Setting up a SIP (Session Initiation Protocol) connection in a dual stack network using connection oriented transports

The Session Initiation Protocol (SIP) supports multiple transports running both over IPv4 and IPv6 protocols. In more and more cases, a SIP user agent (UA) is connected to multiple network interfaces. In these cases setting up a connection from a dual stack client to a dual stack server may suffer from the issues described in RFC 6555 [RFC6555] – Happy Eyeballs – significant delays in the process of setting up a working flow to a server. This negatively affects user experience. This document builds on RFC 6555 and explains how a RFC3261 [RFC3261] compliant SIP implementation can quickly set up working flows to a given hostname (located by using DNS NAPTR and SRV lookups) in a dual stack network using connection oriented transport protocols. A solution for connectionless transport protocols is discussed in a separate document.