Unstable network manager connection


i bought a Sierra Wireless card EM7455, that I would like to use for a 4G internet connection.

Strange is, that sometimes the connection is steady without any interruptions. But on some days it is either not working at all, or on and off.

Today I have an LTE connection with RSSI: -71 dBm

There is nothing strange with dmesg:

[    8.863745] cdc_mbim 1-1.3:1.12: cdc-wdm0: USB WDM device
[    8.871548] cdc_mbim 1-1.3:1.12 wwan0: register 'cdc_mbim' at usb-3f980000.usb-1.3, CDC MBIM

But on Luci under network interfaces, the interface goes between the following three statuses:

  • Error: Network device is not present
  • Error: Modem connection in progress. Please wait. This process will timeout after 2 minutes.
  • IPv4: x.x.x.x/24

I use the card via modem manager. My config is as follows:

config interface 'sierra'
	option proto 'modemmanager'
	option device '/sys/devices/platform/soc/3f980000.usb/usb1/1-1/1-1.3'
	option iptype 'ipv4'
	option apn '****'
	option pincode '****'

But maybe there is a better way to use this card. Maybe via mbim? But how would I connect via mbim?

Thanks for your help