3 General procedures in the network related to Location Management

23.0123GPPLocation management proceduresRelease 17TS

3.1 Procedures in the MSC related to Location Updating

The MSC shall pass messages related to location updating between the MS and the VLR.

3.2 Procedures in the VLR related to Location Updating

FFS

3.3 Procedures in the HLR related to Location Updating

FFS

3.4 Normal Location Updating and IMSI detach/attach operation

When receiving a Location Updating Request or an IMSI detach/attach message from an MS, the MSC shall convey the message to its associated Visitor Location Register. Any response from the location register shall similarly be conveyed to the MS.

3.5 IMSI enquiry procedure

The MS shall identify itself by either the IMSI or the TMSI plus Location Area Identification of the previous VLR. In the latter case the new VLR shall attempt to request the IMSI and authentication parameters from the previous VLR by the methods defined in 3GPP TS 29.002 [8].

If this procedure fails, or if the TMSI is not allocated, the VLR shall request that the MS identifies itself by use of the IMSI.

3.6 Information transfer between Visitor and Home Location Registers

3.6.1 Procedures for location management

Detailed procedures for exchange of and location updating information between visitor and home location registers are given in 3GPP TS 29.002 [8]. Below follows an overview of these procedures.

3.6.1.1 Location updating procedure

This procedure is used when an MS registers with a Visitor Location Register.

The VLR provides its address to the HLR.

The VLR may also allocate an optional identity for the MS at location updating: the Local Mobile Station Identity (see 3GPP TS 23.003 [3]).

3.6.1.2 Downloading of subscriber parameters to the VLR

As a part of the location updating procedure, the Home Location Register will convey the subscriber parameters of the MS which need to be known by the visitor location register for proper call handling. This procedure is also used whenever there is a change in the subscriber parameters that need to be conveyed to the VLR (e.g. change in subscription, a change in supplementary services activation status).

If the HPLMN applies the multinumbering option, different MSISDNs are allocated for different Basic Services (see 3GPP TS 29.007 [9]) and stored in the HLR. Among these MSISDNs, the Basic MSISDN Indicator as part of the HLR subscriber data (see 3GPP TS 23.008 [5]) marks the ‘Basic MSISDN’ to be sent to the VLR at location update. It is used in the VLR for call handling as calling party and as line identity.

If the HPLMN applies the Administrative Restriction of Subscribers’ Access feature, the HLR shall convey the subscriber access restriction parameter (AccessRestrictionData) to the VLR. The VLR shall check this subscription parameter against the radio access technology that supports the LA/RA in which the UE is roaming to decide whether the location update should be allowed or rejected.

For further information of the Subscriber access restriction see 3GPP TS 23.008[5].

3.6.1.3 Location cancellation procedure

The procedure is used by the home location register to remove a MS from a visitor location register. The procedure will normally be used when the MS has moved to an area controlled by a different location register. The procedure can also be used in other cases, e.g. an MS ceases to be a subscriber of the Home PLMN.

3.6.1.4 Mobile subscriber purging procedure

A VLR may purge the subscriber data for an MS which has not established radio contact for a period determined by the network operator. Purging means to delete the subscriber data and to "freeze" the TMSI that has been allocated to the purged MS in order to avoid double TMSI allocation. The VLR shall inform the HLR of the purging.

When the HLR is informed of the purging, it shall set the flag "MS purged" in the IMSI record of the MS concerned. Presence of the "MS purged" flag will cause any request for routing information for a call or short message to the MS to be treated as if the MS were not reachable.

In the VLR, the "frozen" TMSI is freed for usage in the TMSI allocation procedure by location updating for the purged MS in the same VLR, location cancellation for the purged MS or, in exceptional cases, by O&M.

In the HLR, the "MS purged" flag is reset by the location updating procedure and after reload of data from the non-volatile back-up that is performed when the HLR restarts after a failure.

3.6.1.5 Support for subscription without MSISDN

An MSC/VLR may support delivery of SMS destined to an MS without MSISDN for GPRS and EPS operation whereby a MSISDN is not allocated as part of the subscription data (see 3GPP TS 23.060 [3] clause 5.3.17 and 3GPP TS 23.401 [72]).

An MSC/VLR which supports MSISDN-less operation shall indicate such support to the HLR in the MAP Update Location request.

The HLR should reject a MAP Update Location request received for an MSISDN-less subscription from a VLR not indicating support of MSISDN-less operation, with a cause indicating that roaming is not allowed.

The HLR shall download the subscriber parameters to the VLR as per clause 3.6.1.2 but without an MSISDN for an MSISDN-less subscription if the VLR indicates support of MSISDN-less operation.

NOTE 1: VLRs not supporting MSISDN-less operation can face unpredictable problems if the HLR was downloading subscriber parameters without an MSISDN or with a dummy MSISDN shared across multiple subscriptions.

NOTE 2: Some services have unresolved MSISDN dependencies and are not supported at operation without MSISDN. See 3GPP TS 23.060 [3] clause 5.3.17.

NOTE 3: The HLR can accept a MAP Update Location request received for an MSISDN-less subscription from a VLR not indicating support of MSISDN-less operation if the HLR knows by proprietary means that the VLR supports MSISDN-less operation in a proprietary way (e.g. with a dummy MSISDN value).

3.7 Overload Protection

3.7.1 Overview

As the number of mobile devices increase and become more automated (Machine Type Communication, MTC type devices) the network is at greater risk of becoming overloaded. Additional mechanisms may be deployed to prevent and or control overload and congestion. This clause describes such optional mechanisms.

The succeeding descriptions applies to Network Mode of Operation II (requesting CS only). For NMO I (requesting both CS and PS) the procedures are described in 3GPP TS 23.060 [20].

3.7.2 Congestion Control during Mobility Management

The MSC or VLR may support the capability to reject Location Updating Requests or IMSI Attach messages from an MS if the node is experiencing congestion.

The MSC/VLR may indicate the rejection is due to congestion with a specific congestion cause value and a specific back-off timer, see 3GPP TS 24.008 [13].

The Mobility Management back-off timer shall not impact Cell/RAT and PLMN change. Cell/RAT and RA change do not stop the Mobility Management back-off timer. The Mobility Management back-off timer shall not be a trigger for PLMN reselection. The back-off timer is stopped as defined in 3GPP TS 24.008 [13] when a new PLMN that is not an equivalent PLMN is accessed.

While the Mobility Management back-off timer is running, the MS shall not initiate any Mobility Management procedures. However, the MS is allowed to initiate Mobility Management procedures for priority/emergency services and mobile terminated services even when the Mobility Management back-off timer is running.

If the MS receives a paging request from the MSC/VLR while the Mobility Management back-off timer is running, the MS shall stop the Mobility Management back-off timer and initiate the CM Service Request procedure.To avoid that large amounts of MSs initiate deferred requests (almost) simultaneously, the MSC/VLR should select the Mobility Management back-off timer value so that deferred requests are not synchronised.

The decision to apply congestion control is made by the MSC/VLR, the detailed criteria for which is outside the scope of this specification but may for example take into account the low access priority indication if signalled by MSs.

The MSC/VLR should use implicit detach timer values that are larger than the Mobility Management back-off timer values to avoid that the MSC/VLR implicitly detaches the MS before the MS has performed a LAU procedure, which could lead to unneccessary signalling after the back-off timer expires.

3.7.3 Extended periodic LAU Signalling

To reduce network load from periodic location updating (LAU) signalling and to increase the time until the MS detects a potential need for changing the RAT or PLMN (e.g. due to network problems) longer values of the periodic LAU timer and implicit detach timer should be supported.

A long periodic LAU timer value may be locally configured at the MSC/VLR for MS configured for low access priority (see 3GPP TS 24.368 [19]) or may be stored as part of the subscription data in the HLR. During the IMSI Attach and Location Updating procedures, the MSC/VLR should allocate the periodic LAU timer value for the MS based on VPLMN operator policy, low access priority indication from the MS, and subscription information received from the HSS. If the allocated periodic LAU timer value is longer than T3212, the MSC/VLR shall provide the MS with the periodic LAU timer in the Location Updating Accept message as specified in 3GPP TS 24.008 [13].

If the subscriber is not roaming and the MSC/VLR receives a subscribed periodic LAU timer value from the HSS, it should allocate the subscribed value to the MS as periodic LAU timer. If the subscriber is roaming and the MSC/VLR receives a subscribed periodic LAU timer value from the HSS, the MSC/VLR may use the subscribed periodic LAU timer value as an indication to decide for allocating a locally configured periodic LAU timer value to the MS.

3.8 Information transfer between VLR and CSG Subscriber Server

3.8.1 Procedures for location management

3.8.1.1 General

Detailed procedures for exchange of and location updating information between VLR and CSG Subscriber Server are given in 3GPP TS 29.002[8]. This clause follows an overview of these procedures.

3.8.1.2 Updating VCSG Location procedure

This procedure is used when an MS registers with a Visitor Location Register and there is a need to do a registration with the CSS.

The VLR provides its address to the CSS.

3.8.1.3 Downloading of VPLMN CSG subscription data to the VLR

As a part of the location updating procedure, the CSG Subscriber Server shall convey the VPLMN CSG subscription data of the roaming MS which needs to be known by the visitor location register for determine whether the MS can access the current cell to have CS services. This procedure is also used whenever there is a change in the VPLMN CSG subscription data that needs to be conveyed to the VLR.

3.8.1.4 VCSG Location cancellation procedure

The procedure is used by the CSS to remove a MS from a CSS. The procedure will normally be used when there is a removal of the CSG subscription data in CSS and of the MS registration including the case where a MS was registered in CSS but without CSG data.