Will a Back-to-Back User Agent always proxy both media and SIP signaling?

The correct interpretation is that a Back-to-Back User Agent (B2BUA) does not proxy media. Instead, it acts as an intermediary that terminates two SIP sessions, meaning it handles SIP signaling separately for each leg of the call. When B2BUA is involved, it can modify, control, and manage the signaling messages exchanged between the caller and the callee. However, unlike a SIP proxy, it does not forward the media streams between the endpoints. Instead, it can handle media locally, which often means the media is either sent to and from the B2BUA or processed in some other way.

This distinction is crucial as it highlights the B2BUA's role in managing the SIP session itself and emphasizes that media handling is an internal process. Thus, indicating that a B2BUA does not proxy media aligns with the specific functionality and operational behavior of B2BUAs. Understanding this concept is essential for managing and configuring VoIP solutions effectively.