4.7.4 S1 and X2 control plane aspects

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

The S1 control plane protocol stack for supporting RNs is shown in Figure 4.7.4-1. There is a single S1 interface relation between each RN and its DeNB, and there is one S1 interface relation between the DeNB and each MME in the MME pool. The DeNB processes and forwards all S1 messages between the RN and the MMEs for all UE-dedicated procedures. The processing of S1-AP messages includes modifying S1-AP UE IDs, Transport Layer address and GTP TEIDs but leaves other parts of the message unchanged.

All non-UE-dedicated S1-AP procedures are terminated at the DeNB, and handled locally between the RN and the DeNB, and between the DeNB and the MME(s). Upon reception of an S1 non-UE-dedicated message from an MME, the DeNB may trigger corresponding S1 non-UE-dedicated procedure(s) to the RN(s). If more than one RN is involved, the DeNB may wait and aggregate the response messages from all involved RNs before responding to the MME. Upon reception of an S1 non-UE-dedicated message from an RN, the DeNB may trigger associated S1 non-UE-dedicated procedure(s) to the MME(s). In case of the RESET procedure, the DeNB does not need to wait for the response message(s) from the MME(s) or RN(s) before responding with the RESET ACKNOWLEDGE message to the originating node. Upon reception of a PAGING message, the DeNB sends the PAGING message toward the RN(s) which support any tracking area(s) indicated in the List of TAIs. Upon reception of an S1 MME overload START/STOP message, the DeNB sends the MME overload START/STOP message towards the RN(s), including in the message the identities of the affected CN node. The RN uses this information received from the OVERLOAD START message to identify to which traffic the above defined rejections shall be applied. The RN shall apply the defined rejections until reception of an OVERLOAD STOP message applicable to this traffic, or until the RN receives a further OVERLOAD START message applicable to the same traffic, in which case it shall replace the ongoing overload action with the newly requested one. Upon reception of the GUMMEI from a UE, the RN shall include it in the INITIAL UE MESSAGE message; upon reception of the GUMMEI Type from the UE, the RN shall also include it in the message.

The X2 control plane protocol stack for supporting RNs is shown in Figure 4.7.4-2. There is a single X2 interface relation between each RN and its DeNB. In addition, the DeNB may have X2 interface relations to neighbouring eNBs. The DeNB processes and forwards all X2 messages between the RN and other eNBs for all UE-dedicated procedures. The processing of X2-AP messages includes modifying S1/X2-AP UE IDs, Transport Layer address and GTP TEIDs but leaves other parts of the message unchanged.

All non-UE-dedicated X2-AP procedures are terminated at the DeNB, and handled locally between the RN and the DeNB, and between the DeNB and other eNBs. Upon reception of an X2 non cell related non-UE-associated message from RN or neighbour eNB, the DeNB may trigger associated non-UE-dedicated X2-AP procedure(s) to the neighbour eNB or RN(s). Upon reception of an X2 cell related non-UE-dedicated message from RN or neighbour eNB, the DeNB may pass associated information to the neighbour eNB or RN(s) based on the included cell information. If one or more RN(s) are involved, the DeNB may wait and aggregate the response messages from all involved nodes to respond to the originating node. Further, parallel Cell Activation procedures are not allowed on each X2 interface instance. The processing of Resource Status Reporting Initiation/ Resource Status Reporting messages includes modification of measurement ID.

The S1 and X2 interface signalling packets are mapped to radio bearers over the Un interface.

Figure 4.7.4-1: S1 control plane protocol stack for supporting RNs

Figure 4.7.4-2: X2 control plane protocol stack for supporting RNs