Non-intrusive speech quality assessment method and apparatus for storing a sequence of intercepted packets associated with a call, each packet containing speech data, and an indication of a transmission time of the packet; storing with each intercepted packet an indication of an intercept time of the packet; extracting a set of parameters from the sequence of packets; and generating an estimated mean opinion score in dependence upon the set of parameters. The extracting step comprises the sub steps of: generating a jitter parameter for each packet of the sequence of stored packets; generating a long term average jitter parameter for the stored packet; and generating a differential jitter parameter in dependence upon the jitter parameter for the stored packet and the long term average jitter parameter.