Abstract:
A method is provided for synchronizing Connection IDentifiers (CIDs) of a first station and a second station in a communication system. The CID synchronization method includes sending, by the first station, a first message for requesting addition of a service flow identified by a CID to the second station; sending, by the second station, a second message which is a response message to the first message, and at the same time, setting a number of a frame where the second message is transmitted as a first start frame number; sending, by the first station, a third message for acknowledging receipt of the second message to the second station, and at the same time, setting a number of a frame where the third message is transmitted as a second start frame number; performing, by each of the first station and the second station, a modulo operation on a frame having the first or second start frame number and its succeeding frames using a positive integer for each frame, and detecting a number of a frame where a result value of the modulo operation becomes zero (0); and simultaneously updating CID lists of the first station and the second station at a frame having the detected frame number with regard to a CID of the added service flow.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY 
       [0001]    The present application claims priority to application entitled “SYSTEM AND METHOD FOR CONNECTION IDENTIFIER SYNCHRONIZATION IN A COMMUNICATION SYSTEM,” filed with the Korean Intellectual Property Office on Nov. 23, 2007 and assigned Serial No. 2007-0120372, the contents of which are incorporated herein by reference. 
       TECHNICAL FIELD OF THE INVENTION 
       [0002]    The present application relates generally to a communication system and, in particular, to a system and method for Connection IDentifier (CID) synchronization between a mobile station (MS) and a base station (BS) in a communication system. 
       BACKGROUND OF THE INVENTION 
       [0003]    In communication systems, a BS should rapidly allocate bandwidth in response to an uplink bandwidth allocation request from an MS. The uplink bandwidth allocation request is made based on CIDs of an MS, and the BS&#39;s bandwidth allocation in response thereto is achieved based on each MS. That is, an MS requests allocation of a bandwidth necessary for each individual CID, and a BS gathers the bandwidth requested for each individual CID and allocates the gathered bandwidths to corresponding MS independently. 
         [0004]    The CID is allocated to each MS through addition/deletion of a service flow. The term ‘service flow’ as used herein means a connection for data transmission/reception by an MS, and while the addition of a service flow is called Dynamic Service Addition (DSA), the deletion of a service flow is called Dynamic Service Deletion (DSD). 
         [0005]    With reference to  FIGS. 1A to 1D , a description will now be made of a DSA/DSD procedure between an MS and a BS in a general communication system. 
         [0006]      FIG. 1A  is a diagram illustrating an MS-initiated DSA procedure in a general communication system. 
         [0007]    Referring to  FIG. 1A , an MS  101  sends to a BS  103  a Dynamic Service Addition REQuest (DSA-REQ) message including a service parameter for a service flow it will add in order to add a new service flow (step  110 ). Upon receipt of the DSA-REQ message, the BS  103  sends a Dynamic Service Addition ReceiVeD (DSA-RVD) message to the MS  101  (step  112 ), notifying that it has normally received the DSA-REQ message and is handling the received message. 
         [0008]    The BS  103  adds a CID caused by the service flow addition, requested by the MS  101  (step  114 ), and adds the CID even to its own MS CID list to update the CID list. Thereafter, the BS  103  sends the result to the MS  101  through a Dynamic Service Addition ReSPonse (DSA-RSP) message (step  116 ). Upon receipt of the DSA-RSP message, the MS  101  adds a corresponding CID, and adds the corresponding CID even to its own CID list to update the CID list. Thereafter, the MS  101  sends to the BS  103  a Dynamic Service Addition ACKnowledgement (DSA-ACK) message for acknowledging the addition of the corresponding CID (step  118 ). 
         [0009]      FIG. 1B  is a diagram illustrating a BS-initiated DSA procedure in a general communication system. 
         [0010]    Referring to  FIG. 1B , if addition of a new CID is detected, a BS  107  adds the CID to its own MS CID list to update the CID list (step  120 ), and sends to an MS  105  a DSA-REQ message for requesting service flow addition for the added CID (step  122 ). Upon receipt of the DSA-REQ message, the MS  105  adds a CID caused by the service flow addition and adds the CID even to its own CID list to update the CID list. Thereafter, the MS  105  sends the result to the BS  107  through a DSA-RSP message (step  124 ). Upon receipt of the DSA-RSP message, the BS  107  sends to the MS  105  a DSA-ACK message for acknowledging the MS&#39;s addition of the CID (step  126 ). 
