Bluetooth GSM ↔ SIP Gateway

Turn your Linux PC into a softphone for your mobile’s GSM calls. This project runs Asterisk with the chan_mobile Bluetooth gateway inside a Docker container, so you can:

• Receive incoming GSM calls on your PC (ring a SIP client like Linphone)
• Place outgoing calls from your SIP client via your mobile phone over Bluetooth

It uses BlueZ + D-Bus for Bluetooth, and Asterisk to bridge GSM↔SIP audio.

How It Works

• A privileged container starts dbus, bluetoothd (BlueZ), and asterisk.
• Asterisk loads chan_mobile and connects to your phone over Bluetooth RFCOMM/HFP.
• Dialplan bridges calls:
  • Incoming GSM → rings SIP extension 1001.
  • Outgoing from SIP → dials out using the paired mobile device.

Key files in this repo configure that flow:

• docker-compose.yml — host integration and device access
• Dockerfile — Ubuntu 18.04 + BlueZ + Asterisk runtime
• chan_mobile.conf / mobile.conf — Bluetooth adapter and phone mapping
• sip.conf — local SIP account 1001 for your softphone
• extensions.conf — dialplan bridging SIP↔Mobile
• rtp.conf, logger.conf — media and logging
• start.sh — launches dbus, bluetoothd, and asterisk in-foreground
• host/linphone-tel, host/linphone-tel.desktop — optional tel: link handler for Linphone

Requirements

• Linux host with working Bluetooth adapter
• Docker and Docker Compose
• A SIP softphone on the host (e.g., Linphone)
• A mobile phone with Bluetooth Hands‑Free support (HFP)

Notes

• Container runs with privileged, network_mode: host, and /dev bind. This is necessary for BlueZ/Bluetooth access and Asterisk audio bridging.
• Ubuntu 18.04 base is used to match Asterisk and BlueZ versions known to work with chan_mobile.
• Not compatible with Docker Desktop installed via App Center/Snap/Flatpak. Those setups typically cannot expose host D-Bus and the physical Bluetooth adapter to containers. Use a native Docker Engine installation on the host OS.

Why Docker?

• Asterisk’s chan_mobile has long‑standing compatibility issues with the modern Bluetooth stack in newer Ubuntu releases (e.g., 24.04). On up‑to‑date hosts, Asterisk often fails to cooperate reliably with BlueZ/DBus for HFP/RFCOMM, causing unstable pairing, device discovery, or Audio Gateway operation. This container pins an older, known‑good userspace (Ubuntu 18.04 with matching BlueZ/Asterisk) so you don’t need to downgrade your entire OS just to make GSM↔SIP bridging work.

Docker on Ubuntu 24.x (native install)

Avoid Docker Desktop from App Center/Snap/Flatpak — it won’t pass through host D-Bus or the Bluetooth adapter in the way this stack requires. Install Docker Engine natively from Docker’s official APT repository.

1. Optional: remove conflicting packages (Docker Desktop, legacy docker.io)

• These commands are safe if those packages are absent.

  sudo apt remove -y docker-desktop || true
  sudo apt remove -y docker.io docker-doc podman-docker containerd runc || true
  # Do NOT remove your data unless you intend to:
  # sudo rm -rf /var/lib/docker /var/lib/containerd

2. Install prerequisites and add Docker’s APT repo

sudo apt-get update
sudo apt-get install -y ca-certificates curl gnupg
sudo install -m 0755 -d /etc/apt/keyrings
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg
sudo chmod a+r /etc/apt/keyrings/docker.gpg

echo "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu $(. /etc/os-release; echo $VERSION_CODENAME) stable" | \
  sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
sudo apt-get update

3. Install Docker Engine + Compose plugin

sudo apt-get install -y docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin
sudo systemctl enable --now docker

4. (Optional) Run Docker as your user

sudo usermod -aG docker $USER
# Log out and back in (or reboot) so your group membership applies

5. Verify

docker run --rm hello-world
docker compose version

Quick Start

0. Host prep (first-time or as needed)

• If you see conflicts with the host's bluetoothd, let the container own Bluetooth (dbus + bluetoothd) and claim the adapter. Many systems only need this once; after reboots it often keeps working without repeating these steps.

  # Give control to the container (only if needed)
  sudo systemctl stop bluetooth || true
  sudo systemctl disable bluetooth || true
  sudo rfkill unblock bluetooth
  sudo modprobe btusb bluetooth rfcomm
  sudo hciconfig hci0 up
  hciconfig -a   # look for UP RUNNING

  To use Bluetooth on the host again (e.g., to connect unrelated devices), stop the container and re-enable the host service:

  # Stop the container that owns the adapter
  docker compose down
  
  # Return control to the host
  sudo systemctl enable bluetooth
  sudo systemctl start bluetooth
  sudo rfkill unblock bluetooth
  sudo hciconfig hci0 up
  # Or via bluetoothctl: power on

  When switching back to the container, repeat the "Give control to the container" snippet above if the host has reclaimed the adapter.

