tailieunhanh - VoIP Technologies Part 2

Tham khảo tài liệu 'voip technologies part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 16 VoIP Technologies using network and terminal quality parameters. In the E-model the original or reference signal is not used to estimate the quality as the estimation is based purely on the terminal and network parameters. Network parameters such as packet loss rate can be estimated from information contained in the headers of Real-time Transport Protocol RTP and Real-time Transport Control Protocol RTCP . The E-model is a non-intrusive method of measuring the quality as it does not require the injection of the reference signal ITU-T 2009 Sun 2004 Takahashi et al. 2004 . In the E-model the subjective quality factors are mapped into manageable network and terminal quality parameters. Among the network quality parameters are network delay and packet loss. Among the terminal quality parameters are jitter buffer overflow coding distortion jitter buffer delay and echo cancellation. Example of mapping is the mapping of delay subjective quality parameter into network delay and jitter buffer delay. The fundamental principle of the E-model is based on a concept established by J. Allnatt around 35 years ago Allnatt 1975 Psychological factors on the psychological scale are additive It is used for describing the perceptual effects of diverse impairments occurring simultaneously on a telephone connection. Because the perceived integral quality is a multidimensional attribute the dimensionality is reduced into one-dimension so-called transmission rating factor -R-Rating Factor. Based on Allnatt s psychological scale all the impairments are - by definition - additive and thus independent of one another. In the E-model all factors responsible for quality degradation are summed on the psychological scale. Due to its additive principle the E-model is able to describe the effect of several impairments occurring simultaneously. The E-model is a function of 20 input parameters that represent the terminal network and environmental quality factors quality degradation introduced by .