Method for re-registering a smart electricity meter

A modem of a smart electricity meter obtains, following a registration in the powerline communication network of the ad hoc type, routing information and encryption information, by exchanges of messages in the powerline communication network. The smart electricity meter saves in non-volatile memory the routing information and the encryption information, the routing information being saved in association with information representing an instant at which the backup is made. At the time of a subsequent re-registration of the smart electricity meter following a disconnection of the powerline communication network, the smart electricity meter retrieves the routing and encryption information previously saved in the non-volatile memory, updates it by deleting any route information that is no longer valid, and uses it to communicate in the powerline communication network.

FIELD OF SOME EMBODIMENTS

The present invention relates to the re-registering of a smart electricity meter in a powerline communication network, following a disconnection of the smart electricity meter.

BACKGROUND

Powerline communication networks for systems of the AMM (automated meter management) type have made their appearance during the past years. Mention can be made for example of the PRIME (PowerLine Intelligent Metering Evolution) specifications and the G3-PLC standard specified in the ITU-T recommendation G.9903. In such powerline communication networks, communications are established between so-called smart electricity meters and a data concentrator device, sometimes referred to as a base node or coordinator, in order in particular to allow a remote automated reading of electricity consumption measurements made by said smart electricity meters. A plurality of such data concentrator devices are typically deployed geographically so as to distribute the management load at a distance from a multitude of smart electricity meters, each data concentrator device then being connected to the same management entity of the AMM system that is managed by the operator of the electrical supply system to which said smart electricity meters are connected.

A communication system comprising a data concentrator DC110to which a plurality of smart electricity meters C120are connected logically is illustrated schematically inFIG. 1. To make it possible to exchange data between smart electricity meters C120and the data concentrator device DC110, powerline communications are established. A powerline communication network101is thus formed between the data concentrator device DC110and the plurality of smart electricity meters C120that are connected thereto, relying on an electricity supply network100serving to supply electricity to the electrical installations that said smart electricity meters C120are responsible for monitoring. Thus the data concentrator device DC110and each smart electricity meter C120thus comprises a powerline communication interface111enabling it to communicate via the powerline communication network101. According to an example embodiment, the powerline communication network101is an ad hoc routing network, e.g. one in accordance with the G3-PLC standard.

Powerline communications must deal with interference related to crosstalk phenomena, and/or to a lack of reliability of certain communication links in the powerline communication network (e.g. limit of range due to the length of the cables), and/or noises of various natures (white noises, coloured noises, impulse noises mainly), and/or impedance mismatches. For the record, crosstalk is a phenomenon that enables signals, typically by capacitive coupling, to propagate without passing through copper pairs proper, but through non-visible parasitic links. This phenomenon is unstable since it may vary according to the temperature or the activity on the powerline communication network. It should be noted that there may also be crosstalk within the same apparatus via copper connections on printed circuits or certain components that constitute said apparatus. These phenomena may cause losses of packets or messages, in particular of signalling packets or messages, and cause disconnections of smart electricity meters from the communication network.

When a smart electricity meter is disconnected from an ad hoc powerline communication network, and this smart electricity meter seeks to reintegrate the ad hoc powerline communication network, a re-registration procedure is triggered, and the smart electricity meter must exchange a set of messages in order to fill in a routing table representing communication routes that can be used in the ad hoc powerline communication network. This aspect is illustrated schematically inFIG. 2, where a said smart electricity meter C120shows a modem part MDM251, managing the powerline communications, and an application part APP252, which uses the modem part MDM251to transmit application data in the powerline communication network101.

When the smart electricity meter C120is brought into service, in a step201, the application APP252sends a reset signal RESET to the modem MDM251, which consequently initialises itself. In a step202, the application APP252sends to the modem MDM251a signal DISCOV_RQ requesting network discovery.

