Abstract:
A method for setting ciphering activation time in a user equipment of a wireless communications system includes receiving a first RRC (radio resource control) message for activating a first ciphering key, setting an activation time of a first SRB (signaling radio bearer) as a predefined number plus a first SN (sequence number) of a last PDU (protocol data unit) of a sequence of PDUs that carry a second RRC message utilized for indicating completion of activating the first ciphering key, transmitting the second RRC message on the first SRB, prohibiting the transmission of RRC messages using the first ciphering key on the first SRB, and allowing the transmission of RRC messages on the first SRB when the successful delivery of the second RRC message has been confirmed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/746,986, filed on May 10, 2006 and entitled “Method and Apparatus to Setting Ciphering Activation Time in a Wireless Communications System,” the contents of which are incorporated herein by reference. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to methods and related devices for configuring ciphering activation time in wireless communications systems, and more particularly, to a method and related devices that prevent deciphering errors in a user end or a network end of a wireless communications system for obtaining radio resource control messages, such as a measurement report message and a HANDOVER message. 
         [0004]    2. Description of the Prior Art 
         [0005]    The third generation (3G) mobile telecommunications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. 
         [0006]    For the universal mobile telecommunications system (UMTS), the 3G mobile communications system comprises User Equipment (UE), the UMTS Terrestrial Radio Access Network (UTRAN), and the Core Network (CN). Communications protocols utilized include Access Stratum (AS) and Non-Access Stratum (NAS). AS comprises various sub-layers for different functions, including Radio Resource Control (RRC), Radio Link Control (RLC), Media Access Control (MAC), Packet Data Convergence Protocol (PDCP), and Broadcast/Multicast Control (BMC). The sub-layers mentioned, and their operating principles, are well known in the art, and detailed description thereof is omitted. The RRC is a Layer  3  protocol, and is the core of communications protocols related to access, performing all radio resource message exchange, radio resource settings control, QoS control, channel transmission format settings control, packet segmentation and recombination processing control, and NAS-related communications protocol transmission processing. 
         [0007]    The RRC is located in radio network controllers (RNC) of the UTRAN and the UE, and is primarily used to manage and maintain packet switching and sequencing of a Uu Interface. The RRC layer performs radio resource control in the following manner. After the RRC of the UE obtains various measurement results from the MAC and the Physical Layer, the RRC generates a Measurement Report from the various measurement results. After processing by the RLC, the MAC, and the Physical Layer, the Measurement Report is sent to the RRC of a network end, e.g. UTRAN. After a Radio Resource Assignment message sent from the RRC of the network end is received, the RRC of the user end can perform lower layer control and setting based on a result of resolving the message, e.g. setting the operation mode, packet length, and encryption method of the RLC layer, setting the channel multiplexing mapping method and channel transmission format of the MAC, and setting the operating frequency, spreading code, transmission power, synchronization method, and measurement items of the Physical Layer. 
         [0008]    Between the user end and the network end, the RRC layer uses RRC Messages, also known as signaling, to exchange information. RRC Messages are formed from many Information Elements (IE) used for embedding necessary information for setting, changing, or releasing protocol entities of Layer  2  (RLC, MAC) and Layer  1  (Physical Layer), thereby establishing, adjusting, or canceling information exchange channels to perform data packet transportation. Through RRC Messages, the RRC layer can embed control signals needed by an upper layer in the RRC Message, which can be sent between the NAS of the user end and the CN through the radio interface to complete the required procedures. 
         [0009]    From the standpoint of the RRC, all logical data communication exchange channels, be they for providing data transmission exchange to the user or for providing RRC layer control signal transmission exchange, are defined in the context of a Radio Bearer (RB). In the user end, the RB comprises one unidirectional or a pair of uplink/downlink logic data transmission exchange channels. In the network end, the RB comprises one unidirectional or a pair of uplink/downlink logic data transmission exchange channels. 
         [0010]    According to different usage goals, the RB can be divided into different categories, wherein the RB specifically used for transmitting RRC signals is generally called a Signaling Radio Bearer (SRB), which includes: 
         [0011]    1. SRB 0 : Uplink (UL) uses Transparent Mode (TM) transmission, Downlink (DL) uses Unacknowledged Mode (UM) transmission, and data is exchanged through a Common Control Channel. 
         [0012]    2. SRB 1 : The UL and DL both use UM transmission, and data is exchanged through a Dedicated Control Channel. 
         [0013]    3. SRB 2 : The UL and DL both use Acknowledged Mode (AM) transmission, and data is exchanged through a Dedicated Control Channel. 
         [0014]    4. SRB 3 : The same as SRB 2 , but the content of the data transmitted is specifically for the upper layer of the RRC protocol with higher priority. 
