We continue to see a growing number of service providers using SIP Express Router (also known as SER) and OpenSER as infrastructure SIP proxies for their carrier operations. SER (www.iptel.org) and OpenSER (www.openser.org) are mature open source projects for a very stable, high performance SIP proxy. SER was the original project and OpenSER is fork of SER started a couple of years ago. Both projects are excellent and OpenSER has growing popularity because it more rapidly introduces new features.


We often hear the question, “What is the capacity of OpenSER?” There have been benchmark tests that show OpenSER and SER can manage thousands of SIP calls per second. But how about a benchmark test that simulates a real production environment with call failures, retries and call detail reporting? Since we have not seen such a test report, we decided to perform our own benchmark test. For our test we configured OpenSER V1.1 on a Dell Precision 490 server with two Intel Xeon 5140 2.33 GHz CPUs and 4 GB of RAM. To reduce the traffic load requirements, we disabled one CPU and one core on the remaining CPU. We ran the test on a single core of a dual core chip. The operating system was CentOS 4.4.


To simulate a production environment, we configured OpenSER to communicate with an OSP server for call routing and CDR collection. For each call there were five possible destinations returned in random order. Four of the five destinations were configured to simulate call setup failures (no TCP response, no SIP response, call rejected and no route). We found that 200 calls per second was the maximum the single core processer could handle. If we had used all four CPU cores we expect the results would have been 800 calls per second. To be conservative, we would recommend service providers to plan on maximum CPU utilization of about 60%. This would establish the OpenSER planning gauideline of 500 calls per second on a server with two, dual core Xeon CPUs.


If you assume 15% of a service provider’s traffic occurs during the busy hour, a 50% Answer Seizure Ratio (ASR) and a 3 minute average call duration, then 500 calls per second equates to 540 million minutes of VoIP traffic per month! We think this is impressive for an open source SIP proxy running on a server with a retail price of $2,967. If you want a copy of the test plan and results, send an e-mail to me at [email protected].


We will run the same benchmark test on OpenSER V1.2 and then on SER to get a clear comparison of the different releases. When we are done, we will publish the results on www.transnexus.com.