When an SGSN fails, it deletes all MM and PDP contexts affected by the failure. SGSN storage of subscriber data is volatile. Based on configuration data, the SGSN may send a Reset message to each of its associated VLRs. If a Reset message is sent, the VLR may mark all associations containing the restarted SGSN as unreliable. See TS 29.018. In the case of optional CAMEL interaction the failing SGSN shall invoke the CAMEL-GPRS-Exception procedure towards the GSM-SCFs. If data or signalling, except GPRS attach and RA update, is received in an SGSN from an MS for which no MM context exists in the SGSN, the SGSN shall discard the data or signalling. If an RA update request is received in an SGSN from an MS for which no MM context exists in the SGSN, or in the old SGSN for the inter-SGSN RA update case, the SGSN shall reject the RA update with an appropriate cause. In order to remain GPRS-attached, the MS shall then perform a new GPRS attach and should (re-)activate PDP contexts. If a service request is received in a 3G-SGSN from an MS for which no MM context exists in the 3G-SGSN, the 3G-SGSN shall reject the service request with an appropriate cause. In order to remain GPRS-attached, the MS shall then perform a new GPRS attach and should (re-) activate PDP contexts. When the SGSN receives a PDU Notification Request message for which no MM context exists, the SGSN returns a PDU Notification Response message to the GGSN with an appropriate cause (see clause "Unsuccessful Network-Requested PDP Context Activation Procedure" in TS 23.060), and the SGSN may search the MS by paging with the IMSI in the SGSN area. An MS that is paged for PS services with IMSI as the identifier shall perform a new GPRS attach and should (re-)activate PDP contexts. When the SGSN receives a GTP-U PDU from the GGSN for which no PDP context exists, it shall discard the GTP-U PDU and send a GTP error indication to the originating GGSN. When the SGSN receives a GTP-U PDU from the RNC for which no PDP context exists, the SGSN shall discard the GTP-U PDU and send a GTP error indication to the originating RNC. When the SGSN receives a mobile-terminated SM from the SMS-GMSC for an IMSI unknown in the SGSN, it rejects the request. When the SGSN receives a paging request over the Gs interface for an IMSI unknown in the SGSN and the SGSN has not completed recovery, the SGSN may page the MS for packet services with IMSI as identifier in the area specified by the location information provided by the MSC/VLR. If no such location information is provided, the SGSN may page the MS in the routeing areas corresponding to that MSC/VLR. After the MS performs a combined GPRS attach, the SGSN may continue serving the Gs interface paging request.

When the SGSN receives a GTP-U PDU from the Serving GW for which no Bearer context exists, it shall discard the GTP-U PDU and send a GTP error indication to the originating Serving GW. When the SGSN receives a GTP-U PDU from the MBMS GW for which no MBMS Point to Point Bearer context exists, it shall discard the GTP-U PDU and send a GTP Error Indication to the originating MBMS GW. An S4-SGSN and an SGW supporting the optional network triggered service restoration procedure shall behave as specified in clause 25. When the S4-SGSN which does not support the optional network triggered service restoration procedure as specified in clause 25 receives a Downlink Data Notification message for which no MM context exists, the S4-SGSN returns a Downlink Data Notification Acknowledge message to the Serving GW with an appropriate cause. The Serving GW shall delete the related Bearer context related to S4-SGSN; and if there is no ISR associated MME recorded on the related Bearer context the Serving GW shall also notify the PDN GW to delete the Bearer context.

When a Gn-SGSN receives a tunnel PDU for which no PDP context or MBMS Bearer Context exists it discards the tunnel PDU and sends an Error indication message to the originating GGSN. An S4-SGSN and an SGW supporting the optional network triggered service restoration procedure shall behave as specified in clause 25.

When the SGSN receives a request for CS paging from an MSC/VLR for an IMSI unknown by the SGSN, if the "SGSN-Reset" indicator is set to "true", the SGSN sends the paging request with the location information provided by the VLR. If no such location information is provided, the SGSN should page for the MS in all the routeing areas corresponding to that SGSN. If the "SGSN-Reset" indicator is set to "false" and the IMSI is unknown or the MS is marked as GPRS or non-GPRS detached by the SGSN, the paging request is rejected. If the "SGSN-Reset" indicator is set to "false" and the IMSI is known and the MS is marked as GPRS and is non-GPRS attached by the SGSN, the paging request shall be sent to the MS.

The state of the indicator "Location Information Confirmed in HLR" does not affect the Mobile Terminated SMS procedure.

For attach, where the MS is unknown in the SGSN (i.e. the SGSN has no MM context for the MS) the SGSN creates an MM context for the MS and sets the indicators "Location Information Confirmed in HLR", "Subscriber Data Confirmed by HLR", "Location Information Confirmed by CSS" and "Subscriber Data Confirmed by CSS" to "Not Confirmed". If authentication is required, the SGSN retrieves authentication data. The SGSN then performs an "Update GPRS Location" to the HLR. If this is successful, the SGSN sets the indicators "Location Information Confirmed in HLR" and "Subscriber Data Confirmed by HLR" to "Confirmed". If the VPLMN supports Autonomous CSG Roaming and the HPLMN has enabled Autonomous CSG Roaming in the VPLMN, the SGSN may perform an "Update VCSG Location" to the CSS if the requested cell is a CSG/hybrid cell. If this is successful, the SGSN sets the indicators "Location Information Confirmed by CSS" and "Subscriber Data Confirmed by CSS" if the CSS has the valid CSG subscription data to "Confirmed". For routing area update, where the MS is unknown in the SGSN (i.e. the SGSN has no MM context for the MS) or for inter-SGSN routing area update, where the MS is unkown in the old SGSN, the SGSN shall reject the RA update with an appropriate cause. In order to remain GPRS-attached, the MS shall then perform a new GPRS attach and should (re-)activate its PDP contexts. If the SGSN has an MM context for the MS, and the indicators "Location Information Confirmed in HLR" or "Subscriber Data Confirmed by HLR" is set to "Not Confirmed" the SGSN performs an "Update GPRS Location" to the HLR. If this is successful, the SGSN sets the indicators "Location Information Confirmed in HLR" and "Subscriber Data Confirmed by HLR" to "Confirmed". If the indicators "Location Information Confirmed by CSS" or "Subscriber Data Confirmed by CSS" if the CSS has the valid CSG subscription data is set to "Not Confirmed", and the VPLMN supports Autonomous CSG Roaming and the HPLMN has enabled Autonomous CSG Roaming in the VPLMN, the SGSN may perform an "Update VCSG Location" to the CSS if the requested cell is a CSG/hybrid cell. If this is successful, the SGSN sets the indicators "Location Information Confirmed by CSS" and "Subscriber Data Confirmed by CSS" if the CSS has the valid CSG subscription data to "Confirmed". If the SGSN has an MM context for the MS with the indicator "Subscriber Data Confirmed by HLR" marked "Confirmed" the originated transmission is handled in the normal way. The SGSN retrieves subscriber data from the HLR by sending an "Update GPRS Location" request, which triggers one or more "Insert Subscriber Data" operations from the HLR. The SGSN retrieves CSG subscriber data from the CSS by sending an "Update VCSG Location" request, which triggers one or more "Insert Subscriber Data" operations from the CSS if the CSS has the valid CSG subscription data.

If an SGSN receives an LLC frame for which no MM context exists in the SGSN, and if the LLC frame does not contain an Attach Request or a Routeing Area Update Request signalling message, then the LLC frame shall be discarded. The MS may determine that the network is not responding and attempt to re-attach or eventually a periodic Routing Area Update message is sent by the MS which initiates the attach procedures.

For service request, where the MS is unknown in the SGSN (i.e. the SGSN has no MM context for the MS), the SGSN shall reject the service request with an appropriate cause. In order to remain GPRS-attached, the MS shall then perform a new GPRS attach and should (re-)activate its PDP contexts. If the SGSN has an MM context for the MS, and the indicators "Location Information Confirmed by CSS" or "Subscriber Data Confirmed by CSS" if the CSS has the valid CSG subscription data is set to "Not Confirmed", and the VPLMN supports Autonomous CSG Roaming and the HPLMN has enabled Autonomous CSG Roaming in the VPLMN, the SGSN may perform an "Update VCSG Location" to the CSS if the requested cell is a CSG/hybrid cell. If this is successful, the SGSN sets the indicators "Location Information Confirmed by CSS" and "Subscriber Data Confirmed by CSS" if the CSS has the valid CSG subscription data to "Confirmed". The SGSN retrieves CSG subscriber data from the CSS by sending an "Update VCSG Location" request, which triggers one or more "Insert Subscriber Data" operations from the CSS if the CSS has the valid CSG subscription data.

When an SGSN detects that a peer SGW has failed with or without restart (relying on restart counter as specified in clause 18 "GTP-C based restart procedures" or implementation e.g. preconfigured path failure timer) it shall either:

• as a default delete all PDN connection table data/MM bearer contexts associated with the peer node that has failed as well as freeing any internal SGSN resources associated with those PDN connections. The SGSN may optionally perform other implementation specific actions such as to clear external resources (e.g. Iu messages to clear UTRAN resources) or more advanced forms of restoration;

or

• follow the procedures specified in clause 27 to restore the PDN connections affected by the SGW failure, if the SGSN and the PGW support these procedures.

The behaviour of an SGSN when it detects that a peer MBMS GW has restarted is described in clause 17A.1.