Socket behavior API mode behavior for outgoing UDP data
Digi XBee® 3 Cellular LTE Cat 1 AT&T Smart Modem User Guide
162
API mode behavior for outgoing UDP data
To send a UDP datagram to a remote host, send a Transmit (TX) Request: IPv4 - 0x20 frame to the
XBee Smart Modem's serial port specifying the destination address and destination port of the
remote host. If you use a source port of 0, the device creates a new socket for the purpose of sending
to the remote host. The XBee Smart Modem supports a finite number of sockets, so if you need to
send to many destinations:
1. The socket must be closed after use.
or
2. You must use the socket specified by the C0 (Source Port) setting.
To use the socket specified by the C0 setting, in the Transmit TX request frame use a source port that
matches the value configured for the C0 setting.
The device sends a Transmit (TX) Status - 0x89 frame in reply to the Transmit TX Request to indicate
the status of the request. A status of 0 indicates the connection and/or data was successful, a value of
0x32 indicates a temporary Resource Error (see Socket limits in API mode), and other values indicates
a failure.
Any data received on the UDP socket is sent out the XBee Smart Modem's serial port as a Receive (RX)
Packet: IPv4 - 0xB0 frame.
A UDP socket is closed when:
n No data has been sent or received for longer than the socket timeout set by TM (IP Client
Connection Timeout).
n A transmit TX Request is sent with the CLOSE flag set.
API mode behavior for incoming TCP connections
For incoming connections and data in API mode, the XBee Smart Modem uses the C0 (Source Port)
and IP (IP Protocol) settings to specify the listening port and protocol used. The XBee Smart Modem
does not currently support the TLS protocol for incoming connections.
When the IP setting is TCP the XBee Smart Modem allows multiple incoming TCP connections on the
port specified by the C0 setting. Any data received on the connection is sent out the XBee Smart
Modem's serial port as a Receive (RX) Packet: IPv4 - 0xB0 frame.
To send data from the device over the connection, use the Transmit (TX) Request: IPv4 - 0x20 frame
with the corresponding address fields received from the Receive RX frame. In other words:
n Take the source address, source port, and destination port fields from the Receive (RX) frame
and use those respectively as:
n The destination address, destination port, and source port fields for the Transmit (TX) Request
frame.
A connection is closed when:
n The remote end closes the connection.
n No data has been sent or received for longer than the socket timeout set by TS (IP Server
Connection Timeout).
n A Transmit (TX) Request frame is sent with the CLOSE flag set.
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