Speech Signal Power in the Switched Message Network

Speech signal power at the main distributing frame in class 5 switching offices is characterized in terms of equivalent peak level (EPL) and average conversational signal power measures. The results indicate that there is little dependence of speech signal power on call destination or originating class of service. Small differences between various sub-populations are explained for the most part by loop characteristics. The switched telecommunications network is essentially transparent to customers in the sense that talker signal power has not been found to be sensitive to factors which affect the transmission path between class 5 central offices. Present-day speech volumes for toll calls, which average −21.6 VU (volume units), are substantially lower than those found in a survey conducted in 1960,1which averaged −16.3 VU, and the ranges of volumes within all call destination categories are substantially smaller than the 1960 ranges. Several substantial changes have been introduced into the telephone plant since 1960 which tend to increase the uniformity of service in the network from the viewpoint of speech volumes. These include a decrease in the proportion of toll grade battery, loss plan improvements, replacement of the 300-type telephone set with the 500-type set, and an increase in direct trunking between class 5 offices.