GB2591479A - Method and device for ghost central coordinator (CCo) avoidance - Google Patents

Abstract

A method of controlling operation of a HomePlug Audio Video (HPAV) network comprises, at a device: searching for a probe signal S601 signalling that a remote Audio Video Logical Network (AVLN) is in operation within the HPAV network; and upon detecting the signal S602, either maintaining operation of the remote AVLN or causing its deactivation, based on an arbitration procedure S604. The signal occupies a frequency band out of, and possibly below, that reserved for HPAV communications. The device may be associated with a local AVLN which, when maintaining operation of the remote AVLN, may be deactivated by deactivating its central coordinator (CCo). If no probe signal is detected, the device may itself activate a CCo function to form a local AVLN. Consequently, formation of distinct AVLNs over a same network, each managed by a distinct CCo, is avoided. This avoids unexpected behaviour due to two devices being elected CCo in the same network (i.e. one being a ghost CCo). The invention may be employed in the context of HPAV communication in a network comprising powered devices (PDs), such as IP or PTZ cameras or VoIP phones, powered by a power source equipment (PSE) via Power over Ethernet (PoE).

Description

METHOD AND DEVICE FOR GHOST CENTRAL COORDINATOR (CCo) AVOIDANCE

FIELD OF THE INVENTION

The present invention relates to a HomePlug AV (HPAV) network. More specifically, the present invention relates to a method and device for preventing the formation of two or more distinct HPAV networks, each managed by a distinct Central Coordinator (CCo) device, over a same physical network.

BACKGROUND OF THE INVENTION

According to HPAV system architecture, a Central Coordinator (CCo) controls an AV Logical Network (AVLN) which consists of several AV stations which all share a common Network Membership Key (NMK).

A station must be capable of communicating with the CCo in order to join an AVLN and to establish connections. If stations are hidden from (i.e., unable to communicate with) the CCo, due for example to signal attenuation over long cables, a proxy capability is provided in the HPAV specification to relay the signals and allow the hidden stations and the CCo to communicate. The proxy capability provides for the creation of a Proxy Coordinator (PCo) to repeat beacon information in Proxy Beacons and to relay control messages between the hidden station and the CCo.

However, the proxy capability is optional in the HPAV specification and in practice this capability is not implemented in most of available HomePlug AV chipsets. Consequently, two devices (stations) may be elected CCo in a same network of interconnected devices (having the same NMK) without being aware of each other (hence we say we have one "ghost CCo"). Having more than one CCo creates unexpected behaviors within the network.

Aim of the invention is to propose an alternate solution to address the problem of ghost CCo.

SUMMARY OF THE INVENTION

The present invention has been devised to address the foregoing concern. In particular the invention aims to provide means for ensuring that only one network device, amongst a plurality of physically connected network devices having the same NMK, is behaving as the coordinator device, therefore preventing the formation of two distinct networks.

To that end, according to embodiments of the invention, the invention concerns a method of controlling operation of a HomePlug Audio Video (HPAV) network, the method comprising at a device: searching for a probe signal signaling that a remote Audio Video Logical Network (AVLN) is in operation within the HPAV network; and upon detecting the probe signal, either maintaining operation of the remote AVLN or causing its deactivation based on an arbitration procedure, wherein the probe signal occupies a frequency band that is out of the frequency band reserved for HPAV communications.

Correspondingly, the embodiments of the invention provide a device for controlling operation of a HomePlug Audio Video (HPAV) network, the device is configured to carry out the steps of: searching for a probe signal signaling that a remote Audio Video Logical Network (AVLN) is in operation within the HPAV network; and upon detecting the probe signal, either maintaining operation of the remote AVLN or causing its deactivation based on an arbitration procedure, wherein the probe signal occupies a frequency band that is out of the frequency band reserved for HPAV communications.

Optional features of embodiments of the invention are defined in the appended claims. These features are explained here below with reference to a method, while they can be transposed into system features dedicated to any device according to embodiments of the invention.

In an embodiment, the device is associated with a local AVLN, and wherein if the arbitration procedure results into maintaining operation of the remote AVLN, then causing deactivation of the local AVLN.

In an embodiment, operation of each AVLN is controlled by a central coordinator (CCo) and is formed by stations that possess a common network identifier (N ID).

In an embodiment, deactivating an AVLN comprises deactivating the CCo of that AVLN.

