What is the actual byte breakdown of overhead and payload sent over the air in 9160 to LTE-M1 network?

[Johan]

We have an implementation where we need to limit data, and to be able to KNOW how much is actually being sent with the operator, to limit costs.

In a normal Ethernet condition this overhead applies I believe (source: https://forum.automationdirect.com/forum/communications/119077-modbus-tcp-vs-ethernet-ip-implicit-overhead)

In nRF9160 and the SDK, the maximum packet size is currently 2048 bytes. This means Nordic is using a modified version of the above?

We need answers about the exact amount of data spent in packages.

Also since we use TLS, we also need to know the additional overhead data added for packages encrypted.

Who can take this one in Nordic and give answers?

[Heidi]

Hi, unfortunately checking the data usage on the nRF9160 is not a supported feature nor has it been planned in the future. When it comes to the structure of the data packets, that is defined in the LTE-M specifications defined by the 3GPP. 

Best regards,

Heidi

[Johan]

That's unfortunate.

How do you suggest we protect our customer for whom we build a product using 9160, from overusing data / month if we have NO feedback from your design on data usage?

We know what we write to the socket, but what is appended by you, hidden, we have NO CLUE of.

[Heidi]

We have no way of counting how much data is transferred over the interface. You could do this at the application level but it seems like a very difficult solution.

Have you considered contacting your SIM-card provider and asking them to provide the data usage. This would also give the most accurate value.

As far as anything that is appended to the payload, this would be defined by the TCP / IP protocol and the information is available for anybody willing to look into it.

Good luck!

Heidi

[Johan]

Yes I guess we will contact the operator/sim-card provider to get access to some live usage for guiding us in implementation some what.

Since we use activated encryption (TLS and X.509) in your modem as well, there are more happening, but perhaps I can google the protocol for that and get an approximate info.

All right, thanks Heidi.