Meaning
Network attachment failures occur when a device requests access to a network in a region where it cannot be served. The response code known as cause 15 indicates that there are no suitable cells in the tracking area for the requesting terminal. It informs the device that while the network operates in the area, the specific cells cannot provide service due to subscription constraints.
Coverage Assessment
Controller interfaces return this code during the registration procedure to prevent unauthorized access. The device receives the rejection and immediately stops trying to connect to the current cell or tracking area.
Search Penalty
The subscriber terminal places the tracking area identity into a list of forbidden tracking areas to modify its roaming behavior. This prevents the modem from continuously initiating registration attempts on the same frequencies, saving critical power reserves. Active entries remain on the list until the device moves to a different region or the user performs a manual scan.
Carrier Redirection
Mobile hardware adjusts its scanning routines to find alternative carriers that might accept the registration request. The device prioritizes other frequencies and network technologies that do not fall under the active restriction. This transition ensures that the equipment maintains some level of network connectivity even when its primary operator cannot provide service in that physical zone.
