This depends on what is meant by calls. There are two kinds of call limitations:
- Number of calls that can be concurrently established;
- The number of calls that can be set up per second (CPS);
In a SIP proxy-based architecture like that of CSRP, only the second limitation is significant.
The ongoing resource consumption incurred by a call is negligible. As a practical matter, there is
no limit to the amount of concurrent calls that can be set up through CSRP per se: on commodity
hardware today, the number would be in the millions.
RTP media relay introduces resource consumption and can alter this arithmetic significantly,
The Sipwise rtpengine can handle about 12,000 to 15,000 concurrent calls on a single host. Of course,
you can deploy as many RTP relay hosts as you like; CSRP's Kamailio will distribute calls among them in a round-robin fashion (with failover).
At the time of this writing, peak CPS performance of 2500 CPS has been demonstrated in a stock CSRP installation,
in a relatively low-performance virtual environment. However, this was in an
idealised testing environment with simple call scenarios and using a database server with SSDs (Solid State Drives).
Actual results will vary, chiefly with the hardware that can be devoted to the database workload.