An empirical approach towards characterization of encrypted and unencrypted VoIP traffic

VoIP traffic classification plays a major role towards network policy enforcements. Characterization of VoIP media traffic is based on codec behaviour. With the introduction of variable bit rate codecs, coding, compression and encryption present different complexities with respect to the classification of VoIP traffic. The randomness tests do not extend directly to classification of compressed and encrypted VoIP traffic. The paper examines the applicability of randomness tests to encrypted and unencrypted VoIP traffic with constant bit rate and variable bit rate codecs. A novel method Construction-by-Selection that constructs a test sequence from partial payload data of VoIP media session is proposed in this paper. The results based on experimentations on this method show that such construction exhibit randomness and hence allows differentiation of encrypted VoIP media traffic from unencrypted VoIP media traffic even in the case of variable bit rate codecs.