Patent Publication Number: US-2013244674-A1

Title: Mobile terminal, radio base station, control method for a mobile terminal and method for a radio base station

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese patent application No. 2012-062174, filed on Mar. 19, 2012, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     The exemplary embodiments relate to a mobile communication system, a communication apparatus, and a communication method. 
     A mobile communication system in LTE (Long Term Evolution) defined by 3GPP (Third Generation Partnership Project) includes a mobile station (UE: User Equipment), a base station (eNB: evolved Node B), an MME (Mobility Management Entity), and an S-GW (Serving Gateway). 
     As shown in  FIG. 1 , a UE wirelessly communicates with an eNB, and the interface therebetween is defined as Uu. The eNB communicates with an MME and an S-GW that are nodes in a core network, and the interface therebetween is defined as S1-AP (S1 Application Protocol). Communication may also be conducted between eNBs, and the interface therebetween is defined as X2-AP (X2 Application Protocol). 
     As shown in Non-patent literature 1 (Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 [3GPP TS36.300 V9.9.0]), an RRC (Radio Resource Control) protocol is used as an L3 (Layer 3) protocol for a control plane between the UE and the eNB. Further, as shown in Non-patent literature 2 (Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification [3GPP TS36.331 V9.9.0]), a message of RRC includes a plurality of IEs (information elements). The specification of RRC includes the definition of Need ON in which a predetermined IE may be optionally included in the message, and if the message is received by the UE and in case where the IE is not included in the received message, the UE takes no action for this IE and uses the currently held set value for the IE. Accordingly, when the IE specified as Need ON is not included in an RRC message transmitted from the eNB, the UE keeps holding the currently held set value for the IE. Meanwhile, when the IE is included in the message, the UE updates the set value for the IE with the value set in the message. In this way, for the IE specified as NeedON, the eNB is able to notify the UE of only the difference information (delta configuration). 
     Accordingly, when transmitting the RRC message to the UE, if the set value that is currently held by the UE can be continuously used for the IE specified as Need ON, the eNB may not include the IE in the message. Accordingly, it is possible to reduce the size of the RRC message to be transmitted, whereby it is expected to improve utilization efficiency of radio resources. 
     The aforementioned background art has a problem that it is impossible to effectively use the function of delta configuration in a sequence in which the RRC message cannot be successfully transmitted or received between the UE and the eNB. Hereinafter, with reference to the drawings, description will be made with specific examples. 
       FIG. 2  is a diagram showing a normal sequence regarding an RRC Connection Reconfiguration message according to a related art. First, in a state in which each of a UE  100 , an eNB  200 , and an MME  300  is active (S 1000 ), the eNB  200  transmits RRC Connection Reconfiguration to the UE  100  by using as a trigger one of three cases shown in S 1100  (S 1200 ). The first case is a case in which the eNB  200  receives an RRC message from the UE  100  (S 1110 ), and upon receiving this message, the eNB  200  generates an RRC message (S 1111 ). The second case is a case in which the eNB  200  receives an S1-AP message from the MME  300  (S 1120 ), and upon receiving this message, the eNB  200  generates an RRC message (S 1121 ). The third case is a case in which the eNB  200  generates an RRC message by its internal trigger (S 1130 ). After that, the UE  100  receives the RRC Connection Reconfiguration (S 1200 ), and transmits an RRC Connection Reconfiguration Complete message to the eNB  200  (S 1201 ). The detail of each message described above is disclosed in Non-patent literature 2. 
