Abstract:
A signaling processing method for allocating a UATI (Unicast Access Terminal Identifier) to a given AT (Access Terminal) in a mobile communication system including ANs (Access Networks) each having an BS (Access Network Controller), for communicating by radio with ATs, and at least one DLR (Data Location Register) connected to BSs, for storing a plurality of UATIs, which can be allocated to the ATs, and managing the remaining UATIs that are not allocated. Upon receipt of a UATI Request message from the AT, the BS transmits a UATI Allocate Request message to the DLR. Upon receipt of the UATI Allocate Request message, the DLR allocates one of the remaining UATIs to the AT and transmits a UATI Allocate Response message including the allocated UATI to the BS. Upon receipt of the UATI Allocate Response message, the BS transmits a UATI Allocate message including the allocated UATI to the AT.

Description:
PRIORITY 
   This application claims priority to an application entitled “Method for Allocating UATI in a Mobile Communication System for High-Speed Packet Data Transmission” filed in the Korean Industrial Property Office on Jun. 3, 2002 and assigned Serial No. 2002-31188, the contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to a method for allocating an identifier to an access terminal in a mobile communication system, and in particular, to a method for allocating a UATI (Unicast Access Terminal Identifier) to an access terminal in a mobile communication system. 
   2. Description of the Related Art 
   In general, a CDMA2000 1× (IS-95C) system can transmit data at 144 Kbps, two or more times faster than an IS-95B system having a maximum data rate of 64 Kbps. Further, the CDMA2000 1× system supports services provided through a radio multimedia platform such as Java, Brew, etc., a multimedia service such as a streaming type of AOD/VOD (Audio On Demand/Video On Demand) etc., and a text service. 
   A CDMA2000 1×EV-DO (Evolution-Data Only) system, which has evolved from the CDMA2000 1× system having a maximum data rate of 144 Kbps, has a maximum data rate of 2.4 Mbps, at least 16 times faster than the CDMA2000 1× system, and can support bidirectional data transmission as well as high-speed Internet search. If the CDMA2000 1× EV-DO technology acknowledged by the ITU (International Telecommunication Union) is used, a large amount of traffics can be transmitted with superior quality by optimizing existing voice and data spectrum. 
   However, while the CDMA2000 1×system uses an IMSI (International Mobile Subscriber Identity) permanently allocated to an access terminal (AT), the CDMA 1×EV-DO system uses a UATI temporarily allocated to the AT by an access network controller (ANC), corresponding to a base station controller (BSC), in order to provide a high-speed packet data service. Therefore, in order to provide a high-speed packet data transmission service efficiently in the CDMA 1×EV-DO system, which is a mobile communication system for high-speed packet data transmission, a specific UATI allocation method is needed for determining when the UATI is to be allocated to the AT and which UATI is to be allocated. 
   SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to provide a method for allocating a UATI to an AT in a mobile communication system for high-speed packet data transmission. 
   It is another object of the present invention to provide a method for exchanging messages between an AT, an ANC, and a data location register (DLR) in order to allocate a UATI to the AT in a mobile communication system for high-speed packet data transmission. 
   According to an aspect of the present invention, there is provided a signaling processing method for allocating a UATI to a given AT (Access Terminal) in a mobile communication system including access networks, each having an ANC (Access Network Controller), for communicating by radio with ATs, and at least one DLR (Data Location Register) connected to ANCs, for storing a plurality of UATIs, which can be allocated to the ATs and managing the remaining UATIs that are not allocated. In the method, upon receipt of a UATI Request message from the AT, the ANC transmits a UATI Allocate Request message to the DLR. Upon receipt of the UATI Allocate Request message, the DLR allocates one of the remaining UATIs to the AT and transmits a UATI Allocate Response message including the allocated UATI to the ANC. Upon receipt of the UATI Allocate Response message, the ANC transmits a UATI Allocate message including the allocated UATI to the AT. 
