Content for TS 23.040 Word version: 17.3.0

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K.1 General K.2 Support for SMS when UE is registered to both 5GS and EPS

K (Normative) SMS in 5GS |R15| p. 212

K.1 General p. 212

A 5GS network delivers short message services over 5GS NAS signalling.

For the architecture and the definition of reference points for SMS in 5GS see clause 4.4.2 of TS 23.501.

Between the architecture and the reference points for SMS in 5GS and the architecture and the reference points shown in clause 4.1, in Figure 5 of the present specification, the following mapping is used:

Table K.1: Mapping between architecture and reference points for SMS in 5GS and the present specification

	SMS in 5GS	present specification
Network entities	UDM	HSS/HLR
	SMSF	MSC + VLR
	UE	MS
	AMF	MME (NOTE 1)
Reference points	N20/Namf/Nsmsf	(not shown in Figure 5)
	N21/Nsmsf	(not shown in Figure 5)
	N8/Nudm	(not shown in Figure 5)
	Not shown in TS 23.501 (NOTE 3)	2
	Not shown in TS 23.501 (NOTE 2)	3
	(not applicable)	4
	N1	5
	(not applicable)	6
NOTE 1: In Figure 5, the MME is only acting as a relay for SMS transfer via the SGs. NOTE 2: Reference point 3 is used between the SMSF and SMS-GMSC/IWMSC and SMS Router. NOTE 3: Reference point 2 or S6c is used between the UDM and SMS-GMSC/SMS Router. With reference point 2, the UDM and the SMS-GMSC/SMS Router use MAP as defined in TS 29.002 between HLR and SMS-GMSC/SMS Router or use HTTP/2 as defined in TS 23.540 between UDM and SMS-GMSC/SMS Router. With reference point S6c, the UDM and the SMS-GMSC/SMS Router use Diameter as defined in TS 29.338 between HSS and SMS-GMSC/SMS Router.

For the purpose of supporting SMS in 5GS, the SMSF shall implement the requirements specified in the present specification for the MSC and the VLR with the following modifications:

"GSM/UMTS system" is to be replaced with "5GS".
Throughout the text and in the figures, message names, parameter names and cause values:
- "MSC" is to be replaced with "SMSF";
- "VLR" is to be replaced with "SMSF internal subscriber register";
- "HLR" is to be replaced with "UDM/HSS/HLR";
- "MS" is to be replaced with "UE"; and
- "non GPRS" is to be replaced with "5GS".
The protocol used on reference point 2 is based on MAP as specified in TS 29.002. In addition, it optionally may be based on Diameter as specified for reference point S6c (see TS 29.338) or based on HTTP/2 as specified for Nudm and Nrouter service-based interfaces (see TS 23.540).
The protocol used on reference point 3 is based on MAP as specified in TS 29.002. In addition, it optionally may be based on Diameter as specified for reference point SGd (see TS 29.338) or based on HTTP/2 as specified for Nrouter service-based interface (see TS 23.540).
Reference point 4 is SMSF internal, and operations performed on this reference point are not standardized. In the message flows of clause 10, the SMSF replaces the combination of MSC and VLR, and messages exchanged between MSC and VLR are replaced with SMSF internal communication.

The architecture for SMS in 5GS is defined in TS 23.501 and uses the following reference points:

N1:

Reference point between the UE and the AMF.

N8:

Reference point between the UDM and the AMF.

N20:

Reference point between the AMF and the SMSF.

N21:

Reference point between SMSF and the UDM.

The following service based interfaces are used for SMS in 5GS:

Namf:

Service-based interface exhibited by AMF. Usage of Namf service operations for SMS in 5GS is defined in TS 23.502 and in TS 23.540.

Nsmsf:

Service-based interface exhibited by SMSF. Usage of Nsmsf service operations for SMS in 5GS is defined in TS 23.502.] and in TS 23.540.

Nudm:

Service-based interface exhibited by UDM. Usage of Nudm service operations for SMS in 5GS is defined in TS 23.502 and in TS 23.540.

K.2 Support for SMS when UE is registered to both 5GS and EPS p. 213

When a UE is operating in dual-registration mode as specified TS 23.501 and is registered to the network via:

MME; and
AMF;

and SMS in EPS uses SMS over SGs, the network shall deliver an MT short message either via SMS over SGs in EPS or SMS over NAS in 5GS based on local policy. In case the network determines the MT short message delivery fails, e.g. the UE is not reachable, the network may try delivering the short message via the not yet tried option for delivering the MT short message. If the network tries to deliver an MT short message via SMS over SGs in EPS and SMS over NAS in 5GS then the mobile not reachable flags specified in clause 3.2.8 of this specification are only set if MT short message delivery fails via both options.