Cisco Technology, Inc.

Wei-Sing Chen

Guenter E Roeck

Mark E Millet

Charles J Naegeli

Sunil Khaunte

Alejandro Schwartzman

Hung-San Chen

Apparatus, methods, and computer program products for detecting or locating a viable data carrier in a downstream channel by a cable modem. Potential channels for data carriers can be eliminated quickly by going through a 'screening' process, i.e., the first constellation diagram match, thereby preventing those potential channels from going through a significantly more time-consuming second constellation match. The determination of whether the signal in the potential channel is modulated according to the first particular modulation scheme is done rapidly and only potential channels containing a signal likely to be modulated according to the second particular modulation scheme are examined for the second determination step.

Fast and reliable data carrier detection by a cable modem in a cable television plant

Methods, apparatus, and computer-readable media are disclosed for performing diagnostic tests of a communication link between a headend and a cable modem without having to assign an IP address to the cable modem. The diagnostic tests are performed at the MAC layer and test the state of the hardware between and including the cable modem termination system (CMTS) and a selected cable modem. By doing so, a network operator is able to more easily focus in on a potential problem in cable RF/MAC connectivity between the two components by first eliminating (or identifying) a problem with hardware before focusing on problem-solving at the software level, typically at the Network layer, at which point the cable modem is assigned an IP address.

Media access layer ping protocol for diagnosing cable modem links

A method and system for locating faulty components in a cable modem network configured within a hybrid fiber-coaxial cable television system by tabulating modem performance data are described. A method of isolating problematic components in a cable modem network includes determining whether a cable modem transmitted a polling message to a central destination during the modem's allotted time interval. A media access control layer, located within a cable modem termination system (CMTS), keeps a miss count for the cable modem that reflects the number of times the cable modem does not transmit a polling message to the CMTS during its allotted time. The media access control layer determines whether the cable modem is changing states. This data and the miss count are tabulated in a form that can be analyzed by a correlation module to determine characteristics of the cable television plant.

Method and apparatus for locating a faulty component in a cable television system having cable modems

A method and system for locating faulty components in a cable modem network configured within a hybrid fiber-coaxial cable television system by tabulating modem performance data are described. A method of isolating problematic components in a cable modem network includes determining whether a cable modem transmitted a polling message to a central destination during the modem's allotted time interval. A media access control layer, located within a cable modem termination system (CMTS), keeps a miss count for the cable modem that reflects the number of times the cable modem does not transmit a polling message to the CMTS during its allotted time. The media access control layer determines whether the cable modem is changing states. This data and the miss count are tabulated in a form that can be analyzed by a correlation module to determine characteristics of the cable television plant. A cable modem entry is inserted into a list of modems experiencing irregular behavior according to the tabulated network topology data relating to the miss count.

Methods, apparatus, and computer-readable media are disclosed for performing diagnostic tests of a communication link between a headend and a cable modem without having to assign an IP address to the cable modem. The diagnostic tests are performed at the MAC layer and test the state of the hardware between and including the cable modem termination system (CMTS) and a selected cable modem. By doing so, a network operator is able to more easily focus in on a potential problem in cable RF/MAC connectivity between the two components by first eliminating (or identifying) a problem with hardware before focusing on problem-solving at the software level, typically at the Network layer, at which point the cable modem is assigned an IP address. A network command is received from a network operator causing the CMTS to place a service identifier corresponding to a cable modem in possible need of diagnosing into a poll list. The service identifier is placed in the poll list the number of times specified in the network command as the number of polls desired for the test. This causes the cable modem to receive a map message with a station maintenance time slot for itself from the CMTS the specified number of times. Periodic ranging is performed between the CMTS and the cable modem associated with the service identifier. If it is determined that the service identifier is in the poll list as a result of the network command, results are then evaluated from the periodic ranging and reported to the network operator as a DOCSIS ping success/failure. It is then determined whether the cable modem should remain on the poll list based on results from the periodic ranging.

A method and system for locating faulty components in a cable modem network configured within a hybrid fiber-coaxial cable television system by tabulating modem performance data are described. A method of isolating problematic components in a cable modem network includes determining whether a cable modem transmitted a polling message to a central destination during the modem's allotted time interval. A media access control layer, located within a cable modem termination system (CMTS), keeps a miss count for the cable modem that reflects the number of times the cable modem does not transmit a polling message to the CMTS during its allotted time. The media access control layer determines whether the cable modem is changing states. This data and the miss count is tabulated in a form that can be analyzed by a correlation module to determine characteristics of the cable television plant. A cable modem entry is inserted into a list of modems experiencing irregular behavior according to the tabulated network topology data relating to the miss count.

