Abstract:
The present invention provides systems and methods for digitally certifying and monitoring a hybrid fiber coaxial (HFC) cable plant. The present invention may be used to automate the characterization of the upstream and/or downstream channels of the cable plant and provide a path for establishing a performance baseline for the cable plant. After certification of the plant, the present invention provides for monitoring of cable plant performance and the use of a performance baseline to provide warnings and alerts prior to system downtime. The present invention also discloses cable plant characterization and monitoring functions being provided from a single site to a plurality of remote cable plant operators.

Description:
BACKGROUND  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to certification and monitoring of a cable system or plant, and more particularly to certifying a hybrid fiber coaxial (HFC) cable plant and subsequently monitoring its performance.  
         [0003]     2. Description of Related Art  
         [0004]     In the early 1980&#39;s the benchmark for modem transmission speed over standard analog telephone lines was 300 bits per second (bps). This benchmark reached 56,000 bps (56 Kbps) in modems in 1998, essentially the limit of data transmission using “plain old telephone service” (POTS). However, with the broad acceptance of the World Wide Web (WWW) and associated applications such as electronic mail (e-mail), the sale and delivery of software via the WWW and other interactive data services, this 56 Kbps rate is becoming inadequate for widespread consumer use.  
         [0005]     One non-POTS solution to the need for higher data throughput is a high-speed cable network, for example, an HFC cable television (CATV) network. However, CATV networks are generally constructed asymmetrically to maximize delivery of downstream data, that is, the signal flow from the cable plant headend downstream to users. Thus, a typical CATV network may have a hundred or more 6 megahertz (MHz) downstream channels and six 6 MHz upstream channels. Even where additional upstream channels are part of an original design or part of a system upgrade, high throughput or bandwidth for upstream transmissions is difficult to obtain and maintain. One reason for these difficulties with upstream data transmission is the physical plant layout. As a signal travels downstream through splitters on its way to all of the users, it is attenuated on the splitters&#39; outputs. Any noise carried with the signal is also attenuated and the signal-to-noise ratio (SNR) remains unchanged. However, for upstream signal flow, the splitters&#39; downstream outputs become upstream inputs, and incoming signals and noise are combined. Where a signal is present on only one input of a splitter but noise is present on both, the combined signal has a reduced SNR. As this combining process can take place many times, the SNR of an upstream signal is often reduced dramatically. This SNR reduction phenomena is referred to as noise funneling, which would have to be reduced or eliminated to maximize upstream data transmissions.  
         [0006]     Another problem for CATV systems attempting to provide interactive data services is providing service uptime and reliability comparable to that of telephone services. However, a cable system operator, whether a single system operator or a multiple system operator (MSO), does not typically have the staff to address the new problems associated with this enhanced service uptime and reliability and the upstream data transmission capability needed for interactive data services. In addition to this shortage of maintenance personnel, the existing staff typically lacks experience in interactive data services and digital communications, as well as the required digital test equipment and new problem solving skills.  
         [0007]      FIG. 1  is a simplified flow diagram of operational steps in currently known analog methods for certifying and maintaining a CATV cable plant  100 A that is not a hybrid fiber coaxial (HFC) cable plant. A CATV cable plant capable of interactive data service and digital certification will be referred to as HFC CATV cable plant  100 B. Beginning in step  110 , a CATV cable plant  100 A is newly constructed, upgraded or re-adjusted. In step  115 , CATV cable plant  100 A is tested until analog certification is established. If in step  115  the testing fails to establish certification, then the process returns on “No” path  112  to step  110  for additional adjustments and upgrades. The adjustments of step  110  and the tests of step  115  are repeated until CATV cable plant  100 A is certified.  
         [0008]     Analog testing methods are well known and will not be discussed in detail here, but it is useful to note that these methods are not readily automated. Rather, most analog testing methods used for cable plant certification require the physical presence of one or more maintenance personnel at each node of the cable plant to make the necessary measurements, evaluations and adjustments. When knowledge of the frequency response of a data channel is required for step  115  to grant analog certification to the plant, technicians must travel to each of several node locations and tap frequency analyzers into the cable to measure frequency responses over a range of settings. If a measurement indicates a problem, additional measurements are taken at other physical locations to determine the source of the problem. Such a process of measuring, changing location and re-measuring is time consuming and costly.  
         [0009]     Once step  115  grants analog certification, the process follows “Yes” path  118  to step  120  where the plant is considered “certified” to begin commercial operation. However, these analog methods are not capable of fully testing the data transmissions flowing upstream.  
         [0010]     While the certified plant is operating, it is essential to maintain plant performance standards and timely responses to user complaints.  FIG. 1  depicts the plant maintenance process in step  121 , step  131  and step  135 . In step  121  a user complaint is received and correlated with similar complaints. In step  127 , if the system has not received complaints sufficient enough to be reported for further action, then the process returns on “No” path  126  to step  121  to await additional complaints. If enough complaints have been received then the process follows “Yes” path  128  to step  131  for attention by a cable plant operator. For example, based upon those user complaints, a multiple system operator (MSO) may dispatch maintenance personnel to appropriate locations to correct the corresponding cable plant problem. Since the analog testing processes used for plant certification do not generally result in data baselines for the plant and its components, maintenance personnel must both diagnose and repair the problem, which is often not straightforward. For example, a user complaint received in step  121  can be as simple as “I can&#39;t access the Internet.” Thus, repairing the problem generally encompasses a diagnostic phase in step  135  where a technician visits the user&#39;s site to make various measurements and then determine the nature of the problem. After the diagnosis and repair of step  135 , if recertification is necessary, the process follows “Yes” path  138  back to step  110  at the start. If recertification is not necessary, the process follows “No” path  132  back to step  121  to await additional complaints. At other times step  127  may determine that the operator will have to wait for additional user complaints to gain a better understanding of a problem before the first technician is dispatched. This waiting period is undesirable as it increases plant downtime for the user who registered the initial complaint.  
         [0011]     Since CATV cable networks primarily provide television programming, most of the available bandwidth is dedicated to maximizing the number of channels available to users. Upstream bandwidth is therefore limited. Hence it would be desirable to maximize the usability of the available upstream data paths in CATV infrastructures. In addition, it would be desirable for the automated systems and methods that increase cable plant uptime and reliability to at least parallel those of the telephone companies. It would also be advantageous if these automated systems and methods could be employed to identify problems before they result in plant downtime, and to identify those portions of the cable plant that require upgrades to maintain high quality interactive data services. It would also be useful to identify the location of failed or about-to-fail equipment and thus enable rapid and inexpensive repairs. Finally, it would be valuable to have automated systems and methods that could monitor multiple cable plants from a single location.  
       SUMMARY  
       [0012]     The present invention provides digital certification and monitoring methods for a hybrid fiber coaxial (HFC) cable plant. The digital certification methods of some embodiments of the invention provide, among other things, a path for establishing a cable plant performance baseline or database and for after-certification monitoring of an HFC cable plant using the database. The monitoring methods include provisions such as warnings, messages, and alarms that anticipate problems with plant performance.  
         [0013]     Some embodiments in accordance with the invention automate the characterization of an HFC cable plant. For example, in some embodiments a small number of cable modems (CM&#39;s) can be positioned at predetermined locations of a cable plant to provide information useful in plant characterization. Information about the radio frequency (RF) quality of the plant can be collected via the RF management information base (MIB) of the CM&#39;s and the cable modem termination system (CMTS). Typically, automated digital certification encompasses the collection of data over a day or more to identify any periodic effects on plant performance, such as those caused by daytime heating and nighttime cooling of components.  
         [0014]     In some embodiments, digital certification of the cable plant is automated for both the upstream and downstream paths. Upstream certification generally includes characterization of the entire upstream band. Thus the certification process determines ingress or noise regions in each upstream band and uses this information to establish an optimal frequency allocation plan for each band. In addition, nonlinearity and noise versus the packet error rate (PER) are evaluated at the CMTS for data received from each of the several CM&#39;s over a spectrum of power levels and frequencies. This determines the dynamic range of each CM-to-CMTS upstream path, determines an optimal set of receive conditions, validates the alignment of reverse path amplifiers, and identifies the nature of any physical impairments.  
         [0015]     Digital downstream certification is generally less complex as HFC cable plants have historically been designed to optimize downstream data flow. However, some embodiments of the invention evaluate and certify downstream channels with respect to SNR, tilt and channel distortion, and forward error correction rates. This identifies the most useable channels as well as any specific problems that limit channel usability.  
         [0016]     A plant certification process, particularly of downstream channels, also uses analog methods and tools. For example, analog methods generally record analog data “snapshots” for a variety of channel characteristics such as hum, noise, carrier-to-noise ratio (CNR), and group delay.  
