Untitled record

REFERENCE TO RELATED APPLICATIONS

0001This applicationis an application for reissue of U.S. Pat. No. 9,900,114, issued Feb. 20, 2018, which issued from U.S. patent application Ser. No. 15/504,977, filed Feb. 17, 2017, which is the U.S. National Phase of International Application PCT/IB2015/056343, filed Aug. 21, 2015, and claims priority to ZA Application No. 2014/06162, filed Aug. 21, 2014. This application is a continuation of U.S. patent application Ser. No. 16/796,178, filed Feb. 20, 2020, which is an application for reissue of U.S. Pat. No. 9,900,114, now RE 49,217. Each of the priority applications is hereby incorporated by reference in its entirety.

INTRODUCTION AND BACKGROUND

0002This invention relates to distributed antenna systems, more particularly to a monitoring system and method for a distributed antenna system.

0003Distributed antenna systems (DAS) are known in the art and are typically employed to provide in-building coverage, but more recently are also used to provide area coverage outside of buildings. DAS may be passive or active. A passive DAS comprises a central or base transceiver station linked by a radio frequency (RF) signal transmission network comprising RF transmission lines (coaxial or other) to a plurality of distributed antenna devices (DAD) distributed through the area to be covered with power diverted according to some propagation plan to each DAD, such that adequate coverage is ensured throughout the building or area for which the DAS is installed.

0004An active DAS is similar, but in these systems the RF signals are modulated up to convert them to optical fibre frequencies. Optical fibers are then used to distribute the resulting signals to a point close to the DAD. An optic-to-radio converter unit is used to convert the signals back to their original RF band. The optic-to-radio convertor is coupled using RF transmission lines which provide the last mile to one or more DAD's, which provide coverage to sub-areas of the area covered by the DAS. Other active DAS systems may involve bi-directional amplifiers and/or frequency convertors in between the central transceiver and the DADs.

0005A DAS may employ between a few to many hundreds of DAD's to provide coverage throughout the area. These DAD's or the signal transmission network and intermediate devices used to link these DAD's to the base transceiver station may fail or degrade over time. Currently such faults are difficult to detect or monitor. One known solution is to use regular “walk tests” to measure network coverage throughout the coverage area, but these are time consuming, costly and faults are detected well after they had occurred.

0006In U.S. Pat. No. 8,254,848 there is disclosed another solution which comprises a plurality of statically deployed monitoring devices. The monitoring devices are remote from the DAD's being monitored and test results are reported to a central and remote collection component directly or indirectly through other monitoring devices having an Ethernet connection. This solution may be unnecessarily costly. Furthermore, due to the separation between DAD's and the monitoring devices, individual DAD's and branches in the network may be difficult to pinpoint. Hence, the solution may not be suitable for at least some applications.

OBJECT OF THE INVENTION

0007Accordingly it is an object of the present invention to provide a monitoring system and method with which the applicant believes the aforementioned disadvantages may at least be alleviated or which may provide a useful alternative for the known systems and methods.

SUMMARY OF THE INVENTION

0008According to the invention there is provided a monitoring system for a distributed antenna system comprising at least a central transmitter and a plurality of distributed antenna devices connected to the transmitter via a respective physical branch of a signal transmission network comprising a plurality of branches, each of the distributed antenna devices comprising at least one antenna which is associated with a frequency band having a centre frequency f_cand a corresponding wavelength λ_c, the monitoring system comprising: <ul id="ul0001" list-style="none"><li id="ul0001-0001" num="0000"><ul id="ul0002" list-style="none"><li id="ul0002-0001" num="0009">a central monitoring unit which is coupled to the network;</li><li id="ul0002-0002" num="0010">at least one monitoring device associated with at least one of said distributed antenna devices and permanently mounted a distance d away from the at least one antenna of the distributed antenna device, the distance d being less than 2 times λ_c(2λ_c);</li><li id="ul0002-0003" num="0011">the at least one monitoring device comprising a local controller, a transceiver and an antenna;</li><li id="ul0002-0004" num="0012">the local controller being configured, upon being polled by the central monitoring unit via the network and the distributed antenna device, to cause the transceiver to respond to the poll by transmitting a response signal to the central monitoring unit via the distributed antenna device and the network.</li></ul></li></ul>

0013The distance d may be less than λ_c, preferably less than λ_c/2 and even less than λ_c/4.

