Plan 55-A

[1] It is an automated successor to Plan 51, which commenced service in 1951 in a nationwide network of the U.S. Air Force, but required semi-automatic operation.

[2][3] Based on the technology of punched paper tape storage, the systems of the design were called reperforators.

Output from each sending console was transmitted via outgoing lines to other switching centers or to destination teleprinters.

[3] Nationwide, Western Union's switching centers were arranged in a hub and spokes architecture involving fifteen locations.

An analysis of the queueing delays in Plan 55-A by Leonard Kleinrock formed part of his doctoral research in the early 1960s.