LTE-M registered home versus registered roaming and eDRX

[tedhavelka]

Hello Devzone,

I'm in the development stages on a battery based sensor device, utilizing nRF9160 System in Package for LTE-M connectivity and application processor.  I have been working with the aws_iot sample app from Nordic's ncs v1.6.1.  In testing LTE-M based mobile network connectivity I find that our modem plus SIM card combinations always seem to register in roaming mode, rather than "registered home" home.  My question is, does this impact whether a device can be granted valid and practical eDRX timer values?

In my working situation I am not physically moving anywhere, so it is a little unclear to me why our modem and SIM card are kept in roaming mode.  In LTE-M terms is roaming more of a policy that's determined by network operators, and not necessarily a reflection of a device moving in and out of cell tower ranges?

In deference to a couple of earlier Devzone tickets which I posted, I understand that Nordic does not have specific PSM and eDRX coverage information.  These power savings features / modes are determined and sometimes granted by network operators, not the modem manufacturers.  I ask this question, however, because a part of Nordic's engineering teams has written the modem firmware.  For this I believe there may be an understanding with these engineers what functional or feature differences there are between an LTE modem in "registered home" state versus "registered roaming" state.

Thanks ahead of time for any help the team here can provide!

- Ted

[Håkon Alseth]

Hi Ted,

 

I'm in the development stages on a battery based sensor device, utilizing nRF9160 System in Package for LTE-M connectivity and application processor.  I have been working with the aws_iot sample app from Nordic's ncs v1.6.1.  In testing LTE-M based mobile network connectivity I find that our modem plus SIM card combinations always seem to register in roaming mode, rather than "registered home" home.  My question is, does this impact whether a device can be granted valid and practical eDRX timer values?

Depending on the roaming agreement that your SIM card vendor has, you can connect to a given list of other networks. This is a list inside the SIM card, named "PLMN": https://en.wikipedia.org/wiki/Public_land_mobile_network

In addition, each network has unique boundaries/settings/permissions for certain features and timing parameters, like PSM and eDRX.

That being said, even if you are able to successfully connect to a given network when roaming, it does not automatically mean that you are provided with PSM / eDRX power saving modes.

I would recommend that you contact your SIM vendor and ask specifically if they support NB1 / LTE M + if they are granted eDRX / PSM in the specific networks that you are likely to roam towards.

 

In my working situation I am not physically moving anywhere, so it is a little unclear to me why our modem and SIM card are kept in roaming mode.  In LTE-M terms is roaming more of a policy that's determined by network operators, and not necessarily a reflection of a device moving in and out of cell tower ranges?

Do you use a specific SIM from a network that does not have coverage in your area, thus you roam to another network? Or maybe its a MVNO SIM card (https://en.wikipedia.org/wiki/Mobile_virtual_network_operator - like iBasis/Hologram/etc) ?

If its the latter, you will always be roaming registered.

 

In deference to a couple of earlier Devzone tickets which I posted, I understand that Nordic does not have specific PSM and eDRX coverage information.  These power savings features / modes are determined and sometimes granted by network operators, not the modem manufacturers.  I ask this question, however, because a part of Nordic's engineering teams has written the modem firmware.  For this I believe there may be an understanding with these engineers what functional or feature differences there are between an LTE modem in "registered home" state versus "registered roaming" state.

We do not have a list of which networks can roam to what networks. You should get this information from your SIM vendor.

We have AT commands, like XMONITOR, which can show the link state.

 

Kind regards,

Håkon

[tedhavelka]

Hello Håkon,

Thank you for the fast and complete response!  To your question my team is thus far working with iBasis and Hologram SIMs.  Sounds like this puts us squarely in the virtual network operator space.  We are seeking SIMs from at least one non-virtual network operator in our geography.  My hope is that we can see some successful tests with the nRF9160 and our hardware and firmware requesting eDRX.

So far we have not been able to obtain PSM nor eDRX.  This has put something of a damper on our efforts to implement a practical battery powered sensor with celular capabilities, using the nRF9160.

Thanks also for sharing the information about Public Land Mobile Network (PLMN) lists particular to each SIM, and stored within them.  I am curious, is there any AT command (standard command or Nordic proprietary) which reports back the particular network operators stored in an MVNO SIM card?

My team is also in process of communicating with our network operators, at least those we can track down.  We've conducted a couple of meetings and have a third yet this week on the calendar.  There seems to be very little sure knowledge about who provides PSM and or eDRX in any given geography state side.

I'm poised to mark this ticket "Verified answer" but will wait to hear back on my AT command PLMN question.

Thank you again, Håkon.

- Ted

[Håkon Alseth]

Hi Ted,

 

tedhavelka said:

Thank you for the fast and complete response!  To your question my team is thus far working with iBasis and Hologram SIMs.  Sounds like this puts us squarely in the virtual network operator space.  We are seeking SIMs from at least one non-virtual network operator in our geography.  My hope is that we can see some successful tests with the nRF9160 and our hardware and firmware requesting eDRX.

yes, you're then in the "always roaming" scenario.

tedhavelka said:

So far we have not been able to obtain PSM nor eDRX. 

This would be crucial in order to extend the battery life time. A workaround in networks that does not grant PSM or eDRX can be to turn off the link (AT+CFUN=4 for instance) and wake up again when you're to communicate again.

tedhavelka said:

Thanks also for sharing the information about Public Land Mobile Network (PLMN) lists particular to each SIM, and stored within them.  I am curious, is there any AT command (standard command or Nordic proprietary) which reports back the particular network operators stored in an MVNO SIM card?

We have a generic AT+CRSM command that we support:

https://infocenter.nordicsemi.com/topic/ref_at_commands/REF/at_commands/access_uicc/crsm_set.html?cp=2_1_12_4_0

which shows an example on how to read the forbidden plmn (ie. networks you should not connect to). I would recommend that you ask the provider of the SIM for specific commands or a list of these networks.

 

Kind regards,

Håkon