• What is QAM
• What is a DTA? What channels can I get with a DTA
• How does Comcast's Video Distribution Network Work?
• What are the national 3:1 HD muxes from Comcast?

QAM stands for Quadrature amplitude modulation. It's a modulation scheme that transmits data by changing the amplitude of two carrier waves. The two carrier waves are out of phase with each other by 90 degrees. Digital Cable uses QAM to transmit the majority of their signals. Two major QAM schemes are 64QAM and 256QAM. 64QAM contains data throughput around 28 mbps, where 256QAM has data throughput of 38.8 mbps.

If your TV has a QAM tuner, it has the ability to read this signal and display it. The cable company can encrypt the digital video carried in a QAM signal and this is commonly referred to as Encrypted QAM. To receive Encrypted QAM, you would require a cable card or an official Comcast digital receiver. A QAM tuner on a TV or DVD recorder does not 'map' the channels to the same location on the Comcast channel lineup card. A QAM tuner will display unencrypted channels on their physical location in relation to the frequency they are carried on.

Some area's are able to pass PSIP data along with local broadcasts. PSIP data is embedded in the digital information that tells your TV what channel number to display. For example, Channel 3 in HD may embed 3.1 in it's video stream. Your TV would be able to tune this by typing in 3-1. Each Comcast area is different, and some may not pass PSIP, so look for HD locals on odd numbers, such as 113.1, etc..

It's also recommend to force your TV or DVD recorder to rescan the QAM channel lineup from time to time. Additional channels may show up unencrypted or may of changed frequencies. Comcast does not guarantee channel availability through a free QAM tuner.

If your looking for a QAM channel lineup, there is no official one from Comcast. You could try the SiliconDust HD-Home Run page. Enter your zip code at this following website:
»www.silicondust.com/hdhomerun/channels

Then choose your Comcast service from the pick list menu.

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by cypherstream edited by sortofageek
last modified: 2011-01-26 14:57:52

DTA stands for Digital Transport Adapter. It's a very cheap and basic cable box that allows you to watch, with digital quality picture and sound, in Comcast words, all Limited Basic and Expanded Service channels, as well as "certain" Digital Starter channels. In other words, a DTA is a unencrypted QAM receiver for an analog TV. Comcast can remotely program the DTA with the correct channel lineup up until Expanded Basic. (Usually the first 99 channels). Consult your local Comcast center for an applicable channel lineup card for details.

Currently Comcast is offering in many markets the first 2 DTAs for free and it's charging 1.99(plus taxes and fees) per DTA after the first 2 ones. You should keep in mind that usually Comcast doesn't charge anything for the first digital box if you subscribe to a Digital Starter and above package.

The main reason Comcast is offering the DTAs is to allow Comcast to push as many analog channels to digital as possible, freeing up bandwidth for faster Internet speeds, more HD channels, etc.

Special credit to SND2005 for taking pictures of the DTA and allowing us to post them in the FAQ.

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by Travelfan1 edited by cypherstream
last modified: 2009-05-22 15:21:07

The Master Headend or does their bit in aggregating and sending the video signals in MPEG format across the CRAN network. From the cran it goes to the various local headends via Multicast UDP through routers. Finally the local hub picks up the signal and converts it to RF to shoot out over the network. There is also a VOD server farm, which could reside in it's own building or in a regional headend depending on the local archetecture either built by Comcast, or inherited from acquisitions. VOD has been known to spread apart to other larger headends in the region for redundancy. There are various hubs spread out along the plant house the OOB communications equiptment and the VOD (and potentially SDV) edge qams.

There are digital controllers that address all of the set top boxes in the area's. For Scientific Atlanta sites there's a *NIX based server called the DNCS, while Motorola sites there is a server called the DAC. While DNCS's and DAC's pretty much do the exact same job, the way they do it on a SA plant vs Motorola plant are ENTIRELY different. Motorola tends to break things out a bit more with NC1500's, RPD's, etc.....While SA tends to centralize things a bit more within it's DNCS/Appserv setup.

Definitions:
Headend - The control center of a cable-television system, where incoming signals are amplified, converted, processed, and combined into a common cable for transmission to subscribers.
CRAN - Comcast's Reginal Area Network
Multicast - network technology for the delivery of information to a group of destinations simultaneously using the most efficient strategy to deliver the messages over each link of the network only once, creating copies only when the links to the multiple destinations split.
UDP - A communications protocol that is mostly used to send streamed material over a Network
VOD - Video On Demand
SDV - Switched Digital Video - A method of broadcasting only channels that are currently tuned, rather than every channel offered at once.
DNCS -Digital Network Control System
DAC - Digital Addressable Controller
SA - Scientific Atlanta (now owned by Cisco).
NC1500 - Motorola device that links application servers and set-tops using Internet Protocol (IP) to deliver data packets through the out-of-band data channel.
RPD - Motorola's Return Path Demodulator for interpreting commands from the Motorola Cable Box back to the Cable Headend.
OOB - Out of Band communication. Method used to program cable boxes remotely, while allowing their tuners to be on any channel.

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by cypherstream
last modified: 2009-05-22 15:51:09

Although this list is not complete, here are the majority of the Muxes from Comcast Media Center. They are available on the CRAN network, and some of them are available via Satellite. For an explanation of CRAN and what it means for you, please see this entry courtesy of our friends in Comcast HSI: »Comcast High Speed Internet FAQ »What is CRAN?

A 3:1 HD mux means 3 HD channels in 1 38.8mbps QAM. Instead of dedicating 19.4mbps for one HD channel, it is varied depending on the channels on each QAM. As of late Comcast has modified their "muxes" in order to improve picture quality; they place 2 1080i channels and 1 720p channel together.

Mux 1 Starz East, HGTV, A&E
Mux 2 Food, SciFi, UniversalHD
Mux 3 Discovery, USA, NatGeo
Mux 4 HDTheater , Animal Planet, History
Mux 5 HBO East, Max East, TLC
Mux 7 AMC, Golf, CNN
Mux 8 Disney, ABC Family, Science
Mux 9 FX, Speed, Fox News
Mux 11 IFC HD, WE HD, Fuse HD
Mux 12 Encore HD, Fox Bsiness, Hallmark Movie Channel
Mux 14 Bravo, CNBC, QVC
Mux 15 MGM HD, ESPNews, Toon Disney
Mux 16 Lifetime Movies, Biography, Planet Green
Mux 17 E!, Travel, Cartoon
Mux 18 Starz Edge, Starz K&F, Starz Comedy
Mux 19 Spike, Lifetime, Nickelodeon
Mux 20 G4, Style, TV One

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by cypherstream edited by sansri88
last modified: 2009-02-13 17:01:47