Abstract:
A method for connecting to a network from a mobile terminal capable of forming a high-performance radio channel in a Universal Mobile Telecommunication System (UMTS), and an apparatus implementing the same are provided. The method includes transmitting a Radio Resource Control (RRC) connection request message indicating a first release version to the network, receiving an RRC connection setup message indicating a second release version from the network, comparing the first and second release versions, determining whether there is a third release version lower than the first release version and higher than the second release version when the second release version differs from the first, and, if there is the third release version lower than the first release version and higher than the second release version, transmitting an RRC connection request message indicating the third release version to the network when the second release version differs from the first release version.

Description:
PRIORITY 
     This application claims the benefit under 35 U.S.C. §119(a) of a Korean patent application filed on Sep. 27, 2010 in the Korean Intellectual Property Office and assigned Serial No. 10-2010-0092977, the entire disclosure of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and an apparatus for connecting to a network from a mobile terminal. More particularly, the present invention relates to a method for connecting to a network from a mobile terminal capable of forming a high-performance radio channel in a Universal Mobile Telecommunication System (UMTS), and an apparatus implementing the same. 
     2. Description of the Related Art 
     UMTS, which is an updated system based on the Global System for Mobile Communications (GSM) European standard, is a third generation mobile communication system that aims to provide an improved mobile communication service based on a combination of a GSM core Network and a Wideband Code Division Multiple Access (WCDMA) network. 
     A User Equipment (UE), which includes a user terminal in the UMTS, forms a radio channel with a network through a network connection procedure. In the network connection procedure, the UE transfers a currently supportable release version to the network. Accordingly, the network determines and transfers a release version of a radio channel to be allotted to the UE, and the UE forms the radio channel with the network using the received release version. However, when the network does not support the release version provided from the UE, the network optionally determines and transfers the release version to the UE with the result that the UE may use the release version determined in the network. In this case, there arises a problem in that a suitable radio channel between the UE and the network cannot be formed using release versions supported by the UE. 
     SUMMARY OF THE INVENTION 
     Aspects of the present invention are to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a method for connecting to a network from a mobile terminal and for forming a radio channel suitable for a release version that the mobile terminal may support, and an apparatus implementing the same. 
     In accordance with an aspect of the present invention, a method for connecting to a network from a mobile terminal is provided. The method includes transmitting a Radio Resource Control (RRC) connection request message indicating a first release version to the network, receiving an RRC connection setup message indicating a second release version from the network, comparing the second release version with the first release version, determining whether there is a third release version lower than the first release version and higher than the second release version when the second release version differs from the first release version, and, if there is the third release version lower than the first release version and higher than the second release version, transmitting an RRC connection request message indicating the third release version to the network when the second release version differs from the first release version. 
     In accordance with another aspect of the present invention, a mobile terminal is provided. The terminal includes a message transceiver for transmitting an RRC connection request message and an RRC connection setup complete message to a network, and for receiving an RRC connection setup message from the network, a message generator for adding a release version to generate an RRC connection request message or an RRC connection setup complete message, and a controller for comparing a first release version included in the RRC connection setup message transmitted to the network with a second release version included in the RRC connection request message received from the network, for controlling the message generator to add a third release version that is lower than the second release version and higher than the first release version and generating an RRC connection request message by including the third release version when the second release version differs from the first release version, and for controlling the message transceiver to transmit the generated RRC connection request message to the network. 
     In accordance with yet another aspect of the present invention, a method for connecting to a network from a mobile terminal is provided. The method includes transmitting an RRC connection request message indicating a first release version to the network, receiving an RRC connection setup message indicating a second release version from the network, comparing the second release version with the first release version, and transmitting an RRC connection setup complete message to the network. 
     Exemplary embodiments of the present invention may form a radio channel between a mobile terminal and a network suitable for a release version that the mobile terminal may support. Because a higher-performance radio channel is formed between a mobile terminal and a network in comparison with the related art, the performance of communication between the mobile terminal and the network may be improved. 
     Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram illustrating a configuration of a mobile communication system according to an exemplary embodiment of the present invention; 
         FIG. 2  is a block diagram illustrating a configuration of a User Equipment (UE) according to an exemplary embodiment of the present invention; 
         FIG. 3  is a signal flow diagram illustrating a network connecting method achieved by a UE and a network according to a first exemplary embodiment of the present invention; 
         FIG. 4  is a flowchart illustrating a network connecting method achieved by a UE according to the first exemplary embodiment of the present invention; 
         FIG. 5  is a signal flow diagram illustrating a network connecting method achieved by a UE and a network according to a second exemplary embodiment of the present invention; and 
         FIG. 6  is a flowchart illustrating a network connecting method achieved by a UE according to the second exemplary embodiment of the present invention. 
     
    
    
     Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures. 
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness. 
     The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention is provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. 
     It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces. 
       FIG. 1  is a block diagram illustrating a configuration of a mobile communication system according to an exemplary embodiment of the present invention. 
     The mobile communication system may be configured as a Universal Mobile Telecommunication System (UMTS) of the 3rd Generation Partnership Project (3GPP). 
     Referring to  FIG. 1 , the mobile communication system includes a User Equipment (UE)  100  and a network  200 . The network  200  includes a core network  210  and a plurality of Radio Network Subsystems (RNSs)  220  and  230 . 
     The plurality of RNSs  220  and  230  are configured as UMTS Terrestrial Radio Access Networks (UTRANs). The core network  210  may include a Mobile Switching Center (MSC) and a Visitor Location Register (VLR) for connecting the UTRANs to a circuit network such as during the reception or transmission of a call. The network  210  may also include a Serving General Packet Radio Service (GPRS) Support Node (SGSN) and a Gateway GPRS Support Node (GGSN) for connecting the UTRANs to a packet data network such as the Internet. 
     The RNSs  220  and  230  include Radio Network Controllers (RNCs)  221  and  231 , and a plurality of Nodes B  222 ,  223  and  232 ,  233 , respectively. The RNS  220  includes a Radio Network Controller (RNC)  221  and a plurality of Nodes B  222  and  223 . The RNS  230  includes an RNC  231  and a plurality of Nodes B  232  and  233 . 
     The RNC  221  or  231  may be classified into a Serving RNC, a Drift RNC, and a control RNC according to its function. The serving RNC manages information of the UE  100  and processes calls with the core network  210  and transmission of packet data. The drift RNC directly accesses the UE  100  in a radio scheme. The control RNC controls a radio resource of the Nodes B  222 ,  223 ,  232 , and  233 . 
     Each of the RNC  221  or  231  allots a radio resource for the Nodes B  222 ,  223 ,  232 , and  233  that it manages. The Nodes B  222 ,  223 ,  232 , and  233  relay provided radio resources allotted from the RNC  221  or  231  to the UE  100 . According to exemplary embodiments of the present invention, the radio resources are configured by cells. The radio resources provided from the Nodes B  222 ,  223 ,  232 , and  233  correspond to a radio resource for a cell managed by a corresponding Node B. The UE  100  sets a radio channel using the radio resources provided from the Nodes B  222 ,  223 ,  232 , and  233 , and transmits and receives a call or data through the set radio channel. 
     The UE  100  performs a Radio Resource Control (RRC) Connection Procedure for a circuit service call or a packet service session. If a channel is formed between the UE  100  and the RNSs  220  and  230  through the RRC Connection Procedure, the UE  100  performs communication with the RNSs  220  and  230  through the channel. More particularly, the UE  100  sets a radio bearer with the RNSs for transmitting and receiving packet data, and transmits and receives the packet data through the set radio bearer. 
     Hereinafter, an exemplary configuration of a UE will be described. 
       FIG. 2  is a block diagram illustrating a configuration of a UE according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 2 , the UE  100  includes a message transceiver  110 , a message generator  120 , a memory  130 , and a controller  140 . 
     The message transceiver  110  executes transmitting and receiving functions of corresponding data for radio communication of the UE  100 . The message transceiver  110  may include an RF transmitter for up-converting a frequency of a transmitted signal and amplifying the signal, and an RF receiver for low-noise-amplifying a received signal and down-converting the signal. Further, the message transceiver  110  may receive data through the radio channel and output the data to the controller  140 . The message transceiver  110  may transmit data received from the controller  140  through the radio channel. The message transceiver  110  performs radio communication with a network. The message transceiver  110  transmits an RRC Connection Request message to the network in the RRC connection procedure. If the message transceiver  110  receives an RRC Connection Setup message, it transmits an RRC Connection Setup Complete message to the network. 
     The message generator  120  generates messages to be transmitted to the network under the control of the controller  140 . The message generator  120  generates the RRC Connection Request message and the RRC Connection Setup Complete message. The message generator  120  generates the RRC Connection Request message and the RRC Connection Setup Complete message by adding a supportable release version that the UE may support. 
     The memory  130  stores programs and data necessary for an operation of the UE  100 . The memory  130  may be divided into a program area and a data area. The memory  130  may be configured by a volatile storing medium, a nonvolatile storing medium, or a combination thereof. The volatile storing medium includes a semiconductor memory such as a Random Access Memory (RAM), a Dynamic RAM (DRAM), or a Static RAM (SRAM). The nonvolatile storing medium may include a hard disk. In an exemplary implementation, the memory  130  stores information regarding a 3 GPP release version that the UE  100  may support. 
     The controller  140  controls an overall operation of respective elements of the UE  100 . For example, the controller  140  controls the message generator  120  to add information regarding a release version that the UE  100  may support, thereby generating an RRC connection request message. The controller  140  controls the message transceiver  110  to transmit the generated RRC connection request message to the network. If the controller  140  receives an RRC connection setup message containing a release version of a channel to be allotted from the network through the message transceiver  110 , it compares a release version in the RRC connection request message with that included in the RRC connection setup message. When it is determined that the release version in the RRC connection request message differs from that included in the RRC connection setup message, the controller  140  controls the message generator  120  to add a release version between the release version in the RRC connection request message and the release version included in the RRC connection setup message, thereby generating the RRC connection request message, and controls the message transceiver  110  to transmit the RRC connection request message to the network. If the controller  140  receives an RRC connection setup message included in a release version from the network through the message transceiver  110 , it compares the release version included in the RRC connection request message with that included in the RRC connection setup message. When it is determined that the release version included in the RRC connection request message is identical with that included in the RRC connection setup message, the controller  140  controls the message generator  120  to generate an RRC connection setup complete message containing a release version included in the RRC connection request message, and controls the message transceiver  110  to transmit the RRC connection setup complete message to the network. If the network receives the RRC connection setup complete message from the UE  100 , a radio channel is formed between the UE  100  and the network. 
     In an exemplary embodiment of the present invention, if the controller  140  receives an RRC connection setup message containing a release version of a channel to be allotted from the network through the message transceiver  110 , it controls the message generator  120  may add a release version included in the RRC connection setup message, thereby generating an RRC connection setup complete message, and controls the message transceiver  110  to transmit the RRC connection setup complete message to the network. In a state that a radio channel is formed between the UE  100  and the network, the controller  140  compares a release version included in an RRC connection setup message with that included in the RRC connection request message. When the release version included in an RRC connection setup message differs from that included in the RRC connection request message, the controller  140  controls the message generator  120  to add a release version between the release version included in the RRC connection request message and the release version included in the RRC connection setup message, thereby generating an RRC connection request message, and controls the message transceiver  110  to transmit the RRC connection request message. 
     In an exemplary embodiment of the present invention, the controller  140  compares a release version included in an RRC connection setup message with that included in an RRC connection request message. When the release version included in an RRC connection setup message differs from that included in an RRC connection request message, the controller  140  may determine whether intermediate release versions exist between the release version included in the RRC connection request message and the release version included in the RRC connection setup message. When the intermediate release versions do not exist between the release version included in the RRC connection request message and the release version included in the RRC connection setup message, the controller  140  may control the message generator  120  to add a release version included in the RRC connection setup message, thereby generating an RRC connection setup complete message, and control the message transceiver  110  to transmit the RRC connection setup complete message to the network. 
     In an exemplary embodiment of the present invention, when the intermediate release versions do not exist between the release version included in the RRC connection request message and the release version included in the RRC connection setup message, the controller  140  may control the message transceiver  110  to transmit a firstly generated RRC connection request message to the network. 
     In an exemplary embodiment of the present invention, when the intermediate release versions exist between the release version included in the RRC connection request message and the release version included in the RRC connection setup message, the controller  140  may determine how many release versions there are. When there is one release version, the controller  140  may control the message generator  120  to add the intermediate release versions, thereby generating an RRC connection request message, and control the message transceiver  110  to transmit the RRC connection request message to the network. When there are a plurality of release versions, the controller  140  may select the highest release version from the intermediate release versions, control the message generator  120  to add the selected release version, thereby generating an RRC connection request message, and control the message transceiver  110  to transmit the RRC connection request message to the network. 
     The foregoing exemplary description has illustrated a configuration of the UE for performing a connection procedure with a network. Hereinafter, an exemplary method for connecting to a network by a UE will be described. 
       FIG. 3  is a signal flow diagram illustrating a network connecting method achieved by a UE and a network according to a first exemplary embodiment of the present invention. 
     Referring to  FIG. 3 , the UE  100  generates and transmits an RRC Connection Request message with a release version Y to a network  200  in step  301 . In an exemplary implementation, the UE  100  stores information regarding one or more supportable release versions in a memory. When the RRC connection request message is generated, supportable release versions as listed in the following table are displayed as a parameter to generate an RRC connection request message. The 3GPP defines a communication standard according to a release version. If the UE  100  requests network connection using one release version, the network  200  determines a release version in the UE  100  to allot a channel to the UE  100 . Table 1 is a table illustrating only items regarding release versions among information included in the RRC connection request message. 
     
       
         
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Information 
                   
                   
                   
                   
                   
               
               
                 Element/ 
                   
                   
                 Type and 
                 Semantics  
                   
               
               
                 Group name 
                 need 
                 Multi 
                 reference 
                 description 
                 Version 
               
               
                   
               
             
             
               
                 Access  
                 MP 
                   
                 Enumerated 
                 Absence of the IE  
                 REL-4 
               
               
                 Stratum 
                   
                   
                 (REL-4. 
                 implies R99. The  
                 REL-5 
               
               
                 Release  
                   
                   
                      REL-5. 
                 IE also indicates 
                 REL-6 
               
               
                 Indicator 
                   
                   
                      REL-6. 
                 the release of the  
                 REL-7 
               
               
                   
                   
                   
                      REL-7) 
                 RRC transfer syntax 
                   
               
               
                   
                   
                   
                   
                 supported by the  
                   
               
               
                   
                   
                   
                   
                 UE 12 spare values  
                   
               
               
                   
                   
                   
                   
                 are needed 
               
               
                   
               
             
          
         
       
     
     Referring to Table 1, the UE  100  may support release versions REL-4, REL-5, REL-6, and REL-7. In the description of  FIG. 3 , it is assumed that a ‘release version Y’ is an ‘REL-7’. 
     The network  200  transmits an RRC connection setup message with a release version Z to the UE  100  in step  302 . When the UE  100  requests RRC connection with a release version Y, it is preferred that the network  200  allots a channel of the release version Y to the UE  100 . However, when the network  200  does not support the release version Y, it optionally determines and allots a different release version to the UE  100 . The network  200  optionally determines a release version Z and transmits an RRC connection setup message with the release version Z to the UE  100 . In the description of  FIG. 3 , it is assumed that a ‘release version Z’ is an ‘REL-5’. 
     The UE  100  compares a release version included in an RRC connection setup message with that included in an RRC connection request message in step  303 . That is, the UE  100  compares a release version Z with a release version Y. If the network  200  transmits an RRC connection setup message with the release version Y to the UE  100 , the UE  100  determines that a release version included in an RRC connection setup message is identical with that included in an RRC connection request message. However, if the network  200  transmits an RRC connection setup message with a release version Z lower than the release version Y to the UE  100 , the UE  100  determines that the release version included in the RRC connection setup message is lower than that included in the RRC connection request message. Because the ‘release version Y’ is a ‘REL-7’, and the ‘release version Z’ is a ‘REL-5’ in  FIG. 3 , the UE  100  determines that the release version included in the RRC connection setup message is lower than that included in the RRC connection request message. 
     The UE  100  adds a release version X lower than the release version Y and higher than the release version Z to generate and transfer an RRC connection request message to the network  200  in step  304 . It is assumed in  FIG. 3  that the network  200  may support the release version X. The UE  100  may determine whether there are release versions lower than the release version Y and higher than the release version Z. If the release version Z is just below the release version Y, the UE  100  determines that there are no release versions lower than the release version Y and higher than the release version Z. In this case, the UE  100  may determine a release version as the release version Z, and generate and transmit an RRC connection setup complete message with the release version Z to the network  200 . Meanwhile, if there are no release versions lower than the release version Y and higher than the release version Z, the UE  100  may again transmit an RRC connection request message with the release version Y to the network  200 . 
     If a release version X exists between the release version Y and the release version Z, the UE  100  adds the release version X to generate and transmit an RRC connection request message to the network  200 . If there are a plurality of release versions between the release version Y and the release version Z, the UE  100  may select the highest release version from the plurality of release versions, and add the selected release version to generate and transmit an RRC connection request message to the network  200 . When the ‘release version Y’ is a ‘REL-7’ and the ‘release version Z’ is a ‘REL-5’, the UE  100  adds a release version ‘REL-6’ between a ‘REL-7’ and a ‘REL-5’ to generate and transmit an RRC connection request message to the network  200 . 
     The network  200  transmits an RRC connection setup message with the release version X to the UE  100  in step  305 . When the network  200  may support a release version requested from the UE  100 , it allots a channel corresponding to the release version requested from a user to the UE  100 . Because the network  200  may support the release version X requested from the UE  100 , it generates and transmits an RRC connection setup message with the release version X to the UE  100  in step  305 . 
     The UE  100  compares release versions included in the RRC connection setup message with those included in the RRC connection request message in step  306 . Because the release versions included in the RRC connection request message and release versions included in the RRC connection setup message are the release version X, which are the same value, the UE  100  determines that the release versions have the same value. 
     The UE  100  generates and transmits an RRC connection setup complete message with the release version X to the network  200  in step  307 . Because the UE  100  receives allotment of a channel of the same release version for the requested release version X from the network  200 , it transmits an RRC connection setup complete message with the release version X to the network  200  to report termination of the RRC connection procedure thereto. When the RRC connection procedure is terminated, a radio channel according to the release version X is formed between the UE  100  and the network  200 , and the UE  100  and the network  200  perform circuit communication and packet data communication on the formed channel. 
     Conventionally, a UE  100  adds the release version Y to generate and transfer the RRC connection request message to the network  200 . If the UE  100  receives an RRC connection setup message with a release version Z, it transmits an RRC connection setup complete message with the release version Z to the network  200  to complete an RRC connection procedure. When the network  200  supports a release version X higher than the release version Z, although the UE  100  may form a channel with the network  200  by the release version X, it forms the channel with the network  200  by the release version Z. In exemplary embodiments of the present invention, the UE  100  compares a release version of an RRC connection setup message with a release version of an RRC connection request message, and sequentially reduces the release version to generate and transmit the RRC connection request message to the network  200 , so that the network  200  may form a channel by a maximum supportable release version. 
       FIG. 4  is a flowchart illustrating a network connecting method achieved by a UE according to the first exemplary embodiment of the present invention. 
     Referring to  FIG. 4 , a controller  140  controls a message transceiver  110  to transmit an RRC connection request message to a network  200  in step  401 . A memory  130  of the UE  100  stores information regarding release versions that the UE  100  may support. The controller  140  controls the message generator  120  to add information regarding supportable release versions, thereby generating an RRC connection request message containing the supportable release versions. Next, the controller  140  controls the message transceiver  110  to transmit the generated RRC connection request message to the network  200 . It is assumed in  FIG. 4  that the UE  100  may support to a release version ‘REL-7’. As such, the controller  140  controls the message generator  120  to add information ‘REL-7’ regarding the release version, thereby generating an RRC connection request message containing the supportable release version, and controls the message transceiver  110  to transmit the generated RRC connection request message. 
     The controller  140  receives an RRC connection setup message from the network  200  through the message transceiver  110  in step  402  in response to the network  200  receiving the RRC connection request message from the UE  100 . When the network  200  may not support release versions included in the RRC connection request message, it optionally determines a release version, and adds the determined release version to generate and transmit an RRC connection setup message to the UE  100 . The controller  140  receives the RRC connection setup message through the message transceiver  110  in step  402 . It is assumed in  FIG. 4  that the network  200  does not support a release version ‘REL-7’, optionally determines a release version ‘REL-5’, and adds the release version ‘REL-5’ to generate and transmit an RRC connection setup message to the UE  100 . 
     The controller  140  determines whether the release versions are identical with each other in step  403 . That is, the controller  140  determines whether a release version included in an RRC connection setup message is identical with that included in an RRC connection request message. Since the release version included in the RRC connection request message is ‘REL-7’ and the release version included in the RRC connection setup message is ‘REL-5’, the controller  140  determines that the release version included in the RRC connection request message differs from the release version included in the RRC connection setup message. 
     In an exemplary embodiment of the present invention, the controller  140  may determine whether the release version included in the RRC connection setup message is lower than that included in the RRC connection request message in step  403 . Since the release version included in the RRC connection request message is ‘REL-7’ and the release version included in the RRC connection setup message is ‘REL-5’, the controller  140  determines that the release version included in the RRC connection setup message is lower than the release version included in the RRC connection request message. 
     When the release version included in the RRC connection request message differs from the release version included in the RRC connection setup message, the controller  140  lowers the release version in step  404 , controls the message generator  120  to generate an RRC connection request message with the reduced release version, and controls the message transceiver  110  to transmit the generated RRC connection request message to the network  200  in step  401 . In an exemplary embodiment of the present invention, the controller  140  may reduce the release version by one level. For example, when the controller  140  controls the message generator  120  to generate an RRC connection request message by including ‘REL-7’, it may reduce the release version to ‘REL-6’ in step  404 , return to step  401 , and control the message generator  120  to add ‘REL-6’, thereby generating an RRC connection request message. 
     In an exemplary embodiment of the present invention, when it is determined that the release versions are not identical with each other at step  403 , the controller  140  may determine whether there are intermediate release versions between a release version included in the RRC connection request message and a release version included in the RRC connection setup message. If there are intermediate release versions, the controller  140  may determine how many intermediate release versions there are. When the release version included in the RRC connection setup message is a release version just below the level of the release version included in the RRC connection request message, the controller  140  determines that there are no intermediate release versions between the release version included in the RRC connection request message and the release version included in the RRC connection setup message. 
     When there is one intermediate release version between the release version included in the RRC connection request message and the release version included in the RRC connection setup message, the controller  140  reduces a level of the intermediate release version and controls the message generator  120  to add the intermediate release version, thereby generating an RRC connection request message. 
     When there are a plurality of intermediate release versions between the release version included in the RRC connection request message and the release version included in the RRC connection setup message, the controller  140  reduces a level of the highest release version among the plurality of release versions and controls the message generator  120  to add the release version, thereby generating an RRC connection request message in step  404 . The controller  140  may reduce the release version to a level just below the release version included in the RRC connection setup message previously transmitted to the network  200 , and control the message generator  120  to add the release version, thereby generating an RRC connection request message in step  404 . 
     In an exemplary implementation, since the release version included in the RRC connection request message is ‘REL-7’ and the release version included in the RRC connection setup message is ‘REL-5’, the controller  140  reduces the release version to ‘REL-6’ in step  404 , returns to step  401  and controls the message generator  120  to add the ‘REL-6’, thereby generating an RRC connection request message, and controls the message transceiver  110  to transmit the generated RRC connection request message to the network  200 . 
     The controller  140  again receives the RRC connection setup message from the network  200  through the message transceiver  110  in step  402 . When the network  200  may support the ‘REL-6’, it generates and transmits an RRC connection setup message with the ‘REL-6’ to the UE  100 . The controller  140  receives the RRC connection setup message from the network  200  through the message transceiver  110 . 
     The controller  140  determines whether a release version included in the RRC connection setup message is identical with that included in an RRC connection request message in step  403 . Because both of the release version included in an RRC connection request message and the release version included in an RRC connection setup message are ‘REL-6’, the controller  140  determines that the release version included in the RRC connection setup message is identical with that included in the RRC connection request message. 
     If the release versions are identical with each other, the controller  140  controls the message generator  120  to generate an RRC connection setup complete message and controls the message transceiver  110  to transmit the generated RRC connection setup complete message to the network  200  in step  405 . In this case, the controller  140  controls the message generator  120  to generate an RRC connection setup complete message with ‘REL-6’, and controls the message transceiver  110  to transmit the generated RRC connection setup complete message to the network  200 . The UE  100  transmits the RRC connection setup complete message to the network  200  to report termination of the RRC connection procedure to the network  200 . 
       FIG. 5  is a signal flow diagram illustrating a network connecting method achieved by a UE and a network according to a second exemplary embodiment of the present invention. 
     Unlike the first exemplary embodiment, the second exemplary embodiment is characterized in that the UE  100  forms a channel according to a release version from the network  200 , and compares the release versions with each other, and again performs an RRC connection procedure if a request for a higher release version is possible. 
     Referring to  FIG. 5 , step  501  and step  502  have substantially the same functions as step  301  and step  301  of  FIG. 3 . That is, the UE  100  generates and transmits an RRC connection request message with a release version Y to a network  200  in step  501 , and the network  200  transmits an RRC connection setup message with a release version Z to the UE  100  in step  502 . 
     The UE  100  transmits an RRC connection setup complete message with a release version Z to the network  200  in step  503 . The UE  100  first terminates an RRC connection procedure according to the release version Z from the network  200 . This is because the UE first secures a formed channel according to the release version Z. 
     The UE  100  compares a release version included in an RRC connection setup message with that included in an RRC connection request message in step  504 . Step  504  is substantially the same as step  303  of  FIG. 3 . When the ‘release version Y’ is ‘REL-7’ and the ‘release version Z’ is ‘REL-5’, the UE  100  determines that the release version included in the RRC connection setup message is lower than the release version included in the RRC connection request message. 
     Subsequently, the UE adds a release version X lower than the release version Y and higher than the release version Z to generate and transfer an RRC connection request message to the network  200  in step  505 . The network  200  transmits an RRC connection setup message with the release version X to the UE  100  in step  506 . Step  505  and step  506  are substantially the same as step  304  and step  305  of  FIG. 3 , respectively. 
     The UE  100  transmits an RRC connection setup complete message with the release version X to the network  200  in step  507 . A channel of the release version X is formed between the UE  100  and the network  200 . 
     The UE  100  compares a release version included in an RRC connection setup message with a release version included in an RRC connection request message in step  508 . When the release version included in the RRC connection setup message is identical with the release version included in the RRC connection request message, the UE  100  maintains a channel formed by the release version X. Subsequently, the UE  100  and the network  200  perform circuit call communication and packet data communication on the formed channel. 
       FIG. 6  is a flowchart illustrating a network connecting method achieved by a UE according to the second exemplary embodiment of the present invention. 
     Referring to  FIG. 6 , a controller  140  controls a message transceiver  110  to transmit an RRC connection request message to a network  200  in step  601 . The controller  140  receives an RRC connection setup message from the network  200  through the message transceiver  110  in step  602 . Step  601  and step  602  are substantially the same as step  401  and step  402  of  FIG. 4 , respectively. It is assumed that a release version ‘REL-7’ is included in the RRC connection request message, and a release version ‘REL-5’ is included in the RRC connection setup message. 
     The controller  140  controls the message generator  120  to generate the RRC connection setup complete message and controls the message transceiver  110  to transmit the generated RRC connection setup complete message to the network in step  603 . When a release version ‘REL-5’ is included in the RRC connection setup message, the controller  140  controls the message generator  120  to add the release version ‘REL-5’, thereby generating an RRC connection setup complete message, and controls the message transceiver  110  to transmit the generated RRC connection setup complete message to the network  200 . Accordingly, an RRC connection procedure of the UE  100  is terminated and then a channel of a release version ‘REL-5’ is formed between the UE  100  and the network  200 . 
     Subsequently, the controller  140  determines whether a release version included in an RRC connection setup message is identical with that included in an RRC connection request message in step  604 . If the release version included in the RRC connection request message is ‘REL-7’ and the release version included in the RRC connection setup message is ‘REL-5’, the controller  140  determines that the two release versions differ from each other. In that case, the controller  140  lowers a release version in step  605 , returns to step  601 , controls the message generator  120  to add the lowered release version, thereby generating an RRC connection request message, and controls the message transceiver  110  to transmit the generated RRC connection request message to the network  200 . It is assumed that the controller  140  lowers the release version from ‘REL-7’ to ‘REL-6’, controls the message generator  120  to add the release version ‘REL-6’, by generating an RRC connection request message, and controls the message transceiver  110  to transmit the generated RRC connection request message to the network  200 . 
     If the controller  160  receives an RRC connection setup message with the release version ‘REL-6’ through the message transceiver  110  at step  602 , it controls the message generator  120  to add the ‘REL-6’, thereby generating the RRC connection setup complete message, and controls the message transceiver  110  to transmit the generated RRC connection setup complete message to the network  200  in step  603 . 
     If the controller  140  determines that the release version included in the RRC connection request message is identical with the release version included in the RRC connection setup message in step  604 , the controller maintains a channel formed with the network  200  in step  606 . 
     In the second exemplary embodiment, the UE  100  forms a channel according to the release version provided from the network  200 , and continuously lowers a release version until the release version included in the RRC connection request message becomes identical with the release version included in the RRC connection setup message to generate an RRC connection request message. As a result, the UE  100  may connect with the network  200  by a high-performance channel. 
     While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.