to avoid concurrency problems, that new value can be transmitted as a change relative to the old value. Provision can furthermore advantageously be made that upon an interruption of a BLE network connection, a new cluster identifier (cluster ID) is allocated to the smaller cluster that has formed. 
     For initialization of the subscribers, provision can furthermore be made that during a first phase (node initialization) of network establishment, a subscriber not yet connected to a further subscriber has its subscriber identifier (node ID) assigned to it; that on the basis of that subscriber identifier (node ID) a cluster identifier (cluster ID) is generated and/or a cluster size of one is assigned to the unconnected subscriber; and/or that for the unconnected subscriber, the number of subscribers connected per input and per output (connected cluster size) is set to zero. All the information needed in order to connect to further subscribers is thus available to the subscribers at the beginning of network establishment. 
     In order to make it possible for several physically overlapping networks to be established in one physical space, provision can be made in a further embodiment of the invention that during the first phase (node initialization), a network identifier (network ID) is allocated to each network and is stored in the subscribers of the respective network which are already connected or are to be connected. 
     That object of the invention which relates to the beacon is achieved by the fact that the beacon is embodied to establish a network with the further subscribers by means of BLE network connections; and that the beacon is embodied to reduce the frequency with which connection data are sent out and/or searched for, or to halt the transmission of and/or search for connection data, when the subscribers present within range of a bidirectional BLE connection are integrated into the network. The energy consumption of the beacon can be appreciably decreased by reducing the frequency with which connection data are sent out or scanned for. It is thereby possible to establish networks, having at least one or preferably several beacons, which have a long operating time even if the beacon&#39;s energy resources are limited. 
     A mesh network can be established by the fact that the beacon is embodied to form, alone or together with at least one further subscriber connected via a BLE network connection, a first cluster; that the beacon is embodied to select a second subscriber from a second cluster that is smaller or of the same size and to cause it to interrupt its BLE network connections to subscribers of the second cluster; and that the beacon is designed to establish a BLE network connection to the second subscriber. 
     Provision can preferably be made that a unique subscriber identifier (node ID), and/or a unique cluster identifier (cluster ID), and/or a unique network identifier (network ID), and/or a cluster size of the cluster to which the beacon belongs, and/or the number of subscribers in a branch of the network which is connected to a respective input or output of the beacon (connected cluster size), is stored in the beacon. The data can thereby be used to establish and maintain the network. 
     According to a particularly preferred variant embodiment of the invention, provision can be made that the beacon is designed to deliver identifier data (join-me packet), as connection data or as a portion of the connection data, to further subscribers and to receive identifier data from them; and that the identifier data contain at least the subscriber identifier (node ID), and/or the number of unoccupied inputs and/or the number of unoccupied outputs of the beacon, and/or the cluster identifier (cluster ID), and/or the cluster size of the cluster to which the beacon or the further subscriber belongs. The data that are necessary for establishing a BLE network connection between two subscribers are thus available to potential subscribers of a network. 
     The beacon can preferably be designed to determine from the received identifier data (join-me packet), with the aid of a function (cluster score function) stored in the beacon, an evaluation number (connection score) for each of the subscribers whose identifier data have been received from the beacon; and the beacon can be designed to select, on the basis of the evaluation number, a subscriber for establishment of a BLE network connection. The beacon can thus quickly and easily decide as to the further subscriber, for example the further beacon, with which it preferentially wishes to establish a BLE network connection, and can then correspondingly set it up. Because the cluster identifier (cluster ID) is taken into consideration, it is possible to reliably prevent interconnection of subscribers of the same cluster. Multiple connections within one cluster and within one network can thereby be avoided. In accordance with a possible embodiment of the invention, provision can furthermore be made that in the context of selecting a subscriber for establishment of a BLE network connection, a signal strength of the received radio signal of the selected subscriber is taken into account. This can be done, for example, by taking into account a received signal strength index (RSSI). BLE network connections are then preferentially set up to subscribers from which a high signal strength is available. 
