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.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is a divisional of U.S. patent application Ser. No. 10 / 397,508, filed on Mar. 25, 2003, entitled “DOCSIS 2.0 SCDMA Capable Sniffers Which Can Capture Legacy DOCSIS Bursts As Well”.BACKGROUND OF THE INVENTION [0002] In cable modem systems, there is a need to be able to debug by capturing message and burst traffic in the upstream and downstream directions. In DOCSIS systems, there is a need to be able to capture all the data bursts, MAP and UCD messages, timestamp data, ranging request messages, ranging bursts, ranging response messages and all the other DOCSIS messages. [0003] Sniffers exist in the prior art. A DOCSIS traffic sniffer manufactured by Filtronic-Sigtek, Inc. (model number ST260B) can captures data bursts and message traffic in DOCSIS 1.0 and 1.1 systems. However, DOCSIS 2.0 systems include the ability to send spread spectrum bursts, and the Filtronic sniffer cannot capture and demodulate spread spectrum bur...

AI Technical Summary

Benefits of technology

[0013] A second class of sniffers and sniffer / repeaters is characterized by: (1) the use of a slightly modified DOCSIS 2.0 cable modem in the sniffer which registers with the CMTS as one of the CMs in the system so as to capture the system timing of at least one upstream; and, (2) a burst capture line of circuitry which tunes, filters, amplifies and digitizes upstream bursts to be captured and stores samples of each burst in a buffer. In some embodiments, the burst capture circuitry includes a programmable passband filter for precise passband tuning based upon symbol rate and decimation circuitry to reduce the number of samples of lower symbol rate captured bursts.

[0017] In alternative embodiments within this genus, the captured bursts are transmitted upstream from the buffer in the sniffer to a CMTS that has no burst capture circuitry. This embodiment for a sniffer / repeater can be advantageously used to replace the prior art digital return data paths by capturing only the upstream bursts and digitizing them instead of digitizing every minislot including empty one like the digital return technology. In this way, more efficient use of the CMTS can be made, and more optical nodes can share one CMTS receiver. This is because only the bursts are sent upstream so the CMTS can pipeline process burst after burst and need waste no time on processing samples of empty minislots.

Problems solved by technology

However, DOCSIS 2.0 systems include the ability to send spread spectrum bursts, and the Filtronic sniffer cannot capture and demodulate spread spectrum bursts and time division multiplexed bursts at symbol rates faster than symbol rates of DOCSIS 1.0 and 1.1 systems.

Conventional sniffers today are too complicated.

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