DISA stands for Direct Inward System Access. DISA allows outside callers to call into the PBX and obtain an internal dialtone. The user can then dial out from the PBX as if the call were coming from an internal extension.
For example, DISA could be used by staff outside the office to take advantage of lower long-distance rates provided by the PBX trunk lines, or to reduce cell phone minutes by using a call-a-number-free cell phone plan provision. Traveling employees could use any phone to call the DISA and then call a client. The client would see the call coming from the office, even though the employee may be using a cell phone.
The DISA Module is used to create a destination to which you can send calls. Calls sent to a DISA destination will receive a dial tone and they can dial a phone number, and the call will go out through the PBX.
For example, you could create a DISA and set the DISA as a destination in an IVR, so that when a caller presses 1, he will hear a dial tone and can dial a telephone call.
Another option is to assign a dedicated number to go directly to a DISA destination.
Be sure to configure security access controls for a DISA destination, at it opens the PBX up to outside callers.
Options for securing a DISA:
Because the DISA Module creates a destination to which you can route calls, the DISA Module is related to the any module that can route calls to a destination, including the Inbound Routes Module, the IVR Module, the Time Conditions Module, etc.
See the User Guide for configuration.