SFM stands for Selective Forwarding Middlebox.
SFM is the formal IETF terminology for what is more commonly known as an SFU (Selective Forwarding Unit). The term "middlebox" emphasizes that the server sits in the middle of the media path, selectively forwarding streams between participants without mixing or transcoding them.
SFM vs SFU
While both terms describe the same architecture, "SFM" appears primarily in IETF specifications and academic papers, while "SFU" is the term used in practice by developers, vendors, and the WebRTC community. The functionality is identical: receiving multiple media streams and intelligently forwarding them to the appropriate recipients based on network conditions, layout preferences, and device capabilities.
The SFM uses techniques like simulcast and SVC to optimize which streams or layers are forwarded to each participant.
See the full explanation at SFU.
