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UMTS Signaling FlowZTE University

ContentUE State transitionSignaling flow

Classification of FlowsIn terms of protocol stack, signaling flows can be access layer signaling flows or non-access layer signaling flows. In terms of network composition, signaling flows can be categorized as circuit-switched or packet-switched. Access layer and non-access layer signaling flows are actually so named from the perspective of protocol stack.

Classification of FlowsThe flows at the access layer include PLMN selection, cell selection, and radio resource management flows. The radio resource management flows are the flows at the RRC layer, including the RRC connection setup flow, flow of the signaling setup between UEs and CNs, RAB setup flow, call release flow, handover flow, and SRNS redirection flow.

UE Working ModesThere are two basic working modes:IdleUE stands by without any service. Theres no connection between UE and UTRAN.ConnectedUE transferred to the connected mode after accomplishing RRC Connection Setup.UE has 4 states under the connected mode:Cell-DCH, Cell-FACH, Cell-PCH, URA-PCH

UE State

UE States Under the Connected ModeCell-DCHUE is activated, and in service using its dedicated channels.There are dedicated channels in both uplink and downlink.UTRAN knows exactly which cell the UE is in.Cell-FACHUE is activated, but without too much date to transmit, so theres no need to assign dedicated channels to it.Downlink data transmitted in FACH, while uplink in RACH.UTRAN knows exactly which cell the UE is in.

UE States Under the Connected ModeCell-PCHThere is no data transmitted in both uplink and downlink.UE needs to listen to PICH for paging information.UE works in discrete receiving, which saves the power effectively.UTRAN knows exactly which cell the UE is in.UE needs to do cell update procedure when it passes cells.URA-PCHThere is no data transmitted in both uplink and downlink.UE needs to listen to PICH for paging information and receive discretely.UTRAN only knows which URA (UTRAN Registration Area) UE exists.UE updates its location information only when its URA changes, which further reduces the signaling saves resource.

RRC State Transition (I)After RRC Connection Setup, UE will transit to CELL_FACH or CELL_DCH.CN indicates UE using dedicated channel (CELL_DCH) or common channel (CELL_FACH) according to the service request.If there is no service right now, UE will be indicated into PCH mode or release RRC connection back to IDLE mode.URA_PCHCELL_DCHCELL_FACHCELL_PCHIDLEDEADIDLEDEADCELL_DCHCELL_FACHIDLESketch of RRC State Transition Transit from IDLE Mode

URA_PCHCELL_DCHCELL_PCHIDLEDEADIDLEDEADCELL_FACHIDLERRC State Transition (II)UE do not occupy dedicated channels In the mode of CELL_FACH.UE receives downlink data through FACH(S-CCPCH).UE transmits uplink data through RACH(PRACH).Transit from CELL_FACH ModeSketch of RRC State Transition

URA_PCHCELL_DCHCELL_FACHCELL_PCHIDLEDEADIDLEDEADCELL_DCHIDLEURA_PCHCELL_PCHCELL_DCHRRC State Transition (III)UE transceives uplink and downlink data through dedicated channels (DPDCHs and DPCCHs).During the time when there is no data transmitted, CN may indicate UEs transiting to URA_PCH or CELL_PCH.Transit from CELL_DCH ModeSketch of RRC State Transition

URA_PCHCELL_DCHCELL_FACHCELL_PCHIDLEDEADIDLEDEADCELL_DCHIDLECELL_DCHURA_PCHCELL_PCHCELL_FACHCELL_PCHURA_PCHRRC State Transition (IV)UE has no activated uplink.Paging Information makes UE back to CELL_FACH or CELL_DCH mode.In CELL_PCH, UE should transit to CELL_FACH first to finish cell updating, and go back if no service request.In URA_PCH, if URA changes, UE also transits to CELL_FACH to finish cell updating first before it goes back to URA_PCH.System resource can be saved in these two modes.Sketch of RRC State Transition

ContentUE State transitionSignaling flow

Basic Conception (1)RRC (Radio Resource Control)provides information transfer service to the NAS (Non Access Stratum).responsible for controlling the configuration of UMTS radio interface Layers 1 and 2.RRC ConnectionA point to point bi directional connection between the RRC (Radio Resource Control) entities on the UE (User Equipment) and UTRAN (UMTS Terrestrial Radio Access Network). The UE requires an RRC connection to access the services of the UMTS network.