Apparatus, methods, and computer program products are disclosed for detecting or locating a viable data carrier in a downstream channel by a cable modem. When a cable modem is first installed by a cable operator or powered up by a user, it must first locate or tune in to the correct downstream channel in order to receive data from the headend of the cable plant. This time-consuming process can be shortened by performing two matches between the selected, potential downstream data carrier and constellation diagrams of certain modulation schemes. Through this method, potential channels for data carriers can be eliminated quickly by going through a &ldquo;screening&rdquo; process (the first constellation diagram match) thereby preventing those potential channels from going through a significantly more time-consuming second constellation match. The process begins with selecting a potential frequency channel from the downstream band. It is then determined whether the potential channel contains a signal modulated in a particular modulation scheme where the modulation scheme is one not normally used on signals in the downstream channel, such as QPSK. If the signal in the potential frequency channel is not modulated according to the particular modulation scheme, the cable modem determines whether the signal in the potential channel is modulated according to another particular modulation scheme, such as QAM64 or QAM256. These particular modulation schemes, however, are ones normally used on signals in the downstream channel. The determination of whether the signal in the potential channel is modulated according to the first particular modulation scheme is done rapidly and only potential channels containing a signal likely to be modulated according to the second particular modulation scheme are examined for the second determination step.

Provided are methods and apparatuses for quickly and efficiently locating a frequency band for upstream transmission of data in a data communications network system utilizing cable modems. In a preferred embodiment, a cable modem termination system (CMTS) at the headend performs a lookahead in order to determine the noise power spectrum allocated to its upstream channels. Free bands (noise-free bands available for upstream data transmission) may then be determined based on the noise power spectrum and the upstream channel capacity requirements according to a process that is preferably implemented in computer code at the headend. The lookahead is preferably accomplished by using a spectrum analyzer, which is preferably incorporated into the CMTS at the headend, to collect a table of samples of the noise power versus frequency. This table of samples is input to a computational algorithm which determines free band sets for one or more preferred modulation formats rapidly and efficiently in software without the stepping of the upstream receiver frequency as in the blind frequency hop process. Once a band has been located, the CMTS assigns its frequency to an upstream channel and signals the cable modem of the frequency update.

Method and apparatus for selecting optimum frequency for upstream data transmission in a network system utilizing cable modems

Transitions among different upstream frequency channels in a cable television plant in order to transmit data occur while considering the noise level of the upstream frequency channel presently being used to transmit data. By taking into account the noise level of the presently used upstream frequency channel, the CMTS in a cable plant can make a more intelligent decision as to whether it is worthwhile changing the upstream frequency channel for a group of cable modems. A spectrum analyzer determines the noise level of a presently used frequency channel. A bit error rate for the present frequency channel is detected. The spectrum analyzer then determines whether the bit error rate exceeds a threshold value. Is so, it is then determined whether the noise level of the present frequency channel is greater than or less than the noise level of another frequency channel having the lowest noise level plus a buffer noise value. If the present noise level is greater, a transition is made to the other frequency channel with the lower noise level. If not, the cable plant continues using the present frequency channel. The noise level of the presently used frequency channel is measured at the CMTS upon receipt of an empty data packet arriving at a known timing mark.

Method and apparatus for upstream frequency channel transition

A system and method for locating ingress noise gaps for an upstream data carrier in a cable network utilizing cable modems is described. A system for identifying a transmission frequency that has less noise than other available frequency bands includes a packet generator, a rate controller, an echo device, a demodulator, and a packet checker. The packet generator and rate controller, contained in a cable modem termination system, send test data downstream to the echo device which then redirects the test data upstream at a selected test frequency. The echo device, which may be located within the cable modem termination system or outside the termination system, listens on the downstream path for data packets addressed to it. Once received, the echo changes the address of the test data to the address of the packet checker. The packet checker then receives and analyzes the test data packet sent from the echo device to assess the amount of noise on that particular test frequency. The echo device can be a subscriber cable data modem configured to receive test packets sent downstream or a custom-built device located anywhere on the downstream path or within the cable modem termination system.

Echo device method for locating upstream ingress noise gaps at cable

A system and method for locating ingress noise gaps for an upstream data carrier in a cable network utilizing cable modems is described. A system for identifying a transmission frequency that has less noise than other available frequency bands includes a packet generator, a rate controller, an echo device, a demodulator, and a packet checker. The packet generator and rate controller, contained in a cable modem termination system, send test data downstream to the echo device which then redirects the test data upstream at a selected test frequency. The echo device, which may be located within the cable modem termination system or outside the termination system, listens on the downstream path for data packets addressed to it. Once received, the echo changes the address of the test data to the address of the packet checker. The packet checker then recieves and analyzes the test data packet sent from the echo device to assess the amount of noise on that particular test frequency. The echo device can be a subscriber cable data modem configured to receive test packets sent downstream or a custom-built device located anywhere on the downstream path or within the cable modem termination system.

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Fremont, CA, United States of America

Wei-Sing Chen