AU2013200304B2 - Mobile communication method, mobile station and radio base station - Google Patents

Abstract

MOBILE COMMUNICATION METHOD, MOBILE STATION AND RADIO BASE Abstract A mobile communication method according to the present invention including the steps of: generating, at a mobile station (UE), first verification information by use of a first key, a first parameter and an~ algorithm for "Integrity Protection"; generating, at the mobile station (UE), second verification information by taking out predetermined bits of the first verification information; and performing, at the mobile station (UE), cell selection processing, and transmitting, from the mobile station to a radio base station that manages the selected cell, an RRC-PDU for RRC connection re-establishment request through a common control channel, upon detection of a radio link failure in an RRC connection, the second verification information being set in the RRC-PDU for RRC connection re-establishment request.

Description

1 MOBILE COMMUNICATION METHOD, MOBILE STATION AND RADIO BASE STATION 5 Technical Field The present invention relates to a mobile communication method, a mobile station and a radio base station. 10 Background In the LTE (Long Term Evolution) type mobile communication system specified by the 3GPP, a mobile station UE is configured to perform a connection 15 re-establishment procedure, when detecting a radio link failure (RLF) in an RRC connection. Specifically, in the connection re-establishment procedure, the mobile station is configured to perform cell selection processing and to transmit an "RRC Connection Re-establishment Request" through a common control channel (CCCH) to the selected cell. 20 Here, the mobile station UE is configured to select, in the cell selection processing, a cell which meets a certain propagation level and to which the mobile station UE has an access right. In the connection re-establishment procedure, a radio base station eNB 25 that manages the selected cell is configured to verify an "RRC Connection Re-establishment Request" on the basis of "second verification information (short MAC-1)" contained in the "RRC Connection Re-establishment Request" to avoid the following problems. 30 The radio base station eNB cannot distinguish "RRC Connection Re-establishment Requests" from each other, when the mobile stations UE that have detected an RLF in different cells transmit the "RRC Connection Re 8647176 2 establishment Requests" containing the same C-RNTI (Cell-Radio Network Temporary Identifier) and the same PCI (Physical Cell ID) to the selected cell. The radio base station eNB cannot distinguish an "RRC Connection Re 5 establishment Request" from others, when a mobile station UE of a malicious user transmits the "RRC Connection Re-establishment Request" containing a C-RNTI and a PCI which are randomly set. The "short MAC-I" can be used to verify the credibility of the "RRC 10 Connection Re-establishment Request". In other words, the "short MAC-I" can serve as a checksum for performing a tampering check of the "RRC Connection Re-establishment Request". In the LTE type mobile communication system, a tampering check of an 15 RRC message on a dedicated control channel (DCCH) is provided by a PDCP layer function. Specifically, the system is configured to generate a checksum (MAC-1) for the RRC message in a PDCP layer, and to transmit the checksum attached to the PDCP header. 20 Meanwhile, the LTE type mobile communication system is configured to transmit an "RRC Connection Re-establishment Request" through the common control channel (CCCH). Furthermore, the LTE type mobile communication system has no PDCP 25 layer function for the common control channel (CCCH) In consideration of the above circumstances, it is apparent that the "short MAC-I" to be contained in the "RRC Connection Re-establishment Request" cannot be generated under the current LTE specifications. 30 8647176 3 Thus, a need exists to provide a mobile communication method, a mobile station and a radio base station which are capable of generating "short MAC-I" to be contained in an "RRC Connection Re-establishment Request". 5 Summary According to an aspect of the present disclosure, there is provided a mobile communication method comprising the steps of: generating, at a mobile station, first verification information by use of a first key, a first parameter and an 10 algorithm for "Integrity Protection"; generating, at the mobile station, second verification information by extracting predetermined bits of the first verification information; and performing, at the mobile station, cell selection processing, and transmitting, from the mobile station to a radio base station that manages the selected cell, an RRC-PDU for RRC connection re-establishment request through 15 a common control channel, upon detection of a radio link failure in an RRC connection, the second verification information being set in the RRC-PDU for RRC connection re-establishment request. According to another aspect of the present disclosure, there is provided a 20 mobile communication method comprising the steps of: generating, at