GB2530567A

GB2530567A - Backup module for daisy chain networks

Info

Publication number: GB2530567A
Application number: GB1417078.1A
Authority: GB
Inventors: Hervã Merlet; Yacine El Kolli
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2014-09-26
Filing date: 2014-09-26
Publication date: 2016-03-30
Also published as: GB201417078D0

Abstract

In a daisy-chain Local Area Network of devices (eg. cameras 504 in a video surveillance network) fed by both data and power signals (eg. Power over Coax, PoC), an interconnection device 300 (300-0, 300-1 fig. 3) having two ports P1 & P2 provides impedance matching, power management functions and a backup loop for cable or network failures (fig. 7). Detection units 505, 507 detect reference signals controlled by a controller 503, which adapts impedance via switches 511-513 and resistor 514 when the ports are connected or disconnected to allow or block the data or power signals. Devices may be placed in pass through mode (eg. cameras 603, 604, fig. 6) or active mode (601, 602).

Description

TITLE OF THE INVENTION

Backup module for daisy chain networks.

FIELD OF THE INVENTION

The present invention relates to video surveillance systems.

BACKGROUND OF THE INVENTION

Digital video surveillance systems typically comprise at least two types of wire networks: a first LAN network with, for instance, CATS wires for data transport and a second network with a power line wire infrastructure for power distribution to digital cameras.

However, costs may be saved by using mixed data and power distribution technologies.

These technologies allow the carrying of both data and power on the same wire. PoE (Power over Ethernet) is a well-known technology allowing power distribution and Ethernet data to be mixed on one cable.

A system integrator building a new digital camera surveillance infrastructure can save the costs associated with the powerline network by using the LAN wires for power distribution. Part of the costs saved from the power line network may be invested in higher quality LAN cables capable of supporting the power distribution requirements.

Moreover, a system integrator who has to upgrade from an analog surveillance system to a digital video surveillance system may also save costs by reusing the analog cable infrastructure. For example, some analog video surveillance systems use coaxial cables for transporting the video signals from the cameras to a central point. Some technological solutions allow both digital data transport and power distribution over existing analog video distribution cable networks such as coaxial or copper pair networks. The process of reusing the existing analog cable network is referred to as "retrofit setup".

Prior art analog video surveillance systems are often built in a "star" topology. Each camera is connected to a central point by a dedicated cable. A system integrator wishing to increase the coverage of the surveillance system by adding new cameras thus has to run new cables from the cameras to the central point. However, in some configurations, such as in public transportation networks, the cable may be as long as 300 meters. Therefore such star topology may be impractical.

Digital technologies exist that allow daisy chaining of cameras on a same cable. Here, the system integrator can save costs when adding cameras since he simply has to connect them to the pre-existing cable.

As far as large scale monitoring systems are concerned, coaxial cables are currently being used. This is due in part to the fact that in prior CCTV (acronym for "closed-circuit television") networks such cables were used. When upgrading a video surveillance network from analog to digital, reuse of the existing cable infrastructure is usually a requirement for cost reasons.

When upgrading the network to digital communication technology, several IF cameras are installed on the same coaxial cable which is used for communications and for power supply.

Connexion of coax powered IP cameras with daisy chain capability is based on a shared medium access control protocol (bus type), such as, for instance, the "HomeP/ug® AVprotocof'.

The "Power over Coax" technology has several advantages.

Power over Coax makes it possible to save time and costs by avoiding a requirement for separate installations of data and power infrastructures.

Power over Coax can be implemented in a non-complex fashion.

Power supply is fully integrated within the Coax infrastructure; therefore, access to difficult places for power deployment, such as ceilings, is facilitated.

Power over Coax provides mobility. Powered devices can be easily moved without necessitating AC outlets, thereby minimizing business disruption. Wherever there is a Coax connection, a device can be easily deployed. In addition, Power over Coax makes it possible to accelerate the deployment of network cameras because power, which is seldom available above the ceiling, can now be provided over the Coaxial cable.

Power over Coax is reliable technology. The power supplies may be concentrated in a central room and the need for a local backup for each AC outlet is avoided. Maintenance is thus made easier.

Power over Coax is safe. There are no high voltages involved. The voltages are usually below 48V.

Networks implementing power over Coax can be easily controlled, using for example the Simple Network Management Protocol which provides control and monitoring of the Power over Coax device and the powered devices.

Power over Coax provides security since it makes it possible to shut down unused powered devices when people have left the premises.

Power over Coax capabilities require only a low per-pod cost addition.

Another advantage is the bandwidth through the entire cable network. For example, the coaxial cable has to have the appropriate characteristic impedance and the appropriate termination adapted at the appropriate impedance (for example 75 ohms for the video network). This is a requirement in order to have fully exploitable bandwidth and a good quality of signal. Any impedance mismatching or cable deterioration or bad physical set-up may highly decrease the bandwidth. It may also cut the video communication.

In the surveillance camera domain, the quality of service is a main concern. The video data between the camera and the central station where VMS (video management system) is installed must not be disrupted.

However, the cable installation can be deteriorated or partially cut which may provoke communication interruption.

The camera network must continue to send video data even in case of power or cable failure.

In the state of the ad, there is no solution solving the problem of cable deterioration without an intervention by a technician. In the LAN type network technology as the "lOBase2 network" on coaxial cable, document CA1299698 discloses a device detecting short circuits in a coaxial cable. This device is useful for helping the technician find which cable segment on site is causing network dysfunction.

Thus, there is still a need for a device making it possible to automatically allow video data and power distribution continuity through the network. There is also still a need for a device performing impedance matching, and power balancing on each segment of the network, and authorizing a back-up link in case of cable failure.

The present invention lies within this context.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided an interconnection device for managing connection losses between devices of a daisy chain network, the device comprising: -at least two physical ports, each port being configured to exchange data signals and power signals, -at least two detection units, respectively associated with said at least two physical ports, each detection unit being configured to detect a connexion on its associated physical port, -a connexion unit for connecting or disconnecting said at least two physical ports thereby allowing or blocking transfer of data signals and power signals, -a control unit configured to control said connexion unit based on outputs from the detection units, and -an impedance adaptation unit for adapting impedance of at least one of said at least two physical ports when disconnected by said connexion unit.

Embodiments provide a solution to disruption in video surveillance streams due to impedance impairment or a coax cable failure, or cable disconnection.

For example, a device according to the first aspect may be used in a video surveillance system for increasing its reliability. A spare segment may be installed in the network forming a link between two daisy chains of cameras thereby forming a loop. The spare segment makes it possible to change the power distribution in presence of disruption in one of the daisy chains.

According to embodiments, data (for example video data)can be continuously sent even in case of power or cable failure.

Embodiments provide impedance matching, power balancing, and authorize a cable back-up loop.

Embodiments can be easily implemented and provide automatic network recovery in case of cable failure, without any intervention of a technician.

For example, said connexion unit is further configured to connect or disconnect said impedance adaptation unit to at least one of said at least two physical ports.

The control unit may be configured to control said connexion unit to connect said impedance adaptation unit to a physical port from which power signals are received.

For example, said at least two detection units are configured to detect connexion by monitoring receipt of a first reference signal in response to a second reference signal previously sent.

According to embodiments, each detection unit comprises a reference signal detector for detecting said first reference signal and a reference signal generator for generating said second signal.

For example, said control unit is configured to control said connexion unit for connecting said at least two physical ports when: -connexion is detected on one physical pod, -no reference signal is received on said physical port, and -power level on another port is above a power threshold.

According to embodiments, said power threshold depends on a type of device connected on the network.

According to embodiments, said power threshold represents a power level required for powering said type of device.

