LTE / 5G Modem Manual Control (QMI, Linux)

This project provides manual start/stop scripts for bringing up a USB-attached LTE/5G modem on Linux using QMI.

It is designed for:

• Development & debugging
• Laptops, Raspberry Pi, Jetson
• Full control (no auto-connect, no boot-time services)

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What This Does

• Starts a cellular data session using QMI
• Brings up the wwan0 network interface
• Obtains an IP address via DHCP
• Cleanly tears down the connection on demand

No NetworkManager automation. No systemd auto-start. You decide when the modem is up or down.

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Requirements

Hardware

• USB or M.2 LTE/5G modem (SIMCom / Qualcomm-based)
• SIM card with active data plan
• Proper antennas connected
• Stable power (USB 3.0, laptop plugged in)

Software

• Linux kernel with QMI support

• Packages:

  sudo apt install libqmi-utils udhcpc

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Files

5g/
├── 5g-up.sh      # Start LTE/5G data connection
├── 5g-down.sh    # Stop LTE/5G data connection
└── 5g-status.sh  # (Optional) Check modem status

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Usage

1. Make scripts executable

chmod +x 5g-up.sh 5g-down.sh 5g-status.sh

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2. Start LTE / 5G connection

./5g-up.sh

What this does:

1. Checks if a data session is already active
2. Starts a QMI data session if needed
3. Brings up wwan0
4. Requests an IP address via DHCP

If successful, you’ll see an IP like:

inet 100.x.x.x/30 dev wwan0

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3. Stop LTE / 5G connection

./5g-down.sh

What this does:

• Stops DHCP
• Brings wwan0 down
• Stops the QMI data session (best-effort)

NoEffect errors are normal and safely ignored.

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4. Check status (optional)

./5g-status.sh

Shows:

• wwan0 interface state
• QMI packet service status

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Configuration

APN

Edit 5g-up.sh and change:

APN="jionet"

Common APNs (India):

Carrier	APN
Jio	jionet
Airtel	airtelgprs.com
VI	www

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Notes & Behavior

• The script is idempotent Running 5g-up.sh multiple times is safe.
• QMI control endpoints may reset — this is normal.
• DHCP succeeding means the data session is active.
• IP addresses are usually CGNAT (100.64.0.0/10).

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Troubleshooting

Check signal

sudo qmicli -d /dev/cdc-wdm1 --device-open-proxy \
  --nas-get-signal-strength

Check registration

sudo qmicli -d /dev/cdc-wdm1 --device-open-proxy \
  --nas-get-system-info

Check packet service

sudo qmicli -d /dev/cdc-wdm1 --device-open-proxy \
  --wds-get-packet-service-status

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Design Philosophy

• Manual > automatic
• Explicit control over boot-time magic
• Transparent QMI behavior
• Debuggable and predictable

This setup mirrors how embedded systems and field devices are typically operated.

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License

MIT (scripts only)

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