Patent Publication Number: US-2005141546-A1

Title: Method of avoiding collisions between access terminals

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit of the Korean Applications No. P2003-0101345 filed on Dec. 31, 2003 and No. P2004-54427 filed on Jul. 13, 2004, which are hereby incorporated by reference in their entirety.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a method of preventing a same unicast access terminal identifier (UATI) from being simultaneously allocated to separate access terminals (ATs), and more particularly to a method of preventing ATs from colliding with each other if a same UATI is allocated to different ATs when resetting an access network (AN).  
      2. Background of the Related Art  
      Generally, an AN allocates a UATI to each AT to identify the authenticated AT. In doing so, if an allocation and management unit of the AN is reset while a first AT having its allocated UATI closes a service, the entire UATI information of the AN is initialized. Further, the same UATI allocated to the first AT prior to the reset may be allocated to a second AT. When the first AT attempts a service using the same allocated UATI while the second AT receives a corresponding data service using its allocated UATI, the AN detects that the UATIs of the first and second ATs collide with each other and then requests the first AT to perform a service close operation.  
      However, at this time, a traffic channel has not yet been allocated, whereby the AN sends a service close message including the same UATI to both of the first and second ATs via a control channel. Thus, the first and second ATs are unable to receive the corresponding service using the UATI for a predetermined period of time.  
      Moreover, when adding a separate hard disc drive (HDD) to each base station controller (BSC) of the AN, an overall system cost will rise, an additional interface between a processor responsible for UATI allocation and management of the AN and the corresponding HDD is required, and an additional handling time is required for allocating and storing the UATI to the HDD per request of each AT to manage a result thereof  
      Turning now to  FIG. 1 , which is a flowchart of a UATI allocating method according to the related art. As shown, a first AT appends a first random access terminal identifier (RATI) to a UATI request message for a data service request and then transfers the appended message AN (S 111 ).  
      Subsequently, the AN sends a response to the UATI request message of the first AT by allocating a UATI to the first AT (S 112 ). The first AT then stores the allocated UATI in its memory (S 113 ). The first AT having the allocated UATI is then able to receive a data service from the AN (S 114 ). If the AN is reset after completion of the data service, a UATI database is initialized.  
      After the initialization of the UATI database of the AN, a second AT sends a UATI request message including a second RATI to the AN to request a data service (S 116 ). The AN sends a response to the UATI request message of the second AT by allocating a UATI thereto (S 117 ). The second AT then stores the UATI received from the AN in its memory (S 118 ). The second AT is then able to receive a data service from the AN using the allocated UATI (S 119 ).  
      In doing so, the UATI allocated to the second AT may be identical to the UATI allocated to the first AT which was allocated prior to resetting the AN. If so, the following problem occurs. Namely, the first AT having the UATI allocated prior to the reset of the AN sends a connection request message including the allocated UATI (S 120 ). In this case, because a value of the UATI allocated to the first AT is equal to that allocated to the second AT, a collision between the UATIs occurs in the AN.  
      Further, once the AN having detected the collision sends a session close message including the UATI via a control channel (S 121 ), both sessions of the first and second ATs are closed. However, as the UATI value of the first AT is equal to that of the second AT, collisions keep occurring after the section closes.  
     SUMMARY OF THE INVENTION  
      Accordingly, one object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.  
      Another object of the present invention is to avoid collisions between ATs by broadcasting a session close message including a UATI and time identifier to the ATs.  
      To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the present invention provides a novel method of avoiding collisions in a mobile communication system having an access network and at least one access terminal. The method includes receiving, from the at least one access terminal, a service connection request message including an access terminal identifier and a time identifier, and comparing a time information of the received time identifier to a reset time of the at least one access network. Further, if the time information precedes the reset time as a result of the comparison, the method includes broadcasting a session close message including the access terminal identifier and the time identifier to the at least one access terminal.  
      Therefore, the present invention prevents collisions between the access terminals due to a same UATI allocation without adding a separate hard disc drive (HDD) to each base station controller (BSC) of the access network (AN).  
      Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein:  
       FIG. 1  is a flowchart of a UATI allocating method according to the related art;  
       FIG. 2  is a flowchart of a UATI allocating method according to the present invention;  
       FIG. 3  is a flowchart of an operation of an AN for avoiding collisions between ATs according to a first embodiment of the present invention;  
       FIG. 4  is a flowchart of an operation of an AN for avoiding collisions between ATs according to a second embodiment of the present invention;  
       FIG. 5  is a flowchart of an operation of an AN for avoiding collisions between ATs according to a third embodiment of the present invention;  
       FIG. 6  is a flowchart of an operation of an AN for avoiding collisions between ATs according to a fourth embodiment of the present invention; and  
       FIG. 7  is a flowchart of a session close operation of an AT according to the present invention. 
    
    
     BEST MODE OF THE INVENTION  
      Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, the present invention will be described.  
      First,  FIG. 2  is a flowchart of a UATI allocating method according to the present invention. As shown, a first AT transfers a UATI request message for a service request to an AN (S 211 ). The AN then allocates a UATI and time identifier in response to the UATI request message and sends the response to the first AT (S 212 ). The time identifier includes information such as time at which the allocation of the UATI was made including a date, hour, minute, and second, for example.  
