[asterisk-dev] Virtual Modem Pool

Wed Oct 1 06:53:18 CDT 2008

I would look for an ebay deal on a Cisco AS5300 or AS5350.   2 of them, one Prod, one for spare since they are EOL.

-Mark

> -----Original Message-----
> From: asterisk-dev-bounces at lists.digium.com 
> [mailto:asterisk-dev-bounces at lists.digium.com] On Behalf Of John Lange
> Sent: Tuesday, September 30, 2008 10:58 PM
> To: asterisk-dev at lists.digium.com
> Subject: Re: [asterisk-dev] Virtual Modem Pool
> 
> I have to agree. That is the wrong approach.
> 
> I'm not a modem pool expert but Cisco makes routers that take T1 PRI
> cards designed for _exactly_ this purpose. Given the decline 
> in dial-up
> perhaps you can find one on ebay for a reasonable price?
> 
> It would be nice if you could use a T1/PRI card from Digium or Sangoma
> for this but the sticking point is that in order to do modem 
> signalling
> you need a DSP (digital signal processor) or software that simulates a
> DSP (that's what SpanDSP is all about for Asterisk & faxing).
> 
> Unfortunately software DSPs do not scale very well so there is little
> chance you could use software DSPs for more than a few 
> channels at once.
> 
> Hardware DSPs are reasonably expensive and that explains why 
> a WinModem
> (which is a software DSP) is more expensive than a "true" modem which
> uses a hardware DSP.
> 
> In any case you would never do this:
> 
> Device <--> POTs <--> VOIP Gateway <--> IAX2 <--> ??? <--> Clear Text
> 
> Modems simple _do not_ work on VOIP. It would look more like:
> 
> Device <--> POTs <--> Modem Gateway <--> Serial or clear text
> 
> What about high density modem cards? You can get at least 8 modems on
> one card. Put a few of those in a linux box and configure it 
> for dialup.
> 
> I have no idea of the cost but I'd be willing to bet this is 
> by far your
> most cost effective way to go.
> 
> Regards,
> -- 
> John Lange
> www.johnlange.ca
> 
> 
> On Tue, 2008-09-30 at 16:15 -0500, Steven S. Critchfield wrote:
> > Seems like a very stupid way of doing this. Modems do not 
> do well over
> > VoIP connections. Even if you could get a connection to be made and
> > stay up for long, any jitter in the VoIP connection will kill your
> > throughput. You will still be sending the same amount of data per
> > VoIP call and getting much less end to end bandwidth.
> > 
> > You would be SOOO much better off if you just looked at contracting 
> > with some service like TiVo did to provide POP access and 
> do modem to
> > PSTN to POP, then you have internet access for your download. 
> > 
> > Just for the quick math.
> > 
> > uncompressed VoIP ~ 80kbps bandwidth from you to your VoIP gateway
> > 2400bps signal that might be usable over voip.
> > 
> > hmm, you loose 76kbps of data trying to support that idea 
> per line in
> > use.
> > 
> > ----- "Brad Silen" <brads at qualityprocess.com> wrote:
> > 
> > > We are looking to deploy thousands of hardware devices 
> connected to
> > > the PSTN
> > > which will upload data and download firmware updates using v.90
> > > modems. It
> > > will be deployed to a demographic which does not have Internet
> > > access.
> > > 
> > > We are hoping to avoid setting up an old fashion modem 
> pool, POTs or
> > > T1-PRI,
> > > and hope to access the PSTN through a SIP Trunk or IAX2.  This
> > > solution
> > > would be both cost effective and scale to handle peak loads; For
> > > example,
> > > when a firmware download is required.
> > > 
> > > Ideally we would like our application servers to 
> send/receive using
> > > TCP/IP
> > > sockets with the virtual modems which are being driven by the VOIP
> > > infrastructure.
> > > 
> > > The network might look like:
> > > 
> > > Device <--> POTs <--> VOIP Gateway <--> IAX2 <--> ??? 
> <--> Clear Text
> > > on
> > > TCP/IP Socket
> > > 
> > > Solve for ???
> > > 
> > > Has anyone used Asterisk in this way?
> > > 
> > > Is there any reason why the VOIP Gateway (SIP Trunk or 
> IAX2) data path
> > > would
> > > prevent modem communication?
> > > 
> > > Is there any similar solution terminating a v.34 
> connection (aka Fax)?
> > >  A
> > > Fax solution would verify the ability to send data via the VOIP
> > > pathway and
> > > offer sample code as a starting point.
> > > 
> > > Would we extend the Asterisk concept of an "extension"?  
> For example,
> > > instead of forwarding the traffic to a SIP Phone the virtual modem
> > > would be
> > > an "extension" which converts the data stream to ASCII 
> clear text. 
> > > Or, what
> > > would be the suggested architecture choice in Asterisk?
> > > 
> > > Note, I am very open to better, easier, or more clever solutions.
> > > 
> > > If there are service providers offering this type of virtual modem
> > > pool
> > > please have your shameless commerce division email me directly.  I
> > > suggest
> > > they not respond to the list since I am concerned it 
> would violate the
> > > rules
> > > of this list.  I have not been able to find a solution 
> and expect to
> > > contribute.
> > > 
> > > 
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> 
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