1. Adjust Bluetooth addresses

• Edit chan_mobile.conf (and mobile.conf for compatibility) and set:
  • [adapter] address= to your host’s Bluetooth adapter MAC.
  • [redmi] address= to your phone’s Bluetooth MAC.
  • Keep port=3 unless you know your HFP/RFCOMM channel differs. To discover your phone’s HFP/RFCOMM channel, run:
    • sudo sdptool records XX:XX:XX:XX:XX:XX | grep -i -A10 "Audio Gateway\|Handsfree" Replace the MAC and use the reported RFCOMM channel for port.

2. Optional: share host pairings

• If you already paired the phone on the host and want to reuse that, uncomment the bind in docker-compose.yml:
  • - /var/lib/bluetooth:/var/lib/bluetooth

3. Build and run

• docker compose build
• docker compose up -d

4. First-time pairing (container)

• Pair, trust, and connect your phone inside the container using bluetoothctl:

  docker exec -it asterisk-mobile bash
  bluetoothctl
  power on
  agent on
  default-agent
  scan on   # wait until you see your phone (e.g., XX:XX:XX:XX:XX:XX)
  pair XX:XX:XX:XX:XX:XX
  trust XX:XX:XX:XX:XX:XX
  connect XX:XX:XX:XX:XX:XX
  quit

  Then verify from Asterisk:

  asterisk -rvvvvv
  mobile show devices   # should show Connected: Yes, State: Free

5. Register your SIP client

• Configure your SIP softphone to register to:
  • Server: 127.0.0.1
  • User: 1001
  • Password: 1234 (change it!)
  • Transport: UDP

6. Test

• Outgoing: dial a number from your SIP client; it should go out via your phone.
• Incoming: call your mobile; your SIP client should ring as extension 1001.

Linphone Config (Host)

Install and point Linphone (Desktop or CLI) to Asterisk on the host, and use the provided configs.

• Install Linphone

  • Ubuntu 24.x: from App Center (or via apt/flatpak). Any recent Linphone Desktop or linphonec works.

• Copy the config

  • For Linphone Desktop (GUI):
    • mkdir -p "$HOME/.config/linphone"
    • cp host-config/linphone/linphonerc "$HOME/.config/linphone/linphonerc"
  • For Linphone CLI (linphonec):
    • mkdir -p "$HOME/.config/linphone"
    • cp host-config/linphone/linphonerc-asterisk "$HOME/.config/linphone/linphonerc"

• Adjust credentials if needed

  • In ~/.config/linphone/linphonerc, under [proxy_0] set:
    • reg_proxy=sip:127.0.0.1;transport=udp (or your Asterisk IP)
    • reg_identity=sip:1001@127.0.0.1 (or your extension@server)
  • Linphone will prompt for the password on first register unless you add an [auth_info_*] section.

• About these config files

  • They are full configs (not minimal). Linphone may auto-extend/modify them on first run — that’s expected.
  • Personal/Sensitive values was redacted from the versions in this repo:
    • [sip] contact=... replaced with a generic sip:1001@127.0.0.1 to avoid exposing usernames/hosts.
    • [misc] uuid=... replaced with <uuid>.
    • [sound] *_dev_id=... changed to PulseAudio Default to avoid exposing specific hardware names.
    • [auth_info_0] ha1=... replaced with <ha1> because it is a password hash.
  • If you prefer persistent credentials delete the whole [auth_info_*] section and enter credentials via the UI once; Linphone will recreate it.

• Notes

  • You don’t need to remove Linphone’s auto-generated sections; keeping them is fine.

Configuration Details

Asterisk SIP account: sip.conf

• [1001] is a local user for your softphone.
• Change secret, and adapt codecs (alaw/ulaw) to your needs.

Bluetooth gateway: chan_mobile.conf (and mobile.conf)

• [adapter] id=usb and address=<adapter-mac> point to your adapter.
• [redmi] address=<phone-mac>, port=3, context=from-mobile, adapter=usb.
• On some phones the HFP/RFCOMM channel can differ; if calls fail to connect, scan channels with sdptool browse <phone-mac> and update port accordingly.

Dialplan: extensions.conf

• Global MOBILE_IFACE=redmi maps to your phone section.
• from-sip: anything dialed _X. from SIP is sent to Mobile/${MOBILE_IFACE}/${EXTEN}.
• from-mobile: incoming GSM calls dial SIP/1001 to ring your softphone.

RTP/media: rtp.conf

• RTP range narrowed to 10000–10100. Open these UDP ports if you firewall.

Logging: logger.conf

• console and full log files enabled for diagnostics.

