Sierra Wireless DART 200 CDPD Modem - Manual (Page 92)

DART 200 CDPD Modem User’s Guide 7 Vehicle Installation Considerations
Sierra Wireless, Inc. 7-2
The application program in the MAS has no way of knowing before
attempting a send or receive operation if the modem is still in online
mode. The application can be designed to assume that the modem is
always online, or to always check that it is online before performing the
send or receive operation. In the former case, a send operation failure is
indicated by an error return code (in command mode the modem expects
to see all messages start with an AT), while a receive failure is indicated
by a timeout.
If the MAS can sense the RS-232 interface, as described in CDPD status
sensing, p. 8-15, perform this operation to verify that the modem is still
connected before attempting a send/receive operation. For Transmission
Control Protocol (TCP) or User Datagram Protocol (UDP) the connected
state implies that the modem is online. If the MAS cannot sense the
interface leads, it tries the send/receive operation first, and only proceeds
to error-checking if an error or timeout occurs.
For applications using Serial Line Internet Protocol (SLIP), use the
Automatic SLIP restart feature on the modem, to automatically put the
modem back into SLIP mode following a power reset.
If the modem is not online, the next step is to check registration state
through the RS-232 leads or with ATS57? If it is not registered, the
program waits and periodically checks registration status, eventually
proceeding when the modem reregisters. It is assumed that the modem is
set up to register automatically, as described in Auto-Registration when
not registered, p. 8-7.
When the modem becomes registered, the next step depends on whether
or not the MAS is a server or a client. If it is a client, the recovery
procedure for both TCP and UDP is to issue the appropriate dial
command. If it is a server, the recovery procedure for both TCP and UDP
is to wait for a call from a client.
Proximity to other antennas
In general, do not locate the DART 200 antenna closer than 5 feet to
other antennas (specifically, two-way radio antennas) and in certain cases
more separation is required. In many vehicular applications, there are
two-way radio transmitters in use and usually the antenna mountings are
not 5 feet apart. Interference from the radio transmitter can slow down
response times or block modem transmission.