In a step203, the modem MDM251discovers the powerline communication network101managed by the concentrator device DC110by means of a procedure referred to as bootstrap in the 6LoWPAN (the acronym for IPv6 Low Power Wireless Personal Area Network) terminology. In a step204, the modem MDM251acquires an address, referred to as a short address, S_ADDR that is allocated to it to identify the smart electricity meter C120in question in the powerline communication network101. The modem MDM251also obtains a network identifier PAN_ID that identifies the powerline communication network101as well as an encryption key GMK, which is itself encrypted by means of another encryption key OTP_PSK preconfigured in the modem MDM251, e.g. at the manufacture of the smart electricity meter C120, and derived from a key known to the concentrator device DC110. The encryption key GMK then serves for the modem MDM251to encrypt and decipher communications on the powerline communication network101. In a step205, the modem MDM251sends a signal OK to the application252in order to indicate that it has responded to the network discovery request.

Following exchanges of route discovery messages ROUTE_RQ (Route Request) and ROUTE_RSP (Route Reply) in steps206and207in the powerline communication network101, the modem MDM251updates a routing table RT that lists route information in the powerline communication network101, such as:A route destination address (the starting point being the smart electricity meter C120of said modem MDM251);An address of the next relay to be contacted for joining the route destination;Route cost information;Information on the number of relays, referred to as “hops”, on the route;Information on the number of weak links (below a certain performance threshold) on the route;Route-validity time-period information (e.g. time remaining before expiry of the route or instant of lapsing of the route).

Renewals of the encryption key GMK may be initiated, in a step208, by the concentrator device DC110. The modem MDM251then receives a new encryption key GMK, still encrypted by means of the encryption key OTP_PSK.

The procedure for re-registration in the powerline communication network101is therefore lengthy to execute, which delays the moment at which the smart electricity meter, which has been disconnected, is once again in the operational state.

It is desirable to overcome these drawbacks of the prior art and in particular to accelerate the return to the operational state of such smart electricity meters. It is furthermore desirable to find a solution that makes it possible to preserve a high level of security in the protection of sensitive information, such as the encryption keys, of the powerline communication network.

To this end, the invention relates to a method for re-registering a smart electricity meter in an ad hoc powerline communication network. The method is such that, following a registration in the powerline communication network during which a modem of the smart electricity meter has obtained routing information as well as encryption information by exchanges of messages in the powerline communication network, said electricity meter performs the following step: saving in non-volatile memory routing information and encryption information, the routing information being saved in association with information representing an instant at which the saving is performed. And, in a subsequent re-registration of the smart electricity meter following a disconnection from the powerline communication network, said electricity meter performs the following steps: retrieval of the routing and encryption information previously saved in the non-volatile memory; updating of the routing information by deleting therefrom any route information that has lapsed between the instant at which the saving is performed and an instant of retrieval, by the modem, of the saved routing information; and use, by the modem for communicating in the powerline communication network, of the encryption information retrieved and the routing information updated.

According to a particular embodiment, the routing information comprises an address allocated to said smart electricity meter for identifying said smart electricity meter in the powerline communication network and a routing table describing routes in said powerline communication network, each route being associated with time validity information, and the updating of the routing information relates to the deletion of each route the associated time validity information of which after updating shows lapsing of said route.

According to a particular embodiment, said smart electricity meter saves in non-volatile memory the routing table on deletion of one or more routes from the routing table used by the modem for communicating in the powerline communication network, and on addition of one or more routes in said routing table used by the modem for communicating in the powerline communication network.

According to a particular embodiment, said smart electricity meter saves the routing table in non-volatile memory at regular intervals.

According to a particular embodiment, the encryption information comprises an encryption key used by the modem for communicating in an encrypted manner in the powerline communication network.

According to a particular embodiment, the encryption key is saved in non-volatile memory in an encrypted manner.

According to a particular embodiment, said smart electricity meter saves the encryption key in non-volatile memory on reception of a message renewing said encryption key.

According to a particular embodiment, when the updating of the routing information shows that said routing information has all lapsed, the modem performs the re-registration by exchanges of messages in the powerline communication network in order to re-obtain the routing information and the encryption information.

According to a particular embodiment, the smart electricity meter implementing a mechanism for checking the presence of a communication link governing the status of the state of the powerline communication network, the modem performs the re-registration by exchanges of messages in the powerline communication network in order to re-obtain the routing information and the encryption information when the status of the state of the powerline communication network has lapsed.

According to a particular embodiment, the smart electricity meter comprises an application, as well as: a unit controlling the application; a unit controlling the modem; a non-volatile memory accessible to the unit controlling the application but not to the unit controlling the modem; and a volatile memory accessible to the unit controlling the modem but not to the unit controlling the application. In addition, the routing information and the encryption memory are saved in non-volatile memory by the unit controlling the application on behalf of the unit controlling the modem, and the unit controlling the modem uses the volatile memory for storing and updating the routing information and the encryption information used by the modem for communicating in the powerline communication network.

The invention also relates to a smart electricity meter intended to be used in an ad hoc powerline communication network. The smart electricity meter is such that, following a registration in the powerline communication network during which a modem of the smart electricity meter has obtained routing information and encryption information by exchanges of messages in the powerline communication network, said electricity meter implements the following means: means for saving in non-volatile memory routing information and encryption information, the routing information being saved in association with information representing an instant at which the saving is performed. And, at the time of a subsequent re-registration of the smart electricity meter following a disconnection of the powerline communication network, said electricity meter implements the following means: means for retrieving routing and encryption information previously saved in the non-volatile memory; means for updating the routing information by deleting therein any route information that has lapsed between the instant at which the saving is performed and an instant of retrieval, by the modem, of the routing information saved; means for using, by the modem, for communicating in the powerline communication network, the encryption information retrieved and the routing information updated.

According to a particular embodiment, the smart electricity meter comprises an application, as well as: a unit controlling the application; a unit controlling the modem; a non-volatile memory accessible to the unit controlling the application but not to the unit controlling the modem; and a volatile memory accessible to the unit controlling the modem but not to the unit controlling the application. In addition, the routing information and the encryption information are saved in non-volatile memory by the unit controlling the application on behalf of the unit controlling the modem, and the unit controlling the modem uses the volatile memory for storing and updating the routing information and the encryption information used by the modem for communicating in the powerline communication network.

The invention also relates to a computer program that can be stored on a medium and/or downloaded from a communication network in order to be read by a processor. This computer program comprises instructions for implementing the method mentioned above in accordance with any one of the embodiments thereof when said program is executed by the processor. The invention also relates to storage means comprising such a computer program.

DETAILED DESCRIPTION

The invention detailed below is implemented in a powerline communication network that is an ad hoc routing network, e.g. in accordance with the G3-PLC standard, such as the powerline communication network101. According to a preferred embodiment, the powerline communication network is in accordance with the G3-PLC standard.

FIG. 3illustrates schematically an internal arrangement of a smart electricity meter C120, according to an embodiment of the present invention. The modem MDM251of the smart electricity meter C120comprises a control unit MMCU330and the application APP252comprises a control unit AMCU320. The modem MEM251and the application APP252communicate by means of the respective control units thereof.

The control unit AMCU320is associated with a non-volatile memory ANVM310, such as a flash memory. The non-volatile memory ANVM310comprises memory areas intended to store a keychain KSTORE311wherein an encrypted version C_GMK of the encryption key GMK is included. The encrypted version C_GMK of the encryption key GMK is determined by the modem MDM251and is saved in the non-volatile memory ANVM310by the application APP252on behalf of the modem MDM251. This aspect is described below.

The non-volatile memory ANVM310also comprises memory areas intended to save routing information used by the modem MDM251to communicate in the powerline communication network101. These backups preferentially include a saved copy315of the routing table RT, as well as a saved copy of the address S_ADDR314allocated to said smart electricity meter C120for identifying said smart electricity meter C120in the powerline communication network101. These backups preferentially also include a saved copy313of the identifier PAN_ID of the powerline communication network101. This routing information is thus saved in the non-volatile memory ANVM310by the application APP252on behalf of the modem MDM251. This aspect is also described below.

The backups made in the non-volatile memory ANVM310by the application APP252on behalf of the modem MDM251aim to enable the smart electricity meter C120to re-register quickly in the powerline communication network101, as detailed below.

The control unit MMCU330is associated with a volatile memory MVM340, such as a random access memory RAM. The volatile memory MVM340is, by structure of the smart electricity meter C120, inaccessible for the control unit AMCU320. The volatile memory MVM340comprises memory areas intended to store the encryption key GMK, preferably in encrypted form PGMK341in order to avoid being legible in clear by dumping of the volatile memory MVM340. The encrypted version of the encryption key GMK stored in the volatile memory MEM340is obtained by the modem MDM251by encryption by means of an encryption key, referred to as the secret key, preconfigured (like the encryption key OTP_PSK) in the control unit MMCU330and therefore not accessible to the control unit AMCU320.

The volatile memory MVM340also comprises memory areas intended to store the routing information used by the modem MDM251to communicate in the powerline communication network101. Thus the volatile memory MVM340preferentially comprises memory areas for:storing the routing table RT345that the modem MDM251uses for selecting routes in the powerline communication network101; andstoring the address S_ADDR343that the modem MDM251uses as an identifier for communicating in the powerline communication network101.

Preferentially, the volatile memory MVM340preferentially comprises a memory area for in addition:storing the identifier PAN_ID342in the powerline communication network101.

The data stored in the volatile memory MVM340are continually used by the modem MDM251for communicating in the powerline communication network101until the smart electricity meter C120in question is disconnected therefrom.

It should be noted that the control unit MMCU330is provided with a real-time clock RTC enabling the modem MDM251to have available an absolute time reference, that is to say a time reference that remains consistent after disconnection and subsequent re-registration of the electricity meter C120in question in the powerline communication network101. This means that, on re-registration in the powerline communication network101, the smart electricity meter C120in question is directly synchronised in time with the other devices, namely the concentrator device DC110and the other smart electricity meters C120, which makes it possible to avoid any desynchronisation of a mechanism checking the presence of a communication link of the “keep alive” type governing the status of the state of the powerline communication network101.

FIG. 4illustrates schematically an example of hardware architecture of a control unit of a smart electricity meter C120, such as the control unit AMCU320and the control unit MA/ICU330.

The smart electricity meter C120in question then comprises, connected by a communication bus410: a processor or CPU (central processing unit)401, a random access memory RAM402, for example the memory MVM340; a read only memory ROM403; a storage unit404, such as a hard disk HDD (hard disk drive), or a storage medium reader, such as an SD (Secure Digital) card reader; a set of inputs/outputs405enabling the control unit to communicate with other units and/or memories and/or components of the smart electricity meter C120.

The processor CPU401is capable of executing instructions loaded in the RAM memory402from the ROM memory403, from an external memory (not shown), from a storage medium (such as an SD card), or from a communication network other than the powerline communication network101. When the smart electricity meter C120in question is powered up, the processor201is capable of reading instructions from the RAM memory202and executing them. These instructions form a computer program causing an implementation, by the processor201, of all or some of the algorithms and steps described below in relation to the control unit concerned.

All or some of the algorithms and steps described below can be implemented in software form by the execution of a set of instructions by a programmable machine, for example a DSP (digital signal processor) or a microcontroller, or be implemented in hardware form by a machine or a dedicated component, for example an FPGA (field-programmable gate array) or an ASIC (application-specific integrated circuit).

In general terms, each control unit of the smart electricity meter C120thus comprises electronic circuitry configured to implement all or some of the algorithms and steps described below in relation to the control unit concerned.

FIG. 5illustrates schematically an algorithm for commissioning a smart electricity meter C120according to one embodiment of the present invention.

In a step501, the smart electricity meter C120is brought into service and detects the presence of the powerline communication network101. The smart electricity meter C120then seeks to integrate or reintegrate, following a disconnection, the powerline communication network101.

In a step502, the modem MDM251seeks to retrieve from the application APP252any identifier PAN_ID that had previously been saved by the application APP252on behalf of the modem MDM251. If such an identifier PAN_ID was previously saved by the application APP252, this means that the smart electricity meter C120was previously connected to the powerline communication network101and was disconnected therefrom. Otherwise this means that it is the very first commissioning of the smart electricity meter C120.

In a step503, the modem MDM251checks whether the application APP252has supplied the identifier PAN_ID sought. If such is the case, a step508is performed; otherwise a step504is performed.

In the step504, the modem MDM251performs a registration in the powerline communication network101, as could have been dealt with in relation toFIG. 1. Thus, in the step504, the modem MDM251obtains the address S_ADDR allocated by the concentrator device DC110to said smart electricity meter C120, and as well as the encrypted version C_GMK of the encryption key GMK. The modem MDM251deciphers, by means of the key OTP_PSK, the encrypted version C_GMK of the encryption key GMK so as to obtain the encryption key GMK. With a view to a storage in the volatile memory MVM340, the modem MDM251can regenerate a new encrypted version of the encryption key GMK, as already mentioned, using its secret key.

In a step505, the modem MDM251effects a discovery of routes in the powerline communication network101. Thus, in a step506, by virtue of the discovery of routes, the modem MDM251fills in its routing table RT.

The routing information and the encryption information thus obtained by the modem MDM251in the steps504and506are stored by the modem MDM251, as already described in relation toFIG. 3, and are in particular used by the modem MDM251to transmit and receive application data on behalf of the application APP252in the powerline communication network101.

In a step507, the application APP252saves, in the non-volatile memory ANVM310, the routing information and the encryption information on behalf of the modem MDM251, as already described in relation toFIG. 3. This backup may be at the initiative of the modem MDM251or of the application APP252, and serves for any subsequent re-registration of the smart electricity meter C120in the powerline communication network101. This backup also includes time information T representing the instant at which the backup is made; this time information makes it possible to update the temporal validity of the routes entered in the routing table RT at the moment of any subsequent re-registration of the smart electricity meter C120, as described below. The algorithm inFIG. 5is then ended.

In the step508and in a step509, the modem MDM251retrieves, by means of the application APP252, the routing information and the encryption information previously saved by the application APP252in the non-volatile memory ANVM310on behalf of the modem MDM251. More particularly, in the step508, the modem MDM251obtains the address S_ADDR previously allocated by the concentrator device DC110to said smart electricity meter C120, as well as the encrypted version C_GMK of the encryption key GMK. The modem MDM251deciphers, by means of its secret key, the encrypted version C_GMK of the encryption key GMK so as to obtain the encryption key GMK. With a view to storage in the volatile memory MVM340, the modem MDM251can regenerate a new encrypted version of the encryption key GMK, as already mentioned. In addition, in the step509, the modem MDM251obtains its routing table RT, as saved by the application APP252.

Then, in a step510, the modem MDM251performs a temporal updating of the routing table RT retrieved by means of the backup made by the application APP252on behalf of the modem MDM251. In other words, the modem MDM251deletes from this routing table RT the routes that are no longer valid. For example, the routing table RT includes information on the remaining time of validity of each route described in said routing table RT. This information on the remaining validity time is continuously updated by the modem MDM251over time, and at re-registration the modem MDM251takes account of a time D between the instant at which the backup was made by the application APP252(represented by the aforementioned time information T) and the instant at which the routing information (and more particularly the routing table) saved is retrieved by the modem MDM251. The modem MDM251then deducts the time D from the information on remaining validity time of each route entered in the routing table RT retrieved. If this gives a zero or negative result, the modem MDM251deletes the corresponding route from the routing table RT; otherwise the modem MDM251updates the information on remaining validity time with the result obtained.

At the end of the step510, the routing information and the encryption information thus obtained by the modem MDM251are stored by the modem MDM251, as already described in relation toFIG. 3, and are in particular used by the modem MDM251in order to transmit and receive application data on behalf of the application APP252in the powerline communication network101.

When performance of the step510leads to an updated routing table RT that is empty of any route, a new routing table must be constructed. This can be done by exchanges of the route discovery messages ROUTE_RQ and ROUTE_RSP of the steps206and207. In a particular embodiment, a complete re-registration of the smart electricity meter C120in question is performed, as if it were the very first registration of said smart electricity meter C120in the powerline communication network101.

In addition, in a particular embodiment, when the mechanism for checking the presence of a communication link of the “keep alive” type shows, when said smart electricity meter C120is recommissioned, that the status of the state of the powerline communication network101is no longer valid, then a complete re-registration of the smart electricity meter C120in question is performed, as if it were the very first registration of said smart electricity meter C120in the powerline communication network101.

FIG. 6illustrates schematically an algorithm for saving routing information, in accordance with an embodiment of the invention.

