Signaling Flows of Handover from GRPS to WCDMA
7.11 and 7.11 shows the signaling flow for handover from GPRS to WCDMA.
Figure 1.1 Signaling flow for handover from GPRS to WCDMA (1)
SourceRN C
BSC
SG SN(3G)
RR-Cell Change O rder
U E
BT S
N odeB
SG SN(2G)
SGSN Cnt xt Req
H L R
Send A uthen Info
Send A uthent A CK
A uthentication and Ciphering Request
Aut hent i cat i on and Ci pheri ng Response
SGSN Cnt xt ACK
Cancel L ocation
G G SN
Update PDP cntxt Req
U pdate PD P cntxt Rsp
Update GPRS Loc
Cancel L oc A CK
MSC/V L R(2
G)
MSC/V L R(3G)
RRC Connect Set up Req
RL Set up Req
RL Set up Rsp
AAL2 Set up Req
AAL2 Set up Rsp
DL Sync
UL Sync
RRC Conn Set up
RRC Conn Set up Cmp
I ni t i al DT
I ni t UE(RA updat e Req)
SGSN Cntxt Rsp
Figure 1.2 Signaling flow for handover from GPRS to WCDMA (2)
SourceRNC
BSC
SGSN(3G)
SGSN(2G)
NodeB
BTS
UE
HLR
GGSN
Ins Subscriber Dat
Ins Subscrib Dat ACK
Update GPRS Loc ACK
MSC/VLR(2
G)
MSC/VLR(3G)
Location Update Req
Update Location ACK
Update Location
Cancel Location
Cancel Location ACK
Ins Subscriber Data ACK
Insert Subscriber Data
Update Location Accept
RA Update Accept
RA Update Accept Complete
TMSI Reallocation Complete
RAB Ass Req
RAB Ass Rsp
RL Recf g Prep
RL Recf g Ready
AAL2 Setup Req
AAL2 Set up Rsp
DL Sync
UL Sync
RB Setup
RB Setup Compl ete
RL Recf g Commit
Service Req
Signaling Flow at UTRAN Side
The signaling flow at UTRAN side proceeds as below:
The UE reselects a UTRAN cell. During the reselection of UTRAN cell, the
UE originates the RRC connection setup process, with the reason INTERRAT CELLRESELECTION.
After the RNC connection is set up, the UE initiatively originates the INIT DT
process and sets up the SCCP connection at IU interface and the signaling connection in the CN NAS layer. Later the UE NAS layer and CN NAS layer exchange messages by DT process.
The CN commands the RNC to allocate related resources by sends the
RAB ASSIGNMENT REQUEST message at the IU interface. The message contains the RAB ID, QoS, uplink and downlink sequence number of GPT-U, and sequence number of PDCP.
The RNC allocates related resources and informs NodeB by sending RL
SETUP message.
The RNC sends UE the RB SETUP REQUEST message to UE. The
message contains the downlink sequence number of PDCP.
The UE sends RNC the RB SETUP COMPLETE message. The message
contains the downlink sequence number of PDCP. The RNC configure the uplink sequence number of PDCP from CN and the downlink sequence number from UE to the PDCP sample corresponding to the specified RAB.
The RNC sends CN the RAB ASSIGNMENT RESPONSE message. While the traffic flow is being restored, the RNC PDCP sample should drop
CN' data packet of which the sequence number of downlink PDCP is smaller than the sequence number of downlink PDCP replied by UE. The UE should drop the data packet of which the sequence number of uplink PDCP is smaller than the sequence number of uplink PDCP configured by UTRAN/CN.
7.12 Parameters of Handover from 3G to 2G Network
Handover Judgment Process
Now the periodic report is used in inter-frequency handover judgment.
According to the protocol 25.331, the 2D event indicates that the quality of active set is lower than a threshold. In the current handover algorithms (including inter-frequency handover algorithm), the 2D event report serves as a rule for starting compression mode and performing inter-frequency or inter-RAT measurement. Therefore, if the quality of UE active set is worse in inter-RAT measurement, you need to measure the inter-RAT quality only. If the quality of UE active set becomes better, namely, the UTRAN receives the 2F event report, the UE stops compression mode and stops inter-RAT measurement. For the detailed judgment of 2D/2F event, see the 3GPP TS 25.331.
The following paragraphs describe the inter-RAT handover judgment algorithm using periodic reports.
After the network receives the periodic report filtered by layer 3, it compares the obtained inter- RAT measurement result with the preset threshold. The network starts delay trigger timer Trigger-Timer if the following formula is met:
Mother_RAT + CIO >= Tother_RAT + H/2 (formula 1) Wherein,
Mother_RAT indicates the obtained inter-RAT measurement result.
CIO indicates the cell individual offset, namely, the offset configured by the
inter-RAT cell.
Tother_RAT indicates the inter-RAT quality threshold.
