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

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

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

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

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

CP

U L

oad

Concurrent calls number

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

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.)

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