Mobile communication imposes a number of restrictions in terms of resources, memory, capacity,... So as to limit the use of the wireless link between the mobile device and the Base Station, a representation of the user on the wired network will be used; namely the representation agent. It can be viewed as a useful user's delegate caring of important regarding problems such as task delegation, communication strategy and asynchronism. Located on acceptor sites dedicated to them, the correct working of the communication relies upon the ability to be able to detect site failures. As agents can migrate from one site to another under certain circumstances, a site failure leads to two kinds of problems : (1) all agents in the faulty site are lost, and (2) an agent may migrate towards a faulty site. To prevent the latter, and to be able to recover from the former, an important step in the research is thus to be able to provide the system with a site-diagnosis methodology, efficient in terms of message latency and adapted to constraints due to mobility (the number of sites increases).