Explanation of the message flow The Location Update is necessary to inform the network about the actual location of the MS. The MS requires requires a Location Update Update every time it enters enters a new Location Location Area. A Location area can consists of one or more BTS, belonging to one or more BSC’s. 1.
The MS MS sends sends a Channel Channel Reque Request st on the uplin uplink k RACH RACH to reque request st a SDCCH SDCCH..
2.
Afte Afterr succ succes essf sful ul Immedi Immediat ate e Assi Assign gnme ment nt the the MS tells tells the the netw networ ork k with with the the Loca Locati tion on Update Request the cause for the need of a SDCCH. LOC_UPD_REQ contains the LAC and CI of the actual geographical position, and the IMSI of the SIM CARD.
3.
If the MSC MSC accepts accepts the receiv received ed values values itit sends sends the Locati Location on Update Update Accep Acceptt to the MS.
4.
Afterw Afterward ards s all Reso Resourc urces es on all all inter interfac face e will will be relea released sed..
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MOBILE ORIGINATED CALL MS Channel Request --------------------------------------------------->
UI (Immediate Assignment) <--------------------------------------------------SABM (C (CM Se Service Re Request) ---------------------------------------------------> Unnumbered Acknowledge <---------------------------------------------------
Est In Ind (C (CM Service Request) ---------------------------------------------------> ConReq (CMServiceRequest) ----------------------------------------------------> ConConfirm <--------------------------------------------------- Authentication Req <--------------------------------------------------- Authentication Res ----------------------------------------------------> Cipher Mode Com <---------------------------------------------------Cipher Mode Comp ----------------------------------------------------> TMSI Com <---------------------------------------------------TMSI Cmp ---------------------------------------------------->
I (Setup) --------------------------------------------------->
Data Ind (Setup) --------------------------------------------------->
I (C (Call Pr Proceed)
Data Req (Call Proceed) <---------------------------------------------------
Explanation of the message flow 1. The MS initiat initiates es the start of a speech speech or data call call by perfo performi rming ng the Random Random Access Access Proced Procedure ure on the uplink uplink RACH. RACH. The BSS perfor performs ms the Radioli Radiolink nk Establ Establish ishmen mentt Procedure Procedure by reserving reserving and activating activating an SDCCH. SDCCH. The BSC performs performs the Immediate Immediate Assignment Procedure. After successful reception of the Immediate Assignment the MS answers with the CM CM Service Request. Request. The important parameters parameters of this message message are the IMSI, the LAC and the CI to identify the mobile and the location of the mobile in the network. 2. Authe Authenti nticat catio ion n and Ciphe Cipherin ring g are initia initiated ted by the the MSC for norma normall calls. calls. In case case of emergency call, call, no Authentication and Ciphering Ciphering is performed. performed. If no Authentication and Ciphering is performed, the message CM Service Accept is sent to the MS. 3. After After Ciphe Cipherin ring g was was comple completed ted the MS sends sends the SETUP SETUP inclu includin ding g the Called Called Party Party Number. This message message is transferred transferred through through the BSS transparently transparently to the MSC. The MSC sends the CALL PROCEEDING message indicating that the Call Establishment information has been received. 4. The BSC activat activates es the TCH using using the Channe Channell Mode Mode specifi specified ed in the ASSIGN ASSIGNME MENT NT REQUEST REQUEST message. message. Inside Inside the Assignment Assignment Request Request the BSC is informed informed about about the Speech Timeslot Timeslot on the A-Interface. A-Interface. The Data obtained obtained by the PHYSICAL PHYSICAL CONTEXT CONTEXT PROCEDURE and the Ciphering key, which is presently in use on the SDCCH, are also taken for the new TCH. 5. The BSC sends sends the the ASSIGNME ASSIGNMENT NT COMMAND COMMAND to the MS MS on the SDCCH SDCCH to tell tell the MS the new frequency and timeslot. t imeslot. 6. The The MS discon disconne nects cts the the old chan channe nel. l. The The MS conne connect cts s to the the new chann channel el and and establishes the SAPI 0 connection connection at layer 2. The BTS sends the LapDm Establishment Establishment 4
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to the BSC in an ESTABLISHMENT INDICATION, sets the Transcoder and enables the Radiolink failure detection algorithm. 7. The MS MS sends sends the ASSIGNMEN ASSIGNMENT T COMPLETE COMPLETE to to the BTS. BTS. The messa message ge is transferre transferred d transparently to the MSC. At this state the BSC releases the old SDCCH SDCCH channel. 8. The called called user user is is ale alerte rted. d. The MSC detects that the called user is answering answering the call.
