In Differentiated Services networks, packets may receive a different treatment according to their Differentiated Services Code Point (DSCP) label. As a consequence, packet marking schemes can be devised to differentiate packets belonging to a same TCP flow, with the goal of improving the experienced performance. This paper presents an extensive performance evaluation of a new adaptive packet marking scheme, which relies on three different service classes, provided by the DiffServ network. The scheme provides protection of vulnerable packets in the TCP flows and adaptivity through “probes” packets. The performance have been evaluted in a traffic scenario composed of TCP flows with different length. The proposed marking scheme provides excellent performance in all utilization conditions.