Cisco Technology, Inc.

Cisco Systems Inc.

Charles J Naegeli

Mark E Millet

Wei-Sing Chen

Alejandro Schwartzman

Guenter E Roeck

Hung-San Chen

John T Chapman

David J Tsiang

Glenn E Lee

William L Quackenbush

Xiong Yang

Nan Tu

Nozar Azarakhsh

Harihara Mahesh

Chrisanto De Jesus Leano

Hungsan Chen

Joseph C H Fung

Yuzon Hao

Apparatus, methods, and computer program products for utilizing a frequency channel determined to be unacceptably noisy by finding a cleaner, narrower bandwidth within the frequency channel. Initially data is received on a frequency channel at a CMTS, specifically an upstream receiver, and by a narrow bandwidth detector, connected to a processor also used by components in the CMTS. The narrow bandwidth detector performs a Fast Fourier Transform (FFT) on the frequency channel thereby creating multiple FFT points within the frequency channel. A clean bandwidth for transmitting data within the frequency channel is identified where the clean bandwidth is derived from a subset of FFT points from the full set of FFT points. The subset of FFT points are contiguous points that have a noise level below a predetermined noise threshold.

Method and apparatus for locating a cleaner bandwidth in a frequency channel for data transmission

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

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 media access control (MAC) unit in a CMTS assigns a normal time slot to a cable modem being tested for its upstream transmission quality. An FFT generator or engine operating in conjunction with the CMTS is informed of this normal time slot. A dummy time slot, not assigned to any cable modem, is created and the FFT generator is informed of the dummy time slot. A number of FFT measurements of the upstream channel are generated during the normal time slot and during the dummy time slot. FFT measurements of the upstream spectrum taken during the normal time slot are compared to FFT measurements taken during the dummy time slot. Through this comparison, undesirable noise spurs, if any, can be detected in the upstream spectrum caused by the cable modem being tested.

Method and apparatus for measuring quality of upstream signal transmission of a cable modem

Apparatus and methods are disclosed for reducing noise leakage on the upstream channel from a cable modem. Noise leakage from cable modems, such as from a persistently enabled amplifier or other components in the modem, can accumulate on an upstream channel and reduce the overall signal-to-noise ratio of signals sent to the headend. In order to significantly reduce such noise leakage and to provide termination of the cable plant in the modem when the modem is not transmitting data, a cable modem arranged to improve its isolation is disclosed. The modem contains an upstream transmitter having a control line on which the upstream transmitter can emit a control signal. The modem also includes a switch component capable of being enabled and disabled by the control signal on the control line. The control signal from the upstream transmitter to the switch component enables the switch component thereby allowing a data signal to be transmitted on an upstream channel. The switch component includes two switches. One switch is a series switch used to enable and disable the transmission of data. Another switch is a shunt for providing termination of the cable plant. The cable modem also includes an amplifier for amplifying the data signal from the upstream transmitter before being transmitted on the upstream channel.

Method and apparatus for reducing noise leakage from a cable modem

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.

A technique is disclosed for determining a carrier-to-noise ratio (CNR) value for a selected channel of an access network. A background noise level on the selected channel is measured during a first time interval during which none of the network nodes are transmitting signals on the selected channel. A first signal strength on the selected channel is also measured during a second time interval during which a first network node is transmitting at least one signal on the selected channel. A CNR value for the selected channel may then be calculated using the measured background noise level information and the measured first signal strength information. According to a specific implementation, the calculation of the CNR value for the selected channel is not based upon an Error Vector Magnitude value associated with the signal transmitted from the first network node.

Technique for determining carrier-to-noise ratio of selected channels in an access network

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.

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 are disclosed for calibrating a line card having a gain control circuit and memory device. The gain control circuit is configured to receive an input signal and an adjustment signal and to output an adjusted output signal that is based on the input signal and the adjustment signal. The gain control circuit also is configured to alter the adjustment signal to a nominal adjustment value so that an adjusted amplitude value of the adjusted signal converges with a nominal amplitude value. A first input signal, a first adjustment signal, and a nominal amplitude value are provided to the gain control circuit. A first nominal adjustment value is determined. The first nominal adjustment value is substantially permanently stored within a first address of the memory device with the first address being associated with the first input signal.

Method and apparatus for a router line card with adaptive selectable gain control

A pluggable port adapter is used for connecting PCI devices to a host system through a PCI local bus while also adding functionality to the host system. The port adapter communicates with the host system through a port adapter/host interface that includes the PCI local bus and an auxiliary bus. The auxiliary bus is used for controlling the additional circuitry on the port adapter. A PROM on the adapter card is used for identifying the port adapter type, serial number and hardware revision. The auxiliary bus is used for conducting JTAG testing and is used by the host system to program logic devices on the port adapter. The logic devices can be reprogrammed in the field by the host system to repair bugs and to enhance performance and/or functionality. A power control circuit on the port adapter is controlled by the auxiliary bus for conducting hot swap operations.

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Montara, CA, United States of America

Charles J Naegeli