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DOCSIS and Cable Modems – How it works :: Introduction

Over the past several years of training people on troubleshooting DOCSIS® networks and explaining how DOCSIS cable modems and CMTSs work, I have been asked numerous times – “Why don’t you write a book on this?”  You see, there is no definitive book, guide or manual that explains the Data-over-Cable Service Interface Specification (DOCSIS) other than the several hundred page specification itself.  While I recommend that everyone interested in fully understanding DOCSIS read the specification located on the CableLabs website at www.cablelabs.com, I will warn you that it can be very technical.  So what I will do over the next several posts on this DOCSIS 101 blog is provide a boiled-down version of the operation of the DOCSIS specification, i.e. how cable modems connect to the cable modem termination system (CMTS) and transmit data.  While I will provide quite a bit of technical detail, I will try to communicate it in such a way that a Ph.D is not required to comprehend it.

First, some disclaimers.  DOCSIS® is a registered trademark of CableLabs.  Founded in 1988 by cable operating companies, Cable Television Laboratories, Inc. (CableLabs®) is a non-profit research and development consortium that is dedicated to pursuing new cable telecommunications technologies and to helping its cable operator members integrate those technical advancements into their business objectives. CableLabs has been the cornerstone for the development of many standards in the cable telecommunications industry, most notably DOCSIS and a number of standards which have extended the capabilities of the DOCSIS specification.  CableLabs has a brief primer and history of the DOCSIS standards which can be found at: www.cablemodem.com/primer/

Tune in for my next post where I will describe the radio frequency (RF) spectrum allocated to DOCSIS cable modem communication and how this allows the data to be transported from the cable operator to your home or office.

If you are in need of consulting / design services, go to The Volpe Firm, Inc.  You can also contact us through our online web portal or call directly at:
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About the Author:

Brady Volpe is the author of many industry articles and papers and owner The Volpe Firm, Inc.  He has over 20 years of broadband cable and telecommunications industry experience specializing in DOCSIS, EPON, VoIP, video, IPTV, RF, and fiber optic transport.