Mapping of Address and Port

Mapping of Address and Port (MAP) is a proposal that combines A+P port address translation with the tunneling of legacy IPv4 protocol packets over an ISP's internal IPv6 network. MAP uses the extra bits available in the IPv6 address to contain the extra port range identifier bits of the A+P addressing pair that cannot be encoded directly into the IPv4 address, thus eliminating the need for "port routing" within the carrier network by leveraging the provider's own IPv6 rollout.

Source: Wikipedia — Mapping of Address and Port (CC BY-SA 4.0)