   According to another aspect of the present invention, there is provided a signaling processing method for reallocating a UATI to an AT (Access Terminal) while the AT to which the UATI is allocated by a first DLR (Data Location Register) moves to an AN (Access Network) where a second DLR allocates the UATI in a mobile communication system including a plurality of ANs each having an ANC (Access Network Controller), for communicating by radio with a plurality of ATs, and two or more DLRs each connected to the ANC included in at least one AN, for storing a plurality of UATIs and managing remaining UATIs that are not allocated. In the method, upon receipt of a UATI Request message including an old UATI from the AT, the ANC transmits to the second DLR a UATI Allocate Request message for requesting the second DLR to reallocate the UATI. Upon receipt of the UATI Allocate Request message, the second DLR transmits to the first DLR a Session Information Request message for requesting the first DLR to transmit session information relating to the old UATI. Upon receipt of the Session Information Request message, the first DLR transmits a Session Information Response message including the session information relating to the old UATI to the second DLR. The second DLR reallocates one of the remaining UATIs to the AT and transmits a UATI Allocate Response message including the reallocated UATI to the ANC. Upon receipt of the UATI Allocate Response message, the ANC transmits a UATI Allocate message including the reallocated UATI to the AT. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: 
       FIG. 1  illustrates an entire structure of a mobile communication system for high-speed packet data transmission; 
       FIG. 2  illustrates a procedure for exchanging messages when the AT is initially driven to open a session for the first time in a mobile communication system for high-speed packet data transmission according to a preferred embodiment of the present invention; 
       FIG. 3  illustrates a procedure for exchanging messages when the DLR includes session information while the AT hands off in a mobile communication system for high-speed packet data transmission according to a preferred embodiment of the present invention; 
       FIG. 4  illustrates a procedure for exchanging messages when the DLR has no session information while the AT hands off in a mobile communication system for high-speed packet data transmission according to a preferred embodiment of the present invention; 
       FIG. 5  illustrates a procedure for exchanging messages when there is no UATI to be allocated in a mobile communication system for high-speed packet data transmission according to a preferred embodiment of the present invention; and 
       FIG. 6  illustrates a procedure for exchanging messages when a UATI Complete message transmitted by the AT is loss in a mobile communication system for high-speed packet data transmission according to a preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A preferred embodiment of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. 
   Unlike a CDMA2000 1× system in which an IMSI is permanently allocated, a CDMA2000 1×EV-DO system temporarily uses a UATI temporarily allocated to an AT by an ANC(BS, Base Station). The present invention newly proposes UATI allocation-related messages exchanged between a DLR, which determines when the UATI is to be allocated to the AT, and which UATI is to be allocated, an ANC, and an AT in the CDMA2000 1× EV-DO system (hereinafter, referred to as a mobile communication system for high-speed packet data transmission), so that the UATI can be efficiently allocated to the AT. 
     FIG. 1  illustrates an entire structure of a mobile communication system for high-speed packet data transmission. Access network transceiver systems (ANTSs)  103 ,  105 ,  113 , and  115  transmit/receive signals to/from ATs  101  and  111 , respectively. ANCs  107  and  117  control the ANTSs  103 ,  105 ,  113 , and  115 . A general ATM (Asynchronous Transfer Mode) switch network (GAN)  121  connects the ANCs  107  and  117  with peripheral devices. A base station manager (BSM)  123  is connected to the GAN  121 . An access network authentication, authorization and accounting server (AN AAA)  125  connected to the GAN  121  authenticates the ATs  101  and  111 . A DLR  127  connected to the GAN  121  manages a UATI session. A packet data service node (PDSN)  129  connected to the GAN  121  is defined in the CDMA2000 1× system. A home agent (HA)  131  is connected to the PDSN  129 , and an authentication, authorization and accounting server (AAA)  133  is connected to the HA  131 . An Internet protocol (IP) network  135  is connected to the HA  131 . The ANTSs  103  and  105  and the ANC  107  constitute one access network (AN), and the ANTSs  113  and  115  and the ANC  117  constitute another AN. The CDMA 1×EV-DO system, a mobile communication system for high-speed packet data transmission, has a plurality of subnets. The subnet is an area managed by one GAN. The number of ANs constituting one subnet may be variable according to traffic circumstances, and usually one subnet consists of 20 to 30 ANs. 
   In  FIG. 1 , although the DLR  127  covers one subnet, that is, one GAN area, the DLR may cover a plurality of GAN areas or a plurality of DLRs may be connected to one GAN area. The construction between the DLR and GAN is not directly related to the present invention, so a description thereof will not be provided. 
   A description will be made of types and structures of messages exchanged between the ANC and the DLR when the AT requests the ANC to allocate a UATI in a mobile communication system for high-speed packet data transmission with reference to Tables 1 to 6. 
   Table 1 below shows fields constituting a UATI Allocate Request message transmitted by the ANC to the DLR when the AT requests the ANC to allocate the UATI. 
   
