SIPpy is a high-performance, carrier grade RFC3261-compliant SIP stack and Back-to-Back User Agent (B2BUA) software distributed under the terms of GPL Free Software license. The Back-To-Back User Agent (B2BUA) is a Session Initiation Protocol (SIP) based logical entity that can receive and process INVITE messages as a SIP User Agent Server (UAS). It also acts as a SIP User Agent Client (UAC) that determines how the request should be answered and how to initiate outbound calls. Unlike a SIP proxy server, the B2BUA maintains complete call state and participates in all call requests, which allows it to provide accurate real-time call accounting and call control for different pre-paid and post-paid scenarios.


The development of the software started at the late 2003 after negative experience with using Vovida B2BUA. It was designed with robustness and performance in mind and now being used by several hundreds ITSPs all around the globe. The software now is being actively developed and maintained by the Sippy Software, Inc..


  • 5,000-10,000 simultaneous sessions per server;
  • 150-200 calls/second per server;
  • Realtime calls control and call data records (CDRs) generation;
  • Optional ability to use RTPProxy for media relaying;
  • Seamless compatibulity with majority of popular SIP software and hardware on the market today;
  • Robustness and Resilence;
  • Simple and clean internal design making implementing new features and services easy;
  • B2BUA could be easily combined with other Open Source software, such as SIP Express Router to build complete softswitch solution.

Getting SIPpy

The software can be downloaded at


Q: Why using Python? Isn't it slow?
A: For certain class of application Python provides adequate performance. Being 100% text based SIP appears to be one of such applications. Also, when telecommunication applications are considered some other factors, such as reliability and resilence, have much more importance than pure performance. With the performance numbers outlined above (150-200 calls/second) one server running SIPpy can handle tenth of millions billable minites per month. Any network that operates with such vast amount of traffic has no choice but become distributed tp grow further, which limits usefullness of using unsafe languages such as C or C++ to improve performance beyond that point.
Created by: sobomax, Last modification: Tue 04 of Sep, 2007 (05:30 UTC)
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