Mobile Broadband Instability (frequent disconnects)

I have a Dell Latitude 7390 with a Sierra Wireless EM7455 / Dell DE5811e Snapdragon X7 LTE modem. I also have a Mint Mobile SIM card installed. I used the System Settings/Connections control panel and added a new Mobile Broadband connection following the wizard. It works and I can successfully connect to Mint Mobile. A speed test via SpeedTest.net in Firefox showed I was getting about 65Mbps down and about 4.5Mbps up.

If I could leave it right here it seems everything is fine. The setup was easy and without incident, I got connected, and I can even browse with acceptable bandwidth. However, it seems to have a very hard time connecting, telling me is is connected and then immediately disconnected several times before it finally settles down and stays connected. Also, the connection takes about a minute or more, not the few seconds that it should. I also have frequent disconnects, sometimes so frequent it is like not having a connection at all.

When it is connected, everything looks good. The signal strength is strong, and the signal quality good. I just need it to be more stable to be usable, and also prevent it from eating my battery so fast with connection attempts.

❯ mmcli --modem=any
  --------------------------------
  General  |                 path: /org/freedesktop/ModemManager1/Modem/0
           |            device id: 7b65f8ff9d4ff15a20fd6b7064c01bd262d8e931
  --------------------------------
  Hardware |         manufacturer: Sierra Wireless, Incorporated
           |                model: DW5811e Snapdragon™ X7 LTE
           |    firmware revision: SWI9X30C_02.24.03.00
           |       carrier config: default
           |         h/w revision: EM7455B
           |            supported: gsm-umts, lte
           |              current: gsm-umts, lte
           |         equipment id: 352733100762426
  --------------------------------
  System   |               device: /sys/devices/pci0000:00/0000:00:14.0/usb2/2-2
           |              drivers: qcserial, cdc_mbim
           |               plugin: dell
           |         primary port: cdc-wdm0
           |                ports: cdc-wdm0 (mbim), ttyUSB0 (ignored), ttyUSB1 (ignored), 
           |                       ttyUSB2 (at), wwp0s20f0u2i12 (net)
  --------------------------------
  Numbers  |                  own: xxxxxxxxxxx (Edited out)
  --------------------------------
  Status   |                 lock: sim-pin2
           |       unlock retries: sim-pin2 (10)
           |                state: connected
           |          power state: on
           |          access tech: lte
           |       signal quality: 38% (cached)
  --------------------------------
  Modes    |            supported: allowed: 3g; preferred: none
           |                       allowed: 4g; preferred: none
           |                       allowed: 3g, 4g; preferred: 4g
           |                       allowed: 3g, 4g; preferred: 3g
           |              current: allowed: 3g, 4g; preferred: 4g
  --------------------------------
  Bands    |            supported: utran-1, utran-3, utran-4, utran-5, utran-8, utran-2, 
           |                       eutran-1, eutran-2, eutran-3, eutran-4, eutran-5, eutran-7, eutran-8, 
           |                       eutran-12, eutran-13, eutran-20, eutran-25, eutran-26, eutran-29, 
           |                       eutran-41
           |              current: utran-1, utran-3, utran-4, utran-5, utran-8, utran-2, 
           |                       eutran-1, eutran-2, eutran-3, eutran-4, eutran-5, eutran-7, eutran-8, 
           |                       eutran-12, eutran-13, eutran-20, eutran-25, eutran-26, eutran-29, 
           |                       eutran-41
  --------------------------------
  IP       |            supported: ipv4, ipv6, ipv4v6
  --------------------------------
  3GPP     |                 imei: xxxxxxxxxxxxxx (Edited out)
           |        enabled locks: fixed-dialing
           |          operator id: 310260
           |        operator name: Mint
           |         registration: home
           | packet service state: attached
  --------------------------------
  3GPP EPS | ue mode of operation: csps-2
  --------------------------------
  SIM      |     primary sim path: /org/freedesktop/ModemManager1/SIM/0
           |       sim slot paths: slot 1: /org/freedesktop/ModemManager1/SIM/0 (active)
           |                       slot 2: none
  --------------------------------
  Bearer   |                paths: /org/freedesktop/ModemManager1/Bearer/0

Any help is appreciated. Feel free to ask for any additional information you need. Here is the required garuda-inxi output:

❯ garuda-inxi
System:
  Kernel: 6.4.6-zen1-1-zen arch: x86_64 bits: 64 compiler: gcc v: 13.1.1
    parameters: BOOT_IMAGE=/@/boot/vmlinuz-linux-zen
    root=UUID=cd28c1a1-ce9c-46ca-a940-f08d8bd3849f rw rootflags=subvol=@
    quiet quiet rd.udev.log_priority=3 vt.global_cursor_default=0
    resume=UUID=931f2a2d-59cb-4704-8216-338f14645cb5 loglevel=3 ibt=off
  Desktop: KDE Plasma v: 5.27.6 tk: Qt v: 5.15.10 wm: kwin_x11 vt: 2
    dm: SDDM Distro: Garuda Linux base: Arch Linux
Machine:
  Type: Laptop System: Dell product: Latitude 7390 v: N/A
    serial: <superuser required> Chassis: type: 10 serial: <superuser required>
  Mobo: Dell model: 09386V v: A00 serial: <superuser required> UEFI: Dell
    v: 1.32.0 date: 04/10/2023
Battery:
  ID-1: BAT0 charge: 40.0 Wh (93.2%) condition: 42.9/42.9 Wh (100.0%)
    volts: 7.9 min: 7.4 model: LGC-LGC7.78 DELL 2X39G type: Li-ion
    serial: <filter> status: discharging
CPU:
  Info: model: Intel Core i7-8650U bits: 64 type: MT MCP arch: Coffee Lake
    gen: core 8 level: v3 note: check built: 2017 process: Intel 14nm family: 6
    model-id: 0x8E (142) stepping: 0xA (10) microcode: 0xF2
  Topology: cpus: 1x cores: 4 tpc: 2 threads: 8 smt: enabled cache:
    L1: 256 KiB desc: d-4x32 KiB; i-4x32 KiB L2: 1024 KiB desc: 4x256 KiB
    L3: 8 MiB desc: 1x8 MiB
  Speed (MHz): avg: 1450 high: 2100 min/max: 400/4200 scaling:
    driver: intel_pstate governor: powersave cores: 1: 800 2: 800 3: 2100
    4: 2100 5: 800 6: 800 7: 2100 8: 2100 bogomips: 33599
  Flags: avx avx2 ht lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx
  Vulnerabilities: <filter>
Graphics:
  Device-1: Intel UHD Graphics 620 vendor: Dell driver: i915 v: kernel
    arch: Gen-9.5 process: Intel 14nm built: 2016-20 ports: active: eDP-1
    empty: DP-1, DP-2, HDMI-A-1, HDMI-A-2 bus-ID: 00:02.0 chip-ID: 8086:5917
    class-ID: 0300
  Device-2: Microdia Integrated_Webcam_HD driver: uvcvideo type: USB
    rev: 2.0 speed: 480 Mb/s lanes: 1 mode: 2.0 bus-ID: 1-5:2 chip-ID: 0c45:6717
    class-ID: 0e02
  Display: x11 server: X.Org v: 21.1.8 with: Xwayland v: 23.1.2
    compositor: kwin_x11 driver: X: loaded: modesetting
    alternate: fbdev,intel,vesa dri: iris gpu: i915 display-ID: :0 screens: 1
  Screen-1: 0 s-res: 1920x1080 s-dpi: 96 s-size: 508x285mm (20.00x11.22")
    s-diag: 582mm (22.93")
  Monitor-1: eDP-1 model: ChiMei InnoLux 0x1382 built: 2017 res: 1920x1080
    hz: 60 dpi: 166 gamma: 1.2 size: 293x165mm (11.54x6.5") diag: 336mm (13.2")
    ratio: 16:9 modes: 1920x1080
  API: OpenGL v: 4.6 Mesa 23.1.4 renderer: Mesa Intel UHD Graphics 620 (KBL
    GT2) direct-render: Yes
Audio:
  Device-1: Intel Sunrise Point-LP HD Audio vendor: Dell driver: snd_hda_intel
    v: kernel alternate: snd_soc_skl,snd_soc_avs bus-ID: 00:1f.3
    chip-ID: 8086:9d71 class-ID: 0403
  API: ALSA v: k6.4.6-zen1-1-zen status: kernel-api with: aoss
    type: oss-emulator tools: N/A
  Server-1: PipeWire v: 0.3.75 status: active with: 1: pipewire-pulse
    status: active 2: wireplumber status: active 3: pipewire-alsa type: plugin
    4: pw-jack type: plugin tools: pactl,pw-cat,pw-cli,wpctl
Network:
  Device-1: Intel Ethernet I219-LM vendor: Dell driver: e1000e v: kernel
    port: N/A bus-ID: 00:1f.6 chip-ID: 8086:15d7 class-ID: 0200
  IF: enp0s31f6 state: down mac: <filter>
  Device-2: Intel Wireless 8265 / 8275 driver: iwlwifi v: kernel pcie:
    gen: 1 speed: 2.5 GT/s lanes: 1 bus-ID: 02:00.0 chip-ID: 8086:24fd
    class-ID: 0280
  IF: wlp2s0 state: down mac: <filter>
  IF-ID-1: wwp0s20f0u2i12 state: unknown mac: <filter>
Bluetooth:
  Device-1: Intel Bluetooth wireless interface driver: btusb v: 0.8 type: USB
    rev: 2.0 speed: 12 Mb/s lanes: 1 mode: 1.1 bus-ID: 1-7:3 chip-ID: 8087:0a2b
    class-ID: e001
  Report: bt-adapter ID: hci0 rfk-id: 3 state: up address: <filter>
Drives:
  Local Storage: total: 476.94 GiB used: 33.01 GiB (6.9%)
  SMART Message: Unable to run smartctl. Root privileges required.
  ID-1: /dev/nvme0n1 maj-min: 259:0 vendor: Samsung
    model: MZVLB512HAJQ-000H1 size: 476.94 GiB block-size: physical: 512 B
    logical: 512 B speed: 31.6 Gb/s lanes: 4 tech: SSD serial: <filter>
    fw-rev: EXA73H1Q temp: 31.9 C scheme: GPT
Partition:
  ID-1: / raw-size: 459.59 GiB size: 459.59 GiB (100.00%)
    used: 33.01 GiB (7.2%) fs: btrfs dev: /dev/nvme0n1p2 maj-min: 259:2
  ID-2: /boot/efi raw-size: 300 MiB size: 299.4 MiB (99.80%)
    used: 576 KiB (0.2%) fs: vfat dev: /dev/nvme0n1p1 maj-min: 259:1
  ID-3: /home raw-size: 459.59 GiB size: 459.59 GiB (100.00%)
    used: 33.01 GiB (7.2%) fs: btrfs dev: /dev/nvme0n1p2 maj-min: 259:2
  ID-4: /var/log raw-size: 459.59 GiB size: 459.59 GiB (100.00%)
    used: 33.01 GiB (7.2%) fs: btrfs dev: /dev/nvme0n1p2 maj-min: 259:2
  ID-5: /var/tmp raw-size: 459.59 GiB size: 459.59 GiB (100.00%)
    used: 33.01 GiB (7.2%) fs: btrfs dev: /dev/nvme0n1p2 maj-min: 259:2
Swap:
  Kernel: swappiness: 133 (default 60) cache-pressure: 100 (default)
  ID-1: swap-1 type: zram size: 15.5 GiB used: 0 KiB (0.0%) priority: 100
    dev: /dev/zram0
  ID-2: swap-2 type: partition size: 17.05 GiB used: 0 KiB (0.0%)
    priority: -2 dev: /dev/nvme0n1p3 maj-min: 259:3
Sensors:
  System Temperatures: cpu: 66.0 C pch: 60.0 C mobo: N/A
  Fan Speeds (RPM): N/A
Info:
  Processes: 255 Uptime: 41m wakeups: 9683 Memory: total: 16 GiB
  available: 15.5 GiB used: 3.22 GiB (20.8%) Init: systemd v: 253
  default: graphical tool: systemctl Compilers: gcc: 13.1.1 Packages:
  pm: pacman pkgs: 1553 libs: 494 tools: octopi,paru Shell: Zsh v: 5.9
  running-in: guake inxi: 3.3.28
Garuda (2.6.16-1):
  System install date:     2023-07-12
  Last full system update: 2023-07-26
  Is partially upgraded:   No
  Relevant software:       snapper NetworkManager dracut
  Windows dual boot:       Probably (Run as root to verify)
  Failed units:    

Welcome to the community @T313C0mun1s7. :slightly_smiling_face:

The ArchWiki article on mobile broadband modems describes an issue that bears some similarities to yours: Mobile broadband modem - ArchWiki

Connection halts after few minutes running

This problem commonly occurs on some modems which locked by a mobile operator. You can successfully connect to the internet but after few minutes connection halts and your modem reboots. That happens because an operator built a some checks into modem firmware so a modem checks if a branded software is running on your pc, but usually that software is Windows-only, and obviously you do not use it. Fix (it works on ZTE-mf190 at least) is simple - send this command through serial port (use minicom or similar soft):

AT+ZCDRUN=E\r\n

This command will delete a NODOWNLOAD.FLG file in the modem's filesystem - it will disable such checks.

Another possibility for such disconnections is to help the customer save bandwidth, which might be expensive. With Huawei HiLink devices with a web interface, there might be an option there to set a longer period of inactivity before the connection hangs up.

Minicom is in the [extra] repo. Its use is described briefly in the wiki here: Working with the serial console - ArchWiki and not so briefly in the man pages: minicom(1) — Arch manual pages

3 Likes

Thank you for the suggestion. It is a new modem I purchased that has never been used and is suppose to be unlocked. However, I will give it a try.

I have done extensive work repairing laptops, and I know the tiny antenna connectors can be very tight and hard to connect if it is the first time they are being plugged onto a card. So I took extra care to get it right and not damage them. Then I took extra care to ensure the antenna cables were properly routed and would not bind up in the hinge. It took an embarrassingly long time of about 25 minutes just to get the card installed. So I don't THINK that it is a signal issue. However, I will also try several different geographical locations as see if certain places work better than others.

After I made this post yesterday, I ran it for another hour, and gave it a couple reboots. It still took more than a few seconds to connect, but it seemed less likely to disconnect, even when idle. Perhaps I was impatient and there was some kind of initialization or first time connection stuff that had to happen between the carrier and the modem.

The modem is new, but the SIM card got moved from my iPad to the laptop. I called the carrier and they said they didn't need to do anything on their end to change the associated IMEI on the account, and I should be able to move my SIM card to any supported device without issue. I know that this was not true in the past with this carrier, as I have had to call support in the past to move my SIM from a Pixel 4 to a Moto G82 a few months ago. So maybe whatever they use to do manually is now automated, but requires them to disconnect and reconnect a few times? I don't know, I am just blind guessing at this point.

I will try to get more usage on the LTE modem over the next couple days, and I will report back on if it resolves itself and was just an initialization issue, or if the issues persist.

Thanks again.

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