The Bell System Technical Journal, volume 50 no. 8, October 1971.
AT&T, October 1971, pp 2495 - 2856 inclusive, references, diagrams.
AT&T, October 1971, pp 2495 - 2856 inclusive, references, diagrams.
AT&T 1965, pp 207-372 inclusive, diagrams and photographs, references.
Bell System, November 1970, pp 1995-2415 inclusive, diagrams, references, some photographs.