         [0017]     Some embodiments of the invention employ the measurements of simple network management protocol (SNMP) agents and the management information bases (MIB&#39;s) of the smart components of the cable plant to create a certification database. Generally this data is collected throughout the certification process and provides a valuable baseline for the performance of the entire cable plant and its smart components over a period of one or more days. The advantage of having such a database lies in the ability to determine which of the measured parameters are useful for monitoring the HFC cable plant once the certification process is complete. For example, evaluation of PER data can result in the setting of one or more alarm levels to trigger a notification message regarding a predicted CM failure. Thus the notification allows for corrective action before the cable plant encounters downtime. In addition, as the monitoring methods of the invention link the monitored data to a specific component, use of such alarm levels for notification allows for the identification of a specific problem device. Collecting baseline data over time enables identifying various data trends that can be used to predict when a specific component&#39;s performance will begin to deteriorate. Thus an automated message can be dispatched that will allow for dynamic control of some “smart” cable plant components. In some embodiments of the invention, cable plant characterization and monitoring functions are provided by a single site remote from any one cable plant to a plurality of cable plant operators or MSO&#39;s.  
         [0018]     These and other objects, features, and advantages of the present invention will be better understood with reference to the accompanying drawings among which given elements retain the same number.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a simplified flow diagram of operational steps to certify each node of a CATV cable plant with currently known analog testing methods and to maintain cable plant operation once analog certification is granted;  
         [0020]      FIG. 2  is a simplified block diagram of a portion of an HFC CATV cable plant; and  
         [0021]      FIG. 3  is a simplified flow diagram of operational steps to certify and monitor a HFC cable plant with analog and digital testing methodology according to the invention.  
     
    
     DETAILED DESCRIPTION  
       [0022]      FIG. 2  is a block diagram illustrating the interconnectivity of some components of an HFC CATV cable plant  100 B capable of interactive data service. This diagram is greatly simplified for ease of explanation. HFC cable plant  100 B encompasses a headend  180  containing a cable modem termination system (CMTS)  190  coupled to one end of each of three fiber optic trunk cables  210 . Each trunk cable  210  at its other end is coupled to a respective one of three optical network units  220 . Although  FIG. 2  shows three trunk cables  210  coupling to termination system  190 , other configurations having a larger or small number of coupled trunk cables  210  are possible. Similarly, some embodiments in accordance with the invention have multiple termination systems  190 .  
         [0023]     Each optical network unit  220  couples one fiber optic trunk  210  to one coaxial cable run  122 , and thus serves as the initiation point of local distribution networks, one of which, network  130 , is shown in some detail for illustrative purposes. Exemplary distribution network  130  is a branched network of coaxial cable runs  125 . At various points within distribution network  130 , splitters  140  allow a single cable run  122  or  125  to branch into two or more cable runs  125 . Each branched cable run  125  has a number of signal amplifiers  150  positioned appropriately for maintaining the sufficient signal strength being supplied to a user site  392 . Where branched cable run  125  passes a user site  392 , a cable tap  160  couples a cable modem  394  at user site  392  to cable run  125 , providing cable modem  394  with interactive data service. Cable modems may be from various vendors, including but not limited to 3COM Cable Modem CMX, Thomson RCA DCM105, General Instrument SB3100, Sony CMR-1000, or Philips PD10D. The typical distance covered is a few hundred feet. Any Data Over Cable Service Interface Specification (DOCSIS) compliant cable modems would report power levels, signal-to-noise ratios, timing offsets, frame error counts, microreflection levels, and equalizer settings.  
         [0024]     While not shown, each amplifier  150  is a bi-directional amplifier capable of amplifying both downstream and upstream signals. The signal level below which amplification is needed is −15 dBmV, where dBmV (decibels relative to one millivolt across 75 ohms) is a measure of RF power. The cable modem would not be able to receive an input beyond the range of −15 dBmV to +15 dBmV, otherwise known as the dynamic range.  
         [0025]     The optical network unit  220  is a bi-directional optical fiber node. A fiber node provides the interface between a fiber trunking system and a coaxial distribution leg. Each optical network unit  220  includes a bi-directional amplifier  155 , an optical receiver  225  for receiving the signal travelling downstream from optical trunk  210 , and an optical transmitter  230  for transmitting the signal travelling upstream onto optical trunk  210  from cable run  120 . At the simplest level, a fiber node may consist of a single optical receiver whose output is amplified to feed the downstream amplifier, and an upstream optical transmitter. The upstream optical transmitter&#39;s input is driven by the output of a combiner whose inputs are the upstream signals from all connected coaxial distribution legs.  
