Roaming SIM card from Soracom sluggish on NB-IoT

[Burt]

Hi,

If I use a roaming Soracom SIM card in NB-IoT mode and with asset_tracker_v2 application, without doing anything fancy, it will take a very long time, over 4 minutes, to connect to an LTE network. But I found Soracom's web page https://www.soracom.io/blog/sim-activation-cellular-modem-fix/. That has given me hints to add

CONFIG_LTE_LOCK_BANDS=y
CONFIG_LTE_LOCK_BAND_MASK="1000"  #band 4

or

CONFIG_LTE_LOCK_PLMN=y
CONFIG_LTE_LOCK_PLMN_STRING="310260" #MCC=Puerto Rico MNC=T-Mobile

or both and either one will greatly speed things up. I am in North Carolina: I do wonder if it is safe to send out units to various places in the US locking down the network like shown or if moving away from my house there will be problems. Do you have ideas about that?

My other question involves suggestion #3 in the Soracom document I linked to: 3. Allow the SIM to pre-cache network information by placing it into a device known to be more efficient at searching. Once it’s connected, the SIM will cache the network information, and will use that cached information to connect much faster when placed back into the original device.

Can you tell me how I can pre-cache network information or (in your opinion) what it is they are telling me to do? I do not see any evidence of "pre-caching" in the SIM: if I do nothing with the LOCK_BANDS or LOCK_PLMN, the system will take 4 minutes to connect EVERY time I reboot--not just the first time like I would expect with caching.

Thanks very much.

Burt Silverman

[JONATHAN LL]

Hi, 

Have you been in contact with Soracom? 

Can you provide some logs of the situation where this is happening. 

This connection time is repeatable multiple times with same SIM card and and device? 

Regards,
Jonathan

[Burt]

Hi Jonathan,

Thank you for the useful information regarding CFUN and %XCOUNTRYDATA.

Regarding your questions, I have not been in contact with Soracom. I don't have any interesting logs, but I can say that the connection time is repeatable multiple times with the same SIM card. So, I guess there is no special SIM caching to automatically speed things up (as the connection time is repeatable and doesn't decrease), and no obvious way to change that from the asset tracker v2 application. I am going to assume that the techniques available to me are what you have presented here, unless you come up with anything else. Thanks again.

Burt

[JONATHAN LL]

Hi Burt,

Don't have anything else to contribute with not extra logs or such to look at. My guess is that CFUN=0 is you best friend here. But if there is any issues or related questions feel free to ask and i will do my best to help. 

Regards,
Jonathan