An overview of the relationship between objective and subjective assessment for telephony

The setting of standards requires that repeatable measurements can be made of the effect of channel degradations on the user. If such measurements can be devised, then a link can be established between an objective measurement and a subjective response. Subjects are selected randomly from the population of users and exposed to a wide variation of one or more degradations, which have been randomized in their order of presentation. An opinion is recorded on some scale. Armed with objective descriptions of a set of degradations, taken both singly and in various combinations, together with the subjective responses to them, it is then possible to build an opinion model which could be used to predict the performance of a telephony channel. The development, use, and extensions of this opinion model are considered in the context of current and future network evolution