Patent Publication Number: US-2020296651-A1

Title: Method and apparatus for transmitting and receiving data in communication system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 15/344,471, filed Nov. 4, 2016, which claims priority to Korean Patent Application No. 10-2015-0155674, filed Nov. 6, 2015, the entire disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     The present disclosure relates to an apparatus and method for transmitting and receiving data in a communication system, and more particularly, to an apparatus and method for transmitting and receiving data in a communication system supporting dual connectivity. 
     2. Description of Related Art 
     To meet the demand for wireless data traffic, which has increased since deployment of 4th-generation (4G) communication systems, efforts have been made to develop an improved 5th-generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘beyond 4G network’ or a ‘post long-term evolution (LTE) system’. 
     It is considered that the 5G communication system will be implemented in millimeter wave (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To reduce propagation loss of radio waves and increase a transmission distance, a beam forming technique, a massive multiple-input multiple-output (MIMO) technique, a full dimensional MIMO (FD-MIMO) technique, an array antenna technique, an analog beam forming technique, and a large scale antenna technique are discussed in 5G communication systems. 
     In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, a device-to-device (D2D) communication, a wireless backhaul, a moving network, a cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation, and the like. 
     In the 5G system, a hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and a sliding window superposition coding (SWSC) as an advanced coding modulation (ACM) scheme, and a filter bank multi carrier (FBMC) scheme, a non-orthogonal multiple Access (NOMA) scheme, and a sparse code multiple access (SCMA) scheme as an advanced access technology have been developed. 
     A communication network in a general 5G system is generated in a form that a coverage of a master evolved node B (MeNB) of which a coverage is equal to or larger than a threshold coverage overlaps with a coverage of a secondary evolved node B (SeNB) of which a coverage is smaller than the threshold coverage. Here, the term MeNB may be interchangeable with the term anchor evolved node B (eNB), and the term SeNB may be interchangeable with the term small eNB, assisting eNB, and slave eNB. 
     At this time, dual connectivity that one terminal is connected to two or more than two eNBs in a communication system may be implemented in order to a terminal to perform a communication through at least two of eNBs configuring at least one serving cell. 
     The dual connectivity is configured in order that a terminal may use radio resources provided by at least two different network points, e.g., an MeNB and an SeNB at the same time in a radio resource control (RRC) connected (RRC_CONNECTED) mode. At this time, the at least two different network points are connected one another through an X2 interface using an ideal backhaul or a non-ideal backhaul. 
     A conventional communication system has provided an evolved packet system (EPS) bearer service to a terminal through a radio bearer (RB) of one eNB. 
     However, one EPS bearer service has been provided to a terminal through an RB which is set to each of an MeNB and an SeNB, not an RB of one eNB, from a 3rd generation partnership project (3GPP) release-12 (Rel-12), and a bearer form operated like this will be referred to as split bearer. 
     In the split bearer, an S1-U connection from an evolved packet core (EPC) is terminated at an MeNB, and packet data convergence protocol (PDCP) data is delivered through an X2-U interface between the MeNB and an SeNB. For this, the MeNB performs a routing operation of determining to transmit data of one EPS bearer through which one of a transmission path through the MeNB and a transmission path through an SeNB, and the terminal should perform an operation of sequentially reorders data received from the MeNB and data received from the SeNB according to a sequence number (SN). 
     The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure. 
     SUMMARY 
     To address the above-discussed deficiencies, it is a primary object to provide an apparatus and method for transmitting and receiving data in a communication system supporting dual connectivity. 
     Another aspect of the present disclosure is to propose an apparatus and method for transmitting and receiving routing information in a communication system supporting dual connectivity. 
     Another aspect of the present disclosure is to propose an apparatus and method for changing a preset routing path, and transmitting and receiving data through the changed routing path in a communication system supporting dual connectivity. 
     Another aspect of the present disclosure is to propose an apparatus and method for transmitting and receiving data using a transmission control protocol (TCP) layer thereby minimizing transmission delay in a communication system supporting dual connectivity. 
     In accordance with an aspect of the present disclosure, an operating method of a first evolved node B (eNB) in a communication system supporting dual connectivity is provided. The operating method includes detecting that a path between a second eNB and a terminal is blocked; and transmitting, to the terminal, a first data unit of a plurality of data units to be transmitted through the path between the second eNB and the terminal. 
     In accordance with another aspect of the present disclosure, an operating method of a second evolved node B (eNB) in a communication system supporting dual connectivity is provided. The operating method includes detecting that a path between a second eNB and a terminal is blocked; and transmitting, to a first eNB, information indicating that the path between the second eNB and the terminal is blocked. 
     In accordance with still another aspect of the present disclosure, an operating method of a terminal in a communication system supporting dual connectivity is provided. The operating method includes detecting that a path between a first evolved node B (eNB) and a terminal is blocked; transmitting, to a second eNB, information indicating that the path between the first eNB and the terminal is blocked; and receiving, from the second eNB, a first data packet of a plurality of data packets to be transmitted through the path between the first eNB and the terminal. 
     In accordance with still another aspect of the present disclosure, an operating method of an evolved packet core (EPC) in a communication system supporting dual connectivity is provided. The operating method includes transmitting and receiving a message including information indicating that a retransmission function is able to be performed with a terminal through a transmission control protocol (TCP) layer; and receiving a retransmission request message including information related to a data packet which should be retransmitted through the TCP layer, and transmitting the data packet through the TCP layer based on the retransmission request message. 
     In accordance with still another aspect of the present disclosure, a first evolved node B (eNB) in a communication system supporting dual connectivity is provided. The first eNB includes a controller configured to detect that a path between a second eNB and a terminal is blocked; and a transmitter configured to transmit, to the terminal, a first data unit of a plurality of data units to be transmitted through the path between the second eNB and the terminal. 
     In accordance with still another aspect of the present disclosure, a second evolved node B (eNB) in a communication system supporting dual connectivity is provided. The second eNB includes a controller configured to detect that a path between a second eNB and a terminal is blocked; and a transmitter configured to transmit, to a first eNB, information indicating that the path between the second eNB and the terminal is blocked. 
     In accordance with still another aspect of the present disclosure, a terminal in a communication system supporting dual connectivity is provided. The terminal includes a controller configured to detect that a path between a first evolved node B (eNB) and a terminal is blocked; a transmitter configured to transmit, to a second eNB, information indicating that the path between the first eNB and the terminal is blocked; and a receiver configured to receive, from the second eNB, a first data packet of a plurality of data packets to be transmitted through the path between the first eNB and the terminal. 
     In accordance with still another aspect of the present disclosure, an evolved packet core (EPC) in a communication system supporting dual connectivity is provided. The EPC includes a controller configured to control a transceiver to transmit and receive a message including information indicating that a retransmission function is able to be performed with a terminal through a transmission control protocol (TCP) layer; and the transceiver configured to receive a retransmission request message including information related to a data packet that should be retransmitted through the TCP layer, and to transmit the data packet through the TCP layer based on the retransmission request message. 
     Other aspects, advantages, and salient features of the disclosure will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the disclosure. 
     Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith, “as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
         FIG. 1  schematically illustrates an example of a structure of a communication system supporting dual connectivity according to an embodiment of the present disclosure; 
         FIG. 2  schematically illustrates an example of a layer structure of a communication system supporting dual connectivity according to an embodiment of the present disclosure; 
         FIG. 3  schematically illustrates an example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure; 
         FIG. 4  schematically illustrates another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure; 
         FIG. 5  schematically illustrates a format of a PDCP Control PDU in a communication system supporting dual connectivity according to an embodiment of the present disclosure; 
         FIG. 6  schematically illustrates still another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure; 
         FIG. 7  schematically illustrates a process of detecting a temporary blockage or a permanent blockage of a frequency in a communication system supporting dual connectivity according to an embodiment of the present disclosure; 
         FIG. 8  schematically illustrates an example of a format of an X2-UP protocol frame in a communication system supporting dual connectivity according to an embodiment of the present disclosure; 
         FIG. 9  schematically illustrates still another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure; 
         FIG. 10  schematically illustrates another example of a format of an X2-UP protocol frame in a communication system supporting dual connectivity according to an embodiment of the present disclosure; 
         FIG. 11  schematically illustrates still another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure; 
         FIG. 12  schematically illustrates another example of a structure of a communication system supporting dual connectivity according to an embodiment of the present disclosure; 
         FIG. 13  schematically illustrates still another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure; 
         FIG. 14  schematically illustrates still another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure; 
         FIG. 15  schematically illustrates still another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure; 
         FIG. 16  schematically illustrates an inner structure of an MeNB in a communication system supporting dual connectivity according to an embodiment of the present disclosure; 
         FIG. 17  schematically illustrates an inner structure of an SeNB in a communication system supporting dual connectivity according to an embodiment of the present disclosure; 
         FIG. 18  schematically illustrates an inner structure of a terminal in a communication system supporting dual connectivity according to an embodiment of the present disclosure; 
         FIG. 19  schematically illustrates an inner structure of an EPC in a communication system supporting dual connectivity according to an embodiment of the present disclosure; and 
         FIG. 20  schematically illustrates an inner structure of a server in a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     
    
    
     Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures. 
     DETAILED DESCRIPTION 
       FIGS. 1 through 20 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged communication system. 
     The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness. 
     The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustration purpose only and not for the purpose of limiting the present disclosure as defined by the appended claims and their equivalents. 
     It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces. 
     Although ordinal numbers such as “first,” “second,” and so forth will be used to describe various components, those components are not limited herein. The terms are used only for distinguishing one component from another component. For example, a first component may be referred to as a second component and likewise, a second component may also be referred to as a first component, without departing from the teaching of the inventive concept. The term “and/or” used herein includes any and all combinations of one or more of the associated listed items. 
     The terminology used herein is for the purpose of describing various embodiments only and is not intended to be limiting. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “has,” when used in this specification, specify the presence of a stated feature, number, step, operation, component, element, or combination thereof, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, components, elements, or combinations thereof. 
     The terms used herein, including technical and scientific terms, have the same meanings as terms that are generally understood by those skilled in the art, as long as the terms are not differently defined. It should be understood that terms defined in a generally-used dictionary have meanings coinciding with those of terms in the related technology. 
     According to various embodiments of the present disclosure, an electronic device may include communication functionality. For example, an electronic device may be a smart phone, a tablet personal computer (PC), a mobile phone, a video phone, an e-book reader, a desktop PC, a laptop PC, a netbook PC, a personal digital assistant (PDA), a portable multimedia player (PMP), an mp3 player, a mobile medical device, a camera, a wearable device (e.g., a head-mounted device (HMD), electronic clothes, electronic braces, an electronic necklace, an electronic appcessory, an electronic tattoo, or a smart watch), and/or the like. 
     According to various embodiments of the present disclosure, an electronic device may be a smart home appliance with communication functionality. A smart home appliance may be, for example, a television, a digital video disk (DVD) player, an audio, a refrigerator, an air conditioner, a vacuum cleaner, an oven, a microwave oven, a washer, a dryer, an air purifier, a set-top box, a TV box (e.g., Samsung HomeSync™, Apple TV™, or Google TV™), a gaming console, an electronic dictionary, an electronic key, a camcorder, an electronic picture frame, and/or the like. 
     According to various embodiments of the present disclosure, an electronic device may be a medical device (e.g., magnetic resonance angiography (MRA) device, a magnetic resonance imaging (MRI) device, computed tomography (CT) device, an imaging device, or an ultrasonic device), a navigation device, a global positioning system (GPS) receiver, an event data recorder (EDR), a flight data recorder (FDR), an automotive infotainment device, a naval electronic device (e.g., naval navigation device, gyroscope, or compass), an avionic electronic device, a security device, an industrial or consumer robot, and/or the like. 
     According to various embodiments of the present disclosure, an electronic device may be furniture, part of a building/structure, an electronic board, electronic signature receiving device, a projector, various measuring devices (e.g., water, electricity, gas or electro-magnetic wave measuring devices), and/or the like that include communication functionality. 
     According to various embodiments of the present disclosure, an electronic device may be any combination of the foregoing devices. In addition, it will be apparent to one having ordinary skill in the art that an electronic device according to various embodiments of the present disclosure is not limited to the foregoing devices. 
     According to various embodiments of the present disclosure, a transmitting apparatus or a receiving apparatus may be a terminal. 
     According to various embodiments of the present disclosure, a transmitting apparatus or a receiving apparatus may be an evolved node B (eNB). 
     In various embodiments of the present disclosure, it will be noted that the term terminal may be interchangeable with the term user equipment (UE), wireless communication terminal, mobile station (MS), wireless terminal, mobile device, and/or the like. 
     In various embodiments of the present disclosure, it will be noted that the term eNB may be interchangeable with the term access point (AP), base station (BS), and/or the like. 
     An embodiment of the present disclosure provides an apparatus and method for transmitting and receiving data in a communication system supporting dual connectivity. 
     An embodiment of the present disclosure provides an apparatus and method for transmitting and receiving routing information in a communication system supporting dual connectivity. 
     An embodiment of the present disclosure provides an apparatus and method for changing a preset routing path, and transmitting and receiving data through the changed routing path in a communication system supporting dual connectivity. 
     An embodiment of the present disclosure provides an apparatus and method for transmitting and receiving data using a transmission control protocol (TCP) layer thereby minimizing transmission delay in a communication system supporting dual connectivity. 
     An apparatus and method proposed in various embodiments of the present disclosure may be applied to various communication systems such as a long term evolution (LTE) mobile communication system, an LTE-advanced (LTE-A) mobile communication system, a licensed-assisted access (LAA)-LTE mobile communication system, a high speed downlink packet access (HSDPA) mobile communication system, a high speed uplink packet access (HSUPA) mobile communication system, a high rate packet data (HRPD) mobile communication system proposed in a 3rdgeneration project partnership 2 (3GPP2), a wideband code division multiple access (WCDMA) mobile communication system proposed in the 3GPP2, a code division multiple access (CDMA) mobile communication system proposed in the 3GPP2, an institute of electrical and electronics engineers (IEEE) 802.16m communication system, an IEEE 802.16e communication system, an evolved packet system (EPS), and a mobile internet protocol (Mobile IP) system, a digital video broadcast system such as a mobile broadcast service such as a digital multimedia broadcasting (DMB) service, a digital video broadcasting-handheld (DVP-H), an advanced television systems committee-mobile/handheld (ATSC-M/H) service, and the like, and an internet protocol television (IPTV), a moving picture experts group (MPEG) media transport (MMT) system and/or the like. 
     An example of a structure of a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIG. 1 . 
       FIG. 1  schematically illustrates an example of a structure of a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     Referring to  FIG. 1 , the communication system includes a master evolved node B (MeNB)  110 , a secondary eNB (SeNB)  120 , a terminal  130 , and an evolved packet core (EPC)  140 . The term MeNB may be interchangeable with the term anchor eNB, and the term SeNB may be interchangeable with the term small eNB, assisting eNB, and slave eNB. 
     The terminal  130  is located at an area where a coverage of the MeNB  110  overlaps with a coverage of the SeNB  120 , and may configure dual connectivity and communicate with the MeNB  110  and the SeNB  120  at the same time based on the dual connectivity. According to the routing result of the MeNB  110 , a part of data transmitted from the EPC  140  to the MeNB  110  may be directly transmitted from the MeNB  110  to the terminal  130  and the remaining part of the data may be transmitted to the terminal  130  through the SeNB  120 . At this time, data between the EPC  140  and the MeNB  110  is transmitted and received through an S1 interface, and data between the MeNB  110  and the SeNB  120  is transmitted and received through an X2 interface. 
     A frequency link, e.g., an F1 frequency link is allocated to the MeNB  110 , and a frequency link, e.g., an F2 frequency link is allocated to the SeNB  120 . The terminal  130  may receive data through a path for the F2 frequency link from the SeNB  120  while receiving data through a path for the F1 frequency link from the MeNB  110 . 
     An example of a structure of a communication system supporting dual connectivity according to an embodiment of the present disclosure has been described with reference to  FIG. 1 , and an example of a layer structure of a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIG. 2 . 
       FIG. 2  schematically illustrates an example of a layer structure of a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     Referring to  FIG. 2 , the communication system includes an MeNB  110 , an SeNB  120 , a terminal  130 , and an EPC  140 . The MeNB  110  receives data from one EPS bearer from the EPC  140 , and each of the MeNB  110  and the SeNB  120  configures one resource block (RB) for the EPS bearer. 
     The MeNB  110  includes a packet data convergence protocol (PDCP) layer  111 , a radio link control (RLC) layer  113 , a medium access control (MAC) layer  115 , and a physical (PHY) layer  117 , and the SeNB  120  includes an RLC layer  121 , a MAC layer  123 , and a PHY layer  125 . 
     The PDCP layer  111  in the MeNB  110  receives a PDCP service data unit (SDU) from the EPC  140 , generates a PDCP protocol data unit (PDU) based on the PDCP SDU, and transmits a part of the PDCP PDU to the RLC layer  113  in the MeNB  110  and the remaining part of the PDCP PDU to the RLC layer  121  in the SeNB  120  according to a defined rule. A process in which a path through which a PDCP PDU will be transmitted is determined and the PDCP PDU is transmitted through the determined path will be referred to as routing process. 
     A pair of radio protocol entities is configured for one EPS bearer in the terminal  130 . That is, in the terminal  130 , a PDCP layer  137 , an RLC layer  135 , a MAC layer  133 , and a PHY layer  131  which correspond to the MeNB  110  are configured, and an RLC layer  143 , a MAC layer  141  and a PHY layer  139  which correspond to the SeNB  120  are configured. 
     The PDCP layer  137  is an entity which shares a PDCP PDU transmitted from the MeNB  110  and a PDCP PDU transmitted from the SeNB  120  at the same time. That is, one PDCP layer, i.e., the PDCP layer  137  interfaces with the RLC layer  113  included in the MeNB  110  and the RLC layer  121  included in the SeNB  120  at the same time. 
     In the terminal  130 , the PDCP layer  137  has a function of sequentially reordering a PDCP PDU received through the MeNB  110  and PDCP PDUs which is non-sequentially received through the SeNB  120  according to a sequence number (SN). 
     Further, in a case that a PDCP PDU is transmitted through a plurality of paths in a communication system, non-sequential reception for the PDCP PDU occurs in the terminal  130  due to difference among transmission delays among the plurality of paths. In a case that there is a PDCP PDU which is non-sequentially stored at a reception buffer in the PDCP layer  137 , the terminal  130  receives a PDCP PDU after waiting during the difference among the transmission delays among the plurality of paths and starts a reordering timer for delivering the received PDCP PDU to an upper layer. The reordering timer which has been started stops if a PDCP PDU corresponding to an SN which causes the reordering timer to be started is delivered to the upper layer. If the reordering timer expires in the PDCP layer  137 , a PDCP PDU corresponding to an SN which is less than the SN which causes the reordering timer to be started among PDCP PDUs stored at the reception buffer up to now is delivered to the upper layer. 
     The MeNB  110  is connected to the SeNB  120  through an X2 interface. That is, the PDCP layer  111  in the MeNB  110  routes a part of a PDCP PDU to the RLC layer  121  in the SeNB  120  through an X2 interface. Further, an X2-user plane (UP) protocol for the SeNB  120  to exchange feedback information with the MeNB  110  for flow control of adjusting amount of data to be transmitted between the MeNB  110  and the SeNB  120  is defined. 
     The X2-UP protocol provides at least one of information related to an X2-UP dedicated SN to be used for data transmission between the MeNB  110  and the SeNB  120 , information related to the greatest SN among SNs of PDCP PDUs which have been successfully transmitted from the SeNB  120  to the terminal  130 , information related to SNs which have failed in transmission to the terminal  130 , information related to a current-desired buffer size per bearer, and information related to a current-minimum desired buffer size per terminal. 
     A process of transmitting and receiving data among an EPC  140 , an MeNB  110 , an SeNB  120 , and a terminal  130  included in a communication system as described in  FIG. 2  will be described with reference to  FIG. 3 . 
       FIG. 3  schematically illustrates an example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     In  FIG. 3 , it will be assumed that an MeNB  110  receives six data units, e.g., six PDCP SDUs, generates six PDCP PDUs based on the received six PDCP SDUs, and determines to route PDCP PDUs which correspond to SNs 1 to 5 to an SeNB  120  and route a PDCP PDU which corresponds to an SN 6 to a terminal  130 . 
     The SeNB  120  transmits the PDCP PDUs which correspond to the SNs 1 to 5 received from the MeNB  110  to the terminal  130  through a path for an F2 frequency link. If the terminal  130  does not receive the PDCP PDU corresponding to the SN 1 and successfully receives the PDCP PDUs corresponding to the SNs 2 to 5 due to various reasons such as a channel error, and/or the like, the terminal  130  stores the PDCP PDUs corresponding to the SNs 2 to 5 at a reception buffer and starts a reordering timer. 
     The PDCP PDU corresponding to the SN 1 has been lost due to various reasons such as a channel error, and/or the like, so there is no possibility that the PDCP PDU corresponding to the SN 1 is being transmitted through a path different from the path for the F2 frequency link after delay and the terminal  130  waits until the reordering timer expires. Due to this, the PDCP layer  137  in the terminal  130  results in additional delay on data transmission to an upper layer, e.g., a transmission control protocol (TCP) layer. If the F2 frequency link is an mmW band, time of a reordering timer should be set to relatively long time by considering instability of the mmW band, so it is predicted that this will affect throughput of data transmission to an upper layer. 
     An embodiment of the present disclosure provides a scheme for decreasing delay time for data reordering. For this, in an embodiment of the present disclosure, the MeNB  110  transmits routing information including information related to PDCP PDUs transmitted per path to the terminal  130 . At this time, the MeNB  110  may transmit the routing information to the terminal  130  after or before starting transmission of PDCP PDUs. 
     Another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIG. 4 . 
       FIG. 4  schematically illustrates another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     Referring to  FIG. 4 , it will be assumed that an MeNB  110  supports an LTE frequency band, and an SeNB  120  supports an mmW band. An embodiment of the present disclosure may be applied to a case that a frequency band used in the MeNB  110  is different from a frequency band used in the SeNB  120 . In  FIG. 4 , it will be assumed that the MeNB  110  receives six data units, e.g., six PDCP SDUs, generates six PDCP PDUs based on the received six PDCP SDUs, and determines to route PDCP PDUs corresponding to SNs 1 to 3 to the SeNB  120  and route PDCP PDUs corresponding to SNs 4 to 6 to a terminal  130 . 
     The MeNB  110  transmits routing information including the routing result as described above to the terminal  130 . The routing information includes information about an SN range for a PDCP PDU routed per transmission path or a PDCP PDU to be routed per transmission path. For example, the routing information includes information indicating that the SeNB  120  determines to route the PDCP PDUs corresponding to the SNs 1 to 3 and the MeNB  110  determines to route the PDCP PDUs corresponding to the SNs 4 to 6. The routing information is transmitted to the terminal  130  through a PDCP Control PDU. 
     A format of a PDCP Control PDU in a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIG. 5 . 
       FIG. 5  schematically illustrates a format of a PDCP Control PDU in a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     Referring to  FIG. 5 , it will be noted that a format of a PDCP Control PDU is used for transmitting routing information. 
     A PDCP Control PDU includes at least one PATH field  510  and a Routing Information field  530 . 
     The PATH field  510  includes information indicating whether a PDCP PDU corresponding to an SN included in the Routing Information field  530  is transmitted through an MeNB path or an SeNB path. If the number of dual connectivity is 2, the PATH field  510  may be implemented with 1 bit. If the number of dual connectivity is equal to or greater than 3, the PATH field  510  may be implemented with two or more than two bits. 
     The Routing Information field  530  indicates an SN block of a PDCP PDU which is routed or which will be routed through a path which is detected based on the PATH field  510 . An SN block denotes continuous SNs. For example, the SN block may be expressed with a pair of the smallest SN among SNs included in the SN block and the largest SN among the SNs included in the SN block. Here, the smallest SN among the SNs included in the SN block will be referred to as Left edge SN, and the largest SN among the SNs included in the SN block will be referred to as Right edge SN. 
     It is most effective for an MeNB  110  to transmit a PDCP Control PDU as shown in  FIG. 5  used for transmitting routing information to the terminal  130  before routing data. However, for convenience, the MeNB  110  may transmit the routing information to the terminal  130  at time such as the middle of data routing or the end of data routing. 
     Referring back to  FIG. 4 , an SeNB  120  transmits PDCP PDUs corresponding to SNs 1 to 3 received from an MeNB  110  to a terminal  130  through a path with a link of an mmW band, and the terminal  130  does not receive the PDCP PDU corresponding to the SN1 due to various reasons such as a channel error, and/or the like. The terminal  130  may receive a PDCP PDU corresponding to an SN 2 from the SeNB  120  and may receive a PDCP PDU corresponding to an SN 4 from the MeNB  110 . 
     A case that the terminal  130  receives the PDCP PDU corresponding to the SN 2 from the SeNB  120  will be described below. 
     The terminal  130  knows that the PDCP PDUs corresponding to the SNs 1 to 3 will be transmitted through the SeNB  120  based on routing information transmitted through a PDCP Control PDU. An RLC layer  143  in the terminal  130  corresponding to the SeNB  120  facilitates in-sequence delivery with an acknowledged mode (AM) operation, so it will be predicted that transmission of the PDCP PDU, which is normally received, corresponding to the SN 1 which is less than an SN 2 failed in a lower layer of a PDCP layer  137  due to various reasons such as a channel error, and/or the like. 
     The PDCP layer  137  in the terminal  130  processes reception of the PDCP PDU corresponding to the SN 1 as loss, and delivers the PDCP PDU corresponding to the SN2 which has been received up to now to an upper layer. At this time, an embodiment of the present disclosure does not expect delayed transmission through other path by starting a reordering timer unlike a conventional technology, so unnecessary delay time does not occur. 
     A case that the terminal  130  receives a PDCP PDU corresponding to an SN 4 from the MeNB  110 . 
     The terminal  130  knows that PDCP PDUs corresponding to SNs 4 to 6 will be transmitted through the MeNB  110  based on routing information transmitted through a PDCP Control PDU. So, the terminal  130  may be confident that PDCP PDUs corresponding to SNs 1 to 3 which are not received yet are being transmitted through other path, and wait for reception for the PDCP PDUs through the other path by starting a reordering timer. 
     When the terminal receives the PDCP PDU corresponding to the SN 2, an RLC layer  143  in the terminal  130  facilitates in-sequence delivery with an AM operation, so the terminal  130  may be confident that transmission of the PDCP PDU corresponding to the SN 1 which is less than an SN 2 of the PDCP PDU which is normally received failed in a lower layer of a PDCP layer  137  due to various reasons such as a channel error, and/or the like. So, the PDCP layer  137  in the terminal  130  may process reception of the PDCP PDU corresponding to the SN 1 as loss and deliver the PDCP PDU corresponding to the SN 2 which has been received up to now to an upper layer. 
     In a method as described in  FIG. 2 , when data which is not received at a reception buffer, the PDCP layer  137  in the terminal  130  regards that the data is not received due to difference among transmission delays among paths and starts a reordering timer, so unnecessary delay occurs and transmission efficiency of an upper layer decreases due to various reasons such as a channel error, and/or the like. 
     However, in an embodiment of the present disclosure, an MeNB  110  transmits routing information to a terminal  130 , so a PDCP layer  137  in the terminal  130  may operate a reordering timer by effectively classifying delay due to packet loss and delay due to difference between transmission delays between paths. So, the terminal  130  may reduce delay which occurs in a process of sequentially reordering data. 
     Although minimizing delay in a process of reordering data as described in an embodiment of the present disclosure, delay due to data reordering may significantly decrease transmission efficiency for data transmission to an upper layer if difference among transmission delays among paths is very large. 
     If an F2 frequency band of an SeNB  120  is an mmW band, a path through which data is transmitted may be temporarily blocked by an obstacle and/or the like due to a characteristic of the mmW band of which straightness is strong, and the blockage time may be in milliseconds to seconds. In this case, even though a PDCP layer  137  in a terminal  130  successfully receives all data and delivers all of the data to an upper layer, a TCP layer as an upper layer may not deliver a TCP ACK message to a TCP transmission side during reordering delay. This causes retransmission timeout of the TCP transmission side, and a congestion window of the TCP transmission side is initialized thereby significantly decreasing transmission efficiency of a TCP. Further, data transmitted from the PDCP layer  137  to an upper layer, i.e., a TCP layer is also regarded as lost data, so an MeNB  110  performs retransmission. 
     So, various embodiments of the present disclosure will describe schemes of minimizing difference among delays among paths by performing re-routing in an MeNB  110  when a temporary blockage is detected in a path with a link of an mmW band. Various embodiments of the present disclosure includes an embodiment in which an MeNB performs routing, an embodiment in which an EPC performs routing, an embodiment in which a PDCP layer performs routing, and an embodiment in which a TCP layer performs routing. 
     An operation in a case that it will be assumed that an MeNB performs a routing process and an SeNB starts data transmission according to the routing result will be described below. 
     Still another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIG. 6 . 
       FIG. 6  schematically illustrates still another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     Referring to  FIG. 6 , in an embodiment of the present disclosure, a terminal  130  detects a temporary blockage in a path with a link of an mmW band and transmits the detected result indicating the temporary blockage to an MeNB  110 . In the following description, an SeNB  120  and the terminal  130  transmit and receive data through a path with a link of an mmW band, so it will be understood that blockage of the link of the mmW band is blockage of a path with the link of the mmW band. 
     The SeNB  120  transmits PDCP data received from the MeNB  110  to the terminal  130  according to the routing result of the MeNB  110  at operation  601 . The terminal  130  detects a temporary blockage in the link of the mmW band at operation  603 . 
     Time during which a blockage detected in a path between the terminal  130  and the SeNB  120  lasts may be longer than a preset time or may be equal to or shorter than the preset time according to a mobile speed or a mobile direction. That is, the time during which the blockage is detected in the path between the terminal  130  and the SeNB  120  may be temporary time or permanent time. 
     A process of detecting a temporary blockage or a permanent blockage of a frequency in a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIG. 7 . 
       FIG. 7  schematically illustrates a process of detecting a temporary blockage or a permanent blockage of a frequency in a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     Referring to  FIG. 7 , a general LTE communication system defines a radio link failure (RLF) operation for detecting a permanent blockage of a link. If an upper layer receives out-of-sync indication of N 310  from a lower layer corresponding to an SeNB  120 , i.e., a PHY layer  139 , a terminal  130  starts a timer of which a default value is set to 1000 ms, e.g., a T 310  timer. If the T 310  timer expires, the terminal  130  regards that a radio link corresponding to the SeNB  120  is permanently blocked, and reports fail information to an MeNB  110  through a radio resource control (RRC) message. 
     After receiving the RRC message from the terminal  130 , the MeNB  110  checks the fail information reported through the RRC message, and performs the next procedure in which the MeNB  110  changes or releases an SeNB for the terminal  130  according to whether a neighbor SeNB for the terminal  130  exists. 
     After the T 310  timer is started, the terminal  130  stops the T 310  timer when receiving in-sync indication of N 311  from a PHY layer  139  in the terminal corresponding to the SeNB  120 . 
     In an embodiment of the present disclosure, a new timer and a constant are used for detecting a temporary blockage in a link of an mmW band. For convenience, a timer used for detecting a temporary blockage in a link of an mmW band will be referred to as blockage timer or T 320  timer. 
     Referring back to  FIG. 6 , the terminal  130  starts a blockage timer (T 320  timer) when an upper layer receives out-of-sync indication of N 320  from a PHY layer  139  corresponding to the SeNB  120 . N 320  which triggers detecting a temporary blockage of a link should be set to a value which is less than N 310  which triggers detecting a permanent blockage of a link. If the blockage timer expires, the terminal  130  determines that a radio link corresponding to the SeNB  120  is temporarily blocked. In a case that time during which the blockage timer operates is set to a preset value, e.g.,  0 , if the upper layer receives out-of-sync indication of N 320  from the PHY layer  139  corresponding to the SeNB  120 , the terminal  130  may determine that the radio link is temporarily blocked without starting the blockage timer. 
     Upon receiving in-sync indication of N 311  from a lower layer corresponding to the SeNB  120 , i.e., the PHY layer  139 , after the blockage timer is started in an upper layer, the terminal  130  stops the blockage timer. N 320  and T 320  are defined in an embodiment of the present disclosure, and the names thereof may be changed. 
     Upon detecting a temporary blockage in a link of an mmW band using a process of detecting a temporary blockage or a permanent blockage as described in  FIG. 7  at operation  603 , the terminal  130  transmits a report message indicating that the temporary blockage is detected in the link of the mmW band to the MeNB  110  at operation  605 . For example, the report message may be implemented with an RRC message or a status report field in a PDCP Control PDU. 
     If the report message is implemented with the RRC message, the report message may be implemented with a new message, e.g., a blockage report message or be implemented by including a new information element (IE) into a failure information message used in a general communication system, e.g., an SCGFailureInformation message. The new message or the new IE includes information related to at least one of a current Reordering PDCP RX COUNT and remaining time until a current reordering timer expires. 
     For another example, the terminal  130  may transmit report indicating that the temporary blockage is detected in the link of the mmW band to the MeNB  110  using a PDCP Control PDU. A format of a general PDCP Control PDU defines that the terminal  130  should transmit status report to the MeNB  110  if the MeNB  110  requests PDCP re-establishment from the terminal  130 . So, if status report which is transmitted by the terminal  130  without the request for the PDCP re-establishment from the MeNB  110  is analyzed as report indicating the temporary blockage of the link detected by the terminal  130 , the terminal  130  may transmit report indicating that temporary blockage of the link is detected to the MeNB  110  using status report at operation  605 . 
     A PDCP layer  111  in the MeNB  110  performs a re-routing operation in order to directly transmit data which has been routed to the SeNB  120  to a terminal  130  at operation  606 . At this time, the MeNB  110  should determine which data among the data which has been routed to the SeNB  120  should be retransmitted to the terminal  130 . For example, the MeNB  110  may determine a packet to be re-routed per priority by considering a possibility that transmission in the SeNB  120  will be resumed according to recovery of the mmW link as expressed in Table 1. 
     In Table 1, each of Step 1 to Step 3 may denote a priority. 
     Step 1 is a re-routing step in which a packet related to start of a reordering timer of the terminal  130  among packets transmitted through a guaranteed bit rate (GBR) bearer is preferentially retransmitted. Further, Reordering PDCP RX COUNT is a parameter delivered when the terminal  130  reports a blockage to the MeNB  110  at operation  605 , and means an SN which causes the terminal  130  to start a reordering timer. 
     The terminal  130  may stop the reordering timer when all of PDCP data with an SN which is less than the SN, i.e., the Reordering PDCP RX COUNT are received. So, the MeNB  110  should determine the PDCP data with the SN which is less than the SN to be preferentially re-routed (the first criterion of Step 1). 
     Data should be received in the terminal  130  before the reordering timer of the terminal  130  expires, so the MeNB  110  determines the PDCP data with the SN which is less than the SN to be preferentially re-routed if time at which the reordering timer expires (“reorderingTimer expiry time”) is longer than expected transmission time (the second criterion of Step 1). An operation in Step 1 may be sequentially determined according to a priority of each of a plurality of GBR bearers if there is a plurality of GBR bearers. 
     Step 2 is a re-routing step in which a packet related to start of a reordering timer of the terminal  130  among packets transmitted through a Non-GBR bearer is preferentially retransmitted. An operation in Step 2 is similar to an operation in Step 1, and a detailed description thereof will be omitted herein. 
     Step 3 is a re-routing step in which packets which are not re-routed through Step 1 and Step 2 are retransmitted in ascending order of SN. 
     A process of Step 1 to a process of Step 3 are sequentially performed by the MeNB  110 , and are terminated when the MeNB  110  receives data delivery status report from the SeNB  120  according to recovery of an mmW link of the SeNB  120  at operation  611 . 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
            
               
                   
                 Step1: For all GBR bearers in a decreasing priority order, 
               
               
                   
                 PDCP PDUs in which 
               
               
                   
                 1) SN &lt; Reordering_PDCP_RX_COUNT &amp;&amp; 
               
               
                   
                 2) reorderingTimer expiry time &gt; expected transmission time are 
               
               
                   
                 chosen to be rerouted 
               
               
                   
                 Step2: For all Non-GBR bearers in a decreasing priority order, 
               
               
                   
                 PDCP PDUs in which 
               
               
                   
                 1) SN &lt; Reordering_PDCP_RX_COUNT &amp;&amp; 
               
               
                   
                 2) reorderingTimer expiry time &gt; expected transmission time are 
               
               
                   
                 chosen to be rerouted 
               
               
                   
                 Step3: For all bearers, 
               
               
                   
                 PDCP PDU with lowest SNs are chosen to be rerouted 
               
               
                   
                   
               
               
                   
                 Note: 
               
               
                   
                 priority may be determined based on remaining reorderingTimer expiry time 
               
            
           
         
       
     
     The MeNB  110  transmits, to the terminal  130 , data which is determined to be re-routed based on Table 1 at operation  607 . The MeNB  110  transmits, to the SeNB  120 , re-routing information including information about an SN of data which is re-routed and transmitted thereby the SeNB  120  does not transmit the data which is re-routed and transmitted at operation  609 . At this time, the MeNB  110  may transmit the re-routing information to the SeNB  120  using an X2-UP protocol frame in  FIG. 8 . 
     An example of a format of an X2-UP protocol frame in a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIG. 8 . 
       FIG. 8  schematically illustrates an example of a format of an X2-UP protocol frame in a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     Referring to  FIG. 8 , it will be noted that a format of an X2-UP protocol frame in  FIG. 8  is used for transmitting re-routing information in an MeNB. 
     An X2-UP protocol frame includes information about an SN of data which is re-routed through a different path even though an MeNB  110  routes the data to an SeNB  120 . After receiving the X2-UP protocol frame, the SeNB  120  immediately discards data stored at a buffer based on the information about the SN of the re-routed data thereby the data stored at the buffer is not transmitted to a terminal  130 . 
     The SeNB  120  reports, to the MeNB  110 , information about an SN of data which is successfully transmitted to the terminal  130  after a link is recovered through a Downlink(DL) Data Delivery Status frame of an X2-UP protocol frame at operation  611 . 
     After receiving the DL Data Delivery Status frame from the SeNB  120 , the MeNB  110  checks the information about the SN included in the received DL Data Delivery Status frame to determine whether new data is successfully transmitted to the terminal  130 . If the new data is successfully transmitted to the terminal  130 , the MeNB  110  determines that a radio link between the terminal  130  and the SeNB  120  is recovered and terminates the re-routing operation. Thereafter, the MeNB  110  routes a packet received from an EPC  140  to the terminal  130  or the SeNB  120  according to a preset rule. 
     An example of a format of an X2-UP protocol frame in a communication system supporting dual connectivity according to an embodiment of the present disclosure has been described with reference to  FIG. 8 , and still another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIG. 9 . 
       FIG. 9  schematically illustrates still another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     Referring to  FIG. 9 , it will be noted that a process of transmitting and receiving data in  FIG. 9  is a process of transmitting and receiving data in a case that an SeNB  120  detects a temporary blockage in a link of an mmW band and transmits the detected result to an MeNB  110 . 
     The SeNB  120  transmits data according to a routing result of the MeNB  110  at operation  901 . The SeNB  120  detects a temporary blockage in a link of an mmW band at operation  903 . Here, the SeNB  120  detects that a radio link between the SeNB  120  and the terminal  130  is temporarily blocked if retransmission of the data is not performed up to a predetermined retransmission count in an RLC layer  121  in the SeNB  120 . 
     Upon detecting a temporary blockage of a link at operation  903 , the SeNB  120  transmits a Blockage report message to the MeNB  110  at operation  905 . At this time, the SeNB  120  may add a new IE to a DL Data Delivery Status frame of an X2-UP protocol in  FIG. 10 , and transmit the Blockage report message to the MeNB  110  through the added new IE. 
     Another example of a format of an X2-UP protocol frame in a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIG. 10 . 
       FIG. 10  schematically illustrates another example of a format of an X2-UP protocol frame in a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     Referring to  FIG. 10 , it will be noted that a format of an X2-UP protocol frame in  FIG. 10  is used for transmitting blockage detection report in an SeNB. 
     An X2-UP frame protocol includes a Blockage Indication field  1000 . The Blockage Indication field  1000  may be implemented with one bit. For example, if a value of the Blockage Indication field  1000  is “1”, it means that a link is temporarily blocked. For example, if a value of the Blockage Indication field  1000  is “0”, it means that a link is not temporarily blocked. 
     Referring back to  FIG. 9 , the MeNB  110  performs re-routing operation thereby directly transmitting, to the terminal  130 , data which the PDCP layer  111  has routed to the SeNB  120  at operation  906 . At this time, the MeNB  110  should determine which data among the data which has been routed to the SeNB  120  should be retransmitted to the terminal  130 . For example, the MeNB  110  may determine a packet to be re-routed per priority by considering a possibility that transmission in the SeNB  120  will be resumed according to recovery of an mmW link as expressed in Table 2. 
     In Table 2, each of Step 1 to Step 3 denotes a priority. Step 1 is a re-routing step in which a packet which the SeNB  120  reports as a lost packet through a DL Data Delivery Status message at operation  905  among packets transmitted through a GBR bearer is preferentially retransmitted. 
     Step 2 is a re-routing step in which packets which the SeNB  120  reports as lost packets through a DL Data Delivery Status message at operation  905  among packets transmitted through a Non-GBR bearer are preferentially retransmitted. 
     Step 3 is a re-routing step in which packets which are not re-routed through Step 1 and Step 2 are retransmitted in ascending order of SN. 
     A process of Step 1 to a process of Step 3 are sequentially performed by the MeNB  110 , and are terminated when the MeNB  110  receives data delivery status report from the SeNB  120  according to recovery of an mmW link of the SeNB  120  at operation  911 . 
     