     
       
             
             
             
           
         
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
               Field 
               Type 
             
             
                 
                 
             
           
           
             
                 
               Message Type 
               M 
             
             
                 
               Message Length 
               M 
             
             
                 
               TID 
               M 
             
             
                 
               OldUATI 
               O 
             
             
                 
               Authentication Parameter 
               O 
             
             
                 
               Paging Parameter 
               O 
             
             
                 
               Location Registration 
               M 
             
             
                 
               HW ID 
               O 
             
             
                 
                 
             
           
        
       
     
   
   Referring to Table 1, fields for the UATI Allocate Request message are divided into mandatory fields M when carrying of corresponding information is mandatory and optional fields O when information is optionally carried. The mandatory fields M for the UATI Allocate Request message include a Message Type field indicating the type of a message, a Message Length field indicating the length of a message, a TID (Transaction IDentifier) field for identifying ATs, and a Location Registration field consisting of ANC_ID and ANTS_ID, used for registering the location of an AT. The optional fields O for the UATI Allocation Request message include an OldUATI field for transmitting, if the AT has a previously allocated UATI (OldUATI), an Authentication Parameter field consisting of a Security Layer Packet, a Sector ID, and a Time Stamp, used for authenticating the AT, a Paging Parameter field having a maximum of 20 bytes used during paging, and an HW ID (Hardware Identification) field indicating hardware information. If the UATI Allocate Request message includes the OldUATI field, the Authentication Parameter is included therein, and if the UATI Allocate Request message does not include the OldUATI field, the Paging Parameter is included therein. 
   Table 2 below shows fields constituting a UATI Allocate Response message transmitted by the DLR to the ANC in response to the UATI Allocate Request message. 
   
     
       
             
             
             
           
         
             
                 
               TABLE 2 
             
             
                 
                 
             
             
                 
               Field 
               Type 
             
             
                 
                 
             
           
           
             
                 
               Message Type 
               M 
             
             
                 
               Message Length 
               M 
             
             
                 
               TID 
               M 
             
             
                 
               RET 
               M 
             
             
                 
               UATI 
               O 
             
             
                 
               PDSN IP Address 
               O 
             
             
                 
               Access Network Address 
               O 
             
             
                 
                 
             
           
        
       
     
   
   Referring to Table 2, fields for the UATI Allocate Response message are also divided into mandatory fields M when corresponding information is necessarily carried and optional fields O wherein information is optionally carried. The mandatory fields M for the UATI Allocate Response message include a Message Type field indicating the type of a message, a Message Length field indicating the length of a message, a TID field for identifying ATs, and an RET (Return) field indicating the result of a service. A TID received through the UATI Allocate Request message of Table 1 is carried in the TID field, and a return of the UATI Allocate Request message is carried in the RET field. The optional fields O for the UATI Allocation Response message include a UATI field for transmitting, if the AT has an allocated UATI, a PDSN IP Address field indicating an IP address of the PDSN, and an Access Network Address field indicating an address of the AN. Only when the UATI to be allocated exists, corresponding information is carried on the PDSN IP Address field and the Access Network Address field. 
   Table 3 below shows fields constituting a UATI Allocate Complete Request message (hereinafter, referred to as a UATI Complete Request message) indicating that the UATI has normally been allocated to the AT, transmitted by the ANC to the DLR. 
   
