This paper studies countermeasures to traffic analysis attacks. A common strategy for such countermeasures is link padding. We consider systems where payload traffic is padded so that packets have either constant inter-arrival times or variable inter-arrival times. The adversary applies statistical recognition techniques to detect the payload traffic rates by using statistical measures like sample mean, sample variance, or sample entropy. We evaluate quantitatively the ability of the adversary to make a correct detection and derive closed-form formulas for the detection rate based on analytical models. Extensive experiments were carried out to validate the system performance predicted by the analytical method. Based on the systematic evaluations, we develop design guidelines for the proper configuration of a system in order to minimize the detection rate.