5A MME – CSS (S7a) and SGSN – CSS (S7d)
29.2723GPPEvolved Packet System (EPS)Mobility Management Entity (MME) and Serving GPRS Support Node (SGSN) related interfaces based on Diameter protocolRelease 17TS
5A.1 Introduction
The S7a interface enables the transfer of subscriber related CSG data in the VPLMN between the MME and the CSS as described in 3GPP TS 23.401 [2].
The S7d interface enables the transfer of subscriber related CSG data in the VPLMN between the SGSN and the CSS as described in 3GPP TS 23.060 [12].
5A.2 Mobility Services
5A.2.1 Location Management Procedures
5A.2.1.1 Update VCSG Location
5A.2.1.1.1 General
The Update VCSG Location Procedure shall be used between the MME and the CSS or between the SGSN and the CSS to update location information in the CSS or retrieve the CSG subscription data of the UE from the CSS. The procedure allows:
– to inform the CSS about the identity of the MME or SGSN currently serving the user,
– to update MME or SGSN with user CSG subscription data received from the CSS.
This procedure is mapped to the commands Update-VCSG-Location-Request/Answer (UVR/UVA) in the Diameter application specified in clause 7.
Table 5A.2.1.1.1/1 specifies the involved information elements for the request.
Table 5A.2.1.1.1/2 specifies the involved information elements for the answer.
Table 5A.2.1.1.1/1: Update VCSG Location Request
|
Information element name |
Mapping to Diameter AVP |
Cat. |
Description |
|
IMSI |
User-Name (See IETF RFC 6733 [61]) |
M |
This information element shall contain the user IMSI, formatted according to 3GPP TS 23.003 [3], clause 2.2. |
|
Supported Features (See 3GPP TS 29.229 [9]) |
Supported-Features |
O |
If present, this information element shall contain the list of features supported by the origin host. |
|
MSISDN |
MSISDN |
C |
This information element shall contain the user MSISDN, formatted according to 3GPP TS 29.329 [25]. It shall be present if available. |
|
UVR Flags (See 7.3.153) |
UVR-Flags |
M |
This Information Element contains a bit mask. See 7.3.153 for the meaning of the bits. |
|
SGSN number (See 7.3.102) |
SGSN-Number |
C |
This Information Element contains the ISDN number of the SGSN, see 3GPP TS 23.003 [3]. It shall be present when the message is sent on the S7d interface. It may be present when the message on the S7a interface and the requesting node is a combined MME/SGSN. |
Table 5A.2.1.1.1/2: Update VCSG Location Answer
|
Information element name |
Mapping to Diameter AVP |
Cat. |
Description |
|
Supported Features (See 3GPP TS 29.229 [9]) |
Supported-Features |
O |
If present, this information element shall contain the list of features supported by the origin host. |
|
Result (See 7.4) |
Result-Code / Experimental-Result |
M |
This IE shall contain the result of the operation. The Result-Code AVP shall be used to indicate success / errors as defined in the Diameter base protocol (see IETF RFC 6733 [61]). The Experimental-Result AVP shall be used for S7a/S7d errors. This is a grouped AVP which shall contain the 3GPP Vendor ID in the Vendor-Id AVP, and the error code in the Experimental-Result-Code AVP. The following errors are applicable: – User Unknown |
|
VPLMN CSG Subscription Data (See 7.3.155) |
VPLMN-CSG-Subscription-Data |
C |
This Information Element shall contain the list of CSG Ids and the associated expiry dates stored in the CSS. It shall be present if success is reported, unless an explicit "skip subscriber data" indication was present in the request or the Temporary Empty VPLMN CSG Subscription Data flag is set. |
|
UVA Flags (See 7.3.154) |
UVA-Flags |
C |
This Information Element contains a bit mask. See 7.3.154 for the meaning of the bits. |
5A.2.1.1.2 Detailed behaviour of the MME and the SGSN
The MME or SGSN shall make use of this procedure to register the UE in the CSS and to retrieve the "CSG subscription data from CSS" when:
– the VPLMN supports Autonomous CSG Roaming
– and the HPLMN has enabled Autonomous CSG Roaming in the VPLMN
– and the UE has requested an initial attach or a tracking area procedure or a routing area procedure to a CSG cell
– and the MME or SGSN have not yet registered the UE in the CSS.