a radio base station, first verification information using a first key, a first parameter and an algorithm for "Integrity Protection"; generating, at the radio base station, second verification information by extracting predetermined bits of the first verification information; performing, at the mobile station, cell selection processing, and 25 transmitting, from the mobile station to the radio base station that manages the selected cell, an RRC-PDU for RRC connection re-establishment request through a common control channel, upon detection of a radio link failure in an RRC connection, the second verification information being set in the RRC-PDU for RRC connection re-establishment request; and verifying, at the radio base station, the 30 RRC-PDU for RRC connection re-establishment request received from the mobile station by use of the second verification information. 8647176 4 According to another aspect of the present disclosure, there is provided a mobile station comprising: a first verification information generator unit configured to generate first verification information by use of a first key, a first parameter and an algorithm for "Integrity Protection"; a second verification information generator 5 unit configured to generate second verification information by extracting predetermined bits of the first verification information; and a transmitter unit configured to, upon detection of a radio link failure in an RRC connection, perform cell selection processing and transmit an RRC-PDU for RRC connection re establishment request through a common control channel to a radio base station 10 that manages the selected cell, the second verification information being set in the RRC-PDU for RRC connection re-establishment request. According to another aspect of the present disclosure, there is provided a radio base station comprising: a first verification information generator unit 15 configured to generate first verification information by use of a first key, a first parameter and an algorithm for "Integrity Protection"; a second verification information generator unit configured to generate second verification information by extracting predetermined bits of the first verification information; and a verification unit configured to verify, by use of the second verification information, 20 an RRC-PDU for RRC connection re-establishment request received from a mobile station through a common control channel. Brief Description of the Drawings 25 [Fig.1] Fig. 1 is an overall configuration diagram of a mobile communication system according to a first embodiment of the present invention. [Fig. 2] Fig. 2 is a diagram showing a protocol stack between a mobile station and a radio base station according to the first embodiment of the present invention. 30 [Fig. 3] Fig. 3 is a sequence diagram showing an operation of generating "short MAC-I" in the mobile station according to the first embodiment of the present invention. 8647176 5 [Fig.4] Fig. 4 is a sequence diagram showing a connection re-establishment procedure in the mobile communication system according to the first embodiment of the present invention. [Fig.5] Fig. 5 is a sequence diagram showing a connection re-establishment 5 procedure in the mobile communication system according to the first embodiment of the present invention. [Fig.6] Fig. 6 is a sequence diagram showing a connection re-establishment procedure in the mobile communication system according to the first embodiment of the present invention. 10 Detailed Description Overview The present disclosure provides a first mobile communication method 15 including the steps of: generating, at a mobile station, first verification information by use of a first key, a first parameter and an algorithm for "Integrity Protection"; generating, at the mobile station, second verification information by extracting predetermined bits of the first verification information; and performing, at the mobile station, cell selection processing, and transmitting, from the mobile station 20 to a radio base station that manages the selected cell, an RRC-PDU for RRC connection re-establishment request through a common control channel, upon detection of a radio link failure in an RRC connection, the second verification information being set in the RRC-PDU for RRC connection re-establishment request. 25 In the first method, the first parameter can be "COUNT", "bearer ID" and "direction (DL/UL)"; and a physical Cell ID and a C-RNTI can be set in the RRC PDU for RRC connection re-establishment request. 30 The present disclosure further provides a second mobile communication method including the steps of: generating, at a radio base station, first verification information using a first key, a first parameter and an algorithm for "Integrity 8647176 6 Protection"; generating, at the radio base station, second verification information by extracting predetermined bits of the first verification information; performing, at the mobile station, cell selection processing, and transmitting, from the mobile station to the radio base station that manages the selected cell, an RRC-PDU for s RRC connection re-establishment request through a common control channel, upon detection of a radio link failure in an RRC connection, the second verification information being set in the RRC-PDU for RRC connection re-establishment request; and verifying, at the radio base station, the RRC-PDU for RRC connection re-establishment request received from the mobile station by use of the 10 second verification information. In the second method, the first parameter can be "COUNT", "bearer ID" and "direction (DL/UL)". 