Container: docker-compose.yml

• privileged: true, network_mode: host, and /dev passthrough enable Bluetooth access.
• Uncomment /var/lib/bluetooth bind to reuse host pairings.

Entrypoint: start.sh

• Starts a private system dbus, bluetoothd --compat, then asterisk -f -vvv.

Operating Asterisk

Attach to the running Asterisk CLI:

• docker exec -it asterisk-mobile asterisk -rvvvvv

Useful commands:

• core show channels
• core set verbose 5
• mobile show devices
• mobile show connections
• mobile status
• sip show peers (for chan_sip)

Logs:

• docker logs -f asterisk-mobile
• Inside container: check /var/log/asterisk/ if enabled by logger.conf.

Linphone tel: Link Handler (Optional)

If you use Linphone on the host, you can make tel: links dial via Linphone automatically.

1. Create a small helper:

• Save host/linphone-tel to ~/.local/bin/linphone-tel and make it executable:
  • mkdir -p ~/.local/bin
  • cp host/linphone-tel ~/.local/bin/linphone-tel
  • chmod +x ~/.local/bin/linphone-tel

2. Register the desktop handler:

• Copy host/linphone-tel.desktop to ~/.local/share/applications/:
  • mkdir -p ~/.local/share/applications
  • cp host/linphone-tel.desktop ~/.local/share/applications/
• Update and set default handler:
  • update-desktop-database ~/.local/share/applications/
  • xdg-mime default linphone-tel.desktop x-scheme-handler/tel
  • Verify: xdg-mime query default x-scheme-handler/tel → linphone-tel.desktop

The helper normalizes numbers (strips spaces, keeps digits/+, converts + to 00) and launches Linphone with call sip-address=....

Troubleshooting

Switching Bluetooth control (host ↔ container)

• Give control to the container (if host bluetoothd conflicts):

  sudo systemctl stop bluetooth || true
  sudo systemctl disable bluetooth || true
  sudo rfkill unblock bluetooth
  sudo hciconfig hci0 up

• Return control to the host:

  docker compose down
  sudo systemctl enable bluetooth
  sudo systemctl start bluetooth
  sudo rfkill unblock bluetooth
  sudo hciconfig hci0 up
  # Optionally: bluetoothctl → power on

Bluetooth doesn’t start in container

• Check container privileges match docker-compose.yml.
• Inspect docker logs -f asterisk-mobile after start.
• Inside container, run rfkill list, hciconfig -a, dmesg | tail -n 100.

Phone not pairing or connecting

• Use bluetoothctl to trust and connect the phone.
• If using host pairings, ensure /var/lib/bluetooth is bind‑mounted and permissions preserved.

Outgoing calls fail immediately

• Verify port in chan_mobile.conf matches phone’s HFP/RFCOMM channel (sdptool browse <mac>).
• Confirm mobile show devices shows your device as Connected.

No audio / one‑way audio

• Open RTP UDP range in firewall: 10000–10100.
• Check directmedia=no and codec compatibility in sip.conf.

SIP client won’t register

• Confirm SIP points to 127.0.0.1, user 1001, password changed and correct.
• sip show peers should list 1001 as OK with latency.

Asterisk module not loading chan_mobile

• Ensure your Asterisk build includes chan_mobile on Ubuntu 18.04 package.
• If needed, install asterisk extras or build the module; review logs for load errors.

Security Notes

• Change default SIP credentials in sip.conf before use.
• Limit exposed services; this stack uses network_mode: host. Prefer local network only.
• Keep OS and Docker updated. Ubuntu 18.04 is EOL; for long‑term use, consider updating the base and re‑validating chan_mobile.

File Reference

• docker-compose.yml — container runtime configuration
• Dockerfile — builds image with BlueZ + Asterisk
• start.sh — supervised startup for dbus, bluetoothd, asterisk
• chan_mobile.conf, mobile.conf — Bluetooth adapter/phone mapping
• sip.conf — SIP account 1001 for your softphone
• extensions.conf — dialplan for in/out bridging
• rtp.conf — RTP port range and ICE/TURN options (many commented)
• logger.conf — logging setup (console/full/messages)
• host/linphone-tel, host/linphone-tel.desktop — tel: handler for Linphone

FAQ

• Do I need both chan_mobile.conf and mobile.conf?
  • Some Asterisk builds use chan_mobile.conf. This repo includes both (same content) for compatibility; adjust both or prefer chan_mobile.conf.
• Can I avoid pairing in the container?
  • Yes, by sharing /var/lib/bluetooth from the host. Ensure the phone is paired/trusted on the host and MACs match your config.
• Which SIP client should I use?
  • Linphone, baresip, or any basic SIP client. Start simple: PC and container on the same host with UDP transport.

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Contributions and improvements welcome.