The External Port is used to connect the GNSS receiver to the external device, such as telemetry radio.

From Left to Right: 5V Rx Tx SCL SDA GND

The Connector model: JST-GH-1.25 6-pin

I2C interface is for build-in compass, only specific SKUs support this interface.

For example:

Use telemetry radio to broadcast rtk corrections to rover station