       FIG. 3  is a diagram showing a sequence when the sequence shown in  FIG. 2  cannot be successfully executed in the related art. First, each of the UE  100 , the eNB  200 , and the MME  300  executes the sequence at S 1100  shown in  FIG. 2 . After that, it is assumed that any of the two kinds of failures shown in S 2100  and S 2200  occurs for some reason such as degradation of quality of the radio transmission path. The first case (S 2100 ) is the case in which, while the eNB  200  transmitted RRC Connection Reconfiguration, this message does not reach the UE  100  (S 2101 ). In the second case (S 2200 ), the UE  100  receives the RRC Connection Reconfiguration transmitted from the eNB  200  (S 2201 ), and updates the set value for the IE with the set value in the message (S 2202 ). Subsequently, while the UE  100  transmitted RRC Connection Reconfiguration Complete to the eNB  200 , the eNB  200  cannot successfully receive this message (S 2203 ). After S 2100  or S 2200 , the UE  100  transmits an RRC Connection Reestablishment Request message to the eNB  200  to request re-connection (S 2300 ). Upon receiving this message, the eNB  200  transmits RRC Connection Reestablishment to the UE  100  (S 2301 ). Subsequently, upon receiving this message, the UE  100  transmits RRC Connection Reestablishment Complete to the eNB  200  (S 2302 ). Next, the eNB  200  transmits an RRC Connection Reconfiguration message to the UE  100  (S 2303 ). Subsequently, the UE  100  transmits RRC Connection Reconfiguration Complete to the eNB  200  (S 2304 ). The detail of each message stated above is disclosed in Non-patent literature 2. 
     The eNB  200  cannot determine whether the UE  100  has not updated the set value for the IE by the RRC Connection Reconfiguration as in the first case (S 2100 ) or the UE  100  has updated the set value for the IE as in the second case (S 2200 ). Accordingly, even when there is an IE specified as Need ON in the message transmitted to the UE  100  in S 2301  and S 2303 , the eNB  200  needs to include all IEs in the message to set the value, which inhibits reduction in size of messages. 
     SUMMARY 
     An exemplary object of the exemplary embodiments is to provide a mobile communication system, a communication apparatus, and a communication method that are able to solve the aforementioned problems. However, the exemplary embodiments may achieve objectives other than those described above. Further, exemplary embodiments are not required to achieve the objectives described above, and an exemplary embodiment may not achieve any of the objectives described above. 
     A mobile communication system according to the exemplary embodiment is a mobile communication system including a first communication apparatus and a second communication apparatus that communicates with the first communication apparatus. In this communication system, the first communication apparatus includes: a first processor that performs processing regarding a protocol, the protocol defining that a predetermined information element is optionally included in a message, and if a communication apparatus receives the message and in case the information element is not included in the received message, the communication apparatus that received the message takes no action regarding the information element and uses a set value for the information element that is currently held; a first receiver that receives a message defined by the protocol from the second communication apparatus; and a first transmitter that transmits a first message defined by the protocol to the second communication apparatus, the first message including identification information of a message that the first receiver last successfully received. The second communication apparatus includes: a second processor that performs processing regarding the protocol; a second receiver that receives the first message from the first communication apparatus; and a determination unit that determines whether to include a predetermined information element in a second message that is defined by the protocol and is to be transmitted to the first communication apparatus based on the identification information. 
     A first communication apparatus according to the exemplary embodiment is a first communication apparatus that communicates with a second communication apparatus. This first communication apparatus includes: a first processor that performs processing regarding a protocol, the protocol defining that a predetermined information element is optionally included in a message, and if a communication apparatus receives the message and in case the information element is not included in the received message, the communication apparatus that received the message takes no action regarding the information element and uses a set value for the information element that is currently held; a first receiver that receives a message defined by the protocol from the second communication apparatus; and a first transmitter that transmits a first message defined by the protocol to the second communication apparatus, the first message including identification information of a message that the first receiver last successfully received. 
     A second communication apparatus according to the exemplary embodiment is a second communication apparatus that communicates with a first communication apparatus. This second communication apparatus includes: a second processor that performs processing regarding a protocol, the protocol defining that a predetermined information element is optionally included in a message, and if a communication apparatus receives the message and in case the information element is not included in the received message, the communication apparatus that received the message takes no action regarding the information element and uses a set value for the information element that is currently held; a second receiver that receives a first message defined by the protocol from the first communication apparatus, the first message including identification information of a message that is defined by the protocol and that the first communication apparatus last successfully received from the second communication apparatus; and a determination unit that determines whether to include the predetermined information element in a second message that is defined by the protocol and is to be transmitted to the first communication apparatus based on the identification information. 
