Patent ID: 7362773
Filing Date: 2008-04-22
Classification: H04L

Abstract:
1. A sniffer configured to capturing DOCSIS (Data Over Cable Service Interface Specifications) bursts transmitted between one or more cable modems (CMs) under test and a cable modem termination system (CMTS) under test via a hybrid fiber coaxial cable system, comprising: a sniffer upstream receiver capable of receiving DOCSIS upstream bursts; a sniffer cable modem coupled a hybrid fiber coaxial cable (HFC) system by an analog signal path capable of receiving downstream DOCSIS data bursts and messages transmitted by said CMTS; a self ranging circuit coupling said HFC cable system to said sniffer upstream receiver, comprising: a sniffer clock generator for generating a reference clock signal for said sniffer upstream receiver; and a computer coupled to said sniffer cable modem, said sniffer upstream receiver, and said self ranging circuit, for controlling said sniffer cable modem, said sniffer upstream receiver and said self ranging circuit and for receiving data from downstream DOCSIS bursts captured by said sniffer cable modem and for receiving data from upstream DOCSIS bursts captured by said sniffer upstream receiver, wherein said linecard comprises; a computer programmed to receive said commands and generate control signals which control other circuits on said linecard to receive the designated bursts; a sniffer cable modem coupled to said computer by a data path, for receiving commands from said computer regarding which downstream bursts to capture, and for recovering a downstream symbol clock and using it, directly or indirectly, to capture that designated downstream bursts and messages from a cable modem termination system under test and sending said captured bursts and messages to said computer, and for generating a first clock reference signal which is phase coherent with said recovered downstream symbol clock at least when said sniffer is assigned to capture a DOCSIS 2.0 synchronous code division multiplexed burst; a sniffer cable modem termination system coupled to said computer for receiving commands from said computer designating which upstream bursts to capture and for using an upstream clock reference signal to synchronize a timebase which generates an upstream symbol clock and upstream minislot to count in such a way as to put said sniffer cable modem termination system in synchronism with an upstream on which the designated upstream bursts will be transmitted and for capturing said designated burst(s) from a cable modem(s) under test; an RF demodulator circuit coupled to said computer for receiving commands regarding which bursts to capture on which radio frequency carrier signals comprising upstream channels, and functioning, for each such upstream burst to be captured to amplify received radio frequency signals, including the radio frequency signal carrying said burst to be captured, by a gain controlled by a command received from said computer and to filter out at least some unwanted radio frequency signals, and to convert a radio frequency carrier signal carrying said burst to be captured to a predetermined intermediate frequency, and digitizing said radio frequency signal after filtering and conversion to said intermediate frequency into a plurality of digital samples; and means for receiving said plurality of digital samples and imposing a variable delay controlled by a command from said computer and filtering said samples in a digital upstream equalization filter the coefficients of which are controlled by said computer and outputting said filtered samples to said sniffer cable modem termination system for signal processing, wherein said sniffer cable modem is structured and programmed to receive and send to said computer only downstream DOCSIS messages and to recover a downstream clock and generate therefrom an upstream reference clock signal which is phase coherent with said recovered downstream clock, and further comprising a second sniffer cable modem which is coupled to said computer and which is structured and programmed to receive downstream DOCSIS data bursts and transmit data therefrom to said computer, and wherein said sniffer clock generator comprises: a first multiplexer having a first input coupled to receive said upstream reference clock signal and having a second input coupled to receive a 10.24 MHz reference clock from a CMTS under test, and having an output, and having a control input for receiving a control signal from said computer controlling which reference clock signal is applied to said output; a phase lock loop for multiplying whichever reference clock signal is output by said first multiplexer by a factor of 2 or 4, as controlled by a control signal from said computer and outputting a 20.48 MHz frequency reference clock signal; a second multiplexer having a first input coupled to receive said higher frequency reference clock from said phase lock loop, a second input coupled to receive a 20.48 MHz reference clock generated by a CMTS under test, and a third input coupled to receive a 20.48 MHz reference clock generated by said sniffer, and having a control input coupled to receive a control signal controlling which 20.48 MHz clock is supply to an output, and wherein said output is coupled to said sniffer upstream receiver.