Abstract:
An improved method of allocating MAC addresses for an electrical distribution network to make it possible to save a great deal of time during the address allocation phase. The method stores, at the central address allocation device, a list of associations between the serial numbers of the devices and the MAC address allocated. The method also sends a cataloging request serving to allocate the MAC address prior to the sending of a communication frame. In this manner, the discovery phases for allocating the MAC addresses to devices without addresses are appreciably reduced. The time when the network is dedicated to such discovery is reduced, thereby increasing accordingly the useful communication time available in the network.

Description:
This application is the U.S. national phase of International Application No. PCT/EP2009/056501, filed 28 May 2009, which designated the U.S. and claims priority to French Application no. 08/53604, filed 2 Jun. 2008, the entire contents of each of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns the field of the allocation of communication addresses to devices connected to a powerline communication network. More particularly, these are networks of electric meters remotely read from a data concentration apparatus through the electrical network. 
     2. Description of Related Art 
     Remotely reading data on electric meters operating on the electrical network is known. This is generally done by equipment performing the readings and making up a summary for a computer network, for example the invoicing network of the electrical energy distribution operator. This apparatus is known by the term DC (standing for Data Concentrator). 
     In order to be remotely read, the meters are provided with a communication interface on the carrier current. This interface has in memory the serial number engraved on the apparatus. This number constitutes a unique permanent identification of each meter. 
     Communication on the carrier current is performed by means of modulated data frames on the cables of the electrical energy distribution network. These frames, an example of which can be seen in  FIG. 4 , consist of a preamble for identifying the frame  4 . 1 , a part  4 . 2  constituting strictly speaking the transported data packet and a checksum  4 . 3  for checking the integrity thereof, for example by means of a CRC (Cyclic Redundancy Code). The destination of the frame is selected by means of an address, referred to as an MAC address, coded in 12 bits and allocated to each device that is to communicate with the network. Details concerning the format of these frames can be found in French Standard NF EN 61334-5-1 entitled “Distribution automation using distribution line carrier systems—Part 5-1: Lower layer profiles—The spread shift keying (S-FSK) profile”, which completely reproduces the publication CEI 61334-5-1:2001. 
     In order to be able to communicate, a device connected to the electrical distribution network must therefore be allocated an MAC address. The allocation of these addresses is described in the French Standard NF EN 61334-4-511 entitled “Distribution automation using distribution line carrier systems—Part 4-511: Data communication protocols—System administration—CIASE protocol”, which completely reproduces the publication CEI 61334-4-511:2001. This protocol enables a central device of the system to allocate MAC addresses to all the devices connected to the network. The method described involves numerous discovery phases that take up a great deal of time, the connection rate being low. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention aims to propose an improved method of allocating MAC addresses for this type of network making it possible to save a great deal of time during the address allocation phase. This method proposes in particular to store, at the central address allocation device, a list of associations between the serial numbers of the devices and the MAC address allocated. It is also proposed to send a cataloguing request serving to allocate the MAC address prior to the sending of a communication frame. 
     In this way, the discovery phases for allocating the MAC addresses to devices without addresses are appreciably reduced. The time where the network is dedicated to such discovery is reduced thereby, increasing accordingly the useful communication time available in the network. 
     The invention concerns a method of allocating addresses known as MAC addresses to devices connected to an electricity distribution network by a data concentration apparatus, each device being provided with a distinct unchanging serial number, comprising a step of sending a request demanding discovery in general broadcast mode on the network, a step of receiving at least one discovery notification in response to this request coming from a device that does not have an allocated MAC address, the said device being identified by means of its serial number; a step of allocating an available MAC address to the device that replied; a step of sending a cataloguing request to the device that replied containing its serial number and the MAC address that was allocated to it and also comprising a step of storing the association between the serial number of the device and the MAC address that it allocated to it. 
     According to particular embodiment of the invention, the device being liable to lose the MAC address that was allocated to it after the elapse of a given time without communication, the method also comprises a step of sending a cataloguing request prior to the sending of a communication frame to the device. 
     According to a particular embodiment of the invention, the step of sending the registration frame prior to the sending of a communication frame is performed routinely for each sending of a communication frame. 
     According to a particular embodiment of the invention, the moment of the last sending of a communication frame to a device being stored, the step of sending the cataloguing request prior to the sending of a communication frame is performed only if the time since the last communication frame exceeds a given threshold. 
     According to a particular embodiment of the invention, the method also comprises a step of sending a cataloguing request to every device the association of which is stored during a phase of re-initialisation of the system. 
     According to a particular embodiment of the invention, the method also comprises a step of periodic sending of a request to demand discovery in general broadcast mode to enable an MAC address to be allocated to new devices that have appeared on the network. 
     According to a particular embodiment of the invention, the discovery demand requests comprising a first parameter defining a response percentage, the devices not having an MAC address allocated taking a response decision in accordance with a random draw with a probability of response equal to this first parameter, the first parameter is defined with a probability of one hundred percent. 
     According to a particular embodiment of the invention, the discovery demand requests comprise a second parameter defining a response window, the devices responding to this request having to define randomly a response time within this response window, this window being defined as less than 30 seconds. 
     According to a particular embodiment of the invention, the discovery demand requests comprising a second parameter defining a response window, the devices responding to this request having to randomly define a response time within this response window, this second parameter is calculated according to the number of devices that have replied and the number of collisions detected during a previous discovery step. 
     The invention also concerns a device for allocating addresses, referred to as MAC addresses, to devices connected to an electricity distribution network, each collected device being provided with a distinct unchangeable serial number, comprising means of sending a discovery demand request in general broadcast mode over the network; means of receiving at least one discovery notification in response to this request coming from a device that does have an MAC address allocated, the said device being identified by means of its serial number; means of allocating an available MAC address to the device that has responded, means of sending a cataloguing request to the device that has responded containing its serial number and the MAC address that has been allocated to it; the device also comprises means of storing the association between the serial number of the device and the MAC address that it has allocated to it. 
     According to a particular embodiment of the invention, the device being liable to lose the MAC address that was allocated to it after the elapse of a given time without communication, the device also comprises means of sending a registration frame prior to the sending of a communication frame intended for the device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features of the invention mentioned above, as well as others, will emerge more clearly from a reading of the following description of an example embodiment, the said description being given in relation to the accompanying drawings, among which: 
         FIG. 1  illustrates the architecture of an example of an electrical distribution network; 
         FIG. 2  illustrates the sequencing of the exchange of requests during a discovery and communication phase according to an example embodiment of the invention; 
         FIG. 3  illustrates the architecture of the MAC address allocation device according to an example embodiment of the invention; 
         FIG. 4  illustrates the frame format used in the system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  describes an example of an electrical energy distribution network  1 . 2 . A first device  1 . 1  serving as a data concentrator is connected to this network. In the example embodiment of the invention, this device  1 . 1  also has the function of a CIASE client within the meaning of NF EN 61334-4-511, that is to say this device will also be responsible for the allocation of MAC addresses to the devices connected to the network. A certain number of these devices are illustrated under the reference  1 . 3 . Typically, these devices are meters, C 1  to CN, used to meter the quantity of electrical energy consumed by each subscriber. Although described as electricity meters, these, devices can be of any type insofar as they are caused to communicate with the device DC  1 . 1 . In the context of the example embodiment, the DC is responsible for collecting the consumption data from the meters  1 . 3  in order to feed an information system of the operator managing the energy distribution network. 
     In this system, each device is provided with an unchangeable serial number for distinguishing it uniquely on the network. This number is called system_title in the aforementioned standard. It also contains an MAC address field initialised to the value NEW when the system is initialised. This value indicates that the device is new on the network and that it does not have an MAC address allocated, and it will be said that this device is in the non-allocated state. 
     In order to be able to communicate on the network, any device must be allocated an MAC address. This is because the addressing of the destination of a communication frame is done by means of this address. A procedure of discovering the devices connected is necessary in order to allocate this address to them. This procedure is described in the CIASE standard already mentioned. It consists, for the device responsible for allocating the addresses, of sending a so-called search demand request. It should be noted here that the discovery phase is initiated by the DC just like any communication in the network. In this type of network, the communications are never at the initiative of a connected device, but always at the initiative of the central server. This request is sent in general broadcast mode, that is to say it is intended for all the devices connected to the network. Only the devices in the non-allocated state and therefore having an MAC address field at NEW will respond to this request by a search notification indicated their serial number. The MAC address allocation device, here the DC, allocates an address to them and responds by means of a cataloguing request containing the serial number of the device that replied and the MAC address that is allocated to it. The device receiving this request and recognising its serial number in the request then gives its MAC address field with the associated MAC address. It is then in the allocated state and can consequently communicate on the network. In this document the operation consisting, for the allocation device, of sending a discovery demand request, receiving all the responses to this request, allocating MAC addresses to the devices that have responded and sending the corresponding cataloguing messages to the device in order to allocate their MAC address to them, is called the discovery phase. 
     It should be noted that these communications are carried out at 1200 baud and therefore take a great deal of time. Moreover, as soon as the number of devices that are to be allocated increases, the risk of collision between the various search notifications sent by all these devices increases significantly. It is then necessary to reiterate their discovery phases until all the devices have been able to be allocated. The standard provides for two mechanisms for assisting the discovery phase management in the networks containing a large number of devices to be discovered. These mechanisms are based on two parameters that can be used in the discovery demand request. The first parameter is a response percentage represented by an integer between 1 and 100. When the discovery demand is received, a non-allocated device will draw at random an integer number between 1 and 100 and if this number is less or equal to the response probability parameter it takes the decision to respond. It can be seen that by this mechanism it is possible to define the percentage of devices that have to be allocated and that will respond to a given discovery demand request. It is thus possible to limit the number of devices that will attempt to respond and therefore collisions between these responses. It will be understood that, the more this response percentage is limited, the more it is necessary to increase the discovery phases so that all the devices are allocated. 