     A communication method according to the exemplary embodiment is a communication method in a mobile communication system including a first communication apparatus and a second communication apparatus that communicates with the first communication apparatus. This method includes the steps of: performing processing regarding a protocol by the first communication apparatus, the protocol defining that a predetermined information element is optionally included in a message, and if a communication apparatus receives the message and in case the information element is not included in the received message, the communication apparatus that received the message takes no action regarding the information element and uses a set value for the information element that is currently held; receiving, by the first communication apparatus, a message defined by the protocol from the second communication apparatus; transmitting, by the first communication apparatus, a first message defined by the protocol to the second communication apparatus, the first message including identification information of a message that the first communication apparatus last successfully received; performing processing regarding the protocol by the second communication apparatus; receiving, by the second communication apparatus, the first message from the first communication apparatus; and determining based on the identification information by the second communication apparatus whether to include the predetermined information element in a second message that is defined by the protocol and is to be transmitted to the first communication apparatus. 
     A communication method according to the exemplary embodiment is a communication method in a first communication apparatus that communicates with a second communication apparatus. This method includes the steps of: performing processing regarding a protocol, the protocol defining that a predetermined information element is optionally included in a message, and if a communication apparatus receives the message and in case the information element is not included in the received message, the communication apparatus that received the message takes no action regarding the information element and uses a set value for the information element that is currently held; receiving a message defined by the protocol from the second communication apparatus; and transmitting a first message defined by the protocol to the second communication apparatus, the first message including identification information of a message that the first communication apparatus last successfully received. 
     A communication method according to the exemplary embodiment is a communication method in a second communication apparatus that communicates with a first communication apparatus. This method includes the steps of: performing processing regarding a protocol, the protocol defining that a predetermined information element is optionally included in a message, and if a communication apparatus receives the message and in case the information element is not included in the received message, the communication apparatus that received the message takes no action regarding the information element and uses a set value for the information element that is currently held; receiving a first message defined by the protocol from the first communication apparatus, the first message including identification information of a message that is defined by the protocol and that the first communication apparatus last successfully received from the second communication apparatus; and determining whether to include the predetermined information element in a second message that is defined by the protocol and is to be transmitted to the first communication apparatus based on the identification information. 
     According to the exemplary embodiment, a second communication apparatus is able to determine whether to include a predetermined information element in a message to be transmitted to a first communication apparatus based on identification information of a message that is last successfully received by the first communication apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of the exemplary embodiment will become more apparent from the following description of certain exemplary embodiments when taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a diagram showing a configuration of a mobile communication system of LTE defined by the 3GPP; 
         FIG. 2  is a sequence diagram of communication using an RRC protocol according to a related art; 
         FIG. 3  is a sequence diagram of communication using the RRC protocol according to the related art; 
         FIG. 4  is a diagram showing a configuration according to a first exemplary embodiment; 
         FIG. 5  is a sequence diagram showing an operation according to the first exemplary embodiment; 
         FIG. 6  is a diagram showing a configuration of a UE according to a second exemplary embodiment; 
         FIG. 7  is a diagram showing a configuration of an eNB according to the second exemplary embodiment; 
         FIG. 8  is a diagram showing a configuration of an MME according to the second exemplary embodiment; 
         FIG. 9  is a sequence diagram showing an operation according to the second exemplary embodiment; 
         FIG. 10  is a diagram showing an example of messages to be transmitted from the UE to the eNB in the second exemplary embodiment; 
         FIG. 11  is a diagram showing an example of messages to be transmitted from the UE to the eNB in the second exemplary embodiment; 
         FIG. 12  is a sequence diagram showing an operation according to a third exemplary embodiment; 
         FIG. 13  is a sequence diagram showing an operation according to the third exemplary embodiment; and 
         FIG. 14  is a sequence diagram showing an operation according to the third exemplary embodiment. 
     
    
    
     EXEMPLARY EMBODIMENTS 
     Hereinafter, with reference to the drawings, exemplary embodiments will be described. The word “exemplary” is used herein to mean “serving as an example, instance, or illustration”. Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. 
