[TriLUG] VoIP SIP MODEM?

[Greg Brown]

  I have packet8 service here at the house.  The Packet8 service has a 
small
hardware component - basically POTS in and ethernet out.  When I need to
dial out to, say, fax or dial into a distant server I just plug the 56k 
modem
directly into the VoIP Packet8 adapter and it works great.

Greg

On Friday, Jun 25, 2004, at 13:19 US/Eastern, sholton at mindspring.com 
wrote:

> Jon Carnes <jonc at nc.rr.com> fills in the missing details:
>
>> What you are talking about is simply a codec. It would take your UDP
>> packets (not SIP - SIP is only used for control and setup, data/voice
>> uses RTP which is a udp based protocol), and convert the UDP packets
>> into signaling that could understood by a modem.
>
> That's for the "far end".  I was thinking more of a near-end solution.
>
> Here's the hypothetical scenario.  There's a BBS system I want to
> talk to. It isn't "on the net", the only access is through dial-up to a
> 56K modem. But I (hypothetically) don't have a POTS line, so when
> it leaves my computer it's already encoded for VoIP. Somewhere
> betwix hither and yon an ATA decodes my bitstream into the
> "squak and buzz" the Hayes (TM) at the far end is looking for.
> I want to generate that bitstream in software, rather than having
> to use a real Zoom FaxModem looped back into a local ATA
> to get it.
>
>> I don't know of any VoIP codecs that do this. It would be great to 
>> have
>> one for faxing. Right now we have to loop the faxing signal thorough a
>> Fax card/modem to let the hardware inside it decode/encode the fax
>> signaling.
>
> Yes. A similar problem.
>
> Clearly the solution would involve a codec. but I'd need to use one
> of the "standard" encoding/decoding schemes which the far-end
> VoIP-to-analog phone adapter can understand.
>
> An my interface to this scheme (at my end) should look like a
> combination of /dev/modem (so that minicom recognizes it) and
> the 56K modem hardware (My Zoom) and the (local) ATA
> creating the encoded RTP session, but without all that hardware.
>
> A "new" codec for this wouldn't be the complete solution, since I don't
> get to choose what codec gets used at the far end, although I imagine
> the performance characteristics for a codec targeted at modem-type
> "sounds" would be different that one optimized for human voice.
>
> In theory, such a solution should be able to adapt to whatever codec
> the far-end negotiations were willing to accept. If the only 
> acceptable codec
> were a low-quality G.711 then the channel might to be able to support
> the full 56Kbps, but negotiate to a lower rate depending on what the
> modem-behind-the-VoIP-to-analog-phone-adapter was able to handle.
>
> Oh well. An interesting problem to muse about....
>
> -----Original Message-----
> From: Jon Carnes <jonc at nc.rr.com>
> Sent: Jun 24, 2004 7:32 PM
> To: Triangle Linux Users Group discussion list <trilug at trilug.org>
> Subject: Re: [TriLUG] VoIP SIP MODEM?
>
> On Thu, 2004-06-24 at 10:08, sholton at mindspring.com wrote:
>> Perhaps someone on the list can assist.
>>
>> In a VoIP discussion recently, a question came up:
>> If I'm using pure VoIP (from IP phones on a LAN, and/or VoIP
>> software on a PC) but need to connect to a modem, such as on
>> a BBS system, but don't want to use a kludge like
>>   PC -> modem -> SIP box -> Internet -> PSTN gateway -> modem -> BBS
>> what kind of software device would I need for the client end?
>>
>> I'd google on this, but I don't know what it would be called.
>>
>> I'm thinking it would be some sort of software driver which
>> looks like a modem to the kernel and apps but produces
>> and consumes SIP packets from the ethernet interface which
>> contain the CODEC-encapsulated analog squalking of a modem.
>>
>> Is there a name for a beast like this?
>>
>
> What you are talking about is simply a codec. It would take your UDP
> packets (not SIP - SIP is only used for control and setup, data/voice
> uses RTP which is a udp based protocol), and convert the UDP packets
> into signaling that could understood by a modem.
>
> I don't know of any VoIP codecs that do this. It would be great to have
> one for faxing. Right now we have to loop the faxing signal thorough a
> Fax card/modem to let the hardware inside it decode/encode the fax
> signaling.
>
> Most times we can live without faxing in a VoIP world. After all, we're
> pushing around data, so we can just send the document directly - or 
> scan
> in the document and send it as a nicer picture than you would get with 
> a
> Fax.
>
> Good luck - Jon Carnes
>
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>
> -- 
> Steve Holton
> sholton at mindspring.com
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