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<ul><li><p>GSM Mobility ManagementGSM Mobility Management</p></li><li><p>Introduction Location area (LA) is the basic unit for location </p><p>tracking.E LA i t f BTS th t i t ith Every LA consists of BTSs that communicate with the MSs over radio linksM j t k f M bilit M t i t d t Major task of Mobility Management is to update the location of an MS when it moves from one LA to anotherto another.</p><p>February 20, 2013 Girish Kumar Patnaik 2</p></li><li><p>Introduction Location update procedure is referred to as </p><p>registration. BTSs periodically broadcasts the </p><p>corresponding LA addresses to the MSs When an MS receives an LA address </p><p>different from the one stored in its memory, y,it sends a registration message to the network</p><p>February 20, 2013 Girish Kumar Patnaik 3</p></li><li><p>GSM Location Area Hierarchy</p><p>February 20, 2013 Girish Kumar Patnaik 4</p></li><li><p>GSM Basic Location UpdatepProcedure</p><p> In GSM, registration or location update occurs when an MS moves from one LA to another.</p><p> Three cases of location update:Three cases of location update: Case 1. Inter-LA Movement</p><p>Case 2 Inter MSC Movement Case 2. Inter-MSC Movement Case 3. Inter-VLR Movement</p><p>February 20, 2013 Girish Kumar Patnaik 5</p></li><li><p>Inter-LA Registration Message FlowMessage Flow</p><p>February 20, 2013 Girish Kumar Patnaik 6</p></li><li><p>Inter-LA Registration Message Flow</p><p>VLR2</p><p>VLR1 HLR</p><p>VLR2</p><p>LA1 LA2</p><p>February 20, 2013 Girish Kumar Patnaik 7</p></li><li><p>Inter-LA Movement Two LAs belong to the same MSC. Four major steps:j p</p><p> Step 1. MS sends a location update request message (MSBTSMSC) .</p><p>P t i l d d P i LA i MSC d i Parameters included: Previous LA, previous MSC and previous VLR.</p><p> IMSI (International Mobile Subscriber Identity) is used to id tif MSidentify MS.</p><p> However, the MS identifies itself by the Temporary Mobile Subscriber Identity (TMSI).</p><p> TMSI is used to avoid sending the IMSI on the radio path. TMSI is temporary identity is allocated to an MS by the VLR at </p><p>inter-VLR registration</p><p>February 20, 2013 Girish Kumar Patnaik 8</p></li><li><p>Inter-LA Movement Step 2. The MSC forwards the location update </p><p>request to the VLR by a TCAP message, MAP_UPDATE_LOCATION_AREA.</p><p> Parameter includes: Address of the MSC, TMSI, previous Location Area Identification (LAI) targetprevious Location Area Identification (LAI), target LAI, Other related information</p><p> Steps 3 and 4.Steps 3 a d . Part I. The VLR finds that both LA1 and LA2 belong </p><p>to the same MSC. Part II. The VLR updates the LAI field of the MS. Part III. The VLR replies an ACK to the MS through </p><p>the MSCFebruary 20, 2013 Girish Kumar Patnaik 9</p><p>the MSC.</p></li><li><p>Inter-MSC Registration Message FlowMessage Flow</p><p>February 20, 2013 Girish Kumar Patnaik 10</p></li><li><p>Inter-MSC Registration Message Flow</p><p>VLR2</p><p>VLR1 HLR</p><p>A1</p><p>VLR2</p><p>LA1 LA2</p><p>February 20, 2013 Girish Kumar Patnaik 11</p></li><li><p>Inter-MSC Movement The two LAs belong to different MSCs of </p><p>the same VLR. The process is:</p><p> Steps 1 and 2. MS sends a location update request message (MSBTSMSC) .</p><p> Step 3.P I VLR1 fi d h h LA1 d LA2 b l Part I. VLR1 finds that the LA1 and LA2 belong to MSC1 and MSC2, respectively. Two MSCs are connected to VLR1.</p><p> Part II. VLR1 updates the LAI and MSC fields of MS.</p><p> Part III. The VLR1 derives the HLR address of the</p><p>February 20, 2013 Girish Kumar Patnaik 12</p><p>Part III. The VLR1 derives the HLR address of the MS from the MSs IMSI.</p></li><li><p>Inter-MSC Movement Step 3.</p><p> Part IV. The VLR1 sends the MAP_UPDATE_LOCATION to the HLR.</p><p> Parameter includes: IMSI, target MSC Address VLR Address other relatedAddress, VLR Address, other related information</p><p> Step 4 HLR updates the MSC number Step 4. HLR updates the MSC number field of the MS. An acknowledgement is sent to VLR1.</p><p> Steps 5 and 6. The acknowledgement is forwarded to the MS.