Data Communication and Host Modes
RLXIC-SV
♦
Intelligent Cellular
User Manual
RadioLinx Intelligent Cellular Serial Modem for the Verizon Wireless CDMA Network
ProSoft Technology, Inc.
Page 65 of 146
May 29, 2009
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.
When the session is initiated by serial data, the new session will be established
using the destination address specified in S53. The S53 setting can be changed
if the connect to last UDP setting (*UDPLAST=1) is set. The address in S53 will
be updated to reflect the address of the last session initiated by an incoming
UDP packet. So that when new data is received over the host serial port while in
the idle state, a session will be re-established with the last address. (This
behavior is the same as the previous Hybrid2 (MD6) mode).
Tip:
TCP auto answer (S0) may also be set simultaneously with UDP auto answer. Then, when in
the idle state, the modem will accept either a TCP or UDP incoming packet, and enter a TCP or
UDP session as appropriate.
Reliable UDP
Reliable UDP adds a simple protocol on top of UDP to provide reliable delivery of
data. When data is received from the host serial port, a 2 byte header is added to
the data, containing a message type and a sequence number. The RLXIC-SV will
continue to send this data (buffering any received data in the meantime) until it
receives an acknowledgement with this sequence number. If an
acknowledgement is not received within the time-out period (specified in S7), the
data will be retransmitted. This will continue until an acknowledgement is
received or the modem is reset. Likewise any UDP packets received by the
RLXIC-SV are expected to have this simple header. The RLXIC-SV will issue an
acknowledgement for any valid packets which are received.
To configure the RLXIC-SV for a normal UDP session, you need to set the
Startup Mode Default to 73 (ATMD73). If you are using two modems, configure
the Destination IP and Port in each to point to each other. Serial data will then be
sent reliably between the two.
Caution:
Although it adds reliability, the simple implementation of the Reliable UDP mode in the
RLXIC-SV does not check for duplicate packets.
