Best way to minimize cellular network connectivity time?

Question

Hi there, 
 
 I'm using a slightly modified version of coap_client to test out network connectivity with a 1nce SIM card (USA). Essentially, I've modified it from a GET request to a POST request in an effort to talk with the 1nce CoAP endpoint. 
 
 I've noticed that a new nRF9151 takes almost exactly 3.5 minutes to successfully get an IP address and begin sending a message. After modifying the code to end with a graceful modem shutdown (lte_lc_power_off()), subsequent network connections after a reboot take a mere 5-10 seconds. 
 
 In my use case, users will be turning on the device for the first time. 
 
 How do I minimize the time it takes for the nRF9151 to connect to a network? 
 I understand that lte_lc_power_off() saves something to NVM. What is it saving? 
 
 Thank you!

Achim Kraus · Accepted Answer

In my experience, the 1. time is caused by a network search. The second faster connect then only works, if the found network is still reachable. It may also take longer, if that network is not reachable and also a network search is required. 
 To speedup a network search you may limit the bands to search or lock the PLMN. But both comes with the risk, that if in the area the device is turned on that network/bands are not available, the device will not connect. So at least after a timeout of searching for a network in vain, I would not limit the bands nor lock the PLMN and see, if the device gets something. 
 Hope that helps.

Achim Kraus · Answer

As long as the region doesn't change, I don't know a downside. 
 For mid future I would try to make some fallback, e.g. if the device is not able to connect for a day, then remove the "bandlock".

Best way to minimize cellular network connectivity time?

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