Downlink Modes
Devices do not form connections the same way you might expect
other network devices to maintain connections. The Symphony Link Module for example
will only establish a connection and will not communicate with the Gateway
until it has a message to send or receive. The rules around receiving the
DownlinkMessage
are what define the Downlink Modes.
Mailbox Mode
When a Symphony Link Module or LTE CAT-M1 Module is in Mailbox Mode, the module does not
constantly communicate with its associated gateway outside of initial connection.
The module will just “Check its mailbox” at certain intervals. When a Mailbox
Check occurs, the module can receive a “Pending” DownlinkMessage
that
the Gateway has in its Mailbox.
From a cloud perspective, sending a DownlinkMessage
to a module in
Mailbox Mode should include a time_to_live_s parameter in the
Module.send_message()
call
my_mod = account.get_module("$301$0-0-0-03000XXXX")
dl_msg = mod.send_message(b'hello world', time_to_live_s=300.0)
This time_to_live_s value represents the amount of time (in seconds) that the
Mailbox Message can sit on the gateway’s Mailbox before that message “Expires”.
If the module performs a Mailbox Check within the time_to_live_s of the message,
since it was received by their gateway, then the module will receive that
DownlinkMessage
. Otherwise, if the module checks its Mailbox after the
message’s time_to_live_s, the gateway will report no messages to downlink to
the module.
Downlink Always On
This mode allows constant check-ins from the Symphony Link Module to the Gateway,
allowing the fastest possible downlink to occur. This mode does not require any
of the optional parameters of the Module.send_message()
, however, they can
be used when necessary.
Warning
The LTE CAT-M1 Module does not support Downlink Always On Mode.