3.1.4.1 Sending the Initial Offer

The caller attempting to establish a media session with a peer MUST gather its local candidates, as specified in section 3.1.4.8.1. After the candidates are gathered, they MUST be encoded using protocols such as Session Description Protocol (SDP) for sending the gathered candidates to the peer endpoint through the pre-established signaling channel. It MUST designate one of the local candidates as the default candidate in the initial offer. The default candidate MUST be a User Datagram Protocol (UDP) candidate. If no UDP candidate is gathered, the call MUST fail.