Ever wonder why your roaming device fails to connect, even with good signal?
In this real-world log, we manually forced the modem to attach to a specific operator seven times using AT+COPS=1,2,“44010”,7.
The first six attempts returned +CME ERROR: 30 (no network service)
On the 7th attempt: accepted and service was granted.
This wasn’t a signal issue. The SIM simply preferred a different operator and rejected multiple attempts to the non-preferred operator until the fallback condition was met.
Lessons:
• +COPS and +CEREG? are essential tools for understanding attach behavior.
• Global SIMs often rotate IMSIs or delay fallback in hope of finding their preferred roaming partner.
• Retry logic i.e. T3247 Attach Reject Back-off Timer or T3346 TAU Reject Back-off Timer and modem handling can dramatically impact attach delay and user experience.
If you see attach failure despite good signal, the issue may be SIM logic and not RF.
LinkedIn: 