According to embodiments, said control unit is configured to control said connexion unit for connecting said at least two physical pods when: -connexion is detected on one first physical pod, -power level on said first physical port is below a first power threshold, and -power level on a second physical pod is above a second power threshold.

For example, said first and second power thresholds depend on a type of device connected on the network.

For example, said second power threshold represents a power level required for powering said type of device.

For example, said first power threshold represents the presence of a device of said type on a connexion line connected to said first physical port.

According to embodiments, said control unit is configured to control said connexion unit for disconnecting said at least two physical pods when: -connexion is detected on one physical pod, and -power level on said physical pod is above a third power threshold.

According to embodiments, said third power threshold represents the presence of a device of said type on a connexion line connected to said physical port.

For example, said control unit is configured to control said connexion unit to disconnect said at least two physical ports when no connexion is detected on one of said physical pods.

The device according to the first aspect may be implemented as a passive circuit.

According to embodiments, the device according to the first aspect further comprises a connexion port for connecting the module to a device of the network.

The device may also be implemented as an active circuit and configured to be powered by said device through said connexion port.

According to embodiments, a first and second set of devices are respectively connected to two connexion links and each connexion link is connected to a central equipment item of the network at one end and connected to a loop connexion element at the other end, the connexion links thereby forming a connexion loop.

According to embodiments, the device is configured to be connected to a daisy chain network.

According to a second aspect of the invention there is provided a camera comprising a device according to the first aspect.

According to a third aspect of the invention there is provided a system comprising a plurality of devices according to the first and/or second aspect.

For example, the system comprises at least two connexion links respectively daisy chaining a first set of devices and a second set of devices, and each connexion link is connected to a central equipment item of the network at one end and connected to a loop connexion element at the other end, the connexion links thereby forming a connexion loop.

The system may be a video surveillance system.

According to a fourth aspect of the invention there is provided a method for managing connection losses between devices of a daisy chain network.

The objects according to the second third and fourth aspects of the invention provide at least the same advantages as those provided by the device according to the first aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the invention will become apparent from the following description of non-limiting exemplary embodiments, with reference to the appended drawings, in which: -Figure 1 illustrates a general retrofitted video surveillance system, -Figure 2 illustrates an exemplary perturbation in a video stream, -Figure 3 illustrates a device installation according to embodiments,

B

-Figure 4 illustrates advantages provided according to embodiments, -Figure 5 illustrates a device architecture according to embodiments, -Figure 6 illustrates a video surveillance system according to embodiments operating in normal conditions, -Figure 7 illustrates the video surveillance system of Figure 6 operating in case of cable failure, -Figure 8 is a flowchart of steps performed for configuring a device according to embodiments.

DETAILED DESCRIPTION OF THE INVENTION

In what follows, there are described embodiments of a device that aims at detecting impedance impairment due to cable failure or cable disconnection in a video surveillance network having a daisy chain topology. In order to improve reliability of the video surveillance system, a spare segment is installed forming a loop between two daisy chains. Embodiments take advantage of this spare segment for changing the power distribution in the presence of disruption in one of the daisy chains.

Figure 1 illustrates a general retrofitted video surveillance system according to embodiments. For example, the retrofitted video surveillance system is an analog video surveillance system that has been upgraded to support video over IP (Internet Protocol). The analog cameras formerly present in the system have been replaced by IP cameras lOla, lOIb. However, the wire infrastructure, comprising cables 106,107,108 (such as coaxial cables) has been kept as is stood.

Cables 106, 107 and 108 were used in the original analog system for transporting analog video signals. In the retrofitted system they are used for transporting both IP video data, control data and power supply. In the present example, the cables may be coaxial cables. The cables may be 300 meters long for example. However, any other type of cables adapted to transport analog video signals can be used.

