DISA in telephony is the abbreviation of Direct Inward Access System, which in practice is an automated operator that allows direct access to an internal attachment from an outside line in a telephone exchange as well as giving a corporate image to the company. It is somewhat similar to the Interactive Voice Response (IVR). Functionality
It is not a line DISA does not allow a call to an extension (extension) of a telephone exchange delivering the tone of the internal network of this same exchange. Its use allows to make DDI or long distance calls from outside a private telephone network using the same network. Let's assume a company that has its private telephone network that intercommunises all its different branches via Tie Line. If an employee of this company is out and needs to call one of its branches but does not want to pay for long distance, call the number assigned to the DISA line, take the dial tone and dial the access code to the tie line, communicating this way from your cell phone, for example, to the branch office paying only the call to the telephone switchboard of your office.
Depending on the model of the telephone exchange, the line may be program to have security codes in addition to having limits of use by number of calls, by time, by duration, among other variables. DISA Line Operation
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