40356034 Dual Transfer Mode

Dual Transfer Mode in BSC

dn0574492Issue 1-1 en

# Nokia CorporationNokia Proprietary and Confidential

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BSC3119Nokia BSC/TCSM, Rel. S12, ProductDocumentation

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Contents

Contents 3

List of tables 4

List of figures 5

Summary of changes 7

1 Overview of Dual Transfer Mode 9

2 Requirements for Dual Transfer Mode 15

3 Technical description of Dual Transfer Mode 173.1 Architecture 173.2 State transitions 173.3 Restrictions 183.4 Interworking 19

4 IMSI co-ordination 25

5 Paging co-ordination 27

6 GTTP signalling 29

7 Radio resource management 337.1 DTM channel allocation 337.2 DTM multislot classes 347.3 Fragmentation of the PS resources 347.4 Territory management 36

8 Dual Transfer Mode call establishment 398.1 Mobile-originated call establishment 398.2 Mobile-terminated call establishment 41

9 Handover control 459.1 Intra-cell handover 459.2 Inter-cell handover 469.3 External handover 509.4 Inter-system handover 50

10 Dual Transfer Mode call release 53

11 Effect of Dual Transfer Mode on interfaces 55

12 User interface of Dual Transfer Mode 57



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Contents

List of tables

Table 1. Software requirements for Dual Transfer Mode (DTM) 15

Table 2. Hardware requirements for DTM 15




List of figures

Figure 1. Real time video sharing in dual transfer mode 10

Figure 2. DTM state transitions 18

Figure 3. PS paging procedure 28

Figure 4. GTTP signalling procedure in uplink 30

Figure 5. GTTP signalling procedure in downlink 31

Figure 6. DTM multislot allocations 34

Figure 7. DTM allocation example 35

Figure 8. MO call establishment 40

Figure 9. MT DTM call establishment 42



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List of figures

Summary of changes

Summary of changes

Changes between document issues are cumulative. Therefore, the latest documentissue contains all changes made to previous issues.

Changes made between issues 1-1 and 1

Information related to Extended Dynamic Allocation (EDA) and Network-Assisted Cell Change (NACC) has been updated in section Interworking inchapter Technical description of Dual Transfer Mode.

Information in section Inter-cell handover in chaper Handover control has beenupdated.

Section CS-connection-control-initiated DTM call release in chapter DualTransfer Mode call release has been updated.



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Summary of changes

1 Overview of Dual Transfer Mode

Dual Transfer Mode (DTM) provides mobile users simultaneous circuit-switched(CS) voice and packet-switched (PS) data services. This means that users can, forexample, share a video call or send and receive e-mail during an ongoing phonecall. Figure Real time video sharing in dual transfer mode illustrates the DTMconcept.



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Overview of Dual Transfer Mode

Figure 1. Real time video sharing in dual transfer mode

In dual transfer mode, the mobile station (MS) is simultaneously in dedicatedmode and in packet transfer mode so that the timeslots allocated for each MS areconsecutive and within the same frequency. In dedicated mode, the MS has a CSconnection. In packet transfer mode, the MS has a PS connection. The CSconnection is always a single slot connection, whereas the PS connection can alsobe a multislot connection.

User A

NokiaDTM MS

User B

NokiaDTM MS

BTS

BTS

BSC

BSC

MSC/HLR

GGSN

SGSN

SGSN

IMS

IPbackbone

CS voice call

PS stream




The BSC supports only full rate CS connections in dual transfer mode.Simultaneously obtained packet data rates can be up to 118 kbit/s for EGPRS and40 kbit/s for GPRS/CS-4.

Both the CS and PS parts of a DTM call are maintained in the PS territory. ADTM call starts from an existing CS connection in the CS territory. During theDTM call establishment, the CS connection is handed over to the PS territory andcombined with the related PS resources.

DTM is application software and requires a valid licence in the BSC. For moreinformation on licensing, see Licensing in BSC.

In the Nokia implementation, the packet control unit (PCU) is a part of the BSC.Terminology is used in the following way:

. The BSC refers to the entire network element. The term is also used whenit is not necessary to distinguish between the CS and PS functionality.

. The PCU refers to the unit that manages PS connections.

. The CS connection control in the BSC (CS connection control) refers tosoftware that manages CS connections.

Benefits of Dual Transfer Mode

Mobile users require new services. With DTM, you can expand your serviceportfolio to offer users enhanced services in a GSM/EDGE network. DTM allowsyou to provide a wide range of services that demand a simultaneous CS and PSconnection. Mobile users can use data services, such as file transfer, webbrowsing, video sharing, and mobile netmeeting, during a speech call. Thismakes it possible to launch services similar to UMTS class A services also in 2Gnetworks. In addition, these services can be used to complement the 3G coveragein places where there is no 3G network coverage.

Compliance

DTM complies with the 3GPP standard (Rel5).

Related topics in Dual Transfer Mode in BSC

. Requirements for Dual Transfer Mode

. Technical description of Dual Transfer Mode

. IMSI co-ordination

. Paging co-ordination

. GTTP signalling



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. Radio resource management

. Dual Transfer Mode call establishment

. Handover control

. Dual Transfer Mode call release

. Effect of Dual Transfer Mode on interfaces

. User interface of Dual Transfer Mode

Related topics in BSC/TCSM documentation

. Test and Activate

- Data

. Activating and Testing BSS20088: Dual Transfer Mode

. Activating and Testing BSS10083: EGPRS

. Activating and Testing BSS9006: GPRS

. Reference

- Commands

. MML Commands

. EA - Adjacent Cell Handling

. EE - Base Station Controller Parameter Handling inBSC

. EQ - Base Transceiver Station Handling in BSC

. ER - Transceiver Handling

. TP - GSM Measurement Handling

. WO - Parameter Handling

- Counters/Performance Indicators

. Call Control Measurements (CSW)

. 1 Traffic Measurement

. 4 Handover Measurement

. 50 BSC Level Clear Code Measurement

. 51 BSC Level Clear Code (PM) Measurement

. 71 MS Capability Indication Measurement

. 106 CS DTM Measurement. GPRS Measurements (PSW)




. 72 Packet Control Unit Measurement

. 79 Coding Scheme Measurement

. 105 PS DTM Measurement

- Parameters

. BSS Radio Network Parameter Dictionary

. PRFILE and FIFILE Parameter List

. Descriptions

- Functional Descriptions

. Radio Network Performance

. RF Power Control and Handover Algorithm. Operability

. Radio Network Supervision in BSC

- Feature Descriptions

. Radio Network Performance

. Soft Channel Capacity in BSC

. GSM-WCDMA Interworking

. Common BCCH Control in BSC

. Enhanced Speech Codecs: AMR and EFR

. Direct Access to Desired Layer/Band

. Dual Band Network Operation. Data

. Extended Dynamic Allocation in BSC

. Network-Controlled Cell Re-selection

. Network-Assisted Cell Change

. (E)GPRS in BSC

. GPRS in BSC. Macrocellular

. Multi-BCF Control in BSC

. Extended Cell

Related topics in GSM/EDGE BSS system documentation

. Dual Transfer Mode System Feature Description



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2 Requirements for Dual Transfer ModeNetwork element software

Table 1. Software requirements for Dual Transfer Mode (DTM)

Network element Software requirements

BSC S12

Nokia Flexi EDGE BTSs No requirements

Nokia EDGE UltraSite BTSs No requirements

Nokia EDGE MetroSite BTSs No requirements

Nokia 2nd Gen. BTSs Not supported

Nokia Talk-family BTSs No requirements

Nokia PrimeSite BTSs Not supported

Nokia InSite BTSs Not supported

MSC M11 or later

Nokia NetAct OSS4.1

SGSN SG5 or later

Network element hardware

Table 2. Hardware requirements for DTM

Network element Hardware requirements

BSC BSC2i or BSC3i

PCU2



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Requirements for Dual Transfer Mode

Table 2. Hardware requirements for DTM (cont.)

