Patent Publication Number: US-2013252582-A1

Title: Radio access network apparatus, controlling method, mobile communication system, and non-transitory computer readable medium embodying instructions for controlling a device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese patent application No. 2012-069064, filed on Mar. 26, 2012, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     Malicious attacks called Denial of Service (DoS) attacks have been known in the field of wired networks such as the Internet. DoS attacks involve attacks to make systems difficult to use or shut down the systems by increasing traffic on networks and occupying processing capabilities (resources) of servers or lines that process communication. In recent years, measures to counter DoS attacks have been examined also in the field of wireless networks (Published Japanese Translation of PCT International Publication for Patent Application, No. 2008-537385: Patent literature 1). 
     Incidentally, as shown in  FIG. 5 , a mobile communication system of Long Term Evolution (LTE) defined by the Third Generation Partnership Project (3GPP) includes mobile stations (UE: User Equipment), base stations (eNBs: evolved Node Bs) that are radio access network apparatuses, and a core network. When a call connection is performed, a radio control connection is established between the UE  100  and the eNB  200  using Radio Resource Control (RRC) which is a protocol of Layer 3 (L3) (Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification [3GPP TS36.331 V10.4.0]: Non-patent literature 1). 
       FIG. 6  is a sequence diagram of an RRC message that is transmitted and received between the UE  100  and the eNB  200  when the radio control connection is established. First, the UE  100  transmits an RRC Connection Request message which is a radio control connection request signal to the eNB  200  (S 100 ). Upon receiving the RRC Connection Request message, the eNB  200  transmits to the UE  100  an RRC Connection Setup message which is a radio control connection setup signal (S 101 ). Upon receiving the RRC Connection Setup message, the UE  100  transmits an RRC Connection Setup Complete message which is a radio control connection setup completion signal (S 102 ). 
     The aforementioned method and system have the following problem. When the radio control connection is established in the sequence shown in  FIG. 6 , the eNB  200  needs to allocate storage areas for storing context information (UE Context) which is information required to communicate with the UE  100  to a memory. 
     Assume here a case in which a Dos attack as shown in  FIG. 7  is performed. In the Dos attack shown in  FIG. 7 , operations are sequentially repeated in which, while a malicious UE  120  transmits RRC Connection Request (S 200 , S 203 ), the UE  120  does not respond to RRC Connection Setup (S 202 , S 205 ) transmitted from the eNB  200 . In this case, UE Context storage areas in the eNB  200  are sequentially allocated (S 201 , S 204 ), which results in depletion of the UE Context storage area (S 206 ). This causes a problem that, even when a normal UE  110  transmits RRC Connection Request (S 207 ), the eNB  200  cannot allocate the UE Context storage area for the UE  110  (S 208 ) and the UE  110  cannot perform normal communication. 
     SUMMARY 
     One exemplary object of the exemplary embodiments is to provide a mobile communication system, a radio access network apparatus, a communication method, and a non-transitory computer readable medium storing a program that are not susceptible to DoS attacks. 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 radio access network apparatus according to an exemplary embodiment is a radio access network apparatus for performing bidirectional communication with a mobile station, and includes: 
     a first reception unit for receiving a radio control connection request signal transmitted by the mobile station; 
     a first allocation unit for allocating, upon receiving the radio control connection request signal, a first storage area for temporarily storing a part of context information required to communicate with the mobile station to a memory; 
     a first transmission unit for transmitting a radio control connection setup signal to the mobile station; 
     a second reception unit for receiving a radio control connection setup completion signal transmitted by the mobile station; and 
     a second allocation unit for allocating, upon receiving the radio control connection setup completion signal, a second storage area for storing context information required to communicate with the mobile station to a memory. 
     A communication method according to an exemplary embodiment is a communication method by a radio access network apparatus for performing bidirectional communication with a mobile station, and includes the steps of: 
     receiving a radio control connection request signal transmitted by the mobile station; 
     upon receiving the radio control connection request signal, allocating a first storage area for temporarily storing a part of context information required to communicate with the mobile station to a memory; 
     transmitting a radio control connection setup signal to the mobile station; 
     receiving a radio control connection setup completion signal transmitted by the mobile station; and 
     upon receiving the radio control connection setup completion signal, allocating a second storage area for storing context information required to communicate with the mobile station to a memory. 