15 The present disclosure further provides a mobile station including: a first verification information generator unit configured to generate first verification information by use of a first key, a first parameter and an algorithm for "Integrity Protection"; a second verification information generator unit configured to generate second verification information by extracting predetermined bits of the first 20 verification information; and a transmitter unit configured to, upon detection of a radio link failure in an RRC connection, perform cell selection processing and transmit an RRC-PDU for RRC connection re-establishment request through a common control channel to a radio base station that manages the selected cell, the second verification information being set in the RRC-PDU for RRC connection 25 re-establishment request. In the mobile station, the first parameter can be "COUNT", "bearer ID" and "direction (DL/UL)"; and a physical cell ID and a C-RNTI can be set in the RRC PDU for RRC connection re-establishment request. 30 In the mobile station, the transmitter unit can be configured to set, as the physical cell ID, a physical cell ID of a cell in which a radio link failure has occurred 8647176 7 during the RRC connection, and to set, as the C-RNTI, a C-RNTI used by the mobile station UE in the cell in which the radio link failure has occurred. In the mobile station, the first verification information generator unit can be 5 configured to generate the first verification information for a PDU in which a physical cell ID of a cell in which a radio link failure has occurred during the RRC connection, a C-RNTI used by the mobile station UE in the cell in which the radio link failure has occurred, and a cell ID of the selected cell are set. 10 The present disclosure further provides a radio base station including: a first verification information generator unit configured to generate first verification information by use of a first key, a first parameter and an algorithm for "Integrity Protection"; a second verification information generator unit configured to generate second verification information by extracting predetermined bits of the first 15 verification information; and a verification unit configured to verify, by use of the second verification information, an RRC-PDU for RRC connection re establishment request received from a mobile station through a common control channel. 20 In the radio base station, the first parameter can be "COUNT", "bearer ID" and "direction (DL/UL)". In the radio base station, the radio base station can further include: a notification unit configured to notify, to an neighbor radio base station, the second 25 verification information by use of a handover preparation signal. In the radio base station, the first verification information generator unit can be configured to extract a physical cell ID and a C-RNTI from the RRC-PDU for RRC connection re-establishment request received from the mobile station, to 30 generates a PDU containing the extracted physical cell ID and C-RNTI as well as a (notification) cell ID of a cell that has received the RRC-PDU, and to generate the first verification information for the PDU. 8647176 8 In the radio base station, the radio base station can be configured to verify the RRC-PDU for RRC connection re-establishment request, by determining whether or not the second verification information held after being received through the handover preparation signal from an neighbor radio base station 5 corresponds to second verification information contained in the RRC-PDU for RRC connection re-establishment request. As described above, the present disclosure provides a mobile communication method, a mobile station and a radio base station, which are 10 capable of generating "short MAC-I" contained in an "RRC Connection Re establishment Request". Description of Embodiments (Mobile communication system according to the first embodiment of the present 15 disclosure) With reference to Figs. 1 to 6, a mobile communication system according to a first embodiment of the present disclosure will be described. The LTE system is applied to the mobile communication system according to this embodiment. 20 As shown in Fig. 1, the mobile communication system according to this embodiment includes an exchange MME and multiple radio base stations eNB#1 to eNB#n. Fig. 2 shows a protocol stack between a mobile station UE and the radio 25 base station eNB according to this embodiment. Specifically, each of the mobile station UE and the radio base station eNB according to this embodiment includes an RRC layer function, a PDCP layer function, an RLC layer function, a MAC layer function and a physical layer 30 function. 