SIP Routing in Kamailio: How to Create Complex Routing Rules

Understand SIP Routing Basics

Core Concepts of SIP

SIP, or Session Initiation Protocol, is a communication protocol used in VoIP. It helps start, manage, and end voice and video calls over the Internet. SIP can also be used for instant messaging and multimedia sessions. The protocol is simple yet powerful. This makes it ideal for many communication needs.

SIP works by sending messages between endpoints. These messages help establish a connection. Once connected, the endpoints can exchange data. SIP can process various types of calls and is flexible in different network environments.

Types of SIP Message

SIP messages are the fundamental units of communication in SIP routing. They carry the necessary instructions to start, monitor, and terminate a session. Each SIP message must be routed through various network components (e.g., SIP servers) to reach its destination. Based on the type of message, Kamailio can identify the routing logic that should be applied.

Here are some important types:

INVITE: This message initiates a call. It involves the other party to join.
ACK: This message confirms that a call has been set up.
OPTIONS: This message checks the capabilities of the other party. It helps decide how to handle the call.
BYE: This message ends a call. It signals that the session should be terminated.
CANCEL: This message stops a call that hasn’t been completed yet. It’s used when the call should not proceed.
REGISTER: This message registers a user with the SIP server. It helps locate the user for future calls.

SIP Headers & Their Importance

These headers provide important information about a call. This information involves details about the sender, call status, etc. SIP headers play a role in ensuring the call is correctly processed and directed. Here are several key headers:

From: This header shows who is making the call. It includes the caller’s information.
To: This header shows who is receiving the call. It includes the callee’s information.
Via: This header tracks the path of the message. It shows which servers the message has passed through.
Call-ID: This header gives a unique identifier to each call. It helps keep track of the call throughout its lifecycle.
CSeq: This header contains a sequence number. It helps manage the order of messages within a call.

Basic Routing Principles

SIP messages can be routed in different ways. Here are some basic principles of SIP routing to consider:

Direct Routing: In this routing, the call goes straight from the caller to the receiver. This method is simple but not always possible in complex networks.
Redirect Routing: This involves a server that tells the caller where to send the call. Then, the call is directed to the new destination.
Proxy Routing: In this method, a server acts as an intermediary. It forwards the call from the caller to the receiver. This helps manage and control the call more effectively.

Each routing method has its pros and cons. This all depends on the network setup and requirements. Understanding these principles is crucial to monitor SIP calls efficiently.

Understand Complex SIP Routing Rules with Kamailio

When to Use Complex SIP Routing

Basic SIP routing is not always necessary. In some certain scenarios, complex routing proves more helpful. They include:

High Traffic: When a network handles a large number of users across multiple locations, simple routing can’t process such a setup efficiently. Complex routing rules come into play to help distribute the traffic more evenly.

Specific Call Treatments: If your company wants to route VIP customers differently, you may need their calls prioritized or directed to special support teams. Or in situations where calls need to be routed based on the time of day, complex routing can also help. For example, calls during business hours might be directed to the main office. Meanwhile, after-hours calls can go to an answering service.

Geographic Distribution: Basic routing can handle geographic distribution well in scenarios where conditions don’t change much or a server load is stable. Yet in reality, network conditions and user locations can change. Not to mention that a server can be overloaded, fail to work, or require multiple factors for routing. This is when you need complex routing rules to handle all these issues.

Disaster Recovery: Basic routing can struggle to reroute calls effectively In cases of server failure or network issues. Complex routing includes advanced failover mechanisms that automatically redirect calls to backup servers. This ensures continuity.

Implementing complex routing offers several benefits. It provides more control over call flow and enables customized handling of different call types. Further, complex SIP routing fosters network efficiency and adds flexibility when your business grows. It also includes rules that detect and block suspicious activities. This helps protect the network from cyberattacks.

Different Types of Complex Routing in Kamailio

There are various types of complex SIP routing in Kamailio. Each involves specific rules and logic that go beyond simple call routing. They add layers of control and flexibility, enabling more custom call management.

Below are some types of complex routing to consider:

1. Load Balancing Routing

This type of routing can distribute calls across multiple servers to prevent any one server from being overloaded. This keeps your system responsive and stable, especially when one server is busy.

