Session Description Protocol (SDP) Media Capabilities Negotiation

Miscellaneous Capabilities Negotiation in the Session Description Protocol (SDP)

“…The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, RFC 2119 [RFC2119] and indicate requirement levels for compliant implementations. Garcia The SDP Capability Negotiation Framework [RFC5939] and the SDP Media Capabilities Negotiation [RFC6871] specify attributes for negotiating SDP capabilities. These documents specify new attributes (e.g., "acap", "tcap", "rmcap", and "omcap") for achieving their purpose.…”

“…The new capabilities may be referenced in potential configurations ("a=pcfg") or in latent configurations ("a=lcfg") as productions conforming to the <extension-config-list>, as respectively defined in RFC 5939 [RFC5939] and RFC 6871 [RFC6871].…”

“…For example, extending the example in [RFC6871] with "icap" and "bcap" capability attributes, we get the following SDP: The above SDP defines one PCMU audio stream and one H.264 video stream. It also defines two RTP-based media capabilities ("rmcap" numbered 1 and 2), using 16-bit linear (L16) audio at 8 kbps and 16 kbps, respectively, as well as an RTP-based media capability for H.263 video ("rmcap" numbered 3).…”

“…SDP has been extended with an SDP Capability Negotiation Mechanism Framework [RFC5939] that allows the endpoints to negotiate capabilities, such as support for the Real-time Transport Protocol (RTP) [RFC3550] and the Secure Real-time Transport Protocol (SRTP) [RFC3711]. The SDP Media Capabilities Negotiation [RFC6871] provides negotiation capabilities to media lines as well.…”

“…The capability negotiation is embedded into the widely used SDP offer/answer procedure [RFC3264]. This memo provides the means to negotiate further capabilities than those specified in the SDP Capability Negotiation Mechanism Framework [RFC5939] and the SDP Media Capabilities Negotiation [RFC6871]. In particular, this memo provides a mechanism to negotiate bandwidth ("b="), connection data ("c="), and session or media titles ("i=").…”