If the Autonomous CSG Roaming in the VPLMN is not supported or is not allowed by the HPLMN of the subscriber, the MME or SGSN shall not make use of the Update CSG Location procedure.
For UEs receiving emergency services, in which the UE was not successfully authenticated, the MME or SGSN shall not make use of the Update VCSG Location procedure.
A combined MME/SGSN shall set the "Skip Subscriber Data" flag in the UVR-Flags if the "CSG subscription data from CSS" are already available due to a previously VCSG Location updating.
A combined MME/SGSN that has chosen the option to include the SGSN Number within an Update VCSG Request sent over S7a shall be prepared to receive a single CSG subscription data update message from the CSS when the CSG subscription data is modified in the CSS.
When receiving an Update VCSG Location Answer from the CSS, the MME or SGSN shall check the result code. If it indicates success the MME or SGSN shall delete all the stored "CSG subscription data from CSS" (if any) and then store the received "CSG subscription data from the CSS" (if any), and it shall store the CSS identity as received in the Origin-Host AVP.
If the same CSG Id exists in both "CSG subscription data from CSS" and "CSG subscription data from HSS", the "CSG subscription data from HSS" shall take precedence over the "CSG subscription data from CSS" in further use.
If an error response is received from the CSS, the MME or SGSN shall not reject the UE and shall end the procedure when the UE is attaching to a normal cell. If the UE is attaching to a CSG cell, in this case the MME or SGSN shall check if there is such CSG Id from the HSS. If there is no such CSG Id, the MME or SGSN shall reject the UE.
5A.2.1.1.3 Detailed behaviour of the CSS
When receiving an Update VCSG Location request the CSS shall check whether the user is known.
If the user is not known, and if the Update VCSG Location Request is received over the S7a/S7d interface, the CSS may:
– store the MME or SGSN identity received within the Origin-Host AVP, and include the UVA-Flags AVP with "Temporary Empty VPLMN CSG Subscription Data" flag set, and return a Result Code of DIAMETER_ SUCCESS, or
– return a Result Code of DIAMETER_ERROR_USER_UNKNOWN.
NOTE: A mechanism is needed in the CSS to associate the CSG subscription data of the user with the received IMSI.
If the Update VCSG Location Request is received over the S7a/S7d interface, the CSS shall replace the stored MME or SGSN identity with the received value (the identity is received within the Origin-Host AVP).
If no result code indicating an error is sent to the MME or SGSN, the CSS shall include the VPLMN CSG subscription data in the Update VCSG Location Answer unless an explicit "skip subscriber data" indication has been received in the request, and shall return a Result Code of DIAMETER_SUCCESS.
5A.2.1.2 Cancel VCSG Location
5A.2.1.2.1 General
The Cancel VCSG Location Procedure shall be used between the CSS and the MME and between the CSS and the SGSN. The procedure shall be invoked by the CSS and is used:
– to inform the MME or SGSN about the subscriber’s VCSG subscription withdrawal by the CSS operator and the removal of their registration in the CSS.
This procedure is mapped to the commands Cancel-VCSG-Location-Request/Answer (CVR/CVA) in the Diameter application specified in clause 7.
Table 5A.2.1.2.1/1 specifies the involved information elements for the request.
Table 5A.2.1.2.1/2 specifies the involved information elements for the answer.
Table 5A.2.1.2.1/1: Cancel VCSG Location Request
|
Information element name |
Mapping to Diameter AVP |
Cat. |
Description |
|
IMSI |
User-Name (See IETF RFC 6733 [61]) |
M |
This information element shall contain the user IMSI, formatted according to 3GPP TS 23.003 [3], clause 2.2. |
|
Supported Features (See 3GPP TS 29.229 [9]) |
Supported-Features |
O |
If present, this information element shall contain the list of features supported by the origin host. |
|
Cancellation Type (See 7.3.24) |
Cancellation-Type |
M |
Defined values that can be used are: – Subscription Withdrawal, applied to the VPLMN CSG subscription. |
Table 5A.2.1.2.1/2: Cancel VCSG Location Answer
|
Information element name |
Mapping to Diameter AVP |
Cat. |
Description |
|
Supported Features (See 3GPP TS 29.229 [9]) |
Supported-Features |
O |
If present, this information element shall contain the list of features supported by the origin host. |
|
Result (See 7.4) |
Result-Code / Experimental-Result |
M |
The result of the operation. The Result-Code AVP shall be used to indicate success / errors as defined in the Diameter base protocol (see IETF RFC 6733 [61]). |
5A.2.1.2.2 Detailed behaviour of the MME and the SGSN
When receiving a Cancel VCSG Location request the MME or SGSN shall check whether the IMSI is known.
