Cellular connection process
Connecting
Digi XBee Cellular LTE Cat 1 Embedded Modem User Guide
39
Connecting
In normal operations, the XBee Cellular Modem automatically attempts both a cellular network
connection and a data network connection on power-up. The sequence of these connections is as
follows:
Cellular network
1. The device powers on.
2. It looks for cellular towers.
3. It chooses a candidate tower with the strongest signal.
4. It negotiates a connection.
5. It completes cellular registration; the phone number and SMS are available.
Data network connection
1. The network enables the evolved packet system (EPS) bearer with an access point name
(APN). See
if you have APN issues.
2. The device negotiates a data connection with the access point.
3. The device receives its IP configuration and address.
4. The
command now returns a
0
and the sockets become available.
Data communication with remote servers (TCP/UDP)
Once sockets become available, communication with remote servers can be initiated in several ways:
n
Transparent mode data received over a serial connection (see
and
for timing).
n
API mode:
Transmit (TX) Request: IPv4 - 0x20
received over the serial connection.
n
Digi Remote Manager connectivity begins.
Data communication begins when:
1. A socket opens to the remote server.
2. Data is sent.
3. The XBee Cellular Modem listens for incoming data.
Data connectivity ends when:
1. The server closes the connection.
2. The
TM
timeout expires (see
TM (TCP Client Connection Timeout)
).
3. The cellular network may also close the connection after a timeout set by the network
operator.
Disconnecting
When the XBee Cellular Modem is put into Airplane mode or deep sleep is requested:
