Multi-Tech MultiConnect mDot MTDOT Series, Developer'S Manual

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FOTA (FUOTA) OVERVIEW
12 MultiConnect
®
mDot
TM
MTDOT Developer Guide for Japan
Chapter 3 – FOTA (FUOTA) Overview
This requires mDot firmware Version 3.1 or higher and a Conduit
®
with AEP (mPower) 1.6 or higher.
Firmware Over the Air (FOTA) also known as Firmware Upgrade Over the Air (FUOTA) is a way to upgrade Dot end
devices using multicast and file fragmentation packages defined in the LoRaWAN specification. FOTA allows the
Conduit to update the firmware on many Dots at once using multicast and error correction packets. FOTA is still in
its early stages of revision and does have potential problems, which are included in this topic.
Note: FOTA is enabled by default.
To start the FOTA process, the Conduit sends two setup downlinks to the Dot. First, the Conduit then sends a
multicast session setup request to the Dot. The Dot responds with a multicast session setup answer. The Conduit
sends a fragmentation setup request. The Dot responds by sending back a fragmentation setup answer. Once
setup is complete, the Dot waits until the start of the multicast session. At the start of the session, the Dot
switches to class C with the specified data rate and frequency to receive the file fragments sent by the Conduit.
After the file fragments are sent, the Conduit starts sending parity fragments. At any point when the Dot is able to
reconstruct the firmware file, the CRC is calculated and the CRC message id sent in Class A. This could happen any
time after the last fragment is sent to after the last parity is sent.
For details on the FOTA AT Commands, go to mDot AT Command Reference Guide (S000643).
FOTA Stages
A FOTA session has four stages: 1) session setup, 2) fragmentation, 3) parity, and 4) verification.
Session Setup
For a multicast session to work with class A devices, a start time must be agreed upon by the network server and
each device. This requires the devices to synchronize their time with the server. These critical tasks are done
during session setup.
Class A devices must periodically send uplinks to open downlink windows making the time required to complete an
operation setup directly tied to the frequency of device uplinks. For each device involved in the operation, some
extra time should be added to the total setup time to account for latency in queuing each device’s message.
Setup messages are sent up to 3 times. Worst-case timing for operation setup would be ((3 * device_uplink_period
* 2) + (overhead * number_of_devices)).
The included diagram illustrates the events that occur during a best-case setup with no messages missed and well-
timed device uplinks. Each device follows these steps:
1. FOTA operation queues Multicast setup message with network server.
2. Device sends an uplink.
3. Multicast setup message is downlinked to the device.
4. Device sends a multicast setup response.
5. FOTA operation queues fragmentation setup message.
6. Device sends an uplink.
7. Fragmentation setup is downlinked to the device.
8. Device sends a fragmentation setup response from device.