请教一个问题，openwrt + EC20，同样的配置，有的sim卡可以正常的拨号上网，有的注册网络后，不能正常的获取IP，提示提示Modem hangup，Connection terminated，然后断开连接，感觉是哪个参数没设置对。
不正常的日志信息（物联网卡，固定IP）
Mon Oct 11 16:38:00 2021 daemon.info [3096]: [modem0] simple connect started…
Mon Oct 11 16:38:00 2021 daemon.info [3096]: [modem0] simple connect state (3/8): enable
Mon Oct 11 16:38:00 2021 daemon.info [3096]: [modem0] state changed (disabled → enabling)
Mon Oct 11 16:38:05 2021 daemon.info [3096]: [modem0] power state updated: on
Mon Oct 11 16:38:05 2021 daemon.info [3096]: [modem0] simple connect state (4/8): wait to get fully enabled
Mon Oct 11 16:38:05 2021 daemon.info [3096]: [modem0] state changed (enabling → enabled)
Mon Oct 11 16:38:05 2021 daemon.info [3096]: [modem0] simple connect state (5/8): register
Mon Oct 11 16:38:05 2021 daemon.info [3096]: [modem0] 3GPP registration state changed (unknown → registering)
Mon Oct 11 16:38:05 2021 daemon.info [3096]: [modem0] 3GPP registration state changed (registering → home)
Mon Oct 11 16:38:05 2021 daemon.info [3096]: [modem0] state changed (enabled → registered)
Mon Oct 11 16:38:06 2021 daemon.info [3096]: [modem0] simple connect state (6/8): bearer
Mon Oct 11 16:38:06 2021 daemon.info [3096]: [modem0] simple connect state (7/8): connect
Mon Oct 11 16:38:06 2021 daemon.info [3096]: [modem0] state changed (registered → connecting)
Mon Oct 11 16:38:06 2021 daemon.info [3096]: [modem0] state changed (connecting → connected)
Mon Oct 11 16:38:06 2021 daemon.info [3096]: [modem0] simple connect state (8/8): all done
Mon Oct 11 16:38:06 2021 daemon.notice netifd: wwan0 (21663): successfully connected the modem
Mon Oct 11 16:38:06 2021 daemon.notice netifd: wwan0 (21663): signal refresh rate is not set
Mon Oct 11 16:38:06 2021 daemon.notice netifd: wwan0 (21663): network operator name: CHN-UNICOM
Mon Oct 11 16:38:06 2021 daemon.notice netifd: wwan0 (21663): network operator MCCMNC: 46001
Mon Oct 11 16:38:06 2021 daemon.notice netifd: wwan0 (21663): registration type: home
Mon Oct 11 16:38:06 2021 daemon.notice netifd: wwan0 (21663): access technology: lte
Mon Oct 11 16:38:06 2021 daemon.notice netifd: wwan0 (21663): signal quality: 80%
Mon Oct 11 16:38:06 2021 daemon.notice netifd: wwan0 (21663): IPv4 connection setup required in interface wwan0: ppp
Mon Oct 11 16:38:06 2021 daemon.notice netifd: wwan0 (21663): IPv6 connection setup required in interface wwan0: ppp
Mon Oct 11 16:38:06 2021 daemon.notice pppd[22049]: pppd 2.4.9 started by root, uid 0
Mon Oct 11 16:38:06 2021 daemon.info pppd[22049]: Using interface ppp0
Mon Oct 11 16:38:06 2021 daemon.notice pppd[22049]: Connect: ppp0 <–> /dev/ttyUSB2
Mon Oct 11 16:38:07 2021 user.notice ModemManager: hotplug: add network interface ppp0: event processed
Mon Oct 11 16:38:07 2021 user.notice ModemManager: hotplug: event reported: action=add, name=ppp0, subsystem=net
Mon Oct 11 16:38:07 2021 user.notice ModemManager: hotplug: error: parent device sysfspath not found
Mon Oct 11 16:38:07 2021 daemon.notice pppd[22049]: Modem hangup
Mon Oct 11 16:38:07 2021 daemon.notice pppd[22049]: Connection terminated.
Mon Oct 11 16:38:07 2021 user.notice ModemManager: hotplug: remove network interface ppp0: event processed
Mon Oct 11 16:38:07 2021 user.notice ModemManager: hotplug: event reported: action=remove, name=ppp0, subsystem=net
Mon Oct 11 16:38:08 2021 daemon.info pppd[22049]: Exit.
正常的日志信息（物联网卡，不是固定IP）
Tue Oct 12 12:42:28 2021 daemon.notice netifd: wwan0 (5018): signal quality: 80%
Tue Oct 12 12:42:29 2021 daemon.notice netifd: wwan0 (5018): IPv4 connection setup required in interface wwan0: ppp
Tue Oct 12 12:42:29 2021 daemon.notice netifd: wwan0 (5018): IPv6 connection setup required in interface wwan0: ppp
Tue Oct 12 12:42:29 2021 daemon.notice pppd[5247]: pppd 2.4.9 started by root, uid 0
Tue Oct 12 12:42:29 2021 daemon.info pppd[5247]: Using interface ppp0
Tue Oct 12 12:42:29 2021 daemon.notice pppd[5247]: Connect: ppp0 <–> /dev/ttyUSB2
Tue Oct 12 12:42:29 2021 user.notice ModemManager: hotplug: add network interface ppp0: event processed
Tue Oct 12 12:42:29 2021 user.notice ModemManager: hotplug: event reported: action=add, name=ppp0, subsystem=net
Tue Oct 12 12:42:29 2021 user.notice ModemManager: hotplug: error: parent device sysfspath not found
Tue Oct 12 12:42:30 2021 daemon.warn pppd[5247]: Could not determine remote IP address: defaulting to 10.64.64.64
Tue Oct 12 12:42:30 2021 daemon.notice pppd[5247]: local IP address 10.2.236.50
Tue Oct 12 12:42:30 2021 daemon.notice pppd[5247]: remote IP address 10.64.64.64
Tue Oct 12 12:42:30 2021 daemon.notice pppd[5247]: primary DNS address 221.5.88.88
Tue Oct 12 12:42:30 2021 daemon.notice pppd[5247]: secondary DNS address 116.116.116.116
Tue Oct 12 12:42:30 2021 daemon.notice netifd: Network device ‘ppp0’ link is up
Tue Oct 12 12:42:30 2021 daemon.notice netifd: Interface ‘wwan0’ is now up
Tue Oct 12 12:42:30 2021 daemon.info dnsmasq[1]: reading /tmp/resolv.conf.d/resolv.conf.auto
Tue Oct 12 12:42:30 2021 daemon.info dnsmasq[1]: using nameserver 221.5.88.88#53
Tue Oct 12 12:42:30 2021 daemon.info dnsmasq[1]: using nameserver 116.116.116.116#53