Interfaces (GSM Originating Call)Cell Mobile Network Fixed Network

Mobile Station Base Stations NSS PSTNUser Mobile BSS MSC VLR PSTN

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LEG: GSM Mobile Originated Call RR CHANNEL REQUEST

RACHRR connection establishment is triggered bysending the Channel Request message. Thismessage requests the Base Station System (BSS)for allocation for radio resources for the RRconnection setup. The mobile now waits for anassignment on the Access Grant Channel (AGCH).At this point the mobile is listening to the AGCHfor a reply.

RR IMMEDIATE ASSIGNMENTAGCH, Radio_Resource = (TCH, Frequency,

Timeslot), Time Correction, FrequencyCorrection

The BSS transmits the radio resource assignmentto the Mobile via the AGCH channel. The messagealso contains the time and frequency corrections.The time corrections allow the mobile to time it'stransmissions so that they reach the BSS only inthe specified slot. The frequency correctionscorrect for the Doppler shift caused by themobile's motion.

RR SABM + MM CM SERVICE REQUESTTCH, SAPI = 0

This is the first message that is sent after tuningto the channel. The Mobile initiates a LAPmconnection with the BSC by sending a SetAsynchronous Balanced Mode (SABM) message.The service request message meant for the MSCis also sent in this message.

RR UATCH, SAPI = 0

The BSS replies with Unnumbered Acknowledge(UA) to complete the LAPm setup handshake

LEG: Initiate Authentication Procedure RR CIPHERING MODE COMMAND

mode = CLEARThe BSS sends the CIPHERING MODECOMMAND to the mobile. The mobile will be ableto receive this message as the transmission fromthe BSS is still in clear.

RR CIPHERING MODE COMPLETEmode = CIPHERED

Ciphering has already been enabled, so thismessage is transmitted with ciphering. The BSSwill receive this message as it is alreadyexpecting ciphered data in the receive direction.

RR CHANNEL MODE MODIFY The BSS notifies the Mobile about the changeoverto voice mode.

RR CHANNEL MODE MODIFY ACKNOWLEDGE Mobile acknowledges.

LEG: Mobile initiates call release RR CHANNEL RELEASE The BSS initiates RR release with the mobile.

RR DISC The mobile sends a disconnect message torelease the LAPm connection.

RR UA The BSS replies with an UnnumberedAcknowledge message.

Interfaces (GSM Location Update)Highway Virginia GSM Maryland

GSM Mobiles VirginiaLocation

Area

Virginia GSMEquipment

GSMDatabases

Maryland Location Area MarylandGSM

EquipmentOther GSM

MobileGSM

MobileVienna Cell Virginia

BSCVirginia

MSC VLRHLR Rockville

CellBethesda

CellMarylandMSC VLR

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RR CHANNEL REQUEST The mobile establishes a RRconnection to send the locationupdate to the network.

RR CHANNEL REQUEST

RR IMMEDIATE ASSIGNMENT

RR IMMEDIATE ASSIGNMENT A radio channel has beenassigned to the GSM mobile.

RR SABM + MM LOCATION UPDATING REQUESTMaryland TMSI, Maryland LAI

The mobile tunes to theassigned radio channel andsends the SABM to initiate theradio connection. The locationupdate is also piggybacked onthe message.

RR UA The RR connection setup iscompleted by responding withUA for the received SABM.

RR UA

LEG: Inter MSC-VLR locationupdate

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.

RR CHANNEL RELEASE The BSC initiates RR releasewith the mobile.

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

RR UA The BSC replies with anUnnumbered Acknowledgemessage.

Interfaces (GSM Terminating Call)Highway Maryland GSM Fixed

NetworkGSM Mobiles Maryland Location Area Maryland GSM

EquipmentGSM Common

EquipmentPSTN

GSMMobile

Other GSMMobile

RockvilleCell

BethesdaCell

MarylandBSC

MarylandMSC VLR

HLR GMSC PSTN

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RR PAGING REQUEST TYPE 3TMSI

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

RR PAGING REQUEST TYPE 3TMSI

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 pagemessage.

RR CHANNEL REQUESTRACH

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 CHANNEL REQUESTRACH

RR IMMEDIATE ASSIGNMENTAGCH

The network assigns a channelto the terminal and sends theassignment and time/frequencycorrections in the immediateassignment message.

RR IMMEDIATE ASSIGNMENTAGCH

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 responsemessage is piggy backed withthe request.

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.

RR UA

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.LEG: Mobile initiates callrelease

RR CHANNEL RELEASE The BSC initiates RR releasewith the mobile.

Interfaces (GSM Terminating Call)Highway Maryland GSM Fixed

NetworkGSM Mobiles Maryland Location Area Maryland GSM

EquipmentGSM Common

EquipmentPSTN

GSMMobile

Other GSMMobile

RockvilleCell

BethesdaCell

MarylandBSC

MarylandMSC VLR

HLR GMSC PSTN

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

RR UA The BSC replies with anUnnumbered Acknowledgemessage.

GSM Originating CallGSM Mobile Originated CallInitiate Authentication ProcedureMobile initiates call release

GSM Location UpdateInter MSC-VLR location update

GSM Terminating CallMobile initiates call release