     The beacon can preferably be used to carry out the method described above. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The invention will be described in further detail below with reference to an exemplifying embodiment depicted in the drawings, in which: 
         FIG. 1  is a flow chart for establishing a network; 
         FIG. 2  shows a cluster of a network; 
         FIG. 3  shows subscribers, not yet networked, of a network that is to be formed; 
         FIG. 4  shows the subscribers shown in  FIG. 3 , partly networked; 
         FIG. 5  shows the subscribers shown in  FIG. 4 , further networked; 
         FIG. 6  shows a network having the completely networked subscribers of  FIG. 5 ; and 
         FIG. 7  shows two clusters of different sizes during establishment of a network. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a flow chart for establishment of a network. The flow chart provides, successively, for a node initialization phase  10 , a discovery phase  11 , a route setup phase  12 , a route maintenance phase  13 , and a routing phase  14 . The network is established with subscribers  20  shown in  FIGS. 2 to 7 , on the basis of Bluetooth Low Energy (BLE) connections. Subscribers  20  can be identical or different electronic components. In the exemplifying embodiment shown, at least one of the subscribers is embodied as beacon  23  as shown in  FIG. 2 . The individual phases can be cycled through repeatedly, and also in different sequences. 
     During the node initialization phase  10 , a unique subscriber identifier (node ID) and a network identifier (network ID) are assigned to subscribers  20  before they connect to the network. A key for encoding data is preferably also assigned to subscribers  20 . The network identifier allows several physically overlapping networks to be operated. Based on the subscriber identifiers (node IDs), subscribers  20  generate cluster identifiers (cluster IDs). For each subscriber ( 20 ,  21 ,  22 ,  25 ,  26 ,  27 ), a cluster size is set to the initial value of one. 
     As shown in  FIG. 2 , with the Bluetooth LE implementation that is used, a subscriber  20  comprises three outputs  20 . 1 ,  20 . 2 ,  20 . 3  and one input  20 . 4 . A value that indicates the number of subscribers  20  in a branch of the network which is connected to a respective input  20 . 4  or output  20 . 1 ,  20 . 2 ,  20 . 3  of subscriber  20  (connected cluster size) is set to zero for all inputs  20 . 4  and outputs  20 . 1 ,  20 . 2 ,  20 . 3  of subscribers  20 . The initial values thereby constituted are stored in subscribers  20 . 
     During the discovery phase  11 , subscribers  20  successively send out broadcast messages in the form of advertising packets. Broadcast data are not addressed to one subscriber  20 , but instead can be received by all subscribers  20  within range of the transmitter. The advertising packets contain connection data. Between transmissions, subscribers  20  scan the advertising channels, on which the broadcast messages are being transmitted, for connection data transmitted by other subscribers  20 . The transmitted advertising packets convey identifier data (join-me packet) that describe properties of the transmitting subscriber  20 . Those properties allow a receiving subscriber  20  to evaluate the transmitting subscriber  20  with regard to establishment of a BLE network connection. 
     The identifier data (join-me packet) preferably contain the node ID, the number of unoccupied inputs, and the number of unoccupied outputs of the transmitting subscriber, as well as the cluster identifier (cluster ID) and cluster size of a cluster  30 , shown in  FIGS. 2 to 7 , to which the respective subscriber  20  belongs. The advertising packet signals a possible connection if an input of the transmitting subscriber is unoccupied. If the input is occupied, the advertising packet signals that a direct connection is not possible. 
     Received advertising packets having identifier data are stored by the respective subscriber  20  in a buffer. If identifier data are received repeatedly from a transmitting subscriber  20 , older data are overwritten with the more recent data and preferably the reception time is also saved. 
     After a predefined duration of the discovery phase  11 , in the route setup phase  12  the best connection partner is ascertained by the respective subscribers  20  based on the collected identifier data (join-me packets). For each of subscribers  20  whose identifier data are available, an evaluation number (connection score) is ascertained using a function (cluster score function). This evaluation number expresses the subscriber  20  to which a BLE network connection is preferentially to be established. The connection score contains a low value, preferably zero, if the transmitting subscriber  20  is integrated into the same cluster  30  as, or a larger one than, the receiving and evaluating subscriber  20 . A BLE network connection to such a subscriber  20  then cannot be initiated by the evaluating subscriber  20 . The decision as to establishing a connection is thus the responsibility of subscriber  20  of the larger cluster  30 . If the two subscribers belong to different clusters  30  of the same size, a decision as to which subscriber  20  can decide regarding establishment of a connection is made based on the cluster identifier (cluster ID and/or the subscriber identifier (node ID). 