     The second mechanism is based on a second parameter in the discovery demand request which defines a time window for the response. The time is counted in slots, these slots typically lasting for 300 milliseconds. The time window parameter defines a number of slots in 15 bits allocated to the responses of the devices. It can be seen that the time window can be defined up to a period of approximately 3 hours. When a device is to be allocated, it draws a random number that enables it to position its response in time within the time window thus defined. This mechanism makes it possible to spread in time the responses of the devices that are to be allocated within this time window. These two mechanisms therefore make it possible firstly to reduce the number of devices that are to respond and secondly to distribute these responses over time in order to limit collisions. 
     Despite the use of these mechanisms, as soon as the number of the devices that are to be allocated is around a thousand, the discovery involves numerous discovery phases using a low response probability and long time window, which may last for several hours, or even exceed one day of discovery. During this time, the network cannot be used usefully for operations of remote reading of the meters. 
     It should be noted that, at each re-initialisation of the system, all the devices are in a non-allocated state. Re-initialisation then requires a complete discovery of the network. Moreover, discovery procedures must be carried out very regularly in order to make it possible firstly to allocate an address to any new devices that may have been connected to the network and secondly to reallocate an address to any devices that may have lost their address because of the mechanism causing loss of the MAC address after a given time without communication. 
     Moreover, once a certain time has passed without communication, the devices lose their MAC address. This time is typically 12 hours. When the discovery lasts for more than 12 hours, the first devices allocated lose their address and are non-allocated before the end of the discovery. This procedure then never ends. 
     To overcome these problems, the invention proposes storing, at the MAC address allocation device, the addresses allocated to the devices. This storage takes place, for example, in the form of a list of associations between the serial numbers of the devices and the MAC address allocated. In this way, the discovery procedure is initialised by a sending of cataloguing requests to all the devices stored. Once this sending has taken place, it is possible to perform a conventional discovery procedure. It is thus ensured that a small number of devices will have been allocated during this discovery phase. More precisely, only the new devices appearing on the network will have to be allocated. This number being more restricted apart from major modifications to the network, it is then possible advantageously to position the response probability parameter at 100, thereby enabling all the non-allocated devices to respond. Advantageously, also, time windows of short duration will be used. Typically, a time window of around fifteen seconds enabling approximately 25 devices to respond can be used instead of windows lasting typically many minutes. In any event, it will be possible to use time windows of less than 30 seconds. 
     Advantageously, the storage mechanism makes it possible to implement a mechanism consisting of sending a cataloguing request to a device prior to the sending of a communication frame. In this way, the fact that the device may have lost its MAC address is guarded against. This is because the device receiving a cataloguing request will re-initialise its MAC address if it has lost it. It is then in a position to receive the communication frame. This re-initialisation of the MAC address takes place independently of the discovery mechanism. The periodicity of the discovery procedures can then be reduced since they then serve only for the discovery of new devices connected to the network. 
     Advantageously, this cataloguing request is sent systematically prior to the sending of all the communication frames. It is then ensured that the communication frame is intended for the allocated device. 
     Alternatively, it is also possible to store the moment of the last communication with each device. It is then possible to limit the prior sending of the cataloguing request to the devices with which the DC has not communicated for a given time, generally corresponding to the time after which the device loses its MAC address. The number of cataloguing requests that have to be sent is then limited. 
     Advantageously, it may be sought to determine the number of collisions occurring in response to the sending of a discovery demand request. A collision is detected when the DC receives a correct preamble but the checksum is wrong. It is deduced from this that at least one other response has disturbed the sending of the first. If the number of collisions is high, it is possible either to increase the response time window or decrease the response probability, or both, to enable a large number of devices to respond. 
       FIG. 2  illustrates the message exchanges according to an example embodiment of the invention. The DC sends a discovery demand request  2 . 1 , which is received by the devices C 1 , C 2  and C 3 . In the example sketched, only C 2  is non-allocated and responds with a discovery notification  2 . 2  to the DC. The latter then allocates to it an MAC address, which it stores, and sends to it a cataloguing request  2 . 3  containing its serial number and its allocated MAC address. During a communication, the DC once again sends a prior cataloguing request  2 . 4  to the communication frame  2 . 5  in order to ensure that the device C 2  is allocated prior to the communication and therefore in a position to receive the communication frame. 
       FIG. 3  illustrates an example of architecture of the MAC address allocation device according to the invention  3 . 1 . This device is connected to an electrical energy distribution network  3 . 7 . It has a processor  3 . 3  for implementing the previously described method. It also has a memory  3 . 4  containing a means  3 . 5  of storing the association between the serial numbers and the MAC addresses of the devices. This means is for example a list of associations. The processor and the memory communicate by means of a communication bus  3 . 6 , which also affords communication with the carrier code communication interface  3 . 2  connected to the network  3 . 7 .