Section: 4.3.16 Local IP Access (LIPA) function
Content: The LIPA function enables a UE connected via a HeNB to access other entities in the same residential/enterprise network without the user plane traversing the mobile operator's network except HeNB subsystem. The Local IP Access is achieved using a Local GW (L-GW) collocated with the HeNB. LIPA is established by the UE requesting a new PDN connection to an APN for which LIPA is permitted, and the network selecting the Local GW associated with the HeNB and enabling a direct user plane path between the Local GW and the HeNB. The HeNB supporting the LIPA function includes the Local GW address to the MME in every INITIAL UE MESSAGE and every UPLINK NAS TRANSPORT control message as specified in TS 36.413[ Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Application Protocol (S1AP) ]  [36]. 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. 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 Local IP Access. The Local GW (L-GW) shall reject any UE requested bearer resource modification. The direct user plane path between the HeNB and the collocated L-GW is enabled with a Correlation ID parameter that is associated with the default EPS bearer on a PDN connection used for Local IP Access. Upon establishment of the default EPS bearer the MME sets the Correlation ID equal to the PDN GW TEID (GTP-based S5) or the PDN GW GRE key (PMIP-based S5). The Correlation ID is then signalled by the MME to the HeNB as part of E-RAB establishment and is stored in the E-RAB context in the HeNB. The Correlation ID is used in the HeNB for matching the radio bearers with the direct user plane path connections from the collocated L-GW. If the UE is roaming and if the HSS indicates LIPA roaming allowed for this UE in this VPLMN, then the VPLMN (i.e. MME) may provide LIPA for this UE. Furthermore, in the absence of any LIPA information for the requested APN from the HSS, the VPLMN (i.e MME) shall not provide LIPA. The VPLMN address allowed flag is not considered when establishing a LIPA PDN connection. LIPA is supported for APNs that are valid only when the UE is connected to a specific CSG. LIPA is also supported for "conditional" APNs that can be authorized to LIPA service when the UE is using specific CSG. APNs marked as "LIPA prohibited" or without a LIPA permission indication cannot be used for LIPA. MME shall release a LIPA PDN connection to an APN if it detects that the UE's LIPA CSG authorization data for this APN has changed and the LIPA PDN connection is no longer allowed in the current cell. As mobility of the LIPA PDN connection is not supported in this release of the specification, the LIPA PDN connection shall be released when the UE moves away from H(e)NB. Before starting the handover procedure towards the target RAN, the H(e)NB shall request using an intra-node signalling the collocated L-GW to release the LIPA PDN connection. The H(e)NB determines that the UE has a LIPA PDN connection from the presence of the Correlation ID in the UE (E-)RAB context. The L-GW shall then initiate and complete the release of the LIPA PDN connection using the PDN GW initiated bearer deactivation procedure as per clause 5.4.4.1 or GGSN initiated PDP context deactivation procedure as specified in TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [7]. The H(e)NB shall not proceed with the handover preparation procedure towards the target RAN until the UE's (E-)RAB context is clear for the Correlation ID. At the handover, the source MME checks whether the LIPA PDN connection has been released. If it has not been released: - and the handover is the S1-based handover or the Inter-RAT handover, the source MME shall reject the handover. - and the handover is X2-based handover, the MME shall send a Path Switch Request Failure message (see more detail in TS 36.413[ Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Application Protocol (S1AP) ]  [36]) to the target HeNB. The MME performs explicit detach of the UE as described in the MME initiated detach procedure of clause 5.3.8.3. NOTE 2: The direct signalling (implementation dependent) from the H(e)NB to the L-GW is only possible since mobility of the LIPA PDN connection is not supported in this release. During idle state mobility events, the MME/SGSN shall deactivate the LIPA PDN connection when it detects that the UE has moved away from the HeNB.