Content for  TS 23.060  Word version:  18.0.0

The SIPTO function enables an operator to offload certain types of traffic at a network node close to that UE's point of attachment to the access network or to a local network. SIPTO function specified in clause 4.3.15 of TS 23.401 is applicable, with the SGSN node providing the functions specified for the MME. In order to fully utilise the benefit of the SIPTO with GW selection function, direct tunnel functionality as described in clause 15.6 should be applied. In order to select a set of GWs (S-GW/P-GW or GGSN) for SIPTO above RAN service that is most appropriate for that UE's current location (during the PDP Context Activation Procedure (clauses 9.2.2.1 and 9.2.2.1A)), the SGSN checks the APN status for SIPTO for the user during the GW Selection function procedure as described in clause 5.3.7 and Annex A. For SIPTO above RAN, as a result of UE mobility (e.g. detected by the SGSN at RAU), the target SGSN may allocate a different GW that is more appropriate for the UE's current location, e.g. the SGSN may know whether the UE's new location is served by the same GW as the old one. When the SGSN decides upon the need for GW relocation, the SGSN deactivates the impacted PDN connections indicating "reactivation requested" as specified in clause 9.2.4.2. For SIPTO above RAN or SIPTO at the Local network with stand-alone GW (with S-GW and L-GW collocated), if SIPTO PDN connection is initiated as an additional subsequent PDN connection, S4-SGSN should check if the S-GW is optimal for the user's current location. If it is not, S4-SGSN may decide to perform a S4-SGSN triggered Serving GW relocation according to the clause 9.2.2.4, when possible (e.g. no other restriction apply).

SIPTO can be achieved by adding an optional Traffic Offload Function at Iu interface as described in clause B.1. If implemented, and in order to activate SIPTO at Iu-ps, the SGSN shall send charging parameters including MSISDN, APN, Charging Characteristics in the RANAP messages whenever a RAB to be offloaded is requested to be setup as described in clause B.2.

This clause provides an overview about functionality for Machine Type Communications according to service requirements described in TS 22.368. The specific functionality is described in the affected procedures and features of this and other specifications. For discrepancies between this overview clause and the detailed procedure and function descriptions, the latter take precedence. MTC functionality is provided by the visited and home networks when the networks are configured to support machine type communication. It applies to both the non-roaming case and the roaming case and some functionality may be dependent upon the existence of appropriate roaming agreements between the operators. Some of the MTC functions are controlled by subscriber data. Other MTC functions are based on indicators sent by the UE to the network. MTC functionality is performed by UEs that are configured to support different options as described in clause 5.3.13.3. Though motivated by scenarios and use cases defined in TS 22.368, the functions added to support MTC have general applicability and are in no way constrained to any specific scenario or use case except where explicitly stated.

The number of Machine Type Communication devices may be several orders of magnitude greater than "traditional" devices. Many (but not all) MTC devices will be relatively stationary and/or generate low volumes of traffic. However, these MTC devices have the capability to generate normal quantities of signalling. As normal signalling from large numbers of MSs may cause overload independently whether the MS is used for MTC or not, generic functionality for overload and congestion control is required. The total signalling from large numbers of MSs is a concern in at least two situations:

• when an application (running in many MSs) requests many MSs to do "something" at the same time; and/or
• when many MSs are roamers and their serving network fails, then they can all move onto the local competing networks, and potentially overload the not (yet) failed network(s).

To counter these potential problems, the following standardised indications and mechanisms are provided in a generic manner. These permit node specific features to be developed to protect the networks.