         [0011]      FIG. 1C  is a diagram illustrating an MS-initiated DSD procedure in a general communication system. 
         [0012]    Referring to  FIG. 1C , an MS  109  sends to a BS  111  a Dynamic Service Deletion REQuest (DSD-REQ) message including an IDentifier (ID) of a service flow that it will delete in order to delete the existing service flow (step  130 ). Upon receipt of the DSD-REQ message, the BS  111  deletes a CID corresponding to the service flow that the MS  109  has requested to delete (step  132 ), deletes the CID from its own MS CID list to update the CID list, and then sends the result to the MS  109  through a Dynamic Service Deletion ReSPonse (DSD-RSP) message (step  134 ). Upon receipt of the DSD-RSP message, the MS  109  deletes a corresponding CID, and deletes the corresponding CID even from its own CID list to update the CID list. 
         [0013]      FIG. 1D  is a diagram illustrating a BS-initiated DSD procedure in a general communication system. 
         [0014]    Referring to  FIG. 1D , if deletion of an existing CID is detected (step  140 ), a BS  115  deletes the CID from its own MS CID list to update the CID list, and sends to an MS  113  a DSD-REQ message for requesting service flow deletion for the deleted CID (step  142 ). Upon receipt of the DSD-REQ message, the MS  113  deletes a corresponding CID, deletes the corresponding CID even from its own CID list to update the CID list, and then sends the result to the BS  115  through a DSD-RSP message (step  144 ). 
         [0015]    That is, in the communication system, the MS is allocated a corresponding CID through the DSA/DSD process, and the MS and BS update their own CID lists. However, since the BS updates its CID list at the time its own CID is added/deleted, and the MS updates its CID list at the time it is allocated a CID from the BS, the CID lists of the MS and BS may not be identical temporarily. In addition, because the messages exchanged between the BS and the MS in the DSA/DSD process may be lost or may suffer an error, the CID lists of the MS and BS may not be identical to each other. Therefore, it is not possible to immediately withdraw the unused CID(s) and allocate it to another service flow, making it difficult to efficiently manage a limited number of CIDs. 
       SUMMARY OF THE INVENTION 
       [0016]    To address the above-discussed deficiencies of the prior art, it is a primary aspect of the present invention to address at least the problems and/or disadvantages and to provide at least the advantages described below. Accordingly, the present invention provides a system and method for CID synchronization between an MS and a BS. 
         [0017]    Further, the present invention provides a system and method for simultaneously updating CID lists of an MS and a BS. 
         [0018]    According to one aspect of the present invention, there is provided a method for synchronizing Connection IDentifiers (CIDs) of a first station and a second station in a communication system. The CID synchronization method includes sending, by the first station, a first message for requesting addition of a service flow identified by a CID to the second station; sending, by the second station, a second message which is a response message to the first message, and at the same time, setting a number of a frame where the second message is transmitted as a first start frame number; sending, by the first station, a third message for acknowledging receipt of the second message to the second station, and at the same time, setting a number of a frame where the third message is transmitted as a second start frame number; performing, by each of the first station and the second station, a modulo operation on a frame having the first or second start frame number and its succeeding frames using a positive integer for each frame, and detecting a number of a frame where a result value of the modulo operation becomes zero (0); and simultaneously updating CID lists of the first station and the second station at a frame having the detected frame number with regard to a CID of the added service flow. 
         [0019]    According to another aspect of the present invention, there is provided a method for synchronizing Connection IDentifiers (CIDs) of a first station and a second station in a communication system. The CID synchronization method includes sending, by the first station, a first message for requesting deletion of a service flow identified by a CID to the second station, and at the same time, setting a number of a frame where the first message is transmitted as a first start frame number; sending, by the second station, a second message which is a response message to the first message, and at the same time, setting a number of a frame where the second message is transmitted as a second start frame number; performing, by each of the first station and the second station, a modulo operation on a frame having the first or second start frame number and its succeeding frames using a positive integer for each frame, and detecting a number of a frame where a result value of the modulo operation becomes zero (0); and simultaneously updating CID lists of the first station and the second station at a frame having the detected frame number with regard to a CID of the deleted service flow. 
