Problem with TAU configuration for PSM mode

[Isaia Spinelli]

Hello,

Here is some information from my environment :

1. nRF9160 DK
2. SIM iBASIS 
3. Country: Suisse
4. Operator: Swissom AG 
5. roaming mode
6. Use LTE Link Monitor

I have some questions:

First, I configure the modem in PSM mode with a TAU of 3h and an active time of 0 sec:

We can see with the return of + CEREG that the Active time is indeed at 0 and the TAU (10min * 20 = 200min) 3.3 hours

When I read this information via the "AT%XMONITOR" command, the last two arguments are <Periodic-TAU-ext> and <Periodic-TAU>. Could someone explain to me the meaning and use of these please?

Here is my problem, I am trying to configure a TAU of 10min and an active time of 1 min:

And I end up with an inactive TAU ...

Is this due to the fact that iBASIS is limited? or Swisscom? or roaming mode?

Thank you in advance for your answers,

Have a good day !

Pierre

[Albrecht Markus Schellenberger]

Hello Pierre,

When I read this information via the "AT%XMONITOR" command, the last two arguments are <Periodic-TAU-ext> and <Periodic-TAU>. Could someone explain to me the meaning and use of these please?

Nowadays, the <Periodic-TAU> argument is optional. You should always check the <Periodic-TAU-ext> for reasonable values first. See also the description of the %XMONITOR-command:

https://infocenter.nordicsemi.com/topic/ref_at_commands/REF/at_commands/nw_service/xmonitor_set.html

Is this due to the fact that iBASIS is limited? or Swisscom? or roaming mode?

To start with it could be good to know that the <Periodic-TAU> argument in +CEREG represents the <Periodic-TAU-ext> value.

https://infocenter.nordicsemi.com/topic/ref_at_commands/REF/at_commands/nw_service/cereg_read.html

Now, since you got the <Active-Time> of 1min you requested from the operator, you should have PSM. Please doublecheck via %XMONITOR. My assumption is that since you did not receive a value via the <Periodic-TAU> argument in +CEREG, you probably will find the provided TAU from the operator in the <Periodic-TAU> field of %XMONITOR.

Regards,

Markus

[Isaia Spinelli]

Hello Markus,

Thank you for your answer !

Indeed it is strange that the value of <Active-Time> of 1min is well understood but not <Periodic-TAU>. As requested, I double checked with the command "% XMONITOR" but I still see an inactive value (11100000).

Do you have any idea why the value of 10min is not accepted, like all values less than 3h?

Regards,

Pierre

[Albrecht Markus Schellenberger]

Hello Pierre,

Well yes, the <Periodic-TAU-ext> parameter in %XMONITOR says ‘deactivated’, which is equal to what you received as answer in <Periodic-TAU> of +CEREG.

But the <Periodic-TAU> value in %XMONITOR is ‘01001010’ (60min), which means your operator does not allow you the desired TAU of 10min but tells you it is 60min instead.

My assumption here is:

The first time you requested a TAU of 3h, the answer you got from the operator in +CEREG was ‘00010100’ (3.3h). Since 3.3h is greater than the max value you can receive as a <Periodic-TAU> argument in %XMONITOR (which is ‘01011111’ = 3.1h), the operator interprets your requested TAU as a <Periodic-TAU-ext> value.

As mentioned before, the <Periodic-TAU> argument in +CEREG actually represents a <Periodic-TAU-ext> value. Since your request of 3h was interpreted as 3.3h by the operator, a <Periodic-TAU-ext> argument had to be used, which explains the answer of ‘00010100’ in +CEREG.

Your second request of 10min was not interpreted as a <Periodic-TAU-ext> value by the operator though, which is why you received ‘11100000’ as answer in the <Periodic-TAU> field of +CEREG. Instead, you got the answer from the operator in the designated <Periodic-TAU> argument of %XMONITOR. This makes sense in a way, since <Periodic-TAU> actually not represents an extended value.

I hope this was not too confusing after all. Unfortunately, there are no standards or common ways of use here. It is up to the operator itself and can differ quite a bit.

Cheers!

Markus

[Isaia Spinelli]

Hi Marku,

Thank you for your answer I understand now.

I have one last question, why does the network never allow me a TAU period of less than 60 min?

Thanks again and have a nice day

Pierre

[Albrecht Markus Schellenberger]

Hello Pierre,

obviously, Swisscom has decided to set 60min as the minimum allowed value.

This decision is made by each operator itself, but let me give you some possible reasons:

1. From a device point of view, a PSM less than 60min might not make any sense. Since the device can transmit at all times, going to PSM and waking up too often might cost more power than staying alive during a longer period of time.
2. From an operator point of view, handling data of many devices switching between PSM and alive mode frequently can be a challenge.

I hope my answer could help you. Have a good weekend!

Cheers,

Markus