13 Information Storage

03.603GPPGeneral Packet Radio Service (GPRS)Release 1998Service descriptionStage 2TS

This clause describes information storage structures required for GPRS, and the recovery and restoration procedures needed to maintain service if inconsistencies in databases occur and at lost or invalid database information.

13.1 HLR

IMSI is the prime key to the GPRS subscription data stored in the HLR. There may be several sets of GPRS subscription data per IMSI. This is illustrated in Figure 51.

Figure 51: GPRS Subscription Data

As Figure 51 indicates, the GPRS subscription data is at the same level as basic services. Each PDP subscription is seen as a basic service. Supplementary services are provisioned as part of the overall subscription. Activation of SSs is either at the basic service level (SS1) or at the overall subscription level (SS2).

Table 4 shows the GPRS subscription data contained in the HLR.

Table 4: HLR GPRS Subscription Data

Field

Description

IMSI

IMSI is the main reference key.

MSISDN

The basic MSISDN of the MS.

SGSN Number

The SS7 number of the SGSN currently serving this MS.

SGSN Address

The IP address of the SGSN currently serving this MS.

SMS Parameters

SMS-related parameters, e.g., operator-determined barring.

MS Purged for GPRS

Indicates that the MM and PDP contexts of the MS are deleted from the SGSN.

MNRG

Indicates that the MS is not reachable through an SGSN, and that the MS is marked as not reachable for GPRS at the SGSN and possibly at the GGSN.

GGSN‑list

The GSN number and optional IP address pair related to the GGSN that shall be contacted when activity from the MS is detected and MNRG is set. The GSN number shall be either the number of the GGSN or the protocol-converting GSN as described in the subclauses "MAP-based GGSN ‑ HLR Signalling" and "GTP and MAP-based GGSN ‑ HLR Signalling".

Each IMSI contains zero or more of the following PDP context subscription records:

PDP Context Identifier

Index of the PDP context.

PDP Type

PDP type, e.g., X.25, PPP, or IP.

PDP Address

PDP address, e.g., an X.121 address. This field shall be empty if dynamic addressing is allowed.

Access Point Name

A label according to DNS naming conventions describing the access point to the external packet data network.

QoS Profile Subscribed

The quality of service profile subscribed. QoS Profile Subscribed is the default level if a particular QoS profile is not requested.

VPLMN Address Allowed

Specifies whether the MS is allowed to use the APN in the domain of the HPLMN only, or additionally the APN in the domain of the VPLMN.

13.2 SGSN

SGSN maintains MM context and PDP context information for MSs in STANDBY and READY states. Table 5 shows the context fields for one MS.

Table 5: SGSN MM and PDP Contexts

Field

Description

IMSI

IMSI is the main reference key.

MM State

Mobility management state, IDLE, STANDBY, or READY.

P‑TMSI

Packet Temporary Mobile Subscriber Identity.

P‑TMSI Signature

A signature used for identification checking purposes.

IMEI

International Mobile Equipment Identity

MSISDN

The basic MSISDN of the MS.

Routeing Area

Current routeing area.

Cell Identity

Current cell in READY state, last known cell in STANDBY or IDLE state.

Cell Identity Age

Time elapsed since the last LLC PDU was received from the MS at the SGSN.

VLR Number

The VLR number of the MSC/VLR currently serving this MS.

New SGSN Address

The IP address of the new SGSN where buffered and not sent N‑PDUs should be forwarded to.

Authentication Triplets

Authentication and ciphering parameters.

Kc

Currently used ciphering key.

CKSN

Ciphering key sequence number of Kc.

Ciphering algorithm

Selected ciphering algorithm.

Radio Access Classmark

MS radio access capabilities.

SGSN Classmark

MS network capabilities.

DRX Parameters

Discontinuous reception parameters.

MNRG

Indicates whether activity from the MS shall be reported to the HLR.

NGAF

Indicates whether activity from the MS shall be reported to the MSC/VLR.

PPF

Indicates whether paging for GPRS and non-GPRS services can be initiated.

SMS Parameters

SMS-related parameters, e.g., operator-determined barring.

Recovery

Indicates if HLR or VLR is performing database recovery.

Radio Priority SMS

The RLC/MAC radio priority level for uplink SMS transmission.

Each MM context contains zero or more of the following PDP contexts:

PDP Context Identifier

Index of the PDP context.

PDP State

Packet data protocol state, INACTIVE or ACTIVE.

PDP Type

PDP type, e.g., X.25, PPP, or IP.

PDP Address

PDP address, e.g., an X.121 address.

APN Subscribed

The APN received from the HLR.

APN in Use

The APN currently used.

NSAPI

Network layer Service Access Point Identifier.

TI

Transaction Identifier.

GGSN Address in Use

The IP address of the GGSN currently used.

VPLMN Address Allowed

Specifies whether the MS is allowed to use the APN in the domain of the HPLMN only, or additionally the APN in the domain of the VPLMN.

QoS Profile Subscribed

The quality of service profile subscribed.

QoS Profile Requested

The quality of service profile requested.

QoS Profile Negotiated

The quality of service profile negotiated.

Radio Priority

The RLC/MAC radio priority level for uplink user data transmission.

Send N‑PDU Number

SNDCP sequence number of the next downlink N‑PDU to be sent to the MS.

Receive N‑PDU Number

SNDCP sequence number of the next uplink N‑PDU expected from the MS.

SND

GTP sequence number of the next downlink N‑PDU to be sent to the MS.

SNU

GTP sequence number of the next uplink N‑PDU to be sent to the GGSN.

Charging Id

Charging identifier, identifies charging records generated by SGSN and GGSN.

Reordering Required

Specifies whether the SGSN shall reorder N‑PDUs before delivering the N‑PDUs to the MS.

In case of anonymous access the SGSN maintains the MM context and PDP context information for MSs in READY state. Table 6 shows the context fields for one MS.

Table 6: SGSN MM and PDP Contexts for Anonymous Access

Field

Description

A‑TLLI

Auxiliary Temporary Logical Link Identity.

AA‑TID

Anonymous Access Tunnel Identifier.

Routeing Area

Current routeing area.

Cell Identity

Current cell.

PDP Type

PDP type, e.g., X.25, PPP, or IP.

PDP Address

PDP address, e.g., an X.121 address.

APN in Use

The APN currently used.

NSAPI

Network layer Service Access Point Identifier.

TI

Transaction Identifier.

GGSN Address in Use

The IP address of the GGSN currently used.

QoS Profile Requested

The quality of service profile requested.

QoS Profile Negotiated

The quality of service profile negotiated.

Radio Priority

The RLC/MAC radio priority level for uplink user data transmission.

Send N‑PDU Number

SNDCP sequence number of the next downlink N‑PDU to be sent to the MS.

Receive N‑PDU Number

SNDCP sequence number of the next uplink N‑PDU expected from the MS.

SND

GTP sequence number of the next downlink N‑PDU to be sent to the MS.

SNU

GTP sequence number of the next uplink N‑PDU to be sent to the GGSN.

Charging Id

Charging identifier, identifies charging records generated by SGSN and GGSN.

Reordering Required

Specifies whether the SGSN shall reorder N‑PDUs before delivering the N‑PDUs to the MS.

13.3 GGSN

GGSN maintains activated PDP contexts. Table 7 shows the PDP context fields for one PDP Address.

Table 7: GGSN PDP Context

Field

Description

IMSI

International Mobile Subscriber Identity.

NSAPI

Network layer Service Access Point Identifier.

MSISDN

The basic MSISDN of the MS.

PDP Type

PDP type, e.g., X.25, PPP, or IP.

PDP Address

PDP address, e.g., an X.121 address.

Dynamic Address

Indicates whether PDP Address is static or dynamic.

APN in Use

The APN Network Identifier currently used.

QoS Profile Negotiated

The quality of service profile negotiated.

SGSN Address

The IP address of the SGSN currently serving this MS.

MNRG

Indicates whether the MS is marked as not reachable for GPRS at the HLR.

Recovery

Indicates if the SGSN is performing database recovery.

SND

GTP sequence number of the next downlink N‑PDU to be sent to the SGSN.

SNU

GTP sequence number of the next uplink N‑PDU to be received from the SGSN.

Charging Id

Charging identifier, identifies charging records generated by SGSN and GGSN.

Reordering Required

Specifies whether the GGSN shall reorder N‑PDUs received from the SGSN.

If a PDP context is enabled for network-requested PDP context activation, then IMSI, PDP Type, PDP Address, SGSN Address and MNRG contain valid information also when the PDP context is inactive and when the MS is GPRS-detached.

In case of anonymous access the GGSN maintains activated PDP contexts. Table 8 shows the PDP context fields for one MS.

Table 8: GGSN PDP Context for Anonymous Access

Field

Description

AA‑TID

Anonymous Access Tunnel Identifier.

PDP Type

PDP type, e.g., X.25, PPP, or IP.

PDP Address

PDP address, e.g., an X.121 address.

APN in Use

The APN Network Identifier currently used.

QoS Profile Negotiated

The quality of service profile negotiated.

SGSN Address

The IP address of the SGSN serving this MS.

SND

GTP sequence number of the next downlink N‑PDU to be sent to the SGSN.

SNU

GTP sequence number of the next uplink N‑PDU to be received from the SGSN.

Charging Id

Charging identifier, identifies charging records generated by SGSN and GGSN.

Reordering Required

Specifies whether the GGSN shall reorder N‑PDUs received from the SGSN.

A GGSN that supports anonymous access shall have a list of server addresses that are allowed to be accessed by anonymous MSs. The method to maintain the list of the servers is outside the scope of the present document.

13.4 MS

Each GPRS MS maintains MM and PDP context information in IDLE, STANDBY and READY states. The information may be contained in the MS and the TE. Table 9 shows the MS context fields.

Table 9: MS MM and PDP Contexts

Field

SIM

Description

IMSI

X

International Mobile Subscriber Identity.

MM State

Mobility management state, IDLE, STANDBY, or READY.

P‑TMSI

X

Packet Temporary Mobile Subscriber Identity.

P‑TMSI Signature

X

A signature used for identification checking purposes.

Routeing Area

X

Current routeing area.

Cell Identity

Current cell.

Kc

X

Currently used ciphering key.

CKSN

X

Ciphering key sequence number of Kc.

Ciphering algorithm

Selected ciphering algorithm.

Classmark

MS classmark.

DRX Parameters

Discontinuous reception parameters.

Radio Priority SMS

The RLC/MAC radio priority level for uplink SMS transmission.

Each MM context contains zero or more of the following PDP contexts:

PDP Type

PDP type, e.g., X.25, PPP, or IP.

PDP Address

PDP address, e.g., an X.121 address.

PDP State

Packet data protocol state, INACTIVE or ACTIVE.

Dynamic Address Allowed

Specifies whether the MS is allowed to use a dynamic address.

APN Requested

The APN requested.

NSAPI

Network layer Service Access Point Identifier.

TI

Transaction Identifier.

QoS Profile Requested

The quality of service profile requested.

QoS Profile Negotiated

The quality of service profile negotiated.

Radio Priority

The RLC/MAC radio priority level for uplink user data transmission.

Send N‑PDU Number

SNDCP sequence number of the next uplink N‑PDU to be sent to the SGSN.

Receive N‑PDU Number

SNDCP sequence number of the next downlink N‑PDU expected from the SGSN.

The information marked with an "X" in Table 9:

– shall be stored in the SIM if the connected SIM is GPRS-aware; and

– may be stored in the ME after GPRS detach if the connected SIM is not GPRS-aware.

If the SIM is GPRS-aware, then the IMSI, P‑TMSI, P‑TMSI Signature, Routeing Area, Kc, and CKSN stored in the SIM shall be used when accessing the GPRS services.

If the SIM is not GPRS-aware, then the P‑TMSI, P‑TMSI Signature, Routeing Area, Kc, and CKSN stored in the ME shall be used if and only if the IMSI stored in the SIM is identical to the IMSI image maintained in the ME. If the IMSI stored in the SIM is different from the IMSI image in the ME, then the IMSI image in the ME shall not be used, and the MS shall identify itself with the IMSI stored in the SIM when performing a GPRS attach. IMSI, P‑TMSI, P‑TMSI Signature, Routeing Area, Kc, and CKSN may be stored in the ME after the GPRS attach has been successfully performed.

