Showing papers by "Sebastian Möller published in 1999"

Speech quality and the E‐model

Abstract: The E‐model is a quality prediction model for network planning purposes. Its use is going to be recommended by the ITU‐T. In comparison with both listening‐only and conversation tests the model often shows high predictive power. Accordingly, network planners have high confidence in its applicability. However, until now it is not yet discretely understood which aspects of quality are actually covered by E‐model predictions. To name only two, uncertainties do exist, e.g., for the mode of communication (listening only or conversation) and user‐related factors. In the talk, a schematic is presented which covers, besides speech‐communication‐related elements (one‐way voice transmission quality, communication effectiveness, ease of communication) also human‐factor‐related and service‐related elements (comfort, costs). It is shown that matters are simplified by exclusively using the MOS as the basis for a thorough verification of the model. In the course of verification, measures of user acceptance, expectation, etc., are needed in order to understand how human‐ and service‐related features influence the users’ perception of the quality of service. An approach is presented to obtain subjective judgments other than MOS on a scale which is closely related to the scale of the model, namely the transmission rating factor R.

Expectation in quality assessment of Internet telephony

Abstract: Telephony from Internet terminals is getting more and more popular. Thus it is interesting to know which level of quality one user expects from a connection established from a computer terminal in relation to a normal wirebound telephone. For mobile situations, it has been shown that the lower expectation results in more favorable quality judgments in comparison with wirebound systems when assessing physically equal connections. The user’s expectation includes call motivation, attitude, experience, emotions, etc., and it will have an important influence on his/her perception of and judgment on quality. A conversation test has been carried out in order to investigate the quality impact due to Internet‐typical impairments (absolute delay, low‐bitrate codecs), both for users of a conventional wirebound telephone and an Internet terminal. In contrast to what can be observed for mobile phones, it turns out that the expectation level of potential users may result in a disadvantage effect, i.e., quality expectation is so high that Internet terminal connections are rated worse than conventional ones for physically equal connections. The situation is different for subjects who never operated a computer terminal before. Results are discussed regarding user groups and the consequences for the assessment of Internet terminal telephony.