     First Exemplary Embodiment 
       FIG. 4  is a diagram showing one example of a configuration according to a first exemplary embodiment. A mobile communication system according to this exemplary embodiment includes a first communication apparatus  10  and a second communication apparatus  20  that is capable of communicating with the first communication apparatus. 
     The first communication apparatus  10  includes a first processor  11 , a first receiver  12 , and a first transmitter  13 . The first processor  11  performs processing regarding a predetermined protocol. This protocol defines that a predetermined information element is optionally included in a message, and if a communication apparatus receives the message and in case where the information element is not included in the received message, the communication apparatus takes no action regarding the information element and uses the currently held set value for the information element. The first receiver  12  receives a message defined by the protocol from the second communication apparatus. The first transmitter  13  transmits a first message defined by the protocol to the second communication apparatus, the first message including identification information of a message that the first receiver last successfully received. 
     The second communication apparatus  20  includes a second processor  21 , a second receiver  22 , a determination unit  23 , and a second transmitter  24 . The second processor  21  performs processing regarding the protocol. The second receiver  22  receives the above-mentioned first message from the first communication apparatus. The determination unit  23  determines whether to include a predetermined information element in a second message defined by the protocol based on the identification information included in the first message. The second transmitter  24  can transmit the second message based on the result determined by the determination unit  23 . 
     Next, with reference to the drawings, the detail of operations of an UE  100 , an eNB  200 , and an MME  300  in the first exemplary embodiment will be described. 
       FIG. 5  is a sequence diagram showing one example of an operation according to the first exemplary embodiment. 
     In S 11 , the first communication apparatus  10  receives, by the first receiver  12 , messages defined by the protocol from the second communication apparatus. Each of the messages includes identification information of the message. 
     In S 12 , the first communication apparatus  10  adds identification information included in the message that the first receiver  12  last successfully received to the first message, to transmit, by the first transmitter  13 , the first message to the second communication apparatus  20 . 
     In S 13 , the second communication apparatus  20  receives the first message by the second receiver  22 . 
     In S 14 , the second communication apparatus  20  determines by the determination unit  23  whether to include a predetermined information element in the second message that is defined by the protocol and is to be transmitted to the first communication apparatus  10  based on the identification information included in the first message. More specifically, the determination unit  23  determines the set value for the predetermined information element in the first communication apparatus  10  based on the identification information, determines that the predetermined information element should not be included when the determined set value is the same to a set value for the predetermined information element which should be set in the second message, and determines that the predetermined information element should be included when the determined set value is different from the set value for the predetermined information element which should be set in the second message. 
     In S 15 , the second communication apparatus  20  does not transmit the second message by the transmitter  24  when the predetermined information element determined by the determination unit  23  to be included in the second message does not exist, and can transmit the second message to the first communication apparatus  10  when the predetermined information element exists. 
     As described above, the second communication apparatus  20  can determine the set value for the predetermined information element in the first communication apparatus  10  based on the identification information of the message which was last successfully received by the first communication apparatus  10 . Then it is possible to determine whether to include the predetermined information element in the second message to be transmitted to the first communication apparatus  10  based on the determined result. Accordingly, it is possible to reduce the size of the second message under predetermined conditions, and thereby to improve utilization efficiency of transmission path resources. 
     Second Exemplary Embodiment 
     In a second exemplary embodiment, the first exemplary embodiment is applied to the mobile communication system in LTE defined by the 3GPP shown in  FIG. 1 . Hereinafter, with reference to the drawings, a configuration of each apparatus will be described. 
       FIG. 6  is a diagram showing a configuration of the UE  100 . The UE  100  performs processing regarding the RRC protocol by an RRC layer function unit  101  according to the control by a controller  103 , and transmits/receives RRC messages to/from the eNB  200  through a Uu transceiver  102 . 
       FIG. 7  is a diagram showing a configuration of the eNB  200 . The eNB  200  performs processing regarding the RRC protocol by an RRC layer function unit  203  according to the control by a controller  205 , and transmits/receives RRC messages to/from the UE  100  through a Uu transceiver  204 . Further, the eNB  200  performs processing regarding the S1 protocol in an S1-AP layer function unit  202  according to the control by the controller  205 , and transmits/receives S1-AP messages to/from the MME  300  through an S1 transceiver  201 . While not being illustrated in the drawings, since the configurations of an eNB  210 , an eNB  220 , and an eNB  230  are similar to that of the eNB  200 , description thereof will be omitted. 
