7.7 Short Message Service

23.1193GPPGateway Location Register (GLR)Release 17Stage 2TS

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

The Short Message Mobile Terminated is realised by MAP signalling between SMS-GMSC and the visited node (i.e. MSC or SGSN). Signalling address is the E.164 MSC Number or the E.164 SGSN Number. Since in the case of GLR introduction address conversion (see clause 7.1.2) is performed some mechanism is needed to restore the actual visited node address from the converted one generated by the GLR. In principle that restoration is performed by the GLR itself.

7.7.1 Scope

This clause describes only SM MT with GLR under the following condition:

– The recipient MS in the visited PLMN with the GLR is roamed into the PLMN from other PLMN.

Since SM MT in the case that is not applied to the above condition and SM MO have no relation to the introduction of the GLR those cases are not treated in this clause and just refer to 3G TS 23.040 [5]. This clause defines:

– the services and service elements (with regard to the GLR introduction);

– the network architecture (with regard to the GLR introduction);

– the IM-MSC functionality (with regard to the SMS);

– the GLR functionality (with regard to the SMS);

– the protocols and protocol layering (with regard to the GLR introduction);

for the Teleservices 22, as specified in the 3G TS 22.003 [1].

7.7.2 Definitions

This clause only provides definitions specific to the GLR introduction. Other definitions regarding SMS are provided in 3G TS 23.040 [5].

Intermediate-MSC (IM-MSC): The Intermediate MSC is an exchange which performs address interrogation to the GLR and relays the SMS to the MSC in the case of SM MT.

Mobile‑Station‑Not‑Reachable‑Flag (MNRF): The part of the MWI to be stored in the VLR and the HLR. It shall be stored also in the GLR. MNRF is a Boolean parameter indicating if the address list of MWD contains one or more entries because an attempt to deliver a short message to an MS has failed with a cause of Absent Subscriber.

Mobile‑station‑Not-Reachable-for-GPRS (MNRG): The part of the MWI to be stored in the SGSN and the HLR. It shall be stored also in the GLR. MNRG is a Boolean parameter indicating if the address list of MWD contains one or more entries because an attempt to deliver a short message to an MS has failed with a cause of Absent Subscriber.

More‑Messages‑To‑Send (MMS): The GLR shall keep a MAP dialogue open between the SMS-GMSC and the GLR and between the GLR and the SGSN where there are more messages to send. The IM-MSC shall keep a MAP dialogue open between the SMS-GMSC and the IM-MSC and between the IM-MSC and the MSC.

Gateway Location Register (GLR): The Gateway Location Register is an exchange that relays the SMS MT from SMS-GMSC to the SGSN. The GLR shall have interrogation function to forward the SM MT to the correct MSC or the SGSN.

7.7.3 Services and service elements

7.7.3.1 Short Message Service elements

7.7.3.1.1 Messages‑Waiting

Refer to 3G TS 23.040 [5] for the definition of the Message-Waiting service element.

The GLR shall have only the MNRF and the MNRG for the Message-Waiting. The GLR does not have other datum for the Message-Waiting service element.

Setting the MNRF and the MNRG is mandatory in the GLR as in the VLR/SGSN. When the MS has been detected as becoming active, the VLR or the SGSN shall:

– send the "MS Reachable" message (see clause 7.7.7) to the HLR via the GLR, and then

– clear MNRF in the VLR or the MNRG in SGSN (see 3G TS 23.040 [5]).

When the GLR receives the "MS Reachable" message it is mandatory for the GLR to relay the "MS Reachable" message to the HLR and then clear MNRF or MNRG in the GLR.

The MNRG and MNRF in the GLR are updated in the following way:

1a) When a mobile terminated short message delivery fails due to the MS being temporarily absent (i.e. either IMSI DETACH flag is set or there is no response from the MS to a paging request via the MSC), the MNRF is set (if it is not already set).

1b) When a mobile terminated short message delivery fails due to the MS being temporarily absent (i.e. either GPRS DETACH flag is set or there is no response from the MS to a paging request via the SGSN), the MNRG is set (if it is not already set).

1c) When a mobile terminated short message delivery fails due to the MS memory capacity via the MSC being exceeded, the MNRF is cleared.

1d) When a mobile terminated short message delivery fails due to the MS memory capacity via the SGSN being exceeded, the MNRG is cleared.

2a) When either the HLR or VLR detects that the MS (with a non‑empty MWD and the MCEF clear in the HLR and the MNRF set in the VLR) has recovered operation (e.g. has responded to a paging request over MSC), the HLR directly, or on request of the VLR or of the GLR, will invoke operations to alert the SCs within the MWD (see clause 7.7.3.1.2 and clause 7.7.7). Once the Alert SC operations have been invoked, the MNRF is cleared in the VLR and the GLR.

