Abstract:
A method of synchronizing state information of a home wireless system wherein the home wireless system comprises a plurality of peripheral wireless nodes ( 14; 16; 19; 21; 23 ) and a first gateway ( 12 ) having wireless communication means for communicating with and controlling associated peripheral wireless nodes, the method comprising the steps installing at least one second gateway ( 26 ) in said home wireless system, assigning peripheral wireless nodes to said first gateway ( 12 ) or anyone of said at least one second gateway ( 12 ′), and each gateway directing each assigned peripheral wireless node to communicate with an assigned gateway, receiving in a first gateway system state affecting input message from an associated peripheral wireless node, determining in said first gateway a resulting system state based on said input, and communicating said resulting system state as a state change message from said first gateway to said at least one second gateway.

Description:
RELATED APPLICATIONS 
     This application is a 35 U.S.C. 371 national stage filing from International Application No. PCT/EP2013/054760 filed Mar. 8, 2013 and claims priority to European Applications Nos. 12159019.4 filed Mar. 12, 2012 and Ser. No. 12/195,592.6 filed Dec. 5, 2012, the teachings of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The invention relates to a method and a device for controlling a home wireless system. The home wireless system in general can be any type of wireless system comprising a plurality of peripheral wireless nodes, such as an intruder alarm. Specifically it can be a security system having a plurality of wireless detectors sensitive to the presence or passage of persons and objects communicating with a gateway. 
     PRIOR ART 
     Home wireless systems in general comprise a plurality of wireless nodes that can be connected to a communication system through a node control unit or a control panel. An application of home wireless systems is alarm systems. Security and alarm systems used today normally comprise a control panel also referred to as a gateway that is connected to a central station, either by a telephone line or by a wireless telecommunications system such as GSM or other radio frequency systems. The connection also can be through the internet. The gateway can be provided with input means or be activated and controlled by control device such as a keypad which can be a wireless remote device. 
     The alarm system can be armed in different ways and into different alarm system states, such as “Disarmed”, “Armed Home” and “Armed Away”. If the system is set to “Disarmed” it will not alarm to perimeter or interior detectors. Still, fire detectors, other gas detectors, flooding events, power break down events and similar detectors normally will be armed also in the “Disarmed” state. If the alarm system is set to a first armed state referred to as “Armed Home” the alarm system will generate an alarm at the occurrence of a breach of a first group of selected detectors such as perimeter detectors and selected interior detectors, but not to a breach of the interior detectors in general. If the system is set to a second armed state referred to as “Armed Away” it will alarm to a breach of the perimeter or interior detectors and normally to all types of detectors. 
     The state of the system is determined by the needs of the occupants of the premises. If all of the occupants are leaving the premises then the alarm system should be set to “Armed Away”. If the occupants will be staying within the premises for an extended period of time then the alarm system can be set to “Armed Home”. This alarm setting can be appropriate for instance when the occupants are sleeping within the premises or are staying within a defined part thereof. For other scenarios the alarm system should be set to “Disarmed”. 
     In the “Armed Home” state a selected group of detectors is armed. In various embodiments the selected group of detectors includes the perimeter detectors and interior detectors covering sections of the premises that are not used by the occupants. Each installation can be set up with different detectors included in the selected group. 
     A prior art alarm system is disclosed in U.S. Pat. No. 6,895,082 and comprises one alarm unit in combination with a line seize module. The alarm unit includes a transmitter/receiver, a control panel function, a key pad, an input/output port connected to a telephone line and an auto dialer for normally communicating with a remote monitoring station over the public switched telephone network. 
     Another alarm system including a camera device is disclosed in U.S. Pat. No. 6,570,496. In this system a premise-protecting control panel communicates with a sensor, providing a message in some or all cases of sensor signals. A remote receiver receives the messages of the control panel. A camera device is combined with the sensor for acquiring video data that allows further analysis into the matter of a given sensor-detected event. 
     US20060132303 discloses an RFID security network using system component diversity and system spatial diversity. The security network includes a plurality of network base units, each communicating with a plurality of transponders, or security transmitters. Through appropriate distributive placement of the plurality of base units, along with appropriate placement of the transponders, the redundancy and reliability of the RF communication links between one or more base units and one or more transponders is increased. 
     U.S. Pat. No. 8,022,843 discloses a wireless sensor network in an aircraft. A plurality of wireless sensors is provided together with a plurality of wireless routers. Multiple routers may send data to one gateway to provide redundancy. Signals from sensors can be routed through different routers to reach a gateway. 
     Within any one security network in accordance with US20060132303, and at any one particular time, there will generally be only one base unit whose controller function has been assigned to be the master controller for that security′ network. All other controller functions within other base units will generally be slaved to the master controller. The base unit whose controller function is presently the master controller may sometimes be termed the master controller. The term gateway in the document refers to the functional capability of a base unit that includes a telecom interface. Each base unit can communicate with at least one other base unit and is capable of routing. Each base unit has a unique address. 
     When there are multiple controller functions installed in a single security network in accordance with US20060132303, the controller functions arbitrate among themselves to determine which controller function shall be the master controller for a given period of time. The preferred arbitration scheme consists of a periodic self-check test by each controller function, and the present master controller may remain the master controller as long as its own periodic self-check is okay and reported to the other controller functions in the security network. If the present master controller fails its self-check test, or has simply failed for any reason or been disabled, and there is at least one other controller function whose self-check is okay, the failing master controller will abdicate and the other controller function whose self-check is okay will assume the master controller role. In the initial case or subsequent cases where multiple controller functions (which will ideally be the usual case) are all okay after periodic self-check, then the controller functions may elect a master controller from among themselves by each choosing a random number 
     The gateway of a home wireless system acts as a system or network controller in the home or in a building. A drawback of prior art systems is that a failure of the gateway can disable a complete installation of a home wireless system. In alarm systems such a failure could be extremely inconvenient. 
     An object of the invention is to overcome the drawback of prior art systems and to decrease substantially the vulnerability of such systems. At least one second network controller or gateway is installed in the home wireless system and a further object of the invention is to improve the process of binding wireless devices to an available gateway. In an application comprising at least two gateways there could be an integrity problem because each gateway may indicate different states of the application, for instance based on information received from different wireless nodes. It is a further object of the invention to ensure that the application will present a uniform definition of the present state. In various embodiments of the invention communication redundancy within the system is also achieved. By limiting the amount of state indicating information that is exchanged between gateways it is possible to minimize RF message traffic in the application. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention a method of controlling a home wireless system is provided. The home wireless system comprises a plurality of wireless nodes including a first gateway and at least one second gateway and at least one wireless peripheral device. The home wireless system forms an installation that can include a conventional home security system that comprises at least one wireless alarm detector and at least two gateways. Each wireless peripheral device repeatedly runs through a link establishment process and is then bound or associated to one gateway. No gateway of the system operates as a master unit. Instead, all gateways operate in a distributed mode. 
     Generally, a communication path is established between the wireless peripheral device and the associated gateway through a link establishment procedure or a link setup process. The link setup process comprises a link scan, also referred to as discover, a link request and finally a link response. After finalizing the link setup process any communication to and from remote devices is controlled by the associated gateway. In accordance with the invention each gateway is also designed to operate as a system controller in relation to any external systems and a remote central monitoring station (RCMS). Gateways of the system cooperate to automatically distribute system control functions. Each gateway in a multiple gateway cooperative controls a subset of the home wireless system forming a physical installation. 
     Each wireless peripheral device is associated or bound to one gateway for communication. Each gateway instructs all bound peripheral devices how proceed with the wireless communication. Any messages created in a peripheral device are communicated through and acknowledged by the associated gateway. 
     Each wireless peripheral device attempts to establish a link to a gateway, should communicated messages sent to the bound gateway not be acknowledged as expected. After establishing a link to and thus binding to a gateway the non-acknowledged message is sent again. In various embodiments wireless peripheral devices or nodes automatically perform a link establishment process referred to as a login procedure when binding to a gateway. The login procedure is used also when the wireless peripheral device establishes a link to a gateway a first time. In the login procedure an identification message is broadcast by the wireless peripheral device. The broadcast of an identification message corresponds to a link scan. 
     Each gateway receiving the identification message from a wireless peripheral device would be able to bind the wireless peripheral device to itself by responding to the identification message in a predefined way. In various embodiments each gateway that received the identification message delays the transmission of a login or link request message in accordance with a set of rules. The set of rules used for determining the delay can be based on different metrics, such as signal quality metric, previous ownership metric or preassigned rank metric. These metrics are further explained below. 
     When the wireless peripheral device receives the login request message a link or login response signal is transmitted to complete the login procedure. In various embodiments the login request message includes a session encryption key that the gateway and peripheral device can utilize for secure transmission from then on for every message in each direction. 
     Each gateway is provided with a first set of communication means for communicating with a remote security server and with a second set of communication means for communicating with peripheral devices and other gateways. At least the second set of communication means are designed for wireless communication. Peripheral devices comprise corresponding means for wireless communication with the gateway. 
     All nodes share one radio frequency (RF) channel. However, each node must be able to send and receive RF messages to and from other nodes within its subset of the installation while ignoring messages from any other subset. In various embodiments each gateway acts as a master with regard to an RF network comprising the gateway and at least one wireless peripheral device. Other gateways act as masters for their respective RF network. 
     In various embodiments the RF channel can manually or automatically changed in case of detecting noise, jamming or other RF transmission problems on the current RF channel. The peripheral devices will adapt to the channel change by logging into the new RF channel at the next transmission. 
     Each gateway and each peripheral device it controls use specific addresses included in messages. As a result the RF networks are partitioned by a form of CDMA (Code Division Multiple Access). Each gateway will only process messages from the peripheral nodes it controls, and it will ignore messages from peripheral nodes it does not control. Likewise, each peripheral node will only process messages from its controlling gateway. 
     In various embodiments the gateways used in an installation have longer range of use than the wireless peripheral devices. Some reasons for a better performance can be AC mains power, better RF input filtering, better antennas, and dual radio diversity. Because of this, multiple gateways may be more likely to be able to communicate with each other, in large premises, than every node is be able to communicate with every gateway. By placing gateways strategically within premises, it can be guaranteed that every peripheral node has an adequate RF communication link with at least one gateway. In installations where the gateways can all communicate with each other, further improved system performance will be provided. 
     In various embodiments a gateway receiving messages intended for gateways of other installations processes such messages for creating metrics and for monitoring also other installations or systems. Any processed metrics can be used for finding network problems or different kinds of sabotage conditions. The RF communication link between gateways also can be utilized for supervising the network. This could be used for detecting problems caused by RF noise, or intentional sabotage. If a gateway detects or suspects an RF trouble-condition, it can temporary increase the frequency of a supervision cycle on other gateways, to quicker detect and act upon RF trouble. 
     In an installation all wireless peripheral devices must be distributed automatically among a pool of gateways. Furthermore, if a gateway fails, its peripheral nodes must be redistributed among the pool of surviving gateways. In various embodiments an RF protocol login procedure can be used. When a wireless peripheral device starts up it begins broadcasting an identification message. Every gateway that receives the identification message will try to respond with a login request message. By imposing rules or metrics in the RF protocol login procedure it is possible to proceed further with one gateway only by delaying the gateway login request message. 
     One metric can be based on link quality. This metric can comprise radio signal quality based on RF signal strength (RSSI), Link Quality Indicator (LQI) that measures the error in the incoming modulation of successfully received packets (packets that pass the CRC criterion) and other similar properties. The better signal quality for the identification message received in a gateway the shorter the delay. Thus, gateways “closer” (better RF link quality) are favoured and gateways “farther” (worse RF link quality) are disfavoured for capturing a particular peripheral node. 
     Another metric can be based on previous link status in combination with history ownership. If a previous communication link between a gateway and a wireless node had a high quality level a shorter delay is selected. If a gateway has previously owned a peripheral node, the shorter the delay. This results in a more stable network topology; a peripheral node normally will not alternate between two gateways with equal signal quality metrics. 
     A further metric can be based on preassigned rank. A particular gateway can be favoured and be instructed to use a shorter delay. In this way more wireless peripheral devices will be bound to this gateway. Different metrics can be combined. 
     In various embodiments a fail-over procedure is automatically initiated if a gateway fails. In such a case its peripheral nodes are automatically and transparently transferred to another surviving or operative gateway. In a single gateway installation, a peripheral node that has an event (such as an alarm) to report, will attempt to send an RF message to the bound or associated gateway. If the gateway fails to acknowledge the message, the peripheral node will retry a few times and then begin the login procedure again by broadcasting the identification message. 
     From a peripheral node&#39;s perspective, fail-over in a multiple gateway cooperative is no different from a situation where the link is lost to a single gateway. If a gateway fails, the next time a peripheral node it owned attempts to transmit a message, it will fail and begin the login procedure again by broadcasting the identification message. This time, however, another operative gateway will send a login request message first and capture the peripheral node. After the peripheral node has completed the login procedure, it will transmit again the original event message to its new RF master gateway. Thus, fail-over from a failed gateway to a surviving gateway has occurred automatically and transparently. 
     A new link establishment process will also take place if the communication link between a gateway and a wireless node is broken. This may happen when radio signals are blocked or disturbed by objects or interference from other radio signal sources. 
     An application always is placed in a state, such as an arming state (described above), an alarm state, peripheral device low battery state and other dynamic and intermediate states. All gateways in an application need to synchronize the present state, so as to ensure that the application or the system represents a unitary state. Each gateway in a multiple gateway application may receive new information from a wireless peripheral device that can influence the application system status. After receiving such information the gateway determines whether the new information has such an impact that a resulting system status needs to be communicated to other gateways of the application. If this is the case the receiving gateway communicates the resulting system status to other gateways of the application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the manner in which the above recited and other advantages and objects of the invention are obtained will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. 
       Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1  is a schematic view of an installation of a home wireless system controlled in accordance with one embodiment of the invention, 
         FIG. 2  is a schematic block diagram showing an embodiment of an installation in accordance with the invention, 
         FIG. 3  is a schematic flow chart of a general link establishment process of a wireless peripheral device used in accordance with the invention, 
         FIG. 4  is a schematic flow chart showing a process of a wireless peripheral device in a home wireless system in accordance with the invention including a link establishment process, and 
         FIG. 5  is a schematic flow chart showing a process in a network controller in a home wireless system in accordance with the invention including a link establishment process. 
     
    
    
     DETAILED DESCRIPTION 
     In the embodiment shown in  FIG. 1  an installation comprising a home wireless system is installed in a building  10 . The home wireless system is an alarm system installation and comprises a plurality of wireless peripheral nodes including wireless peripheral devices, a first gateway  12  and a second gateway  12 ′. One wireless peripheral node is a first infrared detector  14  mounted in the corner of a room close to the ceiling. The first infrared detector  14  has a sensing area that covers the first gateway  12 . A first perimeter alarm detector  16  is mounted at a window  17  in the same room. The infrared detector operates in a conventional manner to detect presence and movements of objects emitting infrared radiation. The perimeter alarm detector also operates in a conventional manner to detect when a door or a window is opened. In various embodiments the perimeter alarm detector comprises a magnetic sensor that will detect when a magnet attached to the door or window is moved. 
     A second gateway  12 ′ is arranged in a second room separated from the room where the first gateway  12  is arranged. A second infrared detector  14 ′ is mounted in the same room as the second gateway  12 ′ to cover it within its operative area and a second perimeter alarm detector  16 ′ is mounted at a window  17 ′ in the same room. A keypad  19  is mounted close to a front door  20  of the building  10 . The keypad  19  is used by an operator of the alarm system to arm and to disarm the alarm system. Also the keypad  19  is a wireless peripheral node. The front door  20  is covered by a third perimeter alarm detector  21 . Another type of wireless peripheral device is a smoke detector  23  mounted in the ceiling of building. In various embodiments a plurality of smoke detectors  23  are arranged throughout the building  10  to ensure that fire can be detected at an early stage. 
     Depending on different circumstances the first gateway  12  and the second gateway  12 ′ are connected to a remote central monitoring station  22  either through a wired connection  24  or through a wireless connection. The connection to the remote central monitoring station  22  can also be through the internet  26 . The wired connection  24  can be part of a public switched telephone network  25 . In various embodiments the remote central monitoring station  22  comprises an interface module  27 , a database  28  and a web server  29 . The database  28  stores installation and application data relating to the installation including all wireless network nodes and alarm settings. 
     During initial installation of a prior art system each peripheral node attaches to the single gateway in accordance with a specific login procedure. The peripheral node broadcasts an RF signal comprising an identification message including a unique identification number referred to as the node ID. The single gateway receives the broadcast identification message and examines the node ID. If that node ID is part of the gateway&#39;s installation, it responds to the identification message with the transmission of a login request message specifically addressed to the peripheral node that broadcast the identification message. In various embodiments installation and application data including the node ID of all peripheral nodes included in an installation are stored in the remote central monitoring station  22  and are transferred to the gateway. A home wireless system installation can comprise a plurality of different applications, such as alarm, monitoring, measuring and other services. 
     In various embodiments the login request message includes a temporary session encryption key that is used by the gateway and the peripheral node for communicating in both directions. After receiving the login request message the peripheral node responds with the transmission of a login response message specifically addressed to the gateway to complete the login procedure. All RF messages sent from a wireless peripheral device are acknowledged by the gateway that receives and processes the message in an acknowledgement procedure. 
     In an installation in accordance with the invention as shown in  FIG. 1  a first gateway  12  and a second gateway  12 ′ are included in the installation. Both gateways are connected to the remote central monitoring station  22  and have received information regarding the installation. The remote central monitoring station  22  also comprises conventional means for receiving alarm signals from gateways of an installation. The installation procedure of the installation shown in  FIG. 1  starts with the same sequence that is described above. A wireless peripheral device, such as the first infrared detector  14 , broadcasts an identification message that could be received by the first gateway  12  and the second gateway  12 ′. 
     In accordance with the invention only one gateway binds the broadcasting wireless peripheral device to itself. In various embodiments a gateway that receives an identification message delays the transmission of the login request message. The delay is based some metrics. In one embodiment of the invention the metrics is a signal quality metric. A gateway receiving the identification message measures or determines the signal quality of the received signal. The better the signal quality of the identification message received by the gateway the shorter the delay. 
     As a result a gateway arranged in such a relation to the peripheral device that a better signal quality is achieved is favored before other present gateways. The favored gateway will be the first to send a login request message and consequently will bind the peripheral device to itself. Other gateways of the installation also may transmit login request messages but these will not be processed and accepted by the peripheral device because it then is already bound to the first gateway. 
     Another metric can be based on previous ownership or previous link status. If a peripheral node previously has been bound to a specific gateway with good communication link quality a shorter delay can be used by the gateway. This results in a more stable network topology; a peripheral node will not alternate between two gateways with equal signal quality metrics. 
     A further metric can be based on preassigned rank. In some installations it would be preferred to bind a specific gateway to a specific peripheral device. In such cases the delay in the gateway can shortened. The different metrics can be combined in an installation. 
     The described login procedure also provides redundancy and an automatic fail-over function. Should a gateway bound to one or a plurality of wireless peripheral devices fail all bound wireless peripheral devices automatically and transparently will be transferred to another gateway. In various embodiments the acknowledgement procedure is used to ensure this function. If no acknowledgement message is received in a wireless peripheral device after transmitting a message, the wireless peripheral device will retry a few times within a comparatively short time period. The message sent by the wireless peripheral device could be an alarm message, a periodic status message or another type of message. A periodic status message is broadcast by all peripheral devices at some intervals. 
     In the embodiment shown in  FIG. 1  the first infrared detector  14  which is bound to the first gateway  12  detects movement of an object in the detection area (marked). An alarm signal message is transmitted and should be received and processed by the first gateway  12 , which is associated with and previously has been bound to the first infrared detector  14 . However, for some reason the first gateway is not able to transmit an acknowledge signal or for some reason the acknowledge signal is blocked or disturbed. After a few attempts of sending the message again the first infrared detector will begin the login procedure again by broadcasting the identification message. 
     Since the identification message is broadcast all gateways in the installation receive the identification message. If the previously associated gateway, that is the first gateway  12 , does not respond the second gateway  12 ′ will respond with a login request message including a temporary session encryption key. The first infrared detector  14  then will bind to the second gateway  12 ′ by sending a login response signal using the temporary session encryption key received from the second gateway  12 ′. Following the login procedure the original alarm signal message is again transmitted also with use of the temporary session encryption key received from the second gateway  12 ′. After receiving the original alarm signal the second gateway  12 ′ then can send an alarm message to the remote central monitoring station  22  in accordance with normal routines. 
     Where the first gateway  12  as well as the second gateway  12 ′ receive and process the identification message broadcast by the first infrared detector  14  a metric as set out above will be utilized. As a result either the first gateway  12  or the second gateway  12 ′ will transmit the login request message. Using the metric based on signal quality or signal strength the first gateway  12  will be applying a shorter delay and be the first gateway to respond. Also using the metric based on previous ownership or previous link status will result in the first gateway  12  responding first and thereby binding the first infrared detector  14 . The third metric based on a predefined setup or assignment may lead to another result, should the second gateway  12 ′ be a higher ranked unit. 
     A situation similar to a failure situation involves a gateway restart. Since the session encryption keys between the gateway and its peripheral nodes are temporary, all nodes will be marked logged out when the gateway restarts. However, a peripheral node does not know it has been logged out until it attempts to send the next RF message (perhaps an alarm message, perhaps only periodic status). That message transmission and its retries, using the previous temporary session encryption key, will fail, and the peripheral node will begin the login procedure again by broadcasting the identification message. After it has completed login, will transmit the original event message again using the new temporary session encryption key. 
     In the embodiment shown in  FIG. 1  a small storeroom  34  is arranged as an annex connecting to the building  10 . A third perimeter alarm detector  36  is arranged at a storeroom door  38 . Due to fact that several walls separate the third perimeter alarm detector  36  and the first gateway  12  radio frequency signals that are transmitted from the third perimeter alarm detector  36  do not reach the first gateway  12  in a satisfying way. The range of the third perimeter alarm detector  36  is indicated at line  37 . The shorter distance and fewer walls in respect of the second gateway  12 ′ allows it to properly receive the radio signals transmitted by the third perimeter alarm detector  36 . 
     During a login procedure initiated by the third perimeter alarm detector  36  no login response message is transmitted from the first gateway  12  because it does not receive signals having appropriate signal qualities. In various embodiments the gateways in an installation are provided with more powerful radio transmitting means than the wireless peripheral devices. This could be because the gateways comprise higher capacity power supplies or are connected to a power line. The second gateway  12 ′ receives a radio signal that complies with presently applied standards and sends a login response message in accordance with the procedure described above. 
     The first gateway  12  still can be capable of communicating with the second gateway  12 ′ as a result of the more powerful radio transmitting means and may communicate information about the third perimeter alarm detector  36 . By placing gateways strategically within a building it is possible to guarantee that every peripheral node has an adequate RF link with at least one gateway. As long as the gateways can all communicate with each other, the installation will function properly. To achieve full redundancy the installation should include enough gateways for every peripheral node to be able to communicate with at least two gateways. 
     An installation such as the alarm system shown in  FIG. 1  holds a large amount of dynamic state information, such as arm state, alarm status, peripheral battery status, etc. in a total system state information dataset. Similar information is stored also in other types of home wireless systems. Each gateway or controller continuously receives inputs from different authenticated sources such as peripheral nodes, a RCMS, adjacent systems, etc. that affects a distributed state of the application or system. 
     An alarm system with distributed gateways operating as system controllers should synchronize state among the controllers. However, in various embodiments only a small subset of the total system state information dataset needs to be strictly synchronized for successful operation. Preferably, only higher level, abstract system state changes, such as entry alarm, arming state, and smoke detected, are distributed and synchronized. Upon receiving state change information the receiving gateway determines whether the received information relates such a high level system state change. If this is the case a resulting application state is distributed among other gateways of the application. In various embodiments also time stamp data relating to the actual time of the state change is included in a distributed message together with the resulting application state. 
     Other information or data items, especially those pertaining to peripheral nodes and/or low level events, need not to be distributed because they do not jeopardize important functions of the system. They can also be recreated as necessary. Also, the contact status of a peripheral device to an associated gateway needs to be monitored by the associated gate only, not by other gateways. In the case of a gateway failure all peripheral devices associated to the failing gateway will establish contact with another gateway. 
     In various embodiments a message digest of the resulting application state is included when a gateway has determined that received information has changed the state and the resulting state needs to be distributed among the gateways of the installation. It is possible also to include a message digest of the state prior to the state change. Different techniques, such as MD5 or SHA256 and other hash algorithms exist for calculating or determining a message digest. The message digest of an application state is a transformation of status data of system components and will improve application integrity considerations. 
     In case of conflicting application state information different arbitration methods can be used. A simple arbitration method is to compare the age of the applications state changes and to set the gateways to select the latest or newest state change. In various embodiments a source rank for the state change is used for arbitration. Normally, the highest rank state change is selected. The source rank can be based on a combination of the time of state change, source of state change, uptime of the receiving gateway and number of source links. 
     Many data items, especially those pertaining to peripheral nodes, can be recreated as necessary. In accordance with various embodiments of the invention only higher level, abstract system state changes (e.g. entry alarm) rather than low level events (e.g. a specific smoke detector reporting low battery status) are synchronized. As a further example, only the gateway a peripheral node is attached to really needs to track the peripheral&#39;s contact status. If that gateway fails, and the node logs into another gateway, after completing login the peripheral node will send the new gateway a contact state message containing the violation state of all the node&#39;s detector contacts. This scheme minimizes the amount of information that needs to be synchronized between gateways in the cooperative, and minimizes also the resulting RF message traffic. 
     In various embodiments a second gateway can utilize the RF communication link of another gateway for tunnelling messages to a remote central monitoring station (RCMS). For example if the second gateway up-link to RCMS is very slow or unreachable, or has a higher cost, another gateway up-link can be utilized. 
     A home wireless system has a large amount of persistent system configuration information. An alarm system holds information such as alarm detector definitions, user PIN codes, etc. This configuration, which is stored in the central monitoring station and is pushed to each gateway from the central monitoring station, should be identical among the gateways in a multi-gateway installation or the system may behave erratically. For example, if a perimeter alarm detector has been added to the system, and the perimeter alarm detector configuration has been pushed to one gateway but not to another, the new perimeter alarm detector may or may not function correctly. It is therefore important to guarantee that configuration is consistent among all the gateways in a multi-gateway installation. 
     In various embodiments the remote central monitoring station generates a strictly increasing configuration revision number every time the installation&#39;s gateway configuration (which is shared by all gateways in the multi-gateway installation) changes. This configuration revision number is pushed to each gateway along with whatever configuration data has changed. 
     Each gateway includes its configuration revision number in a periodic status messages that it sends to other gateways in the multi-gateway installation. When each gateway receives periodic status from another gateway, it compares its configuration revision number to that in the periodic status message. If the other gateway&#39;s configuration revision number is greater, indicating newer configuration, the receiving gateway will send a special report message to the central monitoring station and request a configuration update. In this way, when new configuration is received in one gateway in the multi-gateway, the changes will quickly propagate to all other gateways. Normally, it is not possible for the central monitoring station to push new configuration to all the gateways in an installation directly, because a gateway is protected behind a network firewall or a similar protection scheme. In such installations the central monitoring station has to wait until the gateway opens a communication session and sends out a report, through the firewall, to the central monitoring station. When the communication session is opened information can be transferred from the central monitoring station to the gateway. 
     In various embodiments an update of state or configuration could be detected by arranging the first gateway to calculate a checksum of all states and configuration. This checksum can then be monitored by any other gateway. If the checksum changes, the other gateway determines that the state or configuration is changed. Such a change can be used by the second gateway to start an update as well. 
     The schematic view in  FIG. 2  shows a basic installation with one remote central monitoring station  22 , a first gateway  12 , a second gateway  12 ′ and a third gateway  32 . A plurality of wireless peripheral devices is also included in the installation. The remote central monitoring station  22  normally is connected to and handles a plurality of installations. A database  28  stores separately data relating to each installation. Such data can include installation configuration and user or owner data. An interface module  27  allows users to interact with the database and to change some settings of the installation. I various embodiments the interface module  27  is arranged to exchange data through the internet. A control and communications unit  31  controls the function of the remote central monitoring station and the communication with all associated gateways. 
     Each gateway comprises first communication means  40  for communication with radio frequency signals and second communication means  42  for communication with remote units such as the remote central monitoring station  22 . The second means for communication is capable of communicating over the internet and/or over telephone lines. In various embodiments the second means for communication comprises cellular telephone module for communication by GSM, GPRS and similar telecommunication standards. Each gateway further comprises a central unit  44  with memory means and timing means. Said timing means continuously keeps track of the time of events handled by or communicated to the gateway. 
     The central unit  44  maintains in the memory means data relating to the installation and communication settings such as temporary encryption keys used during communication with associated wireless peripheral devices. The first communication means  40  is used also for communicating with other gateways present in the installation. A power unit  43  provides the power used by the gateway. In various embodiments the power unit  43  is connected to the mains of the premises. 
     Said first communication means  40  is arranged to receive and to detect the signal strength and the signal quality of radio signals. When a gateway  12  receives a radio signal comprising the identification message from a peripheral device the quality and strength of the signal is determined in said first communication means  40 . A result of the determination is transferred to the central unit  44  where further analysis is performed based on which metric is used in the present system. 
     The memory means of the central unit  44  of the gateways also stores data relating to all bound wireless peripheral devices. In various embodiments the memory means of the central unit  44  of the gateways also stores data received from the remote central monitoring station relating to previously bound wireless peripheral devices and various ranks of different wireless peripheral devices. These data can be used during a link establishment process as described above when other metrics are used. 
     Each wireless peripheral device basically comprises a wireless communication unit  46  used for all communication with a gateway, a sensor unit  48 , a processing unit  49  and a power supply unit  50 . Different wireless peripheral devices comprise different types of sensor units  48 , such as infrared sensor, magnetic sensor, smoke detector, temperature detector. In various embodiments an image capturing device  52  such as a video camera or digital camera is also included in the wireless peripheral device. In the embodiment shown in  FIG. 2  the image capturing device  52  is arranged in an infrared detector  14 . 
     The link establishment process of a wireless peripheral device into the home wireless system is shown in  FIG. 3 . In various embodiments installation information comprising identification data, setup data and application data of each wireless peripheral device and data defining the type of wireless device is maintained in the remote alarm receiving centre  18 . The installation information also is transferred to each one of the gateways of the installation. As shown in  FIG. 3  a binding wireless peripheral device first is activated in block  54  and then initiates the link establishment process by broadcasting an identification message in block  56 . The identification message includes an address of the wireless peripheral device. 
     The identification message is broadcast as a radio frequency signal (RF) and will be received by all gateways receiving a sufficiently strong radio signal. In accordance with the invention all gateways receiving the signal will apply a scheme before transmitting a reply message as set out above. The scheme will ensure that a reply message will be sent first from one responding gateway as a login request message as depicted in block  58 . The login request message is directed specifically to the binding wireless peripheral device by including in the login request message the address of the binding wireless peripheral device. The login request message includes also an address of the responding gateway. If no login request message is received in the binding wireless peripheral device the process will continue in block  56  by broadcasting the identification message again. 
     In various embodiments a temporary session encryption key is generated in the responding gateway. The temporary session encryption key is included in the login request message. The responding gateway and the binding peripheral node will use the temporary session encryption key from then on for every message in each direction. Each message will also be directed to a specific receiving gateway or wireless peripheral device by including in the message the appropriate address. 
     As soon as a login request message is received in the binding wireless peripheral device it will transmit a login confirmation message as depicted in block  60 . The login confirmation message is directed specifically to the responding gateway by the inclusion of appropriate address. As a result the link establishment process is completed, the wireless peripheral device is bound to one gateway and a communication path is established. 
     An operational process of a home wireless system in accordance with the invention shown in  FIG. 4  includes a link establishment process as described above with reference to  FIG. 3 . When a login confirmation message is transmitted in the wireless peripheral device it will enter an operation mode as depicted in block  62 . In an alarm installation it can correspond to an enabled mode where a sensor in the wireless peripheral device is enabled. Any event triggering a sensing unit of the wireless peripheral device, or presence of a previously occurred event (see below), will result the transmission of an alarm message as depicted in block  64 . The message can also be an event message informing the gateway about low battery or other status information of the bound wireless peripheral device. 
     After transmitting the alarm or event message the wireless peripheral device checks in block  64  if an acknowledgement message is received from the bound gateway. During normal conditions an acknowledgement message is received and the wireless peripheral device returns to the operation mode in block  62 . The alarm event or any other message is handled by the bound gateway in a conventional manner. 
     Should an acknowledgement message not be received, for instance because the bound gateway is malfunctioning or radio transmission is disturbed, a fail-over process is initiated and a check is made in block  68  if a predetermined number of retries of transmitting the event messages has been reached. If this is not the case the process returns to block  64  and the event messages is again transmitted. If a predetermined number of retries has been made it is concluded that the bound gateway is more permanently out of order, or that no contact can be established. The process returns to block  56  and a new login process is initiated. When reaching block  62  a previously occurred and unacknowledged event signal still will be present. As a result the process will continue in block  64  by transmitting the unacknowledged event signal. 
     In various embodiments a common situation occurs when a gateway is restarted. After a restart of a gateway all wireless peripheral devices included in the installation are considered logged out from the gateway. As a result any messages received from a wireless peripheral device after restart will not be processed and will not be acknowledged by the gateway. As soon as an identification message is received from a wireless peripheral device the login process starts in the gateway as set out above by the transmission of a login confirmation message. 
     One embodiment of a process of starting or restarting a network controller or a gateway  12  is shown in  FIG. 5 . In block  68  the gateway is activated. A contact then is established between a remote central monitoring station (RCMS) and the gateway. The gateway receives in block  70  a set of installation and application data from the RCMS including the preferred metrics to be used during a link establishment process. The data also can include information relating to previously bound wireless peripheral devices. 
     After receiving installation and application data from the RCMS the gateway  12  is prepared in block  72  to receive an ID message from wireless peripheral devices of the installation searching for a gateway. When an ID message has been received the central unit  44  the gateway  12  determines in block  74  response criteria based on data received from the RCMS. At least one of the metrics as set out above is utilized for calculating a delay. In various embodiments different criteria and metrics are combined and weighted. Signal strength and signal quality, previous relationship with wireless peripheral device, that is whether the wireless peripheral device recently or ever was bound to the gateway, and other criteria can be used. 
     Based on the selected metrics and detected signal strength and or signal quality a login request message is transmitted in block  76 . In various embodiments a delay is calculated on the bases of the selected metrics and detected signal strength and or signal quality and the login request message is transmitted after said delay. The wireless peripheral device that transmitted the ID message will receive the login request message and reply with a login confirmation message that is received in the gateway in block  78 . After receiving the login confirmation message the gateway or network controller is in operation mode as shown in block  80 . 
     While certain illustrative embodiments of the invention have been described in particularity, it will be understood that various other modifications will be readily apparent to those skilled in the art without departing from the scope and spirit of the invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the description set forth herein but rather that the claims be construed as encompassing all equivalents of the present invention which are apparent to those skilled in the art to which the invention pertains.