At a central point of the system infrastructure, an equipment item 102 referred to as the "EoC receiver (E0C is the acronym for "Ethernet over Coax") or "IP over Coaxial receive( connects the cables 106, 107, 108 to a LAN infrastructure 103. The Eoc receiver also provides power through the cables 108, 107, 106 to the cameras connected to them. The EoC receiver encapsulates uplink IF LAN traffic received from its LAN interface into data packets suitable for digital data transport over coaxial cables such as the HomePlug® AV protocol for example and transmits them over the coaxial cables. The EoC receiver extracts IF LAN traffic from packets received on the downlink coaxial interfaces and forwards them through the LAN interface. The EoC receiver may be powered by a 110/220 volt source.

Main coaxial cables can be used for connecting one or several cameras. For example camera lOlb is directly connected to a main coaxial cable 108 whereas camera lOla is connected to a main coaxial cable 106 through a "T" style connector 109 and an intermediary cable 110. "T" style connectors can be used for increasing the number of cameras connected to a main coaxial cable. For example, four cameras are connected to the main cable 106 whereas one camera is connected to the main cable 108.

The LAN infrastructure 103 includes switches, routers and gateways for transporting IP video data to a VMS (acronym for "Video Monitoring System') 104 and to a digital video recorder 105.

The VMS (Video Monitoring System) 104 displays the IF video streams for the purpose of surveillance. Also, the VMS 104 displays power diagnosis information from the cameras when the information is included in OSD (acronym for "on screen display") data as part of the video stream sent by the camera.

The digital video recorder device 105 records the IP video stream for later play back.

Figure 2 illustrates an exemplary perturbation in a video stream. In the video installation of Figure 2, the cable may have a characteristic impedance that ensures good adaptation along the cable and good adaptation of the load which is here the camera. The impedance may be 75 ohm, for

example.

A cable failure or a bad set-up of the camera can create impedance mismatching, signal reflection, or a high return loss. This may result in video signal destruction.

As explained hereinabove with reference to Figure 1, the cable carries the power, for example a 48 V DC voltage. Another material incident may be a cable short circuit, or a cut, or cable degradation. In such case, power is lost.

Figure 2 illustrates this latter case. A cable 202 is connected to an EoC (Ethernet over Coax") receiver 201. A first camera 210 is connected to the cable through a "T" connector 204a. The "1" connector 204a allows addition of a second camera 211 connected through a cable 203 and another "T" connector 204b. The cable and the "T" connector carry the data signal and the power.

In case of cable failure 220 on cable 203 between the two cameras 210, 211, the data signal and the power may be lost or degraded. In particular, damage to the cable may create impedance mismatching which may result in signal reflection 221 of the data signal 222 (both represented by the arrows) of the first camera 210. The signal reflection may generate return losses and signal destruction at the level of the EoC receiver 201. The data signal is thus not detected and the camera is out of order. Additionally, the cable failure may result in power issues.

The damage to the cable may be a short circuit, or a cable cut, or an open circuit or cable crushing, a nibble by a rat, or a bad set-up. Such damage deteriorates the characteristic impedance and the DC resistance of the cable.

As illustrated in Figure 3, according to embodiments, an additional device, or interconnection device 300-0, 300-1 is connected to the camera (it may also be integrated with the camera). Device 300-0 is connected to camera 210 and has at least two ports: one port is connected to the first cable 202 and one port is connected to the second cable 203. Device 300-2 is connected to camera 211 and has at least two ports: one port is connected to the second cable 203 and one port remains not connected if there is no additional camera in the daisy chain.

Devices 300-0 and 300-1 provide impedance matching and power management functions. The devices comprise respective DC and AC switch systems.

With reference to Figure 4, advantages provided by devices according to embodiments are presented.

Since the devices according to embodiments provide impedance matching and power management, an additional loop circuit can be implemented in the network. A first network link comprising cables 202 and 203 connects cameras 210 and 211 to the EoC 201. A second network link comprising cables 206 and 205 connects cameras 212 and 213 to the EoC 201.

