On Feb 27, 2011, at 6:31 PM, Martin Ewing wrote:
> AT&T's U-Verse service is based on VDSL2, which uses frequencies from around
> 100 kHz up to 8.4 MHz in carrier channels of about 4.3 kHz bandwidth.
> Typical phone lines at typical distances limit the maximum usable frequency
> because of excess attenuation. My line, about 2100 ft from the U-Verse
> fiber node, won't carry channels above about 5.7 MHz. (More at
> http://aa6e.net/wiki/Uverse )
I have Verizon FiOS to my home, so they terminate an optical fiber in my
basement on a big white box they call an ONT (Optical Network Terminal,
essentially the telco demarc) from whence both CATV (QAM?) and WAN/Internet
emerge on one 75-ohm coax cable.
By default(*), residential FiOS is configured with the WAN/Internet carried in
a high frequency band on the same 75-ohm coax that carries the digital cable
signal (QAM?) to the set-top box (they call this MoCA or "Multimedia over Coax
Alliance" -- it vaguely reminds me of the old 10-Base-2 ethernet on 50-ohm
coax). The coax emerging from the ONT is divided by a 3dB splitter, with one
leg going to the set-top box and the other to the home router (Actiontec
MI424-WR). The router NATs the Internet connection to provide a LAN on yet
another frequency band on the coax as well as four standard twisted-pair
ethernet jacks.
So the 75-ohm coax in my home carries two IP networks (LAN and WAN) as well as
the CATV signals. The STB is a host on the LAN, and both video on demand and
the program guide are delivered to it over the IP network. I also have a small
MoCA-to-twisted-pair adapter near the television that lets me put my
over-the-top box (Roku) on the wired network to avoid clogging the ISM bands
with streaming video.
>From an RFI perspective, this arrangement seems very robust. Obviously, the
>signals coming into my home on optical fiber generate no RFI. The ONT is well
>grounded and shielded and quiet as a mouse on every band I've tested. The
>long runs from the ONT to the STB and router are in shielded coax; the only
>unshielded runs are relatively short CAT5 twisted pair runs from the router to
>a couple of computers in the same room.
Does anyone have the U-verse fiber-to-the-home service? Is their architecture
similar to Verizon FiOS?
73 de W1CMC
(*) Commercial installations usually use a standard twisted-pair ethernet jack
located on the same ONT. Residential installations can request to use the
twisted-pair jack, but since the STB relies on IP/MoCA for video on demand and
the program guide, those services will be lost.
--
Charles M. Coldwell, W1CMC
"Turn on, log in, tune out"
Belmont, Massachusetts, New England (FN42jj)
GPG ID: 852E052F
GPG FPR: 77E5 2B51 4907 F08A 7E92 DE80 AFA9 9A8F 852E 052F
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