Method of providing dialtone first on step by step telephone systems

A link circuit designed for use with a step-by-step central office to extend a connection via a coin box sub-set from a line finder to a central office trunk through an auxiliary con call testing circuit designed for use with said link circuit and with similar link circuits,

• said link circuit being designed on the extension thereto of a connection from a coin box sub-set via a line finder to extend the connection to said auxiliary coin call testing circuit and to extend a corresponding connection from said auxiliary circuit to said trunk,
• means responsive to the tests made in said auxiliary coin call testing circuit to connect the subscriber's line directly to the trunk bypassing said auxiliary coin call testing or to prevent completion of the subscriber's call.

For a step by step central office having connecting lines from subsets including coin box sub-sets, coin box trunk circuits for connection to coin box sub-sets and a line finder corresponding to a coin box trunk circuit for locating the line from such a coin box sub-set when the coin box sub-set goes off hook, and for connecting to said coin box sub-set line to extend the subset connection;

• the improvement of providing a link circuit for further extending the line connection from the line finder circuit to the corresponding coin box trunk,
• said link circuit being designed at the initiation of a call to extend such connection from said connected line finder to the corresponding coin box trunk through a circuit designed to detect an initial set of digits transmitted from said coin box sub-sets,
• means in said link circuit, responsive to a signal from said detection circuit, to provide an extension of said connection from said line finder to said corresponding coin box trunk circuit, and to release said detection circuit, whereby said detection circuit is available for connection to another link circuit