H indicates hysteresis. The hysteresis helps to reduce mal-operations due
to fluctuation of signals.
After the Trigger-Timer starts and before it expires, the Trigger-Timer is stopped and the network keeps waiting for receiving inter-RAT measurement report if the following condition is met: Mother_RAT + CIO < Tother_RAT - H/2 (formula 2)
If the Trigger-Timer expires, the system judges for inter-RAT handover.
List of Handover Parameters
Table 1.1 Parameters of handover from 3G to 2G
Parameter Meaning configurationDefault
MML Command s for modifying and querying Applic ation scope FilterCoef Filter coefficient at layer 3 of inter- RAT measurement D3 For RNCs: inter-RAT handover algorithm parameter: set RNCs by executing SET INTERRATH O, query RNCs by executing LST INTERRATH O. For cells: inter-RAT handover algorithm parameter: add cells by executing ADD CELLINTER RATHO, query cells by executing LST CELLINTER RATHO, and modify cells by executing MOD CELLINTER RATHO RNC/ Cell GsmRSSICSThd, GsmRSSIPSThd, GsmRSSISIGThd The judgment threshold for inter-RAT handover 21, namely, –90 dBm HystThd Inter-RAT handover hysteresis 4, namely, 2 dB TimeToTrigForVerify The time to trigger delay verified by inter- RAT 0, namely, 0s
TimeToTrigForNonVerify Non-verified delay trigger time
65535, namely, handover to non- verified GSM cell is prohibited.
PenaltyTimeForSysHo Inter-RAT handover penalty time 30, namely, 30s InterRatCSThdFor2DRSCP, InterRatPSThdFor2DRSCP, InterRatSigThdFor2DRSCP, InterRatCSThdFor2FRSCP, InterRatPSThdFor2FRSCP, InterRatSigThdFor2FRSCP The starting/stopping threshold for inter-RAT measurement with RSCP as the measurement value (CS, PS, and single signaling)
The default values of them are as below: InterRatCSThdFor2 DRSCPInterRatPST hdFor2DRSCP: –95; InterRatCSThdFor2F RSCPInterRatPSThd For2FRSCP: –90; InterRatSigThdFor2 DRSCP InterRatSigThdFor2F RSCP: –115 For RNCs: set RNCs by executing SET INTERFREQ HO and query RNCs by executing LST INTERFREQ HO. For cells: RNC/ Cell
add cells by executing ADD CELLINTER FREQHO, query cells by executing LST CELLINTER FREQHO, and modify cells by executing MOD CELLINTER FREQHO InterRATCSThdFOR2DEcNo, InterRATPSThdFOR2DEcNo, InterRATSigThdFOR2DEcNo , InterRATCSThdFor2FEcNo, InterRATPSThdFOR2FEcNo, InterRATSigThdFOR2FEcNo The starting/stopping threshold for inter-RAT measurement with Ec/No as the measurement value (CS, PS, and single signaling) –24, namely, –24 dBm HYSTTHD Hysteresis. The hysteresis and inter-RAT quality threshold decides whether to trigger inter-RAT handover judgment. It can be smaller in areas with small shadow fading. It can be greater in areas with great shadow fading. 4 CellIndividalOffset The individual offset of inter- RAT handover cells. The UE uses it with the initial measured value of the cell
as the measurement result for handover judgment of UE. 0 Set cells by executing ADD INTERRATN CELL, query cells by executing LST INTERRATN CELL, and modify it by executing MOD INTERRATN CELL Cell Note:
7.12 lists the starting/stopping threshold of compression mode and inter-RAT handover threshold in terms of signaling, CS, and PS.
7.13 Data Configuration for Supporting Bi-directional Roaming
and Handover Between WCDMA and GSM/GPRS
To support bidirectional roaming and handover between 3G networks and GSM/GPRS, to support PLMN selection, to support reselection from the 2G network to the 3G network by UE, and to support reselection from the 3G network to the 2G network by UE, data configuration is necessary in the 2G and 3G system.
2G MSC Data Configuration
If the system support the handover from the 2G network to the 3G network, data configuration on the 2G MSC is necessary. According to the 2G-to-3G interoperation strategy of Huawei, the handover from the 2G network to the 3G network supports cell reselection, so data configuration on the 2G MSC is unnecessary.
Data Configuration on the 2G MSC
Data configuration on the 2G MSC proceeds as below:
Add the matching record of 3G MSC/VLR code corresponding to RNC IDs
in the list of cell in the location area. The RNC ID is in the format of: MCC + MNC + LAC + RNC-ID. Select GCI as the type of location area. Select Near VLR area as the property of location area.
Add the corresponding LAI record and the corresponding 3G MSC/VLR
code. LAI = MCC + MNC + LAC. Select Near VLR area as the property of location area.
Change the supported MAP version to PHASE 2PLUS in the MAP function
flow configuration table.
Configure the data at the MTP layer and guarantee the signaling
transmission between the 2G MSC and the 3G MSC.
Configure the data at the SCCP layer, configure the corresponding record of
the 3G MSC in the GT list, SCCP SSN list, and SCCP DSP list, and guarantee the transmission of MAP handover-related signaling between MSCs.
Configure inter-MSC trunk data like configuring common data.
The following paragraphs take Huawei 2G MSC as example. For the MSC, two tables are used for data configuration: location area cell table and neighbor cell table.
Location Area Cell Configuration Table
Figure 1.1 Data configuration in the location area cell table
Pay attention to the following fields:
− GCI code
− Location area MSC code − Location area VLR code − Type of location area − Property of location area
Content of GCI code: corresponding to LAI and RNC ID of the target 3G cell for handover. Query the LAI by running the command LST AC. Query the RNC ID by running the command LST RNCBASIC. You can also obtain the PLMN code of the RNC by running the command LST RNCBASIC.
Content of location area MSC code: the code of MSC configured by MSOFTX3000 of the corresponding 3G network. Query it by running the command LST INFOMSC command on the MSOFTX3000 client.
Type of location area: LAI + RNC ID correspond to GCI. Property of location area: the configuration is Near VLR area.
Neighbor Cell Configuration Table
Figure 1.2 Data configuration of neighbor cell configuration table
Pay attention to the following fields:
− GCI code − Neighbor cells
− The GCI code of 2G source cell corresponding to GCI code.
− Fill from the neighbor cell 1 to the neighbor 2…. The content to be filled in the
neighbor cell 1 is the LAI + RNC ID of target 3G cell for handover. Query the LAI of target 3G cell by running the command LST AC. Query the RNC ID by running the command LST RNCBASIC.
Added Data Configuration on BSCs
SI for Supporting the Roaming from GSM to WCDMA
To support the roaming from GSM to WCDMA, the GSM BSS must complete sending the following system information:
− Add data of WCDMA cells, including downlink frequency, primary scramble,
diversity indicator, MCC, MNC, LAC, RNC ID, and CELL ID.
− Add the information about inter-RAT cell measurement and roaming control in the
idle mode. The information contains the following parameters:
Qsearch_I: the level threshold for searching for 2G cells in the idle mode FDD_Qoffset: the level offset of 3G cell reselection
FDD_Qmin: the level threshold of 3G cell reselection
− The previous information contained in the system information 2ter and 2quater is sent
to UE.
− The UE perform inter-RAT cell reselection based on previous information. SI for Supporting the Handover from GSM to WCDMA
To support the handover from GSM to WCDMA, the GSM BSS must complete sending the following system information:
Add the data of the WCDMA cell. The data contains:
− Downlink frequency point − Primary scramble − Diversity indicator − MCC − MNC − LAC − RNC ID − CELL ID
− Level threshold for handing over to the cell
Add the measurement control information of inter-RAT cells for UE in the
connection mode, including Qsearch_C, namely, the level threshold for searching for 3G cells in the connection mode.
The previous information contained in the system information MEASUREMENT INFORMATION is sent to UE.
When the level of UE in the serving cell meets the conditions for Qsearch_C, the system starts measure 3G cells and sends the periodic reports to BSC.
The BSC originates the handover to WCDMA.
The following paragraphs take the configuration of Huawei BSC as example.
Adding External 3G Cells
Adding external 3G cells proceeds as below:
− Select setting up cells dynamically − Add external cells
Figure 1.1 Configuration table for external 3G cells
Pay attention to several fields: MCC, MNC, LAI, RNC ID, CELL ID, downlink frequency point, and scramble. Using system defaults is recommended for unlisted fields.
− MCC: query it by running the command LST RNCBASIC on the corresponding RNC
client
− MNC: query it by running the command LST RNCBASIC on the corresponding
RNC client
− LAI: query it by running the command LST AC on the corresponding RNC client − RNC ID: query it by running the command LST RNCBASIC on the corresponding
RNC client
− CELL ID: query it by running the command LST CELL on the corresponding RNC
client Note:
The query result is decimal. It can be filled in the CELL ID field after it is converted to hex and removed of the highest bit.
Downlink frequency point: query it by running the command LST CELL on the corresponding RNC client and then inputting the corresponding CELL ID in the CELL Scramble: query it by running the command LST CELL on the corresponding RNC client and then inputting the corresponding CELL ID in the CELL
Configuring Target 3G Cells as the Inter-RAT Neighbor Cell of GSM
Configuring target 3G cells as the inter-RAT neighbor cell of GSM proceeds as below:
− Modify the property of external cells − Select external cells
− Modify the neighbor relationship, as shown in 7.13.
Figure 1.2 Configuration table for GSM inter-RAT neighbor cells
Note:
The target cell for handover from the 3G network can be the directional neighbor cell of GSM only.
Configuring Parameters for 2G Reselection
Configuring parameters for 2G reselection proceeds as below:
− Select setting cells dynamically − Select the current cell
Figure 1.3 Configuration table for 2G reselection parameters
The configuration table for 3G system information includes the following parameters:
− Type of measurement reports: common measurement reports − Number of best cells in the GSM band: the default value is 3
− Threshold for searching for 3G cells in the idle mode: the values range from 0 to 15 − Offset of FDD cell reselection: When the mean receiver level of 3G cells is
FDD_Qoffset greater than that of the serving cell, the UE can reselect 3G cells. 0 = – ∞ (always select a cell if acceptable), 1 = –28 dB, 2 = –24 dB, …, 15 = 28 dB. Select 0 for easy handover.
− The minimum Ec/No threshold for FDD cell reselect: level threshold for 3G cell
reselection: when the receiver level of 3G cell is greater than the FDD_Qmin, the cell can be a candidate cell for reselection.
− Other default values
Configuring 2G Handover Parameters
Figure 1.4 Parameter configuration table for inter-RAT handover
Pay attention to the following parameters:
− Handout permission: select it.
− Permission for handover algorithm of a 3G better cell: select it.
− 2G/3G cell handover priority selection: select 3G cell for handover as priority − 2G cell selection threshold: the greater the threshold is, the difficult the handover to
2G is. The recommended value is 63.
RSCP threshold for handover to a better 3G cell: the smaller the value is, the difficult the handover to 3G is. The recommended value is 10.
Ec/No threshold for handover to a better 3G cell: the smaller the value is, the difficult the handover to 3G is. The recommended value is 10.
Statistics time for a better 3G cell: the recommended value is 5.
The lasting time for handover to a better 3G cell: the smaller the value is, the easier and faster the handover is. Pay attention to frequent handover. The recommended value is 4.
Added Data Configuration on 3G MSCs
Added data configuration proceeds as below:
− Add the cell information about location area near the 2G MSC to the list of cells of
3G MSC location area. LAI = MCC + MISSING NEIGHBOR CELL + LAC. Select LAI as the type of location area. Select Near VLR area as the property of location area. Add the corresponding 2G MSC/VLR code. GCI = MCC + MNC + LAC + CI. Select GCI as the type of location area. Select Near VLR area as the property of location area. Add the corresponding 2G MSC/VLR code.
− If inter-PLMN cell reselection is necessary, the MSC must configure the equivalent
PLMN is the PLMN which provides equivalent services to subscribers. The network side decides whether to tell the control list to UE. The MSC sends the list to UE upon update acceptance and the UE saves it. When the UE reselects an inter-PLMN cell, it reselects a cell from the list by priority.
− Configure the data at MTP layer and guarantee the signaling transmission between
the 2G MSC and the 3G MSC.
− Configure the data at SCCP layer. Configure the corresponding record of 2G MSC in
the GT table, SCCP SSN table, and SCCP DSP table.
− Configure the trunk data between MSCs in the same way as configuring common
data.
Necessary Data Configuration for RNC
Data Configuration for Supporting Roaming from WCDMA to GSM/GPRS
To support the roaming from WCDMA to GSM/GPRS, the UTRAN must complete sending the following system information:
− Add GSM cells and configuration the following data:
MCC
MISSING NEIGHBOR CELL LAC CELL ID NCC BCC FREQ_BAND Frequency number CIO
ADD GSMCELL: MCC="460", MNC="10", LAC="0x0fa0", CID="0x0102", NCC=0, BCC=0, BCCHARFCN=60, BANDIND=DCS1800_BAND_USED, RATCELLTYPE=GSM;
ADD INTERRATNCELL: CELLID=123, MCC="460", MNC="10", LAC="0x0fa0", CID="0x0102", CELLINDIVIDALOFFSET=50, QOFFSET1SN=-50,
QRXLEVMIN=-58;
− Configure the measurement point for FACH to inter-frequency FDD measurement,
inter-frequency TDD measurement, or inter-RAT measurement. If inter-RAT roaming is necessary, configure the measurement point for FACH to inter-RAT measurement; otherwise, according to SIB11, the RNC will not send RNC information about GSM neighbor cells.
MOD CELLMEAS: CELLID=123, INTERFREQINTERRATMEASIND=INTER_RAT, FACHMEASIND=REQUIRE, FACHMEASOCCACYCLELENCOEF=3;
− Configure the SearchRAT of the GSM network by running the command MOD
CELLSELRESEL.
and information about GSM neighbor cells contained in SIB11 are sent.
Data Configuration for Supportint Inter-RAT Handover from WCDMA to
GSM
To support the inter-RAT handover from WCDMA to GSM, configure the following parameters:
− Add GSM cells and configuration the following data: