call_flow

Immediate AssignmentImmediate Assignment

Registration: the Very First Location UpdateLAIHLRIMSIVLR idTMSIIMSITMSIReleaseVLRIMSITMSILAIMSC245261245634TMSI5

Intra VLR Location UpdateVLRIMSITMSILAI1234 new TMSITMSI + old LAI23423TMSINew TMSINew LAIBTSBSSIMSI not Required

New LAI newTMSITMSI + old LAITMSINew TMSIBSS12572572IMSI,TMSILAINew VLRIMSI, TMSIOld LAIOld VLRRAND, SRES, KcHLRnew VLR idsubscriberdata34665IMSI not RequiredRAND, SRES, KcInter VLR Location Update

BTSBSSVLR345464AuthenticationProcedureIMSI Attach

VLR1CHANNELREQUESTIMSI Detach

FTGreat BritainFranceGermanyTelephonenetworkTerminatingMSCBTSBSSVLRGatewayMSCHLROutgoing Call

ACM = Address Complete Message ANM = ANswer MessageIAM = Initial Address MessageDialingRingingPathEstablishedRingingSendingNumberMobile Originating Call

PSTNLA1LA2BTS11BTS21BTS22BTS31BTS12BTS2343512566BSC1BSC2BSC3MSC/VLRGMSCMobile Terminating Call1 - Paging Principle

IAM:Initial Address MessageMSISDN:Mobile Station Integrated Services Digital network NumberMSRN:Mobile Station Roaming NumberIMSI:International Mobile Subscriber IdentityGMSC:Gateway MSCVMSC:Visitor MSCTMSI:Temporary Mobile Subscriber IdentityMSISDN1Mobile Terminating Call2 - Detailed Procedure

DialingRingingPathEstablishedMobile Terminating Call3 - End to End Procedure

Call Release1 - Mobile Initiated

PSTNOn hookPurpose:informs the mobilethen releases radio and network resources.RELRLCBTSBSS1111233455462Call Release2 - PSTN Initiated

Mobile Originated CallRequest for ServiceAuthenticationCipheringEquipment ValidationCall SetupHandoversCall Release

The Immediate Assignment procedure is always initiated by the MS and may be triggered by a Paging Request or by a Mobile Originating Service request.Procedure1- The MS sends a CHANNEL REQUEST message (RACH).2- The BTS decodes this message and indicates it to BSC through CHANNEL REQUIRED message.3- The BSC asks the BTS to activate a dedicated channel: SDCCH or TCH (if no SDCCH available).4- Acknowledgement by the BTS5- The BSC sends an IMMEDIATE ASSIGNMENT COMMAND message to the MS (via the BTS); the MS has to seize the indicated dedicated channel including these values: initial Timing Advance and initial maximum transmission power.6- Then the MS can request a service on the dedicated channel through: LOCATION UPDATING REQUEST message for location.SERVICE REQUEST message including the access reason (call setup, paging etc.),Etc..1- Channel allocation (Connection request procedure):the MS sends (on RACH) a CHANNEL REQUEST message,the network responds with IMMEDIATE ASSIGNMENT (assigns a dedicated channel).2- The MS sends a LOCATION UPDATING REQUEST message to the BSS, with the IMSI.3- The VLR stores the LAI of the MS and informs the HLR which:stores the VLR identity, downloads the subscriber profile, if the MS is allowed to roam.4- The VLR triggers and monitors the Authentication procedure and can also activate Ciphering procedure.5- The VLR may assign a TMSI and sends it to the MS in the LOCATION UPDATING ACCEPT message.6- The MSC releases the connection.1-Channel allocation (Connection request procedure).2-The MS sends a LOCATION UPDATING REQUEST message to the BSS (with the TMSI and the old LAI), relayed to the VLR through the MSC.3-The VLR stores the new Location Area Identity, then if require, assigns a new TMSI and responds to the MS with a LOCATION UPDATING ACCEPT message.4-The MSC releases the connection.1-Channel allocation (connection request procedure).2-The MS sends a LOCATION UPDATING REQUEST message to BSS, (with the TMSI + old LAI) relayed to the VLR through MSC.3-The new VLR asks the old VLR for the MS identity and ciphering items.4-The old VLR backs new VLR IMSI, RAND, SRES, Kc.5-The new VLR assigns a TMSI and sends it to the MS over a LOCATION UPDATING ACCEPT message (with cipher mode if required).6-The new VLR informs the HLR which sends subscriber data and asks the old VLR to erase the previous MS data.7-The MSC releases connection.The IMSI attach procedure is used (if required by the network), to indicate the IMSI as active in the network and is performed by using the Location updating procedure.Procedure1- MS requests (on a RACH) a dedicated channel with CHANNEL REQUEST message using a random number.2- BSS assigns a dedicated channel (on a AGCH) with IMMEDIATE ASSIGNMENT message using this random number.3- MS sends (over this dedicated channel) a LOCATION UPDATING REQUEST message including its identity and the IMSI Attach cause.4- Authentication procedure (if required by the network).5- The MSC responds by sending a LOCATION UPDATING ACCEPT message.6- In the VLR, a flag is set to indicate that the subscriber is active.

This procedure is used only if the update status is updated and if the stored LAI is the same as the one which is actually broadcast on the BCCH of the current serving cell.The IMSI detach procedure may be invoked by a MS:if the MS is switched off,if the SIM card is detached. Procedure1- The MS requests (on a RACH) a dedicated channel with CHANNEL REQUEST message.2- The BSS assigns a dedicated channel (on a AGCH) with an IMMEDIATE ASSIGNMENT message.3- The MS sends an IMSI DETach INDication message to the VLR.4- The VLR sets a flag to indicate that this MS is no longer available; no paging will be done to that MS until an IMSI ATTach occurs.A France Telecom mobile subscriber, registered in the French HLR, is currently roaming in Great Britain. He wants to call a friend in Germany on the fixed line: how is the communication established?1-The MS originates the call by sending a CHANNEL REQUEST message (on RACH).2-Immediate assignment: channel allocation with TCH / FACCH or SDCCH.3-The VLR launches authentication (if required) and completes ciphering.4-The MS initiates call establishment by sending a SETUP message (called party number) to the MSC.5-The MSC in turn checks mobile subscriber capabilities with VLR for desired service.6-If it agrees, the MSC relays the called number over an ISUP Initial Address Message.7-The MSC also sends a CALL PROCEEDING message to the MS (assigning TCH / FACCH EA in case of Early Assignment).8-Recipient PSTN switch rings the land telephone and returns an ISUP Address Complete Message to the MSC.9-Upon receiving this message, the MSC alerts the MS with an ALERTING message.10-The Called party goes off hook, and the PSTN sends an ISUP ANswer Message to the MSC. The MSC then connects the MS (assigning a TCH in case of OACSU).11-The call is accepted (CONNECT/CONNECT ACK) and the conversation starts.In case of Emergency MO Call, the SETUP message (basic call) is replaced by the EMERGENCY one.The main difference with an MO Call procedure is the Paging of the Mobile Station.When the MS is in Idle mode, the network does not know the cell, but only the Location Area where the MS is located.Since RR sessions are only established at the request of the MS, the role of the Paging procedure is to trigger that operation.Principle1-A call from the fixed network (PSTN) is switched to the Gateway MSC (GMSC).2-The GMSC retrieves from the HLR, the identity of the MSC/VLR (or Visitor MSC) handling the Location Area of the Mobile Station.3-The GMSC routes the call to the VMSC.4-The VMSC reads the LA where the MS is located into its VLR.5-The VMSC sends instructions to one or several BSC (BSC1 and BSC2) to page the MS in the different cells of LA1.6-BSC1 and BSC2 page the MS in the BTSs of the Location Area LA1. (BTS11, BTS12, BTS21).GMSC and VMSC are software functions.Use of MSRN = the only case in GSM where a circuit is established before the call is answered.Procedure1-The calling subscriber accesses the ISDN by dialing an MS-ISDN number.2-Transmission of the MS-ISDN number to the GMSC through IAM (Initial Address Message).3-Transmission of the MS-ISDN number to the HLR through SRI (Send Routing Information).4-The HLR interrogates the VLR (Visitor MSC) that is currently serving the user.5-The VLR returns a routing number (MSRN) to the HLR, which passes it back to the GMSC.6-The MSRN is transmitted to the GMSC (address of appropriate VMSC).7-The GMSC calls the VMSC through an IAM (with MSRN).8-The MSC asks the VLR to establish where the called party is located.9-The VLR gives location information (LA) to the MSC with a PAGE message.10-The VMSC alerts all BSCs in charge of cells belonging to this LA,with a PAGING REQUEST message.11-All the BTSs page the MS over a PCH; depending upon the paging type message, up to fourdifferent TMSI may be contained in the page command.Procedure1-PSTN sends an IAM (with the MSISDN) to the GMSC.2-GMSC sends an IAM (with the MSRN) to the VMSC.3-The VMSC sends a PAGING REQUEST MM message to the BSS.4-The BSS sends a PAGING REQUEST (with IMSI or TMSI) to the MS. 5-The MS must request a channel (CHANNEL REQUEST message with paging cause) over the RACH, within 0.5 second. 6-The BSS complies and assigns a dedicated channel (on AGCH) to the MS with IMMEDIATE ASSIGNMENT message.7-The MS sends a PAGING RESPONSE to the VMSC via the BSS.8/9-Authentication and Ciphering procedures (if required).10-Setup, Assignment, Alerting procedures (see MS Originating Call).11-Alerting is sent to the PSTN with an ACM (ISUP message).12-CONNECT and ANM messages are sent to the PSTN. The call is completed.Call release can be initiated by either the PSTN user or the mobile user. The BSC is responsible for BSS resources, and the MSC is responsible for the NSS and PSTN connection.Procedure1- The call is currently in progress.2- The MS initiates the release of a call by sending a DISCONNECT message to the MSC.3- The MSC returns a RELEASE message to the MS.4- The MS acknowledges with a RELEASE COMPLETE message.5- The MSC can send the Release message to the PSTN without waiting for the RELEASE COMPLETE MM message from the MS.6- The BSC requests the MS to return to Idle mode with CHANNEL RELEASE message.7- The BTS informs the BSC with RELEASE INDICATION that the signaling link is disconnected.8- BSC requests the BTS to de-activate the RF Channel (TCH): Channel Release.9- The PSTN informs the land terminal with the appropriate tone.Abnormal termination is monitored by a set of timers (operator configurable) to ensure that resources are not unused/unavailable.Procedure1-The call is in progress.2-The release process starts with an ISUP Release message from the land network.3-Upon receiving this message, the MSC initiates the release of the call by sending a DISCONNECT message to the MS.4-The MS replies by sending a RELEASE CHANNEL message to the MSC.5/6-The MSC in turn, sends a RELEASE COMPLETE message back to the MS and sends a Release Complete message to the PSTN.