GSM Call RoutingRK

GSM-IntroductionMobile Station (ME+SIM)HLR, VLRLocation UpdateCall Routing ScenariosMobile Originated SequenceMobile Terminated SequenceMobile-to-Mobile Long distanceMobile in Roaming (Domestic, International)Call HandoverQuestionsAgenda

Mobile Station(MS)

HLR / VLRHome Location Registers (HLR)

permanent database about mobile subscribers in a large service area(generally one per GSM network operator) database contains IMSI, MSISDN, prepaid/postpaid, roaming restrictions, MSC/VLR, supplementary services.

Visitor Location Registers (VLR)

Temporary database which updates whenever new MS enters its area, by HLR databaseControls those mobiles roaming in its area Reduces number of queries to HLR Database contains IMSI, TMSI, MSISDN, MSRN, Location Area, authentication key

GSM ArchitectureEIRAuC

Three types of Location Update :Brief Introdution to Location Update Periodic Location UpdateIMSI Attach/DetachNormal Location Update

Questions

GMSCMSBSSMSCVLRHLRGMSC((MSISDN+91 9885 xxxxxxInitial and Final 1 Address Message2 Send Routing Info3 Routing Info Ack Subscriber AbsentThe Calling Mobile hears the announcement of mobile is powered off AP VodafoneAP Airtel

CFN4 IFAMMSBSSMSCVLRHLRGMSCPSTNInitial and Final 1 Address Message2 Send Routing Info3 Routing Info Ack MSISDN+91 9885 xxxxxxMSISDN+91 9885 xxxxxx+91 40 66235307

3. The called MS has been barred all incoming call.MSBSSMSCVLRHLRGMSCInitial and Final 1 Address Message2 Send Routing Info3 Routing Info Ack GMSCMSISDN+91 9885 xxxxxxMSISDN+91 9885 xxxxxxCall Barred

4. The Called MS are not known at HLR MSBSSMSCVLRHLRGMSCInitial and Final 1 Address Message2 Send Routing Info3 Routing Info Ack GMSCMSISDN+91 9885 xxxxxxMSISDN+91 9885 xxxxxxUnknown Subscriber

GSM Architecture Cntd

Call Routing Scenarios

2 REQ. FOR SERVICE1 CHANNEL REQUESTDCCH ASSIGNSIGNALING LINK ESTABLISHED6 COMPLETE CALL CALL PROCEEDING 3 AUTHENTICATIONSET Cipher MODE4 SET-UP 5 EQUIP. ID REQ. MSBSSMSCVLRHLRPSTNMobile Originated SequenceSignaling Link requestSignaling Link GrantedCall setup is in ProcessSetup Voice CallDailed digits +91 40 66235307Channel request

MSBSSMSCVLRHLRGMSCGMSC Billing starts7 ConnectConnect ACK ANSRinging stops at Other MobileSubscriber picks upHello...6 Assignment CommandAssignment CompleteAlertRingtone Alert AcknowledgeRing Tone at the Other MobileAddress CompleteSpeech StartedMobile Subscriber AnsweredMobile Terminated SequenceAP VodafoneAP AirtelCall Setup RequestCall Setup Confirmed

Mobile-to-Mobile Long Distance

Mobile is in Roaming2.Receiving Mobile on Roaming3. Both Mobiles are on Roaming

International Roamer terminated call

Handover

Questions ?

The following is intended to help illustrate the four types (levels) of handover. Illustrated is a system consisting of two Mobile Switching Centres (MSCs) with three Base Station Systems (BSSs). Also depicted are cell coverage areas with example global cell identification codes for each base transceiver station.From the mobile station's reference point, it is unaware of the four levels of handover. The mobile station has two handover-related responsibilities: to provide signal measurements to its serving base station and to retune to a new radio channel when ordered to do so.

Assume that the mobile and land stations are active in a call, the call is being controlled by MSC A, and the mobile is currently in cell area 234-01-100-54.

Intra-BSS/Intra Base Transceiver Station For this type of handover, the mobile station is handed off to a different radio channel within the same cell area: 234-01-100-54. This is actually an unusual type of handover, since it is not triggered by poor signal strength if it was, the candidate base station would be different from the serving BTS. A probable cause of this type of handover would be poor signal quality (not strength), possibly due to co-channel interference. For this type of handover, BSC 3 would allocate a new radio channel and instruct the mobile station to retune.