In an LTE-Advanced (Long Term Evolution-Advanced) system, CA (Carrier Aggregation) is under discussion to achieve higher throughput using a plurality of CCs (Component Carriers). According to CA, an MCG (Master Cell Group) and an SCG (Secondary Cell Group) are provided. The MCG is reliable and used to maintain connectivity with a mobile station (UE: User Equipment). The SCG is additionally configured for a mobile station connecting to the MCG.
According to CA, not only a plurality of CCs belonging to the same base station but also CCs belonging to different base stations can be used. Communication using CCs belonging to different base stations is referred to as “Dual Connectivity” (see Non-Patent Document 1). In Dual Connectivity, a base station corresponding to an MCG is referred to as an “MeNB (Master eNB)” and a base station corresponding to an SCG is referred to as an “SeNB (Secondary eNB)”. Dual Connectivity is useful when all CCs cannot be accommodated in a single base station or when higher throughput needs to be achieved in an area where an ideal backhaul cannot be adequately installed.
According to Dual Connectivity, two types of architecture referred to as “MeNB anchor” and “S-GW anchor” are defined for a bearer established between a network and a mobile station. FIGS. 1A and 1B show bearer architecture in Dual Connectivity. MeNB anchor shown in FIG. 1A is a scheme in which an MeNB distributes data received from an S-GW (Serving Gateway) to an SeNB. A bearer provided according to MeNB anchor is referred to as a “Split Bearer”. S-GW anchor shown in FIG. 1B is a scheme in which an S-GW distributes data to an MeNB and an SeNB. A bearer provided according to S-GW anchor is referred to as an “SCG Bearer”.
These types of bearer architecture are implemented upon a procedure to configure a new SCG, upon a procedure to offload an established bearer from an MCG to an SCG, or upon a procedure to establish a new bearer.