Data Communication and Host Modes
RLXIC-SG
♦
Intelligent Cellular
User Manual
RadioLinx Intelligent Cellular Serial Modem for Global GPRS/GSM
ProSoft Technology, Inc.
Page 57 of 136
May 29, 2009
When the modem is in UDP PAD (Packet Assembly and Disassembly) Mode,
all characters received on the serial port are assembled into UDP packets,
and sent to the remote IP address/port or the RLXIC-SG, and any packets
received from the same IP/port-destined for the device port of RLXIC-SG
(see *DPORT)--are disassembled, and dumped onto the serial line.
A UDP session is initiated by one of the following events:
Using the Dial UDP (DP) AT command (example, ATDP192.168.3.23/3456).
Setting the Startup Mode Default (MD) to 3 (UDP) so that a UDP session is
entered automatically when the modem registers onto the network. Serial
data will be sent to the IP/port specified in S53.
Incoming UDP packets will be processed out the serial port if
UDP auto answer is enabled (S82=2);
The destination IP address matches that in S53 (if Friends Mode is enabled,
the IP address also needs to be present on the Friends List);
Or allow any IP is set (AIP=1);
The modem is in AT mode (not in a current UDP or TCP session).
UDP 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).
7.3.3 UDP
Auto
Answer
UDP auto answer (previously called UDP half-open) is set with S82=2. When set,
the RLXIC-SG will automatically establish a UDP session to the source IP
address, and port of the UDP packet received. The RLXIC-SG will remain
"locked" to this one remote IP/port until no data is sent or received for the time
interval defined in the UDP auto answer time-out (S83). During this session,
packets from other IP/port addresses will be rejected, unless *UALL is set.
Whether or not an incoming packet will cause the modem to enter a UDP session
is always dependent on the S53 and AIP settings.
The Normal UDP Mode (MD3) can be combined with UDP auto answer to cause
the incoming serial data to be sent in UDP packets (instead of being treated as
AT commands), while allowing sessions to be established from different UDP
sources. A UDP session will be initiated either by incoming serial data or by an
incoming UDP packet. The session, started by either method, will be terminated
when no data has been sent or received for the S82 period. After the session
terminates, another may be initiated by either means.
When idle, after the time-out has occurred, the modem is in AT command mode
on the serial port, and any valid AT command may be entered during this time.
Tip:
It is best to ensure the idle time-outs for TCP and UDP are never 0 if you're going to be using
auto-answer, or either PAD mode. In those circumstances, you will want the modem to close the
socket if the connection goes idle for too long, particularly if the other side does not normally close
the connection.
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