5 Architecture model and reference points

23.2043GPPRelease 17Stage 2Support of Short Message Service (SMS) over generic 3GPP Internet Protocol (IP) accessTS

5.1 Reference architecture

Figure 5.1 below shows the overall architecture for providing SMS over a generic IP CAN.

Figure 5.1: Architecture for providing SMS over a generic IP-CAN

NOTE: Nodes specific to the CPM functions such as ISF are either collocated with the IP-SM-GW or else are not shown.

5.2 Reference points

5.2.1 General

The clauses below describe the needed enhancements and specific considerations to existing interfaces in order to support SMS over a generic IP-CAN.

5.2.2 C/S6c interface

The C or S6c interface allows the SMS-GMSC, using MAP or a Diameter based protocol, to obtain the address of the IP-Message-GW via mechanisms described in clause 5.3.

5.2.3 Interface between the IP-SM-GW and the HLR/HSS

The interface(s) between the IP-SM-GW and the HLR/HSS is used for:

– Supporting the registration and de-registration from the IP-SM-GW to the HLR/HSS for SMS delivery.

– Forwarding of the Send Routeing Information for Short Message requests from HLR/HSS to IP-SM-GW in order to return the address where the SM should be forwarded.

– Interrogating the HLR/HSS using Send Routeing Information for Short Message to retrieve the IMSI and the current MSC, SGSN, MME and/or SMSF addresses.

– Informing the HLR/HSS when a memory capacity exceeded condition ceases.

– Retrieving SMS related data from the HLR/HSS: subscriber data of the short message service similar to the data for the current CS/PS domain and additional service data on the service authorisation of the encapsulated short message delivery via IMS, SC address for service-level interworking from Instant Message to Short Message if the SC address is stored in the HLR/HSS.

Both a Sh interface and either a J or S6c interface can be deployed between the IP-SM-GW and the HLR/HSS. During the functional allocation the change on existing MAP functions, when used, should be minimized. The deployment of the J or S6c interface is mandatory, since it is used for forwarding the SRI for SM message.

5.2.4 E/Gd/Gdd/SGd interface

The E/Gd/Gdd/SGd interface allows the IP-SM-GW to connect to the SMS‑GMSC, appearing to the SMS‑GMSC as an MSC, SGSN, MME or SMSF.

For interworking with SMS in MME as defined in TS 23.272 [22], Annex C, an IWF may be used as described in that clause.

For interworking with an SGSN supporting the Gdd interface, an IWF may be used as described in TS 23.060 [21].

5.2.5 ISC interface

The ISC interface allows the IP-SM-GW to forward the receiving message to the SIP based UE via IMS core.

5.2.6 Void

5.3 Functional entities

5.3.1 IP-Short-Message-Gateway (IP-SM-GW)

5.3.1.1 General

The IP-SM-GW shall provide the protocol interworking for delivery of the short message between the IP-based UE and the SMS-SC. The message is routed to the SMS-SC for delivery to the SMS-based user or the message is received from the SMS-SC of an SMS-based UE for delivery to an IP-based UE.

The general functions of the IP-SM-GW are:

– to determine the domain (CS/PS or IMS) for delivery of a Short Message;

– to connect to the SMS‑GMSC using established MAP or Diameter based protocols, appearing to the SMS‑GMSC as an MSC, SGSN, MME or SMSF using the E, Gd/Gdd or SGd interfaces;

– to respond to Send Routeing Information for Short Message requests made by the SMS-GMSC, and forwarded from the HSS, with its own address;

– to connect to the SMS-IWMSC using established MAP or Diameter based protocols, appearing to the SMS-IWMSC as an MSC, SGSN, MME or SMSF using the E, Gd/Gdd or SGd interfaces;

– to connect to the HSS using established MAP or Diameter based protocols , to obtain the address of MSC/SGSN/MME/SMSF address(es) for SM termination in CS/PS;

NOTE: The IP-SM-GW need not support all of the functionality defined in MAP in TS 29.002 [6].

– to acquire and maintain knowledge of the association between the MSISDN, IMSI and the address of the S‑CSCF serving of the user;

– to check that it has a valid address in SMS for the sender as well as the recipient when receiving an IMS message for an SMS user. The IP-SM-GW shall obtain a valid address for both from the SIP headers of the IMS message (e.g. the sender would be identified in the asserted id in form of TEL URI);

– for terminating procedures:

– if TEL URI is available, it maps the recipient’s address from an MSISDN/IMSI to TEL URI format when receiving an SMS for an IP-based UE, and then it is the responsibility of the IMS core to perform any further mapping towards a SIP URI as required;

– if TEL URI is not available, it maps the recipient’s address from an IMSI to SIP URI format when receiving an SMS for an IP-based UE.

