Patent Application
20090213737
The present invention relates generally to communication testers, and more particularly to a system for testing a Data Over Cable Service Interface Specification (DOCSIS) network.
Today people demand connectivity to services from all over the world without leaving their homes. They want video on demand, Internet access, live on-line gaming, and access to the world market place from the comfort of their living room. In order to support these ideas and requests a cable industry group developed the Data Over Cable Service Interface Specification (DOCSIS). DOCSIS defines a procedure for transferring digital information through the existing cable television infrastructure.
DOCSIS specifies downstream traffic transfer rates between 27 and 36 mega bits per second (Mbps) over a radio frequency (RF) path in the 50 mega hertz (MHz) to 750+ MHz range, and upstream traffic transfer rates between 320 kilo bits per second (Kbps) and 10 Mbps over a RF path between 5 and 42 MHz. But, because data over cable travels on a shared loop, individuals will see transfer rates drop as more users gain access. New proposals for the DOCSIS 3.0 specification may support transfer rates up to 160 Mbps in the downstream direction and 120 Mbps in the upstream direction in order to extend the useful life of the cable television (CATV) infrastructure.
In order to facilitate these transfer rates, the condition of the cable structure and its proper termination is critical. Many signal processing techniques, Time Division Multiple Access (TDMA), Quadrature Amplitude Modulation (QAM), Quadrature Phase Shift Keying (QPSK), Trellis Coded Modulation (TCM) and the like are used to extend the capabilities of the aging CATV structure.
A critical aspect of the DOCSIS operation requires maintaining the integrity of the cable structure itself. In order to maintain the operational integrity of the cable structure, sophisticated test and analysis equipment must be used to detect and resolve problems. By coupling specific test equipment to the cable test points, signals between the Cable Modem Termination System (CMTS) and the Cable Modem (CM) may be analyzed.
The downstream path, from the CMTS to the CM, is straightforward to analyze because the CMTS manages the transmission of signals into the cable structure. Power and phase of the transmission signals have already been adjusted to compensate for losses prior to the CMTS. In the structure beyond the CMTS there may be many branches or CM attach points that can affect the signal quality. Each node in the cable structure may require different signal processing and amplification in order to deliver good data to the end user. The analysis of the delivery path just accepts the transmitted data and examines the delivered signal for abnormalities in amplitude, phase, or modulation.
In order to analyze the upstream path, from the CM to the CMTS known as a return path, the test equipment must take over the transmission responsibilities by sourcing a signal that provides correct amplitude, frequency, phase, and modulation. The frequency, phase, and modulation may be defined by the specific channel that is under analysis. The amplitude of the signal injected into the upstream path has historically been determined by a best guess, trial and error process. If too much power is injected into the cable structure, distortion may impact all of the signals on the return path.
The process of setting the power limits for diagnostic transmission on the upstream path has historically been a manual process requiring caution not to impair the active signaling on the same cable structure. This process may be tedious and time consuming. It may also cause an undue amount of time to be spent by a highly trained technician adding cost to the maintenance process.
Thus, a need still remains for a return sweep level setting system for simplifying the analysis of the upstream path in the cable structure. In view of the overwhelming popularity high-speed content delivered to the home, it is increasingly critical that answers be found to these problems. In view of the ever-increasing commercial competitive pressures, along with growing consumer expectations and the diminishing opportunities for meaningful product differentiation in the marketplace, it is critical that answers be found for these problems. Additionally, the need to save costs, improve efficiencies and performance, and meet competitive pressures, adds an even greater urgency to the critical necessity for finding answers to these problems.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.
The present invention provides a test system including: providing a conditioning circuit; cabling a cable modem termination system to the conditioning circuit; signaling an initial ranging request to the cable modem termination system; and determining a transmission power limiter by the conditioning circuit monitoring a network for detecting a cable modem termination system response to the initial ranging request.
Certain embodiments of the invention have other aspects in addition to or in place of those mentioned above. The aspects will become apparent to those skilled in the art from a reading of the following detailed description when taken with reference to the accompanying drawings.
The following embodiments are described in sufficient detail to enable those skilled in the art to make and use the invention. It is to be understood that other embodiments would be evident based on the present disclosure, and that process or mechanical changes may be made without departing from the scope of the present invention.
In the following description, numerous specific details are given to provide a thorough understanding of the invention. However, it will be apparent that the invention may be practiced without these specific details. In order to avoid obscuring the present invention, some well-known circuits, system configurations, and process steps are not disclosed in detail. Likewise, the drawings showing embodiments of the system are semi-diagrammatic and not to scale and, particularly, some of the dimensions are for the clarity of presentation and are shown greatly exaggerated in the drawing FIGs. Where multiple embodiments are disclosed and described, having some features in common, for clarity and ease of illustration, description, and comprehension thereof, similar and like features one to another will ordinarily be described with like reference numerals.
For expository purposes, the term “horizontal” as used herein is defined as a plane parallel to the plane or surface of the Earth, regardless of its orientation. The term “vertical” refers to a direction perpendicular to the horizontal as just defined. Terms, such as “above”, “below”, “bottom”, “top”, “side” (as in “sidewall”), “higher”, “lower”, “upper”, “over”, and “under”, are defined with respect to the horizontal plane. The term “on” means there is direct contact among elements. The term “system” as used herein means and refers to the method and to the apparatus of the present invention in accordance with the context in which the term is used.