       
         
           
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
             
            
               
                   
                 Step1: For all GBR bearers in a decreasing priority order, 
               
               
                   
                 PDCP PDUs in which loss has been reported by DL Data 
               
               
                   
                 Delivery Status are chosen to be rerouted 
               
               
                   
                 Step2: For all Non-GBR bearers in a decreasing priority order, 
               
               
                   
                 PDCP PDUs in which loss has been reported by 
               
               
                   
                 DL Data Delivery Status are chosen to be rerouted 
               
               
                   
                 Step3: For all bearers, 
               
               
                   
                 PDCP PDUs with low SNs are chosen to be rerouted 
               
               
                   
                   
               
               
                   
                 Note: 
               
               
                   
                 priority may be determined based on ARP 
               
            
           
         
       
     
     The MeNB  110  transmits, to the terminal  130 , data which is determined to be re-routed based on Table 2 at operation  907 . The MeNB  110  transmits, to the SeNB  120 , re-routing information including information about an SN of data which is re-routed and transmitted thereby the SeNB  120  does not transmit the data which is re-routed and transmitted at operation  909 . At this time, the MeNB  110  may transmit the re-routing information to the SeNB  120  using an X2-UP protocol frame in  FIG. 8 . A method of transmitting re-routing information from the MeNB  110  to the SeNB  120  using the X2-UP protocol frame has been described with reference to  FIGS. 6 to 8 , and a detailed description thereof will be omitted herein. 
     After receiving the X2-UP protocol frame, the SeNB  120  immediately discards data stored at a buffer based on information about an SN of the re-routed data thereby the data stored at the buffer is not transmitted to a terminal  130 . 
     The SeNB  120  reports, to the MeNB  110 , information about an SN of data which is successfully transmitted to the terminal  130  after a link is recovered through a DL Data Delivery Status frame of an X2-UP protocol frame at operation  911 . 
     After receiving the DL Data Delivery Status frame from the SeNB  120 , the MeNB  110  checks the information about the SN included in the received DL Data Delivery Status frame. The MeNB determines whether new data is successfully transmitted to the terminal  130  based on the information about the SN. If the new data is successfully transmitted to the terminal  130 , the MeNB  110  determines that a radio link between the terminal  130  and the SeNB  120  is recovered and terminates the re-routing operation. Thereafter, the MeNB  110  routes a packet received from an EPC  140  to the terminal  130  or the SeNB  120  according to a preset rule. 
     Still another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIG. 11 . 
       FIG. 11  schematically illustrates still another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     Referring to  FIG. 11 , it will be noted that a process of transmitting and receiving data in  FIG. 11  is a process of transmitting and receiving data in a case that an MeNB detects a temporary blockage in a link of an mmW band. 
     The MeNB  110  transmits a part of data to an SeNB  120  according to the determined result for routing at operation  1101 . The MeNB  110  detects a temporary blockage in a link of an mmW band at operation  1103 . The MeNB  110  operates a timer for detecting a temporary blockage in a link of an mmW band. A method of operating the timer in the MeNB  110  will be expressed in Table 3. 
     A method of operating a timer in Table 3 may be understood based on the concepts as described in  FIG. 10 , so a detailed description will be omitted herein. 
     
       
         
           
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Start 
                 Stop 
               
               
                   
               
             
            
               
                 Reception of DL DATA DELIVERY STATUS 
                 Reception of DL DATA DELIVERY 
               
               
                 with lost packet report 
                 STATUS which indicates the successful 
               
               
                 Reception of DL DATA DELIVERY STATUS 
                 delivery of PDCP Sequence Number that 
               
               
                 with no Highest successfully delivered PDCP 
                 triggered the start of rerouting Timer 
               
               
                 Sequence Number update 
               
               
                   
               
            
           
         
       
     
