In a Long Term Evolution (LTE) system, a protocol architecture of a user plane on the side of a User Equipment (UE) or a terminal according to a related technology is shown in FIG.  1, and is divided into the following protocol layers from bottom to top: a Physical (PHY) layer, a Media Access Control (MAC) layer, a Radio Link Control (RLC) layer and a Packet Data Convergence Protocol (PDCP) layer, wherein the PHY layer transmits information to the MAC layer or a higher layer mainly through a transmission channel; the MAC layer transmits data and allocates radio resources mainly through a logical channel, and realizes functions including Hybrid Automatic Repeat Request (HARQ), Scheduling (SCH), priority processing, multiplexing (MUX) and demultiplexing and the like; the RLC layer mainly provides segmentation and retransmission service for user data and control data; and the PDCP layer mainly implements transmission of user data for Radio Resource Control (RRC) or an upper layer of the user level.  When a terminal establishes a Data Radio Bearer (DRB), an eNB may allocate a Logical Channel Group (LCG) to which the DRB belongs, and there are totally four LCGs 0, 1, 2 and 3 at present.  A terminal in a connected state may send a BSR containing the size of buffer data prepared on an LCG to an eNB if there is no uplink resource or grant when needing to send uplink data, the eNB then may configure a corresponding uplink grant for the terminal according to the size of the buffer data after receiving the BSR, and the terminal may send the uplink data after receiving the uplink grant.  The buffer data includes buffer data, in an RLC layer and a PDCP layer, of a corresponding DRB on the LCG. 
After introduction of a Carrier Aggregation (CA) technology, UE may simultaneously communicate with a source eNB through multiple Component Carriers (CCs) (such as CC1 and CC2) after entering a connected state, and a Primary Cell (Pcell) and a Secondary Cell (Scell) are introduced.  Due to increase of a data volume, the number of Scells may be increased, for example, to 4, and a scenario may also be broadened, for example, to support an uplink Remote Radio Head (RRH) and a repeater.  Since multiple serving cells are located in the same eNB, a protocol architecture of a user plane does not change, and a BSR sending manner changes nothing else only with reported buffer data increased for increase of the data volume only. 
Due to lack of spectrum resources and sharp increase of heavy-traffic services of mobile users, a requirement on adoption of a high frequency point such as 3.5 GHz for hotspot coverage becomes increasingly obvious, and adoption of a low-power node becomes a new application scenario, and aims to improve user throughput and enhance mobility.  However, since a signal of a high frequency point is greatly attenuated and a small cell has smaller coverage and does not share a site with an existing cell, many corporations and operating companies tend to seek for new enhancement solutions, one of which is dual connectivity.  A terminal under dual connectivity may simultaneously keep data connections with larger than two network nodes, but a control plane connection only includes a connection with one cell such as a macro cell.  A difference with CA is that multiple serving nodes of a terminal are multiple eNBs, and time delays among the eNBs are not ignorable.  Therefore, FIG.  2 is one of user-plane protocol architectures which are well known at present, a DRB may be segmented among the multiple eNBs, that is, data of the DRB may be sent through the multiple eNBs, macro eNBs are called MeNBs and small-cell eNBs are called SeNBs.  From the figure, it can be seen that a PDCP layer only exists on one eNB, but RLC layers exist on each eNB respectively, that is, a PDCP layer may be associated with multiple RLC layers, wherein a PDCP layer of an MeNB interacts with an RLC layer of an SeNB through an Xn interface.  There is yet no method disclosed for reporting the size of buffer data of a BSR.