In this paper we introduce a test through which the responsiveness of a TCP aggregate can be measured. The first introduced test is based on dropping a few packets from the aggregate and measuring the resulting rate decrease of that aggregate. This kind of test is not robust to multiple simultaneous tests performed at different routers. Extensions are done to make the test robust to multiple simultaneous tests by inspiring from the CDMA approach in the literature of multiple access channels in communication theory. The measurements of responsiveness can be utilized for different purposes like congestion control or mitigating a Distributed Denial of Service Attack.