py-iax2

A complete, pure-Python implementation of the IAX2 VoIP protocol (RFC 5456) for asyncio, built to interoperate with Asterisk — including AllStarLink app_rpt nodes. Where the RFC is vague or Asterisk differs, py-iax2 does what Asterisk 22 LTS does, and its test suite runs against a live Asterisk.

import asyncio
import iax2

async def main():
    async with iax2.Endpoint(port=0) as ep:
        call = await ep.dial("pbx.example.org", "600", username="me", secret="s3cret")
        await call.play_pcm(iax2.audio.tone(440, 2000))
        await call.hangup()

asyncio.run(main())

Features

• Calls, outgoing and incoming, with Asterisk-exact sequencing, ACKs, retransmission and timestamps; ringing, answer, reject, hangup causes.
• Authentication: MD5, RSA (Asterisk key files) and plaintext; call tokens as client and server.
• AES-128 encryption with key rotation, compatible with Asterisk's encryption=aes128.
• Media: μ-law, A-law, slin, slin16 built in (no dependencies), pluggable codecs, payload pass-through for any format, adaptive jitter buffer, trunking, video, DTMF, text, URL and image frames.
• Registration client and registrar, POKE qualification, PING/LAGRQ statistics, dialplan queries, native transfers (endpoint and server).
• A blocking API (iax2.sync) for non-asyncio code.
• iax2-tool CLI: poke, call, serve, register, decode.
• Examples: echo server, mini PBX, AllStarLink client, and more.

Install

pip install iax2              # core, pure Python
pip install "iax2[crypto]"    # + RSA authentication and AES encryption

Python 3.11+. A debian/ directory builds a python3-iax2 package.

Answering calls

import asyncio
import iax2

async def echo(call):
    await call.answer()
    async for frame in call.audio():
        call.send_audio(frame.payload)

async def main():
    users = {"alice": iax2.Credentials(secret="s3cret")}
    async with iax2.Endpoint(port=4569, users=users, allow_guest=False) as ep:
        async for call in ep.incoming():
            asyncio.create_task(echo(call))

asyncio.run(main())

Command line

iax2-tool poke pbx.example.org
iax2-tool call pbx.example.org 600 -u me -s s3cret --tone 440 --record out.wav
iax2-tool serve -u alice:s3cret

Documentation

Full documentation (user guide, Asterisk/AllStarLink notes, protocol notes, API reference) is at https://py-iax2.readthedocs.io/. The source is in docs/; build it locally with sphinx-build -b html docs docs/_build/html.

Testing

pytest                                          # unit + loopback tests
sudo python3 tests/interop/setup_asterisk.py    # configure a *test* Asterisk
pytest -m interop tests/interop                 # interoperability tests

Versioning and API stability

py-iax2 follows Semantic Versioning. While the version is 0.x, minor releases (0.1 → 0.2) may change the public API; such changes are listed in CHANGELOG.md, and where practical the old API keeps working with a DeprecationWarning for at least one minor release. Patch releases (0.1.0 → 0.1.1) are bug fixes only. The public API is everything exported from iax2 and documented in the API reference; names starting with _ and the iax2.session module (other than the SessionStats returned by Call.stats) are internal. From 1.0 onward, breaking changes only happen in major releases.

Contributing and security

See CONTRIBUTING.md and, for vulnerabilities, SECURITY.md.

License

GPL-2.0-only (matching Asterisk). Copyright © 2026 Jason D. McCormick.