     The MeNB  110  performs data re-routing if the timer expires at operation  1104 . That is, the MeNB  110  performs re-routing in order to transmit data which has been routed from a PDCP layer  111  to an SeNB  120  to a terminal  130  at operation  1104 . The MeNB  110  should determine which data among the data which has been routed to the SeNB  120  should be transmitted to the terminal  130 . For example, the MeNB  110  may determine a packet to be re-routed per priority by considering a possibility that transmission in the SeNB  120  will be resumed according to recovery of the mmW link as expressed in Table 2. 
     The MeNB  110  transmits, to the SeNB  120 , re-routing information including information about the SN of the data which is re-routed and transmitted thereby the SeNB  120  does not retransmit the data which is re-routed and transmitted at operation  1107 . At this time, the MeNB  110  may transmit the re-routing information to the SeNB  120  using an X2-UP protocol frame in  FIG. 8 . Here, a method of transmitting the re-routing information from the MeNB  110  to the SeNB  120  using the X2-UP protocol frame has been described with reference to  FIGS. 6 to 8 , so a detailed description thereof will be omitted herein. 
     After receiving the X2-UP protocol frame, the SeNB  120  immediately discards data stored in a buffer based on the information about the SN of the re-routed data thereby the data is not transmitted to the terminal  130 . 
     After a link is recovered, the SeNB  120  reports, to the MeNB  110 , information about an SN of data which is successfully transmitted to the terminal  130  through a DL Data Delivery Status frame in an X2-UP protocol frame at operation  1109 . 
     The MeNB  110  receives a DL Data Delivery Status frame from the SeNB  120 , and checks information about an SN included in the received DL Data Delivery Status frame. The MeNB  110  determines whether new data is successfully transmitted to the terminal  130  based on the checked SN. If the new data is successfully transmitted to the terminal  130 , the MeNB  110  determines that a radio link between the terminal  130  and the SeNB  120  is recovered and terminates performing a re-routing operation. The MeNB  110  re-routes a packet received from the EPC  140  to the terminal  130  or the SeNB  120  according to a predetermined rule. 
     Another example of a structure of a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIG. 12 . 
       FIG. 12  schematically illustrates another example of a structure of a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     Referring to  FIG. 12 , a terminal  130  is located at an area where a coverage of an MeNB  110  overlaps with a coverage of an SeNB  120 , and may configure dual connectivity and communicate with the MeNB  110  and the SeNB  120  at the same time. According to this, data transmitted from the EPC  140  is split on a bearer basis in the EPC  140 , and the data which is split on the bearer basis may be transmitted to the terminal  130  through each of the MeNB  110  and the SeNB  120 . At this time, an F1 frequency band is allocated to the MeNB  110 , and an F2 frequency band is allocated to the SeNB  120 . The terminal  130  may receive data from the SeNB  120  through the F2 frequency band while receiving data from the MeNB  110  through the F1 frequency band. 
     A process of transmitting and receiving data thereby minimizing difference among delays among paths in a case that a temporary blockage is detected in a link of an mmW band in a communication system supporting dual connectivity with a structure as described in  FIG. 12  will be described with reference to  FIGS. 13 and 14 . 
     It will be noted that a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure in  FIGS. 13 and 14  is a process of transmitting and receiving data in a case that a new radio bearer between an MeNB and an SeNB is established if a temporary blockage is detected in a link of an mmW band in a terminal or the SeNB, and data buffered at the SeNB is transmitted to the terminal through the MeNB. 
     In  FIGS. 13 and 14 , it will be assumed that data split to an MeNB or an SeNB is performed in an EOC, and data transmission from the SeNB to a terminal is started according to the data split result in the EPC. 
     Still another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIG. 13 . 
       FIG. 13  schematically illustrates still another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     Referring to  FIG. 13 , it will be noted that a process of transmitting and receiving data in  FIG. 13  is a process of transmitting and receiving data in a case that a new radio bearer between an MeNB and an SeNB is established if a temporary blockage is detected in a link of an mmW band in a terminal, and data buffered at the SeNB is transmitted to the terminal through the MeNB. 
     In  FIG. 13 , it will be assumed that data split to the MeNB or the SeNB has been performed in an EPC, and the SeNB starts transmitting data to the terminal according to the data split result in the EPC. 
     An SeNB  120  transmits data to a terminal  130  according to a split result of an EPC  140  at operation  1301 . The terminal  130  detects a temporary blockage in a link of an mmW band at operation  1303 . Time during which the link of the mmW band is blocked may be temporary or permanent according to a mobile speed or a mobile direction of the terminal  130 . The terminal  130  may detect a temporary blockage or a permanent blockage of a frequency with a method as described in  FIGS. 6 to 8 . The method of detecting the temporary blockage of the frequency has been described with reference to  FIGS. 6 to 8 , so a detailed description thereof will be omitted herein. 
     Upon detecting the temporary blockage of the link at operation  1303 , the terminal  130  transmits a report message indicating that the temporary blockage of the link is detected to an MeNB  110  at operation  1305 . The terminal  130  may detect the temporary blockage of the link with a scheme as described in  FIG. 7 . For example, the report message may be implemented with an RRC message or a status report field in a PDCP Control PDU. 
     The MeNB  110  receives the report message from the terminal  130 , and detects that the radio link between the SeNB  120  and the terminal  130  is temporally blocked based on the report message. The MeNB  110  transmits, to the SeNB  120 , an SeNB Modification Request message for changing the path between the SeNB  120  and the terminal  130  to a path between the MeNB  110  and the terminal  130  at operation  1307 . The SeNB Modification Request message may include information about an address used for setting a tunnel for transmitting and receiving data. 
     The SeNB receives the SeNB Modification Request message from the MeNB  110 , sets up a tunnel for forwarding data with the MeNB  110  based on the SeNB Modification Request message, and notifies that the set up of the tunnel has been completed by transmitting an SeNB Modification Response message to the MeNB  110  at operation  1309 . At this time, it will be noted that a radio bearer set up between the SeNB  120  and the terminal  130  is not released and the SeNB  120  repeatedly tries to transmit data to the terminal  130  through a link of an mmW band. 
     After receiving the SeNB Modification Response message from the SeNB  120 , the MeNB  110  transmits an RRCConnectionReconfiguration message to the terminal  130  at operation  1311 . The RRCConnectionReconfiguration message includes radio bearer setup information for setting up a radio bearer which is identical to a radio bearer which is set up through the SeNB  120  through the MeNB  110 . The terminal  130  sets up a radio bearer based on the radio bearer setup information included in the RRCConnectionReconfiguration message, and transmits an RRCConnectionReconfigurationComplete message to the MeNB  110  at operation  1313 . 
     After receiving the RRCConnectionReconfigurationComplete message from the terminal  130 , the MeNB  110  informs that the MeNB  110  is ready to transmit and receive data with the terminal  130  by transmitting an SeNB Reconfiguration Complete message to the SeNB  120  at operation  1315 . 
     After receiving the SeNB Reconfiguration Complete message from the MeNB  110 , the SeNB  120  transmits, to the MeNB  110 , SN status information including information about an SN of data for which transmission failed or information about an SN of data for which transmission is successful at operation  1317 . 
     The SeNB  120  forwards buffered data to the MeNB  110  using a data transmitting/receiving tunnel which is set up with the MeNB  110  at operation  1319 . At this time, the SeNB  120  may delete the data which is forwarded to the MeNB  110  from a transmission buffer of the SeNB  120 . The MeNB  110  delivers data received from the SeNB  120  to the terminal  130  at operation  1321 . 
     The SeNB  120  determines whether a radio link with the terminal  130  is recovered at operation  1323 . If the radio link is not recovered, the SeNB  120  repetitively performs the forwarding process. If the radio link is recovered, the SeNB  120  informs that the radio link with the terminal  130  is recovered by transmitting an MeNB Modification Request message to the MeNB  110  at operation  1325 . 
     After transmitting all data forwarded from the SeNB  120  to the terminal  130 , the MeNB  110  releases a radio bearer set up for data forwarding by transmitting an RRCConnectionReconfiguration message to the terminal  130  at operation  1327 . After releasing the radio bearer, the terminal  130  notifies that the radio bearer has been released by transmitting an RRCConnectionReconfigurationComplete message to the MeNB  110  at operation  1329 . The MeNB  110  informs that the radio bearer set up for data forwarding between the terminal  130  and the SeNB  120  has been released by transmitting an MeNB Modification Response message to the SeNB  120  at operation  1331 . 
     Still another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure has been described with reference to  FIG. 13 , and still another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIG. 14 . 
       FIG. 14  schematically illustrates still another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     Referring to  FIG. 14 , it will be noted that a process of transmitting and receiving data in  FIG. 14  is a process of transmitting and receiving data in a case that a new radio bearer between an MeNB and an SeNB is established if a temporary blockage is detected in a link of an mmW band in the SeNB, and data buffered at the SeNB is transmitted to the terminal through the MeNB. 
     In  FIG. 14 , it will be assumed that data split to MeNB or to SeNB has been performed in an EPC, and the SeNB starts transmitting data to the terminal according to the data split result in the EPC. 
     An SeNB  120  detects a temporary blockage in a link of an mmW band at operation  1401 . The SeNB  120  may detect a temporary blockage of a frequency with a method as described in  FIGS. 9 and 10 . The method of detecting the temporary blockage of the frequency has been described with reference to  FIGS. 9 and 10 , so a detailed description thereof will be omitted herein. 
     The SeNB  120  transmits an MeNB Modification Request message to the MeNB  110  in order to inform that the temporary blockage of the radio link set up with the terminal  130  is detected at operation  1403 . The MeNB Modification Request message includes information indicating that the SeNB  120  intends to transmit data buffered in the SeNB  120  through the MeNB  110 . 
     After receiving the MeNB Modification Request message from the SeNB  120 , the MeNB  110  transmits an RRCConnectionReconfiguration message to the terminal  130  at operation  1405 . The RRCConnectionReconfiguration message includes radio bearer set up information for setting up a radio bearer which is identical to a radio bearer set up through the SeNB  120  through the MeNB  110 . The terminal  130  sets up a radio bearer based on the radio bearer set up information included in the RRCConnectionReconfiguration message, and transmits an RRCConnectionReconfigurationComplete message to the MeNB  110  at operation  1407 . 
     After receiving the RRCConnectionReconfigurationComplete message from the terminal  130 , the MeNB  110  transmits an MeNB Modification Response message to the SeNB  120  at operation  1409 . The MeNB Modification Response message includes information about an address used for the SeNB  120  to set up a tunnel for data forwarding with the MeNB  110 . 
     After receiving the MeNB Modification Request message from the MeNB  110 , the SeNB  120  sets up a tunnel for forwarding data with the MeNB  110 . At this time, it will be noted that a radio bearer set up between the SeNB  120  and the terminal  130  is not released and the SeNB  120  repeatedly tries to transmit data to the terminal  130  through a radio link. 
     The SeNB  120  transmits, to the MeNB  110 , SN status information including information about an SN of data of which transmission failed or information about an SN of data of which transmission is successful at operation  1411 . 
     The SeNB  120  forwards buffered data to the MeNB  110  using a tunnel for data forwarding set up with the MeNB  110  at operation  1413 . The MeNB  110  transmits, to the terminal  130 , the data forwarded from the SeNB  120  at operation  1415 . At this time, the SeNB  120  may delete the data which the SeNB  120  forwarded from a transmission buffer of the SeNB  120 . 
     The SeNB  120  determines whether a radio link with the terminal  130  is recovered at operation  1417 . If the radio link is not recovered, the SeNB  120  repetitively performs the forwarding process. If the radio link is recovered, the SeNB  120  informs that the radio link with the terminal  130  is recovered by transmitting an MeNB Modification Request message to the MeNB  110  at operation  1419 . 
     After transmitting all data forwarded from the SeNB  120  to the terminal  130 , the MeNB  110  releases a radio bearer set up for data forwarding by transmitting an RRCConnectionReconfiguration message to the terminal  130  at operation  1421 . After releasing the radio bearer, the terminal  130  notifies that the radio bearer has been released by transmitting an RRCConnectionReconfigurationComplete message to the MeNB  110  at operation  1423 . The MeNB  110  informs that the radio bearer set up for data forwarding between the terminal  130  and the SeNB  120  has been released by transmitting an MeNB Modification Response message to the SeNB  120  at operation  1425 . 
     So, in an embodiment of the present disclosure, that in a process of transmitting and receiving data in  FIGS. 12 to 14 , a blockage of a radio link set up between a terminal and an SeNB is detected in the terminal or the SeNB, the terminal may receive, from an MeNB, data which is not normally received from the SeNB. 
     A process of transmitting and receiving data in a case that a split is performed in an EPC according to an embodiment of the present disclosure has been described above, and still another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIG. 15 . 
       FIG. 15  schematically illustrates still another example of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     Referring to  FIG. 15 , it will be noted that a process of transmitting and receiving data in  FIG. 15  is a process of transmitting and receiving data in a case that a TCP layer in a terminal immediately retransmits a TCP segment which is lost due to transmission delay of a radio link. 
