Kamailio - Getting Started Guide

A collection of guidelines and useful links to smoothen the understanding and deploying of Kamailio for newbies.

Feel free to add new content here.

The first version of the tutorial was written for Kamailio v4.3.x.

It is recommended that you read first all the content of this tutorial and then start installing Kamailio, because some more relevant information might be found later for specific use cases.

Prerequisites

SIP

The initial name of the project was SIP Express Router (aka SER) and that says it all: Kamailio is a SIP router at the core. It means that it works at the lower layer of SIP packets, routing each and every SIP message that it receives based on the policies specified in the configuration file.

It is important to understand that it is not a telephony engine at its core, a VoIP call is seen as a sequence of SIP messages sharing the same attributes for caller, callee and signaling tokens such as Call-ID, From tag and To tag.

Given the above, a good understanding of SIP is critical to get faster familiar with Kamailio, especially with its configuration file routing rules.

Session Initiation Protocol (SIP) is specified by IETF (), with the core specification in the RFC 3261:

Many other RFCs add to the core specifications, look at what is published by the IETF Working Groups for SIP and SIMPLE.

IETF RFC documents are a bit dry to read, with particular language suitable for technical specifications, therefore trying to learn SIP directly from RFCs could be not that easy. Fortunately there are plenty of free online resources, tutorials or blogs, as well as books, that can help understanding SIP faster.

A SIP Introduction tutorial was written by SER/Kamailio developers quite some time ago. It is available inside source tree of Kamailio, in the folder doc/sip/. It is docbook xml format, the html version can be read online at:

Other online SIP learning resources:

SIP Books:

Logical Programming

Kamailio configuration file is not just a set of 'parameter=value' line. It has active components for runtime, named routing blocks. A routing block is a group of actions that specify what should be done for each SIP message.

The actions are exported by Kamailio core or modules and are like functions exported by a library. Those actions can be combined in conditional statements like IF and SWITCH or in loops like WHILE. Modularity is provided by the ability to execute a routing block from another routing block.

Therefore, understanding logical programming is important as well. Be sure you are familiar with concepts such as functions, variables, conditions or loops.

IF, SWITCH and WHILE are pretty similar to other imperative languages such as C, Perl, Python or Java. Even Shell/Bash programming is useful to get into Kamailio configuration structure.

Linux/Unix

Being developed for Unix/Linux, managing a Kamailio instance, from installation to runtime and maintenance involves operations specific for Linux administration, like running command line applications from terminal, configure network and firewall to allow sending/receiving SIP and RTP packets, a.s.o.

Troubleshooting Kamailio and SIP requires knowledge of various tools for reading and searching log files (e.g., grep, awk), sniffing the network (e.g., sngrep, ngrep, tcpdump, wireshark). Of course, knowing to work with text editor, especially the ones for terminal if the server is remote, is quite obvious (e.g., vim, joe, nano, pico, emacs, etc.).

Initial Installation

From Sources

Install current stable version:

Install development version (master branch):

When installing from sources:

  • configuration files are deployed in: /usr/local/etc/kamailio
  • binary files are deployed in: /usr/local/sbin/

Debian

Kamailio is part of latest official stable Debian distributions (and its Ubuntu cousin), but might be an older version.

To use most recent Kamailio release, you can use the APT repositories hosted by Kamailio project, see details at:

Then, the typical way of installing packages can be used:

apt-get update
apt-get install kamailio

Various modules are packaged separately, you can search the repository to see what is available:

apt-cache search kamailio

Install the other packages of the modules you may need, like mysql or tls modules -- they can be installed with:

apt-get install kamailio-mysql-modules kamailio-tls-modules

When installing from deb packages:

  • configuration files are deployed in: /etc/kamailio/
  • binary files are deployed in: /usr/sbin/

CentoOS

Kamailio RPMs are available for several distributions, such as RedHat Enterprise, CentOS, OpenSuse and Fedora. For more details, see:

You can add them to YUM configuration and then install Kamailio with usual yum commands:

yum install kamailio
...
yum install kamailio-mysql-modules kamailio-tls-modules

When installing from rpm packages:

  • configuration files are deployed in: /etc/kamailio/
  • binary files are deployed in: /usr/sbin/

Configuration File

Overview

If you installed from sources, then the configuration file is located at:

  • /usr/local/etc/kamailio/kamailio.cfg

If you installed from packages, then the configuration file is located at:

  • /etc/kamailio/kamailio.cfg

Configuration Scripting Language

Kamailio uses its own configuration file language. Its structure is described in the Core Cookbook:

Default Configuration File

The default configuration file is trying to provide the features for a simple VoIP (telephony) provider.

  • user authentication
  • IP authorization
  • accounting
  • registrar and location services
  • attacks detection and blocking (anti-flood protection)
  • NAT traversal
  • short dialing on server
  • multiple identities (aliases) for subscribers
  • multi-domain support
  • routing to a PSTN gateway
  • routing to a voicemail server
  • TLS encryption
  • instant messaging (pager mode with MESSAGE requests)
  • presence services

Not all the above features are enabled by default -- read the comments at the top of kamailio.cfg in order to find what tokens must be defined.

Enabling User Authentication

Initial installation doesn't ask users for authentication. Enabling that means defining WITH_MYSQL and WITH_AUTH -- that means adding the next two lines after the first line (after the one with #!KAMAILIO).

#!define WITH_MYSQL
#!define WITH_AUTH

Obviously, for the above to really work, you need to install MySQL server and create the database required by Kamailio (see kamdbctl tool). You need also to add subscribers (username/password to subscriber database table). You can use kamctl tool for managing subscriber records.

Enabling Persistent Location

Initial installation doesn't have persistent location enabled, meaning that if you restart Kamailio, the registration records are lost. If you enable it, registration records are saved to database and reload at restart.

To enable persistent location records, you have to define WITH_USRLOCDB -- add the next line in kamailio.org after those line you added in the previous section:

#!define WITH_USRLOCDB

Enabling NAT Traversal

The default kamailio.cfg comes with NAT traversal support, relying on RTPProxy for RTP relaying. The NAT traversal support has to be enabled by defining WITH_NAT:

#!define WITH_NAT

You have to install RTPProxy application and configure it to use the same control socket as in kamailio.cfg parameter for rtpproxy module.

Tools

kamctl

Kamctl is part of Kamailio project (in the same source tree) and installed by default.

It has a configuration file named kamctlrc, located in the same folder with kamailio.cfg. You have to edit it to set your SIP domain, the database engine, username/password/... to connect to database, etc.

This is the tool to manage kamailio from command line, providing lots of operations, such as adding/removing/updating SIP users, controlling the ACL for users, managing the records for LCR or load balancing, viewing registered users and internal statistics, etc.

When needed to interact with Kamailio, it does it via FIFO file created by mi_fifo module. Operations to the database are done by connecting directly to the database server.

kamdbctl

Kamdbctl is part of Kamailio project (in the same source tree) and installed by default.

It uses the same configuration file like kamctl, respectively the kamctlrc.

The tool can be used to create and manage the database structure needed by Kamailio, therefore it should be run immediately after Kamailio installation if you plan to run Kamailio with a database backend.

It is not used for managing the records inside the database tables, just for database structure and access to the database (e.g., granting/revoking access to database server). For managing the records inside database table, kamctl is the tool that has to be used.

kamcmd

Kamcmd is part of Kamailio project (in the same source tree) and installed by default.

This is an application that can send RPC commands to Kamailio from command line. It requires that the ctl module is loaded by Kamailio.

siremis

It is a web management interface for Kamailio, written in PHP -- more at:

kamcli

It is a command line application write in Python, more or less an alternative to kamctl. It has a modular architecture, allowing to extend it by writing new plugins.

See more at:

Typical Use Cases

VoIP Provider

The default kamailio.cfg is practically an implementation of simple SIP operator services. See the section above dedicated to default configuration file for more details.

Load Balancing

See dispatcher module:

Least Cost Routing

See the modules:

IMS/VoLTE

Look at the modules that have the name prefixed with ims_ or starting with cdp (the later are for Diameter):

Example of configuration files for different IMS roles (eg., ICSCF, PCSCF, SCSCF) are available in the source tree, look inside the sub-directory examples/.

Instant Messaging and Presence

Look at the modules that have the name prefixed with presence (presence server) or pua (presence user agent):

WebRTC

See the module:

Useful Resources

Kamailio Books

Kamailio Online Tutorials

Open source projects embedding Kamailio that can help rolling out specific use cases.