DOCSIS 2.0 SCDMA capable sniffers which can capture legacy DOCSIS bursts as well

Abstract

A DOCSIS 2.0 compatible sniffer which can receive legacy DOCSIS 1.x TDMA bursts as well as DOCSIS 2.0 SCDMA bursts. One embodiment uses two cable modems in the sniffer, one to capture downstream data bursts and the other to capture downstream messages and to recover the downstream symbol clock and generate an upstream reference clock which is phase coherent with the recovered downstream symbol clock. The reference clock is used by a cable modem termination system to capture upstream SCDMA DOCSIS 2.0 bursts. DOCSIS 1.x TDMA bursts may also be captured. Other embodiments use a DOCSIS 2.0 compatible modem in the sniffer to lock onto a downstream, register as a cable modem in the system and capture downstream messages in order to derive the correct timing to generate control signals to control burst capture circuitry in the sniffer to capture DOCSIS 1.x and 2.0 upstream bursts. The digital samples of each burst can be sent digitally to the CMTS under test after some fixed delay or can be sent to the CMTS under test as an analog RF signal in repeater embodiments. This allows the CMTS under test to be simplified by pushing the burst capture circuitry out to the optical node.

1 . A sniffer capable of capturing DOCSIS 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: 
 an RF demodulator means for amplifying, filtering and digitizing received radio frequency signals carrying upstream DOCSIS bursts;  
 a delay and upstream equalization filter circuit;  
   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.    
   
   
       2 . The apparatus of  claim 1  wherein said sniffer cable modem is structured and programmed to receive and send to said computer only downstream DOCSIS messages, 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.  
   
   
       3 . The apparatus of  claim 1  wherein said sniffer upstream receiver is capable of receiving DOCSIS 2.0 synchronous code division multiplexed upstream bursts.  
   
   
       4 . A sniffer capable of capturing DOCSIS 1.0, DOCSIS 1.1 and DOCSIS 2.0 bursts transmitted by one or more cable modems (CMs) under test to a cable modem termination system (CMTS) under test via a hybrid fiber coaxial cable system (HFC), comprising: 
 a port at which commands are received indicating which DOCSIS 1.0, 1.1 and 2.0 upstream and downstream bursts to capture;    a linecard circuit coupled to said port for capturing the designated upstream bursts and outputting them at said port;    a cable modem coupled to said HFC and to linecard circuit for recovering a downstream symbol clock and recovering said designated downstream bursts and sending said captured downstream bursts to said linecard for output at said port, and for generating a reference clock signal which is phase coherent with said recovered downstream symbol clock when said sniffer is assigned to capture an upstream DOCSIS 2.0 synchronous code division multiplexed burst; and    a clock generator for receiving said reference clock signal and generating an upstream clock reference for said linecard circuit which is phase coherent with said reference clock signal when said sniffer is assigned to capture an upstream DOCSIS 2.0 synchronous code division multiplexed burst.    
   
   
       5 . The apparatus of  claim 4  wherein said linecard circuit includes a computer programmed to receive downstream messages captured by said cable modem and use the content thereof along with measurements and filter coefficients derived by said linecard circuit from captured upstream station maintenance bursts to generate suitable control signals to keep said linecard in synchronism with upstream bursts transmitted by any cable modem under test so as to be able to capture said upstream bursts if said bursts have been designated for capture.  
   
   
       6 . A process to capture upstream DOCSIS 2.0 bursts in a sniffer, comprising: 
 (1) recovering a downstream symbol clock and using it to capture downstream messages transmitted from a cable modem termination system under test, and, if DOCSIS 2.0 synchronous code division multiplexed bursts are to be captured, generating a local upstream reference clock from said recovered downstream symbol clock which is locked to a master clock in said cable modem termination system under test or at least phase coherent with said recovered downstream symbol clock;    (2) using said local upstream reference clock to synchronize a timebase including a local upstream minislot counter in a sniffer to an upstream channel upon which upstream bursts to be captured will be transmitted;    (3) performing a self ranging process using captured upstream initial and periodic station maintenance bursts and captured downstream ranging response message data to get a timebase into synchronization with an upstream on which bursts to be captured will be transmitted;    (4) using said upstream minislot counter and data in captured downstream messages to capture upstream bursts, possibly including DOCSIS 2.0 synchronous code division multiplexed bursts from a cable modem under test.    
   
   
       7 . The process of  claim 6  wherein downstream bursts are captured using first and second DOCSIS 2.0 compatible cable modems in a sniffer which have been modified to capture bursts and messages directed to other cable modems, and using said first cable modem to capture only downstream data bursts and using said second cable modem to capture only downstream messages.  
   
   
       8 . The process of  claim 6  wherein the step of recovering a downstream symbol clock and generating said local upstream reference clock from said recovered downstream symbol clock which is locked to a master clock in a cable modem termination system under test is performed by recovering said downstream symbol clock and using said recovered downstream symbol clock as a reference signal for a phase lock loop which generates said local clock and removes phase noise from said recovered downstream symbol clock.  
   
   
       9 . An sniffer capable of capturing upstream DOCSIS 1.0, 1.1 and 2.0 bursts comprising: 
 burst capture circuitry coupled to a hybrid fiber coaxial cable (HFC) system upstream medium which couples a plurality of cable modems (CM) under test to a cable modem termination system (CMTS) under test for exchange of DOCSIS 1.0, 1.1 and 2.0 bursts therebetween; and    a cable modem coupled to said DOCSIS compatible cable system upstream and downstream mediums and coupled to said burst capture circuitry, and functioning to register with a cable modem termination system (CMTS) under test as another cable modem in the system, recover a downstream symbol clock and use it to capture downstream messages transmitted by said CMTS under test and extract data therefrom needed to time and control said burst capture circuitry to capture upstream DOCSIS 1.0, 1.1 and 2.0 bursts transmitted from cable modems under test.    
   
   
       10 . The apparatus of  claim 9  further comprising means to divert upstream bursts from said CMs under test away from said CMTS and into said burst capture circuitry, and means for transmitting each captured burst stored in said burst capture circuitry to said CMTS a fixed time later after capture of said burst.