Media Description and Control

RFC 2327: SDP Session Description Protocol 

RFC 2327 defines the Session Description Protocol (SDP), which is used to describe multimedia sessions for the purposes of session announcement, session invitation, and other forms of multimedia session initiation. Although SDP is used within SIP for session description, it is actually independent of SIP and can be used in conjunction with other protocols. SDP conveys information about media streams in multimedia sessions to allow recipients to participate in the session.
SDP is fundamental in SIP, as it provides the necessary session parameters like media codec, formats, and connection information that enable the successful setup and modification of calls or multimedia sessions.

RFC 3266: Support for IPv6 in Session Description Protocol (SDP)

RFC 3266 extends the Session Description Protocol (SDP) to support IPv6 addresses. This extension is crucial for enabling SIP-based communications over IPv6 networks, ensuring that SIP applications can operate in environments where IPv6 is used. It specifies the format for representing IPv6 addresses in SDP fields, facilitating the initiation and participation in multimedia sessions over IPv6. By incorporating IPv6 support, this RFC addresses the need for SIP protocols to function in next-generation Internet environments, providing compatibility and future-proofing for SIP applications.
By providing for IPv6 in SDP, RFC 3266 ensures that SIP applications can seamlessly transition to and operate within IPv6 network infrastructures.

RFC 4566: SDP: Session Description Protocol

RFC 4566 provides a comprehensive specification of SDP, which is used for describing multimedia communication sessions for the purposes of session announcement, session invitation, and other forms of multimedia session management.
RFC 4566 replaces RFC 2327, 3266 and several other RFCs related to SDP, integrating IPv6 support directly into the core specification of SDP. It consolidates and updates the protocol’s specifications, offering a more complete and modern guide for implementing SDP in various network environments, including those using IPv6.

RFC 8866: SDP: Session Description Protocol

RFC 8866 obsoleted RFC4566 and updated the Session Description Protocol (SDP) by refining terminology, aligning it with ABNF syntax, and revising normative references. It made technical improvements like mandating RTCP for inactive media streams and updated attribute specifications. The document also removed outdated sections and references, particularly those related to the Session Announcement Protocol (SAP), and reorganized IANA registries for better clarity and management. Changes in address representation, inclusion of IPv6 examples, and the integration of case-insensitivity rules were also notable, aiming to modernize the protocol and enhance its utility in describing multimedia sessions across various network environments

RFC 3264: An Offer/Answer Model with the Session Description Protocol (SDP)

RFC 3264 outlines a framework for initiating and negotiating sessions in a multimedia communication system using the Session Description Protocol (SDP) within the context of the SIP. It establishes the procedures for one participant to present a session description (the offer) and for another participant to accept that session description or to present a counter offer. This offer/answer model is integral to setting up real-time multimedia sessions over IP networks, allowing for the negotiation of session parameters such as codecs, media types, and transport protocols. The mechanism defined in this RFC is essential for the dynamic negotiation of media and network resources, ensuring compatibility and optimal session performance between endpoints.
The use of SDP within the offer/answer model provides a flexible and extensible way to negotiate session characteristics, making it possible to adapt to the capabilities of the participating endpoints and the requirements of the session.

RFC 6157: IPv6 Transition in the Session Initiation Protocol (SIP)

RFC 6157 addresses the transition and interoperability issues between IPv4 and IPv6 within SIP and related protocols, including SDP. It provides guidelines for how SDP should handle the dual-stack IPv4/IPv6 environments, ensuring that the offer/answer model remains effective in transitioning network infrastructures.

RFC 8843: Negotiating Media Multiplexing Using the Session Description Protocol (SDP)

This RFC enhances the SDP to support negotiation of media multiplexing, allowing multiple media streams to be sent over a single transport address, reducing the number of ports and connections needed.

RFC 9143: Negotiating Media Multiplexing Using the Session Description Protocol (SDP)

RFC 9143 updates and supersedes RFC 8843 by refining the negotiation process for media multiplexing in SDP, addressing identified shortcomings and implementation issues. It further refines the multiplexing negotiation process introduced in RFC 8843, ensuring a more effective mechanism for managing media streams in SDP.

RFC 4145: TCP-Based Media Transport in the Session Description Protocol (SDP)

RFC 4145 defines the use of TCP (Transmission Control Protocol) as a transport protocol for media streams in the Session Description Protocol (SDP), which is widely used in conjunction with SIP (Session Initiation Protocol) for initiating, maintaining, and terminating real-time multimedia sessions. This RFC introduces two new SDP attributes, 'setup' and 'connection', which are essential for establishing and controlling the direction of TCP connections for media transport. The specification enables more versatile and secure multimedia sessions by providing a framework for using TCP, known for its reliability and ordered data delivery, in scenarios where UDP (User Datagram Protocol) might not be suitable due to network restrictions or the need for secure transmission. By defining how TCP connections should be negotiated and managed within SDP, RFC 4145 enhances the SIP ecosystem's ability to support a broader range of multimedia applications and services.

RFC 4572: Connection-Oriented Media Transport over the Transport Layer Security (TLS) Protocol in the Session Description Protocol (SDP)

RFC 4572 updates RFC 4145 by specifying how to use Transport Layer Security (TLS) over TCP for media transport in the Session Description Protocol (SDP). This update enhances the security of the TCP-based media transport defined in RFC 4145 by introducing TLS, thus providing a method for encrypted and authenticated media streams.

RFC 8122: Connection-Oriented Media Transport over the Transport Layer Security (TLS) Protocol in the Session Description Protocol (SDP)

RFC 8122 obsoletes RFC 4572, and therefore indirectly updates RFC 4145. It continues the work of RFC 4572 by further refining and updating the standards for using TLS over TCP in SDP. RFC 8122 incorporates advancements and clarifications in the TLS protocol and its usage in SDP, ensuring that the framework for secure, TCP-based media transport in SDP remains up-to-date and robust against evolving security threats. This progression from RFC 4145 through RFC 4572 to RFC 8122 illustrates the ongoing enhancement of security and functionality in TCP-based media transport within the SDP.

RFC 4568: Session Initiation Protocol (SIP) Security Agreement for Media Streams

RFC 4568 specifies a mechanism for establishing security agreements for media streams in Session Initiation Protocol (SIP) sessions. This mechanism allows SIP entities to negotiate the parameters for securing Real-time Transport Protocol (RTP) and Real-time Transport Control Protocol (RTCP) streams, such as encryption keys and authentication methods, during session setup. By integrating security negotiation directly into the SIP signaling process, this RFC addresses the need for a standardized approach to secure multimedia communications over the internet. It introduces the use of the Security Descriptions (SDES) for Media Streams in SIP, which includes defining security profiles and their parameters. This approach ensures that both parties agree on the security settings before any media is exchanged, enhancing the confidentiality and integrity of voice, video, and other real-time multimedia sessions.