Network element Hardware requirements

BTS No requirements

TCSM No requirements

SGSN No requirements

End user equipment

DTM requires DTM-capable mobile stations (MSs).

Frequency band support

The BSC supports DTM on the following frequency bands:

. GSM 800

. GSM 900

. GSM 1800

. GSM 1900

Other requirements

(E)GPRS must be available and active in the network.

The network must support Network Operation Mode I (NOM I) to provide CSpaging co-ordination for DTM-capable MSs. In NOM I, the core networkprovides CS paging co-ordination so that CS paging requests to GPRS-attachedMSs are sent to the PCU via the SGSN. The PCU provides CS paging on thepacket associated control channel (PACCH) if the MS is in packet transfer mode.If the MS is in packet idle mode, it is paged for CS calls on the paging channel(PCH).

In Network Operation Mode II (NOM II), all CS paging requests are sent on thePCH. This means that if a DTM-capable MS is in packet transfer mode (that is,there is ongoing data transfer in normal (E)GPRS mode), it does not necessarilymonitor the PCH channel and, therefore, does not respond to the CS paging.

For an overview, see Overview of Dual Transfer Mode.




3 Technical description of Dual TransferMode

3.1 Architecture

Dual Transfer Mode (DTM) uses a native split between the circuit-switched (CS)and packet-switched (PS) parts of the BSC for radio resource management.

The CS connection control in the BSC (CS connection control) handles thefollowing:

. speech codec mode selection for the DTM CS connection

. handover control

The packet control unit (PCU) handles the following:

. admission control in the PS territory

. channel allocation for both CS and PS connections

. PS territory management

3.2 State transitions

A mobile station (MS) is in dual transfer mode when it has simultaneous CS andPS connections. An MS can enter dual transfer mode only through dedicatedmode. If the MS is in idle mode, it moves to dedicated mode before entering dualtransfer mode. If the MS is in packet transfer mode, the PS connection is releasedbefore the MS moves to dedicated mode. The PCU or the MS re-establishes thePS connection as soon as the MS has a CS connection.



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Technical description of Dual Transfer Mode

If a CS connection is released when the MS is in dual transfer mode, also the PSconnection is released. The PCU or the MS re-establishes the PS connection assoon as the CS channel release has been completed. If a PS connection is releasedwhen the MS is in dual transfer mode, the MS returns to dedicated mode. The MSreturns to idle mode when it has neither a CS nor a PS connection. Figure DTMstate transitions illustrates how an MS can move from one mode to another.

Figure 2. DTM state transitions

3.3 Restrictions

The following restrictions apply to DTM:

RR idle mode/Packet idle mode

Packet transfermode

Dedicatedmode

Dual transfermode

PS release

CS release

DTM assignment




. DTM is not supported in the extended area of the cell. DTM is supported inthe normal area of the cell only.

The BSC does not perform co-ordination of international mobile subscriberidentity (IMSI) for those DTM-capable MSs that are in the extended areaof the cell. This prevents mobile-terminated (MT) DTM call establishmentand GPRS transparent transport protocol (GTTP) signalling in thedownlink direction.

. The single slot operation mode of dual transfer mode is not supported.Only the multislot operation mode is supported.

. CS paging co-ordination is not provided in Network Operation Mode II(NOM II). CS paging co-ordination is provided in NOM I only.

For details on the NOM requirements, see Other requirements.

. The BSC supports only full rate CS connections in dual transfer mode.

3.4 Interworking

GPRS

GPRS must be available and active in the network for DTM to work.

If GPRS is deactivated when DTM is in use, the MSs that have an active DTMconnection keep their CS connection but lose their temporary block flows(TBFs).

For more information on GPRS, see GPRS in BSC. For activation anddeactivation instructions, see Activating and Testing BSS9006: GPRS.

EGPRS

The BSC supports DTM data transfer in both GPRS and EGPRS modes.

A DTM TBF is established in EGPRS mode if the MS is EGPRS capable and ifthe DTM call is allocated from an EGPRS-capable PS territory. If not, the DTMTBF is established in GPRS mode.

For more information on EGPRS, see (E)GPRS in BSC. For activation anddeactivation instructions, see Activating and Testing BSS10083: EGPRS.



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Inter-system handover

An inter-system handover takes place between a GSM and a WCDMA network.The BSC uses the service priority information from both the MSC and the SGSNin the inter-system handover decision for a DTM-capable MS, if such informationis available.

For more information on how inter-system handovers work with DTM, see Inter-system handover. For more information on inter-system handover, see GSM-WCDMA Interworking.

Adaptive Multi Rate

The BSC selects an adaptive multi rate (AMR) speech codec for a new DTM CSconnection if AMR was used on the preceding CS connection of the call.

For more information on AMR, see Enhanced Speech Codecs: AMR and EFR.

Common BCCH Control and Multi BCF Control

By default, RX-level based traffic channel (TCH) access control is not used innormal CS channel allocation for evaluating the usability of resources in differentBTSs of a segment. However, it is used as a standard procedure with DTM.

For more information on Common BCCH Control, see Common BCCH Controlin BSC. For more information on Multi BCF Control, see Multi BCF Control inBSC.

Radio Network Supervision

DTM has an effect on the following supervisions:

. The Too short mean holding time supervision is not used for channels thatare used for DTM CS connections.

. The Cell channel congestion supervision does not count DTM requests.

Other supervisions are used for DTM CS connections as usual.

For more information on Radio Network Supervision, see Radio NetworkSupervision in BSC.




Extended Dynamic Allocation

Extended dynamic allocation (EDA) mode enhances the data transmissioncapability in the uplink direction. In EDA mode, it is possible to allocate two PStimeslots in the uplink direction for a DTM multislot class 11 MS. In Dynamicallocation (DA) mode, it is possible to allocate only one PS timeslot in the uplinkdirection in dual transfer mode.

Note that an MS may reduce its output power depending on the number ofallocated uplink timeslots. The power reduction is not taken into account in theinitial DTM allocation.

For more information on EDA, see Extended Dynamic Allocation in BSC.

For more information on DTM allocations, see DTM multislot classes.

Queueing and Pre-emption

Queuing is not applied to DTM requests.

The DTM CS channels are not targets of pre-emption procedures (forced releaseand forced handover).

For more information on queuing and pre-emption, see Radio Resource Pre-emption and Queuing in BSC.

Soft Channel Capacity

The maximum number of simultaneously active traffic channels in a BSCsignalling unit (BCSU) is determined by the configuration of the unit. With SoftChannel Capacity, the BSC regards the DTM CS allocations as active trafficchannels, that is, just like normal CS connections.

For more information on Soft Channel Capacity, see Soft Channel Capacity inBSC.

Network-Controlled Cell Re-selection

The PCU does not apply network-controlled cell re-selection (NCCR)procedures for an MS in dual transfer mode. However, NCCR is used normallyfor DTM-capable MSs that do not have an ongoing CS connection.

If the PS quality control function triggers NCCR for a DTM call, the BSCperforms an inter-cell handover for the related CS connection.

For more information on NCCR, see Network-Controlled Cell Re-selection.



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Network-Assisted Cell Change

The PCU does not apply the network-assisted cell change (NACC) proceduresfor an MS in dual transfer mode. However, NACC is used normally for DTM-capable MSs that do not have an ongoing CS connection.

Note that NACC procedures (that is, the use of PACKET SI STATUS messages)reduce the PS interruption time when a DTM call is released because of a CS callrelease and the PS connection needs to be re-established in normal (E)GPRSmode.

For more information on NACC, see Network-Assisted Cell Change.

In-call modification

In-call modification takes place when a CS speech call needs to be changed to aCS data call. If an in-call modification procedure is started during a DTM call, theBSC releases the DTM call.

Power control

In a DTM call, the power control algorithm limits the downlink transmissionpower of the DTM CS connection to be between [PMAX - 10 dB, PMAX].PMAX is the maximum downlink transmission power that can be used in thetransceiver (TRX).

Intelligent Underlay-Overlay, Handover Support for CoverageEnhancements, and Enhanced Coverage by Frequency Hopping

The BSC does not support super-reuse frequencies for GPRS. Therefore, it doesnot initiate handovers towards super-reuse resources for ongoing DTMconnections. If a DTM call is started from the super-reuse layer, it leads to ahandover to the regular layer.

Just like (E)GPRS, DTM is not supported in a child cell, that is, in a cell thatcontains only super-reuse resources.

For more information on Intelligent Underlay-Overlay, see Intelligent Underlay-Overlay. For more information on Handover Support for CoverageEnhancements, see Handover Support for Coverage Enhancements. For moreinformation on Enhanced Coverage by Frequency Hopping, see EnhancedCoverage by Frequency Hopping.




Circuit-switched data

The BSC does not support dual transfer mode for an MS that has an ongoingcircuit-switched data call. The call can be either a high speed circuit switched data(HSCSD) call or a single slot data call.

For more information on circuit-switched data, see HSCSD and 14.4 kbit/s DataServices in BSC.

Direct Access to Desired Layer/Band

Direct Access to Desired Layer/Band (DADL/B) makes it possible to move callsto capacity layer cells during the CS call setup phase. In many cases, in a layeredenvironment (E)GPRS is implemented mainly on the coverage layer. Thecapacity layer serves mainly CS traffic and has only the minimum required (E)GPRS capacity for maintaining the service continuity in the network. Therefore,whenever the BSC detects during the CS call setup phase that an MS requires theDTM service, it prevents the DADL/B handover from taking place for the MS inquestion.

For more information on DADL/B, see Direct Access to Desired Layer/Band.

Extended Cell

An MS can initiate and receive DTM calls only when it is in the normal area ofthe cell. DTM calls are not supported in the extended area of the cell.

For more information on Extended Cell, see Extended Cell.




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4 IMSI co-ordination

The BSC must know the international mobile subscriber identity (IMSI) of amobile station (MS) to be able to provide dual transfer mode for DTM-capableMSs. The IMSI is needed for co-ordination and identification purposes. Withoutthe IMSI, the BSC cannot co-ordinate the circuit-switched (CS) and packet-switched (PS) resources.

During a CS call establishment, the MSC sends the IMSI to the CS connectioncontrol in the BSC (CS connection control) in a COMMON ID message,provided that the IMSI of the MS is available at the MSC and that the MSC hasbeen configured to send the information. In external handovers, the IMSI is sentin the HANDOVER REQUEST message.

The packet control unit (PCU) needs to know when a DTM MS is in dedicatedmode. This information is needed in PS paging co-ordination, DTM callhandling, and GPRS transparent transport protocol (GTTP) signalling procedures.Therefore, CS connection control informs the PCU whenever a DTM-capable MSenters or leaves dedicated mode in a DTM-capable cell. The PCU keeps a record(IMSI record) of all DTM-capable MSs that are in dedicated mode in a DTM-capable cell under the PCU.

The IMSI co-ordination procedure consists of the following steps:

1. During the CS call establishment, the MSC sends the IMSI of the MS toCS connection control in a COMMON ID message.

2. CS connection control sends the IMSI to the PCU.

3. The PCU creates a dedicated IMSI context for the MS that is in dedicatedmode.

4. The PCU receives downlink logical link control (LLC) protocol data units(PDUs) for the MS. Because the PCU has a dedicated IMSI context for theMS, it establishes a temporary block flow (TBF) in dual transfer mode.

5. When the CS call is released, CS connection control informs the PCU.

6. The PCU removes the dedicated IMSI context from the IMSI record.




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IMSI co-ordination

5 Paging co-ordinationCS paging

Dual Transfer Mode (DTM) does not change the circuit-switched (CS) pagingprocedures in the BSC.

. A mobile station (MS) that is not GPRS attached is always paged for CScalls on the paging channel (PCH).

. In Network Operation Mode I (NOM I), the core network provides CSpaging co-ordination so that CS paging requests to GPRS-attached MSsare sent to the PCU via the SGSN. The PCU provides CS paging on thepacket associated control channel (PACCH) if the MS is in packet transfermode. If the MS is in packet idle mode, it is paged for CS calls on thePCH.

. In Network Operation Mode II (NOM II), all CS paging requests are senton the PCH. This means that if a DTM-capable MS is in packet transfermode, it does not necessarily monitor the PCH and, therefore, does notrespond to the CS paging.

PS paging

DTM introduces a packet notification procedure in which a DTM-capable MScan be paged for PS calls in dedicated mode. This means that instead of pagingthe MS on the PCH, CS connection control in the BSC (CS connection control)informs the MS about the PS paging request by sending a PACKETNOTIFICATION message on the main associated control channel (DCCH) ifthe MS is DTM capable and in dedicated mode in a DTM-capable cell.

PS paging is illustrated in figure PS paging procedure.



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Paging co-ordination

Figure 3. PS paging procedure

1. The SGSN sends a PS paging protocol data unit (PDU) to the PCU.

2. The PCU checks from the international mobile subscriber identity (IMSI)record whether the MS is in dedicated state.

Because of IMSI co-ordination, the PCU is always aware of which DTM-capable MSs are in dedicated state.

