[opendtv] Re: Spectrum is too valuable

  • From: Craig Birkmaier <brewmastercraig@xxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Thu, 19 Nov 2015 06:59:47 -0500

On Nov 18, 2015, at 8:00 PM, Manfredi, Albert E <albert.e.manfredi@xxxxxxxxxx>
wrote:



Whoa, Craig, you're *so seriously* uninformed. You're talking nonsense. Why
do you think they are called passive optical networks, Craig? Answer: they
are passively split, shared among multiple households. Read up what a PON is:

No need. I know what a PON is. I know how to read. And I am seeing commercials
from Cox right now promoting Gigablast.

They ARE deploying 1 Gbps to homes now via fiber, and have announced plans to
offer this speed via HFC with DOCSIS 3.1.

Far fewer? Do the math, Craig. We already determined that with DOCSIS 3.1, in
the old 900 MHz plant, you can offer about 5 Mb/s aggregate downstream
capacity in the neighborhood (don't forget that some MHz is taken up by
upstream traffic), but ONLY if you eliminate all broadcast traffic. So tell
us, Craig. **If you repurpose all of the broadcast spectrum**, how many homes
can be passed with a single DOCSIS 3.1 PON, in a 900 MHz cable plant, if each
home wants 1 Gb/s? It's a really simple calculation.

Do you remember a post from 11/7 with the subject Gigablast?

I asked how blasting files at 1 Gbps impacts utilization stats within a PON.
Nobody answered.

You are looking at this problem from the wrong perspective. You are trying to
design the system assuming sustained bit rates for every home. That is, the
bandwidth of the PON divided by the number of homes. But that's not how we use
broadband.

If you have a max bit rate to a home of 5 Mbps, it takes 133 minutes to
download a 5 GB file, as you might need for a HD movie. If you have 1 Gbps to
the home it takes 40 seconds.

This is not idle conjecture. I used to download movies from iTunes way back in
2005. It took several hours on my DSL broadband. The broadband was not fast
enough to support real time streaming of high quality video.

So the dynamics of how TV programming is delivered with gigabit service to the
home is very different than for "slow" broadband. It is not the instantaneous
max bit rate that a PON can support, but the throughput of the PON that
matters. Things may get tight during peak hours, but most programs will be
downloaded quickly, making the PON available to other users.

Only in the worst case, where everyone served by the PON is watching the same
live program does the max bit rate matter; and in that case, an IP multicast
can support everyone watching the program with one stream.

So when I said that there would be fewer homes per PON, I did not mean that
there would only be 10 homes per PON. And remember, they are not turning off
the MPEG streams, which is what many homes will be watching. The cable company
just needs to have enough bandwidth dedicated to DOCSIS 3.1 to support the
broadband demand, which will become relatively short bursts for on demand TV
programming.

First, almost anyone who wants "Internet-delivered TV" can get it today
from the cable/FIOS systems. 80% of U.S. homes have access to 25/3
broadband service today.

A refreshing change of tune, from someone who was claiming we are decades
away from being able to do this. So tell us, Craig, if you have a 2.4 Gb/s
GPON feeding the neighborhood, how many homes can be served, if each one
wants 25 Mb/s downstream>

Amazing.

Bert



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