Hi Mike,
"In other words, SDV delivered via VDSL can support as many channel selections, and even more, as any other competing system. Be it MSO or DBS. The SDV VDSL channel count is limited only by the dollar cost of headend equipment and not much else."
That's absolutely right, if by MSO you mean HFC.
[[Now, there are new forms of digital video being delivered over HFC's. These are being facilitated by new set top boxes and new distribution architectures over reserved spectrum for digital. These do not depend on the rules of "braodcast" HFC, just to keep things honest here. Let me qualify that a bit. They MAY NOT NECESSARILY depend on the same rules. It's up to the individual cable TV operator to decide how they want to treat their individual digital spectrum services. But my take is that they will allow VOD and near-VOD eventually over their digital spectrum, which suggests then that their channel selection functions, like those of VDSL, will be performed upstream as opposed to taking place in the STB.]]
But if we're talking about pre-digital HFC, then your statement is entirely correct.
The two broadcast modes you mentioned are limited in the number of channels they can present only by the bandwidth constraints of their media and the spectral efficiencies of the encoding (as in digital) or modulation techniques (as in analog and digital) used.
The forms you mentioned, HFC and DBS, deliver "all" channels to the residence, simultanesouly; it's up to the end user to select which one they want to view. This is known, broadly, as a "braodcast-and-select" approach to content selection, and it takes place right at the set top box which passes the desired channel through to the TV set, and rejects all others.
"Broadcast" all channels (by the provider) "and select" a single channel (by the user).
As regards the delivery of MPEG video, all digitized streams are not equal, from both (1) quality-of-delivery, and, (2) provider-administration, standpoints.
For example, pre-digitized content that is put on a scheduled release can be "cleaned up," first, which allows for optimal data formats thus permitting lower bandwidth to be used in its delivery. This allows the content preparer to remove any artifacts from the file before placing it in a storage-friendly medium. Such as the "tiling" and blurring which one often sees during live digital sporting events.
Conversely, "live" content which is being aired needs to be oversampled, in comparative terms, requiring richer doses of bandwidth at the same time resulting in 6 Mb/s (or 12 Mb/s in the future, conceivably), instead of 1.5 or 3 Mb/s MPEG, in order to compensate for not being able to do post capture triage.
It's live.. it must be delivered instantaneously, so there is no time to do triage (which is a manual, subjective task)to the file before it's sent, in other words.
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Here, in the following, you begin to present the framework that was once known as Open Video Systems, or OVS, which was intended to work over ADSL, and was designed with a dependency on the early rollouts of ADSL's Switched Digital Video platforms. Do you recall Smith's Stargazer approach at BEL? It never came to pass in its earliest design, but the concept lives on:
"On a completely different tangent, let's say we drop the VOD model out of the VDSL delivery system. Let's say we talk only, "live TV." Sporting events for instance. Let's say the teleco headend is receiving some 200 live channels of content, from the national broadcasters and local affiliates. And the telco needs to get it out to their 3,000 subs as each sub chooses to watch these live events. Some of that content is sent via terrestrial point-point microwave, some via a fiber optic link, some directly from the national broadcasters via satellite link."
Of course, all of these different forms of transmission are taking place from the content houses to the carrier in question, right?
"Let's say some of it's digital, some analog... So taking the 200 channels of live content delivered to the telco headend, making it all digital where needed, and sending it all down the distribution plant(in this case fiber-twisted pair), to their 3,000 subs, is not such a big deal(except for equipment money for course!), right? I just got the impression from reading your comments, that you thought a VDSL TV model could never handle 200 channels of live TV. I just wanted to clear this up."
The model which supports VDSL can easily handle as many channels in its innate architectural design as the operator had access to content providers. There is no gating factor other than, perhaps, the ability to administer a high number of I/Os at the operator's head end, host terminal, or point of presence.
The limitation in VDSL is the number of "simultaneous TV sessions" that can be supported to the home at any point in time. This is because of the restrictions imposed by "only" having 26 or 52 Mb/s available from the start over the copper pair.
Come back if I'm still not addressing your question adequately. If so, maybe Denver Techie or DH would step in here and give us an assist.
FAC |
