New final selector facilities for step-by-step systems

The paper describes a new final selector circuit in which the new features may be summarised as follows: (1) A P.B.X. hunting control arrangement in which the lines of any P.B.X. group need not be consecutive and can be intermingled with other P.B.X. groups; (2) simplicity in providing various classes of line discrimination signals, e.g. changed numbers, dead numbers, etc.; and (3) use of a skeleton multiple permitting a 200-outlet final selector group to provide service for 200 subscribers numbered over a 400 numbering range. These facilities introduce definite advantages: (a) ability to maintain a large proportion of the existing numbers at the time of transfer from manual operation; (b) ability to use a higher proportion of the multiple numbers as working lines; (c) ability to extend P.B.X. groups without number change and without the expense of an abnormal proportion of spare lines initially; (d) simplicity in providing various classes of line discrimination signals; and (e) elimination of main frame, number unobtainable, tone equipment or dead number circuits.