     
       
             
             
             
           
         
             
                 
               TABLE 3 
             
             
                 
                 
             
             
                 
               Field 
               Type 
             
             
                 
                 
             
           
           
             
                 
               Message Type 
               M 
             
             
                 
               Message Length 
               M 
             
             
                 
               TID 
               M 
             
             
                 
               UATI 
               M 
             
             
                 
               Location Registration 
               M 
             
             
                 
                 
             
           
        
       
     
   
   In Table 3, a UATI value allocated to the AT is carried in the UATI field. 
   Table 4 below shows fields constituting a UATI Allocate Complete Response message (hereinafter, referred to as a UATI Complete Response message) transmitted by the DLR to the ANC in response to the UATI Complete Request message shown in Table 3. 
   
     
       
             
             
             
           
         
             
                 
               TABLE 4 
             
             
                 
                 
             
             
                 
               Field 
               Type 
             
             
                 
                 
             
           
           
             
                 
               Message Type 
               M 
             
             
                 
               Message Length 
               M 
             
             
                 
               TID 
               M 
             
             
                 
               RET 
               M 
             
             
                 
               MN ID 
               O 
             
             
                 
               Paging Parameter 
               O 
             
             
                 
               OldUATI 
               O 
             
             
                 
               HW ID 
               O 
             
             
                 
                 
             
           
        
       
     
   
   Referring to Table 4, a return of the UATI Complete Request message is carried in the RET field. In an MN (Mobile Node) ID field, information is carried only when corresponding information exists. Likewise, in an HW ID field, information is carried only when corresponding information exists. 
   Table 5 below indicates the RET field among the fields for the UATI Allocation Response message shown in Table 2. The RET field is included in a response message to a request message. That is, a value representing a return of the request is carried in an RET Value field. 
   
     
       
             
             
             
             
             
             
             
             
             
           
             
             
             
           
         
             
               TABLE 5 
             
             
                 
             
             
               7 
               6 
               5 
               4 
               3 
               2 
               1 
               0 
               Octet 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
               Element Identifier 
               1 
             
             
                 
               Length 
               2 
             
             
                 
               RET Value 
               3 
             
             
                 
                 
             
           
        
       
     
   
   Tables 6 and 7 below indicate meanings of values used in the RET Value field shown in Table 5. In Table 6, the meanings of the RET values are classified by an upper 4 bits of the value of the RET Value field. In Table 7, the meanings of the RET values are classified in more detail. 
   
     
       
             
             
             
           
         
             
               TABLE 6 
             
             
                 
             
             
               Class 
               Binary Value 
               Meaning 
             
             
                 
             
           
           
             
               Normal 
               B′0000~B′0001 
               Return of message is successful. 
             
             
               Resource 
               B′0010 
               Failure due to shortage of resource 
             
             
                 
                 
               etc. 
             
             
               Processing 
               B′0011~B′0101 
               Failure in service. 
             
             
               Message Invalid 
               B′0101 
               Failure in message transmission 
             
             
                 
                 
               due to erroneous message or error 
             
             
                 
                 
               in TID. 
             
             
               Protocol Error 
               B′0110 
               Failure due to error in parameter. 
             
             
               Authentication 
               B′0111 
               Failure in authentication. 
             
             
               Failure 
             
             
               Reserved 
               B′1000~B′1110 
               Unused 
             
             
               ETC 
               B′1111 
               Failure due to the other causes. 
             
             
                 
             
           
        
       
     
   
   
     
       
             
             
             
             
           
         
             
               TABLE 7 
             
             
                 
             
             
                 
               RET 
                 
                 
             
             
               Class 
               Value 
               Name 
               Meaning 
             
             
                 
             
           
           
             
               Normal 
               H′01 
               SUCCESS 
               Return of message is successful. 
             
