In this section, we describe Requests for Comments (RFCs) 4566, 6947, 4570, 3108, and 7195 that provide the Session Description Protocol (SDP) capability negotiation capabilities for different network protocols. Specifically, this section describes the SDP’s support for network protocols such as Internet Protocol (IP) Version 4 and 6 (IPv4 and IPv6) defined in RFCs 4566 and 6947, Asynchronous Transfer Mode (ATM) specified in RFC 3108, and Public Switched Telephone Network (PSTN) standardized in RFC 7195. Note that RFC 4566 (see Section 2) obsoletes both RFCs 3266 and 2327 for support of IPv4 and IPv6 network address in SDP. More importantly, how a given SDP offer can carry multiple IP addresses of different address families (e.g., IPv4 and IPv6) specified in RFC 6947 is described here. The proposed attribute, the “altc” attribute, solves the backwards compatibility problem that plagued ANAT due to its syntax. This solution is applicable to scenarios where connectivity checks are not required. If connectivity checks are required, Interactive Connectivity Establishment, as specified in RFC 5245, provides such a solution. The SDP’s syntax is also extended to express one or more source addresses as a source filter for one or more destination “connection” addresses. RFC 4570 defines the syntax and semantics for an SDP “source-filter” attribute that may reference either IPv4 or IPv6 address(es) as either an inclusive or exclusive source list for either multicast or unicast destinations. In particular, an inclusive source filter can be used to specify a source-specific multicast session. In case of ATM (RFC 3108), this section describes conventions for using the SDP described in RFCs 3266 and 2327 (that are made obsolete by RFC 4566, see Section 2) for controlling ATM Bearer Connections, and any associated ATM Adaptation Layer. In addition, this section deals with use cases, requirements, and protocol extensions for using the SDP offer/answer model for establishing audio and video media streams over circuit-switched bearers in PSTN (RFC 7195).