Tag Archives: QAM

Fresh Tech | DOCSIS Protocol Analyzer – Can’t stop a good idea!

November 22, 2011   Brady   No comments
DOCSIS Xpert Protocol Analyzer

When I first heard rumor that a knew company had a DOCSIS protocol analyzer floating around I had to see it! With full disclosure, many of you know that after 10 years in RF and fiber-optic transport equipment, I spent a few years designing, marketing and selling DOCSIS protocol analyzers. More specifically I focused on making them available to cable operators because I knew they could detect really difficult to isolate problems. Averna know owns the technology from my Sigtek days, so it is nice to see a new competitor in the space. What’s more is that its nice to see this competitor at SCTE Cable-Tec Expo who is interested in cable operator’s issues.

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Fresh Tech | Awesome Spectrum Analyzer at a Cool Price!

November 21, 2011   Brady   No comments
Televe's CATV Spectrum Analyzer

What first caught my eye by Televes H45 Spectrum Analyzer was the HDMI port feeding a flatscreen television. How cool is that? I also noticed the small unit was displaying a QAM “haystack” along with its power, MER, BER, and the demodulated picture just beside the measurements. The picture was on a high resolution display, not the low quality displays I’ve seen in the past, so tiling or macro-blocking would be apparent to the user. See the picture below:

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Fresh Tech from Cable-Tec Expo 2011

November 19, 2011   Brady   No comments
Rohde & Schwarz Cable Load Generator

At this year’s Cable-Tec Expo, Rohde & Schwarz (www.rohde-schwarz.com) introduced a 1U Cable Load Generator (CLG) capable of simulating cable TV networks with full channel loading. This baby is not just limited to North America, but can do channel plans for the World over! Here are the highlights:

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DOCSIS 3.0 Tutorial – Downstream Channel Bonding

July 18, 2010   Brady   2 Comments

Downstream Channel Bonding is perhaps the ball bearings of DOCSIS 3.0, enabling subscriber data speeds in excess of 160 Mbps (4 times that of previous DOCSIS versions). While conceptually simple, the principle of combining multiple downstream DOCSIS channels together to carry the same user data must have tight constraints in order to preserve the integrity of the data and have the data arrive at the correct subscriber’s device and in sequence. This article will cover both the physical layer aspects and DOCSIS protocol aspects that enable channel bonding.

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DOCSIS 3.0 Tutorial – The EQAM

July 01, 2010   Brady   1 Comment

In my article on DOCSIS 3.0 M-CMTS architecture, I talked about the distributed nature of the CMTS with an M-CMTS core (the CPU of the system), a DOCSIS Timing Server, and an edge Quadrature Amplitude Modulator (EQAM). I am going to cover the EQAM in detail in this article because in the past couple of years, EQAM (also spelled eQAM) has rapidly become part of our vocabulary but its operation and value often go unappreciated. Further, in order to fully understand DOCSIS 3.0 operation, downstream channel bonding, and possible issue which may arise, a thorough understanding of the eQAM is critical.

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DOCSIS 3.0 Tutorial – CMTS Architecture

June 21, 2010   Brady   5 Comments

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.

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DOCSIS and Cable Modems – How it works :: Quality of Service

March 09, 2009   Brady   2 Comments
Quality of Service

DOCSIS 1.0 enabled data over coax with a “best effort” service using a data request-grant methodology. DOCSIS 1.1 and subsequent specifications added guaranteed Quality of Service (QoS) by providing Unsolicited Grant Synchronization (UGS) which means that a cable modem does not have to send a data request in order to receive a bandwidth grant from the CMTS. The new UGS service is an enabling technology which has allowed cable operators to successfully deploy the highly revenue generating Voice-over-IP (VoIP) services. In the following sections I will illustrate the differences between best-effort (request-grant) and QoS (UGS) services.

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DOCSIS and Cable Modems – How it works :: Upstream RF

February 05, 2009   Brady   23 Comments

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.

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DOCSIS and Cable Modems – How it works :: Advanced RF

February 02, 2009   Brady   12 Comments

In high speed data communications, the industry has evolved and implemented complex modulation schemes which vary a signals voltage (amplitude), phase, and frequency in order to transmit more data, faster. The following will cover these methods in order to describe how Quadrature Amplitude Modulation (QAM) works in DOCSIS communications.
We live in an analog world. Sure, [...]

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DOCSIS and Cable Modems – How it works :: RF Fundamentals

January 29, 2009   Brady   16 Comments

Most of us are quite comfortable with changing the dial on our FM radios. Don’t like what’s on Soft 95.1 FM, then change the frequency (Kenneth) to 102.5 FM for some classic rock. What you have actually done is changed the RF (radio frequency) tuner in your car stereo from a lower frequency of 95.1 MHz to a higher frequency of 102.5 MHz where there was a different station playing. The fact that two different stations were playing…

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