Data Communication and Host Modes
RLXIC-SG
♦
Intelligent Cellular
User Manual
RadioLinx Intelligent Cellular Serial Modem for Global GPRS/GSM
ProSoft Technology, Inc.
Page 59 of 136
May 29, 2009
7.3.4 TCP and TCP Pad
When the RLXIC-SG is in a TCP session, all characters received on the serial
port are assembled into TCP packets, and sent to the mode's remote IP
address/port, and any packets received from the remote end of the TCP
connection are disassembled, and dumped onto the serial line.
A TCP connection is established by one of the following methods:
Using the Dial TCP (DT) AT command. For example,
ATDT192.168.3.23/3456
.
TCP auto answer is enabled (
S1
), a TCP connection request is received, and
the modem is not in a data session.
Data is received on the serial port, and
o
The Startup Mode Default (
MD
) is
4
(auto TCP)
o
The remote TCP destination, as defined in S53, successfully responds to
the TCP connection request.
The value of
S7
(TCP Connection Time-out) specifies the number of seconds to
wait, after initiating a TCP connection attempt, for a successful connection to be
established. If the connection has not been successfully established before the
time-out occurs, ERROR/BUSY is returned.
TCP packet assembly is affected by the values of
S50
(PAD Forwarding Time-
out) and
S51
(PAD Forwarding Character). Data received in the serial buffer will
be transmitted when the idle inter-character time-out specified in S50 (in tenths of
seconds) occurs or when a character is received that matches
S51
(if non-zero).
The TCP session will be terminated if no data is transmitted or received for the
time interval specified in
TCPT
and
TCPS
. TCPT is the number of minutes
(TCPS=0) or seconds (TCPS=1) used for this idle time-out.
Caution:
TCPT should never be 0 when using the TCP mode. A broken TCP session can result in
the modem being left with a TCP Auto Answer
TCP auto answer (S0=1|2) also allows a TCP connection request to be
"answered" when the modem is idle, not in a data session. The TCP connection
request's destination port has to match the modem's device port.
Note:
UDP auto answer may also be set simultaneously with TCP auto answer. Then, when in the
idle state, the modem will accept either a TCP connection request or UDP incoming packet, and
enter a TCP or UDP session as appropriate.
7.3.5 Hybrid
Mode
Hybrid modes are supported mainly for legacy implementations. Some previous
hybrid modes (MD=5, 6) are no longer implemented as special, unique modes.
Now that UDP auto answer (UDP Half-open, S82=2) can be enabled in
conjunction with UDP PAD mode (MD3), effectively this is the same as MD5 and
MD6 previously accomplished. Setting MD5 and MD6 are still supported, but not
recommended.
Summary of Contents for RLXIC-SG
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