Video Delivery Explained
Seems like several people have recently been confused by some of the acronyms in technology - and rightfully so. It's tough to keep track of all these terms and remember what they mean and which has replaced which. It gets even more confusing because so often in this industry, we tend to use the same term to mean several different things.
To help alleviate some of that, I've attempted to identify some of the items that seem to cause the most confusion. QAM or Quadrature Amplitude Modulation, seems to particularly confuse people, but in order to explain that, you really need to define some of the other elements around it. And to make it even easier, I've provided this handy chart highlighting the technologies (click the image to see it HUGE - and feel free to download it for repeated reference).
Please note this is not meant to be an exhaustive explanation of any of these technologies, just contextualize some of the terms that we use so you can better understand where they fit in.
Terminology
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OTA (Analog TV) - aka NTSC |
NTSC (named for the National Television System Committee who approved it) is the agreed spec for delivering analogue broadcast video in most of North America (and other parts of the world). NTSC was used widely in terrestrial and analog cable systems. It was developed by RCA and was chosen over competing specs being developed in part because it was designed to allow older Black & White TV’s to playback the signal. |
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OTA (Digital TV) - aka ATSC |
In the switch to digital broadcast, new standards were required to support the broader range of resolutions and data that could be transmitted. ATSC standards are a set of standards developed by the Advanced Television Systems Committee for digital television transmission over terrestrial, cable, and satellite networks. A terrestrial (over-the-air) transmission carries 19.39 megabits of data per second (a fluctuating bandwidth of about 18.3 Mbit/s left after overhead such as error correction, program guide, closed captioning, etc.) |
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Digital Cable - aka QAM |
QAM or Quadrature Amplitude Modulation is the format for delivering digital cable. A QAM tuner is analogous to the ATSC tuner that pulls in OTA digital channels. Although QAM uses the same amount of bandwidth in megahertz as ATSC, it can carry up to twice the amount of data (approx 38.5 Mbps). |
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Satellite TV - aka DVB-S |
DVB-S is an abbreviation of Digital Video Broadcasting — Satellite. There are other specs such as DVB-C (Digital Video Broadcasting Cable) that are part of an open standard of digital video specs. DVB-S is the original digital broadcasting & demodulation standard for satellite television and dates from 1994. It is used in North America by Dish Networks. |
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Broadband Video - aka OTT |
Not all video online is OTT. Over the Top (OTT) refers to the delivery via Internet of premium live and VOD video content versus the managed network used for delivery of cable or satellite content. OTT often refers in particular to content that arrives from a third party, such as Netflix, Amazon, or Hulu, and arrives to the end user device, leaving the Internet provider responsible only for transporting IP packets (aka a dumb pipe). |
