Think of a cellular data connection as a function of
your signal strength...The stronger your signal, the
faster your connect speed. Now if your modem isn't
initialized for dynamic negotiation (meaning that even
if you are already connected, if your signal degrades,
then your transmission speed decreases. Additionally,
if your signal improves, than your speed increases),
it can possibly be connecting at a high speed (by
high, don't count on anything higher than 12,400
unless you are directly under a tower) Then as signal
degrades (because you are traveling away from the
tower, or additionla calls begin to crowd the tower,
or the tower notices that you've been on a call for
longer than 5 minutes, and it needs to make some room
for new calls coming in, so it moves you to a tower
that is further away but not with as many calls on it
<called hand-off>, then the modem will still be trying
to transmit at 9600, but the signal quality would
ounly be good enough for 2400...so, what happens? you
get garbage on the screen and you loose carrrier.
That's the problem! cellular is such a Dynamic medium
and data transmission is such a precise requirement
that the two just don't mix too well. I've gotten
quite good connections using a 3-watt transportable, a
TelCell interface and a laptop computer directly in
line of site with a "B" carrier tower and was able to
acheive and maintain 14,000 baud! for over an hour!
oh-joy...not a pretty phone bill!
Oh, here's one more thing that causes problems...in
the analog cellular world, you have two types of
carriers, your wireleine carrier and your non-wireline
carrier. The wireline carrier has phone system trunk
connectivity on each and every tower...your call is
placed into the phone system at every tower...The
non-wireline carrier has one trunk connection for
every 8 cells...meaning that your call can bounce
between two or more cells (as many as 5 cells if your
system is a busy one) before it reaches a trunk...and
like taping a tape on your VCR, every tower jump
increases interferance and loss and decreases signal
quality... that may be partially why your's doesn't
work while your friends will! You may be on a
non-wireline service provider! (The wireline carrier
is also known as the "B" carrier and is usually the
incumbant Bell carrier, like one of the baby
bells...the non-wireline carrier is the "A" carrier
and is usually <but not always> an independant carrier
like Cell One <which is not a single company, but
actually a franchise of independant carriers....> For
instance, the "B" carrier in Washington DC is Bell
Atlantic/Nynex <they merged> the "A" carrier is Cell
One <which is actually a franchise that is owned and
operated by SBC, Southwestern Bell from Texas>)
So, as you can see...cellular data connectivity is
more akin to Voodoo than science...Anybody got a dead
chicken, I need to check my email!
Ed
Web/Cellphone guru
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