This paper describes a measurement methodology for characterizing the performance of secure communication systems, with a particular focus on the third layer of the OSI model (Layer 3). Special emphasis is placed on analyzing the impact of network characteristics such as delay and packet error rate on Quality of Service (QoS). The network environment is simulated using multiple routers and links, incorporating the mentioned network parameters that will be varied. We have presented impact on various types of interactive communications, such as VoIP audio data and video streaming. Special care is also taken on differences when using encryption method.