         [0026]      FIG. 3  is a simplified flow diagram of operational steps using analog and digital methods for certifying and maintaining an HFC cable plant. Beginning in step  310 , an HFC cable plant  100 B is newly constructed, upgraded or re-adjusted. Step  315  tests HFC cable plant  100 B until granting analog certification. If in step  315  the tests fail to establish such certification, the process returns on “No” path  312  to step  310  and additional adjustments and upgrades are made. Once the step  315  analog testing is successfully passed, the process follows “Yes” path  318  and in step  320  grants analog certification for HFC cable plant  100 B.  
         [0027]     Next, step  330  digitally tests HFC cable plant  100 B. Unlike the analog testing of step  315 , digital testing is generally automated and thus does not require travel to various cable plant locations for testing purposes. The digital testing processes generally take advantage of the “smart” nature of the digital components used in building or upgrading HFC cable plant  100 B. Thus components such as cable modems  394  ( FIG. 2 ), digital amplifiers  150  ( FIG. 2 ) and the like are configurable to automatically provide performance and status data to a central site.  
         [0028]     In some embodiments in accordance with the invention, cable modems (CM&#39;s)  394  are coupled into a number of selected representative locations within the cable plant for digital testing purposes. At the cable plant&#39;s headend  180  ( FIG. 2 ) a cable modem termination system  190  is coupled through the cable plant&#39;s network to each of the CM&#39;s  394 . During digital testing, signals are sent through the CMTS  190  to each of the CM&#39;s  394  to query for status and other information. In response to these queries, each CM  394  sends a return signal to the CMTS  190  providing the requested information as well as a unique identifier portion or ID code. The ID code keys the response to the specific modem sending it. As responses are received, they are evaluated for establishing digital certification and to create a database that is useful for establishing a plant performance baseline. Advantageously, this automated process allows for requesting information, through the CMTS  190 , from each CM  394  in a specific predetermined order and at a specific predetermined rate to enhance the testing process of step  330 . Additionally, in some embodiments of the invention, the digital testing is initiated by signals sent to the CMTS  190  from a central, remote site coupled to the CMTS  190 . As the digital testing of step  330  generally does not require sending personnel to various cable plant locations, it is well suited to the collection of data over a period of time, for example one or more days, to establish performance trends over the selected time period. This performance trend data can also be incorporated into the plant performance baseline. It will be understood that the digital testing of step  330  can also employ “smart” devices other than or in addition to CM&#39;s. For example, some embodiments of the invention use bi-directional amplifiers for testing HFC cable plant  100 B in step  330 . Other components that may be used include two-way digital set-top boxes and two-way network interface units.  
         [0029]     If in step  330  the digital testing is failed, then the process returns on “No” path  332  to step  310  and additional adjustments and upgrades are made as required. If in step  330  the digital testing is passed, then the process continues on “Yes” path  336  to grant digital certification in step  338 , and in step  339  to create the previously mentioned cable plant performance database. While  FIG. 3  depicts the steps of analog testing and analog certification preceding those of digital testing and digital certification, this order is presented for illustrative purposes only. Analog and digital testing can proceed in any order, and often analog testing is concurrent with digital testing. Due to this flexibility in testing sequence, where testing for certification fails and the process returns on “No” path  312  or “No” path  332 , some retesting in steps  315  or  330  may not be needed.  
         [0030]     As previously mentioned, during the digital testing of step  330 , “smart” devices such as cable modems (CM&#39;s  394 ) return ID codes to identify themselves. This ID code information can be correlated to physical location information to reduce the amount of testing required to grant digital certification. For example, where a first and a second CM  394  are positioned along a single cable run  125  ( FIG. 2 ) with an amplifier  150  positioned therebetween, a good response from the second CM  394 , furthest from the CMTS  190 , indicates that the intermediate amplifier  150  is functioning properly. Therefore, some or all testing of that amplifier  150  can often be bypassed. Similarly, a poor or lost response from the second CM  394  indicates that a problem is located either at the second CM  394  or the amplifier  150 . By requesting information from the suspect amplifier  150 , the problem can be precisely identified and a repair or adjustment started. In some embodiments of the invention, it is possible to perform such digital testing by automated testing methods. That is to say, some digital testing processes of step  330  have a computing apparatus (not shown) and appropriate computing instructions to allow automatic polling of “smart” devices upon receipt of failed or suspect test data. Thus, devices located between a good device and a device reporting failed or suspect test data are polled until the actual failed or poorly performing device is identified and the problem with that device is determined. In addition, for some problems, repairs or adjustments are possible through remote reconfiguration of the failed or poorly performing device. A reconfiguration signal could be sent to the device in order to change various smart device settings. For example, settings such as the upstream transmit power, the upstream channel frequency, or the upstream pre-equalizer coefficients may be changed remotely.  
         [0031]     After HFC cable plant  100 B is certified and operating commercially, plant performance maintenance and timely responses to user complaints are essential. In  FIG. 3 , the process of maintaining HFC cable plant  100 B is encompassed in step  340 , step  346 , step  348 , step  355 , step  356 , step  359 , step  360 , step  365  and step  370 . In step  340 , user complaints are received and correlated with similar complaints. In step  346  and step  348 , digital performance data is received from various “smart” devices within HFC cable plant  100 B. Once received, this data is evaluated, for example by comparing the data to the plant performance baseline database created in step  339 .  
         [0032]     If there are current user complaints but no current problems indicated by the digital performance data, the maintenance process follows “No” path  351  and a technician is dispatched for field repair or maintenance in step  365 .  
         [0033]     If there are no current user complaints, but the digital performance data collected in step  348  indicates a problem through a warning, alarm, or message, the maintenance process follows “Yes” path  352  and remote adjustment or maintenance in step  360  is performed.  
         [0034]     Advantageously, if problems are indicated by both user complaints and digital performance data, the maintenance process follows “Yes” path  350  and the complaints are correlated to the performance data in step  355 . The correlation process of step  355  enhances identification of problems, both as to cause and location, which results in more rapid and more accurate maintenance responses. Thus, to affect the proper repair or adjustment procedures, step  356  determines whether the necessary adjustment can be done remotely. If remote adjustment only is necessary, “Yes” path  358  is followed to step  360  where remote adjustment occurs. If remote adjustment alone will not remedy the problems, “No” path  357  is followed to step  359 , which determines whether the problems can be resolved only in person. If adjustment in person only is necessary, “Yes” path  362  is followed to step  365  where the adjustment is made in person. If the repairs cannot be accomplished solely by remote adjustment or by in person adjustment, “No” path  361  is followed to step  370  for both remote and in person adjustments.  
         [0035]     Where the repairs or adjustments performed in step  360 , step  365 , or step  370  significantly change HFC cable plant  100 B, recertification may be necessary. If so, the process follows “Yes” path  380  and recertification is begun. If not, “No” path  390  is followed and plant monitoring is continued.  
         [0036]     It should be understood that due to the branched nature of an HFC cable plant, as depicted in  FIG. 2 , recertification might entail one or several branches and not necessarily the entire plant. In addition, in some embodiments of the invention, one portion of HFC cable plant  100 B is undergoing a certification process while another portion is in commercial operation and is being monitored.  
         [0037]     Certification and maintenance processes in accordance with the invention provide significant benefits over prior techniques. Rather than maintaining a cable plant using methodologies based primarily on user complaints, the  FIG. 3  maintenance methodology of the invention employs both user feedback and digital performance data. In addition, this methodology advantageously provides for maintenance response based on user feedback or digital performance data that is used either singly, or combined and correlated with each other as well as with the plant performance baseline database created in step  339 .  
         [0038]     The above-described processes for digital testing, certification and monitoring also advantageously enable collecting and evaluating data generated at a remote site. In addition, where a cable plant operator has multiple cable plants, one remote site is capable of collecting and evaluating data for all plants. Thus, some embodiments of the invention provide a remote data collection and evaluation site.  
         [0039]     Generally, this remote site encompasses a device for establishing a two-way communication channel to each cable plant. This communication channel is used for collecting data during the certification and monitoring processes, as well as sending signals to “smart” devices installed in the plant. The remote site also encompasses a computing apparatus and appropriate computer instructions or software.  
         [0040]     In some embodiments of the invention, the software provides instructions-for evaluating data collected during testing for certification and/or during the plant monitoring processes. In some embodiments the software has instructions for creating a database from the collected data and establishing the previously mentioned cable plant performance baseline. In addition, some embodiments provide software instructions for comparing data collected during the monitoring processes with the performance baseline, and for issuing warnings, alarms and messages based on that comparison. Some embodiments of the invention also provide software instructions that automate data collection during both certification testing and plant monitoring processes. Thus these instructions provide for sending queries, as well as reconfiguration and adjustment instructions, to “smart” devices installed in the cable plant. Finally, in some embodiments of the invention, the ID portion of a device&#39;s response is automatically correlated to a physical location to provide for displaying a map of locations for HFC cable plant  100 B on a display device at the remote site.  
         [0041]     A detailed description of illustrative embodiments of the present invention has been presented. Various modifications or adaptations of the methods and specific structures described may have become apparent to those skilled in the art. Hence, these descriptions and drawings should not be considered in a limiting sense, as it is understood that the invention is limited only by the following claims.