</p><p>February 20, 2013 Girish Kumar Patnaik 13</p></li><li><p>Inter-VLR Registration Message FlowMessage Flow</p><p>4</p><p>1</p><p>5</p><p>61</p><p>VLR1</p><p>February 20, 2013 Girish Kumar Patnaik 14</p></li><li><p>Inter-VLR MovementT LA b l MSC d Two LAs belong to MSCs connected to different VLRs.Th i The process is: Step 1. MS sends a location update request. </p><p>MSC2 sendsMSC2 sends MAP_UPDATE_LOCATION_AREA to VLR 2 with MSs TMSI.</p><p> Steps 2 and 3. VLR2 does not have the record of MS. VLR2 identifies the address the VLR1 and sends </p><p>MAP_SEND_IDENTIFICATION (with TMSI) to VLR1.</p><p>February 20, 2013 Girish Kumar Patnaik 15 VLR1 sends IMSI to VLR2.</p></li><li><p>Inter-VLR MovementSt 4 d 5 Steps 4 and 5. VLR2 creates a VLR record for the MS.</p><p>VLR2 d i i HLR VLR2 sends a registration message to HLR. HLR updates the record of the MS.</p><p>HLR d k l d b k t VLR2 HLR sends an acknowledge back to VLR2. Step 6.</p><p>VLR2 t TMSI d d it t VLR2 generates a new TMSI and sends it to the MS.</p><p>Steps 7 and 8 Steps 7 and 8. The obsolete record of the MS in VLR1 is </p><p>deleted.February 20, 2013 Girish Kumar Patnaik 16</p><p>deleted.</p></li><li><p>Call Origination Operation</p><p>4</p><p>February 20, 2013 Girish Kumar Patnaik 17</p></li><li><p>GSM Basic Call Origination The process is</p><p> Step 1. MS sends the call origination request to MSCMSC.</p><p> Step 2. MSC forwards the request to VLR with messagemessage MAP_SEND_INFO_FOR_OUTGOING_CALL.</p><p> Step 3. VLR checks MSs profile and sends MAP_SEND_INFO_FOR_OUTGOING_CALL ack to MSC to grant the call requestL_ack to MSC to grant the call request.</p><p> Step 4. MSC sets up the trunk according to the standard PSTN call setup procedure.</p><p>February 20, 2013 Girish Kumar Patnaik 18</p><p>standard PSTN call setup procedure.</p></li><li><p>Call Termination Message Flow</p><p>February 20, 2013 Girish Kumar Patnaik 19</p></li><li><p>Call Termination Routing information for call termination can </p><p>be obtained form the serving VLR.be obtained form the serving VLR. The basic call termination process:</p><p>Step 1 A MS ISDN (MSISDN) b i Step 1. A MSs ISDN (MSISDN) number is dialed by a PSTN user. The call is routed to a gateway MSC by an SS7 ISUP IAM messagegateway MSC by an SS7 ISUP IAM message.</p><p> Step 2. GMSC sends MAP SEND ROUTING INFORMATION _S N _ OU NG_ N O ONwith the MSISDN to HLR.</p><p>February 20, 2013 Girish Kumar Patnaik 20</p></li><li><p>Call Termination Step 3. HLR sends a </p><p>MAP_PROVIDE_ROAMING_NUMBER to VLR. Parameter included: IMSI of the MS, the MSC number.</p><p> Steps 4 and 5. VLR creates Mobile Subscriber Roaming Number (MSRN) by using the MSCRoaming Number (MSRN) by using the MSC number stored in the VLR record.</p><p> MSRN is sent back to the gateway MSC through HLR.g y g MSRN provides the address of the target MSC where the </p><p>MS resides.Step 6 An SS7 ISUP IAM message is directed from Step 6. An SS7 ISUP IAM message is directed from the gateway MSC to the target MSC to setup the voice trunk.</p><p>February 20, 2013 Girish Kumar Patnaik 21</p></li><li><p>Mobility Databases The hierarchical databases used in GSM.</p><p>The home location register (HLR) is a database The home location register (HLR) is a database used for MS information management.The visitor location register (VLR) is the The visitor location register (VLR) is the database of the service area visited by an MS.</p><p>February 20, 2013 Girish Kumar Patnaik 22</p></li><li><p>Home Location Register (HLR) An HLR record consists of 3 types of </p><p>information: Mobile station information</p><p> IMSI (used by the MS to access the network)MSISDN (th ISDN b Ph N b f th MS) MSISDN (the ISDN number - Phone Number of the MS)</p><p> Location information ISDN number of the VLR (where the MS resides) ISDN number of the VLR (where the MS resides) ISDN number of the MSC (where the MS resides)</p><p> Service information service subscription service restrictions</p><p>l iFebruary 20, 2013 Girish Kumar Patnaik 23</p><p> supplementary services</p></li><li><p>Visitor Location Register (VLR) The VLR information consists of three parts:</p><p> Mobile Station Information IMSI MSISDN TMSI</p><p> Location Information MSC Number Location Area ID (LAI)</p><p> Service Information A subset of the service Information stored in HLR</p><p>February 20, 2013 Girish Kumar Patnaik 24</p></li><li><p>Two Issues of GSM MobilityDatabasesDatabases</p><p> Fault Tolerance. If the database fail, the loss or corruption of </p><p>location information will seriously degrade the serviceservice.</p><p> Database Overflow.VLR fl if t VLR may overflow if too many users move into the VLR-controlled area in a short period.</p><p> If VLR is full a new arrival user fails toIf VLR is full, a new arrival user fails to register in VLR and thus cannot receive service.</p><p> This phenomenon is called VLR overflow.</p><p>February 20, 2013 Girish Kumar Patnaik 25</p><p>p</p></li><li><p>VLR Failure RestorationAft VLR f il VLR i f ti After a VLR failure, VLRs information: Mobile Station Information</p><p> Recovered either by the first contact with HLR or MSRecovered either by the first contact with HLR or MS. Location Information</p><p> Recovered by the first radio contact with MS. Service Information</p><p> Recovered by the first contact with HLR or the corresponding MS.corresponding MS.</p><p> After a VLR failure, the VLR record restoration is initiated by one of the following three events: MS registration MS call origination</p><p>MS call terminationFebruary 20, 2013 Girish Kumar Patnaik 26</p><p> MS call termination</p></li><li><p>Restoration- MS Registration After a VLR failure:</p><p> No record of MS in VLRNo record of MS in VLR VLR considers the registration as an inter-VLR </p><p>movement.movement. VLR ask MS to follow the normal registration </p><p>procedure defined in inter-VLR movement.p The TMSI sent from the MS to the VLR cannot </p><p>be recognizedg VLR asks MS to send IMSI over the air.</p><p>February 20, 2013 Girish Kumar Patnaik 27</p></li><li><p>Restoration-MS Call Origination After a VLR failure:</p><p> VLR receives the call origination request g qMAP_SEND_INFO_OUTGOING_CALL from the MSC (and MS).No record of MS in VLR No record of MS in VLR</p><p> VLR considers it as a system error: unidentified subscriber and rejects the request.j q</p><p> VLR asks MS to initiate the registration procedure of inter-VLR movement.</p><p> After the registration procedure, the VLR record is recovered.</p><p>February 20, 2013 Girish Kumar Patnaik 28</p></li><li><p>Restoration - Call TerminationM FlMessage Flow</p><p>February 20, 2013 Girish Kumar Patnaik 29</p></li><li><p>Restoration - Call TerminationM FlMessage Flow</p><p>February 20, 2013 Girish Kumar Patnaik 30</p></li><li><p>HLR Failure Restoration In HLR, it is mandatory to save the updates </p><p>into backup storage.into backup storage. The service information is immediately </p><p>transferred from the HLR into the backuptransferred from the HLR into the backup. The location information is periodically </p><p>t f d f th HLR i t th b ktransferred from the HLR into the backup. After an HLR failure, the data in the backup </p><p>are reloaded into the HLR</p><p>February 20, 2013 Girish Kumar Patnaik 31</p></li><li><p>HLR Restoration ProcedureMessage Flow</p><p>February 20, 2013 Girish Kumar Patnaik 32</p></li><li><p>Questions in HLR RestorationProcedureProcedure</p><p> The HLR restoration procedure is not probust. HLR does not know a VLR at checkpoint.p An MS move into the VLR during the </p><p>uncovered period. HLR will not ask the VLR to send location </p><p>information. VLR Identification Algorithm is to solve </p><p>the problem.February 20, 2013 Girish Kumar Patnaik 33</p><p>p</p></li><li><p>VLR Identification AlgorithmVLR Identification Algorithm VIA identifies the exact VLRs to be </p><p>contacted by the HLR after an HLR failure. Extra data structures are needed.Extra data structures are needed. Extra procedures are needed:</p><p>Check point procedure Check-point procedure Registration procedure</p><p>R t ti d Restoration procedure</p><p>February 20, 2013 Girish Kumar Patnaik 34</p></li><li><p>Data Structure in VLR Identification Algorithm (VIA)Identification Algorithm (VIA) To simplify the description we assume thatTo simplify the description, we assume that </p><p>every VLR covers exactly one MSC. An extra data structure VLR List* is a set An extra data structure VLR_List* is a set </p><p>of VLRs that have been contacted by HLR during the uncovered periodduring the uncovered period.