     Once all the identifier data have been evaluated, subscriber  20  attempts to create a BLE network connection to subscriber  20  having the highest connection score. For that purpose, a subscriber  20  will preferentially select a further subscriber  20  that has an unoccupied input  20 . 4 , and attempt to connect to it as master. 
     During the handshake, the two relevant subscribers  20  exchange further data (cluster welcome packet) having their most recent, and therefore up-to-date, identifier data. If it is found in that context that the two subscribers  20  already belong to the same cluster  30 , the connection that has just been established is interrupted again. It is thereby possible to prevent a subscriber  20  from being connected to the same cluster  30  via several connections. Otherwise, authorization is given for subscriber  20  of the smaller cluster  30  to interrupt all BLE network connections to the smaller cluster  30 . A BLE network connection is then established between the selecting and selected subscribers  20 . The new subscriber  20  stores its new cluster identifier and its new cluster size, which has been incremented by one as compared with the cluster size of the larger cluster  30 . The accepted subscriber  20  then delivers a cluster ACK packet with which it acknowledges its entry into the new cluster  30 . This is followed by a message (cluster update message) to the other subscribers of cluster  30 , having the new cluster size. The change in cluster size is made incrementally. This is advantageous because at a specified point in time, for example while a further handshake is currently occurring, not all subscribers  20  of a cluster  30  have stored the same cluster size. 
     If a BLE network connection is interrupted, the cluster size is reduced by a value equal to the number of lost subscribers  20 . This too is accomplished incrementally. It is necessary for this purpose for each subscriber  20  to store, for each input and output  20 . 1 ,  20 . 2 ,  20 . 3 ,  20 . 4 , the number of subscribers  20  contained in the branch to which it is connected (connected cluster size). To avoid identical cluster identifiers (cluster IDs), a new cluster identifier (cluster ID) is generated for the smaller cluster  30  that has been formed, based on the subscriber identifier (node ID) of subscriber  20  whose connection was interrupted. The larger cluster  30  retains its cluster identifier. 
     Subscribers  20  of a larger cluster  30  can decide which connection to enter into. Smaller clusters  30  thereby become dissolved until only one cluster  30  exists. The result is that a mesh network forms with no need for a higher-order coordinator. 
     Once the network has formed, all the identifier data (join-me packets) have the same cluster identifiers (cluster IDs). Once this is the case, in the route maintenance phase  13  subscribers  20  are then switched over to a “slower discovery” mode; this is preferably done if no changes in the transmitted cluster identifiers occur over a longer period of time. During the slower discovery phase, the subscribers scan the network less frequently, and transmit fewer advertising packets, as compared with the previously described discovery phase  11 . It is also conceivable to completely shut off the discovery of further subscribers  20 . This has the disadvantage, however, that new subscribers  20  can no longer be discovered and integrated into the network. If the connection to a subscriber  20  becomes lost, its previous connection partner switches the network back into the discovery phase with the corresponding high transmission and search frequency. The network will thus reconnect subscribers  20  to which a connection was interrupted, alternative connection routes possibly being selected. The network is thus self-healing. The disconnected subscriber  20  is, with high probability, reconnected at the edge of the network. Subscribers  20  whose connection to the network is more frequently interrupted are thus shifted to the edge of the network, thereby enhancing the stability of the network. 
     During the routing phase  14 , data can then be delivered via the network. As is known for mesh networks, the data can be forwarded from subscriber  20  to subscriber  20 , and to the addressee. Possible messages are broadcast messages directed to all subscribers  20 , or messages between two subscribers  20 . Messages can also be transmitted to a connecting point (sink or gateway) integrated into the network and from there to another network, or messages can be received from the connecting point. 