             
                 
               H′02 
               DUPLICATED_UATI 
               Duplicated UATI having the same 
             
             
                 
                 
                 
               MN ID exists. 
             
             
               Resource 
               H′21 
               NO_UATI_AVAILABLE 
               UATI resource to be 
             
             
                 
                 
                 
               allocated is short. 
             
             
               Processing 
               H′31 
               UNKNOWN_UATI 
               Received UATI is not 
             
             
                 
                 
                 
               allocated UATI. 
             
             
                 
               H′32 
               AUTHENTICATION_FAILED 
               Failure in SHA-1 
             
             
                 
                 
                 
               authentication specified in 
             
             
                 
                 
                 
               IS-856. 
             
             
                 
               H′33 
               STAIL_OLDUATI 
               MN ID or session 
             
             
                 
                 
                 
               information corresponding 
             
             
                 
                 
                 
               to received OldUATI does 
             
             
                 
                 
                 
               not exist. 
             
             
                 
               H′34 
               MN_ID-MISMATCHED 
               Transmitted MN ID is 
             
             
                 
                 
                 
               different from stored value. 
             
             
                 
               H′35 
               LOC-Unavailable 
               Location information of 
             
             
                 
                 
                 
               AT is not clear. 
             
             
               Protocol 
               H′41 
               INVALID_MESSAGE- 
               Message type is unknown. 
             
             
                 
                 
               TYPE 
             
             
                 
               H′42 
               MANDATORY- 
               Mandatory parameter has 
             
             
                 
                 
               ELEMENT_OMITTED 
               been omitted. 
             
             
                 
               H′43 
               UNKNOWN_ELEMENT 
               Unknown parameter has 
             
             
                 
                 
                 
               been received. 
             
             
                 
               H′44 
               INVALID_ELEMENT 
               Contents of parameter are 
             
             
                 
                 
                 
               invalid. 
             
             
                 
               H′4F 
               GENERAL- 
               Failure in processing of 
             
             
                 
                 
               PROTOCOL_ERROR 
               other protocol. 
             
             
               PPS 
               H′51 
               PPS_Not-OK 
               PPS (Pre-Paid Service) 
             
             
                 
                 
                 
               subscribers are unlimited. 
             
             
               ETC 
               H′FF 
               GENERAL_ERROR 
               Failure due to the other 
             
             
                 
                 
                 
               causes. 
             
             
                 
             
           
        
       
     
   
   In Table 7, NO_UATI_AVAILABLE is used to represent that there is no available UATI when the UATI resource to be allocated is short, UNKNOWN_UATI is used to represent that the received UATI is not the allocated UATI when the OldUATI received from the ANC cannot be found, AUTHENTICATION_FAILED is used to represent failure in authentication for the received OldUATI, and STALE_OldUATI is used to represent that the MN ID or session information corresponding to the received OldUATI does not exist. 
   Table 8 below shows the MN ID field among fields for the UATI Complete Response message indicated in Table 4. 
   
     
       
             
             
             
             
             
             
             
             
             
           
             
             
             
           
             
             
             
             
             
           
             
             
             
             
           
             
             
             
           
             
             
             
             
           
         
             
               TABLE 8 
             
             
                 
             
             
               7 
               6 
               5 
               4 
               3 
               2 
               1 
               0 
               Octet 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
               Element Identifier 
               1 
             
             
                 
               Length 
               2 
             
           
        
         
             
                 
               Identity digit 1 
               Odd/even 
               Type of Identity 
               3 
             
           
        
         
             
                 
               Identity digit 3 
               Identity digit 2 
               4 
             
           
        
         
             
                 
               . . . 
               . . . 
             