2b) When either the HLR or SGSN detects that the MS (with a non‑empty MWD and the MCEF clear in the HLR and the MNRG set in the SGSN) has recovered operation (e.g. has responded to a paging request via the SGSN), the HLR directly or on request of the SGSN or the GLR will invoke operations to alert the SCs within the MWD (see clause 7.7.3.1.2 and clause 7.7.7). Once the Alert SC operations have been invoked, the MNRG is cleared in the SGSN and the GLR.

2c) When the HLR receives (via the MSC, the VLR and the GLR) a notification that the MS (with a non‑empty MWD and the MCEF set in the HLR) has memory capacity available to receive one or more short messages, the HLR will invoke operations to alert the SCs within the MWD (see clause 7.7.3.1.2 and clause 7.7.7). Once the Alert SC operations have been invoked, the MNRF is cleared in the VLR and the GLR.

2d) When the HLR receives (via the SGSN and the GLR) a notification that the MS (with a non‑empty MWD and the MCEF set in the HLR) has memory capacity available to receive one or more short messages, the HLR will invoke operations to alert the SCs within the MWD (see clause 7.7.3.1.2 and clause 7.7.7). Once the Alert SC operations have been invoked, the MNRG is cleared in the SGSN and the GLR.

7.7.3.1.2 Alert‑SC

Considering the Alert-SC service element, when the GLR receives the Update Location or the Update GPRS Location from the VLR or the SGSN if and only if the MNRF or the MNRG is set in the GLR the GLR shall send "MS Reachable" message (see clause 7.7.7) to the HLR. That enables the HLR to initiate Alert-SC.

7.7.3.2 Unsuccessful short message TPDU transfer SC ‑> MS

Some error(s) may occur in the IM-MSC or the GLR (see clauses 7.7.5 and 7.7.7).

7.7.4 Network architecture

7.7.4.1 Basic network structure

The exchange of messages between an MS and an SME involves the entities shown in figure 7.7/1.

The basic network structure of the SM MT with GLR is depicted in figure 7.7/2.

Figure 7.7/1: Entities involved in the provision of SM MT with GLR

The links of figure 7.7/2 support the SM MT with GLR in the following way:

– the operations performed on links 1, 2, 3 and 4 is described in 3G TS 29.002 [10];

– interface E is internal interface in one physical node. Procedure in the IM-MSC, the GLR and between them regarding interface 5 is described in 3G TS 29.002 [10].

Figure 7.7/2: The main network structure serving as a basis for the SM MT with GLR

7.7.5 Node functionality related to SM MT

7.7.5.1 General

In the case of the GLR introduction as an option for the visited network operator, the existing functionality of the GSM entities regarding SMS MT (i.e. SMS-GMSC, MSC, VLR, SGSN and HLR) shall not be needed to modify.

7.7.5.2 Functionality of the GLR

When receiving a short message TPDU from the SMS‑GMSC ("forwardShortMessage", see clause 7.7.7.1), the GLR is responsible for the following operations:

– reception of the short message TPDU;

if errors are detected by the GLR:

– returning the appropriate error information to the SMS‑GMSC in a failure report (negative outcome of "forwardShortMessage" see clauses 7.7.7.1);

if no errors are detected by the GLR:

– retrieve the SGSN Number from the identity of the recipient MS;

– transferring the short message to the SGSN.

When a delivery report is received by the GLR:

– relaying the delivery report (positive outcome of "forwardShortMessage" see clause 7.7.7.1) to the SMS‑GMSC.

When a failure report is received by the GLR:

– relaying the failure report (negative outcome of "forwardShortMessage" see clause 7.7.7.1) to the SMS‑GMSC.

When receiving "ReadyForSM" from the MSC or the SGSN:

if errors are detected by the GLR:

– returning the appropriate error information to the MSC or the SGSN in a failure report (negative outcome of "ReadyForSM", see clause 7.7.7.3);

if no errors are detected by the GLR:

– relaying the "ReadyForSM" to the HLR (see clause 7.7.7.3).

7.7.5.3 Functionality of the IM-MSC

When receiving a short message TPDU from the SMS‑GMSC ("forwardShortMessage", see clause 7.7.7.1), the IM-MSC is responsible for the following operations:

– reception of the short message TPDU;

– retrieving information from the GLR ("ObtainMSCNumber", see clause 7.7.7.1); MSC Number and, when appropriate, error information;

if errors are indicated by the GLR:

– returning the appropriate error information to the SMS‑GMSC in a failure report (negative outcome of "forwardShortMessage" see clauses 7.7.7.1);

if no errors are indicated by the GLR:

– relaying the "forwardShortMessage" to the MSC is indicated by the retrieved MSC Number.

