Subject: Mobile Communication and Computing

Topic: GSM cellular telephony-architecture and system aspects

Difficulty: Low

Mobile terminated call (MTC)

1. If the subscriber receives the call, he is involved in a mobile terminated call (MTC). Then, the mobile subscriber is the called party.
2. In this case, all entities cooperate to direct an incoming call to the mobile subscriber.
3. First of all, only the home location register (HLR) knows the subscriber’s location. Therefore, during call setup, a certain switch in the network has to ask the HLR for this information, i.e. interrogation.
4. If the call originates in the same PLMN, the interrogation procedure is started by the originating MSC/VLR, otherwise by the gateway MSC (GMSC).
5. Secondly, when the call arrives at the servicing MSC/VLR, i.e. the MSC/VLR in whose area the subscriber is located, contact is made with the mobile subscriber and call setup is completed.