0014The monitoring device may comprise a local power supply, for example in the form of a battery. Alternatively or in addition, the monitoring device may comprise an energy harvesting circuit for collecting energy from the DAD through the antenna of the monitoring device. The energy may be used to recharge the battery.

0015Each monitoring device may be associated with a unique address which may be stored in a memory arrangement of the monitoring device.

0016Each monitoring device may also comprise indicator means for providing a human perceivable indication relating to a monitored status of the associated DAD and/or the branch of the network connected thereto.

0017The monitoring device may be mounted in or on the DAD. It may for example be retrofitted on a radome of the DAD. In such a case, the monitoring device may be housed in a housing or encapsulated in a flexible sleeve or envelope, which may be adhered to the radome.

0018The central monitoring unit may comprise means for measuring the strength of the response signal received from the at least one monitoring device and a database for storing data relating to the unique addresses of each monitoring device, data relating to a monitored status of each DAD and optionally data relating to the position of the DAD associated with the monitoring device.

0019The central monitoring unit may be coupled to the network by a suitable coupler to inject a weak monitoring message or signal or tone into the network. The message or signal or tone may be in-band or out of specific DAS communication bands, but within the overall band which the DAS system is designed to operate over.

0020The monitoring message may be addressed to a targeted monitoring device by using the unique address of the monitoring device.

0021The invention also includes within its scope a DAS comprising a monitoring system as herein defined and/or described.

0022Still further included within the scope of the present invention are a central monitoring unit as herein defined and/or described and a monitoring device as herein defined and/or described.

0023The invention also includes within its scope a method of monitoring performance of a distributed antenna system comprising at least a central transmitter and a plurality of distributed antenna devices connected to the transmitter via a respective physical branch of a signal transmission network comprising a plurality of branches, each of the distributed antenna devices comprising at least one antenna which is associated with a frequency band having a centre frequency f_cand a corresponding wavelength λ_c, the method comprising: <ul id="ul0003" list-style="none"><li id="ul0003-0001" num="0000"><ul id="ul0004" list-style="none"><li id="ul0004-0001" num="0024">for at least some of the distributed antenna devices, providing a respective monitoring device at a distance d&lt;2λ_cfrom the at least one antenna;</li><li id="ul0004-0002" num="0025">transmitting from a central monitoring unit, along the network and via the distributed antenna device to at least one targeted monitoring device a monitoring signal;</li><li id="ul0004-0003" num="0026">at the at least one targeted monitoring device generating a response signal and transmitting the response signal to the central monitoring unit via the distributed antenna device and the network; and</li><li id="ul0004-0004" num="0027">utilizing at least one of the monitoring signal and the response signal to monitor performance of at least part of the distributed antenna system.</li></ul></li></ul>

0028The monitoring signal may addressed to the at least one targeted monitoring device by utilizing a respective unique address of the at least one targeted monitoring device.

0029The strength of the monitoring signal may be measured at the at least one targeted monitoring device.

0030Data relating to the measured strength may then be sent from the at least one targeted monitoring device via the associated distributed antenna device and the network to the central monitoring unit and the data may be identified at the central monitoring station by the respective unique address.

0031The strength of the response signal may be measured at the central monitoring unit.

0032In some embodiments, the strength of the monitoring signal may be measured at the at least one targeted monitoring device and the strength of the response signal may be measured at the central monitoring unit and the results of the measurements may be utilized to monitor the status of asymmetrical up and down paths between the central monitoring unit and the at least one targeted monitoring unit.

0033The method may include the step of utilizing switches which are distributed in the network selectively to attenuate or divert power propagating to at least some of the distributed antenna devices, thereby selectively to switch the at least some of the distributed devices out of the distributed antenna system.

0034The switches may be controlled by command signals from at least the central monitoring unit.

0035The monitoring signal, the response signal and the command signals may be at a suitable signal level to ensure communication and sensing between central monitoring unit, but below the level of a main signal transmitted by the central transmitter and below regulatory or operator requirements in terms of signal radiated from DADs as to meet regulatory requirements or DAS user requirements.

0036The monitoring signal, response signal and command signals may be transmitted according to a standard protocol and at a level of −30 dB relative to the main signal.

0037The monitoring signal, response signal and command signals may be transmitted out of band relative to the main signal.

0038The method as claimed in the may include the step of indicating the monitored status at the monitoring device and orand/or transmitting status information to other locations or a database to be accessed by various interested parties.

0039The monitored status may be determined by the monitoring device and the monitoring device may then indicate the status. In other embodiments the monitored status may be determined at the central monitoring unit and then the status may be indicated in response to a command sent from the central monitoring unit to the monitoring device.

BRIEF DESCRIPTION OF THE ACCOMPANYING DIAGRAMS

The invention will now further be described, by way of example only, with reference to the accompanying diagrams wherein:

<figref idref="DRAWINGS">FIG. <b>1</b></figref> is a diagram of an example embodiment of a simple distributed antenna system (DAS) and a monitoring system for the DAS;

<figref idref="DRAWINGS">FIG. <b>2</b></figref> is a diagrammatic representation of an example embodiment of a distributed antenna device (DAD) forming part of the DAS in <figref idref="DRAWINGS">FIG. <b>1</b></figref> and an associated monitoring device of the monitoring system;

<figref idref="DRAWINGS">FIG. <b>3</b></figref> is a basic block diagram of an example embodiment of the monitoring device;

<figref idref="DRAWINGS">FIG. <b>4</b></figref> is a basic block diagram of another example embodiment of the monitoring device with an example embodiment of an energy harvesting circuit for powering the monitoring device;

<figref idref="DRAWINGS">FIG. <b>5</b></figref> is a diagrammatic representation of example embodiments of monitoring devices for a multiple-input and multiple-output (MIMO) DAD;

<figref idref="DRAWINGS">FIG. <b>6</b></figref> is a diagrammatic representation of another example embodiment of a DAS and monitoring system comprising RF path diagnostic devices or switches and further signal monitoring devices which may be either fixed or roaming; and

<figref idref="DRAWINGS">FIG. <b>7</b></figref> is a block diagram of an example embodiment of an RF path diagnostic device or switch.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

0048An example embodiment of a distributed antenna system (DAS) is generally designated by the reference numeral <b>10</b> in <figref idref="DRAWINGS">FIG. <b>1</b></figref>. The DAS comprises at least a central transmitter <b>12</b> which is connected by a signal transmission network <b>14</b> to a plurality of distributed antenna devices (DAD) <b>16</b>.<b>1</b> to <b>16</b>.n to transmit a main signal propagating in a downward direction from the central transmitter <b>12</b>. The network comprises physical branches, such as branches <b>14</b>.<b>1</b> and <b>14</b>.<b>2</b>. Each of the DAD's <b>16</b>.<b>1</b> to <b>16</b>.n is connected to a respective sub-branch part or last mile <b>14</b>.<b>11</b>, <b>14</b>.<b>12</b>, <b>14</b>.<b>21</b> and <b>14</b>.<b>22</b> of branches <b>14</b>.<b>1</b> and <b>14</b>.<b>2</b>. The network <b>14</b> may be passive and comprise cables with splitters or may be active as defined in the introduction of this specification. Hence, the network may comprise one or more of frequency converting devices, radio-to-optic and reverse devices, point-to-point wireless components and bidirectional amplifiers.

0049An example embodiment of a DAD <b>16</b>.<b>1</b> is shown in <figref idref="DRAWINGS">FIG. <b>2</b></figref>. Each DAD comprises at least one antenna <b>18</b>. The antenna is associated with a frequency band having a centre frequency f_cand an associated wavelength λ_c. The DAD may optionally comprise a radome <b>20</b>.

0050An example embodiment of a monitoring system is generally designated by the reference numeral <b>22</b> in <figref idref="DRAWINGS">FIG. <b>1</b></figref>. The monitoring system comprises a central monitoring unit CMU <b>24</b> which is coupled to the network <b>14</b>. At least one monitoring device <b>28</b>.<b>1</b> to <b>28</b>.n is associated with at least one of said distributed antenna devices <b>16</b>.<b>1</b> to <b>16</b>.n and permanently mounted a distance d (see <figref idref="DRAWINGS">FIG. <b>2</b></figref>) away from the antenna of the associated distributed antenna device. The distance d is less than 2λ_c, preferably less than λ_c, more preferably less than λ_c/2 and even less than λ_c/4. Referring to <figref idref="DRAWINGS">FIG. <b>3</b></figref>, the monitoring device comprises a local controller <b>30</b>, a transceiver <b>32</b> and an antenna <b>34</b>. The local controller being configured, upon being polled by the CMU <b>24</b> with a monitoring signal in a downward direction and along a downward path via the network <b>14</b> and the distributed antenna device <b>16</b>.<b>1</b>, to cause the transceiver <b>32</b> to respond to the monitoring signal by transmitting a response signal in an upward direction and along an upward path to the CMU <b>24</b> via the distributed antenna device <b>16</b>.<b>1</b> and the network <b>14</b>. In some embodiments, especially in active networks, the upward and downward paths may not be the same and may hence be asymmetrical.

0051The CMU <b>24</b> may comprise a transceiver which may be connected to the network <b>14</b> by coupler <b>26</b> in a region of the network <b>14</b> towards the central transmitter <b>12</b> and before or upstream of a first branch <b>14</b>.<b>1</b>, <b>14</b>.<b>2</b>.

0052Referring to <figref idref="DRAWINGS">FIG. <b>3</b></figref> and as stated above, the monitoring device <b>28</b>.<b>1</b> comprises the local controller <b>30</b> which is connected to the transceiver <b>32</b> and which is connected to poles <b>34</b>.<b>1</b> and <b>34</b>.<b>2</b> of a broadband dipole antenna <b>34</b>. Each monitoring device may be associated with a unique address which is stored in a memory arrangement of the controller. The address may be used by the CMU <b>24</b> to poll or interrogate individual monitoring devices. The address may also be used to identify responses received by the CMU <b>24</b> from monitoring devices by virtue of the monitoring device appending its unique address to a response signal sent back to the CMU <b>24</b>.

0053The CMU <b>24</b> may use any suitable communication standard to communicate with or poll via the network <b>14</b> any one or more of the monitoring devices <b>28</b>.<b>1</b> to <b>28</b>.n. As an example, the ZigBee communication protocol and devices operating in the 2.4 GHz licensed frequency bands may be used to effect communication and addressing between the CMU <b>24</b> and other devices of the monitoring system and the same signals may additionally be used to monitor RF path and DAD operation. The ZigBee units may additionally be equipped with the ability to generate test signals at other frequencies used in the DAS system, if required. Other protocols operating at other frequencies may serve a similar purpose, such as Bluetooth, Wifi and/or similar communication protocols.

0054As shown in the example embodiment in <figref idref="DRAWINGS">FIG. <b>4</b></figref>, the monitoring device <b>28</b>.<b>1</b> may comprise an indicator arrangement <b>36</b>, for example in the form of one or more LED's which may be used to indicate a status of the DAD <b>16</b>.<b>1</b>, as explained below. Each monitoring device may comprise means (not shown) for measuring the strength of a received monitoring signal. Furthermore, the monitoring device may comprise a power supply comprising a battery <b>40</b>, alternatively a battery plus an energy harvesting circuit, which may for example comprise diode <b>42</b> and capacitor <b>44</b>. In some embodiments, the monitoring device <b>28</b>.<b>1</b> may be encapsulated in any suitable encapsulation <b>38</b>, for example a flexible sleeve or envelope, which may be adhered to a surface of the radome <b>20</b>. This may be particularly advantageous when retrofitting monitoring devices on existing DAD's comprising radomes.

0055The CMU <b>24</b> may comprise or be connected to a database (not shown) for storing said unique addresses, monitored status of each DAD as well as data relating to the position of the associated DAD. Hence, the monitoring devices may comprise complementary circuitry to respond via the network <b>14</b> to the CMU <b>24</b>. The CMU <b>24</b> may also comprise means for measuring the strength of a response signal received from any of the monitoring devices and processing means for processing such measurements.

0056In order not to interfere with the DAS, the CMU <b>24</b> is coupled to the main branch of the network <b>14</b> via coupler <b>26</b> to transmit via the network weak monitoring signals (at say −10 dB of the main signal, preferably −30 dB) and/or out of band monitoring signals which are received and processed by the monitoring devices <b>28</b>.<b>1</b> to <b>28</b>.<b>2</b> as will be described below.