     A non-transitory computer readable medium storing a program according to an exemplary embodiment stores a program for causing a computer to execute the following processing of: 
     receiving a radio control connection request signal transmitted by a mobile station; 
     upon receiving the radio control connection request signal, allocating a first storage area for temporarily storing a part of context information required to communicate with the mobile station to a memory; 
     transmitting a radio control connection setup signal to the mobile station; 
     receiving a radio control connection setup completion signal transmitted by the mobile station; 
     upon receiving the radio control connection setup completion signal, allocating a second storage area for storing context information required to communicate with the mobile station to a memory. 
     A mobile communication system according to an exemplary embodiment is a mobile communication system including a mobile station and a radio access network apparatus for performing bidirectional communication with the mobile station, in which 
     the radio access network apparatus includes:
         a first reception unit for receiving a radio control connection request signal transmitted by the mobile station;   a first allocation unit for allocating, upon receiving the radio control connection request signal, a first storage area for temporarily storing a part of context information required to communicate with the mobile station to a memory;   a first transmission unit for transmitting a radio control connection setup signal to the mobile station;   a second reception unit for receiving a radio control connection setup completion signal transmitted by the mobile station; and
           a second allocation unit for allocating, upon receiving the radio control connection setup completion signal, a second storage area for storing context information required to communicate with the mobile station to a memory, and   
               

     the mobile station includes:
         a second transmission unit for transmitting the radio control connection request signal to the radio access network apparatus;   a third reception unit for receiving the radio control connection setup signal from the radio access network apparatus; and   a third transmission unit for transmitting the radio control connection setup completion signal to the radio access network apparatus.       

     A communication method according to an exemplary embodiment is a communication method by a mobile communication system including a mobile station and a radio access network apparatus for performing bidirectional communication with the mobile station, and includes the steps of: 
     transmitting, by the mobile station, a radio control connection request signal to the radio access network apparatus; 
     upon receiving the radio control connection request signal, allocating, by the radio access network apparatus, a first storage area for temporarily storing a part of context information required to communicate with the mobile station to a memory; 
     transmitting, by the radio access network apparatus, a radio control connection setup signal to the mobile station that transmitted the radio control connection request signal; 
     transmitting, by the mobile station that received the radio control connection setup signal, a radio control connection setup completion signal to the radio access network apparatus; and 
     upon receiving the radio control connection setup completion signal, allocating, by the radio access network apparatus, a second storage area to store context information required to communicate with the mobile station to a memory. 
     The above and other exemplary objects, features and advantages will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a configuration according to a first exemplary embodiment; 
         FIG. 2  is a sequence diagram showing an operation according to the first exemplary embodiment; 
         FIG. 3  is a diagram showing a configuration according to a second exemplary embodiment; 
         FIG. 4  is a sequence diagram showing an operation according to the second exemplary embodiment; 
         FIG. 5  is a diagram showing a configuration of an LTE mobile communication system defined by the 3GPP; 
         FIG. 6  is a message sequence diagram when a radio control connection is established; 
         FIG. 7  is a sequence diagram when a DoS attack is carried out; 
         FIG. 8  is a sequence diagram showing additional operations according to an exemplary aspect; and 
         FIG. 9  is a diagram showing a configuration of a 3G mobile communication system defined by the 3GPP. 
     
    
    
     DETAILED DESCRIPTION 
     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. 1  is a diagram showing one example of a configuration according to a first exemplary embodiment. A mobile communication system according to the first exemplary embodiment includes a mobile station  10  and a radio access network apparatus  20  for performing bidirectional communication with the mobile station  10 . 
     The mobile station  10  includes a second transmission unit  11  for transmitting a radio control connection request signal to the radio access network apparatus  20 , a third reception unit  12  for receiving a radio control connection setup signal from the radio access network apparatus  20 , and a third transmission unit  13  for transmitting a radio control connection setup completion signal to the radio access network apparatus  20 . 
     The radio access network apparatus  20  includes a first reception unit  21  for receiving the radio control connection request signal from the mobile station  10 , a first transmission unit  25  for transmitting the radio control connection setup signal to the mobile station  10 , and a second reception unit  26  for receiving the radio control connection setup completion signal from the mobile station  10 . The radio access network apparatus  20  further includes a first allocation unit  22  for allocating, upon receiving the radio control connection request signal from the mobile station  10 , a first storage area  23  for temporarily storing a part of context information required to communicate with the mobile station  10  to a memory. The memory is not illustrated in  FIG. 1 . The radio access network apparatus  20  further includes a first storage unit  24  for storing, when the first allocation unit  22  allocates the first storage area  23 , a value of a predetermined information element included in the radio control connection request signal in the first storage area  23 . The radio access network apparatus  20  further includes a second allocation unit  27  for allocating, upon receiving the radio control connection setup completion signal from the mobile station  10 , a second storage area  28  to store context information required to communicate with the mobile station  10  to a memory. The radio access network apparatus  20  further includes a second storage unit  29  for copying, when the second allocation unit  27  allocates the second storage area  28 , information stored in the first storage area  23  to store the information in the second storage area  28 . 
       FIG. 2  is a sequence diagram showing one example of an operation according to the first exemplary embodiment. Hereinafter, with reference to  FIG. 2 , operations of the mobile station  10  and the radio access network apparatus  20  will be described. 
     In S 200 , the mobile station  10  transmits the radio control connection request signal to the radio access network apparatus  20 , and the radio access network apparatus  20  receives the radio control connection request signal. 
     In S 201 , the radio access network apparatus  20  allocates the first storage area  23  for temporarily storing a part of context information required to communicate with the mobile station  10  to a memory. 
     In S 202 , the radio access network apparatus  20  stores a value of a predetermined information element included in the radio control connection request signal received in S 200  in the first storage area  23 . Further, minimum information required to communicate with the mobile station  10  before completion of the reception of the radio control connection setup completion signal (S 204 ) may be stored in the first storage area  23 . 
     In S 203 , the radio access network apparatus  20  transmits the radio control connection setup signal to the mobile station  10 , and the mobile station  10  receives the radio control connection setup signal. The radio access network apparatus  20  uses the information stored in the first storage area  23  when generating the radio control connection setup signal. 
     In S 204 , the mobile station  10  transmits the radio control connection setup completion signal to the radio access network apparatus  20 , and the radio access network apparatus  20  receives the radio control connection setup completion signal. 
     In S 205 , since the operation of S 204  has successfully been performed, the radio access network apparatus  20  determines that the mobile station  10  is not a malicious mobile station and allocates the second storage area  28  for storing context information required to communicate with the mobile station  10  to a memory. 
     In S 206 , the radio access network apparatus  20  copies the information stored in the first storage area  23  in S 202  to store the information in the second storage area  28 . 
     As described above, the radio access network apparatus according to this exemplary embodiment allocates areas for storing context information required to communicate with the mobile station to the memory after receiving the radio control connection setup completion signal. Accordingly, the radio access network apparatus can be protected from a DoS attack in which only a large volume of radio control connection request signals are transmitted and a normal sequence to establish the radio control connection is never completed. 
     Second Exemplary Embodiment 
     A second exemplary embodiment is an exemplary embodiment according to the first exemplary embodiment an applied to an LTE radio communication system shown in  FIG. 5 . A mobile communication system according to the second exemplary embodiment includes, as shown in  FIG. 5 , UE  100 , eNBs  200 , and a core network  300 . Hereinafter, with reference to the drawings, the detail of a configuration of the eNB  200  will be described. 
       FIG. 3  is a diagram showing one example of the configuration of the eNB  200  according to the second exemplary embodiment. The eNB  200  includes a signal reception unit  210 , a call controller  220 , a signal transmission unit  230 , and a memory  240 . 
     The signal reception unit  210  receives control signals in the form of messages from the UE  100  or the core network  300 . 
     The signal transmission unit  230  transmits control signals in the form of messages to the UE  100  or the core network  300 . 
     The call controller  220  performs various types of call control processing required by the eNB  200  based on the control signals received by the signal reception unit  210  to perform control so that the signal transmission unit  230  is able to transmit appropriate control signals based on the processing. When performing a call control operation, the call controller  220  accesses a variety of information stored in the memory  240 . 
     The memory  240  includes a UE Context storage area  241 , a UE Context management information  242 , a Tmp UE Context storage area  243 , a Tmp UE Context allotter information  244 , and a C-RNTI/UE association table  245 . 
     The UE Context storage area  241  is an area to store UE Context which is information required to communicate with the UE  100  for each UE, and includes areas (N areas in  FIG. 3 ) whose number corresponds to the number of UE according to the cell radius or the like. Examples of information elements for each UE stored in the UE Context storage area  241  may include the number of the UE, a call state, resources of the radio section assigned to the UE (hereinafter referred to as UL dedicated resources), and information that was previously transmitted or received. The size of the area for one UE in the UE Context storage area  241  is about 50 kilobytes, for example. 
     The UE Context management information  242  is information for managing the usage state of the UE Context storage area  241 . Since UE Context is the information required to communicate with the UE, the eNB  200  performs blocking management using the UE Context management information  242  upon receiving a call from the UE. The blocking management is the processing for allocating an area for the UE to the UE Context storage area  241  and not releasing the area until completion of the communication. 
