Uplink payload format
On receiving an uplink, the Relay creates and re-transmits a Relay encapsulated LoRaWAN payload. The Relay encapsulation overhead is 14 bytes.
Bytes:
| 1 byte | 5 bytes | 4 bytes | n bytes | 4 bytes |
|---|---|---|---|---|
| Uplink MHDR | Uplink Metadata | Relay ID | LoRaWAN PHYPayload | MIC |
Uplink MHDR
Bits:
| 7..5 | 4..3 | 2..0 |
|---|---|---|
| MType | Payload type | Hop count |
- MType =
111(= Proprietary LoRaWAN MType) - Payload type =
00(= Relayed uplink) - Hop count =
000= 1, ...111= 8
Note: The hop count is incremented each time the uplink payload is relayed by an other Relay Gateway. As this changes the uplink payload, the MIC must be re-calculated.
Uplink Metadata
Bytes:
| 2 bytes | 1 byte | 1 byte | 1 byte |
|---|---|---|---|
| Uplink ID + Data-rate | RSSI | SNR | Channel |
Uplink ID + Data-rate
Bits:
| 15..4 | 3..0 |
|---|---|
| Uplink ID | Data-rate |
Uplink ID
Unique identifier (to the Relay Gateway) identifying the received uplink. Internally the Relay Gateway must temporarily store this in the Uplink table.
Data-rate
Uplink data-rate, unsigned integer with a minimum value of 0 and a maximum
value of 15.
RSSI
Encoded as RSSIdBm = -1 x RSSI
SNR
Bits:
| 7..6 | 5..0 |
|---|---|
| RFU | SNR |
SNR is a signed integer with a minimum value of -32 and a maximum value of
31.
Channel
Uplink channel, unsigned integer.
Relay ID
This contains the Relay ID which received the uplink from the End Device.
Bytes:
| 4 bytes |
|---|
| Relay ID |
LoRaWAN PHYPayload
The received LoRaWAN PHYPayload.
MIC
Message integrity code, used by other Relay and Border gateways to check the data integrity of the packet. This is obtained by calculating the CMAC over the uplink payload (- MIC bytes), and using the first 4 bytes of the calculated CMAC as MIC.