If it is not known, a result code of DIAMETER_SUCCESS is returned.
If it is known, the MME or SGSN shall check if the Cancellation Type is Subscription Withdrawal. In this case, the MME or SGSN shall remove the information of their registration in the CSS and the stored VPLMN CSG subscription if any. Also in this case a result code of DIAMETER_SUCCESS is returned.
When a UE is served by a single combined MME/SGSN for both E-UTRAN and non-E-UTRAN access, the combined MME/SGSN shall check if the Cancellation Type is Subscription Withdrawal. In this case, the Cancel VCSG Location request is processed both in the MME part and in the SGSN part of the combined node.
5A.2.1.2.3 Detailed behaviour of the CSS
The CSS shall make use of this procedure when the user’s VPLMN CSG subscription is withdrawn by the CSS operator and shall include a cancellation type of "Subscription Withdrawal.
5A.2.2 Subscriber Data Handling Procedures
5A.2.2.1 Insert VCSG Subscriber Data
5A.2.2.1.1 General
The Insert VCSG Subscriber Data Procedure shall be used between the CSS and the MME and between the CSS and the SGSN for updating CSG subscription data in the MME or SGSN in the following situations:
– due to administrative changes of the user data in the CSS and the user is now located in an MME or SGSN, i.e. if the user was given a CSG subscription and the CSG subscription has changed;
If the CSS knows that the UE has attached to the same combined MME/SGSN via both the E-UTRAN and UTRAN/GERAN, i.e. the CSS has received the Update VCSG Location Request over both the S7a interface and S7d interface respectively with the same SGSN number, the CSS should invoke this procedure for a single time to update CSG subscription data in the combined MME/SGSN, i.e. the CSS should not invoke this procedure for each of the MME and the SGSN registered respectively.
This procedure is mapped to the commands Insert-Subscriber Data-Request/Answer (IDR/IDA) in the Diameter application specified in clause 7.
Table 5A.2.2.1.1/1 specifies the involved information elements for the request.
Table 5A.2.2.1.1/2 specifies the involved information elements for the answer.
Table 5A.2.2.1.1/1: Insert VCSG Subscriber Data Request
|
Information element name |
Mapping to Diameter AVP |
Cat. |
Description |
|
IMSI |
User-Name (See IETF RFC 6733 [61]) |
M |
This information element shall contain the user IMSI, formatted according to 3GPP TS 23.003 [3], clause 2.2. |
|
Supported Features (See 3GPP TS 29.229 [9]) |
Supported-Features |
O |
If present, this information element shall contain the list of features supported by the origin host. |
|
VPLMN CSG Subscription Data (See 7.3.2) |
VPLMN-CSG-Subscription-Data |
M |
This Information Element shall contain the list of CSG Ids and the associated expiry dates stored in the VPLMN CSS. |
Table 5A.2.2.1.1/2: Insert VCSG Subscriber Data Answer
|
Information element name |
Mapping to Diameter AVP |
Cat. |
Description |
|
Supported Features (See 3GPP TS 29.229 [9]) |
Supported-Features |
O |
If present, this information element shall contain the list of features supported by the origin host. |
|
Result (See 7.4) |
Result-Code / Experimental-Result |
M |
This IE shall contain the result of the operation. Result-Code AVP shall be used to indicate success / errors defined in the Diameter base protocol (see IETF RFC 6733 [61]).The Experimental-Result AVP shall be used for S7a/S7d errors. This is a grouped AVP which shall contain the 3GPP Vendor Id in the Vendor-Id AVP, and the error code in the Experimental-Result-Code AVP. The following errors are applicable in this case: – User Unknown. |
5A.2.2.1.2 Detailed behaviour of the MME and the SGSN
When receiving an Insert VCSG Subscriber Data request, the MME or SGSN shall check whether the IMSI is known.
