Advanced Configuration in Kamailio: A Comprehensive Guide

Understand 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.

1. Core

This is the heart of Kamailio. It includes different core functionalities to handle the main processing tasks. Below are some of the core features:

SIP Message Handling: This is responsible for handling SIP messages. It monitors the sending, receiving, and parsing of these messages. This is crucial for the server’s communication functions.

Transaction Management: This handles SIP transactions. It tracks the state of each SIP request and response. This ensures that messages are properly correlated and managed.

User Location Service: This tracks the location of registered users. It allows Kamailio to route SIP messages to the correct destination based on the user’s current location.

Transport Layer Management: This monitors the transport layer protocols. This includes handling TCP, UDP, and TLD connections. It ensures reliable message transmission over the network.

Script Execution: This core executes the configuration scripts written in Kamailio’s scripting language of the KEMI (Kamailio Embedded Interface) framework. These scripts define the server’s behavior and routing logic.

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.

2. Internal Libraries

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.

3. Module Interface

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.

4. Configuration Files

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.

How All These Factors Interact

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: 10 Key Aspects

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:

1. External Scripting Languages through KEMI

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:

Handle complex business logic (like decision-making processes) when the built-in scripting language falls short.
Integrate external systems (e.g., databases or other servers) with ease.
Quickly test new ideas or features.
Create custom scripts or extensions to add unique features or incorporate Kamailio with other systems.
Gain some performance benefits in such certain scenarios as heavy data manipulation & analysis, database queries, and parallel processing.
Possibly increase development speed.

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.

2. SIP Trunking

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:

Identify Your Providers: When setting SIP trunking in Kamailio, you’ll connect to external SIP trunking providers. So, the first step is to define a reliable provider (like Twilio, Plivo, and 8×8). Also, consider how your provider is compatible with your specific needs. To set up SIP trunking with a provider, you need to configure Kamailio with the provider’s server IP addresses, the correct port numbers for SIP traffic, and authentication details (depending on the provider). This information helps you establish a secure and functional connection.

Configure the Routing Script: Next, use the information above to create entries in your Kamailio routing script. This script tells Kamailio where to send outgoing calls.

Authentication: Set up authentication if required. Many providers need your system to authenticate before using their services.

Handle SIP Headers: SIP headers are crucial for ensuring calls go through. Sometimes, providers have specific requirements for these headers. So, you might need to modify or add headers in your SIP messages with Kamailio’s script functions.

Test Calls: Make test calls to verify everything works well.

3. NAT Traversal

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:

Configure the 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.

Set up 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.

Monitor SIP signaling: NAT can disrupt SIP signaling. So, configuring Kamailio handles SIP signaling correctly. This includes setting up rules to manage SIP messages that pass through NAT devices.

Handle RTP (Real-Time Protocol) streams: These streams, used for media communication, can also face NAT issues. So, it’s essential to establish RTP relays or proxies to monitor media traffic.

Use STUN & TURN servers: STUN (Session Traversal Utilities for NAT) helps discover the public IP address. Meanwhile, TURN (Traversal Using Relays around NAT) relays traffic when direct communication isn’t possible. Configuring Kamailio to work with these servers helps with NAT traversal.

Set up ICE (Interactive Connectivity Establishment): This framework eases the negotiation of the best path for SIP communication. Ensure Kamailio is configured to use ICE for improved NAT traversal.

4. Advanced Database Integration

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:

Complex Schema Design: Design and manage complex database schemas that support many SIP functionalities. This might include tables for detailed user profiles, advanced routing rules, and detailed call records.

Custom Queries and Procedures: Write custom SQL queries and stored procedures to handle complex operations. This can involve dynamic routing, advanced user authentication mechanisms, and integration with other services.

Real-Time Data Updates: Dynamically modify call routing based on information in the database.

Scalability: Set up database replication and clustering to manage large volumes of data and high transaction loads.

Backup and Recovery Strategies: Implement robust measures like regular backups, disaster recovery plans, and testing recovery procedures. This ensures data integrity and availability.

And more!

5. Routing Logic

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:

Dynamic Routing: This adjusts the message path in real time based on your current network’s conditions. It considers factors like server loaf, network congestion, and availability. Dynamic routing helps maintain optimal performance and reliability.

Routing Modules: Kamailio offers various modules to improve routing logic. Each module adds specific functionalities to handle complex routing requirements. For example, the dispatcher module is useful for load balancing and failover scenarios. Meanwhile, drouting is often used for managing domain-based routing.

Load Balancing: Using load balancing distributes SIP traffic evenly across various servers. This ensures no single server becomes a bottleneck. It then can enhance overall system performance and reliability.

Geographic Routing: This routes SIP messages based on the geographical location of the caller and receiver. This can reduce latency and improve call quality by choosing the closest available servers.

6. High Availability (HA) and Clustering

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:

Careful Configuration: This involves more than just installing Kamailio on numerous servers. Here’s what to consider:
- You need to carefully configure each instance to work harmoniously within the HA or cluster environment.
- Ensure that all Kamailio instances have the same configuration to avoid inconsistencies.
- Configure failover mechanisms and routing to process SIP traffic properly. This might involve DNS settings, load balancer configurations, and failover scripts.
- Configure access to a shared database or data synchronization methods so that all instances have consistent data.

Additional Components: Achieving HA and clustering also requires Kamailio to integrate with other components. For example:
- Load balancers: This distributes SIP traffic across the Kamailio instances evenly. It helps manage the load and improve performance.
- Health Monitoring: Such tools as Prometheus or Nagios check the status of Kamailio instances and trigger failover if needed.
- Shared Databases: You should set up and configure a shared database (e.g., MySQL or PostgreSQL) to store user information and SIP routing data. Ensure that the data is also highly available and synchronized.
- Configuration Management: Such tools as Ansible or SaltStack automatically deploy and monitor Kamailio across multiple servers.

Besides these factors, you can consider performance optimization and testing. These components ensure that the setup is reliable and performs well under various conditions.

7. Advanced Security Measures

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:

Advanced Authentication & Authorization: The server adds an extra layer of security by two-factor authentication (2FA). It also supports OAuth for secure and token-based authentication.

Transport Layer Security (TLS): TLS encrypts SIP messages as they travel across your network. This ensures no one can read or change them when they intercept these messages. To enable TLS in Kamailio, load the tls module in your Kamailio configuration. This module handles all TLS-related operations.

End-to-End Encryption (E2EE): This helps encrypt SIP messages from the sender to the receiver. This prevents unauthorized users from accessing the content.

Intrusion Detection & Prevention Systems (IDPS): Kamailio can integrate external IDPS tools like Suricata or Fail2Ban to monitor, detect, and block malicious activity in real time.

Dynamic Blacklisting and Whitelisting: Kamailio can be configured to automatically update blacklists and whitelists based on real-time threat intelligence and traffic analysis. Then, it can analyze user behavior to identify and block suspicious IP addresses dynamically.

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.

8. Monitoring and Logging

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:

Detailed Custom Logs: Kamailio uses modules like log_custom to define specific log formats and SIP message parameters. This enables highly detailed and customizable logging.

Database Logging: Kamailio uses modules like db_mysql to log SIP transactions and events to a database for more structured and queryable records.

Log Rotation: Kamailio uses tools like logrotate to manage log file sizes and maintain long-term records without consuming excessive disk space.

Advanced Real-Time Monitoring: Kamailio can integrate with real-time monitoring tools like Grafana and Prometheus. It also uses the rtpengine module to monitor RTP streams and gather metrics for analysis.

SIP Capture and Analysis: Kamailio can incorporate tools like Homer and HEP (Homer Encapsulation Protocol) for advanced SIP capture, logging, and real-time analysis.

Event-Driven Monitoring: Kamailio uses the 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).

9. Performance Optimization

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:

Database Connection Pooling: Modules like db_mysql can support connection pooling. This helps improve the performance of database operations.

Asynchronous Database Queries: Kamailio supports asynchronous database operations in some modules. This allows Kamailio to handle database interactions more efficiently. For example, the 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.

Caching: Kamailio allows caching, which is another advanced configuration feature. Such caching as DNS caching and user location caching reduces latency and improves performance.

Stateless Processing: Stateless processing of SIP messages can reduce the overhead of maintaining transaction state. This is particularly useful for high-throughput scenarios.

Profiling and Performance Monitoring: Tools like SIPp for load testing and Homer for SIP capture and analysis can identify performance bottlenecks and optimize accordingly. Kamailio can integrate Prometheus to monitor performance metrics in real time and Grafana to visualize them.

10. Custom Module Development

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.

Conclusion

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!