0057In <figref idref="DRAWINGS">FIG. <b>5</b></figref>, there is shown an example embodiment of a multiple-input and multiple-output (MIMO) DAD <b>116</b> comprising a first antenna <b>118</b>.<b>1</b> and a second antenna <b>118</b>.<b>2</b> which are orthogonally polarized. Associated monitoring devices <b>128</b>.<b>1</b> and <b>128</b>.<b>2</b> with corresponding antenna orientations are provided in close proximity d (as defined above) from the first and second antennas, to ensure that both can be monitored independently. If the number of monitoring devices is equal to the number of MIMO elements in a MIMO DAD and close enough to the respective associated elements, the monitoring system may be used to monitor status of specific MIMO antennas within a DAD.

0058The CMU <b>24</b> may be pre-programmed to poll each monitoring device <b>28</b>.<b>1</b> to <b>28</b>.n on an intermittent, alternatively periodic basis. This is done by sending the monitoring signal with each monitoring device's address successively and waiting for the response signal from the monitoring devices. Upon receiving the response signal from a monitoring device, the strength of that response signal is measured, compared to a reference and/or previous values and stored and/or communicated to an external control centre. If no response is received from a monitoring device, after a predetermined number of polls, the monitoring device and/or DAD is tagged as defective. If a signal strength measurement on a response signal indicates degradation in or to the transmission path below a predetermined limit, then that monitoring device is instructed from the CMU <b>24</b> to update locally its status to “low level” and the indicator means <b>36</b> is caused to indicate that status. Further for example, failure of both devices <b>28</b>.<b>1</b> and <b>28</b>.<b>2</b> could be interpreted by the CMU <b>24</b> as likely failure of branch <b>14</b>.<b>1</b>, rather than failure of DAD <b>16</b>.<b>1</b> and <b>16</b>.<b>2</b>.

0059The monitoring device may be programmed to activate the local indicator <b>36</b> or may be configured in response to a command signal from the CMU <b>24</b> to display status, depending on where the measurement is done, at the monitoring device or at the CMU <b>24</b>. Status indications may include: failure, power reduction below predetermined limit, working status, low battery etc.

0060Hence, the monitoring devices may use the polling or monitoring signal received via its associated DAD to measure the signal quality and report back by means of the response signal such signal quality to the CMU <b>24</b>. Alternatively, the strength of the response signal as measured at the CMU <b>24</b> may be used to determine the path quality between the DAD and the CMU <b>24</b>. Whether sensing is done at the CMU <b>24</b> or at the respective monitoring devices, the monitoring system <b>22</b> may be configured to sense both a) failure vs operational and b) relative signal level.

0061As explained in more detail below, additional components which operate on the same protocol as the CMU <b>24</b> and the monitoring devices <b>28</b>.<b>1</b> to <b>28</b>.n may be inserted into the network <b>14</b>, to adjust network configurations or parameters. Such components could be inserted in-line to switch off certain DAD's or branch lines leading to DAD's or to attenuate/increase signal levels to DAD's or sections of DAD's.

0062Tones may be inserted at different frequencies used by the DAS <b>10</b> by either monitoring devices <b>28</b>.<b>1</b> to <b>28</b>.n or CMU <b>24</b>, to enable in-band or band related and/or more accurate measurements on the system <b>10</b>.

0063Monitoring devices <b>28</b>.<b>1</b> to <b>28</b>.n could use wireless mesh or other communication to adjacent or closely located other monitoring devices to establish an alternative response or up path back to the CMU <b>24</b>, in the event of failure of a line or branch to which they are connected.

0064<figref idref="DRAWINGS">FIG. <b>6</b></figref> is a figure similar to <figref idref="DRAWINGS">FIG. <b>1</b></figref>, but with RF path diagnostic devices or switches <b>50</b>.<b>1</b> to <b>50</b>.n included in at least some of the branches of the network. The switches may be used selectively to switch a major part of signal power (for example reducing the through signal by 30 dB and diverting the major part to a suitable dummy load) as will be described below. Additionally, some further distributed signal monitoring units <b>60</b>.<b>1</b> to <b>60</b>.n are included. These may be stationary or mobile.

