Assignment of addresses for server devices by client device

Abstract

A client device in communication with a plurality of server devices, where each server device is initialised to have the same default server address, and each server device is associated with a respec

Description

Networks of electronic devices, such as charging points of an EV charging station, may communicate using specified communication protocols. Modbus RTU provides a communication protocol that is preferred in many applications to more recent communication protocols due to its simplicity and robustness. A shortcoming of Modbus RTU and similar protocols is the inability to automatically detect new devices on the serial bus and assign a unique server address to the new device. A known approach for addressing this problem is the manual setting of a unique address to each server device. This may be performed, for example, using a DIP switch located on the device. Manual assignment of server device addresses is time consuming and liable to human error. Other approaches for assigning server device addresses require special software enhancements, such as the approach described in US 9,015,267 B2, or additional hardware systems. There is a need for methods of automatically assigning server device addresses that are efficient, robust and suitable for use with communication protocols such as Modbus RTU over RS-485. Summary of Invention In one aspect of the disclosure, a computer-implemented method is performed by a client device that is in communication with a plurality of server devices. Each server device is initialised to have the same default server address, and each server device is associated with a respective unique identifier key that belongs to a first range. The method comprising the following steps: a) sending a response request to the default server address, the response request referencing the first range of identifier keys and an instruction causing any server devices associated with an identifier key lying within the range referenced in the response request to provide a predefined response to the client device; b) using an interval bisection method to send further response requests to the default server address referencing different sub-ranges of the first range to search for a sub-range of the first range for which a response request referencing the sub-range causes a predefined response to be received from a server device without a collision; and c) assigning the responding server device to a unique server address. The above method provides an efficient and reliable process for allowing a client device to automatically assign server devices to addresses using existing communication protocols, such as Modbus RTU over RS-485. In some examples, the method further comprises repeating steps b) and c) until all server devices of the plurality of server devices have been assigned to respective unique server addresses. In some examples, the interval bisection method comprises: bl) sending, by a client device, a series of response requests to the default server address until either a predefined response is received from a server device without a collision or no response is received from any server devices, wherein the first response request of the series of response requests references the first range and wherein each subsequent response request of the series of response requests references the first half of the range of identifier keys referenced in the previous response request of the series of response requests. In some examples, the interval bisection method further comprises: based on no response being received for a response request, performing the step of: b2) sending a further series of response requests to the default server address until either the predefined response is received from a server device without a collision or no response is received from any server devices, wherein the first response request of the further series of response requests includes a second half of a range of identifier keys for which the first half of the range has been previously searched, and wherein each subsequent response request of the further series of response requests references a first half of the identifier key range referenced in the previous response request of the further series of response requests. In some examples, the interval bisection method further comprises: based on no response being received for a final request of the further series of response requests, repeating step b2) until the predefined response is received from a server device without a collision. In some examples, the method further comprises: maintains a last-in-first-out, LIFO, container of identifier key ranges and sub-ranges that are to be searched, wherein the order of identifier key ranges and sub-ranges in the LIFO container determines the order in which identifier key ranges and sub-ranges are searched; and based on receiving no response to a response request referencing a first identifier key range or sub-range, removing the first identifier key range or sub-range from the LIFO container, and based on receiving an erroneous response to a response request referencing the first identifier key range or sub-range, replacing the first identifier key range or sub-range with second and third sub-ranges corresponding respectively to the first and second halves of the first identifier key range or sub-range. In some examples, the communication protocol between the client device and the plurality of server devices is configured such that more than one server device providing a predefined response to the client device from the same server address within a first period of time causes the client device to receive an erroneous response due to collision of the responses. In some examples, the communication protocol used by the client device and server devices is Modbus RTU and, preferably, using RS-485 signalling. In some examples, the method further comprises communicating with an individual client device by sending communications using the unique server address assigned to the individual client device. In some examples, the predefined response comprises the respective identifier key