If it is not known, a result code of DIAMETER_ERROR_USER_UNKNOWN shall be returned.
If the request does not contain any CSG-Subscription-Data AVP, Experimental-Result shall be set to DIAMETER_ERROR_SUBS_DATA_ABSENT.
If the request contains at least one CSG-Subscription-Data AVPs, the MME or SGSN shall delete all the stored "CSG subscription data from CSS" (if any), and then store the received "CSG subscription data from CSS".
If the MME or SGSN cannot fulfil the received request, e.g. due to a database error, it shall set the Result-Code to DIAMETER_UNABLE_TO_COMPLY.
If the same CSG Id exists in both "CSG subscription data from CSS" and "CSG subscription data from HSS", the "CSG subscription data from HSS" shall take precedence over the "CSG subscription data from CSS" in further use.
5A.2.2.1.3 Detailed behaviour of CSS
The CSS shall make use of this procedure to delete the "CSG subscription data from CSS" stored in the MME or SGSN and replace them with the CSG subscription data sent.
If the CSS receives a Insert VCSG Subscriber Data answer with the Result Code DIAMETER_ERROR_USER_UNKNOWN, the CSS shall clear the stored MME or SGSN identity.
5A.2.2.2 Delete VCSG Subscriber Data
5A.2.2.2.1 General
This procedure shall be used between the CSS and the MME or between the CSS and the SGSN, to remove all the "CSG subscription data from CSS" stored in the MME or SGSN. The procedure shall be invoked by the CSS.
If the CSS knows that the UE has attached to the same combined MME/SGSN via both E-UTRAN and UTRAN/GERAN, i.e. the CSS has received the Update VCSG Location Request over both the S7a interface and S7d interface respectively with the same SGSN number, the CSS should invoke this procedure for a single time to remove all the "CSG subscription data from CSS" stored in the combined MME/SGSN, i.e. not invoke this procedure for each of the MME and the SGSN registered respectively.
This procedure is mapped to the commands Delete-Subscriber-Data-Request/Answer (DSR/DSA) in the S7a/S7d Diameter application specified in clause 7.
Table 5A.2.2.2.1/1 specifies the involved information elements for the request.
Table 5A.2.2.2.1/2 specifies the involved information elements for the answer.
Table 5A.2.2.2.1/1: Delete VCSG Subscriber Data Request
|
Information element name |
Mapping to Diameter AVP |
Cat. |
Description |
|
IMSI |
User-Name (See IETF RFC 6733 [61]) |
M |
This information element shall contain the user IMSI, formatted according to 3GPP TS 23.003 [3], clause 2.2. |
|
Supported Features (See 3GPP TS 29.229 [9]) |
Supported-Features |
O |
If present, this information element shall contain the list of features supported by the origin host. |
|
DSR Flags (See 7.3.25) |
DSR-Flags |
M |
This Information Element shall contain a bit mask. See 7.3.25 for the meaning of the bits. |
Table 5A.2.2.2.1/2: Delete VCSG Subscriber Data Answer
|
Information element name |
Mapping to Diameter AVP |
Cat. |
Description |
|
Supported Features (See 3GPP TS 29.229 [9]) |
Supported-Features |
O |
If present, this information element shall contain the list of features supported by the origin host. |
|
Result (See 7.4) |
Result-Code / Experimental-Result |
M |
This IE shall contain the result of the operation. The Result-Code AVP shall be used to indicate success / errors as defined in the Diameter base protocol (see IETF RFC 6733 [61]). The Experimental-Result AVP shall be used for S7a/S7d errors. This is a grouped AVP which shall contain the 3GPP Vendor ID in the Vendor-Id AVP, and the error code in the Experimental-Result-Code AVP. The following errors are applicable in this case: – User Unknown |
5A.2.2.2.2 Detailed behaviour of the MME and the SGSN
When receiving a Delete VCSG Subscriber Data request, the MME or SGSN shall check whether the IMSI is known.