       FIG. 8  is a diagram showing a configuration of the MME  300 . The MME  300  performs processing regarding the S1 protocol by an S1-AP layer function unit  301  according to the control by a controller  303 , and transmits/receives S1-AP messages to/from the eNB  200  through an S1 transceiver  302 . 
     Next, with reference to the drawings, the detail of operations of the UE  100 , the eNB  200 , and the MME  300  according to the second exemplary embodiment will be described. 
       FIG. 9  is a sequence diagram showing an example of an operation according to the second exemplary embodiment.  FIG. 9  shows an operation when the exemplary embodiment is applied to the sequence shown in  FIG. 3 . 
     In S 3000 , each of the UE  100 , the eNB  200 , and the MME  300  executes the sequence at S 1100  shown in  FIG. 2 . 
     The first case shown in S 3100  will be described. The sequence at S 3100  corresponds to S 2100  shown in  FIG. 3 . The eNB  200  transmits to the UE  100  RRC Connection Reconfiguration in which RRC-TransactionIdentifier is set to “n+1”. However, for some reason such as degradation of quality of the radio transmission path, the UE  100  cannot successfully receive the message (S 3101 ). Note that RRC-TransactionIdentifier is an IE for identification information to identify the transmitted RRC Connection Reconfiguration message. While not shown in  FIG. 9 , it is assumed that the value of the identification information has already become “n” according to the transmission and reception of messages between the eNB  200  and the UE  100  that are executed before start of the sequence. Accordingly, the value of the identification information at S 3101  is counted up by one and becomes “n+1”. Subsequently, the UE  100  transmits RRC Connection Reestablishment Request to the eNB  200  to request re-connection, and the eNB  200  receives this message. This message includes Latest RRC-TransactionIdentifier, which is an IE to indicate identification information of the message that was last successfully received by the UE  100  from the eNB  200 . In S 3101 , the eNB  200  sets “n+1” for RRC-TransactionIdentifier to be transmitted. Thus, if the UE  100  could successfully receive the message, the value of Latest RRC-TransactionIdentifier in S 3102  is “n+1”. However, since the UE  100  cannot successfully receive the message at S 3101 , the UE  100  sets the existing value “n” for Latest RRC-TransactionIdentifier (S 3102 ). Note that the Latest RRC-TransactionIdentifier is an IE that is not disclosed in Non-patent literature 2. 
       FIGS. 10 and 11  each show a configuration example of a message when the IE for Latest RRC-TransactionIdentifier is added to the RRC Connection Reestablishment Request message disclosed in Non-patent literature 2. The term latest-rrc-TransactionIdentifier in  FIGS. 10 and 11  corresponds to the Latest RRC-TransactionIdentifier.  FIGS. 10 and 11  also show that the set value that latest-rrc-TransactionIdentifier may have is RRC-TransactionIdentifier. 
     The second case shown in S 3200  will now be described. The sequence at S 3200  corresponds to S 2200  in  FIG. 3 . The eNB  200  transmits messages to the UE  200  as is similar to S 3101 . As is different from S 3101 , the UE  100  successfully receives the message (S 3201 ). The UE  100  then updates the set value for the IE with the value set in the message at S 3201  (S 3202 ). Subsequently, while the UE  100  transmits RRC Connection Reconfiguration Complete to the eNB  200 , the eNB  200  cannot receive this message (S 3203 ). Accordingly, the UE  100  transmits RRC Connection Reestablishment Request to request re-connection to the eNB  200 , and the eNB  200  receives this message (S 3204 ). In this case, the UE  100  sets the value of Latest RRC-TransactionIdentifier to “n+1”. This is because the UE  100  successfully received the message in which RRC-TransactionIdentifier is “n+1” at S 3201  and also updated the set value for the IE at S 3202 . 
     The operations from S 3301  to S 3307  shown in S 3300  will be described hereinafter in detail. 
     In S 3301 , the eNB  200  determines the set value for the IE in the UE  100 . More specifically, in the first case (S 3100 ), it is found at S 3102  that the Latest RRC-TransactionIdentifier is “n”. Therefore, the eNB  200  determines that the set value for the IE in the message at S 3101  is not reflected in the current set value for the IE in the UE  100 , and the current set value is the value before the transmission of the message. On the other hand, in the second case (S 3200 ), it is found at S 3204  that the Latest RRC-TransactionIdentifier is “n+1”. Therefore, the eNB  200  determines that the current set value for the IE in the UE  100  is the value set in the message at S 3201 . 
     In S 3302 , the eNB  200  determines whether to include a predetermined IE in the message to be transmitted next. More specifically, the eNB  200  determines, for the IE which is specified as Need ON among the IEs of RRC Connection Reestablishment to be transmitted at the next S 3303 , whether the set value which should be set in the message is the same to the current set value in the UE  100  determined at S 3301 . When the result shows that the values are the same, there is no need to notify it by the message. Therefore, the eNB  200  determines that the IE should not be included in the transmission message. In contrast, when the set value which should be set in the message is different from the current set value in the UE  100 , the eNB  200  determines that the IE should be included in the transmission message. 
     In S 3303 , the eNB  200  transmits to the UE  100  RRC Connection Reestablishment in which the determined result at S 3302  is reflected, and the UE  100  receives this message. 
     In S 3304 , the UE  100  transmits to the eNB  200  RRC Connection Reestablishment Complete, and the eNB  200  receives this message. 
     In S 3305 , the eNB  200  determines whether to include a predetermined IE in the message to be transmitted next, as is similar to S 3302 . More specifically, for the IE which is specified as Need ON among the IEs of RRC Connection Reconfiguration to be transmitted at the next S 3306 , the eNB  200  determines whether the set value which should be set in the message is the same to the current set value in the UE  100  determined at S 3301 . When the result shows that the values are the same, there is no need to notify it by the message. Therefore, the eNB  200  determines that the IE should not be included in the transmission message. In contrast, when the set value which should be set in the message is different from the current set value in the UE  100 , the eNB  200  determines that the IE should be included in the transmission message. 
     In S 3306 , the eNB  200  transmits to the UE  100  RRC Connection Reconfiguration in which the determined result at S 3305  is reflected, and the UE  100  receives this message. 
     In S 3307 , the UE  100  transmits to the eNB  200  RRC Connection Reconfiguration Complete, and the eNB  200  receives this message. 
     As described above, the eNB  200  can determine whether to include the IE which is specified as Need ON in the message to be transmitted based on the result obtained by determining the current set value for the IE in the UE  100 . Accordingly, the eNB  200  can reduce the size of the message to be transmitted to the UE  100 , thereby being able to improve utilization efficiency of radio resources. 
     Third Exemplary Embodiment 
     In a third exemplary embodiment, the exemplary embodiment is applied to a sequence in which the eNB  200  successively transmits RRC Connection Reconfiguration to the UE  100  twice, while the eNB  200  transmits the RRC Connection Reconfiguration to the UE  100  once in the second exemplary embodiment. 
     Since the configuration in the third exemplary embodiment is similar to that in the second exemplary embodiment, description thereof will be omitted. 
     Hereinafter, with reference to  FIGS. 12 to 14 , an example of an operation according to the third exemplary embodiment will be described according to the patterns of failures that may occur. 
