[opendtv] Re: Spectrum is too valuable

  • From: Craig Birkmaier <brewmastercraig@xxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Sat, 07 Nov 2015 07:51:07 -0500

On Nov 6, 2015, at 7:50 PM, Manfredi, Albert E <albert.e.manfredi@xxxxxxxxxx>
wrote:


Craig Birkmaier wrote:

There is no question that a system could serve more homes
with broadband if they repurposed spectrum now used for
analog or digital TV streams.

Amazing how long it took to get that point across, though, right? A real
struggle.

No Bert. It's irrelevant, as there is no good financial reason to do it. We
still have analog cable here in Gainesville for two reasons:
1. It's making a profit;
2. It serves multiple TVs in a home. Without the need for a STB for each screen.

The reality is that these cabled systems have enough spectrum to offer multiple
services, and they do not need to rush to build out more PONs until the demand
increases enough to justify the expense.

The question is how much bandwidth is needed in any
neighborhood to replace the broadcast TV service with on
demand UDP TV streams?

Simple, Craig. You only need, say, two or three broadband streams per home
for this, depending on how many people are watching TV simultaneously. So, if
a single DOCSIS 6 MHz channel can support 38 Mb/s downstream (256-QAM), that
should be more than adequate for two homes, each steaming 3 HD shows
simultaneously (or many more streams in SD). So, rough estimate, how many
homes can be fed with the spectrum used up by the broadcast MPEG-2 TS streams?

Assuming 950 MHz is available for downstream, the answer is 158 channels or 316
homes, each getting 19 Mbps service.

I think you are under estimating the bandwidth needed per home; three HD
streams in 19 Mbps is clearly insufficient for MPEG-2, and on the low end for
h.264, especially for high action content. But you are at least heading in the
right direction in terms of mother natures limits.

The wide distribution of the TV programs is made possible by the servers
feeding the head-ends. And these servers, in turn, can be updated via
satellite out-of-band links. So you don't have to clutter up the ISP backbone
networks with *all* of the TV programs, especially not the popular ones.

This is irrelevant to this discussion.

Don't know why you changed subjects and started talking about
upstream bandwidth.

Because I know what I'm talking about?

Obviously not. Most systems allocate the spectrum from 5 to 42 MHz for upstream
broadband. They may use a bit more to handle in band upstream signaling for
on-demand services. This frequency allocation is probably sufficient if
everything else were dedicated to broadband, so it is irrelevant to this
discussion.

There is no way the current FOTA broadcast TV service could
deliver unicast said to every home in a market without massive
spectral reuse - i.e. tons of cells serving a small number of
homes. Cable is no different.

Do some numbers, Craig. It's funny how you finally did some, below, and yet
you couldn't go and retract this statement before posting?

This statement was a rhetorical set-up Bert. Just a point of reference that I
knew you would jump on.

Clearly broadcasting is only useful because a very large audience is looking at
the same content. Cable systems are no different, other than the fact that some
channels have much larger audiences than others.

So the best we can do today with DOCSIS 3.0 is 6.33 X 900,000,000
= 5.697 Gbps

Yes, I just finished telling you that yesterday, Craig.

Sorry Bert, you did no such thing. You said it would be sufficient without
doing the math. You were mistaken.

Today PONs serve between 25 and 2000 homes, with the average
being 500.

By reclaiming all of the broadcast bandwidth, how many homes can be fed from
a single PON? You have all the number you need, Craig. Hint: in many cases,
*no change* will be required in the PON cabling, going by your figure of 25
to 2000 being the current status, and 500 the current average. And no matter
what, the PON changes can be reduced. You can't fool mother nature, Craig.

You're a trip. I did the math and showed you that the most homes a PON can
serve is between 148 and 295 depending on how much bandwidth is allocated per
home (50 Mbps vs 25 Mbps). And that this is the theoretical best with DOCSIS
3.1 technology. Clearly a PON serving 500 homes will fall far short of the
spectrum needed.

Mother Nature is not the fool here...

Regards
Craig




Bert



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