Hi, we are using RAK8213 BG96 modules for an IoT sensor communicating over the Telstra CatM1 network.
We are investigating the use of Power Saving Mode to lower data usage (from tcp reconnections) and power consumption.
As a test we are trying to set the active timer (T3324) to 30 seconds and the periodic timer (T3412) to 60 seconds.
We have been working with Quectel support to figure out why the modules only go to sleep for approximately 6 seconds.
In the case above, we checked the network supplied timers with
which indicates the periodic timer is set to 12H
We are also using Hologram sims on this particular module.
Are limitations around using PSM on Telstra CatM1 networks around the Albury Wodonga region that we should be aware that might be complicating things?
First up, apologies for a delay in replying to your post. I thought I had an auto prompt configured to highlight when new posts arrived and clearly that's not working. Only spotted this after returning from Xmas break.
You say you are getting 12 hours but by my calculations, 3240 seconds is 54 minutes.
Just to clarify the operation of PSM. When you issue a command to configure PSM whether it's the Quectel proprietary command AT+QPSMS or the standardised command AT+CPSMS, the module sends a request to the network. That request transits the base station and goes to a server in the network core. This means the operation of PSM is normally the same across the whole of Australia and not localised to specific places. Eg Albury.
The other thing to recognise about PSM is that when a device wakes up from sleeping, the first thing it does is sends to the network what's called a tracking area update. It's a bit like a heart beat to tell the network it's still alive. This heart beat signal is sent even if the device has no data to send. In that case the device would send it's tracking area update and then go back to sleep after T3324 expires. Don't worry, you aren't charged for the heart beat signal :-) If that heart beat signal isn't sent before the expiry of T3412 (maybe your battery has gone flat), your device is disconnected from the network. You then just have to reconnect to the network when you put fresh batteries in or whatever caused that problem is resolved.
One of the challenges with sending that heart beat is that there is a possibility for lots of devices will get into step with each. eg Imagine you have an area full of smart meters, the power goes off and they all come back on at pretty much the same time. If they are all configured with the same PSM settings, then for the next couple of years, those meters will be all waking up at pretty much the same time and sending that heart beat signal at the same time. Not something you really want to see happen.
To resolve this potential problem, the network adds a random interval to the value each device requests for it's T3412 setting. This is not a problem for the device because that doesn't mean the device has to stay asleep the whole time. For example, if a device requests an hour for it's T3412 timer setting and instead gets something longer, there is nothing stopping the device from still waking up after an hour has elapsed. That T3412 setting is the maximum amount of time the network will wait for a heart beat signal before disconnecting the device and using an hour for example, if it's a bit longer than say an hour, it just means you have a bit more time to get that heart beat signal back than you really needed.
I suspect the issue you are seeing when you display your PSM settings is the impact of the random time interval being added. You are asking for 60 seconds and the network is adding a random amount of time onto what you asked for. In the example you provided, you asked for 1 minute and were give a maximum interval to get your heart beat back of 54 minutes. Might sound like a massive increase from 1 to 54 but you need to remember that maximum setting you could have asked for is 413 days. 60 seconds is an unusually small time interval for PSM.
If that's not the issue, maybe you could contact your service provider, Hologram and see if they can shed some light on the issue.