Explanation of the message flow 1. The MSC MSC initiates initiates the the Paging Paging proced procedure ure for an an MS which which is is connected connected to the LAC. LAC. The BSS initiates the Paging Procedure by sending a PAGING REQUEST to the MS on the PCH. PCH. The MS detects detects that the PAGING PAGING REQUES REQUEST T contai contains ns it’s IMSI IMSI or TMSI and respon responds ds by perfor performin ming g the Rand Random om Access Access Proced Procedure ure by sendin sending g a CHANN CHANNEL EL REQU REQUES EST T on the RACH. RACH. The The BTS BTS tran transf sfer ers s this this to the the BSC BSC as a CHAN CHANNE NEL L REQUIRED message and the Radio & Link Establishment Procedure is initiated. 2. Authentica Authentication tion and and Cipheri Ciphering ng are initi initiated ated by the the MSC. MSC. 3. After the CIPHE CIPHERING RING MODE MODE COMPLETE COMPLETE is receiv received ed from the the MS, the MSC sends sends the SETUP messa message ge to the MS. MS. The MS checks checks ifif it can accept accept the call. call. After succe success ss it responds with a CALL CONFIRMATION. 4. The TCH TCH has been been assigne assigned d and the MS starts starts to alert alert the user, user, at the same same time the MS sends the ALERT message to the MSC. 5. The Mobile Mobile User User (or Equipment Equipment for Data Data calls) calls) answers answers the call and and the MS sends sends the CONNECT CONNECT message. message. If the Calling Calling User is still there, there, the MSC sends sends the CONNECT CONNECT ACK to the MS. These events are transparent transparent to the BSS. BSS.
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INTER BSC ASYNCHRONOUS HANDOVER MS
Serving BTS
Serving BSC
Target BTS
Target BSC
MSC
MEAS REP ------------------> MEAS RESULT ------------------------> BSC detects need for HO DT 1 (Handover Required) -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------> -------------->
Chn Act <----------------------Chn Act Ack -----------------------> DT 1 (HO Request Ack) ------------------------------> DT 1 (HO Command) <---------------------------------------<--------------------------------------------------------------------------------------------------------------------------------------------------------DR (HO Cmd) <-----------------------HO Cmd <-----------------HO Access ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------> DI (HO Detection) -----------------------> DT 1 (HO Detection) ------------------------------> Phy Info <----------------------------------------<---------------------------------------------------------------------------------------------------------------------------------SABM ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------> Est Ind -----------------------> UA <----------------------------------------<---------------------------------------------------------------------------------------------------------------------------------HO Complete ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------> DI (HO Cmp) -----------------------> DT 1 (HO Cmp) ------------------------------>
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Explanation of the message flow 1. The servin serving g BSC has has detecte detected d a need need for an externa externall handove handover. r. All parame parameters ters which which check the need for an external handover are set via OMC. 2. The external external handove handoverr is initiated initiated by sending sending a HANDOVER HANDOVER REQUIRE REQUIRED D message message with a cell list obtained from the handover handover alarm. Whilst a timer is running running all new handover handover alarms are ignored. 3. The MSC MSC chooses chooses one one of the cells cells withi within n the cell cell list and and identi identifie fies s the target target BSS. BSS. It then sends a HANDOVER REQUEST to the new BSS. 4. The The targ target et BSC BSC acti activa vate tes s an appr approp opri riat ate e RF chan channe nel, l, buil builds ds the the HAN HANDOVE DOVER R COMMAND message destined for the MS and sends it to the MSC in the HANDOVER REQUEST ACK. The target BTS starts ciphering ciphering immediately immediately (if applied). applied). 5. The The MSC MSC forw forwar ards ds the the mess messag age e to the serv servin ing g BSS BSS in a HAND HANDOV OVER ER COMMA COMMAND ND message. The serving BSC sends the HANDOVER HANDOVER COMMAND to the the MS via the BTS, and starts to ignore error messages coming from the BTS. 6. The MS on recep receptio tion n of the HANDOV HANDOVER ER COMMA COMMAND ND discon disconnec nects ts the old chann channel. el. It synchronizes to the new cell and sends continuously a HANDOVER ACCESS to the RF channel indicated indicated in the HANDOVER HANDOVER COMMAND message message with a TA of 0. The target BTS calculates the timing advance from the reception of the HANDOVER ACCESS and relays a HANDOVER DETECTION DETECTION to the target BSC. The target BTS starts the sending of SYSTEM INFORMATION 5 & 6 messages on the SACCH and starts deciphering (if applied) applied).. The target target BSC relays relays a HANDOVER HANDOVER DETECT DETECT to the MSC and makes makes the switch path (TCH only). 7. The The targ target et BTS send sends s the the PHYS PHYSICA ICAL L INFO INFORM RMAT ATIO ION N mess messag age e to the the MS with with the the calculated timing advance. 8. The MS establish establishes es with with an SABM SABM the new link. link. The target target BTS BTS sends sends an ESTABL ESTABLISH ISH INDICATION to the target BSC and sends a UA to the MS. 9. The MS MS sends sends a HANDOV HANDOVER ER COMPLETE COMPLETE message message to to the targe targett BTS. The messa message ge is forwarded through through the BSC to the corresponding corresponding MSC. MSC. The external handover handover is now complete. 10. The serving BSS RF channel channel and terrestrial resources resources are released. This is performed by the MSC sending the CLEAR CLEAR COMMAND (cause (cause “Handover “Handover successful”). Then the old SCCP connection connection is released.
Explanation of the message flow 1. The servin serving g BSC has has detected detected a need need for for an Intra-ce Intra-cellll handove handover. r. These means means that that the quality of the call is bad but the level is high. Both thresholds can be set via OMC-R. OMC-R. 2. The servin serving g BSC then then starts starts a Physic Physical al Context Context Procedu Procedure re by sendi sending ng a PHYSI PHYSICAL CAL CONTEXT message to the old channel. channel. The serving BTS notes the timing advance, advance, MS power power and and BS powe powerr on the old channe channell and and then then sends sends a PHYSI PHYSICAL CAL CONTEXT CONTEXT CONFIRM message to the serving BSC. 3. The servin serving g BSC now activa activates tes the channel channel using using timing timing advance advance,, MS and BS power power values obtained from the PHYSICAL CONTEXT CONFIRM message and the ciphering key on the old channel. channel. The BTS ensures that that transmission occurs occurs on the new channel channel with the power and the timing advance commanded in the Channel Activation Procedure. 4. The serving serving BSC BSC sends sends via the old old channel channel an ASSIGNM ASSIGNMENT ENT COMMAN COMMAND D to the MS via the BTS to inform t he mobile about the new frequency, power and TA level. 5. The MS on reception reception of the the ASSIGNMEN ASSIGNMENT T COMMAND COMMAND disconnec disconnects ts the old channel channel and switc switch h to the new channe channel. l. The servin serving g BTS relay relays s the SABM SABM as an ESTAB ESTABLIS LISH H INDICATION INDICATION to the serving serving BSC. The serving serving BSC makes the switch switch through (TCH only) and starts MS and BS power control if appropriate. appropriate. 6. The The MS send sends s the the ASSI ASSIGN GNME MENT NT COMP COMPLE LETE TE to the BTS. BTS. The The BTS pass passes es it transpare transparently ntly.. The serving serving BSC sends a HANDOVER HANDOVER PERFORMED PERFORMED to the MSC to indicate the successful INTRA I NTRA CELL Handover. The serving BSC releases the old channel by the use of the RF Channel Release Procedure.
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CALL RELEASE RELEASE BY THE MOBILE MS
BTS
I (Disconnect) --------------------------------------------->
BSC
MSC
Data Ind (Disconnect) --------------------------------------------->