Content for TS 23.272 Word version: 19.0.0

1… 4… 5… 5.4… 6… 6.3 6.4… 7… 7.3 7.4… 7.5a… 8… 8.2.4a… 8.3… 8.4… B… B.2… B.2.2… B.2.3a… B.2.3a.4… B.2.4… B.3… C… C.8…

B.1 Overall Description B.1.1 General Considerations B.1.2 Reference Architecture B.1.3 Functional entities B.1.4 Co-existence with IMS services B.1.5 CSFB Priority Call Handling
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B (Normative) CS Fallback to 1xRTT p. 71

This annex describes a CS Fallback to 1xRTT and an SMS solution for dual mode 1xRTT/E-UTRAN terminals.

CS Fallback to 1xRTT is supported for UEs with both single Rx and dual Rx configuration (see TS 36.331). UEs with single Rx configuration are not able to camp in 1xRTT when they are active in E-UTRAN. The network therefore provides mechanisms for the UE to perform registration to 1xRTT, receive 1xRTT paging, SMS etc. while the UE is in E-UTRAN. UEs with dual Rx configuration can camp in 1xRTT while they are active in E-UTRAN, they may however not be able to stay in E-UTRAN when they handle a CS call and/or perform registration signalling, and/or sending or receiving SMS in 1xRTT.

Clause B.1 and Clause B.2 describes the architecture and procedures for CS Fallback (and enhanced CS Fallback) to 1xRTT when the UE has single Rx, dual Rx, or dual Rx/Tx configuration. In this scenario the network need to support the S102 interface between the MME and 1xCS system in order to support CS Fallback (this is indicated by the presence of CSFB registration parameters on E-UTRAN broadcast channel, TS 36.331).

Clause B.3 describes the procedures for CS Fallback when the UE has dual Rx configuration. In this scenario the network needs to support the Extended Service Request procedure in order to support CS Fallback (this is indicated by either the presence of CSFB registration parameters or indication of support for dual rx CSFB on E-UTRAN broadcast channel, TS 36.331).

If the UE has a dual Rx configuration and indicates support for enhanced CS fallback to 1xRTT in the UE radio capabilities, the principles and procedures in Clause B.1 and Clause B.2 are followed when the network indicates support for S102.

B.1 Overall Description p. 71

B.1.1 General Considerations p. 71

The CS fallback for 1xRTT in EPS enables the delivery of CS-domain services (e.g. CS voice) by reuse of the 1xCS infrastructure when the UE is served by E-UTRAN. A CS fallback enabled terminal, while connected to E-UTRAN may register in the 1x RTT CS domain in order to be able to use 1xRTT access to establish one or more CS services in the CS domain. The CS Fallback function is only available where E-UTRAN coverage overlaps with 1xRTT coverage.

This specification also specifies the architecture required for SMS over S102 in EPS. The MO SMS and MT SMS are tunnelled in EPS and over S102 and do not cause any CS Fallback to CDMA 1xRTT, and consequently does not require any overlapped CDMA 1xRTT coverage.

CS Fallback to 1xRTT and IMS-based services shall be able to co-exist in the same operator's network.

CS Fallback to 1xRTT with PS Handover procedure to HRPD access for Optimised HO, non-Optimised HO, and Optimised Idle mode mobility as defined in TS 23.402 shall be able to co-exist in the same operator's network.

B.1.2 Reference Architecture p. 71

The CS fallback to 1xRTT and SMS over S102 in EPS function is realised by reusing the S102 reference point between the MME and the 1xCS IWS. The reference architecture described in Figure B.1.2-1 is similar to the SRVCC architecture for E-UTRAN to 3GPP2 1xCS described in TS 23.216, with the additional aspect that the S102 session is long-lived (similar to pre-registration for S101).

Copy of original 3GPP image for 3GPP TS 23.272, Fig. B.1.2-1: Reference architecture for CS fallback to 1xRTT CS

Figure B.1.2-1: Reference architecture for CS fallback to 1xRTT CS
(⇒ copy of original 3GPP image)

Reference architecture for PS handover procedure between E-UTRAN and HRPD access is defined in TS 23.402.

B.1.2.1 Reference points p. 72

S102:

It is the reference point between the MME and the 1xCS IWS. The S102 reference point provides a tunnel between MME and 3GPP2 1xCS IWS to relay 3GPP2 1xCS signalling messages. 1x CS signalling messages are those messages that are defined for A21 interface as described in 3GPP2 A.S0008-C [16] and 3GPP2 A.S0009 [17].

