Kamailio is a powerful open-source SIP server. It helps manage and route voice, video, and messaging over the Internet. One key aspect of using Kamailio effectively is understanding advanced configuration in Kamailio.
Advanced configuration in Kamailio means setting up the server in detailed and specific ways. In other words, it goes beyond Kamailio’s basic setup. This can make Kamailio perform better, stay secure, and handle more calls or messages. For anyone using Kamailio, knowing these advanced settings is crucial. It helps optimize performance, protect against threats, and ensure the system can grow with their needs.
To better understand such advanced configuration, keep reading this article. Here, you’ll learn about the different parts of advanced configuration in Kamailio. They cover scripting languages and database integration to performance tuning and security measures. But beforehand, let’s take a quick look at Kamailio’s architecture.
Kamailio is a robust SIP server using a hybrid approach. This approach is a perfect combination of modular architecture and a centralized configuration file (kamailio.cfg). Accordingly, Kamailio’s architecture includes several key components that work together smoothly.
This is the heart of Kamailio. It includes different core functionalities to handle the main processing tasks. Below are some of the core features:
These core components work together to offer the basic functionalities needed for Kamailio to operate as a SIP server. They form the foundation upon which additional features and modules are built. This allows Kamailio to be highly customizable and scalable.
Internal libraries are developed by the Kamailio project. Kamailio uses them to provide essential functions. Here are several outstanding libraries already built in Kamailio:
libkcore: This library offers core functions for memory management, string manipulation, and process handling. It’s fundamental to the operation of Kamailio.libsl: It handles stateful logic. It includes SIP transactions and dialog management. This library helps maintain the state of SIP sessions. libpv: It manages pseudo-variables. Pseudo-variables are used in configuration scripts to represent dynamic values, like SIP headers and message attributes.libut: It contains utility functions for many tasks. They involve data parsing, encoding, and decoding. The library helps simplify and standardize common operations. libsrdb1: This library provides database connectivity functions. It supports interactions with databases like MySQL, PostgreSQL, and others. This allows Kamailio to store and retrieve data. These internal libraries ensure that the server operates efficiently and can be extended with additional features through modules.
Please note that Kamailio also allows for the integration of external libraries and apps in many ways. This improves Kamailio’s flexibility and functionality beyond its native capabilities. You can use external libraries through Kamailio’s dynamic modules, KEMI, database connectors, and more. These external libraries can be libmysqlclient for MySQL to foster database connectivity with performance or Lua’s luasocket for network communication.
Before talking about Kamailio’s interface, let’s discover modules first.
In Kamailio, a module is a separate, pluggable component that extends the functionality of the core SIP server. As such, modules add extra features to Kamailio without modifying the core. In other words, changes or updates to modules do not affect the core as the core and modules are separated.
These modules can handle many tasks. They include user authentication (auth, auth_db), NAT traversal (nathelper, rtpproxy), load balancing (dispatcher, pdt), security (permissions, pike), database integration (db_mysql, db_postgres), etc.
Kamailio’s module interface connects these modules with the core. It’s designed to be a plug-and-play interface. Accordingly, administrators can dynamically load or remove these modules. This design ensures great stability for the core components and easy customization.
The core also provides a stable API that modules use to interact with it. This ensures that modules can rely on a consistent set of functions and data structures. Also, you can reduce the risk of instability when adding new extensions.
Kamailio’s configuration files are used to define the server’s behavior and control its operations. These files contain settings, directives, and scripts. They clarify how Kamailio should process SIP messages, interact with databases, load modules, and perform other tasks.
The main configuration file of Kamailio is kamailio.cfg. But there are also other related configuration files that may be used for specific purposes. For example, db_mysql.cfg contains settings specific to the MySQL database’s connectivity and interactions. Meanwhile, kamctlrc configures the kamctl tool, which is a command-line utility for managing Kamailio. This configuration file involves settings for database access, SIP domains, and other parameters.
Here, we focus on Kamailio’s core configuration file. kamailio.cfg is where most of the server’s behavior is defined. It dictates the initial server state, including global settings, module loading instructions, routing logic, and other configurations.
Here’s an example of kamailio.cfg:
Proper configuration is essential to optimizing Kamailio’s performance. By fine-tuning and advancing configuration in Kamailio, you can ensure efficient memory usage and fast message processing. Configuring modules correctly can improve security, foster load balancing, and handle more traffic. Good configuration leads to a stable, high-performing SIP server.