8647176 9 Moreover, in the LTE type mobile communication system, three kinds of radio bearers for C-plane called "SRBs: Signalling Radio Bearers" (SRBO, SRB1 and SRB2) are specified. 5 The "SRBO" is a radio bearer for a common control channel (CCCH). In an uplink, the "SRBO" is used for transmitting the "RRC Connection Establishment Request" and the "RRC Connection Re-establishment Request". In a downlink, the "SRBO" is used for transmitting "RRC Connection Establishment", "RRC Connection Reject", "RRC Connection Re-establishment" and "RRC Connection 10 Re-establishment Reject". In general, "C-RNTI", "PCI" and "short MAC-I" are specified as information elements contained in the "RRC Connection Re-establishment Request". 15 Here, the "C-RNTI" includes 16 bits, and is specified as a "UE-ID" used by the mobile station UE in a serving cell until just before detection of an RLF. Moreover, the "PCI" includes 9 bits, and is specified as an ID of a serving cell connected to the mobile station UE until just before detection of an RLF. Furthermore, the "short MAC-I" is assumed to include 15 or 16 bits. 20 Specifically, the "SRBO" is used for transmitting a message in a situation where a sender and a receiver cannot be uniquely specified. Moreover, since the "SRBO" is the radio bearer for the common control 25 channel (CCCH), the "SRBO" has no PDCP layer. Therefore, neither an "Integrity Protection" function nor a "Ciphering" function can be applied to the "SRBO". Furthermore, the "SRB1" is a radio bearer for a dedicated control channel (DCCH), and is used for transmitting all RRC messages (including NAS messages 30 connected to the RRC messages) which are not transmitted by the "SRBO". 8647176 10 Note that the "Integrity Protection" function and the "Ciphering" function can be applied to the "SRB1". Moreover, the "SRB2" is a radio bearer for a dedicated control channel 5 (DCCH), and is applied to "NAS Direct Transfer". The "SRB2" has lower priority than the "SRB1", and the "Integrity Protection" function and the "Ciphering" function can be applied to the "SRB2". 10 Moreover, in the LTE type mobile communication system, a radio bearer for U-plane called a "DRB: Data Radio Bearer" is specified. The "DRB" is a radio bearer for a dedicated traffic channel (DTCH), and a necessary number of DRBs are provided depending on communication services. 15 Note that, since the "DRB" has a PDCP layer, the "Ciphering" function can be applied to the "DRB" within the PDCP layer. With reference to Fig. 3, a description will be given below of an operation of generating the "short MAC-I (second verification information)" in the mobile 20 station UE and the radio base station eNB. As shown in Fig. 3, in Step S1001, the RRC layer function generates an RRC-PDU for "RRC Connection Re-establishment Request" containing a predetermined "short MAC-I". 25 For example, the RRC layer function may set, as the predetermined "short MAC-I", a "short MAC-I" in which all bits have a value of "0". Moreover, the RRC layer function is configured to set a "C-RNTI" and a 30 "PCI", which are known to both the mobile station UE and the radio base station eNB, in the RRC-PDU for "RRC Connection Re-establishment Request". 8647176 11 For example, the RRC layer function may set values currently used by the mobile station UE as the "C-RNTI" and the "PCI" in the RRC-PDU for "RRC Connection Re-establishment Request". 5 Moreover, the RRC layer function may set a predetermined number of higher order or lower order bits in the "short MAC-I" to a "PCI" of a target cell and pad the rest with "0" in the RRC-PDU for "RRC Connection Re-establishment Request". 10 In the case of the mobile station UE, a "PCI" of a cell selected by cell selection after an RLF detection (i.e., a cell to which the mobile station UE actually transmits the "RRC Connection Re-establishment Request") can be set as the "PCI" of the target cell. 15 On the other hand, in the case of the radio base station eNB, a "PCI" of a cell which performs "HO preparation" (i.e., a cell which is likely to receive the "RRC Connection Re-establishment Request" from the mobile station UE) can be set as the "PCI" of the target cell. 20 In Step S1 002, the RRC layer function transmits the generated RRC-PDU for "RRC Connection Re-establishment Request" to the PDCP layer function. In Step S1003, the PDCP layer function generates "MAC-I (first verification information)" from the received RRC-PDU for "RRC Connection Re-establishment 25 Request" by using a predetermined algorithm (e.g., an algorithm for "Integrity Protection" that is currently in use) To be more specific, the PDCP layer function calculates the "MAC-I" by inputting a first key KRRC_ lp and three parameters "COUNT (32 bits)", "bearer ID (8 30 bits)" and "direction (DL/UL)" to the currently-used algorithm for "Integrity Protection". 