MJ directly off my VoIP modem?

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mianne
MagicJack Newbie
Posts: 4
Joined: Mon May 26, 2008 2:45 pm

MJ directly off my VoIP modem?

Post by mianne »

Here's my current situation. MagicJack works reasonably well now that I've put it onto an old laptop that I have plugged in to my router. I like the idea of a thin client setup, but ultimately an even more elegant solution would be this:

I have an Arris TM402P cable modem (PDF) which has two RJ-11 jacks for VoIP support. I originally had VoIP through Comcast, so this is their provided equipment. So monkeying with it might violate Comcast's TOS as well as MagicJack's, though I could readily obtain my own identical box to possibly step on fewer toes and save an additional $3/month rental fee to boot. The Arris modem has an internal battery backup, so VoIP calls (via Comcast) worked even during power outages. But needless to say, once the initial year's promo ended, I really did not want to spend $40+/mo. on VoIP through my ISP.

Given that the modem is: 1) on 24/7 already anyway, 2) should be able to function as a standalone ATA, and 3) the built-in UPS, I'd really like to use it instead of having the laptop running as a dedicated MJ server. Mind you, I'm relatively competent with poking through registry settings and whatnot, but telephony is largely greek to me and I'm regularly googling acronyms like SIP and PSTN. The PDF I lnked to above didn't go into specifics beyond "Contact your cable company" for configuring the modem itself.

So with that in mind, if anyone is willing to help a newb through trying to hack both my MagicJack service and my cable modem into playing nice with each other, I would be most grateful.
Stewart
Dan Should Pay Me
Posts: 663
Joined: Tue Nov 13, 2007 2:58 pm

Post by Stewart »

This is an incredibly complex issue. The voice section of a cable modem uses a protocol, packet cable NCS, which is very different from the SIP used by MJ and most other VoIP providers. NCS is a variant of MGCP. An introduction can be found at http://www.iec.org/online/tutorials/voc ... pic02.html . While e.g. Asterisk can convert between MGCP and SIP, that would require an intermediate server, which is exactly what you're trying to eliminate. In addition cable modems transmit, the NCS on a private IP address (that's also used to administer and monitor the modem) over the coax interface. NCS packets never appear on, nor are they accepted from, the Ethernet interface.

To make this work as a self-contained system, you would have to write a lot of firmware for the modem's processor. Even if you found a suitable cross compiler and related tools, you'd still have to learn a lot about the boot process, updating flash, recovering a bricked modem, etc. Cable modems attempt to be quite secure devices, containing technical measures that make reverse engineering difficult.

It would be far simpler to obtain a SIP ATA and a small UPS to power it. Or, forget the backup and get a minimal landline, available in most areas for ~$12/mo. That would give you reliable access to 911 and for your alarm system, would work well if you ever need to connect a modem, fax, Tivo, etc., and also would serve as a second line.
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