Basic Conception (2)RAB -Radio Access BearerIdentify the service the AS (Access Stratum) provides to the NAS (Non Access Stratum) for transfer of user data between the UE (User Equipment) and the CN (Core Network). RB -Radio BearerThe service provided by the Layer 2 for the transfer of user data between UE (User Equipment) and UTRAN (UMTS Terrestrial Radio Access Network).

Basic Conception (3)RL (Radio Link)RL is a logical association between single UE (User Equipment) and a single UTRAN (UMTS Terrestrial Radio Access Network) access point. Its physical realization comprises one or more radio bearer transmissions. It is possible for a UMTS mobile to have many radio links established, when this occurs the mobile is said to be in a soft handover.

Sketch of the basic conceptions

UE Calling FlowPower onCell selection

Location Update

Idle ModeRRCEstablishNASEstablishHand OverCell/URA updateChannelreconfigurationRB/RAB ModificationRAB EstablishRRCReleaseCallInitiate

UE in Idle Mode

What Information needed for UE?1 Strongest cell2 Slot boundary3Frame boundary4 Primary SC5 Information in broadcasts channel

1st Step: Cell Selection and Slot Synchronization

DL Scrambling Code Rule218-1 DL Scrambling Codes in total(0..262142)The left 8192 Scrambling codes are used for compression modeThe left 8192 Scrambling codes are used for compression mode

#0 Scrambling Code Cluster#63 Scrambling Code Cluster

#511 Scrambling Code Group81768177

81918176P-SC8177S-SC8191S-SC


8175816081618175


8079806480658079


1278176P-SC8177S-SC8191S-SC


3116P-SC17S-SC31S-SC


150P-SC1S-SC15S-SC

2rd Step: Frame synchronization and Scrambling code-group

Scrambling-code identificationCPICH is predefine sequenceSpreading Factor is 256 (Cch,256,0)Scrambling by P-scrambling codeUE identified through symbol-by-symbol correlation over the primary P-CPICH with all the scrambling codes within the code group.

Obtain broadcast information in P-CCPCHP-CCPCH contain the current SFN and system broadcast informationP-CCPCH SF=256 (Cch,256,1)P-CCPCH scrambling by primary scrambling codeUE can use obtained primary scrambling code to descrambling the P-CCPCH and obtain the BCH information

UE Calling FlowPower onCell selectionLocation UpdateIdle ModeRRCEstablishNASEstablishHand OverCell/URA updateChannelreconfigurationRB/RAB ModificationRAB EstablishRRCReleaseCallInitiate

UE Initiate Random Access

Establish Dedicated RRC ConnectionUENode BSRNC2.Allocate RNTIL1 and L2 Parameters1. RRC Connection Request5. ALCAP Establish and Synchronization3. NBAP RL Setup Request7. RRC Connection Setup Complete6. RRC Connection Setup4. NBAP RL Setup Response

RRC Connection RejectionIf the RNC determines that the RRC connection cannot be established (for example, due to insufficient resources), the RNC directly sends the UE an RRC CONNECTION REJECT message which contains the reason for the rejection of the RRC connection.

1. RRC Initial Direct TransferEstablish Signaling Link with CNUESRNCCN3. SCCP CC(Success)2. RANAP Initial UE MessageSCCP Connect Request3. SCCP CJ(Failure)

1.1 Send Authentication Info4. Security Mode Command5. Security Mode Complete6. Security Mode Complete3.Security Mode ControlAuthentication and Security ModeUERNSMSC Server/VLR1. Authentication Request2. Authentication ResponseHLR2.1 Send Authentication Info Ack

MAP Cancel Location ACKMAP_Cancel_LocationLocation Update RequestMAP Update LocationMAP_Insert _Subscriber_DataMAP_Update _Location_ACKLocation Update Confirm ACKTMSI_Allocation_CompleteUERNSMSC Server/VLRPVLRHLRMAP_Insert _Subscriber_Data_ACKRelease CN Signaling ConnectionRelease RBCS Location Update ProcessEstablish RRC ConnectionEstablish CN Signaling ConnectionAuthentication and Security Mode

UE Calling FlowPower onCell selectionRRCEstablishNASEstablishHand OverCell/URA updateChannelreconfigurationRB/RAB ModificationRAB EstablishRRCReleaseCallInitiate

Location Update

Idle Mode

UE Work Mode TransformingRRC connectionAll the Status exist in UTRAN and UE, and transparent for CNNetwork Selection (PLMN)Cell CampingProbe paging channelCell ReselectionHigh level Signaling Triger (CN)Dedicated ChannelRB Transport Service


Location Update


Procedure of Call Initiate

Call Setup FlowCN initiates a paging message to RNC. RNC judges the paging message from the CN and then sends a paging message to the corresponding UE. If no RRC connection is available, UE will send a RRC connection setup request message (RRC Connection Request) to RNC. RNC determines to set up a RRC connection according to the service request and system resource occupation then sends a RRC connection setup message (RRC Connection Setup) to UE. After signaling connection setup, the higher layer of UE (NAS) sends a service request message to CN through a directly transfer message. CN sends a RAB assignment message (RAB Assignment Request) to the RNC to allocate resource for UEs request.

3. NBAP RL Reconfigure PrepareRAB Establish FlowUENode BSRNC1. RANAP RAB Assignment Request4. NBAP RL Reconfigure ReadyMSC2. ALCAP Establish and Synchronization5. ALCAP Establish and Synchronization6. NBAP RL Reconfigure Commit7. RRC RB Setup8. RRC RB Setup Complete9. RANAP RAB Assignment Response

8. ISUP IAMUE Initiate CallUERNSMSCCalled MSC1. RRC establish6. RRC DT(Call Proceeding)3. RRC DT(CM Service Request)2. CN signaling establish4. Authentication and Security5. RRC DT(Setup)7. RAB establish10. ISUP ACM11. RRC DT(Alert)12. ISUP ANM13. RRC DT(Connect)14. RRC DT(Connect ACK)15. Conversation9. CN bearer establish

UE Receiving Call1. ISUP IAMUERNSCalled MSCCalling MSC4. RRC establish8. RRC DT(Setup)6. RRC DT(Paging Response)5. CN signalling establish7. Authentication and Security9. RRC DT(Call Confirm)10. RAB establish2. Paging 3. Paging 11. RRC DT(Alerting)12. ISUP ACM13. RRC DT(Connected)14. ISUP ANM16. Conversation15. RRC DT(Connect ACK)


Location Update


Handover CategoryIntra-system handoverSofter handover, soft handover, hard handoverDepending on the Ec/No of CPICHInter-system (mode) handoverBetween FDD and TDDHandover with different system (inter RAT)2G/3G handoverCompression mode

Softer/Soft Handover Gain and CostsSofter/Soft Handover Gain:The optimal fast close loop power control (MS always keep connection with the most powerful cell)Seamless handover, without RB interruptionWhen MS moves to the edge of the cell, and could not obtain enough signal power, it can obtain Macro diversity from multiple cellsThe UL signaling quality can be improved through obtaining Macro diversity when Node B (Softer HO) and RNC (Soft HO) combine the receiving signal and lower the required Transport power of UE.Softer/Soft Handover Costs:Additional Rake receiver channel on Node BAdditional DL channelization codeAdditional DL powerAdditional Rake receiver channel on MSAdditional transport link between Node B and RNC (RNC internal Soft Handover)Additional transport link between S-RNC and D-RNC (Soft handover between RNCs)

Soft Handover FlowMeasurementreportRL creation requestRL setup requestActive set update commandSRNCRL setup responseRL setup responseActive set update completionRL Deletion requestRL Deletion responseAB

Hard Handover Flow


Location Update


Forward Hard Handover

CN

Source RNC

Target RNC

RRC

5.DCCH: RNTI Reallocation Complete

UE

RRC

RRC

[S-RNTI, SRNC-ID, new S-RNTI,

new SRNC-ID, new C-RNTI]

4.DCCH: Cell Update Confirm

RRC

3. Serving RNC Relocation

RNSAP

RNSAP

RRC

RRC-relay

[Cell Update Cause,U-RNTI,Measured results on PRACH]

1.CCCH: Cell Update

[new C-RNTI, D-RNTI,

UL message]

2. Uplink Signalling Transfer Indication


Location Update


RAB Release Flow

RRC Connection Release5. ALCAP Release

Call setup flow (1)

Call setup flow (2)

Call setup flow (3)

Call setup flow (4)

Call setup flow (5)

Call setup flow (6)

URA es para reducir el paging.**************Q.AAL2 en IP usa IPBSP IP Bearer *Q,AAL2 es usado en ATM*