 for processing and deciding on RRM actions, including possible handovers. The measurement reports may also LTE Small Cell Optimization be provided to the SeNodeB when SCells are requested to be added, to aid in the SeNodeB decision-making process of whether to accept the MeNodeB request or not. To understand how the dual connectivity functions, one must understand how the MeNodeB and SeNodeB split the responsibilities, as the control of the dual connectivity is partially split between the MeNodeB and the SeNodeB: The MeNodeB retains full control over the dual connectivity and can always decide to release any configured SCell from the SeNodeB or even the SeNodeB itself, and the SeNodeB shall comply. The MeNodeB also controls the overall bearer structure, RRC connectivity and measurements at the UE side. Only MeNodeB can choose to request addition of SCells to the SeNodeB part. The SeNodeB retains control over its own resources and decides on its own radio con- figuration part: When MeNodeB requests dual connectivity, the SeNodeB is in control of its radio configuration and MeNodeB will not modify it. The SeNodeB can also neither request to start dual connectivity nor add an SCell, but can choose to reject such request from MeNodeB. But like MeNodeB, SeNodeB can at any time request to release an SCell or the dual connectivity itself, and MeNodeB will comply. This division of responsibilities is depicted in Figure 4.3. Release 12 bearer split defines how the bearer can be divided in downlink domain for UEs that support dual connectivity and necessary signalling is in place to support such a situation. RRC only in MeNB UE has connection to both MeNB and SeNB and does radio link monitoring for both PCell and PSCell Physical Layer Physical Layer Physical Layer Figure 4.3 Division of control between MeNodeB and SeNodeB Small Cell Enhancements in Release 12/13 X2 requests SCG addition request RRC configuration SCell/DRB addition request SCell addition/release DRB/SCell release request SCG configuration SCG addition/rele