The paper summarizes and proofs that existing VoIP programs are powerful and flexible enough to build complex applications. The applications are independent and can be used either stand-alone or within carrier-grade Telco environments. The described example of building a call center application (outbound calling) shows the power that lies not only in existing open-source Session Initiation Protocol (SIP) servers, but also in simple SIP tools. The costs for implementing those systems are at a very low level, as the functions each project performs are rather kept simple, but the combination possibilities are tremendously flexibility. The presented application has been deployed successfully within NGNlab (http://www.ngnlab.eu) as a Proof of Concept (PoC). Presented at Elmar 2009 in Zadar, Croatia.

1. Motivation
Work and Results
Summary
Building Complex Voice Over IP (VoIP)
Applications Based on Open-Source
Sebastian Schumann Ondrej Lábaj Pavol Podhradský
Department of Telecommunications
Faculty of Electrical Engineering and Information Technology
Slovak University of Technology, Bratislava
51. International Symposium ELMAR 2009,
28.-30. September, Zadar, Croatia
Schumann, Lábaj, Podhradský Complex Open-Source Based VoIP Applications

2. Motivation
Work and Results
Summary
Outline
1 Motivation
Prerequisits
Definition
2 Work and Results
System
Utilization
Schumann, Lábaj, Podhradský Complex Open-Source Based VoIP Applications

3. Motivation
Work and Results
Summary
Prerequisits
Definition
Open-Source Software in Telecommunications
Open-source world offers many applications
in the area of Voice over IP (VoIP)
Wide range of developed software
Tools
Applications
Carrier-grade software
Not too many complex systems at the moment
Idea
Combine open-source software and environments
to perform large tasks in a flexible way.
Schumann, Lábaj, Podhradský Complex Open-Source Based VoIP Applications

4. Motivation
Work and Results
Summary
Prerequisits
Definition
Task
Aim
Fulfill typical tasks of a call-center:
The target application should call a list of users
and send successfull calls to a media system/agents.
Application components should be independent
Cost-effective IP based solutions
Simple task flow:
Input List of users
System Attempt calls, route successful attempts
Output Provide statistics, clean terminations
Schumann, Lábaj, Podhradský Complex Open-Source Based VoIP Applications

5. Motivation
Work and Results
Summary
System
Utilization
Input
List of users to call (CSV)
Destination(s) (cron)
Max. timeout/retransmissions of initial INVITE (cron)
Time period for calling users
Schumann, Lábaj, Podhradský Complex Open-Source Based VoIP Applications

6. Motivation
Work and Results
Summary
System
Utilization
Component Interaction
timer
.csv
user data
GeneratorAnalyzer
cron
Media
media stream
Schumann, Lábaj, Podhradský Complex Open-Source Based VoIP Applications

7. Motivation
Work and Results
Summary
System
Utilization
Tools
Call Generator: SIPp
SIPp is a free Open Source test tool / traffic
generator for the SIP protocol.
Call Evaluation System: OpenSIPS
OpenSIPS (Open SIP Server) is a mature Open
Source implementation of a SIP server.
Media System Asterisk
Asterisk is the world’s leading open source PBX.
Execution environment for all applications is GNU/Linux.
Schumann, Lábaj, Podhradský Complex Open-Source Based VoIP Applications

8. Motivation
Work and Results
Summary
System
Utilization
Logical Actions
LOG Release call
LOG
LOG
Call user
Yes
Media
End condition on
media system*
No
Call established
user side
Call released on Interruption
Connect to media system
* Timer ends, SIPp receives BYE...
Schumann, Lábaj, Podhradský Complex Open-Source Based VoIP Applications

9. Motivation
Work and Results
Summary
System
Utilization
Call Flow (Establishment)
User
200 OK+SDP1
PBXSIPpOpenSIPS
INVITEINVITE
INVITE+SDP1
200 OK+SDP2
ACK
off-hook
200 OK+SDP1
ACK+SDP2ACK+SDP2
RTP
Schumann, Lábaj, Podhradský Complex Open-Source Based VoIP Applications

10. Motivation
Work and Results
Summary
System
Utilization
Call Flow (User hangs up)
User PBXSIPpOpenSIPS
BYE BYE
200 OK200 OK BYE
200 OK
Schumann, Lábaj, Podhradský Complex Open-Source Based VoIP Applications

11. Motivation
Work and Results
Summary
System
Utilization
Call Flow (System closes call)
User PBXSIPpOpenSIPS
BYE
200 OKBYE
200 OK200 OK
BYE
Schumann, Lábaj, Podhradský Complex Open-Source Based VoIP Applications

12. Motivation
Work and Results
Summary
System
Utilization
Examples
Automatic calling of users with voice advertising
provided by media server.
Certain call center agents (i.e., SIP users) will be
connected to successful call establishments.
(maximum amount of parallel calls monitored on SIPp,
maximum utilization of call center)
Schumann, Lábaj, Podhradský Complex Open-Source Based VoIP Applications

13. Motivation
Work and Results
Summary
1 Motivation
Prerequisits
Definition
2 Work and Results
System
Utilization
Schumann, Lábaj, Podhradský Complex Open-Source Based VoIP Applications

14. Motivation
Work and Results
Summary
Summary
Existing VoIP applications are very powerful
Carrier-grade IP based Telco environments can be
easily extended
Usage of presented work (e.g., within ad campaigns) is
very cost effective
Outlook
Continue with useful call-center use cases
(e.g., extend OpenSIPS with call queuing functionality)
Elaborate other use cases where IP based telephony
systems or applications can enhance functionality
Schumann, Lábaj, Podhradský Complex Open-Source Based VoIP Applications

15. Motivation
Work and Results
Summary
Contact
Sebastian Schumann
Department of Telecommunications
Slovak University of Technology
Bratislava, Slovak Republic
schumann@ktl.elf.stuba.sk
Schumann, Lábaj, Podhradský Complex Open-Source Based VoIP Applications