When a caller sends a SIP The SBC monitors and detects early media from the egress call leg. The SBC plays a Ring Back Tone (RBT). P-Early-Media and DLRBT
INVITE
to the SBC (irrespective of the presence of "P-Early-Media: supported
" header in the Session Description Protocol (SDP) of the INVITE
), the SBC adds P-Early-Media header in its 18x
(180
or 183
) response towards ingress call leg only if: