dail_3gpp connection sequence query

Gupta, Anubhav Anubhav.Gupta at digi.com
Wed Jun 9 15:41:55 UTC 2021

Hi all,

I am currently working on a 450MHz modem where as per the vendor the dial step is to send following commands to the modem:

AT+CGATT=0 //Sleep 2 seconds

As soon as I send AT+CGATT=0, the modem receives unsolicited message (CEREG) which causes the registration state to go into idle. This causes Modem Manager to disconnect. I am trying to understand if this is how other modems behaves for dial_3gpp and how exactly I can handle such a case. Can someone please provide some guidance?

<debug> [000027.244498] [modem3/ttyACM0/at] --> 'AT+CGATT=0<CR>'
<debug> [000028.276663] [modem3/ttyACM0/at] <-- '<CR><LF>+CEREG: 0,"","",7<CR><LF>'
<debug> [000028.277071] [modem3] building consolidated registration state: cs 'unknown', ps 'unknown', eps 'idle', 5gs 'unknown' --> 'idle'
<info>  [000028.277197] [modem3] 3GPP Registration state changed (home -> idle)
<debug> [000028.277768] [modem3] 3GPP location updated (MCC: '0', MNC: '0', location area code: '0', tracking area code: '0', cell ID: '0')
<debug> [000028.278253] [modem3/bearer3] bearer not allowed to connect, not registered in 3GPP network
<debug> [000028.278340] [modem3/bearer3] forcing disconnection

Anubhav Gupta
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