</p><p> After an HLR failure, the HLR only needs d h MAP RESETto send the MAP_RESET messages to </p><p>VLRs listed in VLR_List*.</p><p>February 20, 2013 Girish Kumar Patnaik 35</p></li><li><p>Data Structure in VLR Identification Algorithm (VIA)Identification Algorithm (VIA)</p><p> In HLR, every record includes two extra fields.t th l t ti f l ti d t ts = the last time of location update</p><p> PVLR = the address of VLR where the MS resided at the last check-pointing time. Thus, for any MS p, we have</p><p> HLR*[p].VLR = HLR[p].PVLR</p><p> Two extra data structures in the HLRTS th l t h k i ti b k ti TS= the last check-pointing or backup time</p><p> VLR_Counter = {(VLR1,Count 1), (VLR2,Count 2), , (VLRn,Count n)} where Count n represents the effective number of MSs entering the VLRn during the uncovered period.</p><p> Note that the VLRs recorded in VLR Counter are the VLRs </p><p>February 20, 2013 Girish Kumar Patnaik 36</p><p>_in VLR_List*.</p></li><li><p>VIA Data Structure</p><p>February 20, 2013 Girish Kumar Patnaik 37</p></li><li><p>VIA Procedure 1: Check-P i tiPointing</p><p> In VIA, information of the HLR is periodically , p ysaved into the backup by this procedure.</p><p> Step 1. For every entry p in HLR* do: p y y pHLR[p]*.VLR HLR[p].VLR </p><p> Step 2. TS current time;p ; Step 3. For every location entry p in HLR do: </p><p>HLR[p].tsTS; HLR[p].PVLR HLR[p].VLR[p] ; [p] [p] Step 4. VLR-Counter NULL; VLR-List* NULL;February 20, 2013 Girish Kumar Patnaik 38</p><p>;</p></li><li><p>VIA Procedure 2: Registration Step 1. Update HLR:</p><p>V HLR[p] VLR;Vold HLR[p].VLR; Send message, </p><p>MAP CANCEL LOCATION to cancelMAP_CANCEL_LOCATION, to cancel the VLR entry of p at Vold;</p><p>HLR[p] VLR V ;HLR[p].VLR Vnew;told HLR[p].ts;HLR[ ] t tHLR[p].ts t;</p><p>February 20, 2013 Girish Kumar Patnaik 39</p></li><li><p>VIA Procedure 2: Registration Step 2. Update the Vnew Count field in VLR_Counter:</p><p>If (HLR[p].VLR HLR[p].PVLR){( [p] [p] ){If (VLR_Counter[Vnew] exists){</p><p>VLR_Counter[Vnew].Count </p></li><li><p>VIA Procedure 2: Registration Step 3. Update the Vold counter entry:If (t &gt; TS and V HLR[p] PVLR){If (told &gt; TS and Vold HLR[p].PVLR){</p><p>VLR_Counter[Vold].Count </p></li><li>VIA Procedure 3: Restore Step 1. TS </li><li><p>VLR Overflow Control</p><p> VLR may overflow if too many mobile users i h LA i h i dmove into the LA in a short period.</p><p> When a VLR is full, a new arrival user can not i t d t iregister and get service.</p><p> If we want to let the new arrival user can get service all of the following procedures need to beservice, all of the following procedures need to be modified: registration cancellation call origination callregistration, cancellation, call origination, call </p><p>termination</p><p>February 20, 2013 Girish Kumar Patnaik 43</p></li><li><p>Overflow Registration O (O )Operation (O-I)</p><p>February 20, 2013 Girish Kumar Patnaik 44</p></li><li><p>Cancellation Operation withO f (O )Overflow VLR (O-II)</p><p>February 20, 2013 Girish Kumar Patnaik 45</p></li><li><p>Call Origination with Overflow VLR (O-III)Overflow VLR (O-III)</p><p>February 20, 2013 Girish Kumar Patnaik 46</p></li><li><p>Call Termination with Overflow VLR (O-IV)</p><p>February 20, 2013 Girish Kumar Patnaik 47</p></li><li><p>Call Termination with Overflow VLR (O-IV)</p><p>February 20, 2013 Girish Kumar Patnaik 48</p></li><li><p>AcknowledgementAcknowledgement</p><p> Slides obtained from home page of Prof.Phone Lin </p><p> Slides obtained from home page of Prof Gerald Q Maguire JrProf.Gerald Q. Maguire Jr. </p><p>February 20, 2013 Girish Kumar Patnaik 49</p></li></ul>