1. Where applicable, MSs can be configured for enhancements as described in subsequent bullets. Post-manufacturing configuration can be performed remotely as described in clause 5.3.13.3.
2. For mobile originated services, MSs configured for low access priority provide:
   • the UTRAN with information indicating that the RR(C) connection establishment request has low access priority (see clause 5.3.13.3); and
   • the GERAN with information indicating that the RR connection establishment request has low access priority (see clause 5.3.13.3), when accessing the network for the purpose of PS domain signalling.
   In GERAN, "Implicit Reject" functionality permits the BSS to inhibit Random Access Channel signalling (see TS 44.018).
   Clause 5.3.13.3 describes when low access priority is not applicable.
3. RRC signalling has the capability of providing 'extended wait timers' when rejecting messages.
4. SGSN can initiate rejection of RR(C) connection establishment in the GERAN/UTRAN MSs that access the network with low access priority. In addition, SGSN signalling or GERAN/UTRAN O&M can trigger GERAN/UTRAN to initiate Extended Access Barring in the GERAN /UTRAN. These mechanisms are further described in clause 5.3.6.4.
5. Overload messages from the SGSN to RNS/BSS are extended to aid the RAN in performing the functionality in bullets b, c and d above.
6. MSs configured with a long minimum periodic PLMN search time limit (see TS 24.368) have an increased minimum time inbetween their searches for more preferred PLMNs.
7. At PLMN change, MSs configured to perform Attach with IMSI at PLMN change (see TS 24.368) do this rather than an RA update with P-TMSI (thus avoiding the need to reject the RA update, and to request the IMSI following the subsequent Attach with P-TMSI).
8. For mobile originated services, MSs configured for low access priority (see TS 24.368) provide a low access priority indication to the SGSN in NAS signalling that permits the SGSN to undertake protective measures (e.g. to permit the SGSN to immediately command the MS to move to a state where it does not need to generate further signalling messages and/or does not reselect PLMNs), as described in clause 5.3.6.4. Clause 5.3.13.3 describes when low access priority is not applicable.
9. Using periodic RAU timer information sent by the HSS and/or MS provided indication (bullet h above), the SGSN can allocate a long periodic RAU timer to the MS. A long periodic RAU timer is likely to slow down the rate at which an MS detects a network failure and thus it slows down the rate of movement of MSs from a failed network to other local competing networks (see clause 5.3.13.5).
10. Mechanisms for the SGSN and GGSN/P-GW to detect congestion associated with a particular APN (see clauses 5.3.6.2 and 5.3.6.3 and TS 23.401).
11. The addition of 'back off timers' to GMM and SM signalling messages (e.g. to rejection messages). These include some time randomisation to guard against a repeat of a load peak. The SGSN should be able to apply this behaviour on a per-APN basis as described in clause 5.3.6.2.
12. Mechanisms that permit the GGSN/P-GW to handle per-APN congestion (see clause 5.3.6.3 and TS 23.401).
13. When using the S4 architecture, an SGSN overload control mechanism to selectively limit the number of Downlink Data Notification requests the S-GW sends to the SGSN for downlink low priority traffic received for MSs in idle mode (see clause 5.3.6.5).
14. The BSS and RNS are provided with low access priority indications from the MS that permit them to steer "new MTC entrants into a pool area" to specific SGSNs (e.g. to an SGSN optimised for MTC devices by having a larger subscriber data base, see TS 23.236).
15. GERAN and/or UTRAN broadcast signalling can be used to command MSs configured to use the extended NMO I system information (see TS 24.368) to operate in Network Mode of Operation I while leaving other MSs operating in NMO II. This reduces the amount of signalling from MSs configured as above and may be particularly useful at times of the failure of another PLMN. Maintaining NMO II for existing MSs avoids changes to their existing service levels (see clause 6.3.3.1).
16. MS configured for specific handling of the invalid USIM state, the "forbidden PLMN list" and the "forbidden PLMNs for GPRS service list" remembers that the (U)SIM is invalid and keeps the PLMN forbidden lists even if the MS is switched off and then switched on.
17. When the MS has an activated PDP context that is without low access priority or the MS is requested to activate such a PDP context and the MS is configured with a permission for overriding low access priority, then the MS does not provide a low access priority indication to the SGSN in MM NAS signalling and also not to the RAN in the RR(C) requests. In the NAS request for activating a PDP context, this MS always indicates what the upper layers requested, i.e. the MS indicates low access priority in that NAS request unless the upper layers request activation of a PDN connection without low access priority.
18. When the MS has an activated PDP context that is without low access priority or the MS is requested to activate such a PDP context and the MS is configured with a permission for overriding Extended Access Barring, then the MS ignores any Extended Access Barring (if it is activated in the network) as defined in TS 22.011.

A subscriber can by agreement with its operator be required to use MSs that are configured (see TS 24.368) to support one or more of the following options:

• MS configured for low access priority; and/or
• MS configured with a permission for overriding low access priority, which is only applicable for an MS that is also configured for low access priority; and/or
• MS configured to use the extended NMO I system information; and/or
• MS configured to perform Attach with IMSI at PLMN change; and/or
• MS configured with a long minimum periodic PLMN search time limit; and/or
• MS configured for Extended Access Barring; and/or
• MS configured with a permission for overriding Extended Access Barring, which is only applicable for a UE that is also configured for Extended Access Barring;and/or
• MS configured for specific handling of the invalid (U)SIM state, the "forbidden PLMN list" and the "forbidden PLMNs for GPRS service list".

MSs can be configured for one or more of the above options with the following restrictions:

• in this Release of the specification, an MS that is configured for low access priority shall also be configured for Extended Access Barring; and
• in this Release of the specification, an MS that is configured for Extended Access Barring shall be configured for low access priority.
• in this Release of the specification, an MS that is configured for overriding low access priority shall also be configured for overriding Extended Access Barring; and
• in this Release of the specification, an MS that is configured for overriding Extended Access Barring shall also be configured for overriding low access priority.

Post-manufacturing configuration of these options in the MS can be performed only by OMA DM or (U)SIM OTA procedures. MSs capable of the above options should support configuration of these options by both OMA DM and (U)SIM OTA procedures. An MS configured for low access priority shall transmit the low access priority indicator to the SGSN during the appropriate NAS signalling procedures and transmit the corresponding low access priority to the UTRAN/GERAN during RR(C) connection establishment procedures, unless the MS is also configured with a permission for overriding low access priority where bullet q from clause 5.3.13.2 applies. Low access priority shall not be applicable in the following situations:

• for all procedures related to an emergency PDN connection; used for IMS Emergency sessions that are to be prioritized as per the requirements for IMS Emergency session procedures (see clause 5.10). When an emergency PDN connection gets established, the SGSN may, based on SGSN configuration, initiate the deactivation of any non-emergency PDN connection using the SGSN-initiated PDP Context Deactivation Procedure described in clause 9.2.4.2 and, in S4 mode, the SGSN Initiated PDN connection Deactivation Procedure described in clause 9.2.4.1A.1;
• for all procedures when preferential access to the network is provided to the MS by the Access Class 11-15 mechanism according to TS 44.018, TS 44.060, TS 25.331 and TS 22.011;
• for RR(C) connection establishment procedures when responding to paging;
• for an MS configured with a permission for overriding low access priority under conditions described by bullet bullet q from clause 5.3.13.2; or
• other specific situations described in TS 24.008.

If the NAS session management request message used to establish a new PDN connection contains a low access priority indication, the SGSN shall forward the low access priority indication in the Create PDP Context Request message to the GGSN and, in S4 mode, in the Create Session Request message to the S-GW/P-GW. The low priority indication gets associated with a PDN connection when it is established and it shall not change until the PDN connection is deactivated. The low access priority indication may be included in charging records by the visited and home networks. In order to permit the S-GW and/or Gn/Gp SGSN to include the low access priority indicator in the charging records, the low access priority indicator should be stored in the SGSN EPS/PDP Bearer contexts and should be passed as part of these contexts to other SGSN/MME or S-GW nodes in mobility management procedures. A network node may invoke one or more of the following mechanisms based on the indicators received in signalling from MSs or forwarded by other network nodes:

• based on the low access priority indicator in NAS request messages, bullets e, h, i, k and l as defined in clause 5.3.13.2; and/or
• based on the low access priority for RR(C) connection establishment, bullets b, c and n as defined in clause 5.3.13.2.

An MS shall invoke one or more of the following mechanisms based on the configuration and capabilities of the MS:

• when MS is configured with a long minimum periodic PLMN search time limit, MS invokes actions as described in bullet f in clause 5.3.13.2; and/or
• when MS is configured to perform Attach with IMSI at PLMN change, MS invokes actions as described in bullet g in clause 5.3.13.2; and/or
• when MS is configured to use the extended NMO I system information, MS invokes actions as described in bullet o in clause 5.3.13.2; and/or
• when MS is configured for low access priority, MS invokes actions as described in bullets b and h in clause 5.3.13.2; and/or
• when MS is configured for Extended Access Barring, MS invokes actions as defined in bullet d in clause 5.3.13.2; and/or
• when MS is configured for specific handling of the invalid (U)SIM state, the "forbidden PLMN list" and the "forbidden PLMNs for GPRS service list", MS invokes actions as defined in bullet p) in clause 5.3.13.2; and/or
• when MS is configured with a permission for overriding low access priority and Extended Access Barring, the MS invokes actions as described in bullets q and r in clause 5.3.13.2.

