GPRS Attach and PDP Context Activation for a Class B …

1 gprs Attach and PDP Context Activation for a Class B Core Network Old Core Network GGSN Site GSM Databases UT SGSN DNSS erver MSCVLR OldSGSN OldMSCVLR GGSN RadiusServer DHCPS erver EIR HLR This sequence diagram was generated with EventStudio System Designer ( ). We explore the sequence of interactions involved in a gprs terminal attaching to the network. The combined Attach and PDP Context Activation of a Class BGPRS terminal will be covered here. gprs Attach 1:GMM Attach RequestTMSI,MNC,MCC ,LAC,RAC The terminal initiates theattach procedure after poweron. The message contains thepreviously used TMSI(Temporary Mobile SubscriberId). The mobile networkidentity, the location area androuting area information isalso included in the message. Search for the TMSIThe SGSN (Serving GPRSS upport Node) searches forTMSI in its database.

2 2:Identity RequestTMSI No entry is found for theTMSI, so the SGSN uses theold location area informationto identify the old SGSN wherethis terminal was beingserved. 3:Identity ResponseIMSI The old SGSN responds withthe gprs mobile's IMSI(International MobileSubscriber Identity) to theSGSN. 4:Identity RequestThe SGSN asks the terminal toidentify itself. 5:Identity ResponseThe terminal responds back. 6:Authentication RequestRAND The SGSN authenticates theGPRS mobile by sending aRAND value (a random value).128-May-17(c) Attach and PDP Context Activation for a Class B Core Network Old Core Network GGSN Site GSM Databases UT SGSN DNSS erver MSCVLR OldSGSN OldMSCVLR GGSN RadiusServer DHCPS erver EIR HLR Pass the RAND value to theSIM and obtainthe Kc andSRES values The SIM applies secret GSMalgorithms on the RAND andthe secret key Ki to obtain thesession key Kc and SRES.

3 7:Authentication ResponseSRES The computed SRES value ispassed to the SGSN. 8:Identity Check RequestThe SGSN then requests theidentity of the gprs mobile. 9:Identity Check ResponseGPRS mobile responds backwith the identity. 10:IMEI Check RequestVerify that that gprs mobilebeing used by the user is not astolen one. The IMEI(Internaional MobileEquipment Identity) obtainedfrom the gprs mobile is sentto the Equipment IdentificationRegister (EIR). 11:IMEI Check ResponseThe EIR clears the subscriberand responds back to theSGSN with the status. 12:Update LocationThe SGSN now informs theHome Location Register(HLR) about the new locationof the gprs mobile. 13:Cancel LocationThe HLR informs the oldSGSN that the gprs mobilehas moved to a new location. 14:Cancel Location AckThe old SGSN acknowledgesback. 15:Insert Subscriber DataThe HLR updates the newSGSN with all the subscriberinformation.

4 228-May-17(c) Attach and PDP Context Activation for a Class B Core Network Old Core Network GGSN Site GSM Databases UT SGSN DNSS erver MSCVLR OldSGSN OldMSCVLR GGSN RadiusServer DHCPS erver EIR HLR 16:Insert Subscriber Data AckThe SGSN responds back tothe HLR. 17:Update Location AckThe HLR now responds backto the SGSN's "UpdateLocation" message. 18:Location Updating RequestThe mobile had initiated acombined Attach , so the SGSN also updates the locationinformation at the MSC-VLRthat will handle the voice :Update LocationThe MSC also initiates anupdate at the HLR. Thesequence of actions here isidentical to that of the SGSN'sHLR update. 20:Cancel Location21:Cancel Location Ack22:Insert Subscriber Data23:Insert Subscriber Data Ack24:Update Location Ack25:Location Updating AcceptThe MSC informs the SGSN that it has finished the locationupdate.

5 26:GMM Attach AcceptThe SGSN responds back tothe original GRPS combinedattach request from themobile. 27:GMM Attach CompleteThe gprs mobileacknowledges the receipt of" Attach Accept". 28:TMSI Reallocation CompleteThe Attach Complete signalsthe completion of the attach328-May-17(c) Attach and PDP Context Activation for a Class B Core Network Old Core Network GGSN Site GSM Databases UT SGSN DNSS erver MSCVLR OldSGSN OldMSCVLR GGSN RadiusServer DHCPS erver EIR HLR procedure. This is passed tothe MSC-VLR as "TMSIR eallocation Complete". PDP Context Activation 29:Activate PDP ContextAPN The gprs mobile nowinitiates the PDP contextactivation procedure to obtainthe IP address for the Access Point Name (APN)specified by the serviceprovider is passed as aparameter. 30:DNS QueryAPN The SGSN initiates a DNSquery to find the GGSN corresponding to the APNspecified by the mobile.

6 (GGSN - Global gprs SupportNode.) 31:DNS ResponseGGSN IPAddress The DNS provides the GGSNIP address. 32:Create PDP Context RequestPAP,CHAP,PDP Request The SGSN routes the PDPcontext Activation request tothe GGSN corresponding tothe APN. 33:Radius Authentication RequestPAP,CHAP The GGSN authenticates theGPRS subscription at theRADIUS server. 34:Radius Authentication ResponseThe RADIUS serversuccessfully authenticates thesubscriber and replies back tothe GGSN. 428-May-17(c) Attach and PDP Context Activation for a Class B Core Network Old Core Network GGSN Site GSM Databases UT SGSN DNSS erver MSCVLR OldSGSN OldMSCVLR GGSN RadiusServer DHCPS erver EIR HLR 35:DHCP Address RequestThe GGSN now requests aDHCP server for an dynamicIP address for the gprs mobile. 36:DHCP Address ResponseThe DHCP server provides theIP address.

7 37:Create PDP Context ResponseThe GGSN responds back tothe SGSN, indicatingcompletion of the PDP contextactivation procedure. 38:Activate PDP Context AcceptThe SGSN replies back to theGPRS mobile. This signalscompletion of the PDP contextactivation. 528-May-17(c)