การวิเคราะห์และทดสอบคุณภาพการให้บริการเสียงบนเฟรมรีเลย์ ของธนาคารเพื่อการเกษตรและสหกรณ์การเกษตร / พงษ์เทพ พรหมศิริ = An analysis and testing of the service quality of voice over frame relay of Bank for Agriculture and Agricultural Co-operatives / Pongthep Promsiri
Jitter is one of some key indicators showing the degrading quality of voice transmission over frame-relay network. The rates of voice frames being lost over the frame-relay network transmission directly impact the performance of the quality of voice transmission. Over-size data frames, which shared the same channel with voice frames, have been identified as the cause of jitter. Generally, decreasing the rate of Jitter can be achieved by reducing the frame-size of data frames being transmitted. Unfortunately, by utilizing this method the performance of data transmission are degrade as well. Another method is devised by the adoption of an extra delay at the decoder inorder to compensate the irregular arrival of voice frames. Two major algorithms had been adopted which are fixed buildout delay and adaptive buildout delay ones. In this thesis the author used the wide area network of The Bank for Agriculture and Agricultural Co-operatives (BAAC) as a case study model. A simulation model was required developed to analyze the maximum average data frame size and the minimum buildout delay for the fixed delay algorithm. The minimum buildout delay was 71 ms and the maximum average data frame size was 198 bytes. Next the rate of frame loss was measured as the quality of voice service (QoS) for the adaptive buildout algorithm. The adaptive buildout delay algorithm gave better QoS with 2% lower loss rate. Lastly, the author performs a voice quality subjective test by transmitting voice and data frames over BAAC network. By voice ITU P.800 testing procedure the maximum average data frame size provided good voice quality is 198 bytes which is in agreement with the objective test.
