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Posted by John Gray on May 13, 2006, 12:00 pm
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> "I am asking if the telephony is totally outside and has no impact on
> the
> interent.. or viceversa... "
>
> Well, the answer depends on what they using. For the past several
> years, phone over cable systems were switched digital phone systems.
> The cable company would mount a box called a NIU or some other
> acronym, that would have a cable connection and a phone wire block.
> It would connect to the cable drop before anything else on the line
> and pass through signal for television or internet. This would
> connect to a 5ESS switch, just like the baby bells use, and was
> switched data, meaning 64Kbps all the time. It uses different
> upstream and downstream bandwidth from the Internet traffic. They
> were sometimes powered by the cable system, sometimes from a battery
> backup on site.
>
> Now, many cable companies are moving to VoIP systems that run on the
> current Internet infrastructure they've built for the high speed
> internet. They use a special cable modem that has 2 phone jacks on
> the back, next to the Ethernet and USB ports:
> http://www.arrisi.com/products_solutions/product_families/Touchstone/t
> elephony_modems.asp
> http://broadband.motorola.com/catalog/productdetail.asp?ProductID=388
> These do share the bandwidth used in the house, usually not that much
> though. They also require a battery backup for lifeline service,
> which at some point may stop working and I'm sure will requie a
> technician to come out and replace.
I recently had TW Digitalphone(VoIP) installed. The modem is the
Motorola SBV5220 on the site linked to above. TW didn't install the
batteries, nor provide them. When I called, they stated that they
weren't installing them in any of their installations as during a power
outage the network would probably be down anyway.
I am behind a NAT router and my internet IP didn't change. The modem is
between the TW cable and the router. I think(don't know) that the modem
issues two IPs so perhaps the bandwidth isn't shared. I do know that if
the phone is in use, I can still download a huge file from a fast server
as fast as before. Granted, that is just a subjective observation with
no measurement other than Firefox's Download window showing 768KB during
download. RR is capped here at 7Mbit down, 384Kb up. Again, I'm
guessing on all this.
Also, TW is doing something a little different with their VoIP. The
phone call is handled by TW network initially, but is routed the either
MCI or Sprint for the majority of the call over their phone network. I
think that virtually all phone companies do VoIP after a certain point
on their network, so as to reduce the cost of long distance calls. That
way they avoid a dedicated connection spanning a long distance.
> The best thing to do is call in and ask what all is involved in an
> installation. In some areas I'm sure they are running both systems at
> the same time, with the idea of eliminating the switched service at
> some point, so that's yet another thing to consider.
>
>
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