FOOD FOR THOUGHT Arris TM512

riche

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We are just about to switch our telephone providers from analog POTS (5 lines) to small-business class cable/VOIP service that outputs analog phone lines. This isn't a problem because it's an easy switch since we're already using a analog TDM card in our Asterisk box. The cable company is Comcast and they are using the Arris TM512 cable/telephony modem. Anyone have any advice or experience on connecting this cable modem to an asterisk box with a digital connection instead of an analog connection?

Thanks,
Rich
 
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I don't exactly know what you mean by digital instead of analog. The TTM uses a technology called PacketCable (see Cablelabs website) to perform the digital to analog conversion. Think of the TTM as basically a big ATA device (with 12 lines) built into the cable modem. PacketCable enables the TTM to provide you reliable service via DOCSIS QoS mechanisms.

If I may try to guess what you are asking, you will lose QoS and likely quality if you choose to use a standard SIP provider instead of Comacst. In that case, you would be using the TTM as a standard cable modem and not the telephony portion. I think in this situation you will be better off using the TTM analog ports with your TDM card.

Full disclosure: I am an ARRIS employee and have worked on the TTM project in the past.
 

kenn10

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Anyone have any advice or experience on connecting this cable modem to an asterisk box with a digital connection instead of an analog connection?
Do you mean as in a T1 connection or possibly via SIP? I don't believe Comcast can support that due to the network infrastructure utilized and the nature of the Arris box.

As Troy mentions, you can use a VOIP provider and just run SIP or IAX over the cable modem rather than having the Comcast analog lines.
 

riche

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To clarify, I was wondering if there was someway to interface into the Arris box using something other than the RJ11 connections via my TDM card. My thinking was that the TDM card is analog and has all the negatives associated with the analog TDM cards. I was hoping (through some convoluted logic, perhaps) that maybe I could interface with the phone lines provided by the arris box (not an external SIP provider) either through a digital interface card or via a protocal (SIP, IAX,etc) over a network connection, but it sounds like that the arris box does not offer features like that. Is that correct, based on the answers above?

-Riche
 
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Correct. The ARRIS TTM will provide you up to 12 lines of analog service, depending on how many you activate with your provider. It is analogous to a sip->analog ATA, except using the PacketCable protocol instead of sip.
 

Alex728

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I had a (brief) look at the packetcable protocol and it appears to be based on SIP but with more security/billing procedures bolted on

also it appears these things operate on "premium" bandwidth away from the main Internet / with guaranteed quality of service (might also explain the wider brouhaha over net neutrality!)

Although it would be technically possible to communicate digitally with the box I very much doubt the cable companies are going to permit small customers to connect in such a manner (at least not for a fair few years) as it wouldn't be worth their while dealing with the more complex support and security issues.

TBH I think for a smaller business you are better off using the FXS ports this box provides anyway (it also provides you with a backup facility to just plug in a phone or two should your Asterisk server fail). The only potential gotcha would be whether these FXS ports provide a CPC signal when the remote party hangs up (to enable the use of kewlstart)...
 
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I had a (brief) look at the packetcable protocol and it appears to be based on SIP but with more security/billing procedures bolted on

also it appears these things operate on "premium" bandwidth away from the main Internet / with guaranteed quality of service (might also explain the wider brouhaha over net neutrality!)
Close. PacketCable is based on MGCP, although there was a push for SIP early on.

Although it would be technically possible to communicate digitally with the box I very much doubt the cable companies are going to permit small customers to connect in such a manner (at least not for a fair few years) as it wouldn't be worth their while dealing with the more complex support and security issues.
Actually, it is not possible to communicate digitally with the TTM (it just isn't designed that way), you would have to bypass it to talk to the DOCSIS network directly, which I don't think is possible given the security involved. The only thing close would be something called a stand-alone MTA, but you would have to build one yourself (I don't know if anyone ever sucessfully made one). As you indirectly observed earlier, PacketCable is intimately tied to DOCSIS...the modem is critical for reserving the bandwidth required, and even PacketCable call servers are involved in dynamically requesting bandwidth on a per-call basis. In addition, the devices must pass extensive sercurity checks involving certificates and KDC servers before they are even allowed to communicate with the call servers.

Although I don't doubt someone might eventually figure out how to defeat the PacketCable security measures and use the network directly, I don't think it will be anytime soon and I would be even be surprised if they did.

The only potential gotcha would be whether these FXS ports provide a CPC signal when the remote party hangs up (to enable the use of kewlstart)...
All our TTMs provide Call Party Control, or what we commonly call Forward Disconnect, so kewlstart should work.
 

benhadad

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I know this is an old thread, but it seems this is perhaps true of some modems but Arris own documentation states that this is possible via firmware. They even advertise it as a platform, but it seems the cable companies are choosing not to use it?
 

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