4.8 Support of SIPTO at the Local Network

36.3003GPPEvolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN)Overall descriptionRelease 17Stage 2TS

4.8.1 General

E-UTRAN supports SIPTO at the Local Network with a collocated L-GW in the eNB or a standalone GW (with S-GW and L-GW collocated), as specified in TS 23.401 [17].

4.8.2 SIPTO at the Local Network with collocated L-GW

Figure 4.8.2-1 shows the logical architecture for the eNB when it supports SIPTO@LN with a collocated L-GW.

Figure 4.8.2-1: E-UTRAN – SIPTO@LN with collocated L-GW – Logical Architecture

For a SIPTO@LN PDN connection, the eNB sets up and maintains an S5 connection to the EPC.

The mobility of the SIPTO@LN PDN connection is not supported in this release of the specification. The SIPTO@LN PDN connection is released after a handover is performed, and the collocated L-GW in the source eNB triggers the release over the S5 interface, as described in TS 23.401 [17].

In case of SIPTO@LN with collocated L-GW support, the eNB supports the following additional functions:

– transfer of the collocated L-GW IP address of the eNB over S1-MME to the EPC at every idle-active transition;

– transfer of the collocated L-GW IP address of the eNB over S1-MME to the EPC within every Uplink NAS Transport procedure;

– support of basic P-GW functions in the collocated L-GW such as support of the SGi interface corresponding to SIPTO@LN;

– additional support of first packet sending, buffering of subsequent packets, internal direct L-GW-eNB user path management and in sequence packet delivery to the UE;

– support of the necessary restricted set of S5 procedures corresponding to the support of SIPTO@LN function as specified in TS 23.401 [17];

– notification to the EPC of the collocated L-GW uplink TEID(s) or GRE key(s) for the SIPTO@LN bearer(s) over S5 interface within the restricted set of procedures to be forwarded over S1-MME and further used by the eNB as "SIPTO correlation id" for correlation purposes between the collocated L-GW and the eNB;

– triggering SIPTO@LN PDN connection release by the collocated L-GW after a handover is performed, as specified in TS 23.401 [17].

In case of SIPTO@LN with collocated L-GW support, the MME supports the following additional functions:

– SIPTO@LN activation for the requested APN based on SIPTO permissions in the subscription data and received collocated L-GW IP address;

– transfer of the "SIPTO correlation id" to the eNB via the initial context setup procedure and E-RAB setup procedure;

– release of the SIPTO@LN PDN connection of an idle-mode UE when the UE moves away from the coverage area of the eNB, as specified in TS 23.401 [17].

4.8.3 Support for SIPTO@LN with Stand-Alone Gateway

SIPTO@LN is supported using a stand-alone gateway (with co-located S-GW and L-GW) deployed in the local network. The MME may decide to trigger S-GW relocation without UE mobility, as specified in TS 23.401 [17]. Mobility for the SIPTO@LN PDN connection is not supported in this release: the SIPTO@LN PDN connection shall be released after handover, unless the source and target eNBs are in the same LHN (i.e. they have the same LHN ID), as specified in TS 23.401 [17].

In case of SIPTO@LN support with stand-alone gateway, the eNB supports the following additional functions:

– signalling of its LHN ID to the MME in the INITIAL UE MESSAGE, UPLINK NAS TRANSPORT, HANDOVER NOTIFY and PATH SWITCH REQUEST messages;

– support for MME-triggered S-GW relocation without UE mobility through the E-RAB MODIFY REQUEST message.

In case of SIPTO@LN support with stand-alone gateway, the MME supports the following additional functions:

– SIPTO@LN PDN activation for the requested APN based on subscription data and received LHN ID;

– S-GW relocation without UE mobility.