Continuous Evaluation of Time Varying Speech Quality (CETVSQ) is a method of subjective assessment of transmitted speech quality for long speech sequences containing quality fluctuations in time. This method is modeled for continuous evaluation of long speech sequences based on two subjective tasks. First task is to assess the speech quality during the listening and second task is to assess the overall speech quality after listening to the speech sequences. The development of CETVSQ was motivated by fact that speech quality degradations are often not constant and varies in time. In modern IP telephony and wireless networks, speech quality varies due to specific impairments such as packet loss, echo, handover in networks etc. Many other standard methods already exist, which are being used for subjective assessment of short speech sequences. These methods such as ITU-T Rec. P.800 are well suited for only time constant speech quality. It has been revealed that if long speech sequences are divided into short segments and evaluated using P.800 ACR, then P.800 ACR results will be different from the results obtained from CETVSQ methodology. The study proves the necessity of CETVSQ.