4.3.15a Selected IP Traffic Offload (SIPTO) at the Local Network

23.4013GPPGeneral Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) accessRelease 18TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

4.3.15a.1 General

The SIPTO at the Local Network function enables an IP capable UE connected via a (H)eNB to access a defined IP network (e.g. the Internet) without the user plane traversing the mobile operator’s network.

The subscription data in the HSS are configured per user and per APN to indicate to the MME if offload at the local network is allowed or not.

SIPTO at the Local Network can be achieved by selecting a L-GW function collocated with the (H)eNB or selecting stand-alone GWs (with S-GW and L-GW collocated) residing in the Local Network. In both cases the selected IP traffic is offloaded via the Local Network.

Specific to the HeNB subsystem, the applicability of SIPTO at the Local Network does not depend on CSG membership and the feature can be applied to any UE, as long as the UE is allowed to access the cell.

For this release of the specification, no interface between the L-GW and the PCRF is specified and there is no support for dedicated bearers on the PDN connection used for SIPTO at the Local Network. The Local GW (L-GW) shall reject any UE requested bearer resource modification.

For this release of the specification, SIPTO at the Local Network is intended for offloading Internet traffic only, thus the L-GW does not provide APN specific connectivity. Therefore if the subscription data in the HSS indicate that offload at the Local Network is allowed, this implies that the related APN is typically used for providing Internet connectivity.

If the MME detects a change in SIPTO permissions in the subscription data for a given subscriber for a given APN and the subscriber has already established a SIPTO at the local network PDN connection to that APN, the MME shall release the SIPTO at the Local Network PDN connection for that APN with "reactivation requested" cause as specified in clause 5.10.3.

NOTE: In this release of the specification it is assumed that the target S-GW selected during the Handover also has connectivity to the L-GW.

4.3.15a.2 SIPTO at the Local Network with stand-alone GW (with S-GW and L-GW collocated) function

SIPTO at the Local Network is achieved using a stand-alone GW (with S-GW and L-GW collocated) residing in the Local Network.

A (H)eNB supporting SIPTO at the Local Network with the stand-alone GW includes the Local Home Network ID to the MME in every INITIAL UE MESSAGE, every UPLINK NAS TRANSPORT control message, HANDOVER NOTIFY and PATH SWITCH REQUEST messages.

If a SIPTO PDN connection is initiated as an additional subsequent PDN connection, the MME should check if the S‑GW is optimal for the user’s current location. If it is not, and if the network supports S-GW relocation without being triggered by a mobility event, the MME may decide to perform an MME triggered Serving GW relocation according to clause 5.10.4, when possible (e.g. no other restrictions apply).

For SIPTO at the Local Network with a stand-alone GW, the location of the Serving GW may be determined based on the operator policy and user’s profile regarding support of SIPTO at Local Network so that:

– At attachment to the (H)eNB, a local S-GW can always be selected independent of whether a SIPTO at the Local Network PDN connection is established or not. If mobility is performed to the macro network without having a SIPTO connection, a S-GW relocation can be performed as specified via existing mobility procedures with S-GW relocation.

– At attachment to a (H)eNB, a macro S-GW may be allocated for PDN connection in the operator’s network. If a new PDN connection is requested by the UE that requires that a local S-GW is selected to provide for SIPTO at the Local Network, S-GW relocation from the macro S-GW to the local S-GW shall be performed as specified in clause 5.10.4.

As IP data session continuity for SIPTO at the Local Network PDN connection is not supported in this release of the specification, subsequent to handover completion the (target) MME should disconnect the SIPTO at the Local Network PDN connection with "reactivation requested" cause as specified in clause 5.10.3, unless the Local Home Network ID is not changed. The IP data session should be maintained if the Local Home Network ID is not changed. If the UE has no other PDN connection and the Local Home Network ID is changed, the (target) MME initiates "explicit detach with reattach required" procedure according to clause 5.3.8.3.

Upon completion of Tracking Area Update procedure, the (new) MME shall trigger the re-establishment of the SIPTO at the Local Network PDN connection when it detects that the UE has moved away from the (H)eNB and to a (H)eNB with different Local Home Network ID, as specified in clause 5.3.3 and clause 5.3.4.

NOTE: It is expected that all MMEs/SGSNs in a PLMN have support for SIPTO at the Local Network where the operator deploys this feature, in order to support mobility procedures. For a mobility event where target MME/SGSN does not support SIPTO at the Local Network, the handling of PDN deactivation for SIPTO at Local Network PDN connection is not specified.

4.3.15a.3 SIPTO at the Local Network with L-GW function collocated with the (H)eNB

SIPTO at the Local Network is achieved using a Local GW (L-GW) function collocated with the (H)eNB and using the same procedures as described in clause 4.3.15, with the following additions:

– The (H)eNB supporting the SIPTO at the Local Network function includes the Local GW address to the MME in every INITIAL UE MESSAGE and every UPLINK NAS TRANSPORT control message specified in TS 36.413 [36].

– The PDN GW selection function uses the L-GW address proposed by (H)eNB in the S1-AP message, instead of DNS interrogation.

– Specific to the HeNB subsystem, the Local GW information for SIPTO at the Local Network is signalled on S1 separately from the Local GW information for LIPA. The L-GW shall be able to discriminate between PDN connection for SIPTO at the Local Network and for LIPA.

NOTE 1: The protocol option (i.e. GTP or PMIP) supported on the S5 interface between Local GW and S‑GW is configured on the MME.

The direct user plane path between the (H)eNB and the collocated L-GW is enabled with a SIPTO Correlation ID parameter that is associated with the default EPS bearer on the PDN connection used for SIPTO at the Local Network. Upon establishment of the default EPS bearer the MME sets the SIPTO Correlation ID equal to the PDN GW TEID (GTP-based S5) or the PDN GW GRE key (PMIP-based S5). The SIPTO Correlation ID is then signalled by the MME to the (H)eNB as part of E-RAB establishment and is stored in the E-RAB context in the (H)eNB. The SIPTO Correlation ID is used in the (H)eNB for matching the radio bearers with the direct user plane path connections from the collocated L-GW for SIPTO at local network PDN connection.

As IP data session continuity for the SIPTO at the Local Network PDN connection is not supported in this release of the specification, the SIPTO at the Local Network PDN connection shall be re-established when the UE moves away from (H)eNB. During the handover procedure, when the source (H)eNB releases its resources related to the UE, the (H)eNB shall request using intra-node signalling the collocated L-GW to re-establish the SIPTO at the Local Network PDN connection. The L-GW starts a timer. When the timer expires, the L-GW shall initiate the release of the SIPTO at the Local Network PDN connection using the PDN GW initiated bearer deactivation procedure according to clause 5.4.4.1 with the "reactivation requested" cause value.