When a delivery report is received by the IM-MSC:

– relaying the delivery report (positive outcome of "forwardShortMessage" see clause 7.7.7.1) to the SMS‑GMSC.

When a failure report is received by the IM-MSC:

– relaying the failure report (negative outcome of "forwardShortMessage" see clause 7.7.7.1) to the SMS‑GMSC.

7.7.6 Protocols and protocol architecture

SM-RL shall be terminated at the GLR and the IM-MSC, since the GLR and the IM-MSC shall be able to retrieve the actual visited node address (i.e. the MSC Number or the SGSN Number) from the recipient MS identity. The protocol layers of the SMS are structured as shown in figure 7.7/3.

Figure 7.7/3: Protocol layer overview for the SM MT with GLR

7.7.6.1 Service provided by the SM‑RL

7.7.6.1.1 General

SM-RL messages and its information elements are the same as in the network without the GLR.

7.7.6.1.2 Protocol element repertoire at SM‑RL

Protocol element repertoire at SM-RL is the same as in the network without the GLR. Refer to 3G TS 23.040 [5] for the presence (i.e. mandatory, optional or not present) of each information element by replacing the term in the following manner.

– SMS-GMSC <-> IM-MSC or IM-MSC <-> MSC : MSC <-> MSC.

– SMS-GMSC <-> GLR or GLR <-> SGSN : MSC <-> SGSN.

7.7.7 Fundamental procedures within the point‑to‑point SMS

This clause provides the procedures specific to the GLR introduction.

7.7.7.1 Short message mobile terminated

The entities involved in this procedure are depicted in figure 7.7/4.

Figure 7.7/4: Interface involved in the short message mobile terminated procedure with GLR

NOTE: The GLR and the IM-MSC shall not visible to the other entities. Especially the SMS-GMSC shall regard the GLR and the IM-MSC as the SGSN and the MSC respectively. Further the SGSN and MSC shall regard the GLR and the IM-MSC as the SMS-GMSC.

In figures 7.7/5, sequence diagrams are shown for the following basic situations of short message mobile terminated transfer attempt:

– Successful short message transfer via the MSC;…a).

– Successful short message transfer via the SGSN;…b).

– Short message transfer attempt failing due to error at the MSC;…c).

– Short message transfer attempt failing due to error at the SGSN;…d).

– Short message transfer attempt failing due to error at the IM-MSC;…e).

– Short message transfer attempt failing due to error at the IM-MSC/GLR;…f).

– Short message transfer attempt failing due to error at the GLR;…g).

– Short message transfer attempt failing over the SGSN as the first path and succeeding over the MSC as the second path;…h).

– Short message transfer attempt failing over the SGSN as the first path and over the MSC as the second path;…I).

Figure 7.7/5a): Successful short message transfer attempt via the MSC

Figure 7.7/5b): Successful short message transfer attempt via the SGSN

Figure 7.7/5c): Short message transfer attempt failing due to error at the MSC

Figure 7.7/5d): Short message transfer attempt failing due to error at the SGSN

Figure 7.7/5e): Short message transfer attempt failing due to error at the IM-MSC

Figure 7.7/5f): Short message transfer attempt failing due to error at the IM-MSC/GLR

Figure 7.7/5g): Short message transfer attempt failing due to error at the GLR

Figure 7.7/5h): Short message transfer attempt failing over the SGSN as the first path and succeeding over the MSC as the second path

Figure 7.7/5i): Short message transfer attempt failing over the SGSN as the first path and over the MSC as the second path

Operation 1: Message transfer SMS‑GMSC ‑> GLR or IM-MSC.

This operation is used to transfer a short message from an SMS‑GMSC to a GLR or IM-MSC.

The operation consists of:

– the transfer of a message containing the TPDU from the SMS‑GMSC to the GLR or IM-MSC (see "1a. ForwardShortMessage" in figure 7.7.5), and

– the return of either a "Failure report" (see 1c. in figure 7.7.5) or a "Delivery report" (see 1b. in figure 7.7.5).

"Failure report" is returned to the SMS‑GMSC when the GLR or IM-MSC has received indication from another entity (MSC, SGSN) or when an error has occurred in the GLR or IM-MSC the procedure was unsuccessful. The error indications which the GLR or IM-MSC may receive from the MSC, SGSN, VLR or MS enable the GLR or IM-MSC to return one of the error indications given in Table 23.040/1 back to the SMS-GMSC.

