A dialable extension is an extension that is can be dialed without going through ARS or AAR routing.

A nondialable extension is an extension that can only be dialed using ARS or AAR routing. You cannot dial a nondialable extension as it is administered. You must dial a nondialable extension with a prefix as a longer number than the administered extension.

An internal extension is an extension of up to 16 digits.

Use the following general rules to determine how nondialable extensions interact with a particular feature:

• When a user dials an extension directly from a telephone, or the system dials an extension when a feature is invoked, the ARS or AAR Dialing without a FAC feature must be used.

• When a feature, such as Coverage Paths or Security Violation Notification (SVN), is being administered on behalf of a telephone user, the internal extension must be entered through the administration tool.