Abstract: The device comprises a traffic summator (4) for summing the number of cells which are present on each incoming highway of the switch during each cell instant and are destined for one and the same outgoing highway (p). A highway emulation group (p) is allocated to each outgoing highway. It is composed of a specified number of counters (Bi) simultaneously loaded with the total number of cells which are destined for the outgoing highway and are presented on the incoming highways of the switch. The respective counts of each counter (Bi) are limited by thresholds (Si) so as to estimate, when the number of cells totalled up in a counter (Bi) exceeds a threshold (Si), the number of cells which may be lost on the corresponding outgoing highway (p).