Subject: Mobile Computing

Difficulty: Medium

Marks: 4 Marks

Call Setup in GSM: Mobile Originating Call (MOC): Call setup, which are initiated by an MS

1. Channel Request: The MS requests for the allocationof a dedicated signalling channel to perform the call setup.
2. After allocation of a signalling channel the request for MOC call setup, included the TMSI (IMSI) and the last LAI, is forwarded to the VLR
3. The VLR requests the AC via HLR for Triples [(random number (RAND), Signed Response (SRES) and a Cipher Key (Kc)] (if necessary).
4. The VLR initiates Authentication, Cipher start, IMEI check (optional) and TMSI Re-allocation (optional).
5. If all this procedures have been successful, MS sends the Setup information (number of requested subscriber and detailed service description) to the MSC.
6. The MSC requests the VLR to check from the subscriber data whether the requested service an number canbe handled (or if there are restrictions which do not allow further proceeding of the call setup)
7. If the VLR indicates that the call should be proceeded, the MSC commands the BSC to assign a Traffic Channel (i.e. resources for speech data transmission) to the MS
8. The BSC assigns a Traffic Channel TCH to the MS
9. The MSC sets up the connection to requested number (called party)