An external caller can access internal PBX features on certain CO lines by keying in a special code.
The PBX answers the incoming call with dial tone, and the caller enters the access code (if required) and destination extension number or routing code.
DISA feature is one of useful IP PBX systems in business communication markets. If users outside the office want to make calls by using corporate’s lines. DISA can easily enable outside users using PBX service just like the system extensions. As a result, the company can save a lot of costs by company’ PBX resource instead of the original direct call.