Skip to content


Switch branches/tags

Name already in use

A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?

Latest commit


Git stats


Failed to load latest commit information.

Build Status@GitHub

Sippy B2BUA

Sippy B2BUA is a RFC3261-compliant Session Initiation Protocol (SIP) stack and Back-to-back user agent (B2BUA).

The Sippy B2BUA is a SIP call controlling component. Unlike a SIP proxy server, which only maintains transaction state, the Sippy B2BUA maintains complete call state and participates in all call requests. For this reason it can perform number of functions that are not possible to implement using SIP proxy, such as for example accurate call accounting, pre-paid rating and billing, fail over call routing etc. Unlike PBX-type solutions such as Asterisk for example, the Sippy B2BUA doesn't perform any media relaying or processing, therefore it doesn't introduce any additional packet loss, delay or jitter into the media path.


  • 5,000-10,000 simultaneous sessions per server
  • 150-400 call setups/tear-downs per second
  • Real-time calls control and call data records (CDRs) generation
  • Optional ability to use Sippy RTPproxy for media relaying
  • Optional ability to perform Cisco-compatible RADIUS AAA (Authentication, Authorization and Accounting)
  • RFC3261 compliance
  • Seamless compatibility with majority of popular SIP software and hardware on the market today
  • Robustness and Resilience
  • Simple and clean, yet flexible, internal design making implementing new features and services easy
  • Sippy B2BUA could be easily combined with other Open Source software, such as SIP Express Router / OpenSIPS to build complete softswitch solution


Install latest stable version

pip install sippy

Install latest development version

pip install git+


To get started, you can use the b2bua_simple implementation. The following example will cause the b2bua run in the foreground so you can see the SIP messaging. If you make a call to the IP address of your host machine, the b2bua will recieve the call on its UAC side, and it will send a new call leg out its UAS side to the IP address It is expected that is some sort of SIP switch or termination gateway.

b2bua_simple -f -n


See documentation/

Support us on Patreon!

Sippy B2BUA is available for use at the most liberal Open Source license there is and we promise to keep it this way. If you like our software, find it useful and want to support us moving it forward consider becoming a patron here Sippy Labs Patreon Page. In turn, we would give a priority to bugs and feature requests from our Patrons.


Sippy B2BUA is a RFC3261-compliant Session Initiation Protocol (SIP) stack and Back-to-back user agent (B2BUA) server software.







No packages published