FreeSBC support RTP no-anchoring. RTP no-anchoring is a variant of low-delay media relay where the RTP packets are not “anchored” to the SBC (not going through the SBC).
Instead the RTP path is established directly between the two legs of a call (which send RTP to each other).This greatly reduces the IP bandwidth required by the SBC, while the SBC continues to be involved in SIP signaling and call routing.
Please visit following link for more details; https://docs.telcobridges.com/tbwiki/Parameter:_Use_RTP_no-anchoring