         [0020]    According to further another aspect of the present invention, there is provided a system for synchronizing Connection IDentifiers (CIDs) in a communication system. The CID synchronization system includes a first station and a second station. The first station sends a first message for requesting addition of a service flow identified by a CID to the second station. The second station sends a second message which is a response message to the first message, and at the same time, sets a number of a frame where the second message is transmitted as a first start frame number. The first station sends a third message for acknowledging receipt of the second message to the second station, and at the same time, sets a number of a frame where the third message is transmitted as a second start frame number. The first station and the second station each perform a modulo operation on a frame having the first or second start frame number and its succeeding frames using a positive integer for each frame, and detect a number of a frame where a result value of the modulo operation becomes zero (0). The first station and the second station simultaneously update CID lists of the first station and the second station at a frame having the detected frame number with regard to a CID of the added service flow. 
         [0021]    According to yet another aspect of the present invention, there is provided a system for synchronizing Connection IDentifiers (CIDs) in a communication system. The CID synchronization system includes a first station and a second station. The first station sends a first message for requesting deletion of a service flow identified by a CID to the second station, and at the same time, sets a number of a frame where the first message is transmitted as a first start frame number. The second station sends a second message which is a response message to the first message, and at the same time, sets a number of a frame where the second message is transmitted as a second start frame number. The first station and the second station each perform a modulo operation on a frame having the first or second start frame number and its succeeding frames using a positive integer for each frame, and detect a number of a frame where a result value of the modulo operation becomes zero (0). The first station and the second station simultaneously update CID lists of the first station and the second station at a frame having the detected frame number with regard to a CID of the deleted service flow. 
         [0022]    Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
           [0024]      FIGS. 1A to 1D  are diagrams illustrating a DSA/DSD procedure between an MS and a BS in a general communication system; 
           [0025]      FIG. 2  is a diagram illustrating an MS-initiated DSA procedure in a communication system according to a first embodiment of the present invention; 
           [0026]      FIG. 3  is a flowchart illustrating an MS-initiated DSA procedure for updating a CID list in a communication system according to the first embodiment of the present invention; 
           [0027]      FIG. 4  is a diagram illustrating a BS-initiated DSA procedure in a communication system according to a second embodiment of the present invention; 
           [0028]      FIG. 5  is a flowchart illustrating a BS-initiated DSA procedure for updating a CID list in a communication system according to a third embodiment of the present invention; 
           [0029]      FIG. 6  is a diagram illustrating an MS-initiated DSD procedure in a communication system according to the third embodiment of the present invention; 
           [0030]      FIG. 7  is a flowchart illustrating an MS-initiated DSD procedure for updating a CID list in a communication system according to the third embodiment of the present invention; 
           [0031]      FIG. 8  is a diagram illustrating a BS-initiated DSD procedure in a communication system according to a fourth embodiment of the present invention; and 
           [0032]      FIG. 9  is a flowchart illustrating a BS-initiated DSD procedure for updating a CID list in a communication system according to the fourth embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]      FIGS. 2 through 9 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged wireless communication system. 
         [0034]    Preferred embodiments of the present invention will now be described in detail with reference to the annexed drawings. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for clarity and conciseness. 
         [0035]    The present invention provides a system and method for CID synchronization between an MS and a BS. Further, the present invention provides a system and method for simultaneously updating CID lists of an MS and a BS. 
         [0036]      FIG. 2  is a diagram illustrating an MS-initiated DSA procedure in a communication system according to a first embodiment of the present invention. 
         [0037]    Referring to  FIG. 2 , in order to add a new service flow, an MS  201  sends to a BS  203  a DSA-REQ message including a service parameter for a service flow it will add (step  210 ). Upon receipt of the DSA-REQ message, the BS  203  sends a DSA-RVD message to the MS  201  (step  212 ), notifying that it has normally received the DSA-REQ message and is handling the received message. The BS  203  adds a CID caused by the service flow addition requested by the MS  201  (step  214 ), and then sends the result to the MS  201  through a DSA-RSP message (step  216 ). At the same time, the BS  203  sets a number of a frame where the DSA-RSP message is transmitted as a start frame number start_frame_number, and then starts a modulo operation (step  218 ). 
         [0038]    Meanwhile, upon receipt of the DSA-RSP message, the MS  201  sends to the BS  203  a DSA-ACK message for acknowledging receipt of the DSA-RSP message (step  220 ). At the same time, the MS  201  sets a number of a frame where the DSA-ACK message is transmitted, as a start frame number, and then starts a modulo operation (step  222 ). That is, the BS  203  and the MS  201  perform a modulo operation on every frame with a preset value N and detect a frame number of a frame where a result value of the modulo operation becomes  0 . Thereafter, if a length of a frame interval from the start frame number to the detected frame number exceeds a threshold, the BS  203  and the MS  201  simultaneously update their own CID lists at the frame corresponding to the detected frame number (step  224 ). 