           
        
         
             
                 
               Identity digit N+1 
               Identity digit N 
               N 
             
             
                 
                 
             
           
        
       
     
   
   Table 9 below indicates meanings of values of the MN ID field shown in Table 8. The MN ID field represents a type of a used identity. Such an MN ID includes an IMSI (International Mobile Subscriber Identity) used to identify international subscribers, an ESN (Electronic Serial Number) assigned as a fixed bit during manufacturing, an MIN (Mobile Identification Number), a broadcast address used for broadcasting. 
   
     
       
             
             
           
         
             
               TABLE 9 
             
             
                 
             
             
               Binary Value 
               Meaning 
             
             
                 
             
           
           
             
               000 
               No Identity Code 
             
             
               001 
               MIN 
             
             
               010 
               Broadcast Address 
             
             
               101 
               ESN 
             
             
               110 
               IMSI 
             
             
                 
             
           
        
       
     
   
   A signaling procedure between the AT, ANC, and DLR, for allocating a UATI in the mobile communication system for high-speed packet data transmission will be described in detail with reference to  FIGS. 2 to 6 . 
     FIG. 2  illustrates a procedure for exchanging messages between the AT, ANC, and DLR, for allocating the UATI when the AT is initially driven to open a session for the first time in the mobile communication system for high-speed packet data transmission. 
   The AT, a CDMA 1x EV-DO terminal, has no UATI therein when power is initially turned ON or a session is initially opened. In this case, the AT transmits to the ANC a UATI Request message for requesting the ANC to allocate a UATI by using a random access terminal identifier (RATI), which is generated at random therefrom, so that the ANC can select any one of a plurality of DLRs existing in a GAN area. A procedure for exchanging messages when the AT initially opens the session will now be described with reference to  FIG. 2 . 
   In  FIG. 2 , the AT transmits the UATI Request message to the ANC using the RATI in step  200  to request the ANC to allocate the UATI. Upon receipt of the UATI Request message, in step  202 , the ANC transmits to the DLR the UATI Allocate Request message illustrated in Table 1, including the Paging Parameter, to request the DLR to allocate the UATI. As described with reference to Table 1, not the Authentication Parameter, but the Paging Parameter is included in the UATI Allocate Request message because the AT has requested the ANC to allocate the UATI by using the RATI rather than the OldUATI. Thus, when the AT transmits the UATI Request message using the RATI to the ANC, the ANC selects any DLR among DLRs within a subnet and transmits the UATI Allocate Request message to the selected DLR. Upon receipt of the UATI Allocate Request message, the DLR checks whether the AT requesting the ANC to allocate the UATI is an AT opening a new session within the subnet of the DLR area or an AT moving from an adjacent subnet. When the RATI is used, the DLR recognizes the AT requesting the ANC to allocate the UATI as an AT opening a new session. Then the DLR stores the Paging Parameter transmitted by the ANC and transmits the UATI Allocate Response message illustrated in Table 2 to the ANC in step  204 . Upon receiving the UATI Allocate Response message, the ANC transmits a UATI Allocate message to the AT in step  206  to allocate a new UATI to the AT. The AT, which has received the UATI Allocate message, transmits to the ANC a UATI Allocate Complete message (hereinafter, referred to as a UATI Complete message) indicating that the new UATI has been allocated in step  208 . Upon receiving the UATI Complete message, the ANC transmits the UATI Complete Request message shown in Table 3 to the DLR in step  210 . Upon receipt of the UATI Complete Request message, the DLR transmits the UATI Complete Response message shown in Table 4 to the ANC in step  212  to terminate a UATI allocating procedure. In this case, since the DLR has no MN ID for the AT, it does not transmit the MN ID to the ANC. 
