The Mapping of Address and Port (MAP) technology provides a high-performance solution to carrying IPv4 traffic over an IPv6-only network. MAP comprises two variants: MAP-E (Encapsulation mode) transports IPv4 packets by encapsulating the IPv4 packet inside an IPv6 packet. MAP-T (Translation mode) transports IPv4 packets by encoding their IPv4 addresses inside the IPv6 addresses and carries the IPv4 payload directly. This whitepaper provides both an introduction and technical details for the MAP protocols and their usage. Note that in this paper "MAP" refers to common functions of MAP-E and MAP-T, but in normal usage "MAP" (without a -T or -E) means MAP-E, as it is the standards track specification.

This whitepaper aims to provide the reader with a technical overview of Mapping of Address and Port (MAP), along with its relevance and benefits as an IPv6 transition and interworking technology. Details of the port mapping algorithm, as well as both variants of the MAP implementation (MAP-E and MAP-T), will be described. This document will enable a solid understanding of MAP technology and the ability to position it effectively with service providers in regard to its benefits, relative to other alternatives (e.g., Dual-Stack Lite).

http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6553/whitepaper_C11-729800.html