1969-70 Connection Survey: High-Speed Voiceband Data Transmission Performance on the Switched Telecommunications Network

Data-Phone service was introduced on the switched network in 1959. Since that time, the number of data sets in service has grown by ap1349 1350 T H E BELL SYSTEM TECHNICAL J O U R N A L , APRIL 1971 proximately 50 percent per year, resulting in the connection of over 100,000 data terminals by 1970. A wide variety of data system applications has evolved with the trend being toward higher speeds, automatic operation, improved performance, and lower costs. Since 1959 the overall switched telecommunications network has also experienced substantial growth and change. During this period the annual growth rate of the number of miles of voiceband channels in the network has been approximately 19 percent. More than half of the facilities in service today have been placed in service since 1959. Accompanying this growth has been the introduction of newly designed transmission and switching equipment. In addition, the growth of data services has resulted in data transmission considerations being reflected to a greater extent in the overall design, operation, and maintenance of the switched network. Since the network has undergone considerable change there is a need for current information on performance. Such information is of value in the design of data systems including the design of modems and error control procedures. It is also of use in establishing performance objectives and in identifying areas where service improvements may be realized. A number of surveys conducted in the past by B T L have provided information on the data transmission characteristics of the switched network.