GB2549953A

GB2549953A - Method and device for determining a power network topology

Info

Publication number: GB2549953A
Application number: GB1607691.1A
Authority: GB
Inventors: Merlet Hervé; Le Scolan Lionel
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2016-05-03
Filing date: 2016-05-03
Publication date: 2017-11-08
Anticipated expiration: 2036-05-03
Also published as: GB2549953B; GB201607691D0

Abstract

The invention relates to a method of determining the topology of a power network, such as power over cable (PoC) or Ethernet, the power network comprising a power source, at least one power segment, at least one generating device coupled to a power segment and capable of generating a physical parameter variation on the power segment, e.g. a voltage pulse, and at least one detecting device coupled to a power segment and capable of detecting the physical parameter variation. The method comprises the steps of: detecting for, on the segment to which the detecting device is coupled, a physical parameter variation generated by the generating device; and causing an update of a table storing the topology of the power network, wherein if the physical parameter variation was detected, the generating device and the detecting device belong to a same power segment, and if the physical parameter variation was not detected, the generating device and the detecting device do not belong to a same power segment. The devices may be coupled via a communication network, for example to coordinate time windows when parameter variations will be generated and report successful parameter detections or otherwise.

Description

METHOD AND DEVICE FOR DETERMINING A POWER NETWORK

TOPOLOGY

FIELD OF THE INVENTION

The present invention relates to a method of determining the topology of a power network, in particular a video surveillance network, and devices allowing such power network topology determination.

BACKGROUND OF THE INVENTION

Power distribution over data cables (also known as Power over Cable or PoC) is a very important topic for several fields such as Information Technology IT and telecommunication related systems comprising video surveillance systems. Several types of power distribution over data cables exist, selected for use according to users’ needs in terms of the power required by the devices, bandwidth limitations, and the distances between the devices and a power source equipment PSE.

Power over Cable or PoC systems, be they Ethernet links or coaxial cable (Coax) links, comprise at least one power source equipment PSE device (acting as a power source and data switch) and a plurality of PoC devices (e.g. cameras, printers, telemeters, etc.) powered via cables by the power source equipment. PoC systems advantageously prevent having to use a parallel power-only network or battery solutions, thereby saving corresponding additional costs.

However, power distribution over data cables suffers from limitations on the total power that can be carried, and from a high power loss in the cables due to a relatively low voltage that is carried (e.g. a low voltage being comprised between 48 to 56 volts). On the contrary, a general power-only network is able to carry a voltage comprised between 110 and 220 volts and thus suffers less power loss but requires AC/DC converters to power the PoC devices.

In general, the power supply in a PoC system is controlled by the power source equipment, which comprises an AC/DC converter from a general power distribution network. The power source equipment comprises one or more ports to which the PoC devices are coupled and by which the PoC devices are powered by means of cables, while data can be transmitted over the same cables.

The power supply in a PoC system is constrained at two levels - the port level and the system level. The power is constrained at the port level because a power source equipment is only able to deliver or supply power to a port up to a fixed maximum amount of power, independent of the number of PoC devices connected to the port.

The power is also constrained at the system level because the sum of powers available per port shall be maintained and limited by the capacity provided by the power source equipment. Typically, the power source equipment has an overall power capacity that is less than the sum of port power capacities of individual switch ports.

The power source equipment is protected against power overrun. The ports have software protection that cuts the power supply when a power overrun is detected at the port level or at the system level, and restores the power supply when the power demand is acceptable again. Moreover, each of the ports may be provided with a fuse protection in case the software protection fails. The power source equipment itself is also protected by software and/or hardware such as a fuse.

However, in IP over Coax systems (and more generally in PoC systems), a power overrun may result in the shut down of a port, a system shut down, or more seriously, a blown fuse either at the port level or at the system level.

In a case where a port is shut down, all devices linked to the port are shut down. When the port restarts, the devices are then powered up again. However, if the conditions of power overrun for the port are met again due to the devices powering up again, the port will be shut down again. An endless loop of shut downs and power ups may thus occur, until one or more devices are deactivated or unplugged from the port.

In a case where the power source equipment itself is shut down, all the PoC devices of the system are shut down and then powered up again as the power source equipment restarts. However, similar to the endless shut down/power up loop issue described above relating to the port level, the power source equipment may shut down again if the conditions of power overrun for the power source equipment are again met upon restarting the system, entering an endless loop of shut downs and power ups until one or more devices are deactivated or unplugged from the system.

It is thus desirable to be able to control and maintain the power consumption in the PoC system under the limits. To this end, there is a need for a method for dynamically determining how many active PoC devices can potentially draw power in the PoC system and their distribution across the ports of the power source equipment, i.e. to which ports they are coupled. In other words, there is a need for a method to determine the topology of the power network.

SUMMARY OF THE INVENTION

The present invention has been devised to address at least one of the foregoing concerns, in particular to determine the topology of the power network of a Power-over-cable system.

Embodiments of the invention relate to a method of determining the topology of a power network, the power network comprising: - a power source, - at least one power segment coupled to the power source, - at least one generating device coupled to a power segment and capable of generating a physical parameter variation on the power segment to which the generating device is coupled, and - at least one detecting device coupled to a power segment and capable of detecting, on the power segment to which the detecting device is coupled, a physical parameter variation generated by a generating device, the method comprising, for the detecting device, the steps of: - detecting for, on the segment to which the detecting device is coupled, a physical parameter variation generated by the generating device; and - causing an update of a table storing the topology of the power network, wherein: - if the physical parameter variation was detected by the detecting device, the table is updated to store an information that the generating device and the detecting device belong to a same power segment, and - if the physical parameter variation was not detected by the detecting device, the table is updated to store an information that the generating device and the detecting device do not belong to a same power segment.

By detecting or not by a device of a physical parameter variation generated on a power segment, the power network topology may be determined.

According to one embodiment, the devices are coupled by means of a communication network, such that the devices can send and/or receive messages concerning at least one of: - a variation generation announcement, sent by the generating device or by a master device, that the generating device will generate the physical parameter variation, - a variation generated announcement, sent by the generating device or by a master device, that the generating device did generate the physical parameter variation, - a variation detected announcement, sent by a detecting device, that the detecting device did detect the generated physical parameter variation, - a variation undetected announcement, sent by a detecting device, that the detecting device did not detect the generated physical parameter variation, - a generate pulse announcement, sent by a master device to the generating device, ordering it to generate the physical parameter variation, and - a respond detection announcement, sent by a master device or by the generating device, ordering the detecting device to send the variation detected announcement or the variation undetected announcement.

The sending and receiving of announcements allow the detecting and updating processes to be optimized.

According to one embodiment, the method further comprises the steps of: - defining, by means of messages exchanged using the communication network, a time window during which the generating device is configured to generate the physical parameter variation, and - updating the table according to a result of the detecting step occurring during the time window.

According to one embodiment, upon receipt of the variation generation announcement, the detecting device detects for the physical parameter variation during a time window.

According to one embodiment, the detecting for the physical parameter variation of the power segment by the detecting device comprises one of the following: - starting a time window of a pre-defined length upon reception of the variation generation announcement, or - detecting for the physical parameter variation according to a timestamp contained in the variation generation announcement, the timestamp indicating an earlier or later time.

According to one embodiment, a detecting device that detected the physical parameter variation sends the variation detected announcement regardless of whether the time window has finished.

This allows for a more rapid update of the table.

According to one embodiment, a detecting device that did not detect the physical parameter variation during the time window sends the variation undetected announcement after the end of the time window or upon receipt of the respond detection announcement.

In this manner, it may be determined that all devices (both detecting and undetecting devices) have responded.

According to one embodiment, the method further comprises the steps by the detecting device of: - detecting for the physical parameter variation, - receiving the variation generated announcement, - determining whether a physical parameter variation was detected in a time window before the reception of the variation detected announcement, and - sending the variation detected announcement or the variation undetected announcement.

According to one embodiment, the time window is defined by a master device or by the generating device.

According to one embodiment, the method further comprises the steps by the detecting device of: - receiving the variation generation announcement, and - receiving the variation generated announcement, wherein the time between the announcements define a time window for detecting for the physical parameter variation.

According to one embodiment, an identifier of the detecting device comprised within the variation detected announcement or the variation undetected announcement is used to update the table.

According to one embodiment, the step of updating the table comprises storing identifiers of the devices and the power segment to which each device belongs.

According to one embodiment, the method further comprises the steps of: - selecting another device to be a new generating device, and - generating, by the new generating device, a physical parameter variation on the power segment to which it is coupled.

In this manner, all or a plurality of the devices of the power network may act as generating device, to better ensure that all segments have been identified.

According to one embodiment, selecting a new generating device comprises selecting a device that did not detect a previous physical parameter variation.

According to one embodiment, the sending of an announcement comprises broadcasting the announcement on the network.

According to one embodiment, the physical parameter variation is a voltage change, and the method further comprises the steps of: - defining a minimum pulse duration and maximum pulse duration, and - upon detection of a voltage pulse by a detecting device, determining whether the voltage pulse occurs between the minimum pulse duration and the maximum pulse duration.

According to one embodiment, a detecting device further comprises an analog-to-digital converter configured to measure the voltage at the inputs of the device and a microcontroller configured to read and store the measured voltage, and wherein detecting the voltage change comprises the steps of: - detecting, by the converter, the voltage at the inputs, - reading, by the microcontroller, the detected voltage, and - storing the detected voltage.

According to one embodiment, the table comprises device identifiers and the method further comprises a step of selecting a new generating device by selecting the next device identifier in the table.

According to one embodiment, the physical parameter variation is a voltage change, and wherein the generating device comprises a resistor, a switch to couple or un-couple the resistor to inputs of the device, and a microcontroller configured to command the switch, and generating the physical parameter variation comprises the steps of: - commanding the switch to close in order to couple the resistor to the inputs of the device, and - commanding the switch to open in order to un-couple the resistor from the inputs of the device.

Embodiments of the invention also relate to a detecting device capable of detecting a generated physical parameter variation on a power segment of a power network, the power network comprising: - a power source, - at least one power segment coupled to the power source, - at least one generating device coupled to a power segment and capable of generating a physical parameter variation on the power segment to which the generating device is coupled, and - at least one detecting device coupled to a power segment and capable of detecting, on the power segment to which the detecting device is coupled, a physical parameter variation generated by a generating device, wherein the detecting device is configured to: - detect for, on the segment to which the detecting device is coupled, a physical parameter variation generated by the generating device; and - cause an update of a table storing the topology of the power network, wherein: - if the physical parameter variation was detected by the detecting device, the table is updated to store an information that the generating device and the detecting device belong to a same power segment, and - if the physical parameter variation was not detected by the detecting device, the table is updated to store an information that the generating device and the detecting device do not belong to a same power segment.

According to one embodiment, the detecting device is coupled to the generating device by means of a communication network, such that the detecting device can send and/or receive messages concerning at least one of: - a variation generation announcement, sent by the generating device or by a master device, that the generating device will generate the physical parameter variation, - a variation generated announcement, sent by the generating device or by a master device, that the generating device did generate the physical parameter variation, - a variation detected announcement, sent by the detecting device, that the detecting device did detect the generated physical parameter variation, - a variation undetected announcement, sent by the detecting device, that the detecting device did not detect the generated physical parameter variation, - a generate pulse announcement, sent by a master device to the generating device, ordering it to generate the physical parameter variation, and - a respond detection announcement, sent by a master device or by the generating device, ordering the detecting device to send the variation detected announcement or the variation undetected announcement.

According to one embodiment, upon receipt of the variation generation announcement, the detecting device is configured to detect for the physical parameter variation during a time window.

According to one embodiment, in order to detect for the physical parameter variation, the detecting device is configured to do one of the following: - start the time window of a pre-defined length upon reception of the variation generation announcement, or - detect for the physical parameter variation according to a timestamp contained in the variation generation announcement, the timestamp indicating an earlier or later time.

According to one embodiment, upon detection of the physical parameter variation, the detecting device is configured to send the variation detected announcement regardless of whether the time window has finished.

According to one embodiment, upon a non-detection of the physical parameter variation during the time window, the detecting device is configured to send the variation undetected announcement after the end of the time window or upon receipt of the respond detection announcement.

According to one embodiment, the detecting device is further configured to: - detect for the physical parameter variation, - receive the variation generated announcement, - determine whether a physical parameter variation was detected in a time window before the reception of the variation detected announcement, and - send the variation detected announcement or the variation undetected announcement.

According to one embodiment, the detecting device is further configured to: - receive the variation generation announcement, and - receive the variation generated announcement, the time between the announcements defining a time window for detecting for the physical parameter variation.

According to one embodiment, the detecting device is further configured to send its identifier within the variation detected announcement or the variation undetected announcement, for updating of the table.

According to one embodiment, the physical parameter variation is a voltage change and a minimum pulse duration and maximum pulse duration are defined, and the detecting device is further configured to determine, upon detection of a voltage pulse, whether the voltage pulse occurs between the minimum pulse duration and the maximum pulse duration.

According to one embodiment, the detecting device further comprising an analog-to-digital converter configured to measure the voltage at the inputs of the device and a microcontroller configured to read and store the measured voltage, and wherein detecting the voltage change comprises the steps of: - detecting, by the converter, the voltage at the inputs, - reading, by the microcontroller, the detected voltage, and - storing the detected voltage.

Embodiments of the invention also relate to a generating device capable of generating a physical parameter variation on a power segment of a power network, the power network comprising: - a power source, - at least one power segment coupled to the power source, - at least one generating device coupled to a power segment and capable of generating a physical parameter variation on the power segment to which the generating device is coupled, and - at least one detecting device coupled to a power segment and capable of detecting, on the power segment to which the detecting device is coupled, a physical parameter variation generated by a generating device, wherein the generating device is configured to generate a physical parameter variation on the power segment to which it is coupled, so that the detecting device may detect for, on the segment to which it is coupled, the generated physical parameter variation, so that a table storing the topology of the power network may be updated, wherein: - if the physical parameter variation was detected by the detecting device, the table is updated to store an information that the generating device and the detecting device belong to a same power segment, and - if the physical parameter variation was not detected by the detecting device, the table is updated to store an information that the generating device and the detecting device do not belong to a same power segment.

According to one embodiment, the generating device is coupled to the detecting device by means of a communication network, such that the generating device can send and/or receive messages concerning at least one of: - a variation generation announcement, sent by the generating device or by a master device, that the generating device will generate the physical parameter variation, - a variation generated announcement, sent by the generating device or by a master device, that the generating device did generate the physical parameter variation, - a variation detected announcement, sent by a detecting device, that the detecting device did detect the generated physical parameter variation, - a variation undetected announcement, sent by a detecting device, that the detecting device did not detect the generated physical parameter variation, - a generate pulse announcement, sent by a master device to the generating device, ordering it to generate the physical parameter variation, and - a respond detection announcement, sent by a master device or by the generating device, ordering the detecting device to send the variation detected announcement or the variation undetected announcement.

According to one embodiment, the generating device is configured to generate the physical parameter variation during a time window defined by means of messages exchanged using the communication network.

According to one embodiment, the generating device is configured to define the time window.

According to one embodiment, the physical parameter variation is a voltage change and wherein the generating device further comprises a resistor, a switch to couple or un-couple the resistor to inputs of the device, and a microcontroller configured to command the switch, so that the physical parameter variation may be generated by commanding the switch to close in order to couple the resistor to the inputs of the device, and commanding the switch to open in order to un-couple the resistor from the inputs of the device.

Embodiment of the invention also relate to a power network comprising: - a power source, - at least one power segment coupled to the power source, - at least one generating device coupled to a power segment and capable of generating a physical parameter variation on the power segment to which the generating device is coupled, the generating device according to one embodiment of the invention, and - at least one detecting device coupled to a power segment and capable of detecting, on the power segment to which the detecting device is coupled, a physical parameter variation generated by a generating device, the detecting device according to one embodiment of the invention.

According to one embodiment, the power source comprises means for preventing a physical parameter variation generated on one power segment from being detected on another power segment.

BRIEF DESCRIPTION OF THE DRAWINGS

Other particularities and advantages of the invention will also emerge from the following description, illustrated by the accompanying drawings, in which: - Figure 1 shows a retrofitted video surveillance network, - Figure 2 shows a power source equipment according to an embodiment of the invention, configured to be implemented in a network, - Figure 3 shows a network wherein a method of determining the topology of the power network is implemented according to an embodiment of the invention, - Figures 4A, 4B, 4C, 4D show different aspects of a method of determining a topology of a power network, - Figure 5 is an electrical diagram of a portion comprising a power source equipment, a Power over Cable device, and cables of the network, - Figure 6 is a graph of voltage over time of a generated test pulse, - Figure 7 is a flowchart of a method of generating a test pulse according to one embodiment, - Figure 8 is a flowchart of a method of detecting a test pulse according to one embodiment, - Figure 9 is a flowchart of a method implemented by a master device for power control of devices according to one embodiment, - Figures 10A, 10B, 10C show tables relating to the power network topology, - Figure 11 is an electrical diagram of a portion of the network according to another embodiment, - Figure 12 is a diagram of a device implementing the invention according to one embodiment, and - Figure 13 is a diagram of a device implementing the invention according to another embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Embodiments of the invention relate in general to the discovery of the topology of a power network, such that available power may be estimated for different segments of the power network, in order to prevent power failures.

For the sake of illustration, embodiments of the invention are presented in the context of a Power over Cable (specifically, coaxial cables) video surveillance network. Of course, other embodiments of the invention may be envisaged outside this context such as a non-video surveillance network and/or a non-Power over Cable network, e.g. dual power and data networks not sharing the same cables (e.g. cable power network and wireless communication network).

Figure 1 shows a retrofitted video surveillance network 100, that is to say, an analogue video surveillance network that has been upgraded to IP (Internet Protocol) video. The network 100 comprises devices 110-m (m being an index from 1 to M, here M=6 in the illustrated example) here IP cameras as examples of PoC devices, a power source equipment PSE 120 (also known as an “Ethernet over Coax receiver”, “EoC receiver”, or “IP over Coax receiver”), a Local Area Network or LAN 130, a Video Monitoring System or VMS 140, a digital video recorder 150, and a power supply 160.

The cameras 110-m are linked to ports 121-n (n being an index from 1 to N, here N=4 in the illustrated example) of the PSE 120 by cables 170-m (m being the same index as of the camera), and may be either directly connected to a cable (as shown by camera 110-2), or by means of connectors 180 (as shown by the other cameras) used to extend the number of cameras connected to a main cable.

In this example configuration, cables 170-1, 170-2, 170-3 were already present in the previous network to transport analogue video signals. New digital cameras 110-1, 110-2, 110-3 replace the previous analogue cameras and additional cameras 110-4, 110-5, and 110-6 have been added, each being coupled to the PSE 120 by new cables 170-4, 170-5, 170-6 respectively. Cameras 110-m and their corresponding ports 121-n are grouped into power segments Sn (n being the same index as of the port), a power segment thus being defined as all devices, cables, connectors, etc. coupled to the PSE 120 by means of a port thereof.

Cameras 110-1, 110-4, 110-6 are indirectly coupled via connectors 180 to port 121-1 and form a first power segment S1; camera 110-2 is directly coupled to port 121- 2 and forms a second power segment S2; cameras 110-3, 110-5 are indirectly coupled to port 121-3 and form a third power segment S3; and no cameras are coupled to port 121-4, which forms a fourth power segment S4.

The cables 170-m can be as long as 300 meters and may be coaxial cables or any type of cable capable of transporting analogue video. The PSE 120 provides power to the cables 170-m, and thus to the cameras 110-m connected thereto, encapsulates uplink IP LAN traffic received from the LAN 130 into packets suitable for digital data transport on the cables, and extracts IP LAN traffic from packets received on cables 170-m and forwards them on the LAN 130.

The LAN 130 includes the necessary switches, routers, and gateways that are necessary to transport the IP video to the VMS 140 and to the recorder 150. The VMS 140 is configured to display the IP video streams for surveillance purposes, and the recorder 150 is configured to record the IP video stream.

The advantage of the Ethernet over Coax protocols is the possibility of linking several cameras to a main cable, for example cameras 110-4 and 110-6 linked to cable 170-1, and camera 110-5 linked to cable 170-3, also known as a “daisy chain” configuration.

Figure 2 shows a power source equipment PSE 220 configured to be implemented in a network 200 that will be shown in more detail in Figure 3.

The PSE 220 comprises ports 221-n (n being an index from 1 to N), here four ports 221-1, 221-2, 221-3, 221-4. As previously, three cameras (shown in Figure 3) are coupled to port 221-1, one camera is coupled to port 221-2, two cameras are coupled to port 221-3, and no cameras are coupled to port 221-4. Though only four ports are shown here, the PSE 220 may have 8, 16 or any other number of ports.

The PSE 220 further comprises a main power supply MPS 222, an internal power network 223, a network controller 224, an internal communication network 225, port protection circuits 226-n (n being the same index as of the ports), a power connection 227, and a data connection 228.

The main power supply 222 (here integrated within the body of the PSE 220, but not necessarily) is coupled to a power supply (e.g. reference 260 of Figure 3) by means of the power connection 227, and supplies a voltage-stabilized power supply to the ports 221-n by means of the internal power network 223. The main power supply 222 comprises a capacitor and a voltage regulator (not shown) forming a low-pass filter that filters any voltage drop pulses originating from ports 221-n. Consequently, a physical parameter variation, such as a voltage drop pulse, occurring at one segment is filtered and is not propagated to other segments of the network. This feature is advantageously used in the embodiments of the invention as it is detailed later in the description.

Each port 221-n is current-limited by its corresponding protection circuit 226-n. Each protection circuit 226-n comprises a resistor and limits the distributed power to prevent destruction of the electronic components of the port and the cables connected thereto due to short circuits.

As an example, in some embodiments of the invention, the main power supply 222 supplies a voltage-stabilized power supply of 56 V (volts) on the internal power network 223, and the protection circuits 226-n limit the power at each port 221-n to 50 W (watts). When the current at a port 221-n exceeds the authorized current, the corresponding protection circuit 226-n cuts the power on the considered port, shutting down the power supply to all cameras coupled thereto.

Each port 221-n of the PSE 220 is coupled to the network controller 224 by means of the internal communication network 225. The controller 224 is coupled to the data connection 228, which is in turn adapted to connect to a Local Area Network or LAN (e.g. reference 230 of Figure 3). The controller 224 is configured to encapsulate uplink IP LAN traffic received from the LAN into packets suitable for digital data transport on cables according to given protocol such as the Home-Plug AV protocol or the HD-PLC protocol, and to transmit them on the internal communication network 225. The controller 224 is also configured to extract IP LAN traffic from packets received on the internal communication network 225 and to forward them to the LAN. The PoC devices 210-m (shown in Figure 3) of the network share the same internal communication network 225 and can therefore communicate with each other. From a data communication point of view, PoC devices 210-m virtually belong to a same segment of the data network.

As the topology of the power network is unknown, that is to say, how many and which devices are coupled to each port 221-n, it is difficult to know in advance the total power consumption that will be drawn on the port so as to prevent a power failure at the network start-up or during a hot-plug of one or several devices (that is to say, adding one or more devices while the system is operating). The total power consumption on one segment or one port is the power dissipated in the cable due to the resistivity of the cable (Joule effect), and the power consumption of each device.

Figure 3 shows a network 200 wherein a method of determining the topology of the power network is implemented according to an embodiment, the network comprising a power source equipment PSE 220 as shown in relation with Figure 2. As described in relation with the network of Figure 1, the same elements comprise similar references, for example 1XX, 2XX.

The network 200 thus comprises IP cameras 210-m (m being an index from 1 to M, here M=6 in the illustrated example), the PSE 220, a Local Area Network or LAN 230, a Video Monitoring System or VMS 240, a digital video recorder 250, and a power supply 260. The cameras 210-m are linked to the PSE 220 by cables 270-m, and may be either directly connected to a cable, or by means of a connector 280 used to extend the number of cameras connected to a main cable.

In order to discover the power network topology, a discovery method is implemented for each power segment connected to the PSE ports 221-n: for N ports, there are N power segments to discover. A power segment may be considered to comprise at least one device 110-m coupled by means of a protection circuit 226-n to a power source 222, wherein the protection circuit limits distributed power to the device or devices coupled thereto.

To discover the power network topology, a voltage change up/down/up or down/up/down, forming a “test pulse” TP, is generated on a given power segment by a device of the segment, and the other devices, both on the same segment and on other segments, monitor the voltage on the segment to determine whether or not the test pulse is detected.