In an embodiment, if the device is different from the CCo of the AVLN to be deactivated, deactivating the CCo comprises sending a disable notification to the CCo of the AVLN.

In an embodiment, the device is associated with a local AVLN, and wherein the method further comprising a sending a probe signal to signal the existence of the local 35 AVLN.

In an embodiment, searching the probe signal is performed after power-on of the device, and wherein if no probe signal is detected, activating a central coordinator (CCo) function of the device to form a local AVLN.

In an embodiment, the probe signal has an operating frequency band lower than the of the frequency band reserved for HPAV communications.

In an embodiment, the probe signal is a baseband signal.

Embodiments of the invention also relates to a computer program product for a programmable apparatus, the computer program product comprising instructions for carrying out each step of any method as defined above when the program is loaded and executed by a programmable apparatus.

Embodiments of the invention also relates to a non-transitory computer-readable medium storing a program which, when executed by a microprocessor or computer system in a device of a power-over-cable system, causes the device to perform any method as defined above.

The non-transitory computer-readable medium may have features and advantages that are analogous to those set out above and below in relation to the methods and devices.

At least parts of the methods according to the invention may be computer implemented. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "circuit", "module" or "system". Furthermore, the present invention may take the form of a computer program product embodied in any tangible medium of expression having computer usable program code embodied in the medium.

Since the present invention can be implemented in software, the present invention can be embodied as computer readable code for provision to a programmable apparatus on any suitable carrier medium, and in particular a suitable tangible carrier medium or suitable transient carrier medium. A tangible carrier medium may comprise a storage medium such as a floppy disk, a CD-ROM, a hard disk drive, a magnetic tape device or a solid-state memory device and the like. A transient carrier medium may include a signal such as an electrical signal, an electronic signal, an optical signal, an acoustic signal, a magnetic signal or an electromagnetic signal, e.g. a microwave or RF signal.

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, illustrates a HomePlugAV network formed by a plurality of AVLNs and comprising a plurality of AV stations; Figure 2 is a flowchart describing a power-on network discovery procedure of a device according to embodiments of the invention; Figure 3 is a flowchart illustrating the operation of a central coordinator, according to embodiments of the invention; Figure 4 is a flowchart illustrating the operation of an association station, according to embodiments of the invention; Figure 5 is a flowchart illustrating a process of probing that may be executed by a central coordinator or an associated station, according to embodiments of the invention; Figure 6 is a flowchart illustrating a process of detection that may be executed by a central coordinator or an associated station, according to embodiments of the invention; Figure 7a, illustrates a data and power over cable system comprising a PSE and a plurality of powered devices (PDs), adapted to communicate using HomePlugAV 20 technology; Figure 7b schematically shows a powered device arrangement that is adapted to embed embodiments of the invention; Figures 8a and 8b provide examples of probe signals, according to embodiments of the invention; and Figure 9 illustrates a functional block diagram of a sensing unit configured to perform line voltage sensing, detection and generation of a probe signal.

Note that same references are used across different figures when designating same elements.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Figure 1, illustrates a HomePlugAV network formed by a plurality of AVLNs and comprising a plurality of AV stations.

The illustrated network 100 is formed by a first AVLN 101 comprising two stations 111 and 112 and a second AVLN 102 comprising two stations 113 and 114.

The two AVLNs are interconnected over a cable 120. The length of the cable may be long enough to cause a significant signal attenuation between farthest stations which may lead to a situation where a HPAV frame, e.g. beacon frame, emitted at one AVLN cannot reach or cannot be decoded at the other AVLN.

Figure 2 is a flowchart describing a power-on network discovery procedure 200 of a device (referred to as AV station or simply STA) according to embodiments of the invention.

Aim of the procedure is to determine at power-on if an existing AVLN is already operating or a new AVLN needs to be established, irrespective of the size of the network.

The STA selects at step S201 a BeaconBackoffTime (BBT). If the STA was the COO of an AVLN before it was powered down, BBT should be chosen as a random value in a first interval (MinCCoScanTime, MaxCCoScanTime). Otherwise, BBT shall be a random value in a second interval (MinScanTime, MaxScanfime). BBT is the maximum duration of time for which a STA will execute the Power-on Network Procedure.

During the Power-On Network Discovery Procedure, while no AVLNs are detected, the STA searches for Beacons and probe signals possibly emitted by other stations (S202).

