In direct load test IP PBX Asterisk on Intel Xeon E5506 Quad-Core CPU shows excellent scalability: it can handle up to 1600 concurrent calls.

1. Load test of IP PBX Asterisk
installed on mid-size server
Direct load test of IP PBX Asterisk on Intel Xeon
E5506 Quad-Core CPU shows that it can handle
up to 1600 concurrent calls
Evgeny Anvaer, Vladimir Dudchenko
SoftBCom, Ltd. (www.softbcom.ru)
21.07.2014

2. IP PBX Asterisk ®:
What is the scalability limit?
• IP PBX Asterisk is an outstanding open source, free
software, having proven reliability and effectiveness,
widely used everywhere over the world, repeating
Linux’ success
• It would be very desirable in call-centers, integrated
B2C systems, in help-desks, service- desks, etc.
But what is the scalability limit for such an attractive
solution?
• Loway Wombat Dialer helps to get answer: it is
integrated with Asterisk and easily can create
necessary number of concurrent calls, playing recorded
voice and music

3. The Asterisk load test scheme
• Wombar Dialer
generates calls
• All the components
are in 100Mb LAN
• The load handled by
tested server includes
media delivered by
RTP
• The calls directed
from separate Asterisk
server to the tested
server
• Tested server plays
back music and
records the calls

4. Some selected results
Number of
concurrent calls
Peak CPU load* Peak RAM load Hearing quality
10 4% Less than 3% Excellent
50 25% Less than 3% Excellent
300 100% Less than 3% Excellent
736 194% Less than 3% Excellent
1137 288% Less than 3% Excellent
1527 351% Less than 3% Excellent
1621 398% Less than 3% Excellent
1626 380% Less than 3% Excellent
1649 400% Less than 3% No connection
*100% corresponds to one core, 400% - to 4 cores

5. The CPU load to # of concurrent calls
in graph presentation
0%
50%
100%
150%
200%
250%
300%
350%
400%
450%
0 200 400 600 800 1000 1200 1400 1600 1800
CPULoad
Concurrent calls number

6. The analysis and conclusions
• Asterisk running on Intel Xeon E5506 Quad-Core
CPU can serve approximately up to 1600
concurrent calls
• The near- linear character of the recorded
dependency (with 8 – 10% deviations) is
noticeable
• Asterisk can fully use the computing power of all
available CPU cores, i.e. it has an effective
mechanism of load balancing for multiple cores
• RAM consumption is very low and almost doesn’t
depend on load

7. Possible errors sources and
limitations
• Accidental errors due to manual determining of load values
recording moments
• The tested Asterisk has not been connected to real phone
devices: all the calls were directed to one single extension (no
connections to devices in separate points of network)
• The media has been transferred mainly in one direction – from
the tested server to the server #1, while it was continuous, not
discrete. So one could suppose that the emulated load is of the
similar level to what we have in real talks
• No additional load factors were emulated (e.g. transcoding,
queues monitoring, applications integration facilities influence,
etc.)

8. Final considerations
• While the emulated load looks like relevant to load level in real
conversation, it is hardly could be declared that it is equivalent
• Developing improved testing methodology we will try to get closer
to real life in future tests
• Our recommendation is to implement CPU load monitoring for all
the cases when planned Asterisk load may reach 50% of estimated
maximum with generating alerts of overcoming the delimited
threshold
The Loway Wombat Dialer was kindly presented
for the test by Swiss company Loway. Designed
for telecasting, it fits 100% to the test demands.
Its easy use and power made this test possible