8647176 12 Here, the first key KRRClP is calculated by use of an incremented master key KeNB[n+1]. The master key KeNB is updated at the time of handover from the current 5 master key KeNB[n] to the next master key KeNB[n+l] to be used after the handover. The incremented master key KeNB[n+l] to be used after the next handover can be used to calculate the first key KRRClp used for calculation of the "short MAC-I". Moreover, the PDCP layer function uses a "bearer ID" for the "SRB1" or 10 the "SRB0" as the "bearer ID". Note that, since the "SRB0" is the radio bearer for the common control channel (CCCH), the "SRB0" normally has no "bearer ID". However, for the above purpose, the "bearer ID" is also specified for the "SRB0". In terms of security, the PDCP layer function needs to avoid securing 15 multiple RRC-PDUs by use of the same master key KeNB and the same parameters (particularly, "COUNT"). In this regard, the PDCP layer function can use the "bearer ID" for the "SRB0" as the "bearer ID" to avoid complexity. When the PDCP layer function uses the "bearer ID" for the "SRB1" as the "bearer ID", there occurs a trouble such that "COUNT=O" can not be used in the original RRC 20 PDU of the "SRB1". In addition, the PDCP layer function sets the "COUNT" to "0". However, the PDCP layer function need not increment the "COUNT" by the "MAC-I" calculation operation. 25 The "COUNT" may be expressed by being divided into "HFN" representing higher order bits and "SN" representing lower order bits. The PDCP layer function inserts only the "SN" portion into an actual 30 header, and only manages the "HFN" portion. Furthermore, the PDCP layer function sets the "direction" to "UL". 8647176 13 In Step S1004, the PDCP layer function transmits the generated "MAC-I" to the RRC layer function. 5 In Step S1005, the RRC layer function extracts predetermined bits (e. g., 16 LSBs, 16 MSBs or the like) of the received "MAC-I", and sets the bits as the "short MAC-I" in the RRC-PDU for "RRC Connection Re-establishment Request". Next, with reference to Figs. 4 to 6, a description will be given of a 10 connection re-establishment procedure in the mobile communication system according to this embodiment. Firstly, with reference to Fig. 4, a description will be given of an example where the connection re-establishment procedure is successfully performed. 15 As shown in Fig. 4, an RRC connection is established between the mobile station UE and the radio base station eNB and an S1 connection is established between the radio base station eNB and the exchange MME. Here, the mobile station UE and the radio base station eNB calculate "short MAC-" by performing 20 the operations shown in Fig. 3, in Steps S2001 and S2002. The mobile station UE and the radio base station eNB may calculate the "short MAC-I" upon completion of a handover procedure, upon completion of a connection re-establishment procedure, upon detection of an RLF, or the like. 25 In Step S2003, the mobile station UE detects an RLF during the RRC connection described above. For example, the mobile station UE detects the RLF in any of the following cases. 30 - When an RSRP (Reference Signal Received Power) in the RRC connection falls below a predetermined threshold for a predetermined period of time. 8647176 14 - When a random access procedure is not successfully performed. - When the handover procedure fails. 5 Thereafter, the mobile station UE performs cell selection processing in Step S2004, and sends the selected cell (or to the radio base station eNB that manages the selected cell) the "RRC Connection Re-establishment Request " containing the "C-RNTI", "PCI" and "short MAC-I" through the common control 10 channel. The radio base station eNB manages a serving cell of the mobile station UE, and previously holds "UE context (short MAC-1)" of the mobile station UE. For this reason, in Step S2006, the radio base station eNB verifies the received "RRC 15 Connection Re-establishment Request" by comparing the previously-held "short MAC-I" with the "short MAC-I" contained in the "RRC Connection Re establishment Request". In the example of Fig. 4, since the validity of the "RRC Connection Re 20 establishment Request" is successful, the radio base station eNB transmits "RRC Connection Re-establishment" to the mobile station UE in Step S2007. In Step S2008, the mobile station UE transmits "RRC Connection Re establishment Complete" to the radio base station eNB. 25 In Step S2009, the radio base station eNB transmits "RRC connection Reconfiguration" to the mobile station UE. In Step S2010, the mobile station UE transmits "RRC connection Reconfiguration Complete" to the radio base station eNB. 30 Secondly, with reference to Fig. 5, a description will be given of an example where the connection re-establishment procedure fails. 8647176 15 As shown in Fig. 5, an RRC connection is established between the mobile station UE and the radio base station eNB#1 and an S1 connection is established between the radio base station eNB#1 and the exchange MME. Here, the mobile 5 station UE and the radio base station eNB#1 calculate "short MAC-I" by performing the operations shown in Fig. 3, in Steps S3001 and S3002. In Step S3003, the mobile station UE detects an RLF during the RRC connection described above. 