     The Tmp UE Context storage area  243  is an area for temporarily storing a part of information of UE Context, and includes areas (M areas in  FIG. 3 ) whose number corresponds to the number of UE. Examples of information elements for each UE stored in the Tmp UE Context storage area  243  may include InitialUE-Identity and EstablishmentCause that are information elements included in RRC Connection Request which is the message that the eNB  200  first receives from the UE  100 . Other information elements of UL dedicated resources such as CQI, schedulingRequest, and soundingRS may be used as well. The eNB  200  determines values that are not overlapped with values for other UE in advance as set values of the information elements of the UL dedicated resources, and stores the values in the area for each UE. The detail of the information elements stated above is disclosed in Non-patent literature 1. The size of the area for one UE in the Tmp UE Context storage area  243  is about 30 bytes, for example, which is much smaller than the size of the area for one UE in the UE Context storage area  241  stated above. Accordingly, the number of areas (M) for each UE in the Tmp UE Context storage area  243  may be a number larger than the number of areas (N) for each UE in the UE Context storage area  241 . 
     The Tmp UE Context allotter information  244  is information for managing the usage state of the Tmp UE Context storage area  243 . 
     The C-RNTI/UE association table  245  is a table for performing mapping of Cell Radio Network Temporary Identity (C-RNTI) for identifying the UE in the radio section and the number (1, . . . , N) of the area for each UE in the UE Context storage area  241  for performing identification of the UE in the eNB or the number (1, . . . , M) of the area for each UE in the Tmp UE Context storage area  243 . 
       FIG. 4  is a sequence diagram showing one example of an operation according to the second exemplary embodiment. Hereinafter, with reference to  FIG. 4 , operations of the UE  100  and the eNB  200  will be described. 
     In S 300 , the UE  100  transmits RRC Connection Request which is a radio control connection request signal to the eNB  200 , and the eNB  200  receives RRC Connection Request. 
     In S 301 , the eNB  200  determines the area for each UE in the Tmp UE Context storage area  243  used for the UE  100 . More specifically, the eNB  200  refers to the value of the Tmp UE Context allotter information  244  to determine the area of the number corresponding to the value obtained by adding one to the current value as the area to be used for the UE. At the same time, the value of the Tmp UE Context allotter information  244  is also updated with the value to which one is added. Since the Tmp UE Context storage area  243  is an area that is temporarily used, the blocking management performed in the UE Context storage area  241  is not performed, but the areas are allocated in the ascending order beginning with the number 1 by a round robin system. By allocating the areas like this, the area that was least recently used is to be used again, whereby it is possible to select the area which is least likely to be used. Further, since the blocking management is not performed, there is no case that determination of the area used by the Tmp UE Context storage area  243  results in failure no matter how high the call amounts may be. Further, as described above, since the size of Tmp UE Context used for one UE is small, it is possible to reserve sufficient number of areas in the memory, which prevents duplicate use of the areas even with high call volumes. 
     In S 302 , the eNB  200  stores, in the area determined in  5301 , InitialUE-Identity and EstablishmentCause that are information elements included in the message received in  5300 . 
     In S 303 , the eNB  200  transmits RRC Connection Setup which is a radio control connection setup signal to the UE  100 , and the UE  100  receives RRC Connection Setup. At this time, the eNB  200  adds information elements of UL dedicated resources stored in the area for the UE of the Tmp UE Context storage area  243  stated above to RRC Connection Setup. Further, the eNB  200  associates C-RNTI of the UE  100  with the number of the area in the Tmp UE Context storage area  243  for the UE determined in  5301 , and stores the associated information in the C-RNTI/UE association table  245 . 
     In S 304 , the UE  100  transmits to the eNB  200  RRC Connection Setup Complete which is a radio control connection setup completion signal, and the eNB  200  receives RRC Connection Setup Complete. 
     In S 305 , the eNB  200  refers to the C-RNTI/UE association table  245  based on C-RNTI received in  5304 , to identify the UE  100  that has transmitted RRC Connection Setup Complete. The eNB  200  determines, at this moment, that the UE  100  is not a malicious user that carries out DoS attacks. Then, the eNB  200  refers to the UE Context management information  242  to allocate the area for the UE to the UE Context storage area  241 . After the allocation, the eNB  200  updates the UE Context management information  242 . 
     In S 306 , the eNB  200  copies InitialUE-Identity and EstablishmentCause stored in the Tmp UE Context storage area  243  in  5302  to the area allocated in S 305 . Further, the eNB  200  updates the number of the area for the UE in the Tmp UE Context storage area  243  in the C-RNTI/UE association table  245  created in  5303  with the number of the area for the UE in the UE Context storage area  241  allocated in S 305 . 
