The Difference Between SIP and PJSIP

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When it comes to Voice over IP (VoIP) communication protocols, two commonly used options are SIP and PJSIP. While both protocols serve the same purpose of enabling audio and video communication over the internet, there are some key differences between them. In this article, we will explore the distinctions between SIP and PJSIP, helping you understand which one might be the best fit for your communication needs.

1. Understanding SIP

SIP, which stands for Session Initiation Protocol, is a signaling protocol widely used for initiating, maintaining, and terminating real-time sessions between two or more participants. It is an open standard protocol that allows for voice, video, and instant messaging communication over IP networks.

SIP operates by establishing and managing communication sessions, handling call setup, modification, and termination. It is highly extensible and flexible, making it compatible with various devices and platforms. SIP has been widely adopted and is supported by many VoIP service providers and devices.

2. Introducing PJSIP

PJSIP, on the other hand, is a free and open-source multimedia communication library that implements various protocols, including SIP, as well as other protocols such as RTP, RTCP, and SDP. PJSIP provides a high-level API for building VoIP applications, making it a popular choice for developers.

One of the key advantages of PJSIP is its modular architecture, which allows developers to select and incorporate only the necessary components, resulting in a smaller and more efficient system. Additionally, PJSIP offers a wide range of features and supports advanced functionalities, such as encryption, NAT traversal, and audio/video codecs.

3. Feature Comparison

While both SIP and PJSIP serve the same purpose, there are some notable differences in terms of features and capabilities.

3.1. Extensibility: SIP is a well-established protocol with a large ecosystem of devices and services built around it. This makes it easier to find compatible hardware and software solutions. PJSIP, on the other hand, offers more flexibility for developers to customize and extend the functionality of their applications.

3.2. Codecs: Both SIP and PJSIP support a wide range of audio and video codecs. However, PJSIP provides a more extensive selection of codecs, including some newer and more efficient options.

3.3. NAT Traversal: Network Address Translation (NAT) traversal is a crucial feature for VoIP communication, especially in scenarios where devices are behind firewalls or routers. While SIP has some NAT traversal mechanisms, PJSIP offers more advanced and robust NAT traversal techniques.

3.4. Encryption: Security is paramount in any communication system. While both protocols support encryption, PJSIP provides more options and flexibility for implementing secure communication channels.

4. Choosing the Right Protocol

When deciding between SIP and PJSIP, it’s essential to consider your specific requirements and circumstances.

If you are looking for a widely supported and established protocol with a large ecosystem, SIP might be the better choice. It is suitable for most standard VoIP applications and offers compatibility with a wide range of devices and services.

However, if you are a developer or require advanced customization and flexibility, PJSIP is worth considering. It provides a powerful API and extensive feature set, allowing you to tailor your VoIP application to your specific needs.


In summary, SIP and PJSIP are both valuable protocols for VoIP communication, each with its own strengths and use cases. Whether you choose SIP for its compatibility and wide support or opt for PJSIP for its flexibility and advanced features, both protocols have proven to be reliable choices in the world of Voice over IP.

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