2. Failover Routing

This helps continue your calls and maintain service during outages. In particular, Kamailio can automatically direct calls to a backup server when a primary server goes down. For this reason, this type of routing is useful in mission-critical environments where downtime is not an option.

3. Geographic Routing

This directs calls based on the physical location of the user. Accordingly, Kamailio can route calls to the nearest and most efficient server. This reduces latency and fosters call quality.

4. Time-Based Routing

This type of routing routes calls based on the time of day.

5. User-Based Routing

This allows calls to be directed based on the specific needs of the user. For example, VIP customers can have their calls routed to specialized support teams.

6. Least Cost Routing (LCR)

LRC chooses the most cost-effective route for a call based on a carrier rate. This helps optimize costs for your business.

7. Number Translation

This involves mapping phone numbers to different destinations. This is useful when numbers need to be altered or rerouted based on specific rules.

8. Call Barring

This type of routing restricts certain calls based on criteria like the caller’s number or destination. This allows you to block unauthorized or unwanted calls.

9. Call Forwarding

This uses complex rules to automatically redirect calls to different destinations based on predefined conditions.

10. IVR Integration

This integrates interactive voice response systems into the routing process. Kamailio can work with IVR systems to guide callers through menus. Then, it routes these callers to a suitable destination based on their requirements.

Considerations Before Creating Complex SIP Routing Rules

You’ve understood when to use complex SIP routing rules and their different types. But what do you need to build complex routing with Kamailio? Let’s look at building blocks, scripting languages, APIs, and tools:

Building Blocks of Complex SIP Routing

Blocks are active parts of the Kamailio configuration. They’re modular units of logic that can be combined and chained together to form complex routing decisions. Accordingly, they allow Kamailio to process SIP messages, make dynamic routing decisions, interact with external systems, and more. These building blocks are key to ensuring that SIP messages are routed efficiently. For this reason, they’re crucial when creating complex SIP routing rules in Kamailio.

Scripting Languages

Kamailio uses two main types of languages:

Kamailio Configuration Language: This is a domain-specific language (DSL) created for configuring SIP routing and related tasks within Kamailio. These tasks include defining global parameters, loading modules, setting module parameters, and creating routing blocks.

External Scripting Languages: Kamailio offers the KEMI (Kamailio Embedded Interface) framework that supports the integration of various scripting languages. This allows for more complex SIP routing logic. Some popular languages supported are Lua, Python, JavaScript, Squirrel, and Perl.

APIs

Kamailio excels at handling SIP standards and protocol-specific tasks like parsing SIP messages or managing SIP headers. But it may not be designed to handle certain business decisions. This is where APIs come into play. They allow Kamailio to interact with external systems that support billing, authorization, etc. They, accordingly provide more dynamic and context-aware routing that can adapt to changing conditions or user preferences.

Tools

When creating complex SIP routing rules with Kamailio, you should consider these tools:

Database: Database integrations are crucial. Kamailio can connect to such databases as MySQL and PostgreSQL to store and retrieve routing information. These databases contain important data, like user profiles, routing tables, and billing information. By querying these databases, Kamailio can make informed routing decisions in real time. For example, you might store carrier rates in a database and use that information to implement least-cost routing.

SIP Testing Tools: These tools simulate SIP traffic. This allows you to test your configurations in a controlled environment. SIPp is a widely used tool for this purpose. It can generate SIP calls and measure the performance of your routing rules. By using SIPp, you can detect potential issues, like delays or incorrect routing, before deploying your configuration in a live environment.

Monitoring and Debugging Tools: Kamailio offers several built-in tools for monitoring and debugging. kamctl is a command-line tool that helps you manage Kamalio in real time. It enables you to view active sessions, check the status of your server, and even reload configurations without restarting Kamailio. For deeper debugging, Kamailio provides modules like debug and siptrace. These modules allow you to trace SIP messages and log detailed information about routing decisions. By analyzing this data, you can troubleshoot issues and refine your routing rules.

