[gentoo-user] Re: Cell phone as modem

[Grant Edwards]

On 2007-12-02, Grant <emailgrant@×××××.com> wrote:

>>> Nice, I'm very glad to hear it works so well.  I guess
>>> something like that would work even over an analog connection.
>>
>> On a true analog (800MHz AMPS service) cell phone, I've had
>> pretty decent success using MNP5 modems up to about 2400 baud.
>> The standard CCITT error dectection/correction schemes used on
>> landline modems isn't resilient enough for RF links. Good luck
>> finding MNP5 analog modems. ;) Multitech in St. Paul was the
>> last vendor I knew about that sold them, and that was 10+
>> years ago.
>>
>> If you're talking about an analog connection to a digital
>> phone, it just won't work. The Codecs that digital phones use
>> are optimized for human speech and won't pass QPSK (or even
>> FSK) modem signals in a usable manner.
>
> What I meant there was that I should be able to dial up in
> this manner even if the signal is reported to be analog
> instead of digital.  Is that true?

I still don't understand what you're asking.  Unless you're
800MHz AMPS service, it's all digital.  There is no analog
signalling on the network.

If you're using an 800MHz AMPS service, then the "voice"
channel is an analog FM link band-limited to 300-3KHz with C
message weighting (just like a landline phone connection).  You
can push an analog modem signal through that voice channel, but
the channel quality varies a lot and you need a really
bullet-proof error-correction scheme like MNP5.

> Are you saying it depends on whether or not the phone is
> capable of 800MHz AMPS service?

I guess so.  The carriers are going to shut down AMPS service
soon anyway.

>> It's just passing on digital data that's carried by the
>> wireless protocol in use (GSM/TDMA or 1xRTT/CDMA).  When you
>> "dial up a landline" with a digital cell phone, the wireless
>> carrier actually has to connect a modem to a landline at the
>> carriers switch and dial the number.  The digital data from the
>> cellphone is then routed to that modem.
>>
>> If you're using the wireless carrier as the ISP, then there are
>> no modems involved at all: the digital data from the modem is
>> simply routed onto the Internet.
>
> I see.  So the only ways you know of to get a laptop online
> with a cell phone are with a data plan in a digital service
> area, or with any Verizon plan in either an analog or digital
> service area?

If you're using analog service, you can use any carrier that
allows normal phone calls to access a dial-up modem.  You just
need a phone with a phone jack into which you can plug an
analog modem.  Motorol "bag" style phones used to have a
accessor that plugged between the handset and the radio which
provided a modem jack.  I don't think you're going to find too
many current phones that provide an analog modem jack.

Sprint also apparently has a free low-speed Internet access
service similar to Verizon's "QNC" service.  I don't know if
Sprint's free low-speed service allows you dial up a
landline-modem or not.

FWIW, I just plugged my VX4400 into my laptop, and Verizons
low-speed QNC service is still working.  There are rumors
that Verizon is about to pull the plug on QNC, but those rumors
have been around for years.

-- 
Grant Edwards                   grante             Yow!  Are you guys lined up
                                  at               for the METHADONE PROGRAM
                               visi.com            or FOOD STAMPS??

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