     FIG. 3  illustrates a procedure for exchanging messages between the AT, ANC, and DLRs while the AT hands off in the mobile communication system for high-speed packet data transmission. In  FIG. 3 , a first DLR (DLR2) within a subnet to which the AT has belonged before handoff has session information, and the AT is to belong to a second DLR (DLR1) through the handoff. The CDMA 1x EV-DO system includes a plurality of subnets. The subnet indicates an area where information representing that the current AT opens the session for the first time and information on the UATT of the AT or the session is managed. If the AT moves from its subnet to another subnet, the AT recognizes that the subnet is changed through an overhead message and requests the ANC to allocate a new UATI. A description will now be made of a procedure for exchanging messages between the AT, ANC, DLR1, and DLR2 when the DLR2 has session information while the AT hands off the subnet in the mobile communication system for high-speed packet data transmission with reference to  FIG. 3 . 
   The AT transmits the UATI Request message to the ANC in step  300  by use of the OldUATI, which has been allocated from the DLR2 within the subnet before the handoff. Upon receipt of the UATI Request message, the ANC transmits to the DLR1 the UATI Allocate Request message illustrated in Table 1, including the OldUATI instead of the Paging Parameter in step  302 , to request the DLR1 to allocate the UATI. Upon receiving the UATI Allocate Request message, the DLR1 transmits a Session Information Request message to the DLR2 having the session information of the AT in step  304  to request the DLR2 to transmit OldUATI-related information. The DLR2 then transmits a Session Information Response message including the OldUATI-related information to the DLR1 in step  306 . Upon receiving the OldUATI-related information, the DLR1 transmits the UATI Allocate Response message illustrated in Table 2 to the ANC in step  308  to allocate the UATI to the ANC. The ANC, which has received the UATI Allocate Response message, transmits the UATI Allocate message to the AT in step  310  to allocate a new UATI to the AT. Upon receiving the UATI Allocate message, the AT transmits to the ANC the UATI Complete message indicating that the new UATI has successfully been allocated in step  312 . The ANC, which has received the UATI Complete message, transmits the UATI Complete Request shown in Table 3 to the DLR1 in step  314 . Upon receiving the UATI Complete Request message, the DLR1 transmits the UATI Complete Response message illustrated in Table 4 to the ANC in step  316  to terminate the UATI allocating procedure. In this case, since the DLR1 has the MN ID, it transmits the MN ID for the AT to the ANC through the UATI Complete Response message. 
     FIG. 4  illustrates a procedure for exchanging messages between the AT, ANC, and DLRs while the AT hands off a subnet in the mobile communication system for high-speed packet data transmission. In  FIG. 4 , a first DLR (DLR2) within a subnet to which the AT has belonged before handoff has no session information, and the AT is to belong to a second DLR (DLR1) through the handoff. 
   Referring to  FIG. 4 , the AT transmits the UATI Request message to the ANC in step  400  by use of the OldUATI, which has been allocated from the DLR2 within the subnet before the handoff. Upon receipt of the UATI Request message, the ANC transmits to the DLR1 the UATI Allocate Request message illustrated in Table 1, including the OldUATI instead of the Paging Parameter in step  402 . Upon receiving the UATI Allocate Request message, the DLR1 transmits the Session Information Request message to the DLR2 in step  404  to request the DLR2 to transmit the OldUATI-related information. If the OldUATI-related information does not exist or the OldUATI fails in authentication, the DLR2 transmits a Session Information Reject message to the DLR1 in step  406 . Upon receipt of the Session Information Reject message, the DLR1 does not allocate the UATI and transmits a UATI Allocate Reject message to the ANC in step  408  to inform the ANC that the OldUATI-related information does not exist. The ANC, which has received the UATI Allocate Reject message, transmits a Session Close message to the AT in step  410 . Upon receipt of the Session Close message, the AT closes the session and transmits the UATI Request message to the ANC in step  412  by use of the RATI, rather than the OldUATI after a lapse of a prescribed time to request the ANC to allocate the UATI again. The next processes are the same as when the session is opened for the first time. 
     FIG. 5  illustrates a procedure for exchanging messages between the AT, ANC, and DLR when the allocation of the UATI fails due to the shortage of the unallocated UATI in the mobile communication system for high-speed packet data transmission. 