If it is not known, a result code of DIAMETER_ERROR_USER_UNKNOWN shall be returned.
If it is known, the MME or SGSN shall delete all the stored "CSG subscription data from CSS".
If the deletion of the subscription data succeeds in the MME or SGSN, the Result-Code shall be set to DIAMETER_SUCCESS.
If the MME or SGSN cannot fulfil the received request for other reasons, e.g. due to a database error, it shall set the Result-Code to DIAMETER_UNABLE_TO_COMPLY.
5A.2.2.2.3 Detailed behaviour of the CSS
The CSS shall make use of this procedure to remove all the CSG subscription data associated to CSS from the MME or SGSN.
NOTE: When a Delete VCSG Subscriber Data procedure occurs, the MME or SGSN remains registered in the CSS
If the CSS receives a Delete VCSG Subscriber Data answer with the Result Code DIAMETER_ERROR_USER_UNKNOWN from the MME or SGSN, the CSS shall clear the stored MME or SGSN identity.
5A.2.3 Fault Recovery Procedures
5A.2.3.1 VCSG Reset
5A.2.3.1.1 General
The VCSG Reset Procedure shall be used by the CSS, after a restart, to indicate to the MME and to the SGSN that a failure has occurred.
This procedure is mapped to the commands Reset-Request/Answer (RSR/RSA) in the S7a/S7d Diameter application specified in clause 7.
Table 5A.2.3.1.1/1 specifies the involved information elements for the request.
Table 5A.2.3.1.1/2 specifies the involved information elements for the answer.
Table 5A.2.3.1.1/1: VCSG Reset Request
|
Information element name |
Mapping to Diameter AVP |
Cat. |
Description |
|
Supported Features (See 3GPP TS 29.229 [9]) |
Supported-Features |
O |
If present, this information element shall contain the list of features supported by the origin host. |
Table 5A.2.3.1.1/2: VCSG Reset Answer
|
Information element name |
Mapping to Diameter AVP |
Cat. |
Description |
|
Result (See 7.4) |
Result-Code / Experimental-Result |
M |
This IE shall contain the result of the operation. The Result-Code AVP shall be used to indicate success / errors as defined in the Diameter base protocol (see IETF RFC 6733 [61]). The Experimental-Result AVP shall be used for S7a/S7d errors. This is a grouped AVP which shall contain the 3GPP Vendor ID in the Vendor-Id AVP, and the error code in the Experimental-Result-Code AVP. There are no Experimental-Result codes applicable for this command. |
|
Supported Features (See 3GPP TS 29.229 [9]) |
Supported-Features |
O |
If present, this information element shall contain the list of features supported by the origin host. |
5A.2.3.1.2 Detailed behaviour of the MME and the SGSN
When receiving a VCSG Reset message, the MME or SGSN or combined MME/SGSN, for all roaming users for which they have a registration in CSS, shall mark "Location Information Confirmed in CSS" record as "Not Confirmed". The MME or SGSN or combined MME/SGSN shall make use of the CSS Identity received in the Origin-Host AVP (by comparing it with the value stored after successful ULA) in order to determine which user records are impacted.
When, as described in 3GPP TS 23.007 [43], an event requiring the MME or SGSN to check the "CSG subscription data from CSS" occurs, and if the user record "Location Information Confirmed in CSS" is marked as "Not Confirmed", the restoration procedure shall be triggered.
5A.2.3.1.3 Detailed behaviour of the CSS
The CSS shall make use of this procedure in order to indicate to all relevant MMEs, SGSNs, and combined MME/SGSNs that the CSS has restarted and may have lost the current MME-Identity and SGSN-Identity of some of its users who may be currently roaming in the MME area and/or SGSN area, and to which the CSS, therefore, cannot send e.g. Insert VCSG Subscriber Data messages when needed.
The CSS should invoke this procedure towards a combined MME/SGSN only for a single time even if some of the impacted subscribers are attached to the combined MME/SGSN via UTRAN/GERAN and some of the impacted subscribers are attached to the combined MME/SGSN via E-UTRAN.