         [0015]    5. SRB 4 : The same as SRB 3 , but the data transmitted is for the upper layer of the RRC protocol with lower priority. 
         [0016]    Through use of the SRBs, the RRC layers of the user end and the network end can exchange RRC messages, as a basis for radio resource settings, and for completing various RRC control processes. In the prior art, RRC procedures can be categorized by function as RRC Connection Management Procedures, RB Control Procedures, RRC Connection Mobility Procedures, and Measurement Procedures. RRC Connection Management Procedures are primarily for establishing, maintaining, and managing the signaling link between the user end and the network end, and include a Security Mode Control Procedure, which is used for performing encryption and integrity protection actions to secure data transmission. 
         [0017]    The primary goal of the Security Mode Control Procedure is starting ciphering or changing a ciphering key for RBs. According to an RRC communications protocol specification (3GPP TS 25.331 V6.9.0) set forth by the 3 rd  Generation Partnership Project (3GPP), initiation or update (modifying settings) of the Security Mode Control Procedure is controlled by the network end. When the Security Mode Control Procedure is initiated or modified, the network end outputs a Security Mode Command (SMC) message to the user end. After the user end receives the SMC message outputted by the network end, the user end initiates or modifies the ciphering key of the Security Mode Control Procedure, and responds with a Security Mode Complete (SMP) message sent to the network end. The SMC message comprises activation times for all downlink SRBs and RBs. The activation time is a sequence number of a packet packed by the lower layer (the RLC layer), i.e. the SN of an RLC PDU. Thus, through the SMC message, the network end notifies the user end that, starting from the PDU having an SN equal to the activation time, the network end will begin using new ciphering key on the SRBs and RBs. Likewise, the SMP message comprises uplink activation times for all the signaling radio bearers (SRB) and all the radio bearers (RB) to indicate that the mobile will use the new ciphering key on and after the activation time for each SRB and RB. 
         [0018]    In the prior art, to ensure that the network end and the user end can change their ciphering key synchronously, before the network end and the user end have received the corresponding SMC message and SMP message acknowledgement signals, the RLC layers of the network end and the user end are prohibited from transmitting PDUs having SNs greater than or equal to the activation time. Namely, all transmission on SRBs and RBs using AM or UM is prohibited. Of course, to ensure that the SMC message and the SMP message can be sent to the user end and the network end, transmission on the SRB used for transmitting the SMC message and the SMP message will not be prohibited, i.e. transmission on SRB 2  will not be prohibited. In this situation, the SMC message and the SMP message are transmitted on SRB 2 , which operates in AM. However, a special characteristic of AM can cause a message reception error because a latter transmitted measurement report may be received in the peer RLC entity earlier than PDUs that carry the SMP message. The measurement report is ciphered with the new key, while it will be deciphered with the old key, because the peer receiver has not received the SMP message successfully. To deal with this situation, the prior art prohibits transmission on SRB 2  until the SMP message is positively acknowledged by the peer RLC entity. However, this method can cause other problems. 
         [0019]    When the UE is in bad radio coverage (experiencing interference from radio waves, terrain, or obstructions), SMP transmission may be delayed because several retransmissions may be needed. In this situation, if a measurement report message cannot be transmitted to the network end, the UE call may be dropped. Thus, the measurement report must be transmitted even when the SMP message has not been positively acknowledged by the peer RLC entity. A straightforward solution is to send the measurement report with the old ciphering key to the network end before the SMP message is positively acknowledged by the peer RLC entity. However, if the network end successfully receives the SMP message and activates the new key, but the ACK corresponding to the SMP message is lost, the measurement report message which was ciphered with the old key will be deciphered with the new key, causing an error. 
       SUMMARY OF THE INVENTION 
       [0020]    According to the present invention, a method of setting ciphering activation time utilized in a user end of a wireless communications system starts with receiving a radio resource control message utilized for activating a first ciphering configuration parameter. Then, a first ciphering activation time of a first signaling radio bearer is set to a predetermined value plus a first sequence number. The first sequence number is a sequence number of a last protocol data unit of a series of protocol data units used for sending a second radio resource control message used for indicating completion of activating the first ciphering configuration parameter. The second radio resource control message is sent through the first signaling radio bearer, and transmission of radio resource control messages using the first ciphering configuration parameter through the first signal radio bearer is prohibited. After successful delivery of the second radio resource control message is confirmed, transmission of any radio resource control message is allowed. 
