13.1.12 Call setup from E-UTRA RRC_CONNECTED / CS fallback to GSM with PSHO / EDTM not supported / MO call

36.523-13GPPEvolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Packet Core (EPC)Part 1: Protocol conformance specificationRelease 17TSUser Equipment (UE) conformance specification

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

13.1.12.1 Test Purpose (TP)

(1)

with { UE in E-UTRA RRC_CONNECTED state }

ensure that {

when { UE is triggered by upper layers to perform a circuit switched voice call }

then { UE transmits an ULInformationTransfer message containing an EXTENDED SERVICE REQUEST message with Service Type IE set to "mobile originating CS fallback or 1xCS fallback” }

}

(2)

with { UE having transmitted an ULInformationTranfer message containing an EXTENDED SERVICE REQUEST message with Service Type IE set to "mobile originating CS fallback or 1xCS fallback” }

ensure that {

when { SS transmits a MobilityFromEUTRACommand message with handover to a GERAN cell and operating in NMO I }

then { UE handovers to GERAN cell }

}

(3)

with { UE having transmitted an ULInformationTranfer message containing an EXTENDED SERVICE REQUEST message with Service Type IE set to "mobile originating CS fallback or 1xCS fallback” and handovered to GERAN cell }

ensure that {
when { UE has handovered to GERAN cell }

then { UE establishes a MO circuit switched voice call on GERAN }

}

13.1.12.2 Conformance requirements

References: The conformance requirements covered in the present TC are specified in: TS 23.272, clauses 6.2, TS 36.331, clause 5.4.3.3.

[TS 23.272, clause 6.2]

This flow may be executed when the eNodeB knows that both the UE and the network support PS HO, in the normal case. Clause 6.6 describes the procedure when the procedure is rejected by the MME.

Figure 6.2-1: CS Call Request in E-UTRAN, Call in GERAN/UTRAN

NOTE 1: DTM is not mandatory for CS Fallback to work and is not linked to PS HO.

1a. The UE sends an Extended Service Request (CS Fallback Indicator) to MME. Extended Service Request message is encapsulated in RRC and S1‑AP messages. CS Fallback Indicator indicates MME to perform CS Fallback. The UE only transmits this request if it is attached to CS domain (with a combined EPS/IMSI Attach) and can not initiate an IMS voice session (because e.g. the UE is not IMS registered or IMS voice services are not supported by the serving IP‑CAN, home PLMN or UE).

1b. The MME sends an S1‑AP UE Context Modification Request (CS Fallback Indicator, LAI) message to eNodeB. This message indicates to the eNodeB that the UE should be moved to UTRAN/GERAN. The registered PLMN for CS domain is identified by the PLMN ID included in the LAI, which is allocated by the MME.

1c. The eNodeB shall reply with S1-AP UE Context Modification Response message.

2. The eNodeB may optionally solicit a measurement report from the UE to determine the target GERAN/UTRAN cell to which PS handover will be performed.

3a. The eNodeB triggers PS handover to a GERAN/UTRAN neighbour cell by sending a Handover Required message to the MME. The eNodeB selects the target PS handover cell considering the PLMN ID and possibly the LAC for CS domain provided by the MME in step 1b. In the following an inter-RAT handover from E-UTRAN to UTRAN or GERAN as specified in TS 23.401 [2] begins. The eNodeB indicates in the Source RNC to Target RNC Transparent container that PS handover was triggered due to CSFB. The eNodeB also indicates whether CSFB was triggered for emergency purpose. As part of this handover, the UE receives a HO from E‑UTRAN Command and tries to connect to a cell in the target RAT. The HO from E-UTRAN Command may contain a CS Fallback Indicator which indicates to UE that the handover is triggered due to a CS fallback request. If the HO from E-UTRAN Command contains a CS Fallback Indicator and the UE fails to establish connection to the target RAT, then the UE considers that CS fallback has failed. Service Request procedure is considered to be successfully completed when PS Handover procedure is completed successfully.

NOTE 2: During the PS HO the SGSN does not create a Gs association with the MSC/VLR.

NOTE 3: Service Request procedure supervision timer shall be sufficiently long considering the optional measurement reporting at step 2.

When the UE arrives at the target cell, if the target RAT is UTRAN, the UE establishes the radio signalling connection by sending an RRC Initial Direct Transfer message as specified in TS 25.331 [7] that contains a NAS message. The CN Domain Indicator is set to "CS" in the Initial Direct Transfer message.

If the target RAT is GERAN A/Gb mode: The UE establishes a radio signalling connection by using the procedures specified in TS 44.018 [4] (i.e. UE requests and is assigned a dedicated channel where it sends a SABM containing a NAS message to the BSS and the BSS responds by sending a UA). Upon receiving the SABM (containing the NAS message) the BSS sends a COMPLETE LAYER 3 INFORMATION message (containing the NAS message) to the MSC which indicates CS resources have been allocated in the GERAN cell. If both the UE and the target cell support enhanced CS establishment in DTM (indicated by GERAN system information included within the HO from E‑UTRAN Command) a RR connection may be established while in packet transfer mode without release of the packet resources, see TS 43.055 [24]. After the establishment of the main signalling link as described in TS 44.018 [4] the UE enters either Dual Transfer Mode or Dedicated Mode.

