Laboratory Practice 2012-2013 course Telecommunication Engineering School, University of Vigo

1. Laboratorio de Conmutación
Kamailio Lab 2012-13
(version 1.0)
Sep. 11, 2012
Introduction
As you know, Quobis Networks is collaborating in the extended practice of Laboratorio de
Conmutación. This is our proposal for the Kamailio exercise. Honestly we can say it is not
difficult at all but it requires you to know a few VoIP concepts and learn how to configure
Kamailio. We recommend to read a SIP tutorial (see bibliography section) before starting the
practice, you will get very valuable skills for the practice and your professional life.
Why Kamailio?
We have already presented the amazing features of Kamailio in previous classes. It is the
most powerful SIP open-source softswitch used in real VoIP operators such as 1&1 and
Freenet. In the bibliography section you can find links to good Kamailio documentation.
Exercise.
Welcome to the LC imaginary real-world. Last year, your colleagues had to start a new operator
from scratch. In this practice you will have to increase the services and the capacity of your
system by implementing new techniques.
As you may know, the United Archipelago Republic is formed by more than 100 islands.
However 99% of population enjoy their lives in the 4 biggest islands, namely, Big Banana, Big
Treasure, Drake Island and Lost Island.
The national telecommunication operator was acquired by a Galician capital risk fund in 2011.
For operative reasons, it was decided to divide the operator in four smaller operator based

2. in each of the main islands. Thanks to the global financial crisis, the Caribbean country is
increasing its GDP and population. They are hiring new VoIP skills and you has been luckily
selected to manage the addition of new functionalities to the SIP system of the island operator
you choose. You will be posted there by your Telecom company, so pack your luggage and
enjoy the experience.
To implement the central softswitch infrastructure your colleagues had a limited budget but they
got very valuable VoIP skills implementing the system on their own with the powerful Kamailio
open-source software.
Basic functionality.
All groups must configure Kamailio so that it can do the following:
1. Register up to 100 users (except for team 2).
2. Establish calls between registered users.
3. Establish calls to each other’s groups.
General considerations
● Users will be provisioned with their complete E.164 number (including the international
prefix).
● Numbering length is up to system administrator however the length of the
complete number must respect E.164 standard (never longer than 15 digits, http:/
/en.wikipedia.org/wiki/E.164). The recommended length is 5 digits after country
prefix. For instance, Big Banana Island numeration would go from 00178800000 to
00178839999, more than enough for an island.
● Users registered on the same Kamailio, thus belonging to the same, island should be
able to call each other without dialing the international prefix.
● Users from different islands must dial the complete number (including prefix) to call each
other.
● As an additional exercise, user numbers can be associated to SIP URIs, for example,
user 00178838888 can be bound to a SIP URI like this mahatma.gandhi@<kamailio
IP>. If you feel capable, you can even substitute <kamailio IP> for a domain name:
bigbanana.ur, bigtreausure.ur, drakeisland.ur, lostisland.ur. If
you were wondering it, yes, ‘ur’ domain root is free: http://www.iana.org/domains/root/db/
)
Additional functionality.

3. Additionally to the basic exercise, every group must chose one of the following options:
Option 1: you will configure Kamailio for Big Banana Island. With a population of 10,000
native residents, they received last year 120,000 people during tourist season. Most of them
comes from Europe and North America so most of the call traffic is international. We want to
balance all the international traffic between a number of SIP providers. In the practice we’ll
simulate just a couple of SIP providers. The SIP providers can be simulated with either Asterisk
or sipp4. However, Kamailio will check every 30 seconds the availability of our SIP providers, to
prevent us from sending calls to an out- of-service SIP provider. To avoid service disruptions
Kamailio must implement peak load protection. To simulate calls you can use sipp. XML sipp
configuration files will be provided by Quobis. The international prefix assigned for Big
Banana island is: 001788[0-3]
Option 2: you will configure Kamailio for Big Treasure Island. This Island it’s a Tax Haven
so it has a lot of corporative customers. Last year we implemented TLS support to be able to
encrypt the signaling exchanged between our customer terminals and Kamailio. This year, as
a massive customer requirement we must support attended call transfer between our users. It
should be supported by default by Kamailio, anyway we need to implement a demo scenario
with sipp so that we can test the scenario easily in an automatic way. So you must implement
the call transfer scenario in sipp from the traces that will be provided to you in due time. The
international prefix assigned for Big Treasure Island is: 001788[4-5]
Option 3: you will configure Kamailio for Drake Island. This island has been a pirate refuge for
centuries. This tradition survives and nowadays this island has the world highest cracker rate
per km2. Last year we used SIPvicious toolkit to test the security of our Kamailio server. Though
simple, it’s quite powerful, hacker community skills improve day after day so you must use more
powerful tools. That’s the reason why this year will use the Metasploit modules implemented
by our colleague jesus.perez@quobis.com to simulate DoS, DDoS and extension brute-force
attacks. Your challenge in the practice option will be implement as many attacks and security
methods as you can. The security of this operator is in your hands. The international prefix
assigned for Drake Island is: 001788[6-7]
Option 4: you will configure Kamailio for Lost island. Last year your colleagues had to force
GSM codec in every calls processed by this operator since they use WiMAX air links whose
capacity dramatically decreases during hurricane and other extreme atmospheric phenomena.
During this year hurricanes our bandwidth saving technique worked pretty well, but operator
CEO says that we should offer a better audio quality when the sky is blue and the Sun is
shining, which is almost all the time. To do so we’ll only force GSM codec in our calls when
wind is over 50km/h or visibility is lower than 3km. To implement it you must get the weather
conditions of our island from a public and free weather webservices server and act accordingly.
Our recommendation is to call a script which checks the Globalweather service from http://
www.webservicex.net calling a Python script from Kamailio (a check every 5 minutes would
be enough), to indicate the need of using GSM codec in a Kamailio pseudovariable which
must be checked when processing every call. In short, the target is to modify SDPs to

4. only allow GSM1 codec in every call when weather conditions are bad2, and leave the
selected codec the rest of the time. The international prefix assigned for Drake Island is:
001788[8-9]
Help!
Take it easy, luckily you are not alone. Quobis is going to support you during the practice, we
will offer at least one more lesson and provide e-mail support: university@quobis.com
On the other side, Kamailio project is supported by a big community formed by developers,
testers and users who are looking forward to helping you in your challenging project. You can
visit the Kamailio web site and subscribe to Kamailio mailing lists.
Note about using Kamailio mailing list: many people is going to invest their time in reading
all the list mails everyday so, please, read carefully the documentation and try to find similar
questions already answered in the list. If you don’t find the answer on your own, do not hesitate
to send a mail to the list trying to write it in an understandable way, including all the progress
you have done so far.
What tools can I use?
There are many tools which can be really useful to carry out this exercise. Below you can find
some of them:
● wireshark: protocol analyzer.
● ngrep-sip: sip-adapted ngrep http://dev.sipdoc.net/projects/sip-stuff/wiki/Ngrep-SIPsipp
● jitsi: a Java softphone.
● SIPp and SIPvicous: check links included in bibliography section.
Bibliography
1. SIP tutorial: http://www.iptel.org/files/sip_tutorial.pdf
2. Kamailio Knowledge Base: http://kb.asipto.com/kamailio:index
3. Kamailio Wiki: http://www.kamailio.org/dokuwiki/doku.php/start
4. SIPp: http://sipp.sourceforge.net/
5. SIPvicious: http://blog.sipvicious.org/
1In a production environment, the right choice would be normally G.729. The thing is that
G.729 codec can only be used after paying a cannon, so open source softphones do not
support it. However GSM is an open standard and it is implemented by most of the open source
softphones.
2Obviously, Globalweather service will only offer weather from real real cities. For this practice
will use the weather conditions from Nassau Airport (Bahamas).