Nokia Research Center DoCoMo USA Labs DoCoMo USA Labs Nokia Research Center Mobile IP [1] has been developed in the IETF for a number of years already. It's simplicity and scalability give it a growing success within the IETF as several Internet drafts are proposed to extend various improvements for Mobile IP and its counterpart designed for IPv6, Mobile IPv6 [2]. Mobile IP suffers from several well-known weaknesses that have led to the definition of the macro/micro-mobility architecture. Such an architecture implies the division of the mobility architecture into two different parts: mobility management at a large scale, between the different domains (macro-mobility), and, on the other hand, at a local scale, inside these domains (micro-mobility). Each type of mobility is then managed by specific mechanisms and protocols. The macro-micro approach results in many advantages that all micro-mobility protocols will have; thereby effectively addressing weaknesses that plague Mobile IP. This document discusses the micro-mobility problem, and is an attempt to enumerate some of the concepts and approaches defining the micromobility problem space. This draft will serve to document the problem space and definition of micro-mobility for discussion in the IRTF micro-mobility working group.