Does XBee LTE-M entering and leaving PSM incur extra metered traffic?

Question

I am trying to determine which is more expensive:

1) Adding additional battery capacity to enable the XBee3 to stay active
or
2) Allow the XBee3 to enter Power Saving Mode between network data updates.

My initial logic would have been to power-down to reduce battery load, but I am finding that entering and leaving Power Saving mode seems to incurr additional network bandwidth which utimately effects the long term cost of deployment.

I am having trouble determining how large this overhead is, because usage reporting (by AT&T at least) is not very granular, and seems to be dependant on the IOT device connection state. The usage-data updates seem to coincide with the device disconnecting from the network, so the "Staying connected" usage data is extremely delayed.

When specifically asked for details, AT&T support reply was to provide me with daily usage numbers and the suggestion: "related to any Device configuration queries please reach out to the device vendor". So here I am.

I would assume that anyone designing Cellular IOT services would need to know how usage is being accumulated and charged before deploying any significant number of units... Is there a best-practices guide/whitepaper for this anywhere or any is it all just shrouded in secrecy?

Thanks.

Answer 1

The connection process on CAT M is simply different with each carrier. What you might be missing is the socket re-connection process each time you go into a sleep state.

Comments

I'm sure there are differences between carriers, but certainly in the US, we are really only talking about AT&T and Verizon, so surely there are some known benchmarks.

I don't know how/when the XBee establishes and closes a socket connection. This would be usefull information, especially if it effects data usage.

All I know is that I issue a single HTTP request once every 30 minutes. I know how much data I'm sending and receiving, but not the network overhead. I was assuming that the XBee would close the socket after the transaction was complete, but that was just an uninformed assumption (I'm having to make a lot of them lately).

Are you saying that if the XBee stays live for the entire period, the socket is held open and does not consume any keep-alive bandwidth? That's great I guess, but it does seem to go against the AT&T policy that I read stating that our devices should not hold a continuous open connection for extended periods (I guess wanting to discourage web servers?)

I'd still really like to see a white-paper on the minimum per-wake-cycle data utilization possible for an IOT device posting data to a website.

Phil.

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No, there is not. The carriers don't publish that data.

No, I am not saying that. There are keep alive functions that can be enabled and adjusted on both the XBee and on the server.  Are you taking them into account?

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>> No, there is not. The carriers don't publish that data.

OK, but as the supplier of a device that can only be used with two carrier in the US, I'm surprized that DIGI has not done a tiny bit of research and published the results so we as consumer can make smart decisions about how to use their devices.  Just saying it souldn't be rocket science.

>>  There are keep alive functions that can be enabled and adjusted on both the XBee and on the server.  Are you taking them into account?

Well, NO, because I don't have any idea how they will impact my data usage.  That's the whole point.  How can I optimize/minimize my data usage if there is no published information (that I can find) on what the XBee/AT&T connection is doing in these situations.  

I can't even use a trial and error approach because the AT&T data usage reporting is so low-tech and unpredictable.

When embarking on this Cellular IoT adventure I had no idea the industry was still in it's infancy.

Suffice it to say I will publish any data can determine with reasonable confidence.