We’ve understood some core components of Kamailio and their functions. So, how do all these components interact? Let’s take a look: The core handles SIP messages based on the settings in the configuration files. Internal libraries support the core by offering necessary functions. Further, the module interface connects the core with various modules, enhancing its capabilities. Configuration files, meanwhile, guide the core and modules on how to operate and interact with each other.
Advanced configuration in Kamailio involves refining the SIP server to meet specific requirements for performance, scalability, and functionality. Here are the ten key aspects you should consider:
Kamailio has its proprietary scripting language for configuration. This language is a domain-specific language (DSL). It’s optimized for high-performance and efficient call processing. It’s ideal for core call routing logic, performance-critical operations, and tight integration with Kamailio internals (like data structures).
But what if you’re not familiar with the native scripting language? Use external scripting languages through KEMI (Kamailio Embedded Interface) to write your configuration scripts. This framework offers more flexibility and power than the native DSL, especially for complex logic and interactions. Some popular languages like Lua, Python, or Ruby are all supported. For this reason, the KEMI framework makes Kamailio more accessible to developers.
Here’s a simple example in Python to illustrate how KEMI works:
def ksr_request_route():
if KSR.pv.get("$rm") == "INVITE":
KSR.info("Received an INVITE request\n")
KSR.sl.send_reply(100, "Trying")
return 1
This script handles incoming INVITE requests. It logs a message and sends a 100 Trying response.
By using external scripting languages through KEMI, you can:
To get started with KEMI, choose a scripting language you know well. Then, write your script, load it into Kamailio, and let KEMI handle the rest. The framework allows you to seamlessly integrate your script with Kamailio’s core.
For those familiar with those external scripting languages, KEMI is a plus. But they can introduce potential challenges, despite those benefits. They might involve performance overhead, resource management issues, or inconsistencies with Kamailio’s core.
SIP trunking and interoperability are considered advanced configuration aspects in Kamailio. Technically, SIP trunking is a digital method of making and receiving calls over the Internet. It connects your IP-based phone systems to the public telephone network using SIP.
SIP trunking helps reduce telephony costs as it replaces traditional PSTN (Public Switched Telephone Network) lines. Further, it provides scalability, advanced features (e.g., call forwarding), and greater control over your telephony infrastructure). With these benefits, the global SIP trunking market is estimated to increase from USD13.87 billion in 2023 to USD36.74 billion in 2031.
In Kamailio, you configure SIP trunks through the routing script. Here’s a simple guide to set up these trunks in this SIP server:
NAT stands for Network Address Translation. It changes IP addresses and ports in SIP packets as they pass through firewalls or routers. This can cause problems with SIP communication. So, Kamailio needs to be configured to process these changes and ensure messages reach their destination.
NAT Traversal is an advanced configuration method in Kamailio. It involves various techniques to let devices behind a router (your office network) interact directly with each other. Here’s how to handle NAT traversal effectively in Kamailio:
nathelper module: This module helps manage NAT traversal by detecting and correcting NAT issues. All you need to do is load and properly configure in your Kamailio setup.Contact header: This header defines the address where a SIP request should be sent. When SIP messages go through a NAT device (e.g., a router or firewall), NAT can change the IP address and port in the Contact header. Configuring Kamailio can adjust or rewrite the header to fit the correct public IP and port. 
Kamailio provides basic features to integrate various databases (e.g., MySQL or PostgreSQL). They involve basic operations and configurations like user authentication, basic routing, or simple SQL queries. These capabilities are often suitable for smaller or less complex setups where the requirements are quite straightforward.
Kamailio also offers advanced database integration features. They help you significantly enhance Kamailio’s capabilities, support larger deployments, and ensure robust SIP operations. Advanced database integration, accordingly, involves more complex configurations and interactions. It includes:
And more!
Routing logic in Kamailio is about deciding how SIP messages are processed and routed within your network. It’s crucial for managing calls, registrations, and other SIP transactions effectively. Therefore, proper routing is a must.
Kamailio allows you to set up basic routing rules in simple scenarios (e.g., directing calls based on dialed number prefixes or caller ID). Accordingly, you can use database lookups, conditional statements, and other built-in functions in Kamailio’s native configuration language to build these rules. Basic routing is often sufficient for smaller networks with clear requirements.