         [0021]    According to the present invention, a communications device utilized in a wireless communications system for accurately setting a ciphering activation time comprises a controller for realizing functions of the communications device, a processor installed in the controller for executing a program code to control the controller, and a memory installed in the controller and coupled to the processor for storing the program code. The program code comprises code for receiving a radio resource control message utilized for activating a first ciphering configuration parameter, and code for setting a first ciphering activation time of a first signaling radio bearer to a predetermined value plus a first sequence number. The first sequence number is a sequence number of a last protocol data unit of a series of protocol data units used for sending a second radio resource control message used for indicating completion of activating the first ciphering configuration parameter. The program code further comprises code for sending the second radio resource control message through the first signaling radio bearer, code for prohibiting transmission of radio resource control messages using the first ciphering configuration parameter through the first signal radio bearer, and code for allowing transmission of any radio resource control message after successful delivery of the second radio resource control message is confirmed. 
         [0022]    According to the present invention, a method of configuring or reconfiguring a ciphering mechanism in a network end of a wireless communications system comprises setting a first ciphering activation time of a first signaling radio bearer to a predetermined value plus a first sequence number. The first sequence number is a sequence number of a last protocol data unit in a series of protocol data units used for transmitting a first radio resource control message used for activating a first ciphering configuration parameter. The method further comprises transmitting the first radio resource control message through the first signaling radio bearer, prohibiting transmission of radio resource control messages using the first ciphering configuration parameter on the first signaling radio bearer, and allowing transmission of any radio resource control message on the first signaling radio bearer after successful delivery of the first radio resource control message is confirmed. 
         [0023]    According to the present invention, a communications device utilized in a wireless communications system for accurately configuring or reconfiguring a ciphering mechanism comprises a controller for realizing functions of the communications device, a processor installed in the controller for executing a program code to control the controller, and a memory installed in the controller and coupled to the processor for storing the program code. The program code comprises code for setting a first ciphering activation time of a first signaling radio bearer to a predetermined value plus a first sequence number. The first sequence number is a sequence number of a last protocol data unit in a series of protocol data units used for transmitting a first radio resource control message used for activating a first ciphering configuration parameter. The program code further comprises code for transmitting the first radio resource control message through the first signaling radio bearer, code for prohibiting transmission of radio resource control messages using the first ciphering configuration parameter on the first signaling radio bearer, and code for allowing transmission of any radio resource control message on the first signaling radio bearer after successful delivery of the first radio resource control message is confirmed. 
         [0024]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is a function block diagram of a wireless communications device. 
           [0026]      FIG. 2  is a diagram of program code in  FIG. 1 . 
           [0027]      FIGS. 3 and 4  are flowchart diagrams of the present invention method. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    Please refer to  FIG. 1 , which is a functional block diagram of a communications device  100 . For the sake of brevity,  FIG. 1  only shows an input device  102 , an output device  104 , a control circuit  106 , a central processing unit (CPU)  108 , a memory  110 , a program code  112 , and a transceiver  114  of the communications device  100 . In the communications device  100 , the control circuit  106  executes the program code  112  in the memory  110  through the CPU  108 , thereby controlling an operation of the communications device  100 . The communications device  100  can receive signals input by a user through the input device  102 , such as a keyboard, and can output images and sounds through the output device  104 , such as a monitor or speakers. The transceiver  114  is used to receive and transmit wireless signals, delivering received signals to the control circuit  106 , and outputting signals generated by the control circuit  106  wirelessly. From a perspective of a communications protocol framework, the transceiver  114  can be seen as a portion of Layer  1 , and the control circuit  106  can be utilized to realize functions of Layer  2  and Layer  3 . 
         [0029]    Please continue to refer to  FIG. 2 .  FIG. 2  is a diagram of the program code  112  shown in  FIG. 1 . The program code  112  comprises an application layer  200 , a Layer  3  interface  202 , and a Layer  2  interface  206 , and is coupled to a Layer  1  interface  218 . The Layer  3  interface  202  comprises a buffer  212  for storing an RRC message  208 , and for forming an RRC PDU  214  according to the RRC message  208 . The application layer  200  provides control signals required by necessary procedures, which can be outputted by attaching the control signals to RRC PDUs  214  for setting, modifying, or releasing the Layer  2  interface  206  and the Layer  1  interface  218 , to establish, modify, or cancel data exchange channels. 
         [0030]    To prevent fake signaling from unrelated parties from compromising security, thereby protecting message transmission on a signaling radio bearer, the Layer  3  interface  202  can initiate a Security Mode Control procedure. In this situation, the present invention embodiment provides Security Mode Control Procedure program code  220 . 
