TABLE OF CONTENTS One of the earliest distinctions between mobility problems is the distinction between location management and handoff management. Even back with the first generation of cellular systems, people noticed that it was one thing to keep track of subscribers while they were not in a call and another to keep track of subscribers while they were in a call.
The main reason for keeping track of idle subscribers (subscribers who are not in a call) is to be able to initiate a call with them, for an incoming call. Tracking a mobile subscriber can be performed at different levels of precision. As explained in Chapter 3, it may be better not to keep track of idle subscribers at the level of a cell, but rather at the level of a location area covering multiple cells, in order to save on radio resources. To contact these subscribers, for instance, to respond to an incoming call, paging is then required. Compared with handoff, updating of the location is not highly time critical, because a slight delay in updating of the location may not be noticeable, given the delay that people expect in call setup.
The handoff management problem involves keeping track of subscribers who are in an active call, as they move from BS to BS. Compared with location management, handoff management requires more careful, timely treatment, because a session is active during the handoff, and even small delays can be irritating to the subscribers.
