I could extract that from log file:
Sat Jan 6 15:27:03 2018 daemon.notice netifd: Interface ‘modem’ is now down
Sat Jan 6 15:27:03 2018 daemon.notice netifd: Interface ‘modem’ is setting up now
Sat Jan 6 15:27:03 2018 user.notice mwan3: ifdown interface modem (unknown)
Sat Jan 6 15:27:15 2018 kern.info kernel: [ 824.580000] usb 1-1.2: new high-speed USB device number 5 using ehci-platform
Sat Jan 6 15:27:15 2018 kern.info kernel: [ 824.700000] option 1-1.2:1.0: GSM modem (1-port) converter detected
Sat Jan 6 15:27:15 2018 kern.info kernel: [ 824.700000] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB0
Sat Jan 6 15:27:15 2018 kern.info kernel: [ 824.710000] option 1-1.2:1.1: GSM modem (1-port) converter detected
Sat Jan 6 15:27:15 2018 kern.info kernel: [ 824.720000] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB1
Sat Jan 6 15:27:15 2018 kern.info kernel: [ 824.730000] option 1-1.2:1.2: GSM modem (1-port) converter detected
Sat Jan 6 15:27:15 2018 kern.info kernel: [ 824.730000] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB2
Sat Jan 6 15:27:15 2018 kern.info kernel: [ 824.740000] option 1-1.2:1.3: GSM modem (1-port) converter detected
Sat Jan 6 15:27:15 2018 kern.info kernel: [ 824.740000] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB3
Sat Jan 6 15:27:15 2018 kern.info kernel: [ 824.770000] qmi_wwan 1-1.2:1.4: cdc-wdm0: USB WDM device
Sat Jan 6 15:27:15 2018 kern.info kernel: [ 824.780000] qmi_wwan 1-1.2:1.4 wwan0: register ‘qmi_wwan’ at usb-ehci-platform-1.2, WWAN/QMI device, 8a:83:3b:7d:21:71
Sat Jan 6 15:27:30 2018 daemon.notice netifd: modem (10850): Waiting for network registration
Sat Jan 6 15:28:17 2018 daemon.notice netifd: modem (10850): Starting network internet.telekom
Sat Jan 6 15:28:17 2018 daemon.notice netifd: modem (10850): Starting DHCP
Sat Jan 6 15:28:17 2018 daemon.notice netifd: Interface ‘modem_4’ is enabled
Sat Jan 6 15:28:17 2018 daemon.notice netifd: Interface ‘modem_6’ is enabled
Sat Jan 6 15:28:17 2018 daemon.notice netifd: Interface ‘modem’ is now up
Sat Jan 6 15:28:17 2018 daemon.notice netifd: Network device ‘wwan0’ link is up
Sat Jan 6 15:28:17 2018 daemon.notice netifd: Network alias ‘wwan0’ link is up
Sat Jan 6 15:28:17 2018 daemon.notice netifd: Interface ‘modem_4’ has link connectivity
Sat Jan 6 15:28:17 2018 daemon.notice netifd: Interface ‘modem_4’ is setting up now
Sat Jan 6 15:28:17 2018 daemon.notice netifd: Interface ‘modem_6’ has link connectivity
Sat Jan 6 15:28:17 2018 daemon.notice netifd: Interface ‘modem_6’ is setting up now
Sat Jan 6 15:28:17 2018 daemon.notice netifd: modem (10850): Command failed: Unknown error
Sat Jan 6 15:28:17 2018 daemon.notice netifd: modem (10850): Command failed: Unknown error
Sat Jan 6 15:28:17 2018 user.notice root: qmi bringup failed, retry in 15s
Sat Jan 6 15:28:18 2018 daemon.notice netifd: modem_4 (13309): udhcpc (v1.24.1) started
Sat Jan 6 15:28:18 2018 daemon.notice netifd: modem_4 (13309): Sending discover…
Sat Jan 6 15:28:21 2018 daemon.notice netifd: modem_4 (13309): Sending discover…
Sat Jan 6 15:28:24 2018 daemon.notice netifd: modem_4 (13309): Sending discover…
Sat Jan 6 15:28:29 2018 user.warn mwan3: Could not find gateway for interface modem (wwan0)
Sat Jan 6 15:28:30 2018 user.notice firewall: Reloading firewall due to ifup of modem (wwan0)
Sat Jan 6 15:28:40 2018 daemon.warn odhcpd[1348]: DHCPV6 SOLICIT IA_NA from 0003000180ea23317c24 on eth1: ok fd63:f302:b65b::d99/128
Sat Jan 6 15:29:53 2018 kern.info kernel: [ 982.530000] IPv6: ADDRCONF(NETDEV_UP): tmp.phy0: link is not ready