esercizio call pstn gsm

8/13/2019 Esercizio Call Pstn Gsm

1/4

GSM Mobile Termining Call Flow (GSM Mobi le Terminated Call)

Highway Maryland GSM FixedNetwork EventHelix.com/EventStudio 2.5

GSM Mobiles Maryland LocationArea Maryland GSMEquipment

GSM CommonEquipment

PSTN

GSMMobile

Other GSMMobile

RockvilleCell

BethesdaCell

MarylandBSC

MarylandMSC VLR

HLR GMSC PSTN 31-Aug-04 22:15 (Page 1)

How does a GSM mobile phone receive a call?

We have already seen that GSM mobiles keep the GSM network informed about their current location area. The knowledge of the location areais not adequate for setting up a terminating call as the location area might spawn several cells.

In this call flow we will look at how a terminating call is handled in GSM. Setting up a terminating call is a two step process. (1) Interrogationprocedure to locate the subscriber (2) Actual call setup after the subscriber has been located.

http://www.EventHelix.com/RealtimeMantra/Telecom/GSM_network_example.htm

Copyright 2000-2004 EventHelix.com Inc. All Rights Reserved.

Interrogation procedure

ISUP INITIAL ADDRESS MESSAGEA PSTN subscriber calls theMSISDN

MAP/C SEND ROUTING INFORMATIONMSISDN

Obtain the SS7 address ofthe MSC VLR currentlyserving the specified

MSISDN

MAP/D PROVIDE ROAMING NUMBERIMSI

allocate

MSRN

MAP/D PROVIDE ROAMING NUMBER RESULTMSRN

mobile phone by dialing the GSMphone number (MSISDN). ThePSTN will use the MSISDN tolocate the GMSC (GatewayMobile Switching Center) for theservice provider. Once theGMSC has been identified, thePSTN sends the ISUP InitialAddress Message to the GMSC.

The GMSC requests routinginformation for the GSMsubscriber from the HLR (HomeLocation Register).

The HLR uses the dialed numberto locate the HLR entry for thesubscriber. The SS7 address forthe MSC VLR serving thesubscriber is obtained from thisrecord. (Recall that the SS7address of the serving MSC VLRwas updated via an inter VLRlocation update.)

The HLR has identified that thesubscriber is currently beingserved by the Maryland MSCVLR. The HLR then asks theMSC VLR to assign a temporaryroaming phone number to the

subscriber.The Maryland MSC VLRallocates a temporary roamingphone number (MSRN -MobileStation Roaming Number)

The MSRN is then passed to theHLR.

MAP/C SEND ROUTING INFORMATION RESULT HLR passes the MSRN to the

MSRN GMSC.

ISUP INITIAL ADDRESS MESSAGEMSRN

free

MSRN

The GMSC uses the MSRN toroute the call to the MarylandMSC VLR.

The Maryland MSC VLR receivesthe call. At this point, the MSRNis marked free and may bereassigned for other calls. (This


2/4

GSM Mobile Termining Call Flow (GSM Mobil e Terminated Call)



GSM CommonEquipment

PSTN

GSMMobile

Other GSMMobile

RockvilleCell

BethesdaCell

MarylandBSC

MarylandMSC VLR


is implementation dependent.)BSSMAP PAGING

TMSI

RR PAGING REQUEST TYPE 3TMSI

RR PAGING REQUEST TYPE 3TMSI

RR CHANNEL REQUESTRACH

RR CHANNEL REQUESTRACH

Now the MSC VLR needs tolocate the subscriber in thelocation area. Since the locationarea might spawn several cells,a paging mechanism is used tolocate the subscriber. The MSCVLR uses a TMSI (TemporaryMobile Subscriber Identify) toaddress the mobile phone. TheTMSI is used so as to protectthe privacy of the calledsubscriber. Note that, theBSSMAP PAGING message willbe sent to all the BSCs that

handle the Maryland LocationArea.

The Maryland BSC receives thepage message. The BSC willsend the Page message to allthe cells that serve thesubscriber's location area.

All cells in the location area willbroadcast the Page message onthe Paging Channel (PCH).Allmobile phones listen to thischannel every few seconds. Themobile is located in the Bethedacell. It receives this page

message.The mobile finds that the TMSIspecified in the page messagematches its own TMSI. Themobile decides to respond to thepage. An RR connectionestablishment is initiated bysending a channel request to thenetwork.

RR IMMEDIATE ASSIGNMENTAGCH

RR IMMEDIATE ASSIGNMENTAGCH

The network assigns a channelto the terminal and sends the

assignment and time/frequencycorrections in the immediateassignment message.

RR SABM + RR PAGING RESPONSE The mobile tunes to theassigned channel and transmitsthe page response and theSABM to initiate the RR session.

RR SABM + RR PAGING RESPONSE

SCCP CONNECTION REQUEST + RR PAGING RESPONSE The BSC sends a SCCPconnection request to the MSCVLR. The page response

message is piggy backed withthe request.


3/4

GSM Mobile Terminating Call Flow (GSM Mobil e Terminated Call)



GSM CommonEquipment

PSTN

GSMMobile

Other GSMMobile

RockvilleCell

BethesdaCell

MarylandBSC

MarylandMSC VLR


Enable Ciphering

RR UA

RR UA The BSC acknowledges theSABM to establish the RRconnection. Note that UAmessages are used in the entiresession for acknowledgingpackets. They will be omittedhere for clarity.

BSSMAP CIPHER MODE COMMAND The MSC initiates ciphering ofthe data being sent on thechannel.

RR CIPHERING MODE COMMANDmode = CLEAR

The BSC sends the CIPHERINGMODE COMMAND to the mobile.

RR CIPHERING MODE COMPLETEmode = CIPHERED

Ciphering has already beenenabled, so this message istransmitted with ciphering.

Call setup

BSSMAP CIPHER MODE COMPLETE BSC replies back to the MSC,indicating that ciphering hasbeen successfully enabled.

CC SETUP The MSC VLR receives the pageresponse and sends a call setupto the mobile.

CC CALL CONFIRMED The mobile acknowledges thereceipt of the setup by sendingthe call confirmed message.

Ring Ring the subscriber.

CC ALERTING The mobile notifies the MSC thatthe subscriber is being alerted.

ISUP ADDRESS COMPLETE MESSAGE The MSC receives the alertindication and sends an ISUPaddress complete message tothe GMSC.

ISUP ADDRESS COMPLETE MESSAGEThe GMSC sends the addresscomplete to the PSTN switch.

OK Button The subscriber answers the callby hitting the "OK" button.

CC CONNECT Notify the MSC that thesubscriber has answered thecall.

Conversation phase

ISUP ANSWER

ISUP ANSWER The call has now entered theconversation phase.

Call Release

LEG: Mobile initiates call

releaseEnd Button The mobile subscriber hits End

to clear the call.


4/4

GSM Mobile Termining Call Flow (GSM Mobi le Terminated Call)



GSM CommonEquipment

PSTN

GSMMobile

Other GSMMobile

RockvilleCell

BethesdaCell

MarylandBSC

MarylandMSC VLR


CC DISCONNECT The mobile sends thedisconnect message to the MSC.

ISUP RELEASESS7

The MSC initiates release on thePSTN side.

Disconnect Voice Path The MSC disconnects the voicepath and also releases the voicecircuit between the BSC and theMSC.

CC RELEASE The MSC informs the mobilethat it has initiated call release

ISUP RELEASEDSS7

ISUP RELEASE COMPLETESS7

The MSC informs the PSTN thatthe call release has beencompleted.

The PSTN informs that callrelease has been completed atits end.

RR Connection Release

CC RELEASE COMPLETE Mobile indicates that the call hasbeen released.

BSSMAP CLEAR COMMAND Call release has been completed,now the RR connection isreleased by the MSC.

RR CHANNEL RELEASE The BSC initiates RR releasewith the mobile.

BSSMAP CLEAR COMPLETE The BSC informs the MSC thatthe RR connection has beenreleased.

RR DISC The mobile sends a disconnectmessage to release the LAPmconnection.

RR UA The BSC replies with anUnnumbered Acknowledgemessage.

Call Released Indication Mobile goes back to the defaultdisplay to indicate that call hasbeen completely released.

esercizio call pstn gsm

Documents