Function answer_ringing 

pub async fn answer_ringing(
    endpoint: &Handle,
    incoming: &Incoming,
    media_address: IpAddr,
    ringing: &Ringing,
) -> Result<Call>

Answer an INVITE that has already been rung (RFC 3262).

The tag comes from the Ringing rather than being fresh, and that is the whole reason this exists. A provisional that established a dialog has already told the caller what this side’s tag is (RFC 3261 §12.1.1); a 200 with a different one creates a second dialog. The caller ACKs the dialog it knows about, this side waits for an ACK to the other, and the 200 is retransmitted for 32 seconds into a call that is actually up.

Answers from the default codec set, Codecs::G711. answer_ringing_with takes a selection.