10 Thereafter, the mobile station UE performs cell selection processing in Step S3004, and sends the selected cell (or the radio base station eNB#2 that manages the selected cell) the "RRC Connection Re-establishment Request" containing the "C-RNTI", "PCI" and "short MAC-I" through the common control 15 channel. The radio base station eNB#2 does not manage a serving cell of the mobile station UE, and does not previously hold "UE context (short MAC-1)" of the mobile station UE. For this reason, in step S3006, the radio base station eNB#2 is 20 unable to verify the "RRC Connection Re-establishment Request". As a result, in Step S3007, the radio base station eNB#2 transmits "RRC Connection Re-establishment Reject" to the mobile station UE. 25 In Step S3008, the RRC connection between the mobile station UE and the radio base station eNB#1 is released, so that the mobile station UE transits to an idle state. As described above, to succeed in the connection re-establishment 30 procedure, the radio base station eNB that manages the cell selected by the mobile station UE needs to previously hold the "UE context" of the mobile station UE. 8647176 16 Here, if the cell selected by the mobile station UE is an original serving cell of the mobile station UE, the connection re-establishment procedure is successfully performed since the radio base station eNB previously holds the "UE 5 context" of the mobile station UE (see Fig. 4). On the other hand, in order to successfully carry out the connection re-establishment procedure even if the cell selected by the mobile station UE is not an original serving cell of the mobile station UE, the radio base station eNB 10 that manages the cell needs to prepare the "UE context" of the mobile station UE in advance. The "UE context" can be prepared by carrying out an "HO Preparation procedure". 15 In the handover procedure, a handover-source radio base station S-eNB can transfer the "UE context" of the mobile station UE to a handover-target radio base station T-eNB by the "HO Preparation". Moreover, in case of an RLF detection, the handover-source radio base 20 station S-eNB can transmit the "HO Preparation" containing the "UE context" of the mobile station UE to one or more neighbor radio base stations any time, even when the handover procedure is not intended. Thirdly, with reference to Fig. 6, a description will be given of operations of 25 the mobile communication system according to this embodiment in the case described above. As shown in Fig. 6, an RRC connection is established between the mobile station UE and the radio base station eNB#1 and an S1 connection is established 30 between the radio base station eNB#1 and the exchange MME. Here, the mobile station UE and the radio base station eNB#1 calculate "short MAC-I" by performing the operations shown in Fig. 3, in Steps S4001 and S4002. 8647176 17 Here, in Step S4003, the radio base station eNB#1 transmits "HO Preparation" containing "UE context (short MAC-1)" of the mobile station UE to the neighbor radio base station eNB#2. 5 In Step S4004, after acquisition of the "UE context (short MAC-1)" of the mobile station UE, the radio base station eNB#2 transmits "HO Preparation Ack" showing that effect to the mobile station UE. 10 In Step S4005, the mobile station UE detects an RLF during the RRC connection described above. Thereafter, the mobile station UE performs cell selection processing in Step S4006, and sends the selected cell (or the radio base station eNB#2 that 15 manages the selected cell) the "RRC Connection Re-establishment Request" containing the "C-RNTI", "PCI" and "short MAC-I" through the common control channel. The radio base station eNB#2 previously holds the "UE context (short 20 MAC-1)" of the mobile station UE. For this reason, in Step S4008, the radio base station eNB#2 verifies the received "RRC Connection Re-establishment Request" by comparing the previously-held "short MAC-I" with the "short MAC-I" contained in the "RRC Connection Re-establishment Request". 25 In the example of Fig. 6, since the validity of the "RRC Connection Re establishment Request" is successful, the radio base station eNB#2 transmits "RRC Connection Re-establishment" to the mobile station UE in Step S4009. In Step S4010, the mobile station UE transmits "RRC Connection Re 30 establishment Complete" to the radio base station eNB#2. 8647176 18 The radio base station eNB#2 transmits "S1 Path Switch" to the exchange MME in Step S4011, and also transmits "RRC Connection Reconfiguration" to the mobile station UE in Step S4012. 5 In Step S4013, the mobile station UE transmits "RRC Connection Reconfiguration Complete" to the radio base station eNB#2. In Step S4014, the exchange MME transmits "S1 Path Switch Ack" to the radio base station eNB#2. As a result, the connection re-establishment procedure described above is 10 successfully performed, so that an RRC connection is established between the mobile station UE and the radio base station eNB#2, and an S1 connection is established between the radio base station eNB#2 and the exchange MME. The mobile communication system according to the first embodiment of 15 the present disclosure enables calculation of the "short MAC-I" contained in the "RRC Connection Re-establishment Request" transmitted through the common control channel having no PDCP layer function. Moreover, according to the mobile communication system according to the 20 first embodiment of the present disclosure, the radio base station eNB that has received "short MAC-I" by the "HO Preparation" does not need to calculate the" short MAC-I". Therefore, the radio base station eNB can verify the "RRC Connection Re-establishment Request" by simply comparing the "short MAC-I" using the RRC layer function. 25 Furthermore, according to the mobile communication system according to the first embodiment of the present disclosure, the validity of the "RRC Connection Re-establishment Request" can be successful even when the algorithm for "Integrity Protection" to be used (in the LTE system, it is possible to select 30 between two types, AES and Snow3G) varies between the handover-source radio base station S-eNB and the handover-target radio base station T-eNB during handover. 8647176 19 (Modified Example) The radio base station eNB#1 may also be configured not to transmit "HO Preparation" that does not contain "short MAC-I". However, note that such "HO Preparation" contains "C-RNTI" and "PCI". 5 In such a case, firstly, the RRC layer function of the neighbor radio base station eNB#2 extracts the "C-RNTI" and "PCI" contained in the "RRC Connection Re-establishment Request" received from the mobile station UE, and temporarily creates an RRC-PDU for "RRC Connection Re-establishment Request" on the 10 basis of the extracted "C-RNTI" and "PCI". Here, the RRC layer function of the neighbor radio base station eNB#2 sets all values of the "short MAC-I" to "0" in the RRC-PDU for "RRC Connection Re-establishment Request". 15 Alternatively, the RRC layer function of the neighbor radio base station eNB#2 sets higher order or lower order bits in the "short MAC-I" to a "PCI" (a "PCI" under the radio base station eNB#2 that has received the "RRC Connection Re establishment Request" from the mobile station UE) and sets the rest to "0" in the 20 RRC-PDU for "RRC Connection Re-establishment Request". Secondly, the RRC layer function of the neighbor radio base station eNB#2 transmits the generated RRC-PDU for "RRC Connection Re-establishment Request" to the PDCP layer function of the neighbor radio base station eNB#2. 25 Thirdly, the PDCP layer function of the neighbor radio base station eNB#2 calculates "MAC-I (which may also be called X-MAC due to "MAC-I" on the receiving side)". Here, the first key KRRCIP, "COUNT", "bearer ID" and "direction" are handled in the same manner as the calculation operation in the mobile station 30 UE. 8647176 20 Fourthly, the RRC layer function of the neighbor radio base station eNB#2 extracts 16 LSBs or 16 MSBs of the "MAC-" received from the PDCP function (which is called "short X-MAC") 5 The RRC layer function of the neighbor radio base station eNB#2 checks if the "short X-MAC" corresponds to the "short MAC-I" contained in the "RRC Connection Re-establishment Request" received from the mobile station UE. Thus, the RRC layer function evaluates the credibility of the "RRC Connection Re establishment Request". 10 Note that, if a "Prepare procedure" is not performed for the neighbor radio base station eNB#2, the neighbor radio base station eNB#2 does not have the first key KRRC -P since the neighbor radio base station eNB#2 does not previously hold "UE context". Therefore, the neighbor radio base station eNB#2 transmits "RRC 15 Connection Re-establishment Reject" without calculating "short X-MAC". Note that operation of the above described mobile station UE and the radio base station eNB may be implemented by means of hardware, a software module executed by a processor, or a combination of both. 20 The software module may be provided in any type of storage medium such as an RAM (Random Access Memory), a flash memory, a ROM (Read Only Memory) , an EPROM (Erasable Programmable ROM) , an EEPROM (Electronically Erasable and Programmable ROM), a register, a hard disk, a 25 removable disk, or a CD-ROM. The storage medium is connected to the processor so that the processor can read and write information from and to the storage medium. Also, the storage medium may be integrated into the processor. Also, the storage medium and the 30 processor may be provided in an ASIC. The ASIC may be provided in the mobile station UE and the radio base station eNB. Also, the storage medium and the 8647176 21 processor may be provided in the mobile station UE and the radio base station eNB as a discrete component. Hereinabove, the present invention has been described in detail using the 5 above embodiment; however, it is apparent to those skilled in the art that the present invention is not limited to the embodiment described herein. Modifications and variations of the present invention can be made without departing from the spirit and scope of the present invention defined by the description of the scope of claims. Thus, what is described herein is for illustrative purpose, and has no 10 intention whatsoever to limit the present invention. 8647176

