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From: seanp%undrground@amix.commodore.com (Sean)
Newsgroups: comp.dcom.telecom
Subject: Re: Questions About the GTE Airfone
Message-ID: <15223@accuvax.nwu.edu>
Date: 4 Dec 90 23:48:34 GMT
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X-Telecom-Digest: Volume 10, Issue 865, Message 12 of 13


> 1.  How is the credit card verified ?  Are they all stored on board
> and downloaded after the airplane lands, or is it real-time ?
 
  Dan- 
  
    When you insert your credit card, the information (number, exp.
date, etc. ) is sent via 300 baud signal to a ground station. (REAL
TIME). The ground station then confirms or denys usage, and proceeds
from there.  Actually, the handset is not released until then card is
approved.

> 2.  What happens if everyone wanted to place a call at the same time?
> On the jet I was on, that would be 56 phones in use at the same time.
> Quite a multiplexer/transceiver, if that's how it's done.
 
 The transmitter section of the setup is IMPRESSIVE. Everyone could
concievably use thier phone at the same time, as there are 400
channels available for use. This concept applies only, however, to one
ground station. There are 80 ground stations in the U.S., though.

> 3.  How is frequency assignment done for numerous planes in the same
> local area (i.e. 20 planes backed up, waiting for takeoff at O'Hare)?
  
Frequency assignment goes something like this:

     894 - 896 MHz (5 KHz spacing). Assignment is done in the same
     manner as cellular. It picks an available frequency from what the
     ground station tells it. AM mode is used for modulation.

> 4.  Has anyone tried a ringback or number announcement from the phone
> ?  I know the phones aren't capable of actually receiving a call or
> ringing, but it would be interesting to see what happens.

This would give the same result as doing it from any other phone, as
in the end, you are connected with the P.S.T.N.

> 5.  Is there a nationwide cellular-like network for these phones, i.e.
> the ground station hands off the call(s) to the next station when the
> plane leaves the service area ?
 
You are absolutley correct. Handing off and signal comparison is done
in much the same way. Really, however, you would have to talk for
quite a while in order to leave a service area. Consider transmitting
with high power, at 35,000 feet. Most planes out of Philadelphia can
hit Atlanta radio right after takeoff, with good/excellent quality.

 
Hope this helps.


Sean Petty
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