B.1.3 Functional entities p. 72

B.1.3.1 UE p. 72

The UE capable of CS fallback to 1xRTT and SMS over S102 supports access to E-UTRAN/EPC as well as access to the 1xCS domain over 1xRTT. It supports the following additional functions:

1xRTT CS registration over the EPS after the UE has completed the E-UTRAN attachment;
1xRTT CS re-registration due to mobility;
CS fallback procedures specified for 1xRTT CS domain voice service;
Procedures for mobile originated and mobile terminated SMS tunnelled over EPS and S102;
Includes enhanced CS fallback to 1xRTT capability indication as part of the UE radio capabilities;
Includes concurrent 1xRTT and HRPD capability indication as part of the UE radio capabilities if supported by the enhanced CS fallback to 1xRTT capable UE.

If the UE is service user with subscription to CS domain priority service, the UE's USIM belongs to one of the special Access Classes as specified in TS 22.011 and the UE shall set the RRC establishment cause to "HighPriorityAccess" as specified in TS 36.331.

B.1.3.2 MME p. 72

The MME enabled for CS fallback to 1xRTT supports the following additional functions:

It serves as a signalling tunnelling end point towards the 3GPP2 1xCS IWS via S102 interface for sending/receiving encapsulated 3GPP2 1xCS signalling messages to/from the UE, which are encapsulated in S1-MME S1 Information Transfer messages, as defined in TR 36.938;
1xCS-IWS (terminating S102 reference point) selection for CSFB procedures;
Handling of S102 tunnel redirection in case of MME relocation;
Buffering of messages received via S102 for UEs in idle state.

If the network supports CSFB priority call handling, the MME supports the following additional functions:

For page message received on the S102 interface with priority indication, the MME provides preferential treatment to this message and also the subsequent CS fallback procedure compared to other normal transactions. If UE needs to be paged, the MME sets priority indication on the paging request to eNodeB. The MME also sets priority indication, i.e. "CSFB High Priority", in S1AP message to the eNodeB, so that eNodeB may initiate the CSFB procedure with priority, as specified in TS 36.413.
For a CSFB request from service user, the MME determines that the CSFB request need priority handling based on the UE's EPS subscription information. The MME in congestion situation provides preferential treatment to this request and also sets priority indication, i.e. "CSFB High Priority", in S1AP message to eNodeB to initiate CSFB procedure, as specified in TS 36.413.

B.1.3.3 E-UTRAN p. 73

The E-UTRAN enabled for CS fallback to 1xRTT supports the following additional functions:

Provision of control information that causes the UE to trigger 1xCS registration;
Forwarding 1x RTT CS paging request to the UE;
Forwarding 1x RTT CS related messages between MME and UE;
Release of E-UTRAN resources after UE leaves E-UTRAN coverage subsequent to a page for CS fallback to 1xRTT CS if PS handover procedure is not performed in conjunction with 1xCS fallback;
Invoking the optimised or non-optimised PS handover procedure concurrently with enhanced 1xCS fallback procedure when supported by the network and UE, and based on network configuration.

If the network supports CSFB priority call handling, the E-UTRAN supports the following additional functions:

For page message received on S1AP with priority indication, the E-UTRAN should provide preferential treatment to this request compared to other normal paging requests.
For CS fallback S1AP message with priority indication and if the UE is idle, the E-UTRAN should provide preferential treatment in allocating E-UTRAN radio bearer resources compared to other normal resource requests. Also, E-UTRAN shall not trigger enhanced 1xCSFB with concurrent optimized PS handover to HRPD access.

B.1.4 Co-existence with IMS services p. 73

Clause 4.5 of this specification also applies here.

B.1.5 CSFB Priority Call Handling |R10| p. 73

Priority call handling support for CSFB ensures that end-to-end priority handling is provided for both mobile originated CSFB calls by a service user in E-UTRAN and for mobile terminated CSFB call from a service user to a normal or service user in E-UTRAN. A service user's EPS subscription information contains an indication of the users 1xRTT CS domain priority status, i.e. a MPS CS priority. If the UE is subscribed to CS domain priority, the UE's USIM shall belong to one of special Access Classes as specified in TS 22.011.

For mobile terminated CS fallback calls from a service user, the 1x MSC via the 1xCS IWS provides a priority indication to the MME along with a page message. The MME shall set a priority indication to the eNodeB when requesting the eNodeB to page the UE if the UE is idle. If the MME, while waiting for a UE response to the paging request sent without priority indication, receives a message with priority indication from the 1xCS MSC via 1xCS IWS, the MME should send another paging request with priority indication. For mobile originated CS fallback calls from a service user in E-UTRAN, the MME determines that the CSFB requires priority handling based on the MPS CS priority in the UE's EPS subscription. For both mobile originated and mobile terminated CSFB, the MME shall also provide priority indication, i.e. "CSFB High Priority", when requesting the eNodeB to execute the CSFB priority procedure. The eNodeB should handle the page message with priority and also prioritize the subsequent CS fallback procedure to 1xRTT as specified in TS 36.413.