Data Communication and Host Modes
RLXIC-EH
♦
Intelligent Cellular
User Manual
RadioLinx Intelligent Cellular Ethernet Gateway for HSUPA (3G GSM) Networks
ProSoft Technology, Inc.
Page 51 of 111
May 29, 2009
7.3.3 UDP
Auto
Answer
UDP auto answer (previously called UDP half-open) is set with S82=2. When set,
the RLXIC-EH will automatically establish a UDP session to the source IP
address, and port of the UDP packet received. The RLXIC-EH 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.
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-EH
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-EH are expected to have this simple header. The RLXIC-EH will issue an
acknowledgement for any valid packets which are received.
Summary of Contents for RLXIC-EH
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