      The first AT renders the UATI and time identifier transferred from the AN into one pair and stores the corresponding pair in its memory (S 213 ). A non-volatile memory such as an EEPROM (electrically programmable read only memory), etc. may be used as the memory to prevent the stored information from being lost if or when the power of the AT is turned off.  
      Meanwhile, the first AT uses the pair of the allocated UATI and time identifier in requesting a service again after completing a previous service. After the first AT has received the service from the AN using the pair of the allocated UATI and time identifier (S 214 ), a UATI database of the AN is initialized if the AN is reset after completion of the service (S 215 ).  
      As shown, after the AN has been reset, a second AT transfers a UATI request message including a second RATI service request to the AN (S 216 ). The AN then allocates a UATI and time identifier in response to the UATI request message of the second AT and then transfers the response to the second AT (S 217 ). The second AT also renders the UATI and time identifier transferred from the AN into one pair and stores the corresponding pair in its memory (S 218 ).  
      The second AT then receives a service from the AN using the pair of the allocated UATI and time identifier (S 219 ). Meanwhile, the first AT having the previously allocated UATI transfers a connection request message including the UATI and time identifier pair to the AN to receive another service from the AN (S 220 ).  
      In this instance, the UATI allocated to the second AT may be identical to that allocated to the first AT. Namely, because the UATI of the second AT was newly allocated after the initialization of the UATI database of the AN, the AN may allocate the same UATI to the second AT without recognizing the same UATI was already allocated to the first AT. Hence, when the first AT requests a service using the UATI allocated prior to the initialization of the UATI database of the AN, a collision with the UATI of the second AT occurs.  
      However, according to the present invention, if at least two or more ATs having the same UATI collide with each other, they can be identified using the time identifiers. In addition, the UATI and time identifier initialization for the rest of the ATs except one UATI/time identifier can be requested by broadcasting via a control channel.  
      The AN, as shown in  FIG. 2 , transfers a session close message including the UATI and time identifier to each of the ATs (S 221 ). The first AT then compares the UATI stored in its memory to the UATI transferred from the AN. If the UATIs are identical to each other as a result of the comparison, the first AT compares the time identifier stored in its memory to the time identifier transferred from the AN. If the time identifiers are identical to each other, the first AT initializes the UATI and time identifier stored in its memory.  
      Turning now to  FIG. 3 , which is a flowchart of an operation of an AN for avoiding collisions between ATs according to a first embodiment of the present invention. As shown, an AN receives a connection request message transferred from an AT (S 311 ). As discussed above, the connection request message transferred from the AT includes a UATI and time identifier allocated to the AT. The AN then checks whether a UATI identical to the UATI included in the connection request message is being used by another AT (S 312 ). If the UATI is not in use as a result of the check, the AN performs a data service on the AT having transferred the connection request message using the UATI (S 313 ).  
      However, if the UATI is already in use as a result of the check, the AN compares the time identifier included in the connection request message to its reset time (S 314 ). If the time identifier is prior to the reset time as result of the comparison, the AN determines that the UATI was allocated prior to the reset. Thus, when the UATI allocated before the reset is being used by the requesting AT, the AN decides that the UATI of the AT is not valid anymore. Hence, the AN transfers a session close message including the UATI and time identifier of the AT to the requesting AT by broadcasting via a control channel (S 315 ).  
      Meanwhile, if the time identifier is later than the reset time as result of the comparison (S 314 ), the AN determines that the UATI was allocated after the reset. Namely, the AN determines the AT is valid.  
      The AN can also determine that the UATI of the another AT using the same UATI is not valid (because the UATI of the requesting AT is valid). Thus, the AN transfers a session close message including the UATI and time identifier to the another AT by broadcasting via a control channel (S 316 ). The AN then performs a data service for the requesting AT.  
      Next,  FIG. 4  is a flowchart of an operation of an AN for avoiding collisions between ATs according to a second embodiment of the present invention. As shown, an AN receives a connection request message transferred from an AT (S 411 ). Further, the connection request message transferred from the AT includes a UATI and time identifier allocated to the AT. The AN then compares the time identifier included in the connection request message to its rest time (S 412 ).  
      If the time identifier is prior to the reset time as result of the comparison, the AN determines that the UATI was allocated prior to the reset. Thus, the AN determines that the UATI allocated prior to the reset is not valid. Hence, the AN transfers a session close message including the UATI and time identifier to the AT by broadcasting via a control channel (S 413 ).  
      Meanwhile, if the time identifier is later than the reset time as result of the comparison (S 412 ), the AN determines that the UATI was allocated after the reset. Thus, the AN determines that the UATI of the AT is valid. Thus, the AN performs a data service on the AT (S 414 ).  
      Turning now to  FIG. 5 , which is a flowchart of an operation of an AN for avoiding collisions between ATs according to a third embodiment of the present invention. As shown, an AN receives a connection request message transferred from an AT (S 511 ). As discussed above, the connection request message includes a UATI and time identifier allocated to the AT. The AN then compares the time identifier included in the connection request message to a current time of the AN (S 512 ). Because the time identifier includes information about the date (e.g., month, day, year), time, minute, and second of the UATI allocation time, the AN can determine that at least one month has passed since the allocation time if the information of the time identifier of the UATI transferred from the AT is later than the current time of the AN. Hence, in this instance, the AN determines that the received UATI is not valid. Thus, when receiving the invalid UATI, the AN transfers a session close message including the UATI and time identifier by broadcasting via a control channel (S 513 ).  
      However, if the information about the date, time, minute, and second of the UATI transferred from the AT precedes the current time of the AN, the AN determines once that the UATI is valid. Further, the time identifier included in the connection request message is also compared to a reset time of the AN (S 514 ). If the time identifier precedes the reset time as a result of the comparison, the AN determines that the UATI was allocated prior to the reset. Hence, the AN determines that the UATI allocated prior to the reset is not valid and transfers a session close message including the UATI and time identifier to the AT by broadcasting via a control channel (S 513 ).  
      Meanwhile, if the time identifier is later than the reset time as result of the comparison (S 514 ), the AN determines that the UATI was allocated after the reset. The AN then determines that the UATI, which is allocated after the reset, is valid. The AN then performs a data service on the AT (S 515 ).  
      Next,  FIG. 6  is a flowchart of an operation of an AN for avoiding collisions between ATs according to a fourth embodiment of the present invention. As shown, an AN receives a connection request message including a UATI and time indentifier transferred from an AT (S 611 ). The AN compares the time identifier included in the connection request message to a current time of the AN (S 612 ).  
      As discussed above, because the time identifier includes information about a date, time, minute, and second of the UATI allocation time, the AN can determine that at least one month has passed since the UATI was allocated if the time information of the UATI is later than the current time of the AN. Hence, the AN determines that the received UATI is not valid. When receiving the invalid UATI, the AN transfers a session close message including the UATI and time identifier to the AT by broadcasting via a control channel (S 613 ).  
      However, if the time information of the UATI precedes the current time of the AN, the AN determines once that the UATI is valid. Subsequently, the AN checks whether the same UATI included in the connection request message is being used by another AT (S 614 ). If the same UATI is not being used as a result of the check, the AN performs a data service on the AT having transferred the connection request message using the UATI (S 615 ). However, if the same UATI is being used as a result of the check, the AN compares the time identifier included in the connection request message to a reset time of the AN (S 616 ).  
      If the time identifier precedes the reset time as a result of the comparison, the AN determines that the UATI was allocated prior to the reset. Thus, if the UATI allocated before the reset is being used by the requesting AT, the AN determines that the UATI of the AT is not valid anymore. Hence, the AN transfers a session close message including the UATI and time identifier to the AT to the requesting AT by broadcasting via a control channel (S 613 ).  
      Meanwhile, if the time identifier is later than the reset time as result of the comparison (S 616 ), the AN determines that the UATI was allocated after the reset. Namely, the AN determines that the UATI, which is allocated after the reset, is valid. Hence, the AN can also determine that the UATI of another AT, which is using the same UATI, is not valid. The AN then transfers a session close message including the UATI and time identifier to the AT by broadcasting via control channel (S 617 ). In such a case, the AN performs a data service on the requesting AT.  
      Next,  FIG. 7  is a flowchart of a session close operation of an AT according to the present invention. As shown, an AT transfers a message for requesting UATI allocation to an AN to receive a service (S 711 ). When receiving the UATI and time identifier from the AN, the AT renders them into one pair and then stores the corresponding pair in a memory (S 712 ).  
      An operation of the AT after the UATI allocation is explained as follows. First, the AT transfers a connection request message including the pair of the UATI and time identifier allocated to itself after the UATI allocation to the AN (S 713 ). When receiving a session close message from the AN (S 714 ), the AT compares the UATI included in the session close message to its UATI (S 715 ).  
      If the UATIs are not identical to each other as a result of the comparison, the AT ignores the session close message (S 716 ). However, if the UATIs are identical, the AT compares the time identifier included in the session close message to its time identifier (S 717 ). If the time identifiers are not identical to each other as a result of the comparison, the AT ignores the session close message (S 716 ). However, if the time identifiers are identical, the AT closes the corresponding session and initializes its UATI and time identifier (S 718 ).  
      This invention may be conveniently implemented using a conventional general purpose digital computer or microprocessor programmed according to the teachings of the present specification, as well be apparent to those skilled in the computer art. Appropriate software coding can readily be prepared by skilled programmers based on the teachings of the present disclosure, as will be apparent to those skilled in the software art.  
      The invention may also be implemented by the preparation of application specific integrated circuits or by interconnecting an appropriate network of conventional component circuits, as will be readily apparent to those skilled in the art. The present invention includes a computer program product which is a storage medium including instructions which can be used to program a computer to perform a process of the invention. The storage medium can include, but is not limited to, any type of disk including floppy disks, optical discs, CD-ROMs, and magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards, or any type of media suitable for storing electronic instructions.  
      The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures.  
      The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures.