P2P4121 stands for “Peer-to-peer for 1 to 1”.

The term was first introduced by the Jitsi team for a feature they added which enabled the use of peer-to-peer communications that gets upgraded to a group SFU session if the number of participants in the meeting increases.

This enables using a lot less media server resources and reducing the cost of delivering a communication service when the number of participants in a session is low (i.e – 2), and when people join, the session can get rerouted to a media server automatically and smoothly with little or no interruption to the users.

There are multiple ways to implement such a feature, as well as enhancing it to larger groups, such as:

• Being able to downgrade back to P2P from an SFU call when the number of participants shrinks back
• Keeping 3-way calls on a P2P mesh architecture and switching to an SFU only from 4 participants or more
• Maintaining SFU ports or allocating them only when needed
• Etc