In a step601, the modem MDM251detects a need to update the routing table RT currently being used, by adding or deleting one or more routes. One or more routes are thus added or removed from the routing table RT used by the modem MDM251.

In a step602, the modem MDM251accordingly updates the routing table RT stored in the volatile memory MVM340.

In a step603, the modem MDM251requests the application APP252to perform a backup, in the non-volatile memory ANVM310, of the routing table RT thus updated, as well as time information T representing the instant at which the backup is made.

Thus the routing information is saved whenever there is a change of route in the routing table RT used by the modem MDM251.

In a variant or in addition, the saving of the routing table RT in non-volatile memory is done periodically. The time information T representing the instant at which the saving is done is also saved on this occasion. This periodic saving can be initiated by the modem MDM251or by the application APP252.

FIG. 7illustrates schematically an algorithm for saving encryption information, according to an embodiment of the present invention.

In a step701, the modem MDM251receives a message coming from the concentrator device DC110indicating a renewal of the encryption key GMK. A new encryption key GMK is then supplied by the concentrator device DC110, this new encryption key being encrypted by means of the secret key of the modem MDM251. The modem MDM251updates the relevant memory area of the volatile memory MVM340accordingly.

In a step702, the modem MDM251requests the application APP252to make a backup, in the non-volatile memory ANVM310, of the encrypted version C_GMK of the encryption key GMK.

FIGS. 8 and 9illustrate schematically exchanges occurring when a smart electricity meter C120is commissioned, according to an embodiment of the present invention.FIG. 8shows the exchanges between the smart electricity meter C120in question and the concentrator device DC110in the case of a very first registration in the powerline communication network101, or at the time of a re-registration, in the event of the previously saved routing table RT no longer being valid.FIG. 8repeatsFIG. 1, and the steps common to the two algorithms bear the same respective references in both FIGS.

When the modem MDM251obtains the identifier PAN_ID, the address S_ADDR that is allocated to it for communicating in the powerline communication network101, and the encryption key GMK, a saving in the non-volatile memory ANVM310is performed in a step801. A message SAV1_RQ from the modem MDM251to the application APP252including the information to be saved is used to do this. This message SAV1_RQ may in a variant be merged with the message OK of the step205.

When the modem MDM251updates the routing table RT following the exchanges of route discovery messages ROUTE_RQ and ROUTE_RSP in the steps206and207, a saving in the non-volatile memory ANVM310is performed in a step802. A message SAV2_RQ from the modem MDM251to the application APP252including the information to be saved is used to do this.

When a renewal of the encryption key GMK is performed, a saving in the non-volatile memory ANVM310is made thereof in encrypted form in a step803. A message SAV3_RQ from the modem MDM251to the application APP252including the information to be saved is used to do this.

Thus, at the time of any subsequent re-registration of the smart electricity meter C120in the powerline communication network101, the modem MDM251has routing and encryption information that can allow a rapid return to the operational state of the smart electricity meter C120in the powerline communication network101.

FIG. 9shows the exchanges between the smart electricity meter C120in question and the concentrator device DC110in the case of re-registration in the powerline communication network101. Following the step201, a message RETRIEVE is transmitted in a step901from the application APP252to the modem MDM251. This message RETRIEVE contains the routing and encryption information previously saved by the application APP252in the non-volatile memory ANVM310on behalf of the modem MDM251. If the processing of this routing information by the modem MDM251shows that said routing data are no longer valid, then the modem MDM251informs the application APP252thereof and the exchanges inFIG. 8are made in order to re-obtain the routing and encryption information via the powerline communication network101.

The above description takes account of a certain current hardware architecture of the smart electricity meters. More particularly, the above description takes account of the fact that the current smart electricity meters have available a non-volatile memory allocated to the control unit responsible for application questions and a volatile memory allocated to the questions of management of the MAC (medium access control) layer. A variant consists however of allocating a non-volatile memory to the modem MDM251to enable said modem MDM251to make the aforementioned backups without having recourse to the application APP252.

In a particular embodiment, when the smart electricity meter C120is disconnected from the powerline communication network101but said smart electricity meter C120remains electrically supplied (e.g. by a backup supply source), the routing information is saved in non-volatile memory so as to save the most recent information held.