Claims (16)

1. A mobile communication method comprising the steps of: generating, at a mobile station, first verification information by use of a first 5 key, a first parameter and an algorithm for "Integrity Protection"; generating, at the mobile station, second verification information by extracting predetermined bits of the first verification information; and performing, at the mobile station, cell selection processing, and transmitting, from the mobile station to a radio base station that manages the 10 selected cell, an RRC-PDU for RRC connection re-establishment request through a common control channel, upon detection of a radio link failure in an RRC connection, the second verification information being set in the RRC-PDU for RRC connection re-establishment request. 15

2. The mobile communication method according to claim 1, wherein the first parameter includes "COUNT", "bearer ID" and "direction (DL/UL)"; and a physical cell ID and a C-RNTI are set in the RRC-PDU for RRC connection re-establishment request. 20

3. A mobile communication method comprising the steps of: generating, at a radio base station, first verification information using a first key, a first parameter and an algorithm for "Integrity Protection"; generating, at the radio base station, second verification information by 25 extracting predetermined bits of the first verification information; performing, at the mobile station, cell selection processing, and transmitting, from the mobile station to the radio base station that manages the selected cell, an RRC-PDU for RRC connection re-establishment request through a common control channel, upon detection of a radio link failure in an RRC 30 connection, the second verification information being set in the RRC-PDU for RRC connection re-establishment request; and 8647176 23 verifying, at the radio base station, the RRC-PDU for RRC connection re establishment request received from the mobile station by use of the second verification information. s

4. The mobile communication method according to claim 3, wherein the first parameter includes "COUNT", "bearer ID" and "direction (DL/UL)".

5. A mobile station comprising: a first verification information generator unit configured to generate first 10 verification information by use of a first key, a first parameter and an algorithm for "Integrity Protection"; a second verification information generator unit configured to generate second verification information by extracting predetermined bits of the first verification information; and 15 a transmitter unit configured to, upon detection of a radio link failure in an RRC connection, perform cell selection processing and transmit an RRC-PDU for RRC connection re-establishment request through a common control channel to a radio base station that manages the selected cell, the second verification information being set in the RRC-PDU for RRC connection re-establishment 20 request.

6. The mobile station according to claim 5, wherein the first parameter includes "COUNT", "bearer ID" and "direction (DL/UL)"; and 25 a physical cell ID and a C-RNTI are set in the RRC-PDU for RRC connection re-establishment request.

7. The mobile station according to claim 6, wherein the transmitter unit is configured to set, as the physical cell ID, a physical 30 cell ID of a cell in which a radio link failure has occurred during the RRC connection, and to set, as the C-RNTI, a C-RNTI used by the mobile station UE in the cell in which the radio link failure has occurred. 8647176 24

8. A radio base station comprising: a first verification information generator unit configured to generate first verification information by use of a first key, a first parameter and an algorithm for 5 "Integrity Protection"; a second verification information generator unit configured to generate second verification information by extracting predetermined bits of the first verification information; and a verification unit configured to verify, by use of the second verification 10 information, an RRC-PDU for RRC connection re-establishment request received from a mobile station through a common control channel.

9. The radio base station according to claim 8, wherein the first parameter includes "COUNT", "bearer ID" and "direction (DL/UL)". 15

10. The radio base station according to any one of claims 8 and 9, further comprising: a notification unit configured to notify, to an neighbor radio base station, the second verification information by use of a handover preparation signal. 20

11. The mobile station according to any one of claims 5 to 7, wherein the first verification information generator unit is configured to generate the first verification information for a PDU in which a physical cell ID of a cell in which a radio link failure has occurred during the RRC connection, a C-RNTI used by the 25 mobile station UE in the cell in which the radio link failure has occurred, and a cell ID of the selected cell are set.

12. The radio base station according to any one of claims 8 to 10, wherein the first verification information generator unit is configured to extract a 30 physical cell ID and a C-RNTI from the RRC-PDU for RRC connection re establishment request received from the mobile station, to generate a PDU containing the extracted physical cell ID and C-RNTI as well as a cell ID of a cell 8647176 25 that has received the RRC-PDU, and to generate the first verification information for the PDU.

13. The radio base station according to claim 10, wherein 5 the radio base station is configured to verify the RRC-PDU for RRC connection re-establishment request, by determining whether or not the second verification information held after being received through the handover preparation signal from an neighbor radio base station corresponds to second verification information contained in the RRC-PDU for RRC connection re-establishment 10 request.

14. A mobile communication method, said method being substantially as herein disclosed with reference to any one or more of Figs. 1-6 of the accompanying drawings. 15

15. A mobile station, said mobile station being substantially as herein disclosed with reference to any one or more of Figs. 1-6 of the accompanying drawings. 20

16. A radio base station, said radio base station being substantially as herein disclosed with reference to any one or more of Figs. 1-6 of the accompanying drawings. NTT DOCOMO, INC. 25 Patent Attorneys for the Applicant SPRUSON & FERGUSON 8647176