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Cellular Communications
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When using a transportable cellular telephone (a 3-watt
telephone), better operation may be obtained by using an
external antenna.
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Performance when stationary is usually better than when
moving. If you encounter problems, stop the vehicle and
place the call from a stationary position
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Z modem protocol is recommended for file transfers.
Most software packages today support this protocol.
Z-modem is an efficient protocol with low overhead, and
it allows a dropped call to resume the file transfer at the
point of disconnect.
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If your cellular telephone supports VOX (Voice Operated
Transmission, also known as Discontinuous
Transmission), you may need to turn VOX off. Contact
your cellular service provider for assistance in disabling
VOX.
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The remote modem should use V.42 error correction (at
a minimum). If this is not possible, then the remote
modem should use Reliable mode.
Overview of Cellular Networks
A cellular network consists of adjacent geographic regions
known as cells. Within each cell, there is a transmission tower
that communicates directly to both the cellular telephone and a
Mobile Telephone Switching Office (MTSO). Cellular
communication uses radio waves to transmit calls between a
cellular telephone and a transmission tower.
The tower and MTSO constantly monitor the location and signal
power of your call. When your call becomes too weak to be
handled by the tower in that cell, either due to distance from the
tower or high activity on the network, it is "handed off" to another
cell. The tower uses radio waves to communicate with the
cellular telephone, and the MTSO uses traditional land lines to
communicate with the transmission tower and the remote party
on the other end of the call.
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Issue 2
May 1995
D-7
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