"The data stored in location registers are automatically updated in normal operation; the main information stored in a location register defines the location of each mobile station and the subscriber data required to handle traffic for each mobile subscriber. The loss or corruption of these data will seriously degrade the service offered to mobile subscribers; it is therefore necessary to define procedures to limit the effects of failure of a location register@ and to restore the location register data automatically. The present document defines the necessary procedures. The basic principles is that restoration should be based on radio contact to avoid faulty data being spread in the system. Subscriber data for supplementary services must also be correctly restored@ although the impact on service of corruption of supplementary service data is less severe. Procedures for supporting functions are defined in GSM 09.02 and 09.60. The MAP operation ""IMSI Attach"" is used only in MAP version 1; in MAP version 2 the same function is performed by the MAP operation ""Update Location Area"". References in this specification to IMSI attach apply only to MAP version 1 network entities. If the restoration of subscriber data in the VLR in triggered by Location Updating or IMSI Attach@ the VLR retrieves subscriber data from the HLR by sending an ""Update Location"" request@ which triggers one or more ""Insert Subscriber Data"" operations from the HRL. The ""Update Location"" request may also be used to send the LMSI to the HLR. If the restoration of subscriber data in the VLR is triggered by a ""Provide Roaming Number"" request@ the behaviour of the VLR depends on whether it is implemented according to MAP version 1 or MAP version 2. For MAP version 2@ the VLR retrieves subscriber data from the HLR by sending a ""Restore Data"" request@ which triggers one or more ""Insert Subscriber Data"" Operations from the HLR. The ""Restore Data"" request is also send the LMSI to the HLR. For MAP version 1@ the VLR retrieves subscriber data from the HLR by sending a ""Send Parameters"" request with parameter type ""Subscriber Data""@ which cannot be used to send the LMSI to the HLR. The VLR number and MSC number in the subscriber data in the HLR are updated by the ""Update Location"" procedure. The GGSN (Gateway GPRS Support Node) is the point of PDN interconnection with the GSM PLMN supporting GPRS. The GGSN contains routing information for GPRS user with a PDP context active. The necessary procedures needed to restore GGSN data information after a restart are described in this document. The SGSN (Serving GPRS Support Node) is the node that is serving the MS. The SGSN stores information regarding e.g. mobility management@ routing and security. The necessary procedures needed to restore this SGSN information after a restart are described in this document. The LMU (Location Measurement Unit) is a network node@ accessed over the GSM air interface@ that is functionally similar to an MS. All requirements associated with a non-GPRS MS in this specification apply also to an LMU except where specified otherwise."