– to act as an Application Server towards the IMS core;

– to perform domain selection to choose the appropriate domain to deliver a message to a recipient and to obtain the MSC, SGSN, MME and/or SMSF addresses from the HSS; and

– to manage flags indicating user availability for SMS termination in the HSS and in IP-SM-GW.

– for MSISDN-less SMS operation:

– if the recipient is not addressed with MSISDN but with SIP-URI, the originating IP-SM-GW sends the SM toward to the target IMS network,

– if delivery to target UE failed, the terminating IP-SM-GW returns MSISDN-less correlation ID to allow the originating IMS network to retry later,

– if originating IP-SM-GW receives temporary delivery failure with MSISDN-less correlation ID from target IMS network, it forwards the SM along with the MSISDN-less correlation ID to SMSC for store and forwarding.

5.3.1.2 Transport-level interworking

The additional functions of the IP-SM-GW when interworking is done by carrying encapsulated Short Messages in IMS messages are:

– to communicate with the UE using IMS messaging as transport while maintaining the format and functionality of the Short Message;

– to carry the SMS status messages as encapsulated bodies of IMS messages;

– to store the subscriber data of the short message service similar to the data for the current CS/PS domain and to perform the short message authorization as performed by the MSC/SGSN/MME/SMSF, as well as to store additional service data on the service authorisation of the encapsulated Short Message delivery via IMS and to perform the service authorization.

NOTE 1: The short message subscriber data of the CS/PS domain and additional service data on the authorisation of encapsulated Short Message delivery via IMS are retrieved from the HLR/HSS via third party registration procedure as specified in the clause 6.1. The IP‑SM‑GW can request the HSS to send a notification whenever the subscriber data and/or additional service data is updated, which the IP‑SM‑GW can then retrieve.

NOTE 2: The mechanism for prioritizing whether the short message is delivered via a GSM/UMTS or other IP‑CAN connection when the terminal is simultaneously connected to both access networks is outside the scope of this specification.

5.3.1.3 Service-level interworking

The additional functions of the IP-SM-GW when service-level interworking is done between Short Messages and Instant Messages in IMS are:

– to determine whether to transform the message format or not, and to perform the transformation of the message format when determined.

– to use the SC address retrieved either as part of the subscriber data from the HSS at registration or as provisioned by configuration, when transforming the Instant Message into Short Message.

– to perform the authorization for service-level interworking.

The additional functions of the IP-SM-GW when service-level interworking is done between Short Messages and CPM Messages in IMS are the same as functions performed for Instant Messages in IMS and additionally:

– to translate a chat session invitation to a short message including instructions for the SMS user how to react (accept/reject) the chat session invitation, if operator policy mandates the consent of the SMS user. Otherwise the IP-SM-GW shall respond a chat session invitation on behalf of the SMS user (accept/reject), according to operator policy;

– to translate the SMS user’s answer to a chat session invitation to a proper response for the chat session invitation request;

– to inform SMS user about the changes of group chat session parameters;

– to translate a chat session teardown request to a short message, if operator policy mandates it; and

– to translate the SMS user’s request to leave a chat session to a proper CPM request.

5.3.2 HSS/UDM

In order to support SMS over generic IP access, the HSS/UDM shall support the following functions:

– storing the pre-configured address of the IP-SM-GW on a subscriber basis;

NOTE: If all subscribers are assigned to a single IP‑SM‑GW address, the IP‑SM‑GW address does not need to be pre-configured in the HSS.

– handling an indication that the terminal is registered with an IP-SM-GW for delivery of SMS;

– storing the SMSF address when the SMSF registers with the UDM as specified in TS 23.502 [24];

– responding to the "send routing information for short message" query from IP‑SM‑GW with the address of the MSC/SGSN/MME/SMSF;

– forwarding the Send Routeing Information for Short Message, from an SMS-GMSC, towards the IP-SM-GW and forwarding any responses to the originator of the Send Routeing Information for Short Message;

– returning the IMSI and the MSC, SGSN, MME and/or SMSF addresses as a response to Send Routeing Information for Short Message required from IP-SM-GW;

– alerting the SCs stored in the message waiting data when the terminal is registered with an IP‑SM‑GW for delivery of short message;

– reporting notification to the IP-SM-GW of the reachability of a UE at the transport layer after a delivery failure;

– accepting delivery status reports from IP-SM-GWs instead of SMS-GMSC.