4 MAC Message Formats

All LoRa uplink and downlink messages carry a PHY payload (Payload) starting with a
single-octet MAC header (MHDR), followed by a MAC payload (MACPayload)¹, and ending
with a 4-octet message integrity code (MIC).

5
6	Radio PHY layer:
		Preamble	PHDR		PHDR_CRC	PHYPayload	CRC*
7		*Figure 5: Radio PHY structure (CRC is only available on uplink messages)**
8	PHYPayload:
			MHDR		MACPayload		MIC
9							or
			MHDR		Join-Request		MIC
10							or
			MHDR	Join-Response		MIC
11				Figure 6: PHY payload structure
12	MACPayload:
				FHDR			FPort	FRMPayload
13				Figure 7: MAC payload structure
14	FHDR:
		DevAddr	FCtrl				FCnt		FOpts
15
				Figure 8: Frame header structure
16
				Figure 9: LoRa message format elements
17

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