One camera (here camera 210-1 in the example illustrated in Figure 3) is the “generating device” and generates a test pulse TP, and the other cameras (here cameras 210-2, 210-3, 210-4, 210-5, 210-6) are “detecting devices” that measure the voltage on their segment in order to detect or not the test pulse. The test pulse TP is present on the power segment of the port corresponding to the segment S1 and can therefore here be detected as a “detected pulse” DP by cameras 210-4, 210-6, but the test pulse TP is filtered by the main power supply 222 (as explained above in relation with Figure 2), and the test pulse is therefore not detected by cameras 210-2, 210-3, 210-5 (figuratively represented as an “undetected pulse” UP at these cameras). The electrical characteristics of the test pulse TP depend on cable resistivity as well as the resistor integrated in the protection circuits 226-n, as will be detailed further below.

Thus, taking advantage of the regulated voltage power supply, cameras of the same segment detect a pulse, whereas cameras on other segments do not detect a pulse. The undetected pulses UP are figuratively shown in Figure 3 as barred pulses, but in reality, are substantially constant voltages, for example having a voltage variation less than a predefined threshold.

It is thus determined from the results of the test pulse TP, detected pulses DP, and undetected pulses UP, that cameras 210-1, 210-4, and 210-6 are on a same power segment, and the other cameras 210-2, 210-3, 210-5 are not on the same power segment as the other cameras, but may be on the same segment as each other.

Next, one of the other cameras 210-2, 210-3, 210-5 generates a test pulse, and so forth until the topology of the power network has been determined. It may be noted that as no devices are connected to the port 221-4, no devices are able to generate, detect, or not detect test pulses. Segment S4 is considered as an unknown entity by the devices of the other segments. It is therefore represented with a question mark “?”.

Figures 4A, 4B, 4C, 4D describe in further detail the method of determining the power network topology. More, particularly, Figure 4A shows steps of a method 400 of determining the power network topology, Figure 4B shows steps of elaboration of a Segment Discovery Table SDT, Figure 4C shows messages circulating on the communication network, and Figure 4D shows pulses (test pulses, detected pulses, and undetected pulses) appearing on the ports of the PSE.

Figure 4A shows steps of a method 400 of determining the power network topology, more particularly of generating and detecting test pulses in order to complete a Segment Discovery Table SDT stored by or accessible by each device. Figure 4B shows different instances of the same table SDT considered at different time instants: an initial table SDT(tO), a first table SDT(t1) after a first update, a second table SDT(t2) after a second update, and the completed table SDT(t3) after a final (here third) update. The method 400 comprises steps 401 to 416.

The table SDT has a first column C11 with the identifiers of each camera 210-m connected to the network 200 and a second column C21 comprising identifiers of the power segment to which the corresponding camera belongs. For simplicity, the camera identifiers are here their references 210-1 to 210-6, but in some embodiments the camera identifiers may be the Media Access Control or MAC address of the equipment or another identifier. The second column C21 is updated when a specific event occurs, such as power up of the network or the installation of a new camera in the network. The table SDT may be stored in a central location and/or in some or all of the cameras themselves.

In particular, a central manager or “Central Coordinator” (CCo) may be employed in the communication network, and be located within the PSE, the first connected device (camera) or another device of the network. Each device must be identified and authorized by the Central Coordinator before it can communicate. Therefore, the list of connected devices is known at least by the Central Coordinator and can be obtained by each connected device. When a new device joins the network, the new device sends a request to the Central Coordinator so that the new device may be identified and allowed to join the communication network.

Initially, the second column C21 of the table SDT(tO) is empty. At step 401, the discovery process is initiated. At step 402, camera 210-1 is selected as the test pulse TP generator (referred to as the generating device). The selection may be done in several ways, such as the first-added identifier, that with the lowest identifier, decision by a master device, etc. At step 403, camera 210-1 sends a “pulse generation announcement’ PGA (or more generally “variation generation announcement’ in the case of a physical parameter variation that is not a test pulse, such as a current variation or another physical parameter variation) on the communication network (also shown in Figure 4C) that it will generate a test pulse TP, and then generates the test pulse TP (also shown in Figure 4D).

At step 404, the cameras 210-4, 210-6 detect the drop pulse (Figure 4D) and send “pulse detected announcements” PDA (or more generally “variation detected announcements"), shown here as a single block for simplicity but may be sequential in time, of the detection on the communication network (Figure 4C). At step 405, after a determined period of time corresponding to a detection window, as determined by the network, the devices that did not detect a pulse, here devices 210-2, 210-3, 210-5, send “pulse undetected announcements" PUA (or more generally “variation undetected announcements"), again shown here as a single block but may be sequential in time, of undetected pulses UP. At step 406, the table is updated as shown in Figure 4B with the discovered segment S1 of devices 210-1, 210-4, 210-6 based on the received detected pulse DP and undetected pulse UP announcements PDA, PUA.

At step 407, camera 210-2 is selected as the test pulse TP generator, for example because it is the next empty line in the table SDT(t1). At step 408, camera 210-2 sends a pulse generation announcement PGA on the communication network that it will generate a test pulse TP, and then generates the test pulse TP (Figures 4C, 4D). At step 409, after the detection window, the remaining devices that did not detect a pulse, here devices 210-3, 210-5, send pulse undetected announcements PUA. At step 410, the table is updated as shown in Figure 4B with the discovered segment S2 of device 210-2 based on the received undetected pulse UP announcements PUA.

At step 411, camera 210-3 is selected as the test pulse TP generator. At step 412, camera 210-3 sends a pulse generation announcement PGA on the communication network that it will generate a test pulse TP, and then generates the test pulse TP (Figures 4C, 4D). At step 413, the camera 210-5 (detecting device) detects the drop pulse (Figure 4D) and sends a pulse detected announcement PDA. At step 414, after the detection window, no pulse undetected announcements PUA are received. At step 415, the table is updated as shown in Figure 4B with the discovered segment S3 of devices 210-3, 210-5 based on the received pulse detected announcement PDA and the lack of received pulse undetected announcements PUA. At step 416, the table is complete, so the method comes to an end.

The method of discovering the power network topology can be performed in different manners. For example, in some embodiments, with respect to the embodiment shown in Figures 4A, 4B, 4C, 4D, there is no time window starting from the pulse generation announcement PGA.

In one further embodiment, the generating device simply generates a test pulse and then broadcasts a “pulse generated announcement’ PPA (or more generally “variation generated announcement’). Upon reception of the pulse generated announcement, the detecting devices determine whether a pulse was detected within a given time before the reception of the announcement. The devices should thus generally remain in a monitoring state.

In another further embodiment, the broadcasting of the pulse generated announcement PPA is dependent upon whether a detecting device has broadcast a pulse detected announcement; in which case, upon receipt of a pulse detected announcement, non-detecting devices may then broadcast pulse undetected announcements. In the case where the generating device is the only device of its power segment, and thus no detecting devices are available to send pulse detected announcements, the non-reception of a pulse detected announcement or pulse undetected announcement may be sufficient for the generating device to deduce that it is the only device of its power segment. Otherwise, after a certain time period (timeout) the generating device can send the post generation announcement.

In one embodiment, a master device controls all actions of devices on the communication network. In this case, to discover the power network topology, the master device broadcasts a “generate pulse announcement’ GPA (or more generally “generate variation announcement’), for example a “device 210-m generate a test pulse" command message. The indicated device 210-m then generates the test pulse as instructed. After a predetermined time, for example a time period beginning at the end of the message reception, or upon the broadcasting of a “respond detection announcement’ RDA to each device individually or to all devices globally, the other devices broadcast corresponding detected or undetected pulse announcements.

Figure 5 is an electrical diagram of a portion of a power segment comprising a port of the PSE, a device, and cables.

More particularly, in Figure 5 a portion of power segment S1 is shown, comprising the cables 270-1, 270-4, camera 210-1, and the PSE 220 with the port 221- 1. Each cable 270-1, 270-4 comprises a first serial resistance SR1, and port 221-1 comprises a second serial resistor SR2 coupled to the main power supply 222 by means of the internal power network 223. The dashed lines represent the connections (such as a Bayonet Neill-Concelman or BNC connector for coaxial cables) between the PSE 220, the cables 270-1, 270-4, and the camera 210-1. The serial resistances SR1 have values depending on the length of the cable, for example approximately 30 Ω (ohms) for cable lengths of several hundred meters. (In Figure 5 the cable between the connector 280 and the camera 210-1 is not shown as in general this cable is short with a negligible serial resistance). The serial resistor SR2 of the port 221-1 has a value of approximately 3 Ω.

The camera 210-1 (and preferably all cameras 210-m) comprises an analog-to-digital converter ADC 211, a first resistor (R1)212, a second resistor (R2)213, a switch 214, and a microcontroller 215. The ADC 211 measures the voltage at the inputs of the camera, the resistor 212 is representative of the current consumption of the camera in the low power mode, the resistor 213 increases current consumption in order to generate test pulses TP, and the switch 214 drives the extra current during the test pulse, and is commanded by a control signal CS sent by the microcontroller 215, which also filters and stores the voltage measured by the converter 211.

The test pulse TP is generated by closing the switch 214, such that the second resistor R2 213 is coupled, increasing current consumption and creating a voltage drop due to the resistances SR1, SR2 of the cables and of the port.

Figure 6 is a graph of voltage V over time T of a generated test pulse. The voltage V changes from a first voltage value Vfirst to a second voltage value Vsecond for a certain time duration At (delta t) before returning to the first value. Here, the voltage Vfirst is high and the voltage Vsecond is low. The time At may be 500 ms in some embodiments, as will be described in further detail. To give an idea, the voltage Vfirst may be 40 Volts, and the voltage Vsecond may be 35 Volts.

Figure 7 is a flowchart of a method 700 of generating a test pulse TP according to one embodiment, the method comprising the steps 701 to 707.

At step 701, the generating device, for example camera 210-1, generates a test pulse, for example upon receipt of a command from a master device or a central processor. At step 702, the microcontroller 215 of the device initializes a value p relating to the number of cycles of a timing loop, the total number of cycles corresponding to the time At of the test pulse. At step 703, the microcontroller sends the control signal CS to close the switch 214, creating a voltage drop and thus the test pulse TP. At step 704, the microcontroller initiates a timer for measuring one cycle. At step 705, the microcontroller determines whether the value of p is equal to 0. If the response is no, at step 706, the value of p is decremented, p = p-1, and the method returns to step 704, launching another cycle. Otherwise, if the response is yes, at step 707 the microcontroller sends the control signal CS to open the switch 214, and the method stops.

Figure 8 is a flowchart of a method 800 of detecting a test pulse TP according to one embodiment, the method comprising the steps 801 to 815. The method 800 is implemented by detecting devices.

At step 801, the microcontroller 215 of each detecting device receives a pulse generation announcement PGA sent on the communication network from a generating device, as described above in relation with Figure 7. The microcontrollers 215 of the detecting devices prepare to detect the voltage at the inputs of its corresponding ADC converter 211. In the following, it is assumed that the detection is sampled over time which results in a set of voltage samples Vi, i being the index of each sample. The granularity of the sampling can be tuned for example to be greater than the duration of a voltage transition low/high or high/low.

At step 802, the microcontroller 215 sets the parameters of the detection method, in particular the index i of a voltage sample Vi, the voltage Vfirst (high or low), and the voltage Vsecond (low or high) to zero, that is to say i = 0, Vfirst = 0 and Vsecond = 0.

The microcontroller 215 also sets a parameter Atmin corresponding to a minimum pulse duration and a parameter Atmax corresponding to a maximum pulse duration. For example, if the average pulse duration is 500 ms, then Atmin may be set to 450 ms and Atmax may be set to 550 ms. These values may be predetermined by a master device. A (valid) test pulse is thus detected if its duration At is in the interval [Atmin, Atmax], i.e. Atmin < At < Atmax. This allows any voltage variations such as spurious voltage pulses, spikes, transient voltages etc. to be disregarded or filtered out.

The microcontroller 215 also initializes a detected pulse flag to a first state, for example 0, to indicate that a pulse is not detected. A second state, for example 1, indicates that a pulse is detected.

At step 803, the microcontroller reads the voltage (for example 40 Volts) and stores the result in a memory, such as will be described in relation with Figures 12 and 13, as value Vi (sample voltage). At step 804, the microcontroller determines whether the detection is being performed for the first time in a cycle of a pulse detection, that is to say, whether i = 0. If the response at step 804 is yes, at step 805 the value of voltage Vfirst is initialized to the current stored value Vi, for an auto-regulation of the detection voltages. At step 806, the value of i is incremented (i = i + 1), and the method returns to step 803 in order to read and store the next voltage sample value Vi.

If however, the response at step 804 is no (i Φ 0), i.e. Vfirst is already initialized, then at step 807, the microcontroller determines whether Vi is equal to Vfirst (or more generally, if there is no significant variation between the detected voltage Vi and the voltage Vfirst). If the response is yes, then there has been no voltage change since the last measurement. The method proceeds to step 806, incrementing the value of i (for detecting the next sample) before returning to step 803.

If however the response at step 807 is no, then there has been a voltage change since the last measurement, and thus a test pulse has potentially started. The method proceeds to step 808. At step 808, the value of voltage Vsecond is set to the current stored value Vi. At step 809, the value of i is incremented (i = i + 1). At step 810, a timer is started by setting At=0.

At step 811, the microcontroller reads the next voltage sample value Vi (for example 35 Volts) and stores the result in a memory. At step 812, the microcontroller determines whether the voltage Vi is equal to Vsecond (or more generally, if there is no significant variation between the detected voltage Vi and the voltage Vsecond).

If the response at step 812 is yes (i.e. no variation has been detected), then at step 813 the microcontroller checks whether the duration of the voltage Vsecond has exceeded the maximum duration value Atmax, i.e. whether At > Atmax. If the response at step 813 is no, then the method proceeds to step 814, to increment the value of i (i = i + 1), before returning to step 811. If however the response at step 813 is yes, then the detected voltage change is not a test pulse as the voltage change has lasted beyond the maximum duration. The method 800 then returns to step 802 and restarts, resetting the parameters.

If however the response at step 812 is no (i.e. variation has been detected), there has been another voltage change, for example back to 40 V. At step 815, the microcontroller checks whether the duration of voltage Vsecond has reached the minimum duration value Atmin, i.e. whether At > Atmin. If the response at step 815 is no, then the voltage change was too short to be a test pulse, so the method returns to step 802 and re-sets the parameters. If however the response at step 815 is yes, then the test pulse has been detected, and at step 816, the microcontroller changes the state of the pulse detection flag, for example to 1, allowing the microcontroller to send a pulse detection announcement on the communication network. The method 800 then returns to step 801 to be ready to detect a new test pulse.

In one embodiment, in the case where no pulse generation or pulse generated announcement is sent concerning the beginning or the end of the test pulse generation, the pulse detection is performed during a pre-determined time window. In this case, an additional loop is performed wherein an index is compared to a parameter corresponding to the time window. At the end of the time window, a “time-out” flag may be set to a first value, and the microcontroller of a detecting device reads the flag and detects a time-out of the detecting process.

Figure 9 is a flowchart of a method 900 implemented by a master device for power control of devices with a low power mode and an operational mode, and Figures 10A, 10B, 10C respectively show a completed Segment Discovery Table SDT, a Device Power Table DPT, and a Segment Power Table SPT.

The master function is to control the sequences of embodiments of the invention, and to centralize the power topology table. In some embodiments, such as those presented in Figures 12 and 13, this role is distributed in each device.

At step 901, the network starts up, and all devices are in low power mode, that is to say, only the network function (port com) of the microcontroller, the converter ADC function, and the power supply function are active. At step 902, all devices on the communication network are aware of the identifiers of the other devices, due to the Central Coordinator, as explained above, and the Device Power Table DPT (shown in Figure 10B) is established comprising a first column C12 comprising the device identifiers 210-m (for example the MAC addresses), a second column C22 comprising the maximum power consumption PCm of each device, and a third column C32 comprising the cable loss CLm calculated by each device by determining the resistance of the cable connected to it.

At step 903, an election of the master device is performed. The elected master device controls the discovery sequence, launches the test pulse generation, and controls the messages exchanged as a result of the pulse detection. The election of the master device may be done by selecting the lowest MAC address of all the MAC addresses of the present devices, selecting the fastest device, etc.

At step 904, the index m relating to the number of a device on the network is initialized to the total number M of devices on the network. At step 905, the master device sends a message ordering the other (non-master) devices to prepare for pulse generation and detection, that is to say, to implement the methods shown in relation with Figures 7 and 8.

At step 906, the master device orders the generation of test pulses TP by the device m, as described in relation with Figure 7. (Alternatively, the master device may begin at the lowest device 210-1 and increment until reaching the value M).

At step 907, the master device listens for detection responses (detected pulse DP or undetected pulse UP) by the detecting devices. Alternatively, the master device requests the detection responses from each device (not shown).

At step 908, upon receipt of the detection responses, the master device records the status in the Segment Discovery Table, as shown in relation with Figures 4B and 10A.

At step 909, the master device determines whether the index m of the device is equal to 0. If the response is no, then the method proceeds to step 910, wherein the value of m is decremented by one, m = m-1, before returning to step 906. Otherwise, if the response at step 909 is yes, then the discovery process is complete, all devices having sent test pulses. Alternatively, repetition is avoided by having only non-detecting devices send test pulses, until there are no more non-detecting devices.

Once the Segment Discovery Table (SDT) is complete, the method 900 proceeds to step 911, wherein the master device computes a Segment Power Table SPT as shown in Figure 10C from the Device Power Table DPT and the Segment Discovery Table SDT.

The Segment Power Table SPT indicates the total power consumption per segment, and comprises a first column C13 comprising the segment identifiers Sn (for example, S1, S2, S3, S4), a second column C23 comprising the total power consumption TPn for each segment, that is to say the sum of the power value in full power mode of the device(s)of the segment, plus the power lost in the cable resistance, and a third column C33 indicating Yes or No as to whether all devices of the segment can begin in full-power mode.

The following example equation provides the total power consumption for the segment S1: TP1 = PC1 + PC4 + PC6 + CLm

The cable loss CLm is calculated by the formula CL = V2 / Rc, where V is the voltage measured as explained above, and where Rc is the cable resistance.

In a first embodiment, only the cable resistance to the first device of the power segment (the device closest to the PSE) is considered, for example only cable loss CL1, the other cable losses CL4, CL6 being disregarded due to the fact that generally only the first cable has a non-negligible length, the other cables being generally short with negligible resistances. However, in other embodiments, the calculation can take into account one or more of the other cable losses. The third column C33 results from a comparison between the total power consumption TPn for a segment Sn and the maximum power supplied by the PSE 220 per segment or per port.

If the maximum power for a segment is for example 50 Watts, then the master device or each device can conclude whether the total power for the segment will be less than or equal to the maximum power, TPn < Maximum Power per Port. Based on this determination, it may be determined whether the device or devices of the segment can start in full power mode.

If the response is yes, all devices of the segment can start in high power mode.

If the response is no, all devices of the segment cannot start at the same time in full power mode. A power management method may be used to indicates which device is authorized to start in high power mode, and the order of the start-ups.

In another embodiment, the network does not have a master device. Every device on the communication network identifies itself to the others, and the Device Power Table is completed as shown in Figure 10B, the tables being stored in each device. The devices generate in turns the test pulses, for example by cycling through the addresses, and the detecting devices respond to all other devices, such that all devices can store the result in their own Segment Discovery Table as shown in Figure 10A. Once the Segment Discovery Tables are complete, each device determines the Segment Power Table as shown in Figure 10C, and from the segment power table, in what mode it can start.

Figure 11 is an electrical diagram of a portion of a power segment comprising a port of a power source equipment PSE 220’ according to another embodiment, a device, and cables, an alternate embodiment to that shown in Figure 5. In this embodiment, the PSE 220’ centralizes the power management functions, acting as the master device of the power network as defined above.

With respect to the diagram shown in Figure 5, like elements are shown with like references, the only difference being an operational amplifier OP connected across the serial resistor SR2 in order to measure the voltage thereacross, and therefore the current flowing therethrough. The measured voltage is then sent to an analog-to-digital converter ADC, which then sends the information to a microcontroller of the PSE (shown in Figures 12 and 13). The microcontroller may thus sense a test pulse as described above, caused by the switch 214 and resistance R1 of a device, creating a voltage drop due to the first serial resistance RC1 of a cable and the serial resistor SR2 of a port. Each port may comprise an operational amplifier OP and an ADC converter, and the microcontroller may be common to all ports or for each specific port.

Figure 12 is a diagram of a device 1200, and more particularly a camera, implementing the invention according to one embodiment. The camera conventionally comprises a lens 1201, a CMOS (Complementary Metal-Oxide-Semiconductor) sensor 1202, a video processor 1203, a network processor 1204, a memory 1205, an internal power supply 1206, and a BNC connector 1207 coupled to a coaxial cable (not shown) transporting power and data. A protection circuit 1208 is coupled to the connector 1207 to protect the camera from an electrical surge. The data and power arriving from the cable are then supplied to two paths, a first path P1 to the internal power supply 1206, and a second path P2 to the network processor 1204. A low pass filter LPF 1209 is arranged on the first path P1 between the protection circuit 1208 and the internal power supply 1206. The filter 1209 filters the data input from the cable, recovering DC power for the internal power supply 1206, which provides power for the various components of the camera. An amplifier 1210 is coupled to the first path, and receives on input the voltage appearing on the first path, and supplies on output an amplified voltage to an Analog Digital Converter or ADC 1211 arranged within the network processor 1204, which further comprises a power management module 1212.

Similar to Figure 5, a resistor 1213 and a switch 1214 are arranged so that when the switch 1214 is closed by a control signal CS from the network processor 1204, a test pulse is generated. The Segment Discovery Table SDT, the Device Power Table DPT, and the Segment Power Table SPT may be stored in the memory 1205 (of the type EPROM, EEPROM, Flash, etc.), so that the parameters may be updated as necessary. A DC isolation circuit 1216, a transformer 1217, and a HPAV module 1218 are arranged on the second path P2 between the protection circuit 1208 and the network processor 1204. The transformer 1217 transforms received signals Rx from the cable to the network processor 1204 and transmitted signals Tx from the network processor 1204 to the cable. The HPAV module 1218 comprises bandpass filters BPF for the transmitted and received data, an Analog Front End AFE circuit and a processor PROC to communicate data packets to and from the network processor 1204. In this embodiment, the camera is in low consumption (less than 2 watts) during the discovery sequence according to the invention. The typical power consumption in normal operating mode is around 10 watts. This means that during the low power mode, only the necessary components are powered, for example the Network Processor 1204, the ADC 1211, the memory 1205, the HPAV module 1218 and the internal power supply 1206. The video processor 1203, the CMOS sensor 1202, and other components not represented and not necessary may be in stand-by mode or switched-off.

The device 1200 is thus an integrated device, wherein all components are comprised in a single housing. The device 1200 has the advantages of lower cost and easier maintainability, as well as all algorithms being run on a single processor, CPU 1204.

Figure 13 is a diagram of a camera 1300 implementing the invention according to another embodiment, comprising an IP camera 1300-1 and a Network adapter 1300-2. The IP camera 1300-1 comprises a lens 1301, a CMOS sensor 1302, a video processor 1303, a network processor 1304, at least one memory 1305, and an Ethernet transceiver 1306 coupled to a power device circuit 1307 (a power device according to the Power over Ethernet Standard). The Network Adapter 1300-2 comprises, similarly to Figure 12, a BNC Connector 1310, a protection circuit 1311, a low-pass filter 1312, an internal power supply 1313, an amplifier 1314, a resistor 1315, a switch 1316, a microcontroller 1317 comprising an analog to digital converter 1318, a memory 1319, a DC isolation circuit 1320, a transformer 1321, and an HPAV module 1322.

The Network Adapter 1300-2 further comprises a three port Ethernet bridge 1323 coupled to a physical interface PI 1324 (such as an Ethernet transceiver), a power supply circuit 1325 (Power Supply Equipment according to the Power over Ethernet standard), and a second switch 1326 controlled by a control signal CS2 from the microcontroller 1317. A cable 1327, such as an Ethernet cable or other connection, couples the physical interfaces 1306, 1324.

According to one embodiment, the IP camera 1300-1 is not powered during the segment discovery process, only the Network Adapter 1300-2 being powered, with the microcontroller 1317, the memory 1319, the HPAV module 1322, and the internal power supply 1313 being powered. The microcontroller 1317 may control the power to the camera 1300-1 by means of the switch 1326, which supplies a voltage V to the camera via the PoE-PSE circuit 1325. At the end of the segment discovery process according to the invention, if the power and the voltage on the power segment are sufficient for each compatible device, then the microcontroller 1323 enables the PoE PSE circuit 1325 to power-on the camera 1300-1. After that, the IP camera can transmit the video stream through the Ethernet link 1306-1326, and it can be controlled by the user. Functions performed by the Network processor 1204 of Figure 12 may be performed by the microcontroller 1317, and the Tables SDT, DPT, SPT may be stored in the memory 1319.

The device 1300 is thus a modular device, wherein the actual camera 1300-1 has an external adapter 1300-2. The device 1300 has the advantages of being able to adapt a conventional existing camera, without replacing the entire camera. All algorithms are run on the processor CPU 1317.

In a variation of the device 1300 shown in Figure 13, the algorithms are run on the network processor 1304 as the master CPU. The CPU 1317 of the adapter is a slave CPU, executing commands sent by the master CPU 1304 via the Ethernet link 1327.

The messages exchanged via the link 1327 may concern the control of the switch 1316 and measurement data sent from the slave CPU 1317 to the master CPU 1304. These messages may be internal synchronization messages and not necessarily sent using the HomePlug AV messaging system, but may be sent by using Ethernet level 2 protocols.

The messages exchanged on the link 1327 may comprise a first group of messages group (Pulse Generation Announcement, Pulse Detected Announcement, Pulse Undetected Announcement, Segment Discovery Table, etc.) relating to the exchange between nodes of the same communication network, with a classical format including the source address, the destination address, an identifier of the power segment, the packet size, the message type, and the message data.

The message type indicates the type of message (pulse generation announcement, a pulse detected announcement, a pulse undetected announcement, a segment discovery table, a pulse generated announcement, etc.). In the case of the third embodiment (variation of the device 1300), the messages pass through the link 1327, as they are generated by the processor 1304.

In the embodiment of device 1300, a second additional group of message data may be considered, the second group allowing the camera module 1300-1 to control pulse generation performed by the adapter module 1300-2, according to the algorithms described above, such as allowing the processor 1304 to control the switch 1316 while allowing the processor 1317 to provide feedback to the “master processor” 1304 concerning the sensing measurements performed by the network devices, as described.

For instance, the message data of the second group may include: - message data indicating the time width of the pulse, - message data indicating the time windows when the pulse can be generated, - message data indicating the beginning and the end of the time windows in the case where the time window is not defined by its duration, - message data indicating the pulse current amplitude in the case where the pulse is generated by a current generator, or by the switching of a resistor with a determined value, - message data indicating the power consumption of the adaptor, for example as needed for the calculation by the main processor of the total power consumption as described above, and - message data indicating the result of the measurement done by the adaptor (voltage values, etc.).

The second group is not limited to the above list and the skilled person may consider additional message data.

All or some of the above message data of the second group may be exchanged between the processors 1304, 1317, and may be sent using a message data field of messages of the general format.

In one embodiment, message data of the second group are concatenated into the message data field of a single message.

In another embodiment of the present invention, message data of the second group are distributed over the message data fields of a plurality of messages.

The link 1327 may preferably be an Ethernet level 2 protocol link, but alternatively may be of any other communication type: classical bus, USB type, etc....

As mentioned above, message data of the second group may be sent using the message data field of a message that also includes a source address, a destination address, packet size, and message type. A power segment identifier may not be used in this case.

Additionally, the adapter and the camera are here considered as paired, therefore the source address and the destination address (i.e. the MAC address of the adapter and of the camera) are known by each, allowing local message exchange between themselves, without having to send messages over the network.

It will be understood by the skilled person that the invention may be implemented in different manners, depending on the materials available, the standards to be applied, and so forth.

In some embodiments the cables are coaxial cables adapted for the CCTV network, with a characteristic impedance of 75 ohm, with low resistivity material; that is to say solid bare copper conductor and bare copper braid or tinned copper braid for the shield. The cable can be a RG11 or a RG59 type cable. In some embodiments, the cables connectors (280), and the PSE ports connectors are BNC connectors adapted for the CCTV network, with a characteristic impedance of 75 ohm.

In some embodiments the communication network is a wired network as a Power Line Communication (PLC) network, for instance the Home-Plug AV (HPAV) or the HD-PLC. In some other embodiments the communication network is a wireless network as the Wi-Fi, thus separate from the power network.

To exchange information between devices on the same communication network, data and management messages use a path through the “High Level Entity” or HLE as defined in the HPAV system, in Broadcast mode or Peer to Peer mode. In the HPAV system, a coordinator or CCO maintains a topology table used to complete the Segment Discovery Table.

In some embodiments, the communication channel is based on a Home-Plug AV network, but it may be based on another type of PLC network, or wireless networks as Wi-Fi. In this embodiment, there is no change on the MAC layer and the convergence layers. As this technology can work on different wired media like Power Line wires, or twist pair wires or coaxial cables some slightly change are done on the Physical Layer. This concerns only hardware components for the characteristic impedance, for the band pass filter.

Though the notification/indication of the detection results (such as the pulse detected or pulse undetected announcements) has been described in the preceding as an exchange of messages on a communication network, it may simply comprise for example changing the state of a flag of the detecting device, from 0 to 1 for example, the flag then being read or communicated by other means.

Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications which lie within the scope of the present invention will be apparent to a person skilled in the art. In particular different features from different embodiments may be interchanged, where appropriate. Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention as determined by the appended claims.

Claims

1. A method of determining the topology of a power network, the power network comprising: - a power source, - at least one power segment coupled to the power source, - at least one generating device coupled to a power segment and capable of generating a physical parameter variation on the power segment to which the generating device is coupled, and - at least one detecting device coupled to a power segment and capable of detecting, on the power segment to which the detecting device is coupled, a physical parameter variation generated by a generating device, the method comprising, for the detecting device, the steps of: - detecting for, on the segment to which the detecting device is coupled, a physical parameter variation generated by the generating device; and - causing an update of a table storing the topology of the power network, wherein: - if the physical parameter variation was detected by the detecting device, the table is updated to store an information that the generating device and the detecting device belong to a same power segment, and - if the physical parameter variation was not detected by the detecting device, the table is updated to store an information that the generating device and the detecting device do not belong to a same power segment.

2. The method according to claim 1, wherein the devices are coupled by means of a communication network, such that the devices can send and/or receive messages concerning at least one of: - a variation generation announcement, sent by the generating device or by a master device, that the generating device will generate the physical parameter variation, - a variation generated announcement, sent by the generating device or by a master device, that the generating device did generate the physical parameter variation, - a variation detected announcement, sent by a detecting device, that the detecting device did detect the generated physical parameter variation, - a variation undetected announcement, sent by a detecting device, that the detecting device did not detect the generated physical parameter variation, - a generate pulse announcement, sent by a master device to the generating device, ordering it to generate the physical parameter variation, and - a respond detection announcement, sent by a master device or by the generating device, ordering the detecting device to send the variation detected announcement or the variation undetected announcement.

3. The method according to claim 2, further comprising the steps of: - defining, by means of messages exchanged using the communication network, a time window during which the generating device is configured to generate the physical parameter variation, and - updating the table according to a result of the detecting step occurring during the time window.

4. The method according to claim 2, wherein upon receipt of the variation generation announcement, the detecting device detects for the physical parameter variation during a time window.

5. The method according to claim 4, wherein the detecting for the physical parameter variation of the power segment by the detecting device comprises one of the following: - starting a time window of a pre-defined length upon reception of the variation generation announcement, or - detecting for the physical parameter variation according to a timestamp contained in the variation generation announcement, the timestamp indicating an earlier or later time.

6. The method according to one of claims 3 to 5, wherein a detecting device that detected the physical parameter variation sends the variation detected announcement regardless of whether the time window has finished.

7. The method according to one of claims 3 to 6, wherein a detecting device that did not detect the physical parameter variation during the time window sends the variation undetected announcement after the end of the time window or upon receipt of the respond detection announcement.

8. The method according to claim 2, further comprising the steps by the detecting device of: - detecting for the physical parameter variation, - receiving the variation generated announcement, - determining whether a physical parameter variation was detected in a time window before the reception of the variation detected announcement, and - sending the variation detected announcement or the variation undetected announcement.

9. The method according to one of claims 3 to 8, wherein the time window is defined by a master device or by the generating device.

10. The method according to claim 2, further comprising the steps by the detecting device of: - receiving the variation generation announcement, and - receiving the variation generated announcement, wherein the time between the announcements define a time window for detecting for the physical parameter variation.

11. The method according to claim 2, wherein an identifier of the detecting device comprised within the variation detected announcement or the variation undetected announcement is used to update the table.

12. The method according to claim 11, wherein the step of updating the table comprises storing identifiers of the devices and the power segment to which each device belongs.

13. The method according to one of claims 1 to 12, further comprising the steps of: - selecting another device to be a new generating device, and - generating, by the new generating device, a physical parameter variation on the power segment to which it is coupled.

14. The method according to claim 13, wherein selecting a new generating device comprises selecting a device that did not detect a previous physical parameter variation.

15. The method according to claim 2, wherein the sending of an announcement comprises broadcasting the announcement on the network.

16. The method according to one of claims 1 to 15, wherein the physical parameter variation is a voltage change, the method further comprising the steps of: - defining a minimum pulse duration and maximum pulse duration, and - upon detection of a voltage pulse by a detecting device, determining whether the voltage pulse occurs between the minimum pulse duration and the maximum pulse duration.

17. The method according to claim 16, wherein a detecting device further comprises an analog-to-digital converter configured to measure the voltage at the inputs of the device and a microcontroller configured to read and store the measured voltage, and wherein detecting the voltage change comprises the steps of: - detecting, by the converter, the voltage at the inputs, - reading, by the microcontroller, the detected voltage, and - storing the detected voltage.

18. The method according to one of claims 1 to 17, wherein the table comprises device identifiers and the method further comprises a step of selecting a new generating device by selecting the next device identifier in the table.

19. The method according to one of claims 1 to 18, wherein the physical parameter variation is a voltage change, and wherein the generating device comprises a resistor, a switch to couple or un-couple the resistor to inputs of the device, and a microcontroller configured to command the switch, and generating the physical parameter variation comprises the steps of: - commanding the switch to close in order to couple the resistor to the inputs of the device, and - commanding the switch to open in order to un-couple the resistor from the inputs of the device.

20. A detecting device capable of detecting a generated physical parameter variation on a power segment of a power network, the power network comprising: - a power source, - at least one power segment coupled to the power source, - at least one generating device coupled to a power segment and capable of generating a physical parameter variation on the power segment to which the generating device is coupled, and - at least one detecting device coupled to a power segment and capable of detecting, on the power segment to which the detecting device is coupled, a physical parameter variation generated by a generating device, wherein the detecting device is configured to: - detect for, on the segment to which the detecting device is coupled, a physical parameter variation generated by the generating device; and - cause an update of a table storing the topology of the power network, wherein: - if the physical parameter variation was detected by the detecting device, the table is updated to store an information that the generating device and the detecting device belong to a same power segment, and - if the physical parameter variation was not detected by the detecting device, the table is updated to store an information that the generating device and the detecting device do not belong to a same power segment.

21. The detecting device according to claim 20, wherein the detecting device is coupled to the generating device by means of a communication network, such that the detecting device can send and/or receive messages concerning at least one of: - a variation generation announcement, sent by the generating device or by a master device, that the generating device will generate the physical parameter variation, - a variation generated announcement, sent by the generating device or by a master device, that the generating device did generate the physical parameter variation, - a variation detected announcement, sent by the detecting device, that the detecting device did detect the generated physical parameter variation, - a variation undetected announcement, sent by the detecting device, that the detecting device did not detect the generated physical parameter variation, - a generate pulse announcement, sent by a master device to the generating device, ordering it to generate the physical parameter variation, and - a respond detection announcement, sent by a master device or by the generating device, ordering the detecting device to send the variation detected announcement or the variation undetected announcement.

22. The detecting device according to claim 21, wherein upon receipt of the variation generation announcement, the detecting device is configured to detect for the physical parameter variation during a time window.

23. The detecting device according to claim 22, wherein in order to detect for the physical parameter variation, the detecting device is configured to do one of the following: - start the time window of a pre-defined length upon reception of the variation generation announcement, or - detect for the physical parameter variation according to a timestamp contained in the variation generation announcement, the timestamp indicating an earlier or later time.

24. The detecting device according to one of claims 21 to 23, wherein upon detection of the physical parameter variation, the detecting device is configured to send the variation detected announcement regardless of whether the time window has finished.

25. The detecting device according to one of claims 21 to 24, wherein upon a non-detection of the physical parameter variation during the time window, the detecting device is configured to send the variation undetected announcement after the end of the time window or upon receipt of the respond detection announcement.

26. The detecting device according to claim 21, wherein the detecting device is further configured to: - detect for the physical parameter variation, - receive the variation generated announcement, - determine whether a physical parameter variation was detected in a time window before the reception of the variation detected announcement, and - send the variation detected announcement or the variation undetected announcement.

27. The detecting device according to claim 21, wherein the detecting device is further configured to: - receive the variation generation announcement, and - receive the variation generated announcement, the time between the announcements defining a time window for detecting for the physical parameter variation.

28. The detecting device according to claim 21, wherein the detecting device is further configured to send its identifier within the variation detected announcement or the variation undetected announcement, for updating of the table.

29. The detecting device according to one of claims 20 to 28, wherein the physical parameter variation is a voltage change and a minimum pulse duration and maximum pulse duration are defined, and the detecting device is further configured to determine, upon detection of a voltage pulse, whether the voltage pulse occurs between the minimum pulse duration and the maximum pulse duration.

30. The detecting device according to claim 29, the detecting device further comprising an analog-to-digital converter configured to measure the voltage at the inputs of the device and a microcontroller configured to read and store the measured voltage, and wherein detecting the voltage change comprises the steps of: - detecting, by the converter, the voltage at the inputs, - reading, by the microcontroller, the detected voltage, and - storing the detected voltage.

31. A generating device capable of generating a physical parameter variation on a power segment of a power network, the power network comprising: - a power source, - at least one power segment coupled to the power source, - at least one generating device coupled to a power segment and capable of generating a physical parameter variation on the power segment to which the generating device is coupled, and - at least one detecting device coupled to a power segment and capable of detecting, on the power segment to which the detecting device is coupled, a physical parameter variation generated by a generating device, wherein the generating device is configured to generate a physical parameter variation on the power segment to which it is coupled, so that the detecting device may detect for, on the segment to which it is coupled, the generated physical parameter variation, so that a table storing the topology of the power network may be updated, wherein: - if the physical parameter variation was detected by the detecting device, the table is updated to store an information that the generating device and the detecting device belong to a same power segment, and - if the physical parameter variation was not detected by the detecting device, the table is updated to store an information that the generating device and the detecting device do not belong to a same power segment.

32. The generating device according to claim 31, wherein the generating device is coupled to the detecting device by means of a communication network, such that the generating device can send and/or receive messages concerning at least one of: - a variation generation announcement, sent by the generating device or by a master device, that the generating device will generate the physical parameter variation, - a variation generated announcement, sent by the generating device or by a master device, that the generating device did generate the physical parameter variation, - a variation detected announcement, sent by a detecting device, that the detecting device did detect the generated physical parameter variation, - a variation undetected announcement, sent by a detecting device, that the detecting device did not detect the generated physical parameter variation, - a generate pulse announcement, sent by a master device to the generating device, ordering it to generate the physical parameter variation, and - a respond detection announcement, sent by a master device or by the generating device, ordering the detecting device to send the variation detected announcement or the variation undetected announcement.

33. The generating device according to claim 32, wherein the generating device is configured to generate the physical parameter variation during a time window defined by means of messages exchanged using the communication network.

34. The generating device according to claim 33, wherein the generating device is configured to define the time window.

35. The generating device according to one of claims 31 to 34, wherein the physical parameter variation is a voltage change and wherein the generating device further comprises a resistor, a switch to couple or un-couple the resistor to inputs of the device, and a microcontroller configured to command the switch, so that the physical parameter variation may be generated by commanding the switch to close in order to couple the resistor to the inputs of the device, and commanding the switch to open in order to un-couple the resistor from the inputs of the device.

36. A power network comprising: - a power source, - at least one power segment coupled to the power source, - at least one generating device coupled to a power segment and capable of generating a physical parameter variation on the power segment to which the generating device is coupled, the generating device according to one of claims 31 to 35, and - at least one detecting device coupled to a power segment and capable of detecting, on the power segment to which the detecting device is coupled, a physical parameter variation generated by a generating device, the detecting device according to one of claims 20 to 30.

37. The power network according to claim 36, wherein the power source comprises means for preventing a physical parameter variation generated on one power segment from being detected on another power segment.