0065<figref idref="DRAWINGS">FIG. <b>7</b></figref> illustrates an example embodiment of switch <b>50</b>.<b>1</b>. The switch may have a first port <b>52</b> for a path part extending to CMU <b>24</b> and a second port <b>54</b> for a path part extending to at least one DAD, such as DAD's <b>16</b>.<b>1</b> and <b>16</b>.<b>2</b>. The switch is connected to a controller <b>56</b> and to a dummy load <b>58</b>. The controller <b>56</b> is in communication with the monitoring system <b>22</b> using the above communication protocol. Path <b>57</b> carries a control signal and optionally some suitable reduced power tap off from the main line signal, to allow communication to the monitoring system. Controller <b>56</b> is configured upon command from the monitoring system or automatically under program control, to either allow the DAS signal to flow between ports <b>52</b> and <b>54</b> or a major part thereof to flow to dummy load <b>58</b>, with say only −30 dB of the original signal to pass from the first to the second port. The small signal still passed allows communication to happen between monitoring units <b>28</b>.<b>1</b> to <b>28</b>.n and CMU unit <b>24</b> while effectively isolating specific DAD's or groups of DAD's, to identify problems such as passive intermodulation (PIM) or perform propagation tests from specific DAD's or groups of DAD's, while others are effectively non-operational.

0066Hence, the system may comprise path diagnostic devices or switches <b>50</b>.<b>1</b> to <b>50</b>.n comprising respective controllers <b>56</b> operating on the same frequency and protocol as the monitoring devices and CMU <b>24</b>. The controller <b>56</b> is operative (under program control or on command from the CMU <b>24</b>) to cause the switch to switch between a first state wherein the switch allows the RF signal to continue unhindered and a second state wherein the switch causes part of the RF signal to be diverted to the dummy load <b>58</b>, so that most power goes to the dummy load with less than −10 dB, but preferably −30 dB continuing along the branch to which it is connected. This switch can be addressed by either the CMU <b>24</b> or any monitoring device or any other transmission diagnostic device, since all operate on the same frequency and uses the same communication protocol. Hence, such switches may be used to selectively isolate parts of the DAS system or specific DADs for diagnostic purposes or to test the monitoring device operation.

0067Furthermore, the system may be configured to measure signal in both directions of the DAS path to a specific DAD. The signals along the “down path” (that is towards the DAD's) and the “up path” (that is towards the CMU) may not be symmetrical due to active components. Utilizing the signal sensing and transmitting capabilities of the monitoring devices and the CMU <b>24</b>, the measurements could be done for “up” and “down” paths. Such measurements allow faults with specific units (up or down amplifiers for example) to be pinpointed by comparison of the signal measurements along both paths and associated with specific DAD's or group of DAD's.

0068Still furthermore, the monitoring system <b>22</b> may in addition to the monitoring devices <b>28</b>.<b>1</b> to <b>28</b>.n and the path diagnostic devices <b>50</b>.<b>1</b> to <b>50</b>.n comprise further distributed signal monitoring devices <b>60</b>.<b>1</b> to <b>60</b>.n (shown in <figref idref="DRAWINGS">FIG. <b>6</b></figref>) and which may be similar to that of the prior art. However, the distributed signal monitoring devices <b>60</b>.<b>1</b> to <b>60</b>.n may operate on the same communication protocol and frequency band as the monitor system <b>22</b>. The signal monitoring devices <b>60</b>.<b>1</b> to <b>60</b>.n may have the same functionality as the monitoring devices <b>28</b>.<b>1</b> to <b>28</b>.n, but may have different form factors and/or antenna configurations and/or energy harvesting circuitry (such as photovoltaic convertors). These devices <b>60</b>.<b>1</b> to <b>60</b>.n may be scattered or distributed through the DAS coverage area in permanent locations or alternatively temporarily located throughout the area to validate correct DAS system coverage after installation, or, may be moved around through the DAS coverage area after final installation to monitor signal and use DAD location either correlated in real time or by correlating mobile position which may be time related by mobile unit during walk-through or other mobile test of coverage. During such measurements, communication (polling) signals and unique identifiers associated with DAD's and further monitoring devices will be used in either up or down or both directional measurements to determine coverage.

0069Communication may happen between the CMU <b>24</b> via DAD's to signal monitoring devices <b>60</b>.<b>1</b> to <b>60</b>.n directly or may also be relayed via monitoring devices <b>28</b>.<b>1</b> to <b>28</b>.n. Monitoring may be performed using information from signal monitoring device <b>60</b>.<b>1</b> to <b>60</b>.n operation in conjunction with information from monitoring device <b>28</b>.<b>1</b> to <b>28</b>.n operation and optionally selective isolation using path diagnostic devices or switches <b>50</b>.<b>1</b> to <b>50</b>.n, to get detailed information of coverage.