For anonymous access each GPRS MS maintains MM and PDP context information in READY state. The information may be contained in the ME and the TE. Table 10 shows the MS context fields.

Table 10: MS MM and PDP Contexts for Anonymous Access

Field

Description

A‑TLLI

Auxiliary Temporary Logical Link Identity.

Routeing Area

Current routeing area.

Cell Identity

Current cell.

PDP Type

PDP type, e.g., X.25, PPP, or IP.

PDP Address

PDP address, e.g., an X.121 address.

NSAPI

Network layer Service Access Point Identifier.

TI

Transaction Identifier.

APN Requested

The APN requested.

QoS Profile Requested

The quality of service profile requested.

QoS Profile Negotiated

The quality of service profile negotiated.

Radio Priority

The RLC/MAC radio priority level for uplink user data transmission.

Send N‑PDU Number

SNDCP sequence number of the next uplink N‑PDU to be sent to the SGSN.

Receive N‑PDU Number

SNDCP sequence number of the next downlink N‑PDU expected from the SGSN.

13.5 MSC/VLR

The MSC/VLR may store the SGSN number of GPRS-attached MSs that are also IMSI-attached. Table 11 shows the MSC/VLR association for one MS.

Table 11: MSC/VLR Association

Field

Description

IMSI

IMSI is the main reference key.

SGSN Number

The SGSN number of the SGSN currently serving this MS.

13.6 Recovery and Restoration Procedures

The recovery and restoration procedures are intended to maintain service if inconsistencies in databases occur and at lost or invalid database information. "Invalid" in this context means that the database entry cannot be regarded as reliable.

13.6.1 HLR Failure

When an HLR restarts, it sends to each SGSN where one or more of its MSs are registered a Reset message. This causes the SGSN to mark the relevant MM contexts as invalid, and to set NGAF if an SGSN – MSC/VLR association exists. After receipt of the first valid LLC frame from a marked MS, the SGSN performs an update location to the HLR as in the attach or inter SGSN RA update procedures, and, if NGAF is set, the procedure in subclause "Non-GPRS Alert" is followed. The update location procedure and the procedure towards the MSC/VLR may be delayed by the SGSN for a maximum operator configuration-depending time period to avoid high signalling load. The periodic back-up of HLR data to non-volatile storage is mandatory as described in GSM 03.07 [5].

13.6.2 SGSN Failure

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 shall send a Reset message to each of its associated VLRs. The VLRs shall mark all associations containing the restarted SGSN as unreliable. See GSM 03.07.

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, then 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 neither in the SGSN, nor in the old SGSN for the inter-SGSN RA update case, then 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.

NOTE: In some cases, user interaction may be required, and then the MS cannot (re‑)activate the PDP contexts automatically.

When the SGSN receives a GTP PDU for which no PDP context exists it discards the GTP PDU and sends an error indication to the originating GGSN. The GGSN marks the related PDP context as invalid. If there is no MM context for the MS, the SGSN may search the MS by paging with the IMSI in the SGSN area. An MS that is paged for GPRS services with IMSI as the identifier shall perform a new GPRS attach and should (re‑)activate PDP contexts.

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, then 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, then 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.

13.6.3 GGSN Failure

When a GGSN fails, all its PDP contexts affected by the failure become invalid and may be deleted. GGSN storage of subscriber data is volatile.

When the GGSN receives a GTP PDU for which no PDP context exists, it shall discard the GTP PDU and return an error indication to the originating SGSN. The SGSN shall mark the related PDP context as invalid and send a Deactivate PDP Context Request message to the MS. The MS may then reactivate the PDP context.

13.6.4 VLR Failure

When a VLR fails, all its associations with SGSNs affected by the failure become invalid and may be deleted. Based on configuration data, the MSC/VLR sends a BSSAP+ Reset message to each of its associated SGSNs. The SGSNs mark all associations containing the restarted VLR as invalid. After receipt of the first valid LLC frame from an MS that is both GPRS-attached and IMSI-attached, the SGSN shall return a Detach Request (Detach Type) message in order to request the MS to perform a combined RA / LA update. Detach Type shall be set to IMSI Detach. The detach procedure may be delayed by the SGSN for a maximum operator-configuration depending time period to avoid high signalling load.