A loop is formed by connecting cameras 211 and 212 through a cable 204. In case of cable failure on one segment of the link, for example on cable 203, the devices 300-0, 300-1, 300-2, 300-3 respectively associated with cameras 210, 211, 212, 213 detect the failure, isolate the damaged segment, adapt the impedance, and adapt the power supply. Thus, the video signal is always available through the network.

This function is referred to hereinafter as the "back-up loop" or "secure ioop".

Compared to the state of the art, there is no conflict between the main signal and the returned signal that may create interference. Therefore, the full bit rate is maintained.

Figure 5 illustrates a device according to embodiments.

The device 300 has at least two ports 501 (P1) and 502 (P2). These two ports are associated with respective reference signal detectors 505 and 507 which detect the voltage, the current and/or a reference signal. The detectors have high input impedance.

Detectors 505 and 507 also have respective Reference signal Generators 506 and 508. The generators are configured to send reference signals on their associated port to a distant device in order to determine whether it is a compatible device and whether it is powered device. Generators 506 and 508 are controlled by a microcontroller 503 through signals Si and S2.

According to the result of the reference signal detection (Signal Detect 1" and "Signal Detect 2"), the microcontroller 503 commutes a switch 511 (SW1) using signal Ri or a switch 512 (SW2) using signal R2 for the AC signal (data signal) in order to adapt the impedance using a resistor 514 (75 ohms for the video application). One end of resistor 514 is grounded and the other end is connected to both switches 511 and 512. A decoupling capacitor is connected between switch 511 and port 501. A decoupling capacitor is connected between switch 512 and port 502. The decoupling capacitors make it possible for AC signals to pass while blocking DC voltage. Still according to the result of the reference signal detection, the microcontroller 503 commutes a switch 513 (SW3) using signal R3 in order to let the DC current pass between the ports 501 and 502.

In view of the above, the device makes it possible to daisy chain cameras and to provide impedance matching. Also, the ports may be isolated using switch 513.

The microcontroller 503 controls the switches and selects and sets up the best configuration based on the signals detected.

Figure 6 illustrates a video surveillance system according to embodiments operating in normal conditions.

A first network link comprising cables 611 and 612 connects two cameras 601 (Equipment item A), 603 to a video receiver 605. A second network link comprising cables 613 and 614 connects two cameras 602 (Equipment item B), 604 to video receiver 605.

Each camera is equipped (connected or embedded) with an interconnection additional device 300 as described hereinabove.

The cameras at the end of each link (cameras 601 and 602) are connected through a cable 610 ("secure ioop cable"). Cameras 603 and 604 are in a "pass-through" mode, i.e. the internal switches SW3 of their associated interconnection devices are closed. In such case, ports Fl and P2 are identically connected thereby transferring the power and the data signal.

Cameras 601 and 602 have the switches 5W3 of their respective associated interconnection devices in open state. Therefore, port P1 of the device associated with camera 601 is active and connected to camera 603. Therefore, camera 601 is connected to the network video receiver through cables 611 and 612. Port P1 of the device associated with camera 601 is adapted at 75 ohms.

Port P2 of this device is connected to cable 610. This port P2 is monitored by the reference signal detector 505 and by the reference signal generator 506 of the device associated with camera 601 in order to detect the presence of a compatible equipment item.

Camera 602 has an active link on port P2 of the device associated with it comprising camera 604 and cables 613 and 614. Port P1 is monitored by the reference signal detector 507 and the reference signal generator 508 of the device in order to detect the presence of a compatible equipment item.

Camera 602 is in the same mode as camera 601. Port P2 and Port P1 of the device associated with it are loaded by the 75 ohms resistor through switch SW2 and SW1 respectively.

Figure 7 illustrates the video surveillance system of Figure 6 operating in case of cable failure.

Cable 611 is deteriorated in portion 620. The data signal and power thereby become unreliable.

Cameras 601 and 603 are switched off. Therefore, it is detected on port P1 of the interconnection device associated with camera 602 that there is no reference signal on cable 610. It is also detected that there is a compatible equipment item 601 still connected. Therefore, the internal switch SW3 is closed in order to transfer power and data signal to camera 601 through cable 610.

Camera 601 is thereby started and the interconnection device associated with it detects compatible equipment item 603 on its port P1. The internal switch SW3 is then closed in order to transfer power and data signal to camera 603.

Camera 603 is thereby started and detects that there is no compatible equipment item on its port P1 (because cable 611 is deteriorated).

Thus, the interconnection device associated with camera 603 open its internal switch SW3, and adapts the terminal impedance to 75 ohms on port P2 by closing switch SW2.

At this stage the power comes from the video receiver through cameras 604, 602, 601 and cables 613, 614, 610, 612. Data is transmitted through the same cameras and cables to the video receiver.

Thus, the video surveillance stream is maintained even in case of cable failure thanks to the loop cable and the interconnection devices. The result is that the video data continues to pass through the network, the Impedance is matched, the power is balanced.

Figure 8 is a flowchart of steps performed for configuring a device according to embodiments.

According to embodiments, the network can be automatically set up with or without a back-up loop.

After the camera is started during step 801, the device performs a test 802 in order to detect a compatible device connected on its ports.

In order to perform the detection of the compatible device, the detection means 505, 507 and the reference signal generation means 506, 508 are used. The reference signal may be based on the voltage variation and the current consumption in a reference resistance (as described in the Power over Ethernet standard, PoE -802.3 af). The device measures the voltage and the current consumption on each port. On the non-active port, i.e. not in communication with a receiver or another device, the device presents a reference voltage and a reference resistance. Thus, when a compatible device is connected to this port, the device detects a voltage variation and a current consumption corresponding to the reference resistance of the compatible device. Reciprocally, the compatible device performs the same test and detects the presence of the device.

According to other embodiments, the reference signal is an AC signal with a given frequency transmitted during a given time slot.

Back to test 802. If there is no compatible equipment item connected to port P1, the device isolates this port by opening switch SW3 during step 803.

During step 812, the device performs a test on the other port P2. If there is no compatible equipment item connected to port P2, the device returns to test 802, until the test is positive. Ports P1 and P2 remain isolated from each other.

If a compatible equipment is connected on this port, the impedance adaptation is performed by closing switch SW2 and opening switch SWI.

Thus, data can be transmitted and received on this port.

If during step 802, a compatible equipment item is detected on port P1, the same test is performed on P2 during step 804.

If test 804 is negative, switch SW3 is opened and thus, ports P1 and P2 are isolated. The impedance adaptation is performed by closing switch SW1 and opening switch SW2. Thus, data can be transmitted and received on this port.

In case of a positive result, a test is performed on port P1 (step 805) and port P2 (step 806) in order to determine if the compatible equipment is powered by another port (of its own) or not.

The results of the tests are obtained by the reference signal generator and the signal detector. When a compatible equipment is powered ON, it sends a reference signal on the non-connected port to be identified by another compatible equipment being connected on this port. Thus, the signal detector module detects the distant equipment power status. For example, the signal can be a periodic burst of AC signal at 100 kHz.

If the result of the test is negative, at step 810 ports P1 and P2 are connected to each other by closing switch SW3. Thus, power and data pass through the device in the continuation of the network cable.

If the distant compatible equipment detected on port P1 and port P2 are powered by other own ports, then during step 807, the device has to determine the best network topology, in particular in case of a loop cable.

Indeed, the loop cable can be placed arbitrarily or by taking account of particular criteria.

According to embodiments, these criteria relate to the power available on such cable or on another cable in order to balance the power equally in each network branch.

According to other embodiments, these criteria relate to the bandwidth available on the cable or another cable, in order to balance the bandwidth equally in each network branch.

During step 808, the device selects the port to activate during step 809 (through switches SW1 and SW2) according to the criteria and the measurement results.

Next, the process goes back to detection step 802 in order to check for any changes in the network due to a cable failure, or cable disconnection, or connection recovery.

In the network, the devices may simultaneously send reference signals without collisions.

It is assumed that each device, after power-up, sends a reference signal to the next connected device if no reference signal has already been received from that next connected device. After all devices of the daisy-chain configuration are powered, one device should receive reference signals from both its ports. This device is then considered the terminal device (for data), i.e. the device which is located where the isolation of the network segments will occur. If one neighbouring device is no longer powered (due to cable cut for example), this is detected because the reference signal in the corresponding port goes below a certain threshold. The advantage of this variant is that the terminal device will not reboot because it is always powered from either port.

Alternatively, it may be assumed that each device, after start up, sends a first reference signal to the next connected device and, only if no first reference signal is also received from the connected device, a power signal is sent to that device. In this variant, two terminal devices will be connected by a non-powered link, over which only reference signals are exchanged. If one neighboring device is no longer powered (due to cable failure for example), this is detected because a first reference signal is no longer received. A power signal is then transmitted to that device to re-power it (however in the mean-time it will reboot).

Other combinations are possible concerning the cable type. The cable can be a coaxial cable for video (characteristic impedance of 75 ohms) or 50 ohm coaxial cable, or telephone type wire pairs, or Ethernet twist pair.

Therefore it is not limited to coax, and not limited at the dual port, but any configurations with two or more ports would work.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive, the invention not being restricted to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in putting into practice the claimed invention, from a study of the drawings, the

disclosure and the appended claims.

In the claims, the word comprising" does not exclude other elements or steps, and the indefinite article a" or "an" does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used. Any reference signs in the claims should not be construed as limiting the scope of the invention.

