Which protocol is used to communicate codec capabilities and Real-Time Transport Protocolports?

The Session Description Protocol (SDP) is a protocol that defines a text-based format for describing the multimedia sessions and the media streams involved in them12.

SDP is used to convey information such as the session name, purpose, originator, timing, media types, codecs, formats, transport protocols, ports, addresses, encryption keys, bandwidth, and other attributes12.

SDP is typically used in conjunction with other signaling protocols, such as SIP, H.323, or RTSP, to establish and control the multimedia sessions12.

SDP does not itself provide any mechanism for transporting the media streams; it only describes them. The actual media transport is done by protocols such as RTP, which uses the information provided by SDP to set up the appropriate ports and codecs12.

References := 1: Session Description Protocol - Wikipedia 2: RFC 4566 - SDP: Session Description Protocol