       FIG. 12  is a sequence diagram showing an example of an operation according to the third exemplary embodiment. First, upon execution of the sequence at S 1100  shown in  FIG. 2  by the UE  100 , the eNB  200 , and the MME  300  (S 5000 ), the eNB  200  transmits to the UE  100  RRC Connection Reconfiguration in which the value of RRC-TransactionIdentifier is “n+1”. However, for some reason such as degradation of quality of the radio transmission path, the UE  100  cannot successfully receive this message (S 5001 ). It is assumed here that the value of RRC-TransactionIdentifier proceeds to the value of “n” as a result of transmission and reception of messages between the eNB  200  and the UE  100  executed before this sequence starts, as is similar to the second exemplary embodiment. Subsequently, after the sequence at S 1100  is further executed (S 5002 ), the eNB  200  transmits to the UE  100  RRC Connection Reconfiguration in which the value of RRC-TransactionIdentifier is “n+2”. However, for some reason such as degradation of quality of the radio transmission path, the UE  100  cannot successfully receive the message (S 5003 ). Therefore, the UE  100  transmits RRC Connection Reestablishment Request to the eNB  200  to start re-connection. Since the UE  100  has not successfully received any of the messages at S 5001  and S 5003 , the value of Latest RRC-TransactionIdentifier is set to “n” (S 5004 ). 
     Then, the eNB  200  and the UE  100  execute the similar sequence as S 3300  in  FIG. 9  (S 5005 ). Since it is found at S 5004  that the value of Latest RRC-TransactionIdentifier is “n”, the eNB  200  determines that the values set in the messages at S 5001  and S 5003  are not reflected in the current set value for the IE in the UE, and the current set value is the value before the transmission of these messages (S 3301 ). The eNB  200  determines whether to include a predetermined IE in a message based on this determined result (S 3302  and S 3305 ), and transmits the message in which the determination is reflected to the UE  100  (S 3303  and S 3306 ). The other operations in S 5005  are similar to those in S 3300 . 
       FIG. 13  is a sequence diagram showing an example of an operation according to the third exemplary embodiment upon occurrence of a failure which is different from that shown in  FIG. 12 . First, upon execution of the sequence at S 1100  shown in  FIG. 2  by the UE  100 , the eNB  200 , and the MME  300  (S 6000 ), the eNB  200  transmits to the UE  100  RRC Connection Reconfiguration in which the value of RRC-TransactionIdentifier is “n+1”, and the UE  100  receives this message (S 6001 ). Next, the UE  100  updates the set value for the IE with the value set in the message (S 6002 ). Subsequently, the UE  100  transmits, as a response to S 6001 , RRC Connection Reconfiguration Complete in which the value of RRC-TransactionIdentifier is “n+1”. However, for some reason such as degradation of quality of the radio transmission path, the eNB  200  cannot successfully receive the message (S 6003 ). Subsequently, after the sequence at S 1100  is further executed (S 6004 ), the eNB  200  transmits RRC Connection Reconfiguration to the UE  100 . However, the UE  100  cannot successfully receive this message. Here, the value of RRC-TransactionIdentifier in the message is “n+2” since the value of n+1 is used at S 6001  (S 6005 ). After that, the UE  100  transmits RRC Connection Reestablishment Request to the eNB  200  to start re-connection, and the eNB  200  receives this message. The UE  100  sets the value of Latest RRC-TransactionIdentifier in the message to “n+1”. This is because, while the UE  100  could receive the message at S 6001 , the UE  100  has not successfully received the message at S 6005  (S 6006 ). 
     After that, the eNB  200  and the UE  100  execute the similar sequence as in S 3300  in  FIG. 9  (S 6007 ). Since it is found at S 6006  that the value of Latest RRC-TransactionIdentifier is “n+1”, the eNB  200  determines that the value set in the message at S 6005  is not reflected in the current set value for the IE in the UE, and the current set value is the value set by the message at S 6001  (S 3301 ). The eNB  200  determines whether to include a predetermined IE in a message based on this determined result (S 3302  and S 3305 ), and transmits the message in which the determination is reflected to the UE  100  (S 3303  and S 3306 ). The other operations in S 6007  are similar to those in S 3300 . 
