[SATLUG] Does Linux have a way to configure a Cisco 7912 series VoIP phone?

FIRESTORM_v1 firestorm.v1 at gmail.com
Tue Sep 2 15:32:09 CDT 2008

I don't work for TWC, but I do work in the digital phone industry and
I'm sad to say but you are asking the impossible.

The way they have their network set up, you would actually be robbing
yourself of the internet connection by using the setup you're

here's why:

Their modem that they gave you, I'd imagine is some kind of maybe a
motorola device or SA Webstar device.  This thing has two(or three)
RF-facing interfaces.  One for the data service which gets sent to the
ethernet port by way of a losely configured bridge, one for monitoring
and managment (for signal levels, firmware updates, hits, etc) and the
last for dedicated VoIP traffic.  In most installations with two
outward interfaces, the first one is data, and the second one is
VoIP/Managment.  These aren't physical interfaces but logical ones.
(think eth0:0, eth0:1, eth0:2)

The issue is that since TW provides a certain service level agreement
they ensure that SLA will be met by overlaying a VoIP network in with
their data network.  The VoIP is closed-loop meaning that your phone
call never traverses the Internet and terminates either at the local
site (headend) or the regional site (uplink).  TW does this overlay
for two reasons, 1: to ensure compatibility they use only one or two
brands of VoIP MTAs SA WebStar is the most common. and 2:Because the
VoIP is closed loop, and to secure the voice network, the VoIP MTA is
the only device that can properly talk to the VoIP network. (Regular
HSD modems ignore that part of the configuration.)

By using your own device (even though it IS a cisco and a decent voip
phone, you potentially become a threat to that SLA (of course you
wouldn't ever do that.) and there is no guarantee that you will be
able to reach the VoIP network because your data-only modem will not
even know the VoIP network exists.

The SLA mentioned above isn't one of "we do it because we want to look
good" things, (well not entirely).  Because they also carry E911
service, the FCC mandates certain guidelines that must be kept,
including interference from devices that cease to operate as
programmed.  In order to comply, they (TW) locked down the VoIP
network to only those devices that they have tested and beaten with a
stick, and smashed with a mallet, you get the idea.

Here's the thing that a lot of people fail to understand about digital
phone service (regardless if it's TW, Vonage, Comcast, Speakeasy,
JoeBobVoIP, etc).

When they say that you can use your existing jacks, they are correct
provided that the apartment complex has an accessible network
interface device (NID).  This box is the demarcation point for all
your unit's wiring between where your wiring stops and the legacy
telco's wiring starts.  In older apartments, this NID didn't really
exist as the legacy providers (bells) didn't ever think that some
other company or that the end user would want to use the copper. In
newer apartments, there are NIDs installed usually in the master
bedroom closet.

This NID contains a jack with a couple of wires going in to it (your
wiring) and a couple of wires (or just a jack) with wires going out to
the legacy provider.  In a standard install where there is a NID
located, the process is to disconnect the house wiring from your side
of the NID and cap it off to prevent shorting or backfeeding. (you
don't want to feed the outside world with your dialtone, do you?)

At this point, the phone wiring in your house is dead.  A duplex jack
(Y-adapter) plugged into a phone, the modem and the wall will activate
the jacks in the house.  Electrically the only thing changing is
<B>where the dialtone comes from!</b>   Instead of it coming from a
local Central Office down a big fat cable split off into smaller
cables then split into your building riser then into your individual
cable pair that has your dialtone into your NID, it comes from the
cablemodem's voice port into your phone jack and all the other jacks
wired to the one they connected the modem to will work as well.

There are various tutorials on how to do your own phone wiring online
and some include pictures and step-by-step.  I'd explain here but I
think I've typed a lot as is. :P

And, if you didn't read any of that, (i guess I got too wordy):
Cisco phone:  Nope, sorry.
House wiring:  Find the NID, disconnect, tape up, plug modem in. all done.


On Tue, Sep 2, 2008 at 1:50 PM, Ian L. Target <ian69 at comcast.net> wrote:
> _Kubuntu 8.04_
> Background:  I called TWC last week to cancel my service 'cause TWC
> was being a tool when it came to what it was charging me.  Well,
> apparently when you call to cancel, you don't get regular customer
> dis-service, you get some 2nd tier CSR's who are able to offer you
> different rates.  I was offered a rate of $99.00 for cable, internet and
> phone.  I don't really use a home phone at all, but the $99.00 was
> cheaper than what I was paying for just internet and cable.  I
> specifically asked /twice/, "Will the phone service work with my regular
> phone outlets?"  The CSR said yes.
> Three days later, an installer shows up with some big ugly-ass modem
> into which I have to plug my phone into to get phone service.  I tried
> my very best not to go off on the installer, but I let him know about my
> conversation with the CSR who said I could use the regular phone outlets
> in my apartment.  He says this only applies to /newer/ apartment
> buildings.    Apparently, my apartment building has some older wiring
> and the outlets will not work, hence the big ugly-ass modem.  I am not
> quite sure what the deal is, but the phone rarely works.  I tried
> calling the number with my cell phone and it does get incoming calls
> about 1/4 of the time.  I have yet to be able to dial out.
> Another call to customer dis-service.  Blah, blah, blah, we'll be out
> Thursday.
> I have a Cisco 7912 VoIP phone.  I have it plugged into my router.  It
> configures it self and and I can make calls out on it.  Some more
> background.  I pulled the phone out of a box of garbage from where I
> used to work.  After plugging in the phone, I realized that the phone
> still was able to make phone calls.  I even recognize the extension.  It
> is to a department that no longer exists.  Even though they (my previous
> employer) are in another state, I can pick up the receiver and dial a
> four digit extension and talk to some of my previous co workers.  I can
> even make regular phone calls if the calls are in the area code of my
> previous employer.  (There is no charge to my previous employer as long
> as the calls are in the same area code as them.)  For long distance, I
> use a calling card or my cell phone.  I am sure it is only a matter of
> time before someone at my previous employment will update their records
> and cancel this particular extension.
> I haven't asked TWC about trying to configure the phone as I don't feel
> like sitting on hold for another 20-30 minutes.  I can see the settings
> of the phone by typing in but I am unable to
> change anything.  Finally, the question:  Does Linux have a program that
> I can use to configure this phone (the Cisco 7912) to use my TWC
> assigned phone number?  This would be great as I could get rid of the
> extra modem that is required to plug in a regular phone to.
> Thanks
> Ian
> --
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