Yet for more complex setups, advanced routing rules come into play. These rules allow you to direct SIP messages based on various factors like user preferences, time of day, and load balancing. Advanced routing enables more flexible and efficient handling of SIP traffic. So, don’t ignore complex routing logic when learning about advanced configuration in Kamailio.
Here’s how you can configure and optimize routing logic in Kamailio:
dispatcher module is useful for load balancing and failover scenarios. Meanwhile, drouting is often used for managing domain-based routing. 
High availability and clustering are advanced configuration features supported by Kamailio. They aim to make the SIP server more reliable and scalable. In particular, HA ensures that Kamailio continues to function without interruptions if one or more of its components fail. Meanwhile, clustering refers to grouping various Kamailio instances and ensuring they work smoothly as a unified system. This helps handle larger volumes of SIP traffic and provides scalability.
Setting up HA and clustering effectively in Kamailio requires careful configuration and additional components. This involves:
Besides these factors, you can consider performance optimization and testing. These components ensure that the setup is reliable and performs well under various conditions.
Kamailio offers several basic security features to safeguard SIP messages and calls. They involve user authentication, IP whitelisting & blacklisting, rate limiting, and more. But to enhance protection and control over SIP communication, Kamailio provides a wide range of advanced security features in its configuration. Here’s an overview of some functionalities available in Kamailio:
tls module in your Kamailio configuration. This module handles all TLS-related operations. Moreover, Kamailio supports other advanced security measures. They include advanced rate limiting & throttling, anti-fraud mechanisms, SIP firewall & access controls, secure RTP (Real-Time Protocol) integration, etc.
These capabilities in Kamailio are about tracking and recording various aspects of the SIP server’s operations and traffic. Proper monitoring and logging are crucial to ensure the server’s seamless performance and security.
Kamailio already integrates basic logging and monitoring capabilities. They include syslog integration, standard log levels, log format customization, and monitoring with standard Linux tools like tail, grep, or awk.
Further, you can leverage Kamailio’s advanced configuration capabilities to enable thorough monitoring, detailed analysis, and proactive management of your SIP server. These features include:
log_custom to define specific log formats and SIP message parameters. This enables highly detailed and customizable logging. db_mysql to log SIP transactions and events to a database for more structured and queryable records.logrotate to manage log file sizes and maintain long-term records without consuming excessive disk space. rtpengine module to monitor RTP streams and gather metrics for analysis. event_route functionality to trigger actions based on specific events. This can involve alerting systems, automated responses to detected anomalies, and integration with SIEM (Security Information and Event Management).
Kamailio offers both basic and advanced features for performance optimization. These features ensure that the SIP server operates efficiently, even under high load conditions. This further helps maintain the overall performance of the VoIP infrastructure.
For simple requirements, adjusting core and module parameters can significantly impact performance. Typically, tuning the tcp_children, udp_children, and shm_mem parameters can optimize resource usage. In addition, you can properly configure the memory settings to ensure each memory is well distributed to handle SIP messages. You may also use the Load Balancing functionality to allocate traffic evenly across Kamailio servers. All these things help improve performance and scalability.
On the other hand, you can leverage Kamailio’s advanced configuration for enhanced performance. Some advanced performance optimization features include:
db_mysql can support connection pooling. This helps improve the performance of database operations.db_async module helps Kamailio initiate a database query and continue processing SIP messages without waiting for the query to complete. This particularly improves the SIP server’s performance and efficiency. 
Kamailio helps you create custom modules beyond its core capabilities. These modules primarily require C and Lua with libraries (GCC or Clang), Kamailio’s internal APIs, and other tools. Further, its KEMI framework supports other scripting languages like Python, Squirrel, or JavaScript for custom module development.
As we already said, Kamailio has a powerful and flexible configuration language. But this language isn’t designed to develop custom modules. Instead, it helps you write scripts and define custom logic within the kamailio.cfg configuration file. This language is sufficient for basic and moderately complex tasks.
Yet for specific and advanced needs, you can develop custom modules to extend Kamailio’s functionality. These modules can be custom SIP message handling, asynchronous operations, and integration with external databases or services.
Now, you’ve gone through a detailed guide of advanced configuration in Kamailio. From external scripting languages and SIP trunking to advanced security measures, Kamailio covers everything to enhance its performance and ensure SIP communication works smoothly. If you want to learn more about Kamailio and other SIP servers, subscribe to our blog to receive the latest articles!
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