Note that the SMS-GMSC shall regard the GLR as a SGSN and the IM-MSC a MSC and it is not aware the GLR and the IM-MSC as individual entities.

Operation 2: ObtainMSCNumber.

When the IM-MSC receives "1a. ForwardShortMessage" from an SMS-GMSC, the IM-MSC interrogates the GLR internally and obtains the E.164 number of the MSC at which the MS is currently located.

Operation 3: forwardShortMessage.

The operation provides a means for the GLR or IM-MSC to transfer a short message to the MSC or to the SGSN respectively at which the MS is currently located.

The operation works in tandem with the forwarding of the short message from the MSC or from the SGSN to the MS. Thus, the outcome of the operation comprises either success, i.e. that the message has been delivered to the MS; or a failure that may be caused by several reasons, e.g. failure in the transfer IM-MSC ‑> MSC or GLR -> SGSN, MS being detached, or no paging response.

Note that the MSC and the SGSN shall not be aware of existence of the GLR and the IM-MSC.

Operation 4: InformSMDeliveryFailure.

When the IM-MSC receives "3c. FailureReport" with absent subscriber cause, IM-MSC informs it to the GLR. The GLR checks if the reason of absent subscriber is due to the purged MS in the serving node (i.e. MSC or SGSN). If so, the GLR deletes the subscriber data for the user. Otherwise the GLR sets MNRF.

When the GLR receives "3c. FailureReport" with absent subscriber cause, the GLR checks if the reason of absent subscriber is due to the purged MS in the serving node (i.e. MSC or SGSN). If so, the GLR deletes the subscriber data for the user. Otherwise the GLR sets MNRG.

7.7.7.2 Functional requirements of GLR

7.7.7.2.1 Process Obtain_MSC_Number_GLR

Figure 7.7/6 shows the SDL chart for Process Obtain_MSC_Number_GLR.

Figure 7.7/6: Process Obtain_MSC_Number_GLR

7.7.7.2.2 Process Inform_SM_Delivery_Failure_GLR

Figure 7.7/7 shows the SDL chart for Process Inform_SM_Delivery_Failure_GLR.

Figure 7.7/7: Process Inform_SM_Delivery_Failure_GLR

7.7.7.2.3 Procedure Check_Absent_SubscriberSM_In_GLR

Figure 7.7/8 shows the SDL chart for Procedure Check_Absent_SubscriberSM_In_GLR.

Figure 7.7/8: Procedure Check_Absent_SubscriberSM_In_GLR

7.7.7.3 Alert transfer

The entities involved in this procedure are depicted in figure 7.7/9.

Figure 7.7/9: Interfaces involved in the Alert procedure with GLR

NOTE: The GLR shall not visible to the other entities. Especially the HLR shall regard the GLR as the VLR or the SGSN. Further the SGSN and the VLR shall regard the GLR as the HLR.

This procedure consists of the operations shown in figure 7.7/10.

Regarding the GLR introduction, the following four cases are distinguished:

– the MS becomes reachable when the MNRF is set in the VLR (figure 7.7/10a);

– the MS becomes reachable when the MNRG is set in the SGSN (figure 7.7/10b);

– the MS performs Location Update when the MNRF is not set in the VLR (figure 7.7/10c);

– the MS performs Routing Area Update when the MNRG is not set in the SGSN (figure 7.7/10d).

The operations between HLR and GLR are equivalent for HLR to those between HLR and VLR or between HLR and SGSN. The operations between GLR and SGSN are equivalent for SGSN to those between HLR and SGSN. The operations between GLR and VLR are equivalent for VLR to those between HLR and VLR.

The procedures in HLR, VLR and SGSN regarding the operations are the same as in the network without GLR. The procedures regarding the operations in GLR and IM-MSC are defined in 3G TS 29.002 [10].

Figure 7.7/10a: The alert procedure when the MS becomes reachable, MNRF is set

Figure 7.7/10b: The alert procedure when the MS becomes reachable, MNRG is set

Figure 7.7/10c: The alert procedure when the GLR receives UpdateLocation,
MNRF or MNRG is set

Figure 7.7/10d: The alert procedure when the GLR receives UpdateGprsLocation,
MNRF or MNRG is set

Operation 5: ReadyForSM (invoked by UpdateLocation or UpdateGprsLocation).

When the GLR receives UpdateLocation (see 7.7/10c) or UpdateGprsLocation (see 7.7/10d) the GLR shall invoke ReadyForSM to the HLR if and only if MNRF or MNRG is set. Note that if the GLR in which the MNRG is set receives Update Location the GLR shall invoke ReadyForSM also in that case. The converse case is also the case.