RLXIC-SG
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Intelligent Cellular
Data Communication and Host Modes
RadioLinx Intelligent Cellular Serial Modem for Global GPRS/GSM
User Manual
Page 58 of 136
ProSoft Technology, Inc.
May 29, 2009
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-SG
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-SG are expected to have this simple header. The RLXIC-SG will issue an
acknowledgement for any valid packets which are received.
To configure the RLXIC-SG 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-SG does not check for duplicate packets.
UDP Multicast Mode
UDP Multicast mode results in any data received from the host serial port being
sent to all the clients in the address list. The remote port number is taken from
S53. To avoid flooding the network, the packets are sent to each client with a
20ms pause in between. The receipt of UDP packets works as in normal UDP
mode (that is, bound by the value S53 and/or AIP). Because it may take a while
to transmit the data to all hosts (especially if all 20 Modbus entries are used and
name resolutions are required), new data received from the host port is buffered
until current transmissions to all hosts are finished.
Enter the list of target IPs in the address list (ADDR LIST). The index numbers in
the list are not used. Configure for a normal UDP session. Set the Startup Mode
Default to 83 (ATMD83). Configure the Destination port to match the device port
of the remote modems.
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