5 Steps to Create Complex SIP Routing Rules

Now, let’s delve into our detailed guide to generating complex SIP routing rules within Kamailio:

Step 1: Define Clear Requirements

The first step in creating complex SIP routing rules is to define clear requirements. Here’s what you can do in this step:

First, outline the desired routing behavior. Think about what you need your routing rules to do. Do you want certain calls to go through specific routes? Are there particular scenarios where calls need special handling? For instance, you might want to prioritize calls from VIP customers or route calls differently based on their destination. Be as detailed as possible. The more specific your requirements, the easier it will be to create precise routing rules.

Next, consider many factors that could influence routing decisions. These might include call types, caller/callee identity, time of day, network conditions, and more. By carefully considering these factors, you can create a set of clear, actionable requirements.

Step 2: Utilize Scripting

Here, you can use the Kamailio configuration and building blocks to create complex SIP routing rules. However, your routing logic requires even more complexity or needs to interact with external systems in a more dynamic way, you must use external scripting languages through KEMI. KEMI allows you to use languages like Lua, Python, or JavaScript to implement advanced, custom logic. Such logic goes beyond what the native configuration language can process.

Step 3: Leverage Kamailio’s Features

With such scripting languages, you can access a range of built-in functions, modules, and pseudo-variables. These components help you design and implement complex routing logic that controls how SIP messages are processed. For instance, you might use a script to dynamically build routing rules based on data from an external API or database. This enables your SIP server to adapt its behavior based on real-time information.

Here are several factors you should consider:

Conditions: Conditions are crucial for defining how to handle SIP messages. They help you create complex routing rules by specifying when and how to take certain actions. Kamailio provides a variety of built-in functions to set these conditions. For example, $rU(“user”) checks the user part of the Request URL, hence becoming useful for routing based on the identity of callers or callees.

Actions: Actions in Kamailio monitor how SIP messages are processed and routed. They allow you to manipulate messages and direct call flow effectively. For instance, $reply sends a SIP rely back to the sender, thus becoming useful for responding to requests with specific status codes.

Modules: Kamailio’s modules offer additional functionalities to advance your routing rules. Each module comes with specific capabilities. For example, db allows Kamailio to query and update database records. Meanwhile, auth handles authentication. It ensures that only authorized users can make and receive calls.

Pseudo-variables: These components allow you to retrieve specific information from SIP messages. It can involve the caller’s ID or destination.

Step 4: Modularize Your Configuration

When creating complex SIP routing rules in Kamailio, you should break down the configuration into smaller, reusable functions or modules. This approach is known as modularization. It’s key to managing complexity effectively while improving readability and maintainability. Modularization also eases testing and debugging.

Here’s why:

Each function or module handles a specific task. This makes the overall logic easier to understand. Instead of dealing with one large, monolithic script, you can work with smaller pieces that are easier to manage and update.

Further, you can test each function in isolation before integrating it into a larger system. This helps you identify errors easily and ensure that each part of your routing logic works as expected. If something goes wrong, you can quickly focus on the specific module, rather than sifting through an entire configuration file.

Step 5: Conduct Thorough Testing

Once you’ve created complex SIP routing rules in Kamailio, carefully test them to ensure they work as expected. Testing helps you discover any issues. It also confirms that your routing logic performs well under different conditions.

Start by designing detailed test cases that cover all aspects of your routing logic. These test cases should verify that the routing functions as intended in various scenarios, including edge cases. For instance, test how calls are routed during peak traffic times or when certain routes are unavailable. By covering a wide range of possibilities, you can ensure that your routing rules are robust and reliable.

Don’t ignore SIP testing tools. These tools allow you to create different types of SIP traffic by simulating various call scenarios. This helps you see how your routing logic handles real-world situations and catch potential problems early.

In addition to functional testing, it’s important to monitor system performance and resource usage. Keep an eye on how your system behaves under load and check for any signs of bottlenecks or inefficiencies. This way, you can ensure that your routing rules are not only correct but also optimized for performance. Then, you can maintain a balance between functionality and efficiency. This helps your SIP server handle traffic seamlessly.

Final Words

Through this article, we elaborated on the basics of SIP routing and the importance of complex routing in Kamailio. Further, we detailed each key step to create complex routing rules in this server. Creating these intricate rules is an ongoing process. This requires you to constantly monitor call traffic, analyze performance metrics, and adapt to your routing logic to changing requirements. Subscribe to our blog for more info about SIP routing!