Claims

CLAIMS1. An interconnection device for managing connection losses between devices of a daisy chain network, the device comprising: -at least two physical ports, each port being configured to exchange data signals and power signals, -at least two detection units, respectively associated with said at least two physical ports, each detection unit being configured to detect a connexion on its associated physical port, -a connexion unit for connecting or disconnecting said at least two physical ports thereby allowing or blocking transfer of data signals and power signals, -a control unit configured to control said connexion unit based on outputs from the detection units, and -an impedance adaptation unit for adapting impedance of at least one of said at least two physical ports when disconnected by said connexion unit.
2. A device according to claim 1, wherein said connexion unit is further configured to connect or disconnect said impedance adaptation unit to at least one of said at least two physical ports.
3. A device according to claim 2, wherein said control unit is configured to control said connexion unit to connect said impedance adaptation unit to a physical port from which power signals are received.
4. A device according to any one of the preceding claims, wherein said at least two detection units are configured to detect connexion by monitoring receipt of a first reference signal in response to a second reference signal previously sent.
5. A device according to claim 4, wherein each detection unit comprises a reference signal detector for detecting said first reference signal and a reference signal generator for generating said second signal.
6. A device according to claim 4 or 5, wherein said control unit is configured to control said connexion unit for connecting said at least two physical ports when: -connexion is detected on one physical port, -no reference signal is received on said physical port, and -power level on another port is above a power threshold.
7. A device according to claim 6, wherein said power threshold depends on a type of device connected on the network.
8. A device according to claim 7, wherein said power threshold represents a power level required for powering said type of device.
9. A device according to any one of the preceding claims, wherein said control unit is configured to control said connexion unit for connecting said at least two physical ports when: -connexion is detected on one first physical port, -power level on said first physical port is below a first power threshold, and -power level on a second physical port is above a second power threshold.
10. A device according to claim 9, wherein said first and second power thresholds depend on a type of device connected on the network.
11. A device according to claim 10, wherein said second power threshold represents a power level required for powering said type of device.
12. A device according to claim 10 or 11, wherein said first power threshold represents the presence of a device of said type on a connexion line connected to said first physical port.
13. A device according to any one of the preceding claims, wherein said control unit is configured to control said connexion unit for disconnecting said at least two physical ports when: -connexion is detected on one physical port, and -power level on said physical port is above a third power threshold.
14. A device according to claim 13, wherein said third power threshold represents the presence of a device of said type on a connexion line connected to said physical port.
15. A device according to any one of the preceding claims, wherein said control unit is configured to control said connexion unit to disconnect said at least two physical ports when no connexion is detected on one of said physical pods.
16. A device according to any one of the preceding claims, implemented as a passive circuit.
17. A device according to any one of claims 1 to 15, further comprising a connexion port for connecting the module to a device of the network.
18. A device according to claim 17, implemented as an active circuit and configured to be powered by said device through said connexion port.
19. A device according to any one of the preceding claims, wherein a first and second set of devices are respectively connected to two connexion links and wherein each connexion link is connected to a central equipment item of the network at one end and connected to a loop connexion element at the other end, the connexion links thereby forming a connexion loop.
20. A device according to any one of claims 1 to 19 configured to be connected to a daisy chain network.
21. A camera comprising a device according to any one of the preceding claims.
22. A system comprising a plurality of devices according to any one of the preceding claims.
23. A system according to claim 22 comprising at least two connexion links respectively daisy chaining a first set of devices and a second set of devices, wherein each connexion link is connected to a central equipment item of the network at one end and connected to a loop connexion element at the other end, the connexion links thereby forming a connexion loop.
24. A video surveillance system according to claims 21 and 23.
25. A method for managing connection losses between devices of a daisy chain network, the method comprising: -detecting a connexion on at least two physical ports of an interconnection device, said physical pods being configured to exchange data signals and power signals, -connecting or disconnecting said at least two physical ports thereby allowing or blocking transfer of data signals and power signals, -controlling said connexion or disconnexion based on said detecting step, and -adapting impedance of at least one of said at least two physical ports when disconnected.
26. A method according to claim 25, further comprising connecting or disconnecting an impedance adaptation unit performing said impedance adaptation to at least one of said at least two physical ports.
27. A method according to claim 26, further comprising connecting said impedance adaptation unit to a physical pod from which power signals are received.
28. A method according to any one of claims 25 to 27, further comprising detecting connexion by monitoring receipt of a first reference signal in response to a second reference signal previously sent.
29. A method according to claim 28, further comprising detecting said first reference signal and generating said second signal.
30. A method according to claim 28 or 29, further comprising connecting said at least two physical ports when: -connexion is detected on one physical port, -no reference signal is received on said physical port, and -power level on another pod is above a power threshold.
31. A method according to claim 30, wherein said power threshold depends on a type of device connected on the network.
32. A method according to claim 31, wherein said power threshold represents a power level required for powering said type of device.
33. A method according to any one of claims 25 to 32, further comprising connecting said at least two physical pods when: -connexion is detected on one first physical port, -power level on said first physical port is below a first power threshold, and -power level on a second physical port is above a second power threshold.
34. A method according to claim 33, wherein said first and second power thresholds depend on a type of device connected on the network.
35. A method according to claim 34, wherein said second power threshold represents a power level required for powering said type of device.
36. A method according to claim 34 or 35, wherein said first power threshold represents the presence of a device of said type on a connexion line connected to said first physical port.
37. A method according to any one of claims 25 to 36, further comprising disconnecting said at least two physical ports when: -connexion is detected on one physical port, and -power level on said physical port is above a third power threshold.
38. A method according to claim 37, wherein said third power threshold represents the presence of a device of said type on a connexion line connected to said physical port.
39. A method according to claims 25 to 38, further comprising disconnecting said at least two physical ports when no connexion is detected on one of said physical ports.
40. A device substantially as hereinbefore described with reference to, and as shown in, Figures 3-7 of the accompanying drawings.
41. A method substantially as hereinbefore described with reference to, and as shown in, Figure 8 of the accompanying drawings.