Session Description Protocol (SDP) Alternate Connectivity (ALTC) Attribute
This document proposes a mechanism which allows to carry multiple IP addresses, of different address families (e.g., IPv4, IPv6), in the same SDP offer. The proposed attribute solves the backward compatibility problem which plagued ANAT, due to its syntax. The proposed solution is applicable to scenarios where connectivity checks are not required. If connectivity checks are required, ICE (RFC 5245) provides such a solution.