The beacon is an HPAV message that carries payload fields, such as a Network IDentifier (NID) and Beacon Type (BT). The Network ID is a 54-bit field that, together with a 4-bit Short Network ID (SNID), uniquely identifies an AVLN. Beacon Type is a 3-bit field that indicates the Beacon type, such as a central beacon (generated by the CCo of each AVLN) and a discovery beacon transmitted by all associated and authenticated STAs periodically to aid in network-topology discovery. Detection of a beacon (of any type) (S203) signals thus the existence of an AVLN, and causes the STA to join the existing AVLN (S204) if it has a matching NID. If the STA successfully joins the AVLN, it terminates the power-on network procedure and becomes an associated STA in the AVLN (S205). Failure to join successfully causes the STA to continue with the power-on network procedure (S202).

The probe signal is a signal adapted to span all potentially existing AVLNs in the same network. The probe signal is preferably a low frequency electrical signal as low frequency signals experience less attenuation than higher frequency signals, and thus they may reach all stations that are on the same power over cable or power-line media. More details on the characteristics and the generation of probe signals according to embodiments of the invention are provided in the description of Figure 5, and particularly of step S502.

If the timer BBT expires without the STA having detected beacons (S206), a check (S207) is performed to determine if probe signals have been detected during that period. Detection of a probe signal (test S207 positive) signals the existence of an AVLN that has not been detected by the reception of beacons, i.e. the AVLN out of reach of the STA. The detection of a probe signal causes the STA to become an unassociated STA (S209) as one possible measure to avoid conflicting AVLNs. If no probe signal is detected (test S207 negative), the STA becomes CCo (S208) for forming a new AVLN.

Once the power-on procedure is completed, a STA can be an unassociated STA, associated STA or CCo of an AVLN. Figures 3 and 4 describe the behavior of, respectively, a CCo and an associated STA according to embodiments of the invention.

Figure 3 is a flowchart illustrating the operation of a central coordinator, according to embodiments of the invention.

Step S301 represents the conventional part of the operation of a STA acting as CCo; e.g. CCo behaviour as described by HPAV specification. Note that according to a conventional behaviour, if no other STA has successfully joined the AVLN a certain time after the STA has become CCo, the CCo operates as an unassociated CCo if there are no other AVLNs detected and as an unassociated STA if at least one other AVLN is detected.

In parallel to step S301, and according to embodiments of the invention, the CCo monitors the existence of other AVLNs gone undetected by conventional means (e.g. beacon), by executing, once or repeatedly, probing (5302) and detection (5303) procedures. The probing procedure aims to signal the existence of a local AVLN in operation and the detection procedure aims to detect remote AVLNs signalled by probe signals. The local AVLN refers to the AVLN of the CCo (or STA) executing the flowchart, a remote AVLN refers to an AVLN other than the local AVLN. Figures 5 and 6 illustrate possible implementations of, respectively, the probing and the detection procedures.

Execution of the detection procedure (5303) results in two possible outcomes (D) and (E) as it is illustrated by Figure 6. A first outcome (D) is to maintain the operation of the local AVLN, and a second outcome (E) requires the disabling of the local AVLN. In the latter, the device executing the flowchart disactivates its CCo function (S304) and changes its state to an unassociated STA (S305).

Figure 4 is a flowchart illustrating the operation of a STA associated with a local AVLN, according to embodiments of the invention.

The flowchart is similar to the flowchart of Figure 3 executed by the CCo and calls same probing (S402) and detection (S403) procedures. Step S401 represents the conventional part of the operation of a STA. Main difference is that the disabling of the CCo of the local AVLN is caused by sending a disable notification to the CCo (S404) because the device executing the flowchart is a station. After sending the disable notification, the station changes its state to an unassociated STA (S405). Optionally, the change of state at step S405 if performed only after receiving a confirmation of disabling (acknowledgment) from the CCo.

Figure 5 is a flowchart of a probing procedure that can be used for implementing the steps S302 and S402 of, respectively, Figures 3 and 4.

