Number Five Crossbar Switching System

The Number Five Crossbar Switching System (5XB switch) is a telephone switch for telephone exchanges designed by Bell Labs and manufactured by Western Electric starting in 1947. It was used in the Bell System principally as a Class 5 telephone switch in the public switched telephone network (PSTN) until the early 1990s, when it was replaced with electronic switching systems. Variants were used as combined Class 4 and Class 5 systems in rural areas, and as a TWX switch.

5XB was originally intended to bring the benefits of crossbar switching to towns and small cities with only a few thousand telephone lines.[1] The typical starting size was 3000 to 5000 lines, but the system had essentially unlimited growth capacity. The earlier 1XB urban crossbar was impractically expensive in small installations,[2] and had difficulties handling large trunk groups. 5XB was converted to wire spring relays in the 1950s[3] and otherwise upgraded in the 1960s to serve exchanges with tens of thousands of lines. The final 5A Crossbar variant, produced starting in 1972, was available only in sizes of 990 and 1960 lines,[4] and generally delivered on one pallet, rather than assembled on site as usual for larger exchanges.

  1. ^ Fagen, M.D.; Amos, E.Joel; Schindler, G. E. (1975). A History of Engineering and Science in the Bell System. Internet Archive. Bell Telephone Laboratories. p. 157. ISBN 978-0-932764-00-3.
  2. ^ Bell Telephone Laboratories (1949). No. 5 Crossbar - Bell Labs Record Compilation. Bell Telephone Laboratories. p. 5.
  3. ^ Petersen, C.V., ed. (1963). No. 5 Crossbar Switching System Volume 1: Equipment Applications. Western Electric Co., Inc. pp. Section II, Page 5.
  4. ^ Fagen, M.D.; Amos, E.Joel; Schindler, G. E. (1975). A History of Engineering and Science in the Bell System. Internet Archive. Bell Telephone Laboratories. p. 168. ISBN 978-0-932764-00-3.