Method of transmitting dual tone multi-frequency during communication in a private branch exchange using keyphones

Claim 1

A DTMF (dual-tone multi-frequency) transmission method during a telephonic communication on a central-office line, in a private branch exchange system comprising keyphones that generate a certain form of dial digit data but not the equivalent DTMF signal for the data within itself, said method comprising: first step of seizing a central-office line, saving digits dialed on a keyphone during a telephonic communication, in a dial buffer and checking if there is any DTMF sender available; second step of setting and registering in a memory area the data showing that the searched DTMF senders are in use of software-base, and allocating time slots in said DTMF sender; third step of allocating DTMF sender's channel to the reception part of the central-office line on its speech path, allocating reception channels for extension lines to dummy tone port, and registering a recovery time for speech path between the central-office line and the keyphone; fourth step of recording dial digits of the first step in the DTMF sender, sending DTMF by enabling the DTMF sender, and blocking DTMF transmission by disabling the same DTMF sender after a given length of time; fifth step of checking if a speech path recovery time registered in said third step has been reached or not; sixth step of freeing the DTMF sender if the registered time has passed in said fifth step and allocating transmission channels of extension line to the speech path on the central-office line; and seventh step of checking if any other dial digits are entered from keyphones when the recovery time hadn't been reached in said fifth step, and if not entered, performing said sixth step, or if entered, saving the entered dial digits in the dial buffer, registering a recovery time for speech path between the central-office line and a keyphone and then repeating this process from said fourth step.