       FIG. 2  shows a cluster  30  of a network having four subscribers  20 . Each subscriber  20  comprises three outputs  20 . 1 ,  20 . 2 ,  20 . 3  and one input  20 . 4 . The subscribers can thus enter into three connections as a master and one connection as a slave. One subscriber is embodied as beacon  23 . Its input  20 . 4  is connected via a BLE network connection to a second output  20 . 2  of an upstream subscriber  20 . A branch having two subscribers  20  is connected to first output  20 . 1  of beacon  23 . Second and third outputs  20 . 2 ,  20 . 3  of beacon  23  are unoccupied and are not connected to a further subscriber  20 . 
     Identifier data are assigned to beacon  23  and to the further subscribers  20  associated with cluster  30  that is shown. All these subscribers  20  connected in cluster  30  have the same network identifier (e.g. network ID=1), the same cluster identifier (e.g. cluster ID=7001), and the same cluster size; in the present exemplifying embodiment, cluster size=4. In addition, a dedicated subscriber identifier is assigned to each subscriber  20 ; for beacon  23 , for example, node ID = 7 . Also stored in each subscriber  20 , for each input and output  20 . 1 ,  20 . 2 ,  20 . 3 ,  20 . 4 , is the number of subscribers  20  connected thereto (connected cluster size). In the example depicted, a connected cluster size of  1  is obtained for input  20 . 4  of beacon  23 . A connected cluster size of 2 is allocated to first output  20 . 1  of beacon  23 , while a connected cluster size of 0 is assigned respectively to second and third outputs  20 . 2 ,  20 . 3  of beacon  23 . If the BLE network connection between first output  20 . 1  of beacon  23  and the following subscriber  20  is interrupted, the cluster size of the remaining cluster  30  is incrementally reduced in accordance with the connected cluster size of 2 associated with the first output. The new cluster size is then equal to 2. 
       FIG. 3  shows subscribers  20 , not yet interconnected, of a network that is to be formed. A range  24  of its Bluetooth transmission module is associated with the respective individual subscribers  20  in the form of exemplifying concentric circles. Ranges  24  differ depending on the respective subscriber  20 , and if applicable on the charge state of its energy supply. A subscriber identifier (node ID), a network identifier (network ID), and a cluster identifier (cluster ID) are allocated to each subscriber  20 . 
     Subscribers  20  are in the discovery phase  11 . Subscribers  20  accordingly transmit identifier data (join-me packet) very frequently. Between transmissions of the data, they receive identifier data from subscribers  20  within whose range  24  they are located. 
     At least a majority of subscribers  20  are embodied as beacons  23 . 
       FIG. 4  shows subscribers  20  shown in  FIG. 3  which are partly interconnected. Some subscribers  20  have connected via BLE network connections into clusters  30  having a cluster size greater than 1. A cluster A  31  and a cluster B  32  are labeled by way of example. Cluster A  31 , having three connected subscribers  20 , is larger than cluster B  32  having only two subscribers  20 . A subscriber A  21  is arranged at the end of cluster A  31 , while a subscriber B  22  is connected at the end of cluster B  32 . A further adjacent subscriber C  25  is additionally marked. Subscribers A  21  and B  22  are each within range  24  of the other subscribers A, B,  21 ,  22 . Based on the exchanged identifier data (join-me packet), both subscribers A, B,  21 ,  22  have the information that cluster A  31  is larger than cluster B  32 . Subscriber A  21  can thus decide whether subscriber B  22  should detach itself from cluster B  32  and enter into a BLE network connection to subscriber A  21 . The same applies to a possible BLE network connection between subscriber A  21  and subscriber C  25 . The decision as to whether a connection is to be created, and with which of the two subscribers A, C,  22 ,  25 , is made by subscriber A  21  on the basis of the evaluation number (connection score) that it has ascertained, with the aid of a stored function (cluster score function), from the identifier data conveyed from subscribers B, C,  22 ,  25 . Because subscriber B  22  has one free input  20 . 4 , a comparatively high connection score is determined; it is higher than the connection score of the adjacent subscriber C  25 , since the latter&#39;s input  20 . 4  is occupied. Subscriber A  21  will therefore preferentially enter into a BLE network connection to subscriber B  22 . The signal strength of a signal received from a transmitting subscriber  20  can also be taken in account in deciding the subscriber  20  with which a BLE network connection is to be entered into. Provision can be made, for example, that connections are preferentially established with subscribers  20  from which a strong transmitted signal is available. The strength of a transmitted signal can be taken into account, for example, in the form of a received signal strength index (RSSI). 
