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Linphone

Technical corner

Description

Linphone is an open source SIP phone for voice/video calls, instant messaging and conference calling. It is available for mobile and desktop environments (iOS, Android, GNU/Linux, macOS, Windows).

Linphone features a separation between the user interfaces and the core engine, allowing the creation of various kinds of user interface on top of the same functionalities.

The user interface frontends are:

A Qt/QML interface for Windows desktop, macOS and GNU/Linux
A console interface (linphone-daemon)
An iPhone application built in Swift
An Android application built in Kotlin

Liblinphone is the core engine, this is the library that implements all the functionalities of Linphone. It is a powerful SIP-based SDK for Voice and Video over IP, that anyone can use to add audio and video calls or instant messaging capabilities to an application. It provides a high-level API to initiate, receive and terminate audio and video calls.

Liblinphone relies on the following software components:

Mediastreamer2, a powerful multimedia SDK for audio/video streaming and processing
oRTP, a simple RTP library
belle-sip, the SIP library

Liblinphone and all its dependencies are written in C++ and C.

Architecture

Console tools

Linphone-daemon is a console-mode program based on Liblinphone that can register, send and receive calls by reading simple text commands from standard input or from a UNIX socket. In response to each command, linphone-daemon writes the execution status of the command to standard output (or a socket).
This tool can easily be used from a shell script to execute simple SIP scenarios by those who do not require the full capabilities of the Liblinphone SDK.

Linphone-daemon supersedes the former "linphonec" console tool, as it uses a more effective syntax for inputs and outputs.

Common Features (Mobile and Desktop)

OVERALL FEATURES

HD audio and video calls
Multiple call management (pause and resume)
Call transfer (blind and attended)
Audio and video conferencing, based on a modern Selective Forwarding Unit (SFU)
Call recording and replay
Instant Messaging and group chat
Message delivery status (IMDN)
File sharing (audio, video, documents, gifs...)
Message forward, copy, reply to
Chat access during calls
Contact list
"Invite your friends" feature
Presence status
Call history
Support for bluetooth headset
Display of advanced call statistics
Echo cancellation
Call quality indicator
Supported languages: English, French
Account creation assistant
Remote provisioning (via Qr code or URL)
Secure user authentication: md5 / SHA256 digest, TLS client certificates
End-to-end encryption for calls via SRTP, zRTP and SRTP-DTLS
End-to-end encryption for messaging, using Linphone Instant Messaging Encryption (LIME)
Post quantum call encryption, using CRYSTALS-Kyber algoritm (the winning of an international competition run by the American NIST between 2016 and 2022).

ADVANCED FEATURES

Audio codecs: opus, speex, g711, g729, gsm, iLBC, AMR, AMR-WB, g722, SILK, iSAC, BV16, Codec2
Video codecs: VP8, H.264 and H.265 with resolutions up to 1080P, MPEG4
Hardware accelerated H.264 and H.265 codec for Mac OSX / iOS (VideoToolbox) and Android (MediaCodec)
Innovative RTP jitter buffer algorithm, which quickly adapts to network conditions with a lot of jitter and improves control of the audio latency
Adaptive bit rate control algorithm: congestion control and estimation of available bandwidth, in order to optimise the quality of audio and video
Integration with push notification (requires compatible SIP server; linphone.org SIP service is push enabled)
ICE (RFC 5245), STUN and TURN (RFC 5766) for optimised NAT traversal, allowing for peer-to-peer audio and video connections whenever possible
Call handover accross a change of network access type (e.g. start a call in wifi and continue in 3G)
Ability to configure multiple proxy accounts with different transports protocols (UDP, TCP, TLS)
IPv6 (dual-stack and v6-only support)
DTMF (telephone tone) support using SIP INFO or RFC 4733

For more information, consult the complete list of implemented standards in the Liblinphone section.

Mobile-specific features (iOS/Android)

Smart contact list (shows people using the service) using list subscription to a presence server
Dedicated tablet user interface
Blind accessibility

Linphone is available on the following mobile platforms:

Apple iOS 9 and more recent (ARM v7, ARM 64)
Google Android 6 and more recent (ARM v7, ARM 64, x86, x86-64)

iOS ADDITIONAL FEATURES

AAC-ELD support

ANDROID ADDITIONAL FEATURES

Video overlay

Desktop-specific features

The Qt (QML) graphical interface runs on GNU/Linux, Windows and macOS.

SPECIFIC FEATURES

HD video calls in full screen mode
Smart search bar
Unified history
Quick access to recent events

PORTABILITY

GNU/Linux: x86, x86-64, ARM v5, v7, arm64 ; Debian 8/9, Centos 7
Windows Desktop: x86 (works also on x86_64), Windows 7 and later
Mac OS X: x86_64 ; 10.11 and later.
GNU/Linux embedded: linphone-daemon is a good candidate to provide the software stack for a hardware phone or hardware communication system.

License

Linphone is dual licensed, and can be licensed and distributed:

under a GNU GPLv3 license for free (open source)
under a proprietary license, to be used in closed source applications. Contact Belledonne Communications for costs and other service information.

Download Mobile versions

Linphone iOS on the App Store
Linphone Android on Google Play and the apk here

Download Desktop versions

Linphone for desktop:

Download Linphone for macOS

Download Linphone for Windows

AppImage package for GNU/Linux:

Download the AppImage package for Linux

Source code

Linphone source code is available from our GitLab, or can be cloned with Git:

Project	Git repository
linphone-desktop, comprising: linphone (Qt user interface) linphone-sdk	git clone https://gitlab.linphone.org/BC/public/linphone-desktop.git --recursive
linphone-iphone (iOS application)	git clone https://gitlab.linphone.org/BC/public/linphone-iphone.git
linphone-android (Android application)	git clone https://gitlab.linphone.org/BC/public/linphone-android.git

For those who are behind a proxy:
You can change the access method from git:// to http:// as follows:
Normal git access:
git clone git://git.linphone.org/msilbc.git
Behind a proxy, use http access:
git clone git.linphone.org/msilbc.git

Daily builds (testing)

Every day, binary packages generated from the current git state are uploaded to http://www.linphone.org/snapshots. It is worth visiting if you want to test and see the latest changes, especially if a long time has elapsed since the last official stable release. These snapshots are generated automatically and are not tested, meaning that certain features might occasionally be broken.

Please refer to the README.md file for each project (linphone-iphone, linphone-android, linphone-desktop) for developer information about the applications.

Additionally, our developer wiki provides details about specific subjects:

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