Abstract Ubiquitous network connectivity for devices does not automatically imply continuous reachability for people.
People move from place to place and switch from one network device to another.
As a result, phones ring in empty offices, email cannot reach most cell phones, and spam clogs expensive, low-bandwidth links to laptops. Whereas existing mechanisms have addressed host mobility or the mobility of people within one network, few have allowed people , the ultimate and most important endpoints of communication, to roam freely, without being constrained to one location, one application, one device, or one network. The central component of MPA is a person-level router called the Personal Proxy . It tracks a mobile person's location, accepts communications on his behalf, converts them into different application formats according to his preferences, and forwards the resulting communications to him. In contrast to similar systems, the Personal Proxy protects the user's privacy, is easily extensible to new network devices and applications, and has been deployed with no modifications to the existing network and telecommunications infrastructure.