     In  FIG. 15 , a terminal  130  includes a TCP layer  145  and a PDCP layer  137 . For convenience, it will be noted that layers which are not directly related to a process of transmitting and receiving data according to an embodiment of the present disclosure are not shown, and a structure of a communication system to which the terminal  130  is connected is the same as a structure of a communication system in  FIG. 1 . 
     Referring to  FIG. 15 , a TCP layer  145  in a terminal  130  generates a TCP session through a TCP 3-way handshake with a server  150 . That is, the server  150  transmits a TCP synchronization (TCP SYN) message to the TCP layer  145  in the terminal at operation  1501 . At this time, the TCP SYN message includes an option for Immediate-Retransmission-Permitted informing that an immediate retransmission function may be performed. 
     The TCP layer  145  in the terminal  130  transmits a response message in response to the TCP SYN message received from the server  150  while transmitting the TCP SYN message to the server  150  at operation  1503 . The TCP SYN message transmitted from the terminal  130  to the server  150  includes an option for Immediate-Retransmission-Permitted informing that an immediate retransmission function may be performed. The server  150  transmits, to the terminal  130 , a response message in response to the TCP SYN message received from the terminal  130  at operation  1505 . 
     If all of the TCP SYN message transmitted from the terminal  130  and the TCP SYN message transmitted from the server  150  include the option for Immediate-Retransmission-Permitted, an immediate retransmission function may be activated in an established TCP session if necessary. 
     After receiving TCP DATA SEGMENTs from the server  150  at operation  1507 , the MeNB  110  determines a routing path through which TCP DATA SEGMENTs received according to a preset routing rule will be transmitted to the terminal  130 . For example, the MeNB  110  may determine that the SeNB  120  will transmit a part of TCP DATA SEGMENTs, e.g., a TCP DATA SEGMENT 1 to the terminal  130 , and the MeNB  110  will transmit the remaining part of the TCP DATA SEGMENTs, e.g., a TCP DATA SEGMENT 2 to the terminal  130 . 
     In this case, the MeNB  110  transmits the TCP DATA SEGMENT 1 to the SeNB  120  at operation  1509 . If a temporary blockage occurs in a link of an mmW band, the SeNB  120  does not succeed in transmitting the TCP DATA SEGMENT 1 to the terminal  130  at operation  1511 . The MeNB  110  successfully transmits the TCP DATA SEGMENT 2 to the terminal  130  at operation  1513 . 
     The PDCP layer  137  in the terminal  130  waits for reception of a TCP DATA SEGMENT from the SeNB  120  and the MeNB  110 . If SNs of one or more than one segments among segments included in the TCP DATA SEGMENT 1 are less than SNs of segments included in the TCP DATA SEGMENT 2, the PDCP layer  137  in the terminal  130  stores a PDCP PDU including the TCP DATA SEGMENT 1 at a reception buffer, starts a reordering timer, and enters into an idle state for receiving a PDCP PDU which is not received in order to sequentially deliver data. If the reordering timer expires at operation  1515 , the PDCP layer  137  in the terminal  130  delivers a PDCP PDU including the received TCP DATA SEGMENT 2 to the TCP layer  145  at operation  1517 . 
     The PDCP layer  137  in the terminal  130  delivers a size of the TCP DATA SEGMENT 1 which is not received to the TCP layer  145  at operation  1519 . Upon receiving the size of the TCP DATA SEGMENT 1 which is not received from the PDCP layer  137 , the TCP layer  145  in the terminal  130  transmits, to the server  150 , a TCP response message including an option for requesting Immediate-Retransmission in order to receive the TCP DATA SEGMENT 1 as soon as possible at operation  1521 . The option for requesting the Immediate-Retransmission includes information related to amount, e.g., bytes, of the TCP DATA SEGMENT 1 which should be immediately retransmitted in a TCP layer in the server  150 . Upon receiving the TCP response message including the option for requesting the Immediate-Retransmission, the server  150  generates a TCP DATA SEGMENT 1 corresponding to amount of a TCP DATA SEGMENT 1 indicated by an Immediate-Retransmission option from information related to an Acknowledgment number included in a header in the TCP response message, and retransmits the TCP DATA SEGMENT 1 to the TCP layer  145  in the terminal  130 . 
     Various examples of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure have been described with reference to  FIGS. 1 to 15 , and inner structures of apparatuses of performing an operation corresponding to various examples of a process of transmitting and receiving data in a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIGS. 16 to 19 . 
     An inner structure of an MeNB in a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIG. 16 . 
       FIG. 16  schematically illustrates an inner structure of an MeNB in a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     Referring to  FIG. 16 , an MeNB  110  includes a transmitter  1601 , a controller  1603 , a receiver  1605 , and a storage unit  1607 . 
     The controller  1603  controls the overall operation of the MeNB  110 . More particularly, the controller  1603  controls an operation related to an operation of transmitting and receiving data in a communication system supporting dual connectivity according to embodiments of the present disclosure. The operation related to the operation of transmitting and receiving the data in the communication system supporting the dual connectivity according to embodiments of the present disclosure has been described with  FIGS. 1 to 15 , and a detailed description thereof will be omitted herein. 
     The transmitter  1601  transmits various signals and various messages to other entities, e.g., an SeNB, a terminal, and/or the like in the communication system supporting the dual connectivity under a control of the controller  1603 . The various signals and various messages transmitted in the transmitter  1601  have been described with reference to  FIGS. 1 to 15 , and a detailed description thereof will be omitted herein. 
     The receiver  1605  receives various signals and various messages from other entities, e.g., an SeNB, a terminal, and/or the like in the communication system supporting the dual connectivity under a control of the controller  1603 . The various signals and various messages received in the receiver  1605  have been described with reference to  FIGS. 1 to 15 , and a detailed description thereof will be omitted herein. 
     The storage unit  1607  stores various programs, various data, and/or the like related to an operation related to an operation of transmitting and receiving data in a communication system supporting dual connectivity according to embodiments of the present disclosure, performed in the MeNB  110  under a control of the controller  1603 . 
     The storage unit  1607  stores various signals and various messages which are received by the receiver  1605  from the other entities. 
     While the transmitter  1601 , the controller  1603 , the receiver  1605 , and the storage unit  1607  are described in the MeNB  110  as separate units, it is to be understood that this is merely for convenience of description. In other words, two or more of the transmitter  1601 , the controller  1603 , the receiver  1605 , and the storage unit  1607  may be incorporated into a single unit. 
     The MeNB  110  may be implemented with one processor. 
     An inner structure of an MeNB in a communication system supporting dual connectivity according to an embodiment of the present disclosure has been described with reference to  FIG. 16 , and an inner structure of an SeNB in a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIG. 17 . 
       FIG. 17  schematically illustrates an inner structure of an SeNB in a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     Referring to  FIG. 17 , an SeNB  120  includes a transmitter  1701 , a controller  1703 , a receiver  1705 , and a storage unit  1707 . 
     The controller  1703  controls the overall operation of the SeNB  120 . More particularly, the controller  1703  controls an operation related to an operation of transmitting and receiving data in a communication system supporting dual connectivity according to embodiments of the present disclosure. The operation related to the operation of transmitting and receiving the data in the communication system supporting the dual connectivity according to embodiments of the present disclosure has been described with  FIGS. 1 to 15 , and a detailed description thereof will be omitted herein. 
     The transmitter  1701  transmits various signals and various messages to other entities, e.g., an MeNB, a terminal, and/or the like in the communication system supporting the dual connectivity under a control of the controller  1703 . The various signals and various messages transmitted in the transmitter  1701  have been described with reference to  FIGS. 1 to 15 , and a detailed description thereof will be omitted herein. 
     The receiver  1705  receives various signals and various messages from other entities, e.g., an MeNB, a terminal, and/or the like in the communication system supporting the dual connectivity under a control of the controller  1703 . The various signals and various messages received in the receiver  1705  have been described with reference to  FIGS. 1 to 15 , and a detailed description thereof will be omitted herein. 
     The storage unit  1707  stores various programs, various data, and/or the like related to an operation related to an operation of transmitting and receiving data in a communication system supporting dual connectivity according to embodiments of the present disclosure, performed in the SeNB  120  under a control of the controller  1703 . 
     The storage unit  1707  stores various signals and various messages which are received by the receiver  1705  from the other entities. 
     While the transmitter  1701 , the controller  1703 , the receiver  1705 , and the storage unit  1707  are described in the SeNB  120  as separate units, it is to be understood that this is merely for convenience of description. In other words, two or more of the transmitter  1701 , the controller  1703 , the receiver  1705 , and the storage unit  1707  may be incorporated into a single unit. 
     The SeNB  120  may be implemented with one processor. 
     An inner structure of an SeNB in a communication system supporting dual connectivity according to an embodiment of the present disclosure has been described with reference to  FIG. 17 , and an inner structure of a terminal in a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIG. 18 . 
       FIG. 18  schematically illustrates an inner structure of a terminal in a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     Referring to  FIG. 18 , a terminal  130  includes a transmitter  1801 , a controller  1803 , a receiver  1805 , and a storage unit  1807 . 
     The controller  1803  controls the overall operation of the terminal  130 . More particularly, the controller  1803  controls an operation related to an operation of transmitting and receiving data in a communication system supporting dual connectivity according to embodiments of the present disclosure. The operation related to the operation of transmitting and receiving the data in the communication system supporting the dual connectivity according to embodiments of the present disclosure has been described with  FIGS. 1 to 15 , and a detailed description thereof will be omitted herein. 
     The transmitter  1801  transmits various signals and various messages to other entities, e.g., an MeNB, an SeNB, and/or the like in the communication system supporting the dual connectivity under a control of the controller  1803 . The various signals and various messages transmitted in the transmitter  1801  have been described with reference to  FIGS. 1 to 15 , and a detailed description thereof will be omitted herein. 
     The receiver  1805  receives various signals and various messages from other entities, e.g., an MeNB, an SeNB, and/or the like in the communication system supporting the dual connectivity under a control of the controller  1803 . The various signals and various messages received in the receiver  1805  have been described with reference to  FIGS. 1 to 15 , and a detailed description thereof will be omitted herein. 
     The storage unit  1807  stores various programs, various data, and/or the like related to an operation related to an operation of transmitting and receiving data in a communication system supporting dual connectivity according to embodiments of the present disclosure, performed in the terminal  130  under a control of the controller  1803 . 
     The storage unit  1807  stores various signals and various messages which are received by the receiver  1805  from the other entities. 
     While the transmitter  1801 , the controller  1803 , the receiver  1805 , and the storage unit  1807  are described in the terminal  130  as separate units, it is to be understood that this is merely for convenience of description. In other words, two or more of the transmitter  1801 , the controller  1803 , the receiver  1805 , and the storage unit  1807  may be incorporated into a single unit. 
     The terminal  130  may be implemented with one processor. 
     An inner structure of an SeNB in a communication system supporting dual connectivity according to an embodiment of the present disclosure has been described with reference to  FIG. 18 , and an inner structure of an EPC in a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIG. 19 . 
       FIG. 19  schematically illustrates an inner structure of an EPC in a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     Referring to  FIG. 19 , an EPC  140  includes a transmitter  1901 , a controller  1903 , a receiver  1905 , and a storage unit  1907 . 
     The controller  1903  controls the overall operation of the EPC  140 . More particularly, the controller  1903  controls an operation related to an operation of transmitting and receiving data in a communication system supporting dual connectivity according to embodiments of the present disclosure. The operation related to the operation of transmitting and receiving the data in the communication system supporting the dual connectivity according to embodiments of the present disclosure has been described with  FIGS. 1 to 15 , and a detailed description thereof will be omitted herein. 
     The transmitter  1901  transmits various signals and various messages to other entities, e.g., an MeNB, an SeNB, and/or the like in the communication system supporting the dual connectivity under a control of the controller  1903 . The various signals and various messages transmitted in the transmitter  1901  have been described with reference to  FIGS. 1 to 15 , and a detailed description thereof will be omitted herein. 
     The receiver  1905  receives various signals and various messages from other entities, e.g., an MeNB, an SeNB, and/or the like in the communication system supporting the dual connectivity under a control of the controller  1903 . The various signals and various messages received in the receiver  1905  have been described with reference to  FIGS. 1 to 15 , and a detailed description thereof will be omitted herein. 
     The storage unit  1907  stores various programs, various data, and/or the like related to an operation related to an operation of transmitting and receiving data in a communication system supporting dual connectivity according to embodiments of the present disclosure, performed in the EPC  140  under a control of the controller  1903 . 
     The storage unit  1907  stores various signals and various messages which are received by the receiver  1905  from the other entities. 
     While the transmitter  1901 , the controller  1903 , the receiver  1905 , and the storage unit  1907  are described in the EPC  140  as separate units, it is to be understood that this is merely for convenience of description. In other words, two or more of the transmitter  1901 , the controller  1903 , the receiver  1905 , and the storage unit  1907  may be incorporated into a single unit. 
     The EPC  140  may be implemented with one processor. 
     An inner structure of an EPC in a communication system supporting dual connectivity according to an embodiment of the present disclosure has been described with reference to  FIG. 19 , and an inner structure of a server in a communication system supporting dual connectivity according to an embodiment of the present disclosure will be described with reference to  FIG. 20 . 
       FIG. 20  schematically illustrates an inner structure of a server in a communication system supporting dual connectivity according to an embodiment of the present disclosure. 
     Referring to  FIG. 20 , a server  150  includes a transmitter  2001 , a controller  2003 , a receiver  2005 , and a storage unit  2007 . 
     The controller  2003  controls the overall operation of the server  150 . More particularly, the controller  2003  controls an operation related to an operation of transmitting and receiving data in a communication system supporting dual connectivity according to embodiments of the present disclosure. The operation related to the operation of transmitting and receiving the data in the communication system supporting the dual connectivity according to embodiments of the present disclosure has been described with  FIGS. 1 to 15 , and a detailed description thereof will be omitted herein. 
     The transmitter  2001  transmits various signals and various messages to other entities, e.g., an MeNB, an SeNB, and/or the like in the communication system supporting the dual connectivity under a control of the controller  2003 . The various signals and various messages transmitted in the transmitter  2001  have been described with reference to  FIGS. 1 to 15 , and a detailed description thereof will be omitted herein. 
     The receiver  2005  receives various signals and various messages from other entities, e.g., an MeNB, an SeNB, and/or the like in the communication system supporting the dual connectivity under a control of the controller  2003 . The various signals and various messages received in the receiver  2005  have been described with reference to  FIGS. 1 to 15 , and a detailed description thereof will be omitted herein. 
     The storage unit  2007  stores various programs, various data, and/or the like related to an operation related to an operation of transmitting and receiving data in a communication system supporting dual connectivity according to embodiments of the present disclosure, performed in the server  150  under a control of the controller  2003 . 
     The storage unit  2007  stores various signals and various messages which are received by the receiver  2005  from the other entities. 
     While the transmitter  2001 , the controller  2003 , the receiver  2005 , and the storage unit  2007  are described in the server  150  as separate units, it is to be understood that this is merely for convenience of description. In other words, two or more of the transmitter  2001 , the controller  2003 , the receiver  2005 , and the storage unit  2007  may be incorporated into a single unit. 
     The server  150  may be implemented with one processor. 
     In accordance with various embodiments of the present disclosure, an operating method of a first evolved node B (eNB) in a communication system supporting dual connectivity is provided. The operating method includes detecting that a path between a second eNB and a terminal is blocked; and transmitting, to the terminal, a first data unit of a plurality of data units to be transmitted through the path between the second eNB and the terminal. 
     Preferably, the operating method further comprises determining that the first data unit is to be transmitted through the path between the second eNB and the terminal and determining that a second data unit among the plurality of data units is to be transmitted through a path between the first eNB and the terminal; and transmitting information indicating the determined result to the terminal. 
     Preferably, the operating method further comprises transmitting, to the second eNB, control information related to a sequence number (SN) of a data unit which is successfully transmitted to the terminal; and receiving information indicating that the path between the second eNB and the terminal is recovered from the second eNB. 
     Preferably, the operating method further comprises receiving, from the terminal, the information indicating that the path between the second eNB and the terminal is blocked. 
     Preferably, the operating method further comprises receiving, from the second eNB, information indicating that the path between the second eNB and the terminal is blocked. 
     Preferably, the first data unit is determined based on priorities of data units which are able to be retransmitted if the blocked path is recovered among the plurality of data units. 
     Preferably, the operating method further comprises establishing a path between the second eNB and the first eNB; and receiving the first data unit from the second eNB through the established path. 
     In accordance with various embodiments of the present disclosure, an operating method of a second evolved node B (eNB) in a communication system supporting dual connectivity is provided. The operating method includes detecting that a path between a second eNB and a terminal is blocked; and transmitting, to a first eNB, information indicating that the path between the second eNB and the terminal is blocked. 
     Preferably, the detecting that the path between the second eNB and the terminal is blocked comprises detecting that the path between the second eNB and the terminal is temporarily blocked if retransmission of a data packet is not performed up to a preset number of retransmission attempts. 
     Preferably, the operating method further comprises receiving information about a sequence number (SN) of a data packet which is successfully transmitted from the first eNB to the terminal; and transmitting information indicating that the path between the second eNB and the terminal is recovered to the first eNB if the path between the second eNB and the terminal is recovered. 
     Preferably, the operating method further comprises establishing a path between the second eNB and the first eNB; and transmitting data to be transmitted through the path between the second eNB and the terminal to the first eNB through the established path. 
     In accordance with various embodiments of the present disclosure, an operating method of a terminal in a communication system supporting dual connectivity is provided. The operating method includes detecting that a path between a first evolved node B (eNB) and a terminal is blocked; transmitting, to a second eNB, information indicating that the path between the first eNB and the terminal is blocked; and receiving, from the second eNB, a first data packet of a plurality of data packets to be transmitted through the path between the first eNB and the terminal. 
     Preferably, the operating method further comprises receiving, from the first eNB, information indicating that the first data packet is transmitted through the path between the first eNB and the terminal, and a second data packet among the plurality of data packets is transmitted through a path between the second eNB and the terminal. 
     Preferably, the detecting that the path between the first eNB and the terminal is blocked comprises detecting that the path between the first eNB and the terminal is temporarily blocked if a timer of detecting a temporary blockage between the first eNB and the terminal expires. 
     In accordance with various embodiments of the present disclosure, an operating method of an evolved packet core (EPC) in a communication system supporting dual connectivity is provided. The operating method includes transmitting and receiving a message including information indicating that a retransmission function is able to be performed with a terminal through a transmission control protocol (TCP) layer; and receiving a retransmission request message including information related to a data packet which should be retransmitted through the TCP layer, and transmitting the data packet through the TCP layer based on the retransmission request message. 
     Preferably, the message is transmitted and received in a procedure of establishing a TCP session with the terminal. 
     Preferably, the information related to the data packet which should be retransmitted includes information about amount of the data packet which should be retransmitted. 
     In an embodiment of the present disclosure, an MeNB may effectively reorder data in a PDCP layer in a terminal by additionally providing routing information for routed data or data to be routed. According to an embodiment of the present disclosure, delay due to data reordering may be reduced and transmission efficiency of data transmitted to an upper layer may be increased. 
     In an embodiment of the present disclosure, a terminal may re-route data which an MeNB has routed through a transmission path for a radio link through other path by detecting a temporary blockage of the radio link and notifying the MeNB of the detected result. According to an embodiment of the present disclosure, delay for transmission that occurs due to a temporary blockage of a radio link may be reduced and transmission efficiency of data transmitted to an upper layer may be increased. 
     In an embodiment of the present disclosure, an SeNB may re-route data which an MeNB has routed through a transmission path for a radio link through other path by detecting a temporary blockage of the radio link and notifying the MeNB of the detected result. According to an embodiment of the present disclosure, delay for transmission that occurs due to a temporary blockage of a radio link may be reduced and transmission efficiency of data transmitted to an upper layer may be increased. 
     In an embodiment of the present disclosure, an MeNB may re-route data which has been routed through a transmission path for a radio link through other path after detecting a temporary blockage of the radio link. According to an embodiment of the present disclosure, delay for transmission that occurs due to a temporary blockage of a radio link may be reduced and transmission efficiency of data transmitted to an upper layer may be increased. 
     In an embodiment of the present disclosure, a terminal detects a temporary blockage of a radio link to notify an MeNB of the detected result, so the MeNB may receive data which is being buffered in an SeNB from the SeNB to transmit the received data to the terminal. According to an embodiment of the present disclosure, delay for transmission which occurs due to a temporary blockage of a radio link may be reduced and transmission efficiency of data transmitted to an upper layer may be increased. 
     In an embodiment of the present disclosure, an SeNB detects a temporary blockage of a radio link to notify an MeNB of the detected result, so the MeNB may receive data which is being buffered in the SeNB from the SeNB to transmit the received data to a terminal. According to an embodiment of the present disclosure, delay for transmission which occurs due to a temporary blockage of a radio link may be reduced and transmission efficiency of data transmitted to an upper layer may be increased. 
     In an embodiment of the present disclosure, a TCP layer in a terminal may reduce delay for transmission which occurs due to a temporary blockage of a radio link and increase transmission efficiency of data transmitted to an upper layer by requesting to immediately transmit loss of a TCP segment due to the temporary blockage of the radio link from a TCP layer in a server. 
     Certain aspects of the present disclosure may also be embodied as computer readable code on a non-transitory computer readable recording medium. A non-transitory computer readable recording medium is any data storage device that can store data, which can be thereafter read by a computer system. Examples of the non-transitory computer readable recording medium include read only memory (ROM), random access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storage devices, and carrier waves (such as data transmission through the Internet). The non-transitory computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. In addition, functional programs, code, and code segments for accomplishing the present disclosure can be easily construed by programmers skilled in the art to which the present disclosure pertains. 
     It can be appreciated that a method and apparatus according to an embodiment of the present disclosure may be implemented by hardware, software and/or a combination thereof. The software may be stored in a non-volatile storage, for example, an erasable or re-writable ROM, a memory, for example, a RAM, a memory chip, a memory device, or a memory integrated circuit (IC), or an optically or magnetically recordable non-transitory machine-readable (e.g., computer-readable), storage medium (e.g., a compact disk (CD), a digital video disc (DVD), a magnetic disk, a magnetic tape, and/or the like). A method and apparatus according to an embodiment of the present disclosure may be implemented by a computer or a mobile terminal that includes a controller and a memory, and the memory may be an example of a non-transitory machine-readable (e.g., computer-readable), storage medium suitable to store a program or programs including instructions for implementing various embodiments of the present disclosure. 
     The present disclosure may include a program including code for implementing the apparatus and method as defined by the appended claims, and a non-transitory machine-readable (e.g., computer-readable), storage medium storing the program. The program may be electronically transferred via any media, such as communication signals, which are transmitted through wired and/or wireless connections, and the present disclosure may include their equivalents. 
     An apparatus according to an embodiment of the present disclosure may receive the program from a program providing device which is connected to the apparatus via a wire or a wireless and store the program. The program providing device may include a memory for storing instructions which instruct to perform a content protect method which has been already installed, information necessary for the content protect method, and the like, a communication unit for performing a wired or a wireless communication with a graphic processing device, and a controller for transmitting a related program to a transmitting/receiving device based on a request of the graphic processing device or automatically transmitting the related program to the transmitting/receiving device. 
     Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.