       FIG. 14  is a sequence diagram showing an example of an operation according to the third exemplary embodiment upon occurrence of a failure which is different from failures shown in  FIGS. 12 and 13 . First, upon execution of the sequence at S 1100  shown in  FIG. 2  by the UE  100 , the eNB  200 , and the MME  300  (S 7000 ), the eNB  200  transmits to the UE  100  RRC Connection Reconfiguration in which the value of RRC-TransactionIdentifier is “n+1”, and the UE  100  receives this message (S 7001 ). The UE  100  then updates the set value for the IE with the value set in the message (S 7002 ). Subsequently, after the sequence at S 1100  is further executed (S 7003 ), the eNB  200  transmits RRC Connection Reconfiguration to the UE  100 , and the UE  100  receives this message. Since the value of “n+1” is used as the value of RRC-TransactionIdentifier in this message at S 7001 , the value of RRC-TransactionIdentifier in this message is “n+2” (S 7004 ). Next, the UE  100  transmits to the eNB  200 , as a response to S 7001 , RRC Connection Reconfiguration Complete in which the value of RRC-TransactionIdentifier is “n+1”, and the eNB  200  successfully receives this message (S 7005 ). Further, since the UE  100  could successfully receive the message at S 7004 , the UE  100  updates the set value for the IE with the value set in the message (S 7006 ). After that, the UE  100  transmits to the eNB  200 , as a response to S 7004 , RRC Connection Reconfiguration Complete in which the value of RRC-TransactionIdentifier is “n+2”. However, the eNB  200  cannot successfully receive the message for some reason such as degradation of quality of the radio transmission path (S 7007 ). Then, the UE  100  transmits RRC Connection Reestablishment Request in order to start re-connection. Since the UE  100  has successfully received the message at S 7004  and completed the processing at S 7006 , the UE  100  sets the value of Latest RRC-TransactionIdentifier to “n+2” (S 7008 ). 
     After that, the eNB  200  and the UE  100  each execute the sequence similar to that in S 3300  shown in  FIG. 9  (S 7009 ). Since it is found here at S 7008  that the value of Latest RRC-TransactionIdentifier is “n+2”, the eNB  200  determines that the current set value for the IE in the UE is the value set in the message at S 7004  (S 3301 ). The eNB  200  determines whether to include a predetermined IE in a message based on the determined result (S 3302  and S 3305 ), to transmit to the UE  100  the message in which the determination is reflected (S 3303  and S 3306 ). The other operations in S 7009  are similar to those in S 3300 . 
     Described above is the exemplary embodiment when the exemplary embodiment is applied to the sequence in which the eNB  200  successively transmits RRC Connection Reconfiguration twice. However, the exemplary embodiment may be applied to a sequence in which the eNB  200  successively transmits RRC Connection Reconfiguration three or more times. 
     As described above, also in the sequence in which the eNB  200  successively transmits a plurality of messages to the eNB  100 , the eNB  200  can determine whether to include the IE specified as Need ON in each message to be transmitted based on the result obtained by determining the current set value for the IE in the UE  100 . Accordingly, the eNB  200  can reduce the size of the message to be transmitted to the UE  100  and therefore it is possible to improve utilization efficiency of radio resources. 
     While the present invention has been described in detail based on the preferred exemplary embodiments, it is needless to say that the present invention is not limited to the aforementioned description but may be changed in various ways without departing from the spirit of the present invention. 
     For example, in the second and third exemplary embodiments, the Latest RRC-TransactionIdentifier, which is the identification information of the message that the UE last successfully received, is included in the RRC Connection Reestablishment Request. However, it may also be applied to another RRC message that the UE transmits to the eNB. 
     Further, for RRC Connection Reestablishment and RRC Connection Reconfiguration, it is determined whether to include the IE specified as Need ON in these messages based on the Latest RRC-TransactionIdentifer in the second and third exemplary embodiments. However, it may also be applied to another RRC message that the eNB transmits to the UE. 
     Furthermore, while description has been omitted in the second and third exemplary embodiments, when the RRC message is transmitted by the UE trigger at S 1100  shown in  FIG. 2  or when the RRC message is transmitted by the MME trigger, the eNB may operate to send an appropriate response message according to the value of Latest RRC-TransactionIdentifer immediately after receiving the RRC Connection Reestablishment Request. Accordingly, the eNB can reduce time from reception of the message to the transmission of the response message. 
     It should be noted that the present inventive concept is not limited to the above exemplary embodiments but modification can be made as needed without deviating from the spirit and scope as defined by the claims.