Sierra Wireless 20070914 - Manual (Page 81)

Data Communication and Host Modes
Rev 3.0B Feb.08 68
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
doesn’t 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 PinPoint X 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 PinPoint X are expected to have this simple
header. The PinPoint X will issue an acknowledgement for any
valid packets which are received.
To configure the PinPoint X 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 does not check for duplicate packets.