Influence of Data Traffic on the Quality of VoIP over Wireless LANs

• Main Authors: Chih-Yuan Li, 李志遠
• Other Authors: Wen-Tzu Chen
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/31211914840051602079

碩士 === 國立成功大學 === 電信管理研究所 === 93 === 　Recent studies in the wireless LANs deployment have generated a lot of interest in making Voice over IP (VoIP) available over error-prone wireless networks. In this thesis, we evaluate the quality of speech over not only a wired-cum-wireless scenario but also a wireless-cum-wireless scenario in the presence of both voice and data flows. Voice traffic is modeled by a silence period and a spurt period both with exponential distribution. Data model is generated by FTP based on TCP, and error model depends on the two-state (Good/Bad) error model. 　In this thesis, we assume that VoIP users use some kinds of codecs, such as G.711/G.723.1/G.729A/iLBC, in signal sampling process. Each codec has specific data rate and packet size. In order to measure voice quality, we select mean opinion score (MOS) and E-model recommended by International Telecommunication Union Telecommunication Standardization Sector (ITU-T). In the MOS model, the users who have listened to some sample voice segments give subjective scores for speech quality. Then, the scores are averaged to get the value of MOS. In the E-model, the evaluation of call quality is calculated from some key parameters including several negative factors, such as delay and packet loss. Based on the two evaluation methods, we study the influence of data traffic on the quality of VoIP over wireless LANs. From our simulation results, we find that especially for downlink transmission, longer delay and plenty of collisions will highly degrade voice quality and drastically decrease the maximum allowable number of calls.