[ale] [semi-OT] CDPD coverage in the ATL?

[Joseph A Knapka]

Christopher Bergeron wrote:
> Does anyone know of any CDPD providers here in Atlanta (specifically
> Buckhead)?  More on topic, though, does anyone know how easy it is to
> configure a CDPD modem under linux?  I've found a few resources but
> I'm wondering if anyone here has done it or is familiar with it.  I've
> been looking at the Nortel G100 Wireless PCMCIA card.  Are these the
> proper steps for configuring?
> 
> a) configure PCMCIA services (it's a desktop computer with a PCMCIA
> adapter)
> 
> b) configure pppd with the CDPD settings
> 
> c) Enjoy the wireless internet?
> 
> 
> Also, does anyone know what speeds (travelling) that I can move at and
> still get CDPD coverage?  I may drive up to 50 MPH at points in the
> city, and I'm wondering what coverage would be like in this regard.
> 
> 
> Much thanks in advance to anyone who's familiar with CDPD and can
> offer pointers...

I've done some work with CDPD. Configuring the modems is pretty
simple (provided you have a modem that's simple to configure -
I've worked with Cincinnati Microwave products, which are
pretty straightforward).

Basically, the modem sits on a serial port, and you can dial
up IP addresses using a variant of the "ATD" Hayes command.
After that, the serial port is the local end of an IP
connection (TCP or UDP, depending on how the modem is
configured). So there's nothing platform-specific about
this, but you may need to have software that's specially
configured to deal with, say, /dev/ttyS1 being a virtual
socket. Some simple Tcl or Python or Perl script could
deal with that by forwarding packets for you, allowing
normal network-aware apps to work (with a little
reconfiguration).

The other thing you can do (with the CM modems, anyway)
is give the modem an IP address, and establish a PPP
connection to it. The modem then forward all the traffic
on that PPP connection to some other IP address on the
CDPD network, which you have to configure before you
establish the PPP connection. So basically the modem
acts like a proxy for the remote host, and all normal
networking operations work as you would expect. But
you can only talk to one host at a time. And again,
there's nothing platform-specific about this, so it
should work fine under Linux.

There may be CDPD modems on the market that can give
you normal Internet access via the CDPD network, but
I'm not familiar with them.

Cheers,

-- Joe


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