In the last decade several wireless access technologies have emerged. Some of them are competing, most are complementary. Today it is clear that there will not be a single wireless access solution appropriate for all the application scenario. On the contrary, it is expected that many of them will coexist in heterogeneous wireless access systems. Users are willing to access the network infrastructure through the best available solution. This leads to the Always Best Connected (ABC) concept. .
Recently, there has been much buzz about ABC, however, a clear statement of the concepts involved is still missing. In fact there are many questions waiting for an answer. The first and most important regards the meaning of best. In fact, which is the best solution strictly depends on the application scenario, on the requirements and on the perspective (e.g., the best in the user perspective does not necessarily coincide with the best in the network operator perspective!).
2. Always Best Connected Concept.
The "Always Best Connected- concept, or ABC as it is also known, was traditionally the vision behind vertical handoff technologies from GSM, EDGE, GPRS or UMTS accesses and networks to unlicensed spectrum technologies such as 802.11b. In that sense, ABC has always been about multi-access networks, although currently the concept has been extended to include some new dimensions, such as adaptive applications, reconfigurable terminals and networks and operator competition. The new scenarios, network environments, service environments, terminal environments and business models implicit in positing ABC as a key and integral feature of the 4G wireless world (4GWW) will require the setting down of carefully crafted definitions of many new terms and system components, first among which is the definition of ABC itself. Throughout this document effort is made to set out initial definitions and system components as they are encountered, as well as to explore their underlying concepts.