         [0039]    However, if the length of the frame interval from the start frame number to the detected frame number is less than or equal to the threshold, the BS  203  and the MS  201  lack the time required for a CID list update and a round robin delay time. Therefore, if the length of the frame interval is greater than or equal to the threshold, the BS  203  and the MS  201  re-set the detected frame number as a start frame number and then perform a modulo operation. Thereafter, as described above, the BS  203  and the MS  201  detect a frame number of the frame where a result value of the modulo operation becomes 0, and simultaneously update their own CID lists at the frame corresponding to the detected frame number. 
         [0040]    If a CID-related operation (for example, an uplink bandwidth request of the MS  201 ) occurs after step  224  (step  228 ), the MS  201  and the BS  203  perform relevant operations using their updated CID lists. However, if an uplink bandwidth request of the MS  201  occurs before step  224  (step  226 ), the MS  201  and the BS  203  perform relevant operations using their non-updated CID lists (for the CID included in the non-updated CID lists) and perform relevant operations independently of the non-updated CID lists for the CID added by the service flow addition. 
         [0041]      FIG. 3  is a flowchart illustrating an MS-initiated DSA procedure for updating a CID list in a communication system according to the first embodiment of the present invention. 
         [0042]    Referring to  FIG. 3 , in step  301 , a BS receives from an MS a DSA-REQ message for requesting the addition of a new service flow. In step  303 , the BS adds a CID caused by the service flow addition requested by the MS. In step  305 , the BS sends a DSA-RSP message to the MS. In step  307 , the BS sets a number of the current frame, or a frame where the DSA-RSP message is transmitted, as a start frame number. 
         [0043]    In step  309 , the BS determines if a result value obtained by performing a modulo operation on a first frame having the set start frame number with a preset value N is 0, and if the result value obtained by performing a modulo operation on the first frame with the value N is not 0, the BS proceeds to a second frame or the next frame of the first frame (step  310 ), where it repeats step  309 . If a result value obtained by performing a modulo operation on the second frame with the value N is 0, the BS proceeds to step  311 . 
         [0044]    In step  311 , the BS determines if a length of a frame interval from the first frame to the second frame where the result value obtained by performing the modulo operation thereon is 0 exceeds a threshold, and if the length of the frame interval exceeds the threshold, the BS proceeds to step  313 . However, if the length of the frame interval is less than or equal to the threshold, the BS proceeds to step  317  where it re-sets a number of the second frame as a start frame number. Thereafter, the BS returns to step  309  where it repeats step  309  for the frame having the re-set start frame number. 
         [0045]    In step  313 , the BS determines if it has received a DSA-ACK message from an MS, and if a DSA-ACK message is received, the BS proceeds to step  315  where the MS and the BS simultaneously update their CID lists. However, if the BS does not receive a DSA-ACK message from the MS in step  313 , it proceeds to step  319 . 
         [0046]    In step  319 , the BS detects the number of times it has transmitted the DSA-RSP message, and determines if the number of DSA-RSP message transmissions exceeds the allowed number of DSA-RSP message retransmissions previously set in the system. If it is determined in step  319  that the number of times the BS has transmitted the DSA-RSP message exceeds the allowed number of DSA-RSP message retransmissions previously set in the system, the BS proceeds to step  321  where it performs a DSD process. However, if the number of times the BS has transmitted the DSA-RSP message is less than or equal to the allowed number of DSA-RSP message retransmissions previously set in the system, the BS proceeds to step  305 . 
         [0047]    In  FIG. 3 , an exemplary operation has been described in which a BS performs a modulo operation and detects a frame where the BS and the MS will simultaneously update their CID lists. However, in order for the BS and the MS to simultaneously update their CID lists, not only the BS but also the MS should perform a modulo operation and detect a frame where it will update its CID list. The MS&#39;s modulo operation is started at the time the MS sends the DSA-ACK message or a response to the DSA-RSP message received from the BS, and since an operation in which the MS performs a modulo operation and detects a frame where it will update its CID list is similar to the above-described operation in which the BS performs a modulo operation and detects a frame where it will update its CID list, a detailed description thereof will be omitted herein. 
