Moving from the Iridium 9603 to the 9704: what has to change?

The 9603 and 9704 are both Iridium data modules, but they use different services: the 9603 uses SBD (Short Burst Data) and the 9704 uses IMT (Iridium Messaging Transport). Changing module is not a part swap; hardware, firmware and back end all change.

Hardware: a new board

The 9704 differs from the 9603 in size and interfaces (31.5 × 42.0 × 3.8 mm, with serial, SPI, GPIO and more), so it is not a drop-in replacement; the antenna and power design follow the 9704's own specifications. One of its design goals is to work with small antennas.

Firmware: from AT commands to a JSON serial protocol

The 9603 sends and receives SBD with AT commands; the 9704 uses a JSON-based serial protocol, so the messaging layer has to be rewritten, while sensing, storage and power-saving logic can stay. The message limit goes from a few hundred bytes to 100 KB, so compression and packet-splitting done to fit 340 bytes can be revisited. Large messages take longer, though: in N3D's tests with a full view of the sky, a message of about 100 KB took roughly three minutes each way, so plan power and sky view before sending.

Back end: from SBD CC to IMT CC

IMT messages are delivered by Iridium CloudConnect to Amazon SQS, with queues per Topic — a different delivery from SBD. On N3D's platforms, SBD devices use SBD CC and the 9704 uses IMT CC: two independent platforms, each with its own token and API. During a transition they can run side by side, with existing devices on SBD CC and new ones on IMT CC.

When the move is worth it

• You need to send photos, voice clips or larger configuration files: the 9704.
• You report position and a few sensor values and power is the tightest constraint: stay on SBD with the 9603, or the 9604 if you want cellular as well.
• You want to evaluate first: try the 9704 developer kit with IMT CC, without finishing either the device or the back end first.