3b. If the target RAT is GERAN and the UE has entered Dedicated Mode, the UE starts the Suspend procedure (see TS 44.018 [4]) unless both the UE and the Target cell support DTM in which case TBF re-establishment may be performed.

3c. A Gn/Gp-SGSN that receives the Suspend message from the UE follows the Suspend procedure specified in TS 23.060 [3], clause 16.2.1.1.1

An S4-SGSN that receives the Suspend message from the UE follows the Suspend procedure specified in TS 23.060 [3]. The S4-SGSN deactivates GBR bearers towards S-GW and P-GW(s) by initiating MS-and SGSN Initiated Bearer Deactivation procedure as specified in TS 23.060 [3], and starts the preservation and suspension of non-GBR bearers by sending Suspend Notification message to the S-GW. The S-GW releases all RNC related information (address and TEIDs) for the UE if Direct Tunnel is established, and sends Suspend Notification message to the P-GW(s). The SGSN stores in the UE context that UE is in suspended status. All the preserved non-GBR bearers are marked as suspended status in the S-GW and P-GW(s). The P-GW should discard packets if received for the suspended UE.

4a. If the LA of the new cell is different from the one stored in the UE, the UE shall initiate a Location Area Update or a Combined RA/LA Update procedure as follows:

– if the network is operating in NMO-I (Network Modes of Operation), the UE may initiate a separate Location Area Update before initiating the RAU procedure instead of a Combined RA/LA Update procedure (to speed up the CSFB procedure); or

– if the network is operating in NMO-II or NMO-III, the UE shall initiate a Location Area Update before initiating the RAU procedure required for PS handover.

When the UE initiates a Location Area Update the UE shall set the "follow-on request" flag in the LAU Request in order to indicate to the MSC not to release the Iu/A connection after the LAU procedure completion. Further the UE performs any Routing Area Update procedure as specified by TS 23.060 [3].

The UE may initiate a Location Area Update procedure immediately when the UE is handed over to the target cell i.e. before the UE receives e.g. LAI or NMO information as part of the RAN Mobility Information.

4b. The UE sends a CM Service Request to the MSC.

5. If the UE is not registered in the MSC serving the 2G/3G target cell or the UE is not allowed in the LA, the MSC shall reject the CM service request, if implicit location update is not performed. The CM Service Reject shall trigger the UE to perform a Location Area Update or a Combined RA/LA Update procedure as specified in TS 23.060 [3] for the different Network Modes of Operation (NMO).

6. The UE initiates the CS call establishment procedure.

7. The UE performs any remaining steps of the inter-RAT handover from E-UTRAN to UTRAN or GERAN as specified in TS 23.401 [2].

If the UE remains on UTRAN/GERAN after the CS voice call is terminated the UE performs normal mobility management procedures as defined in TS 23.060 [3] and TS 24.008 [21].

[TS 36.331, clause 5.4.3.3]

The UE shall be able to receive a MobilityFromEUTRACommand message and perform a cell change order to GERAN, even if no prior UE measurements have been performed on the target cell.

The UE shall:

1> stop timer T310, if running;

1> if the MobilityFromEUTRACommand message includes the purpose set to ‘handover‘:

2> if the targetRAT-Type is set to ‘utra‘ or ‘geran‘:

3> consider inter-RAT mobility as initiated towards the RAT indicated by the targetRAT-Type included in the MobilityFromEUTRACommand message;

3> forward the nas-SecurityParamFromEUTRA to the upper layers;

3> access the target cell indicated in the inter-RAT message in accordance with the specifications of the target RAT;

3> if the targetRAT-Type is set to ‘geran‘:

4> use the contents of systemInformation, if provided for PS Handover, as the system information to begin access on the target GERAN cell;

…

13.1.12.3 Test description

13.1.12.3.1 Pre-test conditions

System Simulator:

– 2 cells, one E-UTRA and one GERAN cell:

– Cell 1 E-UTRA serving cell

– Cell 24 suitable neighbour GERAN cell

– Cell 24 system information indicates that NMO 1 is used

– DTM is not supported on Cell 24.

– The parameters settings and power levels for Cell 1 and Cell 24 are selected according to [18], [5] so that camping on Cell 1 is guaranteed and no cell re-selection to Cell 24 can take place (GERAN priority is lower than serving and S _{Cell 1} > Thresh _{Cell 1,low}).

– System information combination 5 as defined in TS 36.508 [18] clause 4.4.3.1 is used in E-UTRA cells.

– Cell 1 and Cell 24 are in the same LA

UE:

None

Preamble:

The UE is in state Generic RB Established (state 3) according to [18].

13.1.12.3.2 Test procedure sequence

Table 13.1.12.3.2-2: Main behaviour

St	Procedure	Message Sequence		TP	Verdict
		U – S	Message
1	Cause the UE to originate CS call. (see Note 1)	–	–	–	–
2	Check: Does the UE transmit an ULInformationTranfer message containing an EXTENDED SERVICE REQUEST with Service Type IE set to "mobile originated CS fallback or 1xCS fallback” on Cell 1?	–>	ULInformationTransfer NAS: EXTENDED SERVICE REQUEST	1	P
3	The SS transmits a MobilityFromEUTRACommand message on Cell 1 with IE handover.	<–	MobilityFromEUTRACommand	–	–
4	The UE transmits a PS HANDOVER ACCESS message on Cell 24.	–>	PS HANDOVER ACCESS	2	P
5	The SS transmits a PS PHYSICAL INFORMATION message on Cell 24.	<–	PS PHYSICAL INFORMATION	–	–
6-35	Steps 3 to 32 of the generic test procedure described in TS 36.508 subclause 6.4.3.8.2 are performed on Cell 24.	–	–	3	P
–	At the end of this test procedure sequence, the UE is in end state GERAN idle (G1) according to TS 36.508.	–	–	–	–
Note 1: The trigger in step 1 is the same as in the generic procedure in 36.508 clause 6.4.3.5.

13.1.12.3.3 Specific message contents

Table 13.1.12.3.3-1: SystemInformationBlockType7 for cell 1 (preamble and all steps, Table 13.1.12.3.2-2 and Table 13.1.12.3.2-3)

Derivation Path: 36.508 Table 4.4.3.3-5
Information Element	Value/remark	Comment	Condition
SystemInformationBlockType7 ::= SEQUENCE {
carrierFreqsInfoList SEQUENCE (SIZE (1.. maxGNFG)) OF SEQUENCE {
CarrierFreqsGERAN SEQUENCE [n] {
startingARFCN	Same as cell 24
bandIndicator	Same as cell 24
followingARFCNs CHOICE {
equallySpacedARFCNs SEQUENCE {
arfcn-Spacing	Same as cell 24
numberOfFollowingARFCNs	Same as cell 24
}
}
}
commonInfo SEQUENCE {
cellReselectionPriority	3	Lower priority than E-UTRA
}
}

Table 13.1.12.3.3-2: ULInformationTransfer (step 2, Table 13.1.12.3.2-2)

Derivation Path: 36.508 Table 4.6.1-25
Information Element	Value/remark	Comment	Condition
ULInformationTransfer ::= SEQUENCE {
criticalExtensions CHOICE {
c1 CHOICE {
ulInformationTransfer-r8 SEQUENCE {
dedicatedInfoType CHOICE {
dedicatedInfoNAS	Set according to Table 13.1.12.3.3-4	EXTENDED SERVICE REQUEST
}
}
}
}
}

Table 13.1.12.3.3-3: EXTENDED SERVICE REQUEST (step 2, Table 13.1.12.3.2-2)

Derivation Path: 36.508 Table 4.7.2-14A
Information Element	Value/remark	Comment	Condition
Service type	‘0000’B	mobile originating CS fallback or 1xCS fallback

Table 13.1.12.3.3-4: Message MobilityFromEUTRACommand (step 3, Table 13.1.13.3.2-2)

Derivation Path: 36.508 clause 4.6.1-6
Information Element	Value/remark	Comment	Condition
MobilityFromEUTRACommand ::= SEQUENCE {
criticalExtensions CHOICE {
c1 CHOICE {
mobilityFromEUTRACommand-r8 SEQUENCE {
csFallbackIndicator	True
purpose CHOICE {
handover SEQUENCE {
targetRAT-Type	Geran
targetRAT-MessageContainer	PS HANDOVER COMMAND
nas-SecurityParamFromEUTRA	Not Present
systemInformation	Not present
}
}
}
}
}
}

Table 13.1.12.3.3-5: PS HANDOVER COMMAND (step 3, Table 13.1.13.3.2-2)

Derivation Path: TS 36.508 Table 4.7D.1-1

Table 13.1.12.3.3-7: GPRS SUSPENSION REQUEST (step 6, Table 13.1.12.3.2-2)

Derivation Path: 44.018 Table 9.1.13b.1
Information Element	Value/remark	Comment	Condition
Protocol discriminator	RR
Message type	‘00110100’B	GPRS SUSPENSION REQUEST
Suspension cause	‘00000110’B	DTM not supported in the cell

Table 13.1.12.3.3-8: LOCATION UPDATING ACCEPT (step 6a7, Table 13.1.12.3.2-2)

Derivation Path: TS 36.508 Table 4.7B.2-5
Information Element	Value/remark	Comment	Condition
Mobile identity	Not present

Table 13.1.12.3.3-9: ATTACH ACCEPT (Preamble)

Derivation Path: 36.508 Table 4.7.2-1
Information Element	Value/remark	Comment	Condition
EPS network feature support	Not present