         [0048]      FIG. 4  is a diagram illustrating a BS-initiated DSA procedure in a communication system according to a second embodiment of the present invention. 
         [0049]    Referring to  FIG. 4 , if a new CID is added (step  410 ), a BS  401  sends to an MS  403  a DSA-REQ message for requesting addition of a service flow for the added CID (step  412 ). After adding the CID caused by the service flow addition, the MS  403  sends the result to the BS  401  through a DSA-RSP message (step  414 ). At the same time, the MS  403  sets a number of a frame where the DSA-RSP message is transmitted as a start frame number, and then starts a modulo operation (step  415 ). 
         [0050]    Meanwhile, upon receipt of the DSA-RSP message, the BS  401  sends to the MS  403  a DSA-ACK message for acknowledging receipt of the DSA-RSP message (step  416 ). At the same time, the BS  401  sets a number of a frame where the DSA-ACK message is transmitted, as a start frame number, and then starts a modulo operation (step  418 ). That is, the BS  401  and the MS  403  perform a modulo operation on every frame with a preset value N and detect a frame number of a frame where a result value of the modulo operation becomes 0. Thereafter, if a length of a frame interval from the start frame number to the detected frame number exceeds a threshold, the BS  401  and the MS  403  simultaneously update their own CID lists at the frame corresponding to the detected frame number (step  422 ). 
         [0051]    However, if the length of the frame interval from the start frame number to the detected frame number is less than or equal to the threshold, the BS  401  and the MS  403  lack the time required for a CID list update and a round robin delay time. Therefore, if the length of the frame interval is less than or equal to the threshold, the BS  401  and the MS  403  re-set the detected frame number as a start frame number, and then perform a modulo operation. Thereafter, as described above, the BS  401  and the MS  403  detect a number of the frame where a result value of the modulo operation becomes 0, and simultaneously update their own CID lists at the frame corresponding to the detected frame number. 
         [0052]    If an uplink bandwidth request from the MS  403  occurs after step  422  (step  426 ), the MS  403  and the BS  401  perform relevant operations using their updated CID lists. However, if the uplink bandwidth request from the MS  403  occurs before step  422  (step  420 ), the MS  403  and the BS  401  perform relevant operations using the non-updated CID lists for the CID included in the non-updated CID lists, and perform relevant operations independently of the non-updated CID lists for the CID added by the service flow addition. 
         [0053]      FIG. 5  is a flowchart illustrating a BS-initiated DSA procedure for updating a CID list in a communication system according to a third embodiment of the present invention. 
         [0054]    Referring to  FIG. 5 , if a new CID is added, a BS sends to an MS a DSA-REQ message for requesting the addition of a service flow for the added CID in step  501 . In step  503 , the BS determines if it has received a DSA-RSP message from the MS, and upon receipt of the DSA-RSP message, the BS proceeds to step  505  where it sends to the MS a DSA-ACK message for acknowledging receipt of the DSA-RSP message. 
         [0055]    In step  507 , the BS sets a number of the current frame, or a frame where the DSA-ACK message is transmitted, as a start frame number. In step  509 , the BS determines if a result value obtained by performing a modulo operation on a first frame having the set start frame number with a preset value N is 0, and if the result value obtained by performing a modulo operation on the first frame with the value N is not 0, the BS proceeds to a second frame or the next frame of the first frame (step  515 ), where it performs step  509 . However, if the result value obtained by performing a modulo operation on the second frame with the value N is 0, the BS proceeds to step  511 . 
         [0056]    In step  511 , the BS determines if a length of a frame interval from the first frame to the second frame where the result value obtained by performing the modulo operation is 0 exceeds a threshold, and if the length of the frame interval is less than or equal to the threshold, the BS proceeds to step  517  where it re-sets a number of the second frame as a start frame number. Thereafter, the BS proceeds to step  509  where it performs step  509  for the frame having the re-set start frame number. 
         [0057]    However, if it is determined in step  511  that the length of the frame interval exceeds the threshold, the BS proceeds to step  513  where the MS and the BS simultaneously update their CID lists. 
         [0058]    In  FIG. 5 , an exemplary operation has been described in which a BS performs a modulo operation and detects a frame where the BS and the MS will simultaneously update their CID lists. However, in order for the BS and the MS to simultaneously update their CID lists, not only the BS but also the MS should perform a modulo operation and detect a frame where it will update its CID list. The MS&#39;s modulo operation is started at the time the MS sends the DSA-RSP message to the BS, and since an operation in which the MS performs a modulo operation and detects a frame where it will update its CID list is similar to the above-described operation in which the BS performs a modulo operation and detects a frame where it will update its CID list, a detailed description thereof will be omitted herein. 
         [0059]      FIG. 6  is a diagram illustrating an MS-initiated DSD procedure in a communication system according to the third embodiment of the present invention. 
         [0060]    Referring to  FIG. 6 , in order to delete an existing service flow, an MS  601  sends to a BS  603  a DSD-REQ message including an ID of a service flow that it will delete (step  610 ). The MS  601  sets a number of a frame where the DSD-REQ message is transmitted as a start frame number, and then starts a modulo operation (step  611 ). 
         [0061]    Meanwhile, the BS  603  deletes a CID as a result of the service flow deletion requested by the MS  601  (step  612 ), and then sends the result to the MS  601  through a DSD-RSP message (step  614 ). At the same time, the BS  603  sets a number of the frame where the DSD-RSP message is transmitted as a start frame number, and then starts a modulo operation (step  616 ). That is, the BS  603  and the MS  601  perform a modulo operation on every frame with a preset value N and detect a frame number of a frame where a result value of the modulo operation becomes 0. Thereafter, if a length of a frame interval from the start frame number to the detected frame number exceeds a threshold, the BS  603  and the MS  601  simultaneously update their own CID lists at the frame corresponding to the detected frame number (step  618 ). 
         [0062]    However, if the length of the frame interval from the start frame number to the detected frame number is less than or equal to the threshold, the BS  603  and the MS  601  lack the time required for a CID list update and a round robin delay time. Therefore, if the length of the frame interval is less than or equal to the threshold, the BS  603  and the MS  601  re-set the detected frame number as a start frame number, and then perform a modulo operation. Thereafter, as described above, the BS  603  and the MS  601  detect a frame number of the frame where a result value of the modulo operation becomes 0, and simultaneously update their own CID lists at the frame corresponding to the detected frame number. 
         [0063]    If an uplink bandwidth request of the MS  601  occurs after step  618  (step  622 ), the MS  601  and the BS  603  perform relevant operations using their updated CID lists. However, if the uplink bandwidth request occurs before step  618  (step  620 ), the MS  601  and the BS  603  perform relevant operations using their non-updated CID lists for the CID included in the non-updated CID lists, and perform relevant operations independently of the non-updated CID lists for the CID deleted by the service flow deletion. 
         [0064]      FIG. 7  is a flowchart illustrating an MS-initiated DSD procedure for updating a CID list in a communication system according to the third embodiment of the present invention. 
         [0065]    Referring to  FIG. 7 , in step  701 , a BS receives from an MS a DSD-REQ message including an ID of a service flow that it will delete from the existing service flow. In step  703 , the BS deletes a CID indicated by the service flow ID included in the DSD-REQ message. In step  705 , the BS sends a DSD-RSP message to the MS. In step  707 , the BS sets a number of the current frame, or a frame where the DSD-RSP message is transmitted, as a start frame number. 
         [0066]    In step  709 , the BS determines if a result value obtained by performing a modulo operation on a first frame having the set start frame number with a preset value N is 0, and if the result value obtained by performing a modulo operation on the first frame with the value N is not 0, the BS proceeds to a second frame or the next frame of the first frame (step  717 ), where it performs step  709 . However, if the result value obtained by performing a modulo operation on the second frame with the value N is 0, the BS proceeds to step  711 . 
         [0067]    In step  711 , the BS determines if a length of a frame interval from the first frame to the second frame where the result value obtained by performing the modulo operation is 0, exceeds a threshold, and if the length of the frame interval exceeds the threshold, the BS proceeds to step  713 . However, if the length of the frame interval is less than or equal to the threshold, the BS proceeds to step  719  where it re-sets a number of the second frame as a start frame number. Thereafter, the BS proceeds to step  709  where it performs step  709  for the frame having the re-set start frame number. 
         [0068]    In step  713 , the BS determines if it has received a DSD-REQ message retransmitted from the MS, and if a retransmitted DSD-REQ message is not received, the BS proceeds to step  715  where the MS and the BS simultaneously update their CID lists. However, upon receipt of the retransmitted DSD-REQ message, the BS proceeