In the world of real-time communications, SIP (Session Initiation Protocol) continues to be the backbone for applications such as VoIP (Voice over Internet Protocol), video calling, instant messaging, and collaborative tools. Choosing the right SIP library is crucial for developers and organizations looking to build scalable, secure, and reliable communication systems. Open-source SIP libraries are particularly attractive because they provide flexibility, cost-efficiency, and community-driven support.

In this guide, we review the top five open-source SIP libraries as highlighting their features, advantages, and modern use cases. Libraries are ranked based on GitHub popularity, activity, maturity, documentation quality, and real-world adoption.

1. PJSIP – The Complete Multimedia SIP Stack

Overview
PJSIP remains the most robust and widely used open-source SIP stack available. Written in C language, it combines SIP signaling, media transport, NAT traversal, and a rich multimedia framework into a single portable API. First released in 2002 and actively maintained since, PJSIP has become the de facto standard for both desktop and mobile VoIP applications.

Key Features

• Protocols Supported: SIP, SDP, RTP, STUN, TURN, ICE

• Multimedia: Audio, video, instant messaging, presence

• Portability: Works across Windows, Linux, macOS, iOS, Android, and embedded systems

• NAT Traversal: Built-in STUN/TURN/ICE support for seamless communication behind firewalls

• Documentation: Extensive guides, examples, and active community support

• Testing & Reliability: Routinely tested in SIP interoperability events (SIPit)

Use Cases

• Mobile softphones

• Enterprise VoIP solutions

• Embedded SIP devices (IP phones, gateways)

• Custom VoIP apps requiring full multimedia capabilities

Why PJSIP Dominates in 2026
Its combination of high performance, reliability, and a rich feature set makes PJSIP ideal for applications requiring both signaling and media handling. Whether you’re developing a full-fledged softphone or an embedded SIP client for an IoT device, PJSIP remains unmatched.

2. Sofia-SIP – Lightweight and Standards-Driven

Overview
Sofia-SIP is a C-based SIP library originally developed by Nokia Research Center. It strictly follows the IETF RFC 3261 standard, making it a lightweight yet highly flexible option for SIP client implementations. While it doesn’t provide built-in media handling like PJSIP, Sofia-SIP is an excellent choice for developers seeking a pure SIP signaling library.

Key Features

• Supports UDP, TCP, and TLS transports

• Implements session timers, provisional responses, early media, and caller preferences

• Lightweight and modular design

• Compatible with multiple SIP client and server implementations

Use Cases

• SIP client development

• Custom VoIP gateways

• Applications where signaling is separate from media handling

Modern Relevance
Even though Sofia-SIP doesn’t see as frequent updates as some newer JavaScript stacks, it is still highly stable and reliable. For systems where adherence to SIP standards and low footprint is critical—like embedded telecom devices—Sofia-SIP remains a preferred choice.

3. reSIProcate & SipWise NGCP – Carrier-Grade SIP Solutions

Overview
reSIProcate is a modular SIP stack implemented in C++, focusing on scalability, security, and advanced SIP features. SipWise NGCP leverages reSIProcate for carrier-grade deployments, offering a comprehensive platform for service providers. This stack is ideal for scenarios requiring high availability, advanced routing, and SIP security.

Key Features

• Enterprise and carrier-grade SIP routing

• Advanced SIP extensions and proxy functionalities

• Strong security features, including TLS and SRTP support

• Scalable to thousands of concurrent SIP sessions

• Active community and commercial support via SipWise

Use Cases

• Telecom operators and VoIP service providers

• SBC (Session Border Controller) solutions

• SIP trunking platforms and VoIP gateways

Why reSIProcate/SipWise Still Matters
While not designed for casual developers, this stack is essential for high-load, high-security, telecom-grade environments. Active development continues to improve scalability and compliance, making it relevant in 2026 for large service providers.

4. SIP.js – The WebRTC-Friendly SIP Library

Overview
SIP.js is a modern JavaScript library for building SIP clients directly in the browser or Node.js. It bridges the gap between SIP signaling and WebRTC, allowing developers to implement audio, video, and messaging capabilities in web applications.

Key Features

• SIP over WebSocket transport

• Full integration with WebRTC for audio and video

• Lightweight and fast

• Easy-to-use API for rapid development

• Compatible with servers like Asterisk, Kamailio, and OverSIP

Use Cases

• Browser-based softphones

• Web conferencing apps

• Instant messaging platforms with real-time audio/video

Why SIP.js is Relevant in 2026
With the growth of web-based communication apps, SIP.js has become crucial for developers wanting to implement full RTC functionality without native applications. It is actively maintained and continues to adapt to modern browser standards.

5. JsSIP – Pure JavaScript SIP Endpoint

Overview
JsSIP is another powerful JavaScript SIP library designed for real-time communications in browsers. It emphasizes simplicity while providing full SIP compliance, including audio/video calls, instant messaging, and presence features.

Key Features

• 100% JavaScript, easy to embed in web apps

• SIP over WebSocket support

• Compatible with WebRTC for media transmission

• Lightweight and fast, with minimal overhead

• Works seamlessly with popular SIP servers

Use Cases

• Web-based softphones

• Customer support chat platforms with audio/video calling

• Lightweight RTC applications

Modern Advantages
JsSIP remains a top choice for developers needing SIP endpoints in web applications. Its API is beginner-friendly, yet robust enough for enterprise usage. Frequent updates and an active community keep it relevant alongside SIP.js.

Near-Honorable Mentions

While the above libraries dominate in 2026, several other open-source SIP libraries deserve attention:

• Linphone SDK: A complete softphone SDK with cross-platform support and integrated media handling.

• Baresip: Lightweight, modular, and portable SIP client for embedded systems.

• reSIProcate standalone: Direct use of the stack without SipWise NGCP wrapper.

These options are more niche but remain valuable for specialized use cases.

Choosing the Right SIP Library in 2026

The best library depends on project requirements, platform, and development resources:

Factors to Consider

1. Platform Support – Mobile, desktop, embedded, or browser.

2. Media Handling – Whether the library handles audio/video or just SIP signaling.

3. Scalability – High-volume service providers need robust, tested stacks.

4. Community & Maintenance – Active development ensures security patches and feature updates.

5. Ease of Integration – Libraries with clear APIs and documentation reduce development time.

Conclusion

Open-source SIP libraries provide developers with flexible, cost-effective, and reliable solutions for building modern communication systems. From PJSIP’s multimedia capabilities to SIP.js and JsSIP’s web-oriented simplicity, each library serves specific needs:

• PJSIP – Full-featured multimedia for mobile and desktop

• Sofia-SIP – Lightweight, standard-compliant signaling

• reSIProcate / SipWise NGCP – Carrier-grade, high-volume SIP routing

• SIP.js – WebRTC integration for browser-based applications

• JsSIP – Easy-to-use SIP endpoint for modern web RTC

By understanding their features, advantages, and use cases, developers can choose the right SIP stack to power their communication projects in 2026 and beyond.