Referring now to
The conditioning circuit 108 may also be coupled to an RF transmitter 112, having a transmission power limiter 113, which is coupled to an RF output jack 114. A control panel 118 may be used to activate the functions of the test system with return sweep level setting 100. A display screen 116 may be used to present the diagnostic data, set-up information, or status. The test system with return sweep level setting 100 may be used to analyze a data over cable service interface specification (DOCSIS) network. It may be used to maintain the DOCSIS network by detecting problem interconnects. Problems such as damaged cables, high ingress levels, loose connectors, or corroded contacts may severely restrict the communication bandwidth of the network.
Referring now to
The test system with return sweep level setting 100 may be coupled to the test coupling 206 or the cable modem (CM) attach point 208 in the network 200. A radio frequency (RF) input cable 212 may be used to couple the test system with return sweep level setting 100 to the downstream cable 204. An RF output cable 214 may couple the test system with return sweep level setting 100 to an upstream cable 216 through the test coupling 206 or the cable modem (CM) attach point 208. The test couplings 206 and the cable modem attach points 208 are distributed on the downstream cable 204 and the upstream cable 216 at equivalent locations. That is to say, the distance from the cable modem termination system 202 to each of the test coupling 206 or the cable modem (CM) attach point 208 is the same on the downstream cable 204 and the upstream cable 216. Any difference in the transmission characteristics may be the result of damaged cables, loose connectors, corrosion, failed components, or a combination thereof.
The analysis of these problems must occur during the normal operation of the network 200. Downstream frequency sweeps may collect information about noise sources in the path from the cable modem termination system 202 to the cable modem attach point 208. This is the primary data payload delivery path. Just as important to peak performance of the network 200 is a return path 218, such as the upstream cable 216 between the cable modem attach point 208 and the cable modem termination system 202 including any of the test coupling 206 or the cable modem (CM) attach point 208. The return path 218 typically handles smaller payloads, such as requests for data, maintenance requests, or initialization exchanges.
A head end tester 220 may be coupled between the downstream cable 204 and the upstream cable 216. The head end tester 220 may receive a return sweep, such as a frequency sweep, from the test system with return sweep level setting 100 across the return path 218. The head end tester 220 may assemble the return sweep results in a graphical representation for sending the results on the downstream cable 204. An interface device 222, such as a cable modem or a cable branch amplifier, may be attached to the downstream cable 204 and the upstream cable 216 at the cable modem attach point 208.
Referring now to
An ideal response to the return sweep 304 may be a straight line positioned on a zero marker 306 in the vertical scale 308. The vertical scale 308 may reflect a number of decibel milli-volts either added to or subtracted from the original signal level. The return sweep 304 samples a number of frequencies as represented by the horizontal scale 310 representing the frequencies in megahertz. The frequency limits of the return sweep 304 may vary. The frequency limits displayed represent the frequencies defined for the return path 218, of
Historically the set-up for the analysis of the return path 218 required a manual power adjustment so that the testing device could send a proper level signal into the upstream cable 216 of
It has been discovered that information exchanged between the test system with return sweep level setting 100 and the cable modem termination system 202 of
Referring now to
The cable modem termination system 202 allocates time slots 406 and controls the usage for each of the time slots 406 in the upstream communication flow 404. The cable modem termination system 202 sends a map message 408 at regular intervals in the downstream communication flow 402. The cable modem termination system 202 may allocate the time slot 406, such as a contention broadcast slot, that all of the interface devices 222, of
In the example of
The cable modem termination system 202 may complete the ranging process with all of the devices attached to the network 200. The test system with return sweep level setting 100 may determine a power level used by the cable modem termination system 202. The test system with return sweep level setting 100 may then use the power settings determined from the cable modem termination system 202 to set its own copy of the transmission power limiter 113, of
It has been unexpectedly discovered that the test system with return sweep level setting 100 may properly adjust its transmission power regardless of its position on the network 200 without intervention by an operator. This capability has reduced the set-up overhead and contention associated with executing the return sweep 304 in an active network 200.
Referring now to
It has been discovered that the present invention thus has numerous aspects.
A principle aspect that has been unexpectedly discovered is that the present invention may automatically set the transmission power level in preparation for generating the return sweep on the return path.
Another aspect is that the present invention may be attached to any point on the network without having prior special knowledge of the network topology in order to generate the return sweep.
Yet another important aspect of the present invention is that it valuably supports and services the historical trend of reducing costs, simplifying systems, and increasing performance.
These and other valuable aspects of the present invention consequently further the state of the technology to at least the next level.
Thus, it has been discovered that the return sweep level setting system of the present invention furnishes important and heretofore unknown and unavailable solutions, capabilities, and functional aspects for network analyzers. The resulting processes and configurations are straightforward, cost-effective, uncomplicated, highly versatile and effective, can be surprisingly and unobviously implemented by adapting known technologies, and are thus readily suited for efficiently and economically manufacturing network analyzer devices fully compatible with conventional manufacturing processes and technologies. The resulting processes and configurations are straightforward, cost-effective, uncomplicated, highly versatile, accurate, sensitive, and effective, and can be implemented by adapting known components for ready, efficient, and economical manufacturing, application, and utilization.
While the invention has been described in conjunction with a specific best mode, it is to be understood that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the aforegoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations that fall within the scope of the included claims. All matters hithertofore set forth herein or shown in the accompanying drawings are to be interpreted in an illustrative and non-limiting sense.