   Referring to  FIG. 5 , the AT transmits the UATI Request message in step  500 . The ANC, which has received the UATI Request message, transmits the UATI Allocate Request message shown in Table 1 to the DLR in step  502  to request the DLR to allocate the UATI. If there is no UATI to be allocated, the DLR, which has received the UATI Allocate Request message, transmits a UATI Allocate Failure message to the ANC in step  504  to inform the ANC of failure in allocation. Upon receipt of the UATI Allocate Failure message, the ANC terminates the UATI allocating procedure without transmitting a response message to the AT. Because the UATI has not been allocated, the AT retransmits, in step  506 , the UATI Request message to the ANC after a prescribed time period from transmission of the UATI Request message, to request the ANC to allocate the UATI. Preferably, the AT attempts to transmit the UATI Request message up to a maximum of 10 times. The number of attempts for requesting the ANC to allocate the UATI may be arbitrarily set. 
     FIG. 6  illustrates a procedure for exchanging messages between the AT, ANC, and DLR when the UATI Complete message transmitted by the AT is damaged in the mobile communication system for high-speed packet data transmission. 
   Referring to  FIG. 6 , the AT transmits the UATI Request message to the ANC in step  600 . Upon receipt of the UATI Request message, the ANC transmits the UATI Allocate Request message indicated in Table 1 to the DLR in step  602  to request the DLR to allocate the UATI. Upon receipt of the UATI Allocate Request message, the DLR transmits the UATI Allocate Response message shown in Table 2 to the ANC in step  604 . The ANC, which has received the UATI Allocate Response message, transmits the UATI Allocate message to the AT in step  606 . While the AT, which has received the UATI Allocate message, transmits the UATI Complete message to the ANC in step  608 , the UATI Complete message may be damaged due to various reasons. If the UATI Complete Request message is not received for a prescribed time, the DLR transmits to the ANC a Session Close Command message for commanding the ANC to close the allocated UATI-related session and to allocate a new UATI again in step  610 . Upon receiving the Session Close Command message, the ANC transmits a Session Close message to the AT in step  612  to request the AT to close the session. The AT, which has received the Session Close message, transmits a Session Close Complete message to the ANC in step  614 . Upon receipt of the Session Close Complete message, the ANC transmits a Session Close Confirmation message to the DLR in step  616 . The DLR, which has received the Session Close Confirmation message, transmits a Session Close Confirmation Acknowledge message to the ANC in step  618 . After a prescribed time from transmission of the Session Close Complete message, the AT retransmits the UATI Request message to the ANC in step  620  to request the ANC to allocate the UATI again. 
   As described in the message exchanging procedures illustrated in  FIGS. 2 to 6 , upon receipt of the UATI Allocate Request message from the ANC, the DLR implements a function of allocating the UATI and managing the session information. In allocating the UATI, the DLR processes a UATI allocation request of the ANC with respect to the GAN area. The UATI can be allocated and managed irrespective of the defined subnet area. That is, the DLR can simultaneously support several subnets. Moreover, the different ATs should not have the same UATI. To avoid the duplicated UATI, the UATI that has been allocated to the AT should be allocated to another AT after a lapse of a sufficient time. The DLR also supervises the UATI allocating processes. Namely, the DLR determines whether the UATI Complete Request message for the UATI Complete message transmitted by the AT is received from the ANC. If it is not received, the DLR determines that the UATI has been not allocated. Upon receipt of the OldUATI during the UATI allocating processes, the DLR should obtain the OldUATI-related session information from another DLR. Next, in managing the session information, the DLR stores the MN ID for the AT and the session information etc. with respect to the GAN area, and can support several subnets at the same time. If the ANC requests the DLR to send information, the DLR transmits both the MN ID and the session information. 
   As described above, messages required to allocate the UATI in the CDMA2000 1×EV-DO system are newly proposed and they are appropriately exchanged between the DLR, the ANC, and the AT, which are a UATI managing system according to circumstances. Therefore, the UATI can be efficiently allocated to the AT. Meanwhile, an AT of the present invention can be referred to a MS (mobile station), and an ANC can be referred to a BS (base station) 
   While the invention has been shown and described with reference to a certain preferred embodiment 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.