       FIG. 5  shows subscribers  20  shown in  FIG. 4  which have been further interconnected. Proceeding from  FIG. 4 , subscriber A  21  has decided to establish a BLE network connection to subscriber B  22 . For this, firstly the BLE network connection of subscriber B  22  to cluster B  32  was severed. A BLE network connection was then established between an output  20 . 1 ,  20 . 2 ,  20 . 3  (see  FIG. 2 ) of subscriber A  21  and input  20 . 4  of subscriber B  22 . 
     Because input  20 . 4  of subscriber B  22  was unoccupied before the connection was established, it is alternatively also possible for subscriber A  21  not to detach subscriber B  22  from cluster B  32  before establishment of the connection. Instead, subscriber A  21  can directly establish with subscriber B  22  a connection in which subscriber A  22  is configured as master, and subscriber B  22  as slave. The entire smaller cluster B  32  can thereby be coupled to the larger cluster A  31 . 
       FIG. 6  shows a network having the completely interconnected subscribers  20  of  FIG. 5 . For this, subscriber A  21  has entered into a BLE network connection to subscriber C  25 . Before establishment of the connection, input  20 . 4  of subscriber C  25  was occupied. Subscriber C  25  was therefore firstly detached from its original cluster  30  and then connected to subscriber A  21 . The method thus makes it possible for subscribers  20  whose inputs  20 . 4  are already occupied to be capable of being shifted from smaller into larger clusters  30 . 
     According to  FIG. 6 , all subscribers  20  belong to one cluster  30  and therefore have the same cluster identifier (cluster ID). Subscribers  20  thereupon switch to a mode (slower discovery mode) in which advertising packets are less often transmitted and searched for. The energy consumption of subscribers  20  can thereby be appreciably reduced. 
     The mesh network that has been formed does not require a coordinator or central master, but instead can be built up from identical subscribers  20 . It is thus possible, for example, to establish a network having a plurality of subscribers  20  having little battery capacity or rechargeable-battery capacity, for example beacons. They interconnect with one another automatically. Connection between subscribers  20  is effected using a Bluetooth Low Energy standard, preferably in accordance with the Bluetooth 4.1 specification. Subscribers  20  are programmed with a corresponding application software in order to achieve networking capability. That software controls the above-described phases of connection establishment and network maintenance. 
       FIG. 7  shows two clusters D, E,  33 ,  34  of different sizes during establishment of a network. Cluster D  33  has four subscribers  20 , and cluster E  34  has three. An end-located subscriber E  27  of the smaller cluster E  34  is located within range  24  of an end-located subscriber D  26  of the larger cluster D  33 . Conversely, range  24  of subscriber E  27  of the smaller cluster E  34  does not reach subscriber D  26  of the larger cluster D  33 . In both end-located subscribers D, E,  26 ,  27 , input  20 . 4  is occupied. In such a case the possibility exists for subscriber D  26  of the larger cluster D  33  to detach subscriber E  27  of the smaller cluster E  34  from its cluster E  34  but with no possibility for a BLE network connection then to be established between the two subscribers  20 , since the range of subscriber E  27  is too short for that purpose. The result is then that subscriber E  27  having the short range  24  is constantly unconnected and is searching for connection possibilities. The state of a low search and transmission frequency therefore also cannot be achieved for the neighboring subscribers  20 , resulting in high energy consumption. 
     To prevent this, provision is preferably made to add to the identifier data (join-me packet) an ACK field that contains the subscriber identifier (node ID). Subscriber  26  can assign to this ACK field the subscriber identifier of subscriber E  27 . That identifier is known to subscriber D  26  only if it has previously received identifier data (join-me packet) from subscriber E  27  and is thus within range  24  of subscriber E  27 . A subscriber  20  is therefore detached from a further subscriber  20  of a cluster  30  only if both subscribers  20  are located within range  24  of the other subscriber  20 .