         [0031]    Please refer to  FIG. 3 , which is a diagram of a procedure  30  according to the present invention. The procedure  30  is used for configuring a ciphering activation time in a user end of the wireless communications system, and can be seen as the Security Control Mode procedure program code  220 . The procedure  30  comprises the following steps:
       Step  300 : Start.   Step  302 : Receive an SMC message used for activating a first ciphering configuration parameter.   Step  304 : Set an SRB 2  ciphering activation time to a predetermined value plus a sequence number of a last PDU of a series of PDUs that carry a Security Mode Complete (SMP) message.   Step  306 : Send the SMP message through SRB 2 .   Step  308 : Prohibit the transmission of RRC messages that use the new ciphering configuration on SRB 2 .   Step  310 : Allow the transmission of all RRC messages on RB 2  when the successful delivery of the SMP message has been confirmed by the RLC.   Step  312 : End.       
 
         [0039]    According to the procedure  30 , after the receiver receives the Security Mode Command message, the SRB 2  ciphering activation time is set to a sequence number of a last PDU of a series of PDUs used for transmitting the SMP message plus a predetermined value. In other words, after completing sending the SMP message and a certain number of PDUs (equal to the predetermined value) have passed, the user end will use the new ciphering configuration parameter, i.e. the first ciphering configuration parameter, on the uplink SRB 2 . Preferably, the predetermined value will be greater than or equal to a number of PDUs required for transmitting a measurement report message. In this situation, the user end finishes sending the SMP message and at least the measurement report message over SRB 2  before using the new ciphering configuration parameter. In this way, the measurement report message (which uses the old ciphering configuration parameter for ciphering) sent out before delivery of the SMP message is confirmed can be deciphered successfully by the network end using the old ciphering configuration parameter. 
         [0040]    Thus, using the procedure  30 , the user end uses the old ciphering configuration parameter to cipher the measurement report message and send it to the network end before delivery of the SMP message is confirmed, and configures the SRB 2  ciphering activation time, such that the user end will only start using the new ciphering configuration parameter on SRB 2  after finishing transmitting the SMP message and the measurement report message. In this way, deciphering errors can be prevented in the network end. 
         [0041]    The procedure  30  targets the user end. The present invention also provides an embodiment used for processing configuration and reconfiguration of ciphering in the network end. Please refer to  FIG. 4 , which is a diagram of a procedure  40  according to the present invention. The procedure  40  is used for configuring or reconfiguring the ciphering mechanism in the network end of the wireless communications system, and can be seen as the Security Mode Control Procedure program code  220 . The procedure  40  comprises the following steps: 
         [0042]    Step  400 : Start. 
         [0043]    Step  402 : Set the SRB 2  ciphering activation time to a predetermined value plus a sequence number of a last PDU of a series of PDUs used for sending an SMC message used for activating a first ciphering configuration parameter. 
         [0044]    Step  404 : Send the SMC message through SRB 2 . 
         [0045]    Step  406 : Prohibit the transmission of RRC messages that use the new ciphering configuration on SRB 2 . 
         [0046]    Step  408 : Allow the transmission of all RRC messages on RB 2  when the successful delivery of the SMC message has been confirmed by the RLC. 
         [0047]    Step  410 : End. 
         [0000]    According to the procedure  40 , when the network end configures or reconfigures the ciphering mechanism, the SRB 2  ciphering activation time is set to the sequence number of the last PDU in the series of PDUs used for transmitting the SMC message plus the predetermined value. In other words, the network end will only start using the new ciphering configuration parameter, i.e. the first ciphering configuration parameter, on the downlink SRB 2  after finishing sending the SMC message and a certain number (equal to the predetermined value) of PDUs have passed. Preferably, the predetermined value is greater than or equal to the number of PDUs required for transmitting a HANDOVER message. In this situation, the network end will only start using the new ciphering configuration parameter after finishing transmitting the SMC message and at least the HANDOVER message on SRB 2 . In this way, the HANDOVER message (using the old ciphering configuration parameter for ciphering) sent before delivery of the SMC message is confirmed can be accurately deciphered by the user end using the old ciphering configuration parameter. 
         [0048]    Thus, through the procedure  40 , before delivery of the SMC message is confirmed, the network end ciphers the HANDOVER message using the old ciphering configuration parameter and sends it to the user end, then configures the SRB 2  ciphering activation time such that the network end will only start using the new ciphering configuration parameter on the downlink SRB 2  after finishing sending the SMC message and the HANDOVER message. In this way, the present invention can prevent deciphering errors in the user end. 
         [0049]    In summary of the above, the present invention can set the uplink SRB 2  ciphering activation time to the sequence number of the last PDU of the series of PDUs used for sending the SMP message plus the predetermined value, or the present invention can set the downlink SRB 2  ciphering activation time to the sequence number of the last PDU of the series of PDUs used for sending the SMC message plus the predetermined value, so as to prevent deciphering errors from occurring in the network end or the user end, allowing for smooth exchange of RRC messages, such as the measurement report message and the HANDOVER message, which helps maintain normal operation of the system. 
         [0050]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.