     In S 307 , the eNB  200  transmits Security Mode Command to the UE  100 , and the UE  100  receives Security Mode Command. One of skill in the art will understand this operation and further unnecessary the description thereof will be omitted. 
     In S 308 , the eNB  200  transmits RRC Connection Reconfiguration to the UE  100 , and the UE  100  receives RRC Connection Reconfiguration. While the eNB  200  uses values stored in the Tmp UE Context storage area  243  as values of the information elements of the UL dedicated resources included in RRC Connection Setup in S 303 , the eNB  200  determines new unique values as the values of the information elements when transmitting RRC Connection Reconfiguration in S 308 . Then the eNB  200  adds the values to the message to notify the UE  100  of the values. 
     As described above, the eNB according to the second exemplary embodiment allocates areas to store UE Context to the memory after receiving RRC Connection Setup Complete. Accordingly, the eNB is able to continue services such as a call control operation without causing depletion of the storage area of UE Context even when a malicious UE performs a DoS attack in which the UE transmits a large amount of RRC Connection Request and does not respond to RRC Connection Setup. 
     While exemplary embodiments have been described in detail, it should be understood that these embodiments are not limiting but may be changed in various ways without departing from the spirit of the present inventive concept. 
     For example, the second exemplary embodiment may be executed only when a predetermined condition is satisfied. More specifically, the eNB  200  may measure the number of times RRC Connection Request has been received and the number of times RRC Connection Setup Complete has not been received per unit time in the call controller  220 . When the number of reception exceeds a predetermined threshold or the number of unreception exceeds a predetermined threshold, the eNB  200  may determine that a DoS attack is being executed and execute the second exemplary embodiment. 
       FIG. 8  is a sequence diagram showing one example of when certain operations of the second exemplary embodiment are not executed. As is different from  FIG. 4 , the eNB  200  allocates the UE Context storage area  241  (S 401 ) and stores the information element included in the message (S 402 ) after receiving RRC Connection Request (S 400 ). Thus, when a DoS attack for transmitting a large volume of RRC Connection Request is carried out, this may cause depletion of the UE Context storage area  243 . However, since the eNB  200  in  FIG. 8  need not perform the operations of  5301  and  5306  in  FIG. 4  that use the Tmp UE Context storage area  243  and the Tmp UE Context allotter information  244 , the throughput in  FIG. 8  is smaller than that shown in  FIG. 4 . 
     As stated above, certain operations of the second exemplary embodiment are executed only when a predetermined condition is satisfied, thereby being able to implement countermeasures against DoS attacks while mitigating the processing load of the eNB  200  as a whole. 
     The exemplary embodiment may be applied to a Third Generation (3G) mobile communication system. 
       FIG. 9  is a diagram showing a configuration of a 3G mobile communication system defined by the 3GPP. The 3G mobile communication system includes UE  100 , Node Bs (NBs)  400 , radio network controllers (RNC)  500 , and a core network  300 . In this way, the configuration and the operation when the exemplary embodiment is applied to the 3G mobile communication system may be described by replacing the eNB  200  with the RNC  500  in  FIGS. 3 and 4  in the second exemplary embodiment. 
     Furthermore, processing of the radio access network apparatus described in the first exemplary embodiment and the second exemplary embodiment may be controlled by a central processing unit (CPU) of this apparatus. Needless to say, this processing may also be achieved by preparing a storage medium storing program codes of software to achieve the function of each of the exemplary embodiments and operating the CPU by a general-purpose computer reading out the program codes stored in the storage medium. 
     The program can be stored and provided to a computer using any type of non-transitory computer readable media. Non-transitory computer readable media include any type of tangible storage media. Examples of non-transitory computer readable media include magnetic storage media (such as flexible disks, magnetic tapes, hard disk drives, etc.), optical magnetic storage media (e.g. magneto-optical disks), CD-ROM (Read Only Memory), CD-R, CD-R/W, and semiconductor memories (such as mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, RAM (random access memory), etc.). 
     A radio access network apparatus according to an exemplary embodiment is able to allocate, upon receiving a radio control connection request signal, a first storage area for temporarily storing a part of context information required to communicate with a mobile station to a memory, and to allocate, upon receiving a radio control connection setup completion signal, a second storage area to store the context information to a memory. Accordingly, it is possible to avoid a problem that the memory is depleted and the normal mobile stations cannot perform communication even when a DoS attack for transmitting a large volume of radio control connection request signals is carried out. 
     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.