3. As the MS is in dedicated mode, the PCU sends the PS paging request toCS connection control.

4. CS connection control sends the PACKET NOTIFICATION message tothe MS on the DCCH.

If the MS is not in dedicated mode, the PCU sends the PS paging request to CSconnection control, which then sends it onwards on the PCH as usual.


PS paging PDU

PS paging request

SGSNPCUCS connection

control in the BSCBTSMS

PACKET NOTIFICATION

IMSI record check




6 GTTP signalling

When a Dual Transfer Mode (DTM) capable mobile station (MS) is in dedicatedmode in a DTM-capable cell, the CS connection control in the BSC (CSconnection control) and MS can use the main associated control channel(DCCH) for GPRS mobility management and session management (GMM/SM)signalling. The GMM/SM signalling messages are transmitted within GPRSINFORMATION messages (layer 3 message) using a GPRS transparent transportprotocol (GTTP). With GTTP, there is no need for a separate radio connection(that is, no temporary block flows (TBFs) are needed for the GMM/SMsignalling). Therefore, GTTP provides a fast signalling link for GMM/SMmessages.

GTTP signalling in uplink

When a DTM-capable MS is in dedicated mode in a DTM-capable cell, it can usethe GPRS INFORMATION message to send a logical link control (LLC)protocol data unit (PDU) to CS connection control on the DCCH. However, thefollowing conditions must be met:

. The LLC PDU contains upper layer signalling (that is, a GMM or SMsignalling message) or the LLC PDU is used as a cell update message.

. The length of the message in LAPDm frames is equal to or less than thevalue of the MAX_LAPD_LENGTH parameter.

The MAX_LAPD_LENGTH parameter specifies the maximum length of theGTTP message.

Uplink GTTP signalling is illustrated in figure GTTP signalling procedure inuplink.



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GTTP signalling

Figure 4. GTTP signalling procedure in uplink

1. The MS in dedicated mode sends a GPRS INFORMATION message toCS connection control.

The GPRS INFORMATION message contains the temporary logical linkidentity (TLLI) of the MS and the LLC PDU that contains the GPRSsignalling message.

2. CS connection control sends the TLLI and LLC PDU to the PCU.

3. The PCU sends the LLC PDU to the SGSN.

GTTP signalling in downlink

When the PCU receives a downlink LLC PDU for a DTM-capable MS that has aCS connection in the cell without ongoing TBFs, the PCU can use GTTPsignalling to transmit the LLC PDU to the MS. However, the followingconditions must be met:

. The downlink LLC PDU contains a signalling message.

This is indicated by the T bit in the QoS Profile information element (IE) inthe BSSGP DL UNITDATA PDU.

. The length of the message in the LAPDm frames is equal to or less than thevalue of the MAX_LAPD_LENGTH parameter.

Downlink GTTP signalling is illustrated in figure GTTP signalling procedure indownlink.

GPRS INFORMATION

TLLI, LLC PDU

LLC PDU

SGSNPCUCS connection

control in the BSCBTSMS




Figure 5. GTTP signalling procedure in downlink

1. The SGSN sends the LLC PDU to the PCU.

2. The PCU checks from the international mobile subscriber identity (IMSI)record whether the MS is in dedicated state.

Because of IMSI co-ordination, the PCU is always aware of which DTM-capable MSs are in dedicated state.

3. The PCU forwards the LLC PDU to CS connection control.

4. CS connection control uses the GPRS INFORMATION message to sendthe LLC PDU to the MS on the main DCCH.


GPRS INFORMATION

LLC PDU

PCUBTSMS SGSN

LLC PDU

CS connectioncontrol in the BSC

IMSIrecord check



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GTTP signalling

7 Radio resource management

The BSC reserves radio resources for a Dual Transfer Mode (DTM) call from thepacket-switched (PS) territory. This makes it possible to multiplex DTMtemporary block flows (TBFs) and normal TBFs on the same timeslots.

7.1 DTM channel allocation

When a DTM call is to be allocated for a mobile station (MS), the DTM circuit-switched (CS) connection is allocated close to the PS territory border, if possible.If the DTM-capable MS supports DTM multislot class 5 or 9, the PS timeslotfurthest from the CS-PS territory border is selected for the DTM CS connection.If the DTM-capable MS supports DTM multislot class 11, the PS timeslot secondfurthest from the CS PS territory border is selected for the DTM CS connection.

However, if there are DTM PS allocations for other MSs close to the PS territoryborder, the DTM CS connection is allocated to a timeslot that has no DTM PSallocations, if possible. If such a timeslot cannot be found, a timeslot with a DTMPS allocation is considered.

Once a suitable timeslot for the DTM CS connection has been found, the DTMPS resources are reserved for the DTM call so that the DTM CS timeslot and theDTM PS timeslots form a collective allocation configuration that the DTM-capable MS can manage within its multislot capability. For more information, seeDTM multislot classes.

If there are several alternatives for a DTM allocation, a DTM allocation thatavoids the fragmentation of the PS resources and gives optimal resources for thePS part of the DTM allocation is preferred.

Once a suitable DTM allocation has been found, the PCU tries to search for newresources for the PS allocations that are currently using the timeslot selected forthe DTM CS connection. If the PCU finds new resources for all affected PSallocations, the DTM allocation is accepted. If not, the DTM allocation isrejected.



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Radio resource management

7.2 DTM multislot classes

The BSC supports DTM multislot classes 5, 9, and 11. The multislot capability ofan MS is indicated as a part of the radio access capability information of the MS.

The BSC supports dynamic allocation (DA) and extended dynamic allocation(EDA) modes for uplink TBFs that operate in dual transfer mode. In EDA mode,it is possible to allocate two PS timeslots in the uplink direction for a DTMmultislot class 11 MS. In DA mode, it is possible to allocate only one PS timeslotin the uplink direction in dual transfer mode. Figure DTM multislot allocationsillustrates how PS and CS resources can be allocated for multislot classes 5, 9,and 11. The PS and CS resources must be in consecutive timeslots.

Figure 6. DTM multislot allocations

7.3 Fragmentation of the PS resources

A DTM call within the PS territory causes the fragmentation of the PS resourcesif the timeslots configured for PS services become scattered because of the DTMCS resource reservation. If the timeslots configured for PS services are no longerconsecutive, it is more difficult to make multislot PS allocations for other users.

CS

Downlink radio timeslots:

Uplink radio timeslots:

DTM class 5,9,112+2=4 DA

DTM class 5,9,112+2=4 DA

DTM class 9,113+2=5 DA

DTM class 9,113+2=5 DA

DTM class 112+3=5 EDA

0 1 2 3 4 75 6

0 1 2 3 4 75 6

PS

PS CS

CSPS

CS PS

CS PS

PS PS CS

PS CS

PS CS PS

PSCS

PS CS

PS




This is because the timeslots that belong to a multislot PS allocation must besubsequent. Therefore, the timeslots that avoid the fragmentation of the PSresources are preferred over the other timeslots in the DTM channel allocationprocedure.

Sometimes, a trade-off situation may occur. For example, DTM allocationcandidate A that increases the fragmentation of the PS resources may give morecapacity to the DTM PS connection than DTM allocation candidate B that doesnot increase the fragmentation of the PS resources. This kind of a situation can bebalanced with the DTM fragmentation penalty parameter.

The DTM fragmentation penalty parameter specifies the fragmentationpenalty that is used in the DTM channel allocation algorithm if a configurationthat gives the highest capacity for the DTM-capable MS must be found. Thishappens if there are DTM PS allocations for other MSs near the end of the PSterritory.

The capacity of a DTM PS allocation is estimated in terms of radio timeslots. Thefragmentation penalty is subtracted from the estimated capacity value if the DTMallocation would increase the fragmentation of the PS resources.

Example 1.

Figure DTM allocation example illustrates the use of the DTMfragmentation penalty parameter.

Figure 7. DTM allocation example

TSL-0 TSL-1 TSL-2 TSL-3 TSL-4 TSL-5 TSL-6 TSL-7

existingTBF

DTM allocation candidate A:

DTM allocation candidate B:

PS timeslot share:

PS timeslot share: 100%

50% 100%

DTM PS DTM CS DTM PS

DTM CSDTM PS

CS

PS



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DTM allocation candidate A contains two DTM PS timeslots. We assume that theDTM-capable MS gets a 50% share of the first PS timeslot (the other 50% isgiven to another PS connection) and a 100% share of the second PS timeslot. Wealso assume that DTM allocation candidate A increases the fragmentation of thePS resources and that the DTM fragmentation penalty parameter has avalue of 0.3. The capacity of DTM allocation A is therefore 1.2 timeslots (0.5 +1.0 - 0.3 = 1.2).

DTM allocation candidate B contains one DTM PS timeslot. We assume that theDTM-capable MS gets a 100% share of that PS timeslot. We also assume thatDTM allocation candidate B does not increase the fragmentation of the PSresources. The capacity of the DTM allocation B is therefore 1.0 timeslots.

In this example, DTM allocation candidate A is selected for the DTM call. This isbecause the capacity of DTM allocation candidate A is larger than the capacity ofDTM allocation candidate B. However, had the DTM fragmentationpenalty parameter had a larger value, for example 0.6, then DTM allocationcandidate B would have been selected instead.

The DTM fragmentation penalty parameter can have values between 0and 1. Value 0 means that a DTM allocation that does not increase thefragmentation of the PS resources is not preferred over a DTM allocation thatincreases the fragmentation of the PS resources. Value 1 means that a DTMallocation that does not increase the fragmentation of the PS resources is selectedinstead of a DTM allocation that increases the fragmentation of the PS resources.However, if the latter one provides one timeslot more capacity than the formerone, the latter one is selected.

7.4 Territory management

The PCU allocates radio resources for DTM calls from the PS territory. Thismakes it possible to share the PS resources between DTM PS connections andnormal PS connections.

It is not necessary to increase PS capacity when DTM is introduced in thenetwork. However, when DTM is in use and the size of the PS territory isdetermined, all timeslots within the PS territory must be taken into account. Thismeans timeslots configured for PS use and timeslots configured for DTM CS use.It is advisable to have at least two default channels in the PS territory.




Territory upgrade

The CS connection control in the BSC (CS connection control) initiates aterritory upgrade if the number of timeslots configured for PS use in the PSterritory drops below the dedicated (E)GPRS capacity because of the made DTMallocations.

The PCU requests a territory upgrade in the following cases:

. If the PS territory is, by default, too small for a DTM allocation (it containsonly one PS timeslot) during an ongoing DTM call establishment.

If the PS territory is too small for a DTM allocation, CS connection controldelays the DTM call establishment for a short period of time and initiates aterritory upgrade procedure, if possible. After a short while, as the upgradeis expected to have finished, CS connection control continues with thepending DTM call establishment.

. The load on the timeslots configured for PS use increases over the currentthresholds.

When the PS load is determined, only the timeslots configured for PS useare taken into account. The DTM CS timeslots are not considered.

Territory downgrade

The PCU requests a territory downgrade in the following case:

. The load of the timeslots configured for PS use drops below the currentthresholds and the size of the PS territory is larger than the size of thedefault PS territory.

The PCU ensures that the number of the timeslots configured for PS usedoes not drop below the dedicated (E)GPRS capacity.

CS connection control triggers a territory downgrade if the CS load increases.

Timeslot types in the PS territory

A DTM CS timeslot is seen as part of the PS territory when the size of theterritory is determined. However, only a timeslot configured for PS use can beinterpreted as a dedicated (E)GPRS timeslot. The PCU interprets a timeslot with aDTM CS connection as a default (E)GPRS timeslot or as an additional GPRStimeslot but never as a dedicated (E)GPRS timeslot.




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8 Dual Transfer Mode call establishment

8.1 Mobile-originated call establishment

A Dual Transfer Mode (DTM) capable mobile station (MS) can request a DTMcall when it has a circuit-switched (CS) connection in a DTM-capable cell. TheMS requests a DTM call by sending a DTM REQUEST message to the CSconnection control in the BSC (CS connection control). If the MS has a CS trafficchannel (TCH), the DTM REQUEST message is sent on the fast associatedcontrol channel (FACCH). Otherwise, the DTM REQUEST message is sent onthe stand-alone dedicated control channel (SDCCH).

When CS connection control receives a DTM request from a DTM-capable MS,it establishes, with the PCU, a mobile-originated (MO) DTM call for the MS ifthe following conditions are met:

. The DTM MS has a TCH allocated for a CS speech call.

. The international mobile subscriber identity (IMSI) of the MS is known.

. The DTM request is received from the normal area (that is, not theextended area) of the cell.

. The PCU can find suitable radio resources for the DTM call.

The MO DTM call establishment procedure is illustrated in figure MO callestablishment.



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Dual Transfer Mode call establishment

Figure 8. MO call establishment

1. The MS sends a DTM REQUEST message to CS connection control onthe FACCH.

The message contains the temporary logical link identity (TLLI) of the MSand a channel request description.

2. CS connection control forwards the DTM resource request to the PCU.

3. The PCU performs admission control (AC) for the DTM call.

4. The PCU allocates radio resources for the DTM call by using the DTM-specific channel allocation function.

5. The PCU establishes an uplink temporary block flow (TBF) for the MS indual transfer mode.

PCUBTSMS

DTM resource request

DTM REQUEST

Reply to DTMresource request

DTM ASSIGNMENT COMMAND

ASSIGNMENT COMPLETE

Information that the MS hasmoved to the new resources

PS data sending indual transfer mode

AC and radio resourceallocation for the DTM call

Uplink RLC blockscheduling

CS connectioncontrol in the BSC




The TBF is in EGPRS mode if the MS supports EGPRS and if the DTMallocation is made into a PS territory that supports EGPRS. If not, the TBFis in GPRS mode.

6. The PCU sends a reply to the DTM resource request to CS connectioncontrol.

The message contains information on the DTM allocation (CS resourceand TBF allocation).

7. CS connection control sends a DTM ASSIGNMENT COMMANDmessage to the MS on the FACCH.

The message contains the DTM call assignment (new CS resource anduplink TBF assignment).

8. The MS moves to the assigned resources and sends an ASSIGNMENTCOMPLETE message to CS connection control on the FACCH.

9. CS connection control informs the PCU when the MS has moved to thenew resources.

10. The PCU starts to schedule uplink radio link control (RLC) blocks (that is,uplink state flags) for the MS on the timeslots that belong to the uplinkTBF allocation.

11. The MS sends PS data on the assigned resources in dual transfer mode.

Exceptions in MO call establishment

An MS requests for PS resources on the SDCCH

If a DTM-capable MS sends a DTM REQUEST message on the SDCCH beforea traffic channel assignment, CS connection control does not establish a DTMcall but sends a DTM REJECT message to the MS and continues the CS callestablishment as usual. This is because it is not possible to have a DTM call thatconsists of a DTM PS connection and a SDCCH connection.

The DTM REJECT message contains a Wait Indication IE that determines howlong the MS must wait before it can make a new attempt for packet access in thesame cell. The wait indication time used on the SDCCH channel is two seconds.

8.2 Mobile-terminated call establishment

When the PCU receives a downlink logical link control (LLC) protocol data unit(PDU) for a DTM-capable MS that is in dedicated mode in a DTM-capable cell, itinitiates a mobile-terminated (MT) DTM call establishment for the MS. The MTDTM call is established if the following conditions are met:



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. The MS has a TCH allocated for a CS speech call.

. The IMSI of the MS is known.

. The MS is in the normal area (that is, not the extended area) of the cell.

. The PCU can find suitable radio resources for the DTM call.

The MT DTM call establishment procedure is illustrated in figure MT DTM callestablishment.

Figure 9. MT DTM call establishment

AC and radio resourceallocation for the DTM call

LLC PDU

IMSI record check

MT DTM call initiation

TBF in dual transfer mode

DTM allocation information

Information that the MS hasmoved to the new resources

Downlink RLCblock scheduling

PS data receiving indual transfer mode

PCUCS connection

control in the BSCBTSMS SGSN

DTM ASSIGNMENT COMMAND

ASSIGNMENT COMPLETE




1. The SGSN sends the PCU a downlink LLC PDU, addressed to an MS. ThePCU does not have a resource reservation for the MS.

The received MS RAC IE indicates that the MS supports DTM.

2. The PCU checks from the IMSI record whether the MS is in dedicatedstate.

Because of IMSI co-ordination, the PCU is always aware of which DTMMSs are in dedicated state.

3. As the MS is in dedicated mode, the PCU initiates an MT DTM callestablishment procedure for the MS.

4. The PCU performs AC for the DTM call.

5. The PCU allocates radio resources for the DTM call by using the DTMspecific channel allocation function.

6. The PCU establishes a downlink TBF for the MS in dual transfer mode.

The TBF is in EGPRS mode if the MS supports EGPRS and if the DTMallocation is made into a PS territory that supports EGPRS. If not, the TBFis in GPRS mode.

7. The PCU informs CS connection control about the DTM allocation (CSresource and TBF allocation).

8. CS connection control sends a DTM ASSIGNMENT COMMANDmessage to the MS on the DCCH.

The message contains the DTM call assignment (new CS resource anddownlink TBF assignment).

9. The MS moves to the assigned resources and sends an ASSIGNMENTCOMPLETE message to the network on the FACCH.


11. The PCU starts to schedule downlink RLC blocks for the MS on thetimeslots that belong to the downlink TBF allocation.

12. The MS receives PS data on the assigned resources in dual transfer mode.




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9 Handover control

9.1 Intra-cell handover

In an intra-cell handover, the CS connection control in the BSC (CS connectioncontrol) moves the Dual Transfer Mode (DTM) call to other timeslots within thecell. Both CS connection control and the PCU can trigger an intra-cell handover.

CS connection control may initiate an intra-cell handover if the DTM circuit-switched (CS) connection needs to be moved to another timeslot because ofquality reasons.

The PCU may initiate an intra-cell handover when the following procedurestrigger a DTM reallocation procedure:

. territory downgrade

. PS quality control

. DTM PS resource management

The intra-cell handover procedure consists of the following steps. Except for thefirst step, the procedure is identical for a CS-connection-control-initiated and aPCU-initiated intra-cell handover.

1. CS connection control requests new resources for the DTM call from thePCU.

This step only applies to a CS-connection-control-initiated intra-cellhandover.

2. The PCU determines a new DTM allocation for the MS.

3. Once the PCU has found new resources for the DTM call, it stopsscheduling the packet-switched (PS) resources that belong to the old DTMallocation and informs CS connection control about the new DTMallocation.



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Handover control

4. CS connection control sends a DTM ASSIGNMENT COMMANDmessage to the MS on the associated control channel (DCCH).

The message contains the new CS resource and a reassignment for theongoing temporary block flows (TBFs).

5. The MS moves to the assigned resources and sends an ASSIGNMENTCOMPLETE message to the network on the fast associated controlchannel (FACCH).


7. The PCU resumes the uplink state flag (USF) and/or radio link control(RLC) block scheduling for the MS on the new PS resources.

8. The MS continues the DTM call on the new resources.

An intra-cell handover is performed for the CS connection also when the MS ismoved from the CS territory to the PS territory in DTM call establishment.

The following intra-cell handovers are not allowed for DTM calls:

. handovers between regular and super re-used TRXs

. load-based handover between the BTSs in the segment

9.2 Inter-cell handover

CS connection control handles the handover procedure for DTM calls. Therefore,the PCU does not apply the network controlled cell re-selection (NCCR) ornetwork assisted cell change (NACC) procedures for a DTM-capable MS whenit is in dedicated mode. The PCU may, however, request an inter-cell handoverfor a DTM call in the following cases:

. PS quality control triggers a cell change for the DTM PS connection.

. MT DTM call establishment fails because of lack of resources.

When CS connection control performs an inter-cell handover for a DTM-capableMS, it favours cells that support DTM to provide and maintain the DTM servicefor the MS. This means that CS connection control must know whether theadjacent cell supports DTM. This information is provided by the adjacent cellparameter DTM enabled. When an inter-cell handover is triggered, CSconnection control searches the neighbour cells for DTM support. The adjacentcells in which the DTM enabled parameter is enabled and which are notoverloaded or have a smaller load than the serving cell, are put on top of the




candidate cell list. This preference for DTM-capable adjacent cells overrides thepreference rules that are normally followed, that is, the value of the TCH inhandover parameter that defines the traffic channel allocation in intra-BSCinter-cell handovers.

CS connection control triggers an inter-cell handover for a DTM CS connectionby applying existing handover algorithms. In the handover, the CS connection ismoved to the CS territory of the target cell and the DTM call in the source cell isreleased. After the handover has been completed, CS connection control sends aDTM INFORMATION message to the MS on the DCCH if the target cellsupports DTM. The DTM call is then re-established in the target cell.

For more information on existing handover algorithms, see RF Power Controland Handover Algorithm.

The following inter-cell handovers are not allowed for DTM calls:

. MSC-controlled traffic reason handover

. BSC-initiated traffic reason handover

. umbrella handover

. inter-cell direct access

. intelligent underlay overlay (IUO) to a child cell

MO DTM call establishment or DTM call reallocation fails because of lack ofresources

If an MO DTM call establishment or a DTM call reallocation fails because of lackof resources in the PCU, CS connection control searches for another DTM-capable cell in which the DTM call can be established or re-established. CSconnection control performs a handover to another DTM capable cell whenEquation 1 is true.

EQUATION 1

AV_RXLEV_NCELL(n) > RxLevMinCell(n) + MAX(0, Pa)

AND

PBGT(n) > dtmPowerBudgetMargin(n)

where

Pa = (MsTxPwrMaxGSM(ADJ)(n) - P) or (MsTxPwrMaxGSM1x00(ADJ)(n) - P)

P = Maximum power of an MS

A power budget (PBGT) handover back to the source cell is allowed for the samecall after a guard time of 255 seconds.



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Handover control

If an inter-cell handover, triggered by an unsuccessful MO DTM callestablishment attempt, cannot be performed, or if the handover does not succeed,CS connection control rejects the DTM call request.

If an inter-cell handover, triggered by an unsuccessful DTM CS call reallocationattempt, cannot be performed, or if the handover does not succeed, CS connectioncontrol releases the DTM call by performing an intra-cell handover from the PSterritory to the CS territory of the cell.

DTM PS connection reallocation caused by PCU quality control

When the PCU requests an inter-cell handover for a DTM PS connection becauseof quality reasons, CS connection control searches for another DTM-capable cellin which the DTM call can be re-established. CS connection control performs ahandover for a DTM CS connection when Equation 1 is true.

A PBGT handover back to the source cell is allowed for the same call after aguard time of 255 seconds.

Inter-cell handover from a non-DTM-capable cell to a DTM-capable cell

When a DTM-capable MS has a CS call in a non-DTM-capable cell, CSconnection control can move the call to a DTM-capable cell to provide the DTMservice. CS connection control performs a handover for a CS connection whenEquation 2 is true.

EQUATION 2

AV_RXLEV_NCELL(n) > RxLevMinCell(n) + MAX(0, Pa)

AND

HoMarginPBGT(n) > PBGT(n) > dtmPowerBudgetMargin(n)

where

Pa = (MsTxPwrMaxGSM(ADJ)(n) - P) or (MsTxPwrMaxGSM1x00(ADJ)(n) - P)

P = Maximum power of an MS

When the handover is a BSC internal inter-cell handover, a PBGT handover backto the source cell is allowed for the same CS connection when both the PBGThandover equation (for details on the PBGT handover equation, see Target cellevaluation according to radio criteria in RF Power Control and HandoverAlgorithm ) and Equation 3 (reversed PBGT handover equation) are true. Thereversed PBGT handover equation prevents consecutive PBGT handoversbetween the source cell and the serving cell.

EQUATION 3 (reversed PBGT handover equation)

PBGT(SERV_CELL) < dtmPowerBudgetMargin(SERV_CELL) - 2dB




where

PBGT(SERV_CELL) = (A - AV_RXLEV_NCELL(SOURCE_CELL)) -

(B - AV_RXLEV_DL_HO - (BsTxPwrMax - BS_TX_PWR))

where

A = MsTxPwrMaxGSM(ADJ)(n) or MsTxPwrMaxGSM1x00(ADJ)(n)

B = MsTxPwrMaxGSM(BTS) or MsTxPwrMaxGSM1x00(BTS)

When the handover is an external handover, a PBGT handover back to the sourcecell is allowed for the same CS connection after a guard time of 255 seconds.

Inter-cell handover for a DTM CS connection during DTM deactivation

When DTM is deactivated in a cell, CS connection control searches for anotherDTM-capable cell in which the DTM call can be re-established. CS connectioncontrol performs a handover for a DTM CS connection when Equation 1 is true.

When the handover is a BSC internal inter-cell handover, a PBGT handover backto the source cell is allowed for the same CS connection when both the PBGThandover and Equation 3 are true. For details on the PBGT handover equation,see Target cell evaluation according to radio criteria in RF Power Control andHandover Algorithm.

When the handover is an external handover, a PBGT handover back to the sourcecell is allowed for the same call after a guard time of 255 seconds.

If an inter-cell handover cannot be performed for a DTM CS connection, or if thehandover does not succeed, CS connection control releases the DTM call byperforming an intra-cell handover from the PS territory to the CS territory of thecell.

Power budget handover during a DTM call

A PBGT handover for a DTM CS connection is performed as for a normal CSconnection with one exception: the power budget value of a non-DTM-capablecell is evaluated against the dtmPowerBudgetMargin parameter instead ofthe HoMarginPBGT parameter. This makes it possible to prioritise DTM-capable cells over non-DTM-capable cells, because a higher margin can be set fornon-DTM-capable cells.



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Handover control

9.3 External handover

In an external handover, an MS with an ongoing connection moves to another cellso that the BSC changes. When an external handover is triggered, the source BSCsends a HANDOVER REQUIRED message to the MSC. The message containsthe Old BSS to New BSS information information element (IE) that is used topass field elements from the old BSS to the new BSS. For a DTM-capable MSthat has or is requesting a DTM allocation, the Old BSS to New BSS informationIE contains a Dual Transfer Mode information field.

During the external handover procedure, CS connection control performs thehandover for the CS connection as normal and releases the DTM allocation in thesource cell. After the handover has been completed (that is, when the target cellhas received the HANDOVER COMPLETE message), CS connection controlsends a DTM INFORMATION message to the MS on the main DCCH if thenew cell supports DTM and the MS had or requested a DTM call in the old cell.

9.4 Inter-system handover

In an inter-system handover, an MS connection is transferred from the GSMsystem to the wideband code division multiple access (WCDMA) system.

For more information on inter-system handover, see GSM-WCDMAInterworking.

DTM-capable MSs

When an inter-system handover is triggered for a DTM-capable MS, CSconnection control performs the handover for the CS connection as usual. If theMS had an ongoing DTM call, CS connection control releases the DTMallocation in the source cell.

The SGSN may include the Service UTRAN CCO IE in the BSSGP DLUNITDATA PDU or the CREATE BSS PFC PDU messages to control the inter-system handover procedure. The Service UTRAN CCO IE indicates whether aninter-system handover should be performed.

The Service UTRAN CCO IE contains service priority information. If the valueof the WCDMA FDD NCCR enabled parameter is Y (that is, the inter-systemnetwork-controlled cell re-selection (IS-NCCR) procedures are enabled in theBSC) and the DTM-capable MS has a CS connection, the PCU sends the receivedService UTRAN CCO information to CS connection control. If the value of the




WCDMA FDD NCCR enabled parameter is N and the DTM-capable MS has aCS connection, the PCU ignores the received Service UTRAN CCO information.If the DTM-capable MS does not have a CS connection, normal ISNCCR isperformed.

In addition to the service priority information received from the SGSN, CSconnection control receives priority information from the MSC. This means thatCS connection control can receive conflicting service handover recommendationsfrom the SGSN and the MSC. Therefore, CS connection control applies thefollowing rules to inter-system handovers:

1. If the Service Handover IE received from the MSC states that CSconnection control must not perform an inter-system handover for the MS,CS connection control does not initiate an inter-system handover for theMS in question.

2. If the MSC does not forbid an inter-system handover for the MS, CSconnection control bases the inter-system handover decision on the servicepriority information received from the SGSN.

3. If CS connection control has not received any service priority informationfrom the SGSN, it bases all inter-system handover decisions on theinformation included in the Service Handover IE it received from theMSC.

4. If neither the SGSN nor the MSC has sent any service priority informationto CS connection control or if CS connection control did not recognise thereceived information, CS connection control performs an inter-systemhandover as usual, based on load and signal level thresholds.

For more information on inter-system handover, see GSM-WCDMAInterworking.

Non-DTM-capable MSs

CS connection control initiates an inter-system handover to a non-DTM-capableMS as soon as at least one WCDMA radio access network (RAN) cell isavailable and the following conditions are met:

. The MS supports WCDMA.

. The MS has a normal CS call.

. The value of the ISHO_SUPPORT_IN_BSC parameter is TRUE.

. The value of the ISHO preferred for non-DTM MS parameter isTRUE.



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Handover control

Note that when the value of the ISHO preferred for non-DTM MSparameter is FALSE, normal inter-system handover (ISHO) is performed.When the value is TRUE, the non-DTM-capable MS is moved to anavailable WCDMA cell as soon as possible. If the value of theISHO_SUPPORT_IN_BSC parameter is FALSE, ISHO is not triggeredregardless of the value of the ISHO preferred for non-DTM MSparameter.





10 Dual Transfer Mode call release

A Dual Transfer Mode (DTM) call is released when an inter-cell handover isperformed for the circuit-switched (CS) connection or when either a CS orpacket-switched (PS) connection is released. Both the PCU and the CSconnection control in the BSC (CS connection control) can initiate a DTM callrelease.

PCU-initiated DTM call release

The PCU releases the PS resources allocated for the DTM call and informs CSconnection control that the mobile station (MS) has returned to dedicated mode.CS connection control then initiates an intra-cell handover to move the CSconnection to the CS territory.

The PCU informs CS connection control as soon as the temporary block flows(TBFs) have been released. The PCU applies similar TBF release delayprocedures to DTM TBFs that are used to normal TBFs. You can adjust thelength of the DTM TBF release delays with the following DTM-specific PRFILEparameters: DL_DTM_TBF_REL_DELAY , UL_DTM_TBF_REL_DELAY , andUL_DTM_TBF_RELDELAY_EXT.

CS-connection-control-initiated DTM call release

CS connection control initiates a DTM call release when the CS call is released orwhen an inter-cell handover is performed for the MS. In a CS-connection-control-initiated DTM call release, CS connection control informs the PCU that the DTMcall needs to be released. The PCU then releases the PS resources allocated forthe DTM call. If the DTM call is released because of a CS call release, the MSreturns to packet idle mode. After this, the PS connection can be re-established innormal (E)GPRS mode if the MS or the PCU has more data packets to send. Notethat the PCU is unable to re-establish the PS connection in normal mode until CSconnection control releases the DTM-CS resource reservation. If the DTM call isreleased because of an inter-cell handover, the MS moves to a new cell andperforms a cell update or routing area update procedure if the new cell is DTMcapable. After this, the PS connection can be re-established in dual transfer modeif the MS or the PCU has more data packets to send.




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Dual Transfer Mode call release

11 Effect of Dual Transfer Mode oninterfaces

A interface

Dual Transfer Mode (DTM) modifies the following messages:

. HANDOVER REQUEST

. HANDOVER REQUIRED

When DTM is in use, both messages include a Dual Transfer Mode informationfield in the Old BSS to New BSS information information element (IE). Inaddition, the HANDOVER REQUEST message includes an IMSI IE if the MSCknows the international mobile subscriber identity (IMSI) of the mobile station(MS).

Abis interface

DTM introduces several layer 3 messages that are transferred transparently overthe Abis interface.

Gb interface

DTM modifies the following message:

. SUSPEND PDU

Radio interface

The following messages are related to DTM. Unless otherwise stated, themessages are sent on the main associated control channel (DCCH).

. DTM ASSIGNMENT COMMAND

. DTM ASSIGNMENT FAILURE

. DTM INFORMATION

. DTM REQUEST



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Effect of Dual Transfer Mode on interfaces

. GPRS INFORMATION

. PACKET ASSIGNMENT

. PACKET NOTIFICATION

. PACKET SYSTEM INFORMATION TYPE 14

This message is sent on the packet associated control channel (PACCH).

DTM modifies the following messages:

. GPRS SUSPENSION REQUEST

. SYSTEM INFORMATION TYPE 6

. SYSTEM INFORMATION TYPE 13

Q3 interface

DTM introduces several parameters and two BTS-level measurement types thathave an effect on the Q3 interface. For more information, see User interface ofDual Transfer Mode.

BSC-BSC interface

No effect.





12 User interface of Dual Transfer ModeParameters

The following BSC radio network object parameters are related to Dual TransferMode (DTM):

. DTM fragmentation penalty

. DTM PFC packet flow timer

. ISHO preferred for non-DTM MS

The following SEG-specific BTS radio network object parameter is related toDTM:

. DTM enabled

The following adjacent GSM (ADJC) radio network object parameters are relatedto DTM:

. DTM enabled

. DTM power budget margin

The following PRFILE parameters are related to DTM:

. DL_DTM_TBF_REL_DELAY

. DTM_CALL_ASSIGN_TIMER

. DTM_CALL_PENALTY_TIMER

. DTM_MS_CL_11_SUPPORT_EDA

. MAX_LAPD_LENGHT

. UL_DTM_TBF_REL_DELAY

. UL_DTM_TBF_RELDELAY_EXT



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User interface of Dual Transfer Mode

For more information on radio network parameters, see BSS Radio NetworkParameter Dictionary.

For more information on PRFILE parameters, see PRFILE and FIFILEParameter List.

MMLs

Base Station Controller Parameter Handling in BSC (EE )

The following MML commands are used to handle DTM:

. EEJ

. EEO

Base Transceiver Station Handling in BSC (EQ )


. EQO

. EQV

Adjacent Cell Handling (EA )


. EAC

. EAM

. EAO

Transceiver Handling (ER )

The following MML command is used to handle DTM:

. ERO

GSM Measurement Handling (TP )


. TPE

. TPI




. TPM

. TPS

Parameter Handling (WO )


. WOC

. WOI

Counters

The following measurement types are introduced with DTM:

. 105 PS DTM Measurement

. 106 CS DTM Measurement

DTM also modifies the following measurements:

. 1 Traffic Measurement

. 4 Handover Measurement

. 50 BSC Level Clear Code Measurement

. 51 BSC Level Clear Code (PM) Measurement

. 71 MS Capability Indication Measurement

. 72 Packet Control Unit Measurement

. 79 Coding Scheme Measurement

Alarms

DTM modifies the description of alarm 7725 TRAFFIC CHANNELACTIVATION FAILURE.




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User interface of Dual Transfer Mode

40356034 Dual Transfer Mode

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