Mobile terminated call
Mobile Terminated Call ( MTC ) refers to a call within a telephone network in which the destination terminal is a mobile phone . The opposite term, in which the calling terminal is a cell phone, is called Mobile Originated Call ( MOC ).
Localization of the mobile phone
The main task for the cellular network is to locate the selected cell phone.
If you dial the number of a mobile phone ( mobile station ) (usually recognized by the special phone code ),
- Either using the area code or number portability in a shared database of all mobile network operators, the right network operator is found.
- The call is routed through the telephone network to its Gateway Mobile Switching Center (GMSC) .
- This asks the Home Location Register (HLR), a database, whether the call number is valid and the required services, e.g. data services, may be used, as well as the relevant Visitor Location Register (VLR) and the currently valid Mobile Station Roaming Number (MSRN). The MSRN contains the information which Mobile Switching Center (MSC) is currently responsible for the mobile phone. Often the MSC and VLR are one unit. A copy of the data from the HLR is available in the VLR.
- The subscriber's VLR data record and the call itself are forwarded to the responsible MSC. The VLR data record contains the information about the location area in which the mobile phone is located.
- A broadcast (paging) is now started in all radio cells in this location area. Each radio cell is controlled by a Base Transceiver Station (BTS), which is controlled by a Base Station Controller (BSC). The relevant BSCs will be notified accordingly.
As soon as the mobile phone answers the broadcast, the security check is carried out by the visitor location register. If successful, the call is put through from the Mobile Switching Center to the mobile phone.