OpenSIPS vs. Kamailio: Key Differences to Know for Your Next VoIP Project

OpenSIPS and Kamailio are two popular open-source SIP (Session Initiation Protocol) server projects that originated from the same codebase (SER – SIP Express Router). They’re widely used for handling VoIP calls, SIP routing, instant messaging, and other real-time communication services. Though they are similar in many ways, they have diverged over the years, each developing distinct features and communities. Here’s a comparison of key aspects:

1. Community and Development Focus

• Kamailio: Focuses on stability and compatibility. The project has a more conservative approach to feature implementation, ensuring a robust base for handling a wide range of SIP applications.

• OpenSIPS: Often adds newer, experimental features and has a community more focused on rapid feature development and customization. It is particularly popular for applications requiring complex routing logic.

2. Performance and Scalability

Both OpenSIPS and Kamailio are designed for high-performance SIP handling, but the specific implementations differ:

• Kamailio: Known for its efficiency in handling high-volume scenarios. The core developers prioritize optimization for stability over adding features. Kamailio’s architecture is lightweight, making it highly scalable.

• OpenSIPS: Offers excellent performance as well but often includes more tools out of the box for distributed deployments and advanced load balancing. It also has various modules for things like clustering, which can help in complex, large-scale environments.

3. Feature Sets and Modules

• Kamailio: Includes a large set of modules to handle SIP, WebRTC, instant messaging, presence, and security. It also has a wide range of third-party integrations, especially with backend databases, making it ideal for various VoIP applications.

• OpenSIPS: Offers unique modules geared towards complex SIP setups, such as fraud detection, call control, and load balancing. OpenSIPS is often chosen for more advanced SIP routing features, media handling, and real-time monitoring.

4. Configuration and Scripting Language

• Kamailio: The scripting language used by Kamailio is widely considered to have a steeper learning curve, but it offers flexibility for advanced users. Kamailio’s scripting allows for detailed control of SIP message handling and offers various control structures for conditional processing.

• OpenSIPS: Uses a configuration language based on Kamailio’s but has evolved with a focus on simplifying the syntax for complex scenarios. OpenSIPS often abstracts certain functions, making it easier for new users to get started with advanced setups.

5. Use Cases and Target Applications

• Kamailio: Often chosen for carrier-grade solutions, large VoIP providers, and telecom operators where stability, interoperability, and performance are critical.

• OpenSIPS: Popular in contact centers, hosted PBX, WebRTC, and environments needing intricate routing and load-balancing setups. It’s also a preferred choice for businesses focused on distributed, high-availability architectures.

6. Documentation and Community Support

• Both projects have active communities, though OpenSIPS tends to release new features more quickly, resulting in rapid updates to its documentation. Kamailio has a more extensive history of community support and a comprehensive set of stable modules.

7. Integration with Media Servers

• While both can be configured to work with media servers like Asterisk and FreeSWITCH, OpenSIPS provides additional modules that can make it easier to manage and control media resources.

Summary

• Kamailio is more stability-oriented and favored by telecom companies for high-volume SIP processing and compatibility.

• OpenSIPS is often chosen by businesses needing highly customizable, complex routing logic and load balancing in more dynamic, experimental environments.

For most users, the choice depends on their specific requirements in terms of stability vs. feature richness, ease of configuration, and scalability needs.