In this article I am going to further explore the M-CMTS in order to describe two import elements of DOCSIS 3.0 network, the edge-Quadrature Amplitude Modulator or EQAM and the DOCSIS Timing Interface Specification Server or DOCSIS Timing Server. Before I cover these components I will show how they are integrated with the M-CMTS architecture.
Before we dive into bits, bytes and protocol, first we will discus some hardware. During the evolution of DOCSIS 3.0 there were a number of interesting interim steps along the way, shall we say building blocks, to arrive at a full blown D3.0 CMTSs. This left us with two fundamentally different system architectures in production by CMTS vendors, Integrated and Modular CMTSs. It is important to understand these "architectures" from a purchasing, operational and deployment standpoint as they have different requirements in some cases, some are better than others depending on the system layout.
This is the first of a new series of Tutorials focused on the Data Over Cable Service Interface Specifications (DOCSIS) version 3.0. I will make the assumption that you are familiar with the DOCSIS 1.x / 2.0 standards or have already reviewed my DOCSIS Basics Tutorial as I will be using many terms without explanation since they were previously covered. The DOCSIS 3.0 specification is an extension of the DOCSIS 1.x and 2.0 specification which dramatically increases the data throughput by adding a technology known as channel bonding to the DOCSIS downstream and upstream, adding increased security, adding support for IPv6, and substantially improving the back-office management support (MIBs, SNMP, IPDR, etc.) for DOCSIS. Each of these topics will covered in much greater detail in this DOCSIS 3.0 tutorial in multiple posts yet to come.
This article will focus more specifically on DOCSIS 3.0 issues that will occur as you are deploying DOCSIS 3.0 or post -deployment.
The first part of this article (in CT's March 2009 issue) discussed downstream potential issues, while this one focuses on the potential issues associated with upstream deployments. In particular, this article covers the critical upstream areas that one should be aware of when getting ready to deploy or already deploying DOCSIS 3.0.
If you have not had a chance to catch the June issue of Communications Magazine, check out the article penned by John Downey, of Cisco Systems, and I on "the critical upstream areas that one should be aware of when getting ready to deploy or already deploying DOCSIS 3.0." The shortened version of this article can be found on CT's website HERE. The full version should be made available on this blog soon.
DOCSIS Cable Modem Data Burst Defined Previously I have discussed that cable modems share the upstream channel by using Time Division Multiple Access (TDMA). This means that when a cable modem is not transmitting data its RF transmitter is turned off. In order to transmit data it must transmit a burst of data which contains a REQUEST to the CMTS. The REQUEST relays the cable modem's Service IDentifier and the number of bytes of information the modem has to transmit in its buffer. The CMTS prioritizes all incoming
In this blog I will address delay and jitter as they pertain to VoIP in a DOCSIS network. Delay, jitter and packet loss are the three primary impairment in a VoIP network, but packet loss was addressed in my Troubleshooting DOCSIS - VoIP Impairments > Packet Loss blog. After packet loss, delay is the second most disruptive impairment in VoIP networks. The effects of delay to the caller generally appear as echo and talker overlap. In PSTN communications, echo can arise as acoustic echo between the mouthpiece and
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...
