The size of the control unit determines the maximum configuration. These numbers usually refer to the maximum configuration of the system although not always. Computer Telephony Integration provides communication and coordination or operation between computers and the telephone system. Direct Inward System Access is a feature that allows outside callers to access all or some of the called systems features without the assistance of another person. This may include internal paging, making a call, or calling another extension.
DISA is different than auto attendant.
It provides one touch calling to specific extensions and a visual indication of others using telephones within the telephone system. Some telephone systems only allow 1 of these. The term port means circuit. The number of ports on a voice mail system is directly related to the number of users that can be in voice mail at the same time. This system supports up to 72 total system ports.