3G2G Selection & Reselection Handover_BOOK

3G/2G Selection & Reselection Handover

ZTE CORPORATION ZTE Plaza, Keji Road South, Hi-Tech Industrial Park, Nanshan District, Shenzhen, P. R. China 518057 Tel: (86) 755 26771900 800-9830-9830 Fax: (86) 755 26772236 URL: http://support.zte.com.cn E-mail: [email protected]

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Contents

Chapter 1.........................................................................1

Overview .........................................................................1

Applicable Scope..............................................................1

Chapter 2.........................................................................3

Basic Theory....................................................................3

Overview ........................................................................3

Cell Selection and Reselection ...........................................3 Cell Selection Strategy..........................................................4 Cell Reselection Strategy.......................................................5

Inter-system Handover.....................................................7 3G->2G Inter-system Handover Types ...................................7 CS Service 3G->2G Handover................................................9 CS Service 2G->3G Handover.............................................. 11 PS Service 3G->2G Handover .............................................. 12 PS Service 2G->3G Handover .............................................. 16 CS+PS Concurrent Service 3G->2G Handover ........................ 17

Chapter 4.......................................................................19

Typical Flows.................................................................19

Cell Reselection ............................................................. 19 2G->3G Cell Reselection ..................................................... 19 3G-2G Cell Reselection ....................................................... 22

CS Service .................................................................... 29 CS Service 3G->2G Blind Handover Process ........................... 29 CS Service 3G->2G Directed Retry ....................................... 30 CS Service 3G->2G Handover Based On Coverage................... 30 CS Service 2G->3G Handover.............................................. 32

PS Services................................................................... 33 PCH State 3G->2G Handover............................................... 33



FACH State 3G->2G Handover .............................................34 DCH/HS State 3G->2G Handover..........................................34 PS Service 2G->3G Handover（UE Directly sends SERVICE REQUEST） .......................................................................37

PS Service 2G->3G Handover（Launch PS service via RRC connection） .....................................................................38

CS+PS Concurrent Service Handover ............................... 40 CS+PS Concurrent 3G->2G Handover....................................40



Confidential and Proprietary Information of ZTE CORPORATION 1

C h a p t e r 1

Overview

Applicable Scope The document mainly introduces the basic theory, parameters configuration, explanation of handover process instances, symbols and abbreviations about the 3G2G’s selection and reselection handover

AM_RLC acknowledged Mode Radio Link Control

AMR Adaptive Multi Rate

ATM Asynchronous Transfer Mode

BCCH Broadcast Control Channel

BCH Broadcast Channel

BER Bit Error Ratio

BLER Block Error Ratio

CBS Cell Broadcast Service

CCCH Common Control Channel

CCH Common Channel

CCTrCH Coded Composite Transport Channel

CN Core Network

CPICH Common Pilot Channel

CRC Cyclic Redundancy Check

DCCH Dedicated Control Channel

DCH Dedicated Channel

DL Down Link (forward link)

DPCCH Dedicated Physical Control Channel

DPDCH Dedicated Physical Data Channel

DTCH Dedicated Traffic Channel

FACH Forward Access Channel




2 Confidential and Proprietary Information of ZTE CORPORATION

FDD Frequency Division Duplex

FER Frame Erasure Rate, Frame Error Rate

RNTI Radio Network Temporary Identity

PCCH Paging Control Channel

PCH Paging Control Channel

PDU Protocol Data Unit

PICH Page Indication Channel

PU Payload Unit

RAB Radio Access Bearer

RACH Random Access Channel

RB Radio Bearer

RNC Radio Network Controller

RNS Radio Resource System

RRC Radio Network Control

SIB System Information Block

SIR Signal-to-Interference Ratio

SRNC Serving Radio Network Control

TCP/IP Transmission Control Protocol/Internet Protocol

UE User Equipment

UL Up Link(Reverse Link)

UMTS Universal Mobile Telecommunications System

URA UTRAN Registration Area

UTRA Universal Terrestrial Radio Access

UTRAN Universal Terrestrial Radio Access Network

WCDMA Wideband Code Division Multiple Access




C h a p t e r 2

Basic Theory

Overview When making the 3G/2G selection and reselection handover, the function mainly refers to cell selection and reselection, as well as handover and reselection of CS and PS services. Among which, 3G/2G chooses the reselection handover of the CS service currently in the handover way while 3G/2G chooses reselection handover of the PS service currently in the reselection way, and will support the handover way in the future. For the video call service, the 3G to 2G handover will be made in the way in which the visible telephone returns to the voice telephone and the return process should be handled on the 3G side. Because the handover process is the same as that of the common voice call, this document doesn’t describe this process.

Cell Selection and Reselection A 3G user selects the 3G network in priority and always stays in the 3G network during the 3G network initial construction period. This way could guarantee 3G registered users who directly and fast enjoy more fruitful and colorful service functions so as to avoid unnecessary handover and roaming from GSM to WCDMA. During the 3G network initial construction period, the network capability is not an issue for guiding 3G users to select the 3G network and effectively alleviating the load of 2G network. During the network mature period, the network should also guide 3G users to select 3G network in priority. When the problem of network capability is serious, the network should be extended and keep the telephone traffic’s balance based on services and handover of load.





Cell Selection Strategy

The modes of the PLMN selection and reselection have two types: automatic and manual. Automatic network selection is that UE should automatic select a PLMN according to the priority sequence of PLMN, while the manual network selection could show users all current usable networks and could be selected by users. The target of the PLMN selection and reselection is to select a usable PLMN. For this purpose, the UE should maintain a PLMN list, which makes sort for the PLMN according to priority and makes search in this selection process according to this priority.

In this list, the PLMN registered successfully last time has the highest priority. After the UE powers on, it firstly attempts to connect to RPLMN. There is no subsequent operation if the connection is successful; otherwise the UE should make search in the sequence list and attempt to make the location registered.

UMTS evolves from the GSM, however, these two access technologies are totally different (GERAN/UTRAN), and thus it needs to designate a wireless access technology in priority for every PLMN.

Besides, the PLMN reselection needs to be run in the following two cases:

Case one: The user manually requests to enable the PLMN reselection;

Case two: The UE registers to the visited network (VPLMN) and periodically searches the home network (HPLMN), this period could be configured by the operators.

Whatever the 3G network uses the same PLMN number as the 2G network, the network can realize the strategy for the 3G network optimization in different ways.

Method one: the 3G network uses the same PLMN numbers as the 2G network; under this circumstance the network sets the 3G configuration as a prior wireless access technology, and the UE could use the WCDMA as a wireless access in priority when the UE makes the PLMN selection.

Method two: 3G and 2G have the different PLMN numbers: under this circumstance the network deploys 3G as HPLMN.

Network selection and reselection could be totally realized in the UE and operators could make control by configuring the USIM. All the parameters such as attributed network, as wireless access technology selected in priority are deployed in the USIM.



Chapter 2 Basic Theory


Cell Reselection Strategy

The principle of the cell reselection also guarantees 3G users to be hosted in the 3G network as the network selection strategy.

Make use of cell reselection to realize inter-system roaming and reselection under the idle mode, and implement the process as the follow strategies:

Strategy one: The UE only makes the cell reselection from 3G to 2G when the UE leaves the 3G coverage area, and then keeps the continuity of the coverage.

Strategy two: Once the UE returns to the coverage area of 3G, it makes the cell reselection from 2G to 3G.

The configuration principles for the cell reselection threshold are provided as follows, which are based on the above consideration:

Principle one: When the load of the 3G network is normal: Only if the quality of the 3G network could cater for the requirements of the lowest service rate and can be hosted, the reselection threshold of the 3G cell hosted in the 2G network is less than the reselection threshold of the 2G cell and makes 3G users hosted in the 2G network could easily reselect the 3G network;

Principle two: When the load of the 3G network is high: Network should make adjustment for the cell reselection threshold and promote the selection threshold of the 3G cell, and then makes some 3G users hosted in the2G network in order to alleviate the load of the 3G network. This process could be automatically implemented and there is reversibility according to the network load.

Therefore, the network selection strategy and the cell reselection strategy under the idle mode could together guarantee the UE that is hosted in the 3G network in priority and make use of the well coverage of the 2G network to make supplement for the 3G network.

Cell Reselection Processes

3G Cell Reselection To 2G Cell

When the UE is under the idle mode, the cell reselection process is that the UE needs to monitor the signal quality of current cells and adjacent cells at any time in order to select a best cell for providing services. The process that UE makes reselection from 3G to 2G needs the follow steps:

Step one: Trigger condition: Current 3G cell CPICH Ec/No< Qqualmin+Ssearch,RAT

Step two: Cell filter: S criterion

Step three: Cell sort: R criterion





Step four: Cell selection: Treselection, ls

If Sx>SsearchRATn, UE doesn’t implement the diff-system test; if Sx<SsearchRATn, UE implements the diff-system test. Mark: If current cell doesn’t send SsearchRATn to the UE, the UE implements diff-system test (UE always measures GSM adjacent cells when the UE doesn’t configure SsearchRAT).

Use the S criterion for filtering:

For the FDD cell, the S criterion of cell selection is defined as follow:

0Srxlev > AND 0Squal >

For the GSM cell, the S criterion of cell selection is defined as follow:

0Srxlev >

including，

oncompensatirxlevminrxlevmeas PQQSrxlev −−=

qualminqualmeas QQSqual −=

( )0,P_MAX- AX_RACHUE_TXPWR_MmaxP oncompresati =

P_MAX: UE maximum RF output power

For the FDD cell, the Srxlev is aimed at CPICH RSCP, while the Squal is at CPICH Ec/No. Only if the above two conditions are met, the UE should be regarded as the cell selection.

For the GSM cell, the Srxlev uses RXLEV to present as long as the received level meets the condition.

Use R criterion for sorting:

According to test results, the UE should make sort for the cells that meet S criterion of cell selection in terms of the follow principles without considering hierarchical cell selection (HCS):

ssmeas QhystQ += ,sR

nsnmeas QoffsetQ ,,nR −=

Among which：

Rs is the R value of serving cell, while Rn is the R value of the adjacent cells.

Qmeas is the received signal quality value, the FDD cell is designated by the cell selection and reselection quality measure which described by CPICH Ec/No or CPICH RSCP, while the GSM cell is described by the RXLEV;

There is a value called Qhysts for reselection delay of the serving cell. When the cell selection and reselection measure of the FDD cell is set as CPICH RSCP, the UE should use Qhyst1s;





when the measure is set as CPICH Ec/No, the UE should use Qhyst2s;

Serving cell and adjacent cell quality offset is set as Qoffsets,n. For the GSM cell, Qoffset1s, n should be set.

If all the queuing levels of the best new cells are higher than the service cell during a Treselection time interval and the UE has stayed in the current service cell more than one second, the UE should reselect this new cell.

2G Cell Reselection To 3G Cell

If the 3G cell reselection list contains the frequency points of UTRAN, MS could be reselected to the UTRAN when MS meets the conditions provided as follows:

Condition one: Trigger condition, Qsearch_I (Idle State)/ Qsearch_C (Dedicated State) satisfies the diff-system test threshold.

Condition two: The RSCP of the adjacent cell measured by MS is at least FDD_Qoffset higher than the RLA_C of all the adjacent cells and keeps at least 5 seconds (If MS reselect to GSM cell within 15 seconds, then FDD_Qoffset also needs a 5db increment.

Condition three: If Ec/ No (measured by MS) ≥ FDD_Qmin, the time lasts 5 seconds;

Besides, MS could not make the cell reselection of the UTRAN after it is reselected to the GSM within 5 seconds. If many UTRAN cells meet the above criterions, MS needs to select the best cell of the RSCP.

Inter-system Handover 3G->2G Inter-system Handover Types

The handover between the 3G->2G systems mainly contains the follow three types:

First type: handover based on quality

When a user makes a call in the WCDMA system and moves to the edge of the WCDMA system, the wireless quality should become worse. A WCDMA cell where a user is hosted in the GSM cell with the same coverage, (For example: the cell’s coverage area of GSM900 is bigger than the WCDMA’s, the cell of WCDMA may be covered in range of the GSM cell), the UE doesn’t need





to measure or realize the blind-handover from WCDMA to GSM. Or else UE should open the compression mode and inter-system measurement to realize handover from WCDMA to GSM.

Second type: handover based on load

When the WCDMA system has a higher load and satisfies the conditions that make inter-system load balance, the system could assign the user into the GSM system through the oriented-retry if one user accesses the WCDMA system. If the load of the WCDMA system continues to increase and reach the conditions that need to make load control, the system could hand over the user to GSM system for the security of the WCDMA system when the user keeps calling in the WCDMA system. The current handover could be a blind handover based on the same coverage range or handover of the inter-system measurement based on the open compression mode.

Third type: handover based on mobile speed of the MS

Under the HCS (hierarchical cell structure) structure constructed by the WCDMA cell and GSM cell (Actually there exist a GSM macro cell and a UMTS smart cell, and the UMTS provides the island-style coverage), the WCDMA system could be switched to the GSM cell which has a wider range of coverage (Such as GSM900 cell) for avoiding handover to the users who move quickly and cause shock to other users in the WCDMA system.

Besides, there are some inter-system handovers which are based on BLER, uplink/downlink power and service types.

For the above handover types, the main difference is the different conditions of triggering handover; the different handover processes could be divided into blind-handover, oriented-retry and handover of opening compression mode.

Among which:

Blind handover: When the GSM and the UMTS exist in one coverage cell, the UE could directly make the handover process without opening the compression mode and diff-system test after the handover condition is met.

Oriented-retry: When the UE launches the service in the UTRAN cell which has satisfied the threshold of load balance, the service could be set up in the GSM adjacent cell at the RAB stage.

The handover of opening the compression mode: After the UE meets conditions of handover, the UE runs the compression mode and measures inter-system adjacent cells, then makes inter-system handover according to results of measurement.

The handover of opening the compression mode belongs to the most basic process while the subsequent contents should further describe this handover flow.





CS Service 3G->2G Handover

The typical handover process includes the follow steps:

Measurement control-> Measurement report-> Handover decision-> Handover implementing.

The network launches a diff-system test in terms of the cell quality of the UE and the information of adjacent cells. At the measurement control stage, the network should send the measurement control messages which contain measurement parameters to the UE. At the measurement report stage, the UE sends the measurement reports to the network after it meets the report condition of test event. At the handover decision stage, the network judges whether to make handover according to test report. At the handover implementing stage, MS and network make interaction processes via signal network and take action according to signal.

When the UE stays in the edge of the 3G system and triggers the threshold of inter-system test from 3G to 2G, the 3G RNC notifies the double-mode UE and starts the diff-system test. After the UE makes measurement and satisfies the threshold, it reports the measurement event while the RNC judges if to start the inter-system handover signaling flow. The UE that is at the connection state in the 3G system can work continuously within the designated frequency in all the time period, so it is required to enable the condensation mode (as the UE has only one transceiver) for the 3G system and the dual mode in the dif-system measurement so as to keep the session during the period of dif-system measurement.

The signaling flow from 3G to 2G is described as follows:





F I G U R E 1 C I R C U IT D O MAI N I N T E R -S Y ST E M H AN D O V E R F L O W F R O M 3G T O 2G

n When the UTRAN determines to make the inter-system handover on the basis of measurement, the SRNC sends the RANAP message Relocation Required to CN and requests the other end system to get ready for the inter-system handover.

n The WCDMA CN forwards this requirement to the GSM MSC (Through MAP/E message Prepare Handover);

n GSM MSC sends Handover Request to BSC.

n When the GSM BSS prepares enough resources for the inter-system handover, the BSC sends Handover Request Ack back to GSM MSC;

n The GSM MSC sends MAP/E message of Prepare Handover Response to the WCDMA CN;





n The WCDMA CN sends the RANAP message of Relocation Command to respond to the initial request of the SRNC.

n The SRNC sends the Handover From Utran Command message to the UE and requests the MS to make the inter-system handover from WCDMA to GSM through the existed RRC connection.

n When the UE makes handover from WCDMA to GSM (Hard Handover), the UE sends Handover Complete message to the BSC and notifies the BSC that the handover has been completed, and then the BSC sends Handover Complete message to the GSM MSC.

n After the GSM MSC checks that the UE exists under the GSM field, it should send the Send End Signal Request message to WCDMA CN and notifies the WCDMA CN the handover has been completed, and then could release the WCDMA network resources occupied by UE.

n The CN sends Iu Release Command to the RNC and notifies the earlier SRNC to release related resources; after related bearer resources in WCDMA are released, the WCDMA CN responds to GSM MSC, and then the handover signal flow is completed.


After the UE starts the CS services in the 2G cell, the UE should measure the 3G adjacent cells and report the 3G adjacent cell measurement periodically. When the measurement of 3G adjacent cells meets the threshold of handover (this measurement is judged by BSC), the BSC should launch the handover process. Among which the UE covered by 2G cell makes measurement for 3G adjacent cells, or could realize clock opening inter-system measurement through different configurations or opens the inter-system test after meets conditions.

The GSM system doesn’t use the UE event report to determine the handover.





F I G U R E 2 C I R C U IT D O MAI N I N T E R -S Y ST E M H AN D O V E R F L O W F R O M 2G T O 3G

2G MSC

HANDOVER COMMAND

HANDOVER REQUIRED

BSC UE

HANDOVER COMMAND

RELEASE COMPLETE

RELEASE

3G MSCRNC

PREPARE HANDOVERREQUEST

PREPARE HANDOVERRESPONSE

RELOCATION REQUEST

RELOCATIONRESPONSE ack.

IAM

ACM

PROCESS SIGNALLINGRELOCATION DETECT

ANM

SEND END SIGNALRELOCATIONCOMPLETE

The process of handover from 2G to 3G is the same as that from 3G to 2G, the distinction mainly is that UE should make report periodically, and then BSC should determine whether the system launches the handover according to the measurement report. The handover flow is no longer described.

PS Service 3G->2G Handover

The handover ways of the PS service are different according to the state before the handover of the UE. When the UE stays in the DCH state, the UTRAN launches a cell change command for handover. When the UE stays in the FACH state or the PCH state, the UE automatically launches the cell reselection. The idle UE launches the cell reselection automatically while the reselection flow should also take the process of the context interaction between the new and the old SGSN PDP as the UE with the FACH state or PCH state stays at the PMM connection state.

The inter-system handover flow of PS service under the non-DCH state is simple; so it is described in the subsequent signaling trace flow. The following mainly analyzes the inter-system handover of the PS service under the DCH dedicated state.

The signaling handover flow in the packet domain inter-system of SGSN from 3G to 2G is described in the following figure:





F I G U R E 3 PAC K E T D O MAI N I N T E R -S Y ST E M H AN D O V E R P R O C E S S F R O M 3G T O 2G

MS new2G-SGSN

HLRGGSNold3G-SGSN

2. Routing Area Update Request

10. Update PDP Context Request

10. Update PDP Context Response

11. Update GPRS Location

15. Update GPRS Location Ack

5. SGSN Context Response 6. Security Functions

19. Routing Area Update Accept

12. Cancel Location

12. Cancel Location Ack

14. Insert Subscriber Data Ack

14. Insert Subscriber Data

7. SGSN Context Acknowledge

BSS SRNS

3. SGSN Context Request

13. Iu Release Command

13. Iu Release Complete

8a. Forward Packets

9. Forward Packets

4. SRNS Context Request

4. SRNS Context Response

8. SRNS Data Forward Command

22. BSS Packet Flow Context Procedure

1. Intersystem changedecision

C3

C1

20. Routing Area Update Complete

newMSC/VLR

oldMSC/VLR

16. Location Update Request 17a. Update Location

17b. Cancel Location

17c. Cancel Location Ack 17d. Insert Subscriber Data

17e. Insert Subscriber Data Ack

17f. Update Location Ack 18. Location Update Accept

21. TMSI Reallocation Complete

C2

n The UE (UE stays in a non Cell-DCH state) or UTRAN (UE

stays in a Cell-DCH state) decides to launch an inter-system handover of packet domain.





n The UE sends the route update request to the 2G-SGSN, the types of update will designate a route renewal, or combination RA/LA renewal or combination RA/LA renewal affixed with IMSI. The BSS adds the cell global indication (CGI) with RAC and LAC of the local cell in the received message before it sends the message to the SGSN.

n The old 3G-SGSN validates the signature of UE PTMSI, if the result of validation succeeds, the old SGSN should launch a timer. However, if the old SGSN doesn’t know the UE, the old SGSN should return an error reason.

n If the UE stays in the PMM-CONNECTED state before handover, the old 3G-SGSN sends the SRNC Context Request message to SRNC. After the SRNC receives this message, it begins to write buffer and stop sending the PDU data to the UE, and return the SRNS Context Response to the old 3G-SGSN.

n The old 3G-SGSN sends SGSN Context Response to 2G-SGSN, among which there are MM and PDP contexts.

n Implement the security flow.

n The new 2G-SGSN sends the SGSN Context Acknowledge message to the 3G-SGSN and notifies the 3G SGSN that 2G SGSN could accept the related PDU data which is activated at present.

n If the UE stays in the PMM-CONNECTED state, the old 3G-SGSN sends Data Forward Command to the SRNS. After the SRNS receives this command, the SRNS launches the data forward timer, and then sends the PDU data which is be stored in buffer to the old 3G SGSN.

n The old 3G-SGSN sends the GTP PDUs to the 2G-SGSN according to tunnel method. The serial number of the GTP header does not change （which is got from the PDCP serial number）.

n The new 2G-SGSN sends Update PDP Context Request to every corresponding GGSN. After the GGSN updates the PDP context, the GGSN returns the response message of Update PDP Context Response.

n The new 2G-SGSN sends Update GPRS Location to HLR for modifying the SGSN number.

n The HLR sends Cancel Location to the old 3G-SGSN for canceling the location. The old 3G SGSN should respond to the HLR with Cancel Location Ack message. After the operation timeout and operation timing is finished, the old 3G-SGSN deletes the MM and PDP context.

n If the MS stays in the PMM-CONNECTED state, the 3G-SGSN sends the Iu Release Command message to the SRNS which is included in the RNC. After the data forward timing is finished, the SRNS should send Iu Release Complete to 3G-SGSN as response.





n The HLR sends the Insert Subscriber Data message to the new 2G-SGSN, the 2G SGSN inserts the user contract data into the MM context and the PDP context, and then responds to the Insert Subscriber Data Ack message.

n When the HLR makes sure the modification is completed, it sends the Update GPRS Location message to the 2G-SGSN.

n If the relevancy is set up, the new 2G SGSN should send Location Update Request to the VLR to notify the new MSC/VLR to launch the location renewal, and then the VLR could set up or update the relevancy through saving the SGSN number.

n If the user data in the VLR is without any acknowledgement from the HLR, the VLR will notify the HLR. The HLR deletes the old VLR and inserts the user data into the new VLR.

Ñ The new VLR sends Update Location to the HLR;

Ñ The HLR deletes the data in the old VLR through sending the Cancel Location to the old VLR.

Ñ cThe old VLR responds with the Cancel Location;

Ñ The HLR sends the Insert Subscriber Data Ack to the new VLR;

Ñ The new VLR responds with the Insert Subscriber Data Ack;

Ñ The HLR responds the Update Location Ack to the new VLR.

n The new VLR allocates the TMSI for the UE through sending the Location Update Accept message to the 2G-SGSN.

n The new 2G-SGSN validates the legality whether UE can stay in the new route area. If all the checks are successful, the 2G SGSN will set up MM contexts and PDP contexts for user. The 2G SGSN responds one Routing Area Update Accept to the UE through setting up a logical link between the UE and the 2G SGSN.

n Through sending the Routing Area Update Complete to the 2G-SGSN, The UE could acknowledge the newly allocated PTMSI, including acknowledging all the PDU data successfully sent to the UE before the routing area is updated.

n The 2G-SGSN sends the TMSI Reallocation Complete message to the VLR to notify the VLR that the TMSI has been allocated successfully after the UE gets the acknowledgement from the UE.

n The 2G-SGSN and BSS implement BSS Packet Flow Context Procedure.





PS Service 2G->3G Handover

Making handover from 2G to 3G is a cell reselection self-made by the UE. The UE launches the RRC connection and registration in the 3G cell through the way of cell reselection. After the 3G cell is registered, the UE could send the direct message service request for applying for resources when the UE has requirements for signaling or data services. The detailed flows are no longer described in this section while the specified flows are analyzed through the signaling trace in the subsequent content.

The signaling flow of the handover included in packet domain inter-system of SGSN from 2G to 3G are provided is shown in Figure 4:





F I G U R E 4 PAC K E T D O MAI N I N T E R -S Y ST E M H AN D O V E R F L O W F R O M 2G T O 3G

MS BSS SRNS New3G-SGSN

Old2G-SGSN GGSN HLR

Routeing Area Update Request

SGSN Context Request

SGSN Context Response

Send Authentication Info

Authentication and Ciphering Request

Send Authentication Info Ack

Authentication and Ciphering Response

SGSN Context Acknowledge

Forward Packets

Update PDP Context Request

Update PDP Context Response

Update GPRS Location

Cancel Location

Cancel Location Ack

Insert Subscriber Data

Insert Subscriber Data Ack

Update GPRS Location Ack

Routeing Area Update Accept

Routeing Area Update Complete

(Note 1)

(Note 2)

Common ID

Service Request

RAB Assignment Request

RB Setup

RB Setup Complete

RAB Assignment Response

Security Mode Command

Security Mode Command

Security Mode Complete

Security Mode Complete

Note 1: If the number of authentication sets is not enough, SGSN will initiate SendAuthenticationInfo procedure to get authentication sets.Note 2: If the corresponding parameters of security function are configured, SGSN will initiate corresponding security procedure.

CS+PS Concurrent Service 3G->2G Handover

As the GSM doesn’t support that the UE uses CS and PS services at the same time for hybrid concurrent services of CS+PS, the handover of the hybrid service from 3G to 2G makes sure that the successful handover of the CS services is the main function. The PS service will be released, but keeps the PMM connection state. After the UE releases the CS service in the 2G cell, the PS services can be recovered.






C h a p t e r 4

Typical Flows

Cell Reselection 2G->3G Cell Reselection

1. The UE gets the basic parameters of 3G measurement through the 2Quater system messages, the messages contents of the 2Quater are provided as follows:

SYSTEM_INFORMATION_2QUATER

si_2quater_rest

BA_IND = 1 (0x1)

3G_BA_IND = 1 (0x1)

MP_CHANGE_MARK = 1 (0x1)

SI2quater_INDEX = 0 (0x0)

SI2quater_COUNT = 0 (0x0)

measurement_parameters_description_present = 1 (0x1)

Measurement_Parameters Description

REPORT_TYPE = 0 (0x0)

SERVING_BAND_REPORTING = 3 (0x3)

gprs_real_time_difference_description_present = 0 (0x0)

gprs_bsic_description_present = 0 (0x0)

gprs_report_priority_description_present = 0 (0x0)

gprs_measurement_parameters_description_present = 0 (0x0)

nc_measurement_parameters_present = 0 (0x0)

extension_length_present = 1 (0x1)





extension length = 10 (0xa)

SI2q Extension Information

ccn_support_description_present = 1 (0x1)

CCN Support Description

Number_Cells = 3 (0x3)

CCN_SUPPORTED = 7 (0x7)

spare_bits0_count = 0 (0x0)

_3g_neighbour_cell_description_present = 1 (0x1)

3G Neighbour Cell Description

index_start_3g_present = 1 (0x1)

Index_Start_3G = 0 (0x0)

absolute_index_start_emr_present = 1 (0x1)

Absolute_Index_Start_EMR = 32 (0x20)

utran_fdd_description_present = 1 (0x1)

UTRAN FDD Description

bandwidth_fdd_present = 1 (0x1)

Bandwidth_FDD = 0 (0x0)

struct0_count = 1 (0x1)

struct0[0]

const_1 = 1 (0x1)

Repeated UTRAN FDD Neighbour Cells

const_0 = 0 (0x0)

FDD-ARFCN = 10612 (0x2974)

FDD_Indic0 = 0 (0x0)

NR_OF_FDD_CELLS = 1 (0x1)

FDD_CELL_INFORMATION Field = 105 (0x69)

const_0 = 0 (0x0)

utran_tdd_description_present = 0 (0x0)

_3g_measurement_parameters_description_present = 1 (0x1)

3G Measurement Parameters Description

Qsearch_I = 7 (0x7)

Qsearch_C_Initial = 0 (0x0)

fdd_qoffset_present = 1 (0x1)

FDD_Qoffset = 0 (0x0)

FDD_REP_QUANT = 1 (0x1)

FDD_MULTIRAT_REPORTING = 3 (0x3)



Chapter 4 Typical Flows


FDD_Qmin = 0 (0x0)

tdd_qoffset_present = 1 (0x1)

TDD_Qoffset = 8 (0x8)

TDD_MULTIRAT_REPORTING = 2 (0x2)

gprs_3g_measurement_parameters_description_present = 0 (0x0)

padding_bits_L = 0 (L)

spare_padding0_count = 38 (0x26)

spare_padding0 = 0x0000000000

2. After the UE gets the signal measurement of 3G adjacent cells, whether to launch the 5 seconds timer, and the signal strength of 3G cell could be observed through the “GPRS RR 3G Reselection Measurements” of UE code flow.

Day 10160 09:56:34.931 [1C] 0x5263 GPRS RR 3G Reselection Measurements

Num cells : 1------------ If the UE doesn’t search the 3G signal that has the enough strong power, the value is 0

Cell 1

UARFCN : 10612

Scrambling code : 1680

Diversity : No

RSCP : -92 dBm

Five second timer state: Timer Running------ represent the 5 seconds timer has been launched. If the 3G signal strength totally satisfies the demands of the reselection threshold in 5 seconds, then the system launches the reselection.

3. The UE launches the reselection processes after it satisfies the conditions of reselection, the starting and the end of reselection all could be observed from EVENT messages of UE internal.

Day 10160 09:56:36.417 [41] 0x1FFB Event

09:56:36.417 Event 0 : EVENT_GSM_RESELECT_START (ID=433) Payload = 0x07

Payload String = ReselectType=RR_RESELECTION_TRIGGER_GSM_TO_WCDMA

Day 10160 09:56:37.099 [06] 0x1FFB Event

09:56:37.099 Event 0 : EVENT_GSM_TO_WCDMA_RESELECT_END (ID=897) Payload = 0x00 00 00 00 FF

Payload String = UARFCN: 0, Scrambling Code: 0, Reason: 255





3G-2G Cell Reselection

1． The UE gets the inter-system measure parameters from the system message SIB3：

Day 400 12:37:12.279 [C8] 0x412F WCDMA Signaling Messages -- DL_BCCH_BCH

Channel Type = DL_BCCH_BCH, Radio Bearer ID = 40, Message Length = 31

Interpreted PDU:

value BCCH-BCH-Message ::=

{

message

{

sfn-Prime 1379,

payload completeSIB-List :

{

{

sib-Type systemInformationBlockType2,

sib-Data-variable '00000000 00000000 0001'B

},

{


sib-Data-variable '00000000 01000000 00000011 10011100 010 ...'B

}

}

}

}

*****************************************

***** before 2nd level SIB decoding *****

*****************************************

HEX Dump of signalling_msg:

AC6E2213 000011BA 802001CE 216DEA05 6A900210 1FFFFE00 00000000 000001





RRC Decode: Received SIM Type 8 (Complete SIB(s) Short)...

Complete SIB List...

1) SIB: Type=2 (SIB 2), bLen=20


value SysInfoType2 ::=

{

ura-IdentityList

{

'00000000 00000001'B

}

}


{

sib4indicator FALSE,

cellIdentity '00000001 00000000 00001110 0111'B,

cellSelectReselectInfo

{

cellSelectQualityMeasure cpich-Ec-N0 :

{

q-HYST-2-S 1

},

modeSpecificInfo fdd :

{

s-Intrasearch 7,

s-Intersearch 5,

rat-List

{

{

rat-Identifier gsm,

s-SearchRAT 5,

s-Limit-SearchRAT 5

}

},

q-QualMin -15,





q-RxlevMin -58

},

q-Hyst-l-S 1,

t-Reselection-S 1,

maxAllowedUL-TX-Power -50

},

cellAccessRestriction

{

cellBarred notBarred : NULL,

cellReservedForOperatorUse notReserved,

cellReservationExtension notReserved,

accessClassBarredList

{

notBarred,

notBarred,

notBarred,

notBarred,

notBarred,

notBarred,

notBarred,

notBarred,

notBarred,

notBarred,

notBarred,

notBarred,

notBarred,

notBarred,

notBarred,

notBarred

}

}

}

*****************************************

***** after 2nd level SIB decoding *****

*****************************************

2. The UE gets the adjacent cells selection parameters of the diff-system from the system message SIB11





Day 400 12:37:12.419 [D6] 0x412F WCDMA Signaling Messages -- DL_BCCH_BCH

Channel Type = DL_BCCH_BCH, Radio Bearer ID = 40, Message Length = 31

Interpreted PDU:

value BCCH-BCH-Message ::=

{

message

{

sfn-Prime 1386,

payload completeSIB-List :

{

{


sib-Data-variable '10011001 01000000 00011100 11110000 000 ...'B

}

}

}

}

*****************************************

***** before 2nd level SIB decoding *****

*****************************************

HEX Dump of signalling_msg:

AD4E0B89 99401CF0 1004E7A4 0060054F 28525912 05400000 00000000 000002

RRC Decode: Received SIM Type 8 (Complete SIB(s) Short)...

Complete SIB List...



{

sib12indicator FALSE,

fach-MeasurementOccasionInfo

{





fACH-meas-occasion-coeff 3,

inter-freq-FDD-meas-ind TRUE,

inter-freq-TDD-meas-ind FALSE,

inter-RAT-meas-ind

{

gsm

}

},

measurementControlSysInfo

{

use-of-HCS hcs-not-used :

{

cellSelectQualityMeasure cpich-Ec-N0 :

{

intraFreqMeasurementSysInfo

{

intraFreqCellInfoSI-List

{

newIntraFreqCellList

{

{

intraFreqCellID 0,

cellInfo

{


{

primaryCPICH-Info

{

primaryScramblingCode 231

},

readSFN-Indicator TRUE,

tx-DiversityIndicator FALSE

}

}

}

}





},

intraFreqMeasQuantity

{

filterCoefficient fc2,


{

intraFreqMeasQuantity-FDD cpich-Ec-N0

}

},

intraFreqReportingQuantityForRACH

{

sfn-SFN-OTD-Type noReport,


{

intraFreqRepQuantityRACH-FDD cpich-EcN0

}

},

maxReportedCellsOnRACH currentCell

}

},

interRATMeasurementSysInfo

{

interRATCellInfoList

{

removedInterRATCellList removeAllInterRATCells : NULL,

newInterRATCellList

{

{

technologySpecificInfo gsm :

{

cellSelectionReselectionInfo

{

q-Offset1S-N 10,

maxAllowedUL-TX-Power 30,

modeSpecificInfo gsm :

{





q-RxlevMin -49

}

},

interRATCellIndividualOffset 0,

bsic

{

ncc 1,

bcc 1

},

frequency-band dcs1800BandUsed,

bcch-ARFCN 21

}

}

}

}

}

}

}

}

*****************************************

***** after 2nd level SIB decoding *****

*****************************************

3. The UE detects the 2G signal and makes queuing.

Day 400 12:38:42.496 [06] 0x4005 WCDMA Search Cell Reselection Rank

WCDMA GSM

------------------------ ------------------------

Num cells searched = 1 Num cells searched = 1

Cell 1: Cell 1:

RF freq = 10712 ARFCN = 21

PSC = 231 BSIC<ncc,bcc> = <1,1>

ECIO = -9.0 RSSI = -57

rank_ecio = NotUsed rank = -67

RSCP = -111 Band = 0 (900/1800)

rank_rscp = -109





4. The UE launches the reselection flow and completes the reselection after the 2G signal meets the conditions of reselection.

Day 400 12:38:42.549 [BA] 0x1FFB Event

12:38:42.549 Event 0 : EVENT_WCDMA_TO_GSM_RESELECTION_START (ID=531) Payload = 0x15 00 01 01

Payload String = ARFCN: 21 NCC: 1 BCC: 1

Day 400 12:38:43.509 [D3] 0x1FFB Event

12:38:43.509 Event 0 : EVENT_WCDMA_TO_GSM_RESELECTION_END (ID=532) Payload = 0x01 06

Payload String = Success (L1 Stopped) Reason: GSM BSIC Not Found

CS Service CS Service 3G->2G Blind Handover Process

The UE reports the 2D events in the 3G cell, which represents the quality of the 3G signal to become worse.

The RNC decision makes blind handover after the 2D event is reported; it should directly send the retry request, while it doesn’t need to launch the compression mode during the blind-handover process.





CS Service 3G->2G Directed Retry

The UE launches the CS service from the 3G cell and the service can’t be accessed because of reaching the conditioning threshold of the load, the RNC responds to the messages about the RAB allocation failure because of directed retry.

Once the RNC responds to the RAB allocation failure, it sends the requests of retry and makes the handover among systems. The reason of the retry is also a directed retry.

CS Service 3G->2G Handover Based On Coverage

The UE launches the CS service and reports the 2D event in the 3G cell when the signal quality becomes worse because of coverage.





The RNC sends the inter-system measure control to the UE, notifies the UE to make inter-system measure while the RNC issues the inter-system measure parameter 3A or 3C and the compressed mode parameters

The RNC issues the compressed mode parameters to the NODEB.

After the UE tests the signal strength of diff-system adjacent cells satisfies the report threshold of event, the UE forward tells the test reports. This example is 3C.





The RNC launches the retry flow and makes the inter-system handover after the UE reports the 3C.


The RNC receives the Relocation Request issued from CN and indicates the requests of accessible office retry. After the RNC notifies the NODEB to set up a wireless link, the RNC responds the RelocationDetect and the RelocationComplete to the CN for wireless resources successful allocation, and then the RNC indicates the retry is successful. The RNC makes interaction with the UE and allocates the new RNTI as well as the RNC transmits the UTRAN Mobility Information.





PS Services PCH State 3G->2G Handover

After the UE sets up the PS service, it stops transmitting data.

The state becomes the PCH state after the user-panel reports 4B0, and then the user-panel deletes the wireless link.

The UE makes handover to the 2G adjacent cells through the way of reselection under the PCH state. Because of staying under PMM connection state, the RNC could receive the request messages of the SRNC contexts and make transmission for the PDP contexts and retransmission of the PDU buffer. Eventually the RNC releases the IU interface and completes the handover.





FACH State 3G->2G Handover

The UE stops transmitting for data after the UE sets up the PS service and the user-panel reports 4B0.

The user-panel becomes FACH state after it reports 4B0, and then it deletes the wireless link.

The UE makes handover to 2G adjacent cells by the way of reselection under the FACH state. Because of staying under PMM connection state, the RNC could receive the request messages of the SRNC contexts and make transmission for the PDP contexts and retransmission of the PDU buffer. Eventually the RNC releases the IU interface and completes the handover.

DCH/HS State 3G->2G Handover





After the UE sets up the PS service in the 3G cell, it should report the 2D event because of the worse signal quality.

After the 2D events are reported, the RNC issues the inter-system measure control to the UE and notifies the UE to make inter-system measure as well as the UE opens the compression mode, and then the RNC indicates the inter-system parameter 3A or 3C.

The RNC issues the compression mode parameters to the NODEB.





The UE reports the test reports to RNC after the measurements of diff-system adjacent cells meet the 3C threshold.

The RNC notifies the UE to make inter-system cells modification after it receives the test report 3C, and the notification messages contain the basic parameters of the GSM cell.

The UE begins to make interactive processes of the SRNC contexts and makes transmission for the PDP contexts and retransmission of the PDU buffer after the UE completes reselection. Eventually the UE releases the IU interface and completes the handover.





PS Service 2G->3G Handover（UE Directly sends SERVICE REQUEST）

The UE firstly launches the request of the RRC connection by the way of reselection from 2G to 3G because of the inter-system cell reselection.

Considering about the initial direct transmission message here, the UE takes FOR=1 in Route Area Updating from the initial direct messages, this parameter describes that the UE has the requirements of signaling and data. Besides, if the value taken by the “PDP CONTEXT STATUS” in RAU is 0x200, then it presents the PDP is active which appears the UE is under connection state in the GSM side before the UE reselects to 3G. However, if the value is 0x00, it represents the PDP is inactive and shows the UE is under idle state in GSM side before the UE reselects to 3G.





The UE immediately launches the “Service Request” for setting up PS service after the UE finishes RAC update. Whether the UE carries the “PDP CONTEXT STATUS” message also could be observed.

The PS service is set up after the CN responds “Service Accept” to the RNC and issues RAB allocation.

PS Service 2G->3G Handover（Launch PS service via RRC connection）

The UE makes handover from 2G to 3G through the way of reselection. Firstly, the UE launches the RRC connection requests for the inter-system cell reselection.

Considered about the initial direct transmission message here, the UE takes FOR=0 in Route Area Updating, this parameter describes that the UE doesn’t have the requirements of signaling and data. However, the value taken by the “PDP CONTEXT





STATUS” is 0x200, then it presents the UE has been already under PMM connection state.

From the above diagram, the IU resources are immediately released by the subsequent CN.

It is noteworthy of considering that the UE sends another direct message “Services Request” with the active PDP information for setting up the service after the IU is released. Because of the released IU resources, the above message is abandoned.

The UE launches the RRC connection request again, the reason is that the UE launches the interactive service for setting up the PS service.





After the RRC connection is set up, the UE could directly send the service request affixed with the “PDP CONTEXT STATUS” message, which represents the UE stays under the PMM connection state. If the UE stays in IDLE state, then the UE sets up the PS service by the PDP active request and not by sending “service request” directly.

CS+PS Concurrent Service Handover CS+PS Concurrent 3G->2G Handover

The UE sets up the CS+PS concurrent service. Because the quality of the local cell becomes worse, the UE reports the 2D events, while the RNC issues the parameters of the measure control and the compression mode as well as the UE launches the measure of the diff-system.





The UE reports the 3C event when the UE finds the signal strength of the diff-system meets the measure reports thresholds in the diff-frequency testing.

When the RNC launches the processes of the CS service retry, the CS service makes handover to 2G, and then the CN issues messages about the IU release because of retry successful. The PS service is interrupted as well as kept the PMM connection state.

From the observed signaling, the UE keeps CS calling about 9 seconds in the 2G side and on-hooks the CS service, (From retry completed to SRNS context requests received: 10:29:12-





10:29:21). After the CS service is on-hooked, the PS service has a demand on the recovering. The RNC receives the SRNS contexts requests as well as makes the retransmission of the PDP contexts and the data PDU, and then the PS service of the 2G side is recovered.



Documents

3G2G Selection & Reselection Handover_BOOK