To reduce network load from periodic RAU 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) the longer values of the periodic RAU timer and Mobile Reachable timer shall be supported. A long periodic RAU/TAU timer value may be locally configured at SGSN or may be stored as part of the subscription data in HSS. During Attach and RAU procedures the SGSN allocates the periodic RAU timer value as periodic RAU timer to the UE based on VPLMN operator policy, low access priority indication from the MS, periodic RAU/TAU timer value requested by MS and subscription information received from the HSS. If SGSN receives a subscribed periodic RAU/TAU timer value from the HSS it allocates the subscribed value to the MS as periodic RAU timer. A visited PLMN SGSN may use subscribed periodic RAU/TAU timer value, if available, as an indication to decide for allocating a locally configured periodic RAU/TAU timer value to the MS. If no subscribed periodic RAU/TAU timer value is received from the HSS, the SGSN should:

• if the periodic RAU/TAU timer value requested by MS is within the boundaries of the VPLMN operator policy, allocate the value requested by the MS;
• if the periodic RAU/TAU timer value requested by MS is higher than allowed per the VPLMN operator policy, allocate the highest allowed value per the VPLMN operator policy;
• if the periodic RAU/TAU timer value requested by MS is lower than allowed per the VPLMN operator policy, allocate the lowest allowed value per the VPLMN operator policy.

An MS may be configured for low access priority and Extended Access Barring as defined in TS 22.011. This configuration is primarily for usage by applications or users that can tolerate being deferred when competing with other MSs for accessing network resources, e.g. during congestion situations. A subscriber can by agreement with its operator be required to use MSs that are configured for low access priority. The agreement may include a specific tariffing. CDRs show whether a PDN connections was activated for use with low access priority. An MS that is configured for low access priority and Extended Access Barring may be also configured with a permission for an override of low access and Extended Access Barring priority restrictions. This configuration is primarily for usage by applications or users that most of the time can tolerate being deferred due to low access priority when competing with other MSs for accessing network resources, but occasionally the application or user needs access to the network also when the low access priority configuration would prevent getting access. For getting network access also during low priority access or Extended Access Barring restriction conditions, the user or application (upper layers in UE) may request the UE to initiate the activation of a PDN connection without low access priority. The permission for overriding low access priority and Extended Access Barring restrictions by the application or user should be handled with care because as long as such a PDN connection without low access priority is active, the MS is not affected by any access restriction conditions that the network may set for access with low access priority. That is, after the activation of a PDN connection without low access priority, all further MM and RRC access requests of the UE are performed without low access priority as long as such a PDN connection is active. A subscriber can, by agreement with its operator, be required to use MSs that are configured with a permission for overriding low access priority and Extended Access Barring. As the 3GPP system cannot determine whether any overriding of access restrictions by such MSs is justified, the agreement can include a specific tariffing to avoid excessive usage of overriding the low access priority. This can for example be a specific tariffing for the amount of activations and/or the duration of PDN connections that are not with low access priority. CDRs show whether the MS activated the PDN connection with or without low access priority, but not necessarily the access priority the MS uses for the individual data transfer requests.

Functions for High latency communication may be used to handle mobile terminated (MT) communication with UEs being unreachable while using power saving functions e.g. MS Power Saving Mode (see clause 5.3.20) or extended idle mode DRX depending on operator configuration. "High latency" refers to the initial response time before normal exchange of packets is established. That is, the time it takes before a UE has woken up from its power saving state and responded to the initial downlink packet(s). The feature is described in TS 23.682. The High latency communication includes invoking extended buffering of MT data at the Gn/Gp-SGSN or at the Serving GW when the UE is in a power saving state and not reachable. The handling is specified in the Network Initiated Service Request Procedure using Gn/Gp, clause 6.12.2. Establishing the user plane for delivering the buffered data when the UE contacts the SGSN by signalling shall be done in the Routing Area Update procedures. The SGSN uses its parameter DL Data Buffer Expiration Time in the MM context information to remember if there is buffered DL data to be delivered when the UE becomes reachable. When set, the DL Data Buffer Expiration Time shall be cleared at any user plane setup to the RAN, i.e. buffered DL data can been delivered. At RAU procedures with SGSN change, it is indicated in the context response to the new SGSN that buffered DL data is waiting and hence the user plane needs to be established for delivery of the buffer DL data. At RAU procedures the buffered DL data is forwarded to the new Gn/Gp-SGSN or new Serving GW when needed. The High latency communication also includes sending event notifications to application servers that have requested "UE Reachability" or "Availability after DDN failure" monitoring events. If the notifying node is not a Gn/Gp-SGSN, event notifications are sent when a UE becomes reachable, for example as part of the RAU procedures and the MS/UE Initiated Service Request Procedures (see also corresponding procedures in TS 23.401). When "UE Reachability" moniorting is requested for UE's that are using extended idle mode DRX, an event notification is sent to the application server when the UE is about to become reachable for paging. If the SGSN is aware that some signalling or data is pending in the network for an UE, e.g. whether the UE has extended idle mode DRX or PSM enabled, the SGSN may include a Pending Data indication in the next RANAP message towards the UTRAN. If the UTRAN receives this indication, it may take this information into account when determining user inactivity. At inter-RAN node handovers, if some signalling or data are still pending, the target SGSN may send a Pending Data indication to the target UTRAN node.

Cellular Internet of Things GSM Optimisation (CIoT GSM Optimization) provides support of:

• Non-IP data (see clause 5.3.13.8);
• Non-IP data delivery using SCEF (see TS 23.682);
• APN Rate Control (see clause 15.2.3.2).

Support of MSs in Enhanced Coverage is specified in TS 43.064. The usage of Enhanced Coverage may require use of extensive resources (e.g. radio and signalling resources) from the network. This feature enables the operator to prevent specific subscribers from using Enhanced Coverage. The MS indicates its capability of support for restriction of use of Enhanced Coverage for the RAT it is camping on in the Attach and RAU procedure to the SGSN. SGSN receives Enhanced Coverage Restricted parameter from the HLR. This parameter is kept as part of the subscription data in the HLR and specifies per PLMN whether the enhanced coverage functionality is restricted or not for the MS. For roaming MSs, if HLR doesn't provide any Enhanced Coverage Restricted parameter or the provided Enhanced Coverage Restricted parameter is in conflict with the roaming agreement, the SGSN uses default Enhanced Coverage Restricted parameter locally configured in the VPLMN based on the roaming agreement with the subscriber's HPLMN. The UE shall assume that restriction for use of Enhanced Coverage is same in the equivalent PLMNs. If the MS includes the support for restriction of use of Enhanced Coverage, SGSN sends Enhanced Coverage Restricted parameter to the MS in Attach/RAU Accept message. The MS shall use the value of Enhanced Coverage Restricted parameter to determine if enhanced coverage feature should be used or not. The MS assumes Enhanced Coverage is allowed unless explicitly restricted by the network for a PLMN.

This feature enables an operator to deploy multiple core networks within a PLMN with each core network consisting of one or multiple CN nodes. Overview of UE non-assisted DCN selection feature is provided in clause 4.3.25.1 and UE assisted DCN selection feature is provided in clause 4.3.25.1a of TS 23.401. Specific impacts to supporting DCNs for UTRAN and GERAN accesses are captured in this specification and in TS 23.236.

This clause provides an overview about feature for 3GPP PS Data Off according to service requirements described in TS 22.011. 3GPP PS Data Off feature specified in TS 23.401 is applicable, with the SGSN node providing the functions specified for the MME and the GGSN node providing the functions of the PGW. The MSs are configured with up to two lists of 3GPP PS Data Off Exempt Services and the list(s) are provided to the MSs by HPLMN via Device Management or UICC provisioning. When the MS is configured with two lists, one list is valid for the MSs camping in the home PLMN and the other list is valid for any VPLMN the MS is roaming in. If the MS is configured only a single list, without an indication to which PLMNs the list is applicable, then this list is valid for the home PLMN and any PLMN the MS is roaming in. When the MS requests PDP Context Activation, the MS shall send its current 3GPP PS Data Off status (i.e., activated, inactivate) in PCO to the GGSN/PGW as described in clause 9.2.2. If 3GPP PS Data Off status is activated, the MS prevents the sending of uplink IP packets and non-IP data except those related to 3GPP PS Data Off Exempt Service as defined in TS 23.221, based on the pre-configured list of 3GPP Data Off Exempt Services. For those PGWs/GGSNs that indicated support for the 3GPP PS Data Off feature during PDP Context Activation procedure, the MS shall report a change of its 3GPP PS Data Off status in PCO immediately by using MS-initiated PDP Context Modification procedure to those PGWs/GGSNs as described in clause 9.2.3.3, this also applies to the scenario of inter-RAT mobility procedure to GERAN/UTRAN and also to scenarios where the 3GPP PS Data Off status is changed when the session management back-off timer is running as specified in clause 5.3.6. If the MS has not received any 3GPP PS Data Off Support Indication during PDP Context Activation procedure, it shall not report any change of its 3GPP PS Data Off Status for this PDN connection. The MS discovers whether a PGW/GGSN supports 3GPP PS Data Off feature during PDP Context Activation procedure via the presence of the 3GPP PS Data Off Support Indication in the Activate PDP Context Accept message. The additional behaviour of the PGW/GGSN for 3GPP PS Data Off is controlled by local configuration or policy from the PCRF as defined in TS 23.203.