There are several ways network providers could calculate packet size from a device causing differences in pricing structure.
- Depending on the pay structure, some networks might round to the nearest whole number
- It’s also possible to charge for the entire on-air packet, which is a suggestive 24 bytes long
- Packets starts with a preamble and hardware layer LoRa header that is undocumented and generally not counted by networks (20.25 bytes)
- 8 – 23 bytes of LoRaWAN header (depending on number of mac commands going up)
- An optional port number (1 byte)
- User payload for that port (11 bytes max in most restrictive regions)
- 4 bytes of CRC
- So the total size for an 11 byte payload, not including the initial preamble, is 8 + 1 + 11 + 4 = 24 bytes
How much data do the devices use per month?
This depends on a few factors:
- Device Type: the type of device affects how much data is sent and how often
- Device Setup: what is the device setup to do?
- Network: what is the minimum connection charge?
Keep in mind:
- The minimum connection charge could have a massive effect on the data usage. Consider Helium. Helium provides connectivity through the purchase of data credits. Each data credit equals a 24 byte packet. Helium only calculates based on the payload itself but rounded up to the nearest data credit.
- As a general rule of thumb you would expect to use 1 data credit on Helium for each uplink on the Oyster
The PDF attachments found below contain the payload structure for the different LoRaWAN devices.