HeNB Support

The E-UTRAN architecture may deploy a Home eNB Gateway (HeNB GW) to allow the S1 interface between the HeNB and the EPC to scale to support a large number of HeNBs. The HeNB GW serves as a concentrator for the C-Plane, specifically the S1-MME interface. The S1-U interface from the HeNB may be terminated at the HeNB GW, or a direct logical U-Plane connection between HeNB and S-GW may be used.


This version of the specification does not support X2 connectivity of HeNBs.

The S1 interface is defined as the interface:

- Between the HeNB GW and the Core Network.
- Between the HeNB and the HeNB GW.
- Between the HeNB and the Core Network.
- Between the eNB and the Core Network.

The HeNB GW appears to the MME as an eNB. The HeNB GW appears to the HeNB as an MME. The S1 interface between the HeNB and the EPC is the same whether the HeNB is connected to the EPC via a HeNB GW or not.

The HeNB GW shall connect to the EPC in a way that inbound and outbound mobility to cells served by the HeNB GW shall not necessarily require inter MME handovers. One HeNB serves only one cell.

The functions supported by the HeNB shall be the same as those supported by an eNB (with the possible exception of NNSF) and the procedures run between a HeNB and the EPC shall be the same as those between an eNB and the EPC

Functional Split
- Discovery of a suitable Serving HeNB GW.
- A HeNB shall only connect to a single HeNB GW at one time, namely no S1 Flex function shall be used at the HeNB.
- The HeNB will not simultaneously connect to another HeNB GW, or another MME.
- The TAC and PLMN ID used by the HeNB shall also be supported by the HeNB GW.
- Selection of an MME at UE attachment is hosted by the HeNB GW instead of the HeNB;
- HeNBs may be deployed without network planning. A HeNB may be moved from one geographical area to another and therefore it may need to connect to different HeNB GWs depending on its location.

The HeNB GW hosts the following functions

- Relaying UE-associated S1 application part messages between the MME serving the UE and the HeNB serving the UE.
- Terminating non-UE associated S1 application part procedures towards the HeNB and towards the MME. Note that when a HeNB GW is deployed, non-UE associated procedures shall be run between HeNBs and the HeNB GW and between the HeNB GW and the MME.
- Optionally terminating S1-U interface with the HeNB and with the S-GW.
- Supporting TAC and PLMN ID used by the HeNB.
- X2 interfaces shall not be established between the HeNB GW and other nodes.

A list of CSG IDs may be included in the PAGING message. If included, the HeNB GW may use the list of CSG IDs for paging optimization.

MME hosts the following functions

- Access control for UEs that are members of Closed Subscriber Groups (CSG):
- In case of handovers to CSG cells, access control is based on the target CSG ID provided to the MME by the serving E-UTRAN.
- Membership Verification for UEs handing over to hybrid cells
- In case of handovers to hybrid cells Membership Verification is triggered by the presence of the Cell Access Mode and it is based on the target CSG ID provided to the MME by the serving E-UTRAN.
- CSG membership status signalling to the target E-UTRAN in case of attachment/handover to hybrid cells and in case of the change of membership status when a UE is served by a CSG cell or a hybrid cell.
- Supervising the eNB action after the change in the membership status of a UE.
- Routing of handover messages towards HeNB GWs based on the TAI contained in the handover message.

Reference : 3GPP TS 36.300