Previously, only ICE relay candidates with the "prefered" connectivity was offered. However the way the "prefered" connectivity is guessed is not reliable, especially when sending the INVITE to the callee, and it can change during a call, for example when one of the parties moves from an IPv6-only LTE network to an IPv4-only network. For these reasons, it is preferable that ICE relay candidates are added for both IPv4 and IPv6.