The illustrated procedure comprises a step S502 of sending a probe signal adapted to span all potentially existing AVLNs in the same network. As mentioned earlier, the probe signal is preferably a low frequency electrical signal to experience less attenuation than higher frequency signals. For the sake of illustration, a 100 MHz signal is attenuated by about 90dB at 800 meters in a cable of type RG59. With such attenuation, SNR is too low and signals are no more detected, and the messages such as a beacon cannot be decoded. In the contrary, a low frequency signal, such as 1 Hz, is subject to only a voltage drop of about 10% (0.9dB) at 800 meters (considering 100 ohms of cable resistance). A further advantage of a low frequency probe signal is that it does not interfere with HPAV messages. Typically, HPAV employs carriers ranging from 1.80 MHz to 30.00 MHz (or 88 MHz for later version) that are modulated with different modulation schemes for transporting HPAV information. Thus, the frequency of the probe signal, or of the carrier modulated by the probe signal, can be chosen below 1.80 MHz. When operating in power line environments, the carrier may have a frequency that is twice the AC line frequency, i.e. two times 50 or 60 Hz. More generally, the probe signal occupies a frequency band that is out of the frequency band reserved for HPAV communications.

When operating in a power over cable system, such as power over Ethernet or power over Coax, in which a DC power is transported over the cable, the probe signal can be transported as a baseband signal. This is advantageous because no dedicated modulation hardware needs to be added. Implementation of embodiments of the invention can thus be done with existing physical transceivers, at no additional cost.

Figures 8a-8b illustrate different baseband probe signals adapted for a power over cable environment.

In one optional implementation, the probe signal is sent repeatedly, either on a regular basis or not. This implementation can be performed by means of a delay (S503) that is introduced between the emission of one probe signal and another. The waiting time at step S503 can be fixed or variable, e.g. on random basis.

Optionally, at step S501, stations associated with the local AVLN are notified that a probe signal is to be sent. This advantageously allows those stations to know that the probe signal is originating from a local AVLN and thus have to ignore the probe signal that is to be received, or that just has been received. A time interval can be defined to let the stations know when the reception of the probe signal is expected. The notification may be implemented by sending a HPAV message that advantageously addresses only stations of the same AVLN, i.e. the message is only decodable by those stations. Alternatively, the probe signal may encode a signature of the local AVLN, such as the NI D, to let the stations identify the originating AVLN.

Figure 6 is a flowchart of a detection procedure that can be used for implementing the steps S303 and S403 of, respectively, Figures 3 and 4.

The illustrated procedure comprises a step S601 of searching for probe signals that may be sent by other stations of the network (either CCo or simple STA). The searching may consist in detecting at the physical layer of a predetermined pattern identifying a probe signal. The probe signal is sent by another device executing the probing procedure of Figure 5, and in particular step S502.

If a probe signal is detected (test at step S602 positive), optionally a further test (S603) is performed to determine if the detected probe signal is issued by a station belonging to the local AVLN, i.e. same AVLN than that of the station executing the detection procedure, or a remote AVLN, i.e. an AVLN different from the AVLN of the station executing the detection procedure. If no probe signal is detected (test at step S602 negative), or if a probe signal is detected but is issued by a station belonging to the local AVLN (test at step S603 negative), then operation of local AVLN is maintained (connection to branch point D).

Aim of the checking step S603 is to avoid considering the local AVLN as another AVLN when the probe signal is sent by a device (STA or CCo), other than the device executing the detection procedure, of the same AVLN. According to one implementation, determining whether the probe signal is issued from a remote AVLN comprises checking reception of a notification for notifying devices of the local AVLN that a probe signal was, or is to be, received within a defined or predetermined time interval (e.g. in accordance with step S501 of the probing procedure). If a notification is not received, and a probe signal is detected, it means that the probe signal originates from a remote AVLN. Other implementations may be envisaged. For example, the probe signal may embed (e.g. encode) an identifier of the AVLN (e.g. NI D) from which the probe signal originates. The identifier can thus tell if the probe identifier is from a local or a remote AVLN; the checking step S603 comprises then a decoding step for retrieving that identifier and deciding based on it. According to other implementations, the checking step S603 may be optional. For example, if a single device (such as CCo) is elected per AVLN for executing both the probing and detection procedure, there is no need to do the checking as any detected probe signal necessarily originates from a remote AVLN.

If a remote AVLN is detected (step S602 positive, and also step S603 positive if present), an arbitration procedure to determine which AVLN to maintain is executed (S604). Preferably, the arbitration procedure can be run at the two AVLNs independently (i.e. without need of message exchange) and results into a same (deterministic) decision. According to one implementation, in a power over cable environment, the AVLN that has the highest voltage, i.e. closest to the power sourcing equipment (PSE), is chosen. Other criteria leading to a deterministic decision may be based on an address or identifier of the AVLN, such as taking the lowest or the highest value. If the result of the arbitration is to maintain the local AVLN, connection is made to branch point D, otherwise connection is made to branch point E. Embodiments of the invention are hereinafter illustrated in a context of power over cable environment.

Figure 7a, illustrates a data and power over cable system, such as Power over Ethernet (PoE) or Power over Coax (PoC), comprising a PSE and a plurality of powered devices (POs), adapted to communicate using HomePlugAV technology.

The power sourcing equipment (PSE) is a device such as a network switch that provides (sources) power on the network cable. A powered device (PD) refers to an apparatus powered by the PSE and thus consuming energy. Examples of powered devices include analog cameras, IP cameras including pan-tilt-zoom (PTZ) cameras, wireless access points (AP), and Vol P phones.

The illustrated system comprises a PSE 720, a plurality of PDs 710-715 and two network cables 730. In a preferred implementation of the invention, the network cables are coaxial cables. Each network cable 730 connecting, according to a linear bus topology, a plurality of PDs to one port of the PSE 720. Each network cable and associated PDs forming a network segment.

Figure 7b schematically shows a powered device 750 arrangement that is adapted to embed embodiments of the invention.

The powered device comprises a terminal 760 and a controller 770.

The terminal 760 represents the core unit of the powered device providing the main functions of the device. The terminal 760 is for example a camera unit in charge of capturing a scene and transmitting data content -e.g. video stream(s) -over the network to a destination device which may be another device of the network or a remote device connected to the network. More generally, the terminal may be a communication unit configured to send and/or receive data over/from the network and drawing its power over the cable from a PSE.

A sufficient electric power needs to be drawn from the cable in order to run properly the functions of the terminal. For that purpose, the controller 770 is in charge of controlling the startup of the terminal 760 depending on the power available over the cable.

The controller 770 operates at low power conditions (low voltage) compared to the consumption of the terminal. This means that a low voltage, e.g. 5 volts, is sufficient to activate the controller, while the terminal requires a higher voltage, e.g. 40 volts, to activate. Consequently, the controller 760 is started up first and is in charge of executing basic start-up control functions requiring only a limited power amount from the network.

Optionally, the powered device 750 may embed another controller 781 capable of drawing more power (e.g. operating at nominal or intermediate voltage values 36, 48 or 56 V) if more advanced control functions are needed.

In the figure the powered device is represented as a single device comprising the terminal and the one or more controllers. This is for illustration only. The powered device 750 may be physically formed by two or more interconnected devices embedding the terminal and the one or more controllers. For example, one device may contain the terminal 760 and another device may contain the controller 770. The other device may be for example an adapter, such as a PoE/PoC adapter for interconnecting a PoE terminal to a PoC cable.

Also, it is assumed that the voltage supplied at the input 780 of the powered device 750 from the cable (referred to as Vin) will only slightly differ (i.e. less than 2V), if not the same, as the voltage that can be supplied to the terminal 760 (voltage drop due to controller's consumption is limited).

Figures 8a and 8b provide examples of probe signals, according to embodiments of the invention.

In the example of Figure 8a, the probe signal is periodical with period T (810) and formed by a first period of time Ti (811) during which the voltage is at a low-level and a second period of time T2 (812) during which the voltage is at a high-level. In the example of Figure 8b, the probe signal is formed by a voltage drop A (820) of a predetermined duration.

One or more of the parameters T, Ti, T2 and A may be chosen or tuned to adapt the probe signal to the media. They may also be modulated or varied to encode information.

In one implementation, the encoded information is used in the arbitration procedure (S604) to decide which AVLN to maintain. For example, information one may encode in the probe signal is the voltage measured at the input of the device emitting the probe signal (Vin_e). In this way, the device detecting the probe signal may compare that voltage (Vin_e) retrieved from the probe signal with a voltage measured at its input (Vin_d), and determine based on the comparison which of the two devices is the closest to the power source equipment (PSE), and hence which of the associated AVLNs is to be maintained. The rationale behind is to keep operating an AVLN with a higher voltage to reduce the risk of having devices powered with insufficient voltage, i.e. voltage at their input is below a minimum operational voltage level due to the resistive nature of the cable medium. Referring to step S604 of Figure 6, and since the closer the device is from the power source, the higher is the voltage considering a linear bus topology, operation of local AVLN is maintained if Vin_e < Vin_d and is disabled otherwise. The voltage information may be encoded by means of one of the parameters (T, Ti, T2, A), or a combination of two or more of these parameters (e.g. T1/T). The encoding may consist in choosing a value that is proportional to the voltage value to be encoded by a predetermined factor. More generally, the encoded value is function of the measured voltage: value = f(Vin); where f is a reversible function such that the voltage can be derived from the value by a detecting device: Vin = f'(value). Arbitration methods based on encoded information, as exemplified above, are advantageously adapted to be implemented independently by devices of each AVLN, e.g. without requiring message exchange.

Figure 9 illustrates a functional block diagram of a sensing unit 932 configured to perform line voltage sensing, detection and generation of a probe signal as illustrated in Figures 8a and 8b.

The sensing unit 932 comprises a wire 941 coupling it to a connector 931 for connecting to the power source, and a wire 942 coupling it to the controller and terminal for powering the powered device. The sensing unit 932 further comprises lines 943 coupling it to a processor 933.

The sensing unit 932 further comprises a first resistance Ri 951, a second resistance R2 954, a switch 952 (such as a transistor) and an analog to digital converter 953. The first resistance 951 and the second resistance 954 are mounted in parallel to the power source originating from the connector 931. The value of R1 is for example 1 KU and the value of R2 is for example 100 KO. The power consumption of the second resistance R2 is considered negligible compared to both the power consumption of the first resistance 951 and power supply capability. The first resistance 951 is thus used to modify the operating condition of the powered device by increasing its power consumption. This is used to generate specific voltage drops of the probe signals illustrated in Figures 8a and 8b.

The first resistance 951 and the switch 952 are in series between a node A and a node B of the circuit. The switch 952 is controlled by a control signal CS provided by processor 933 (represented in dotted lines). Activation of the switch 952 causes it to close, coupling the resistance 951 between the nodes A and B. Deactivation of the switch 952 causes it to open, de-coupling the resistance 951 from the nodes A and B. The converter 953 measures a voltage value Vab between the nodes A and B, and supplies a measured voltage value to the processor 933. Alternatively, the converter 953 may be integrated within the processor 933 and coupled by wires to the nodes.

Claims (12)

1. CLAIMS1. A method of controlling operation of a HomePlug Audio Video (HPAV) network, the method comprising at a device: searching for a probe signal signaling that a remote Audio Video Logical Network (AVLN) is in operation within the HPAV network; and upon detecting the probe signal, either maintaining operation of the remote AVLN or causing its deactivation based on an arbitration procedure, wherein the probe signal occupies a frequency band that is out of the frequency band reserved for HPAV communications.
2. 2. The method of Claim 1, wherein the device is associated with a local AVLN, and wherein if the arbitration procedure results into maintaining operation of the remote AVLN, then causing deactivation of the local AVLN.
3. 3. The method of Claim 2, wherein operation of each AVLN is controlled by a central coordinator (CCo) and is formed by stations that possess a common network identifier (NID).
4. 4. The method of Claim 3, wherein deactivating an AVLN comprises deactivating the CCo of that AVLN.
5. 5. The method of Claim 4, wherein if the device is different from the CCo of the AVLN to be deactivated, deactivating the CCo comprises sending a disable notification to the CCo of the AVLN.
6. 6. The method of any one of preceding claims, wherein the device is associated with a local AVLN, and wherein the method further comprising a sending a probe signal to signal the existence of the local AVLN.
7. 7. The method of Claim 1, wherein searching the probe signal is performed after power-on of the device, and wherein if no probe signal is detected, activating a central coordinator (CCo) function of the device to form a local AVLN.
8. 8. The method of any one of preceding claims, wherein the probe signal has an operating frequency band lower than the of the frequency band reserved for HPAV communications.
9. 9. The method of Claim 8, wherein the probe signal is a baseband signal.
10. 10. A computer program product for a programmable apparatus, the computer program product comprising instructions for carrying out each step of the method according to Claim 1 when the program is loaded and executed by a programmable apparatus.
11. 11. A non-transitory computer-readable medium storing a program which, when executed by a microprocessor or computer system in a device of a power-over-cable system, causes the device to perform the method of Claim 1.
12. 12. A device for controlling operation of a HomePlug Audio Video (HPAV) network, the device is configured to carry out the steps of: searching for a probe signal signaling that a remote Audio Video Logical Network (AVLN) is in operation within the HPAV network; and upon detecting the probe signal, either maintaining operation of the remote AVLN or causing its deactivation based on an arbitration procedure, wherein the probe signal occupies a frequency band that is out of the frequency band reserved for HPAV communications.