In this blog I am going to digress for a moment from my standard DOCSIS 101 tutorial and spend a little time on DOCSIS troubleshooting basics, especially with respect to Voice-over-Internet Protocol (VoIP). I am doing this as due to many offline questions specific to this topic. Don't worry, though I may start to inter-mix some troubleshooting blogs now and again, just check the DOCSIS 101 page to stay on top of the latest DOCSIS tutorial blogs.
Through DOCSIS tutorial seminars, I have found the most effective way to bring someone up to speed on DOCSIS communications is by teaching the cable modem registration process. During the registration process, we will cover the RF physical layer, theDOCSIS Media Access Layer (MAC) and the Internet Protocol (IP) layer. Yes, the cable modem exercises the first three layers of the Open Systems Interconnection Reference Model (OSI Reference Model or OSI Model)...
Cable modems use RF (radio frequency) signals to transport data over hybrid-fiber coax (HFC) networks according to the DOCSIS® specification. This blog will discuss the finer points extracted from the DOCSIS specification related to how cable modems communicate with the headend Cable Modem Termination System (CMTS), allowing two-way transport of Ethernet traffic over a cable TV network. There are currently three major revisions and one sub-revision of the DOCSIS specification; DOCSIS 1.0, 1.1, 2.0 and 3.0. With each major revision came significant changes to the cable modem upstream specification because the upstream has typically been the bottleneck in terms of data through-put rates as will be discussed.
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...
