In any communication environment including a central equipment and a plurality of remote equipments, especially in digital communication systems operating in multipoint, the central equipment has to control frequently the presence of each remote equipment. Indeed, in any hierarchical system, internal resources are allocated for each remote equipment. The management of such resources must be performed as rapidly as possible after use, as soon as the remote equipment disappears. Such resources can be control blocks, traffic queues, timers, semaphore software . . . As the total resources of the central equipment are size limited, the non-release of unused resources can result in refusing to serve new remote equipments.
A classical method to avoid such a drawback consists for the central equipment to poll successively the remote equipments and invite them to transmit an information confirming they are alive. Unfortunately, the polling protocol results in an overhead, that is the portion of bandwidth consumed to implement the protocol, which is all the more important since the time required to detect that a remote equipment has disappeared is short.