associated with the responding server device. In some examples, each server device is configured such that, based on receiving a response request referencing a range or sub-range of identifier keys containing the respective identifier key of the server device, the respective server device provides the predefined response to the client device comprising the respective identifier key. In another aspect of the disclosure, a computer-implemented method is performed by a system comprising a client device and a plurality of server devices. Each server device is initialised to have the same default server address and wherein each server device is associated with a respective unique identifier key that belongs to a first range, the method comprising the following steps: a) sending, by the client device, a response request to the first server address, the response request referencing the first range of identifier keys and an instruction causing any server devices associated with an identifier key lying within the range referenced in the response request to provide a predefined response to the client device; b) using, by the client device, an interval bisection method to send further response requests to the default server address referencing different sub-ranges of the first range to search for a sub-ranges of the first range for which a response request referencing the sub-range causes a predefined response to be received from a server device without a collision; and c) assigning, by the client device, the responding server device to a unique server address. In some examples, the method comprises sending, by a first server device having a first identifier key, the predefined response to the client device based on receiving a response request including a reference to a sub-range of identifier keys that encompasses the first identifier key. In another aspect of the disclosure, a client device is configured to perform the method of other aspects of the disclosure. In another aspect of the disclosure, a system comprises a client device and a plurality of server devices. The system is configured to perform the method of other aspects of the disclosure. In some examples, the client device is a charging point controller, and the plurality of server devices are different EV charging points of an EV charging station. Brief Description of the Figures A detailed description of embodiments of the disclosure is provided with reference to the following figures: Fig. 1 schematically illustrates a system comprising a client device and a plurality of server devices. Fig. 2 provides a flowchart illustrating steps performed by a client device in embodiments of the disclosure. Figs. 3a and 3b provide schematic illustrations of the assignment of server addresses in examples of the disclosure. Fig. 4 provides a flowchart illustrating steps performed by a client device in embodiments of the disclosure. Detailed Description of the Invention The present disclosure relates to methods performed by one or more devices of a networked system comprising a client device and a plurality of server devices. In the present disclosure, the terms client device and server device define the relationship between the devices in a server / client architecture. The devices communicate with each other according to a suitable communication protocol, such as Modbus RTU over RS-485. While the disclosure is described with reference to Modbus RTU, the methods can be applied to other communication protocols. The client device and the server devices may, for example, be entities in an EV charging station. In this example, the client device is a charging point controller, and the server devices are individual charging points. The charging point controller coordinates and controls the charging points and may perform various other tasks, such as communication with the cloud. The system is initialised such that each server device is assigned to the same default server address. Therefore, an initial communication sent by the client device to the default server address will be received by every server device. Every server device is associated with a unique identifier key (or auto-addressing key, AAK) that is known to the server device. The client device sends a response request to the default server address. The response request specifies a range of identifier keys encompassing the unique identifier keys of all the server devices and requests a response from any server device having an identifier key within the specified range. The request also specifies that the response includes the unique identifier key for the respective server device. As every server device receives the request and every server device has an identifier key within the specified range, each server device responds to the client device with a response including the respective identifier key of the server device. Simultaneous responses from a plurality of server devices in communication protocols such as Modbus RTU results in communication collision, which is detected by the client device as an erroneous response. The client device then searches for ranges of identifier keys that do not result in a communication collision using an interval bisection method. According to the interval bisection method, after receiving an erroneous response due to a collision, the client device sends repeated further requests to the default server address in which each request includes a range of identifier keys that is the first half of the previous range. Eventually, the range of identifier keys is sufficiently narrow that only one or zero server device(s) has an identifier key belonging to the range. When only one server device has an identifier key belonging to the range, the response of the server device is received without collision by the client device. The client device then assigns the server device to a unique communication address. Because the server device no longer belongs to the default server address, the client device does not receive further communications addressed to the default server address. In the case that no server devices have an identifier key belonging to the final range of identifier keys, the client device then changes the identifier key range to a previously unsearched sub-range of identifier keys. The previously unsearched subrange of identifier keys may be the second half of an identifier key range for which the first half has already been searched. The client device then searches this range of identifier keys as before. A range or sub-range of identifier keys may be considered to have been searched when no response has been received for a response request indicating the range / sub-range or no responses have been received to a plurality of response requests that encompass the entire range or sub-range. This process is repeated until a correct response is received from a server device. When a server device provides a correct response (i.e. a response without communication collision), the client device then assigns the responding server a unique server address. These steps are repeated until every server device has been assigned to a unique server address. Fig. 1 figuratively illustrates a system according to embodiments of the disclosure. Client device 1 is in communication with server devices 2a-c. In the illustrated embodiment, three server devices are provided. However, a different number of server devices may be used in other examples. For example, when using the Modbus RTU protocol, up to 246 server devices may be assigned distinct server addresses, with a further address being used as the default server address. The client device 1 and server devices 2a-c may each be EV charging points in an EV charging station. On initialization of the system, each of the server devices 2a-c is assigned to a default server address. This may be set, for example, during manufacture or installation of the device. Each service device 2a-c is also provided with an identifier key (or autoaddressing key). The identifier key may be based on a serial number of the device. For example, the identifier key of a device may correspond to the serial number of the device prepended by a random byte in order to achieve substantially uniform distribution of the identifier keys and increase the speed of the searching process. The client device is provided with the byte length of the identifier keys and therefore is able to infer a first range of identifier keys comprising all of the identifier keys. Fig. 2 illustrates a flow chart showing steps of the interval bisection process performed by the client device during methods of the present disclosure. The skilled person will understand that the order of steps described below may be modified and certain steps may be omitted within the scope of the disclosure. Prior to initiation of the steps illustrated in the flow chart, each server device 2a-c is assigned to the same default server address. Each server device 2a-c is also associated with a unique identifier key known to itself. The unique identifier key for each server device is not necessarily known to any of the other server devices 2a-c. The identifier keys of all the server devices belong to a first range. In step S10, the client device 1 sends a response request referencing the first range of identifier keys to the default server address. The response request is a request including an instruction causing any server devices 2a-c associated with an identifier key lying within the range referenced in the response request to provide a predefined response to the client device 1. The predefined response may include the identifier key of the respective server device 2a-c that is responding to the response request. The initial response request references the entire first range of the default server address. As explained below, subsequent response requests may reference sub-ranges of the first range in order to request responses from sub-sets of the server devices 2a-c that are assigned to the default server address. The response request may comprise a sequence of values representing a function code and a range of identifier keys. Each server device 2a-c may be pre-programmed to provide the predefined response based on receiving a communication includinga first function code and a reference to a range of identifier keys that includes the identifier key of the given server device 2a-c. As such, the instruction may be the first function code and the reference to a range identifier keys. In some examples, the function code consists of a single byte. Each server device 2a-c is pre-programmed such that it only responds to a response request if the response request includes a reference to a range of identifier keys that includes the identifier key of the given server device 2a-c. Therefore, if a given server device 2a-c receives a response request including a reference to a range of identifier keys that does not include the identifier key of the given server device 2a-c, that given server device 2a-c provides no response to the response request. Because every server device 2a-c is assigned to the default server address at the beginning of the process, every server device 2a-c receives the initial response request. Because the initial response request references a first range of identifier keys that encompasses the identifier key of every server device 2a-c, each server device responds to the client device 1 with the predefined response. When the client device 1 receives communications occurring at the same time from more than one server device 2a-c having the same server address in communication protocols such as Modbus RTU, the received responses are corrupted. This corruption of received responses received at the same time is referred to as collision of the responses. The corrupted communication due to collision is registered by the client device 1 as an erroneous response. For example, the communication may be identified as having a CRC error. Because the initial response request causes simultaneous predefined responses from all of the servers 2a-c, the client device 1 receives an erroneous response and does not receive the predefined responses from the respective server devices 2a-c. In step S20, based on receiving an erroneous response, the client device 1 generates a new identifier key range corresponding to the first half of the first range. The client device 1 then sends a further response request by repeating step S10 using the new identifier key range. The further response request is of the same form as the initial response request but references the first half of the first range rather than the entire first range. In response to the further response request, only server devices 2a-c having an identifier key in the first half of the first range provide a predefined response. If a further erroneous response is received due to communication collision, steps S20 and S10 are repeated by iteratively referencing the first half of the previous identifier key range until no communication collision is received. In the case that a predefined response is received from a server device 2a, in step S30, the server device 2a is assigned to a unique server address. Assigning the server device 2a to a unique server address may comprise sending, by the client device 1, a communication to the default server address indicating the identifier key of the server device 2a and the unique server address for that server device 2a. When a server device 2a receives the communication, the server device 2a replaces the default server address with the unique server address as its server address. When a server device 2a is assigned to a unique server address, it no longer receives communications sent to the default server address. Whenever the client device 1 assigns a new server device 2a-c to a unique server address, a new unique server address is chosen that has not previously been assigned to another server device 2a-c. After a first server device 2a has been assigned to a unique server address, the client device may repeat the previous steps starting from S10. In some examples, the identifier key range referenced in the response request may be reset to correspond to the first range. Because one server device 2a has been assigned to a unique server address, this server device will not receive the response request which is addressed to the default server channel. In other examples, the identifier key range is chosen to exclude ranges that have previously been searched in order to improve the efficiency of the searching operation. When a response request references an identifier key range containing none of the identifier keys of the unassigned server devices 2a-c, no response is received from any server devices 2a-c. When no response is received for a particular sub-range of identifier keys, that sub-range of identifier keys may be recorded as having been searched. Recording that a sub-range of identifier keys has been searched may comprise removing that sub-range of identifier keys from a record of sub-ranges of identifier keys that are yet to be searched. When no response is received to a response request, the client device 1, in step S40, sets the identifier key range to correspond to a sub-range of identifier keys that has not previously been searched. For example, the client device may set the identifier key range to correspond to the second half of an identifier key range for which the first half of the identifier key range has returned no responses. The above defined steps are then repeated by iteratively bisecting the new identifier key range until i) no response is received or ii) a predefined response is received, and a server device 2a-c can be assigned to a unique server address. The client device 1 may maintain a memory comprising stack of sub-ranges of identifier keys that have yet to be searched. The client device may search sub-ranges of identifier keys in the order that they are positioned in the stack of sub-ranges. Each time a request referencing a range or sub-range of identifier keys returns an erroneous response, the referenced range or sub-range is bisected and the first and second halves of the previous range or sub-range are provided as separate sub-ranges in the stack of sub-ranges. The bisected range or sub-range is removed from the stack of sub-ranges. When no response is received to a request referencing a given subrange of identifier keys, this sub-range is removed from the stack of sub-ranges without bisecting the sub-range, and the client device 1 proceed to search the next sub-range in the stack. When a response is received without collision from a server device 2a-c, and the responding server device 2a-c is assigned to a server channel, a repeat response request may be sent to the same sub-range of identifier keys to check whether another server device 2a-c belongs to the same sub-range of identifier keys, where the other server device 2a-c avoided collision by providing a delayed response, as described in more detail below. If no response to the repeat response request is received, this sub-range can be removed from the stack of sub-ranges that have yet to be searched. The stack of sub-ranges may be a last-in-first-out (LIFO) data container. In this case, when a sub-range is bisected, the two halves of the bisected sub-range replace the bisected sub-range and are positioned in the stack as the next two sub-ranges to be searched. In some examples, communications from more than one server device 2a-c in the same range of identifier keys may be received without collision due to a second server device 2b providing a delayed response that is received after a response from a first server device 2a. In this example, a predefined response from first server device 2a may be received, and the first server 2a may be assigned to a unique server address in step S30. To avoid leaving a second server device 2b unassigned, after assigning the first server device 2a to a unique server address, the identifier range of step S10 is repeated using the same range of identifier keys. Therefore, when step S10 is repeated, the predefined response from the second server device 2b is received in the same identifier key range as the previous predetermined response from the first server device 2a. The first server device 2a does not receive the repeated request because the first server device 2a is no longer assigned to the default server channel. Therefore, the response from the second server device 2b will not experience a collision, regardless of whether the response from the second server device 2b is delayed. The above steps S10-S40 are repeated until all server devices 2a-c have been assigned to a unique server address. In order to illustrate the steps of the flow chart, a specific example of the method is provided below. Table 1 below illustrates how four server devices 2a-c may be associated with different identifier keys and associated with the same server address at the start of the method. In this example, the default server address is chosen as address 247. In this example, the identifier keys of all the server devices belong to the range 0000-1023. Server Device Identifier Key Server Address #1 184 247 #2 305 247 #3 730 247 #4 938 247 Table 1. The client device 1 provides a response request to server address 247 referencing the range 0000-1023. Each server device 2a-c provides a predefined response to the client device 1 including the respective identifier key. The client device 1 receives a erroneous communication due to collision of the communications from the four server devices. Based on receiving an erroneous communication, the client device 1 provides a further response request referencing the first half of the original identifier key range, that is 0000-0511. Because devices #land #2 all have identifier keys belonging to the new identifier key range, a further collision results. Based on the further erroneous communication, the client device 1 provides a further response request referencing the first half of the previous identifier key range, that is 0000-0255. Only server device #1 has an identifier key in this range, and only server device #1 provides a predetermined response. On receiving the predetermined response, the client device assigns server device #1 to server address 1, as shown in Table 2. Server Device Identifier Key Server Address #1 184 1 #2 305 247 #3 730 247 #4 938 247 Table 2. After server device #1 has been assigned to server address 1, the response request referencing identifier key range 0000-0255 may be repeated to check that there are no further server devices having identifier keys belonging to this range that provided a delayed response to the previous request. As no further server devices have an identifier key in this range, no response is received and the client device 1 records that this identifier key range has been searched and included no unassigned server devices. The client device 1 repeats the previous steps, with the identifier key range being set to a range that has not previously returned no response. The client device 1 identifies the next unsearched identifier key range to be the second half of the previous identifier key range, that is 0256-0511, and provides a further response request. In response to this further response request, only server device #2 provides a predefined response, which is received by the client device 1 without collision. The server device #2 is then assigned to server address 2, as shown in Table 3 below. Server Device Identifier Key Server Address #1 184 1 #2 305 2 #3 730 247 #4 938 247 Table 3. 10 The above steps are repeated until all server devices 2a-c are assigned to unique server addresses and no server devices 2a-c remain assigned to the default server address. Table 4, below, illustrates the sequence of message exchanges between the client device 1 (shown as device #0) and the server devices 2a-c in the above-described example. Line # Response request by client device (#0) Response(s) from server devices (#1, #2, #3, #4) Stack of to-be-searched subranges 1 #0:0000-1023 #1: 0184 #2: 0305 #3:0730 #4: 0938 Erroneous response 0000-1023 2 #0:0000-0511 #1: 0184 #2: 0305 Erroneous response 0000-0511 0512-1023 3 #0:0000-0255 #1: 0184 Correct response 0000-0255 0256-0511 0512-1023 4 #0: assign address 1 to 0184 0000-0255 0256-0511 0512-1023 5 #0:0000-0255 No response 0000-0255 0256-0511 0512-1023 6 #0:0256-0511 #2: 0305 Correct response 0256-0511 0512-1023 7 #0: assign address 2 to 0305 0256-0511 0512-1023 8 #0:0256-0511 No response 0256-0511 0512-1023 9 #0: 0512-1023 #3:0730 #4: 0938 Erroneous response 0512-1023 10 #0:0512-0767 #3: 0730 Correct response 0512-0767 0768-1023 11 #0: assign address 3 to 0730 0512-0767 0768-1023 12 #0: 0512-0767 No response 0512-0767 0768-1023 13 #0 0768-1023 #4: 0938 Correct response 0768-1023 14 #0 assign address 4 to 0938 0768-1023 15 #0 0768-1023 No response 0768-1023 The last column shows what ranges or sub-ranges are kept in the memory so that no sub-range is skipped. The topmost line in the stack is the sub-range that is being used at that particular step. Figs. 3a and 3b illustrate a simplified representation of this process when the first range of identifier keys is 0-3. The first range of identifier keys can be bisected into a plurality of intervals which are systematically searched for predefined responses without collisions. When a predefined response is received without a collision, the responding server device 2a-c is assigned to a unique communication address. This is repeated until all server devices 2a-c are assigned to unique communication addresses. Fig 4. Illustrates steps of a method performed by a client device 1 in embodiments of the disclosure. In step S100, the client device 1 sends a response request to the default server address. The response request references the first range of identifier keys. In step S200, the client device 1 uses an interval bisection method to send further response requests to the default server address to search for a sub-ranges of the first range for which a response request referencing the sub-range causes a predefined response to be received from a server device without a collision. The interval bisection method may comprise steps of the method described in more detail with respect to Fig- 2. In Step S300, the client device 1 assigns a server device 2a-c that responds to a response request without collision to a unique server address. The above disclosure provides an efficient, fast and robust method of automatically assigning server devices to server addresses. The method may be implemented with Modbus RTU using RS-485 signalling. A particularly advantageous use case of the embodiments is in installation of EV charging points of an EV charging station.

Claims

1. A computer-implemented method performed by a client device (1) that is in communication with a plurality of server devices (2a-c), wherein each server device (2a-c) is initialised to have the same default server address and wherein each server device (2a-c) is associated with a respective unique identifier key that belongs to a first range, the method comprising the following steps:a) sending a response request to the default server address, the response request referencing the first range of identifier keys and an instruction causing any server devices associated with an identifier key lying within the range referenced in the response request to provide a predefined response to the client device (1);b) using an interval bisection method to send further response requests to the default server address referencing different sub-ranges of the first range to search for a sub-range of the first range for which a response request referencing the sub-range causes a predefined response to be received from a server device without a collision; andc) assigning the responding server device (2a-c) to a unique server address.

2. The computer-implemented method of claim 1, further comprising repeating steps b) and c) until all server devices of the plurality of server devices (2a-c) have been assigned to respective unique server addresses.

3. The computer-implemented method of claim 1 or claim 2, wherein the interval bisection method comprises:bl) sending, by a client device (1), a series of response requests to the default server address until either a predefined response is received from a server device (2a-c) without a collision or no response is received from any server devices,wherein the first response request of the series of response requests references the first range and wherein each subsequent response request of the series of response requests references the first half of the range of identifier keys referenced in the previous response request of the series of response requests.

4. The computer-implemented method of claim 3, wherein the interval bisection method further comprises:based on no response being received for a response request, performing the step of:b2) sending a further series of response requests to the default server address until either the predefined response is received from a server device without a collision or no response is received from any server devices (2a-c), wherein the first response request of the further series of response requests includes a second half of a range of identifier keys for which the first half of the range has been previously searched, and wherein each subsequent response request of the further series of response requests references a first half of the identifier key range referenced in the previous response request of the further series of response requests.

5. The computer-implemented method of claim 4, wherein the interval bisection method further comprises:based on no response being received fora final request of the further series of response requests, repeating step b2) until the predefined response is received from a server device without a collision.

6. The computer-implemented method of any preceding claim, the method further comprising:maintaining a last-in-first-out, LIFO, container of identifier key ranges and sub-ranges that are to be searched, wherein the order of identifier key ranges and sub-ranges in the LIFO container determines the order in which identifier key ranges and sub-ranges are searched; andbased on receiving no response to a response request referencing a first identifier key range or sub-range, removing the first identifier key range or sub-range from the LIFO container, andbased on receiving an erroneous response to a response request referencing the first identifier key range or sub-range, replacing the first identifier key range or sub-range with second and third sub-ranges corresponding respectively to the first and second halves of the first identifier key range or sub-range.

7. The method of any preceding claim, wherein the communication protocol between the client device (1) and the plurality of server devices is (2a-c) configured such that more than one server device (2a-c) providing a predefined response to the client device (1) from the same server address within a firstperiod of time causes the client device to receive an erroneous response due to collision of the responses.

8. The method of any preceding claim, wherein the communication protocol used by the client device (1) and server devices (2a-c) is Modbus RTU and, preferably, using RS-485 signalling.

9. The method of any preceding claim, further comprising communicating with an individual client device (1) by sending communications using the unique server address assigned to the individual client device (1).

10. The method of any preceding claim, wherein the predefined response comprises the respective identifier key associated with the responding server device (2a-c).

11. The method of any preceding claim, wherein each server device (2a-c) is configured such that, based on receiving a response request referencing a range or sub-range of identifier keys containing the respective identifier key of the server device (2a), the respective server device (2a) provides the predefined response to the client device comprising the respective identifier key.

12. A computer-implemented method performed by a system comprising a client device (1) and a plurality of server devices (2a-c), wherein each server device (2a-c) is initialised to have the same default server address and wherein each server device (2a-c) is associated with a respective unique identifier key that belongs to a first range, the method comprising the following steps:a) sending, by the client device (1), a response request to the first server address, the response request referencing the first range of identifier keys and an instruction causing any server devices (2a-c) associated with an identifier key lying within the range referenced in the response request to provide a predefined response to the client device;b) using, by the client device (1), an interval bisection method to send further response requests to the default server address referencing different sub-ranges of the first range to search for a sub-ranges of the first range for which a response request referencing the sub-range causes a predefined response to be received from a server device (2a-c) without a collision; andc) assigning, by the client device (1), the responding server device (2a-c) to a unique server address.

13. A client device configured to perform the method of any of claims 1 to 10.

514. A system comprising a client device and a plurality of server devices, the system being configured to perform the method of any of claims 11 to 12.

15. The system of claim 14, wherein the client device is a charging point controller, 10 and the plurality of server devices are different EV charging points of an EVcharging station.19

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