1. CCITT Red Book, Volume Ill-Fascicle III. 1 and III. 3, 1984
2. CCITT Red Book, Volume II-Fascicle II. 3, 1984
3. CCITT Rec. X. 140, 1988
4. F.P. Dufiy and T.W. Thatcher, Jr., “Analog transmission performance of the switched telecommunication network”, Bell Syst. Tech. J. pp 1311–1347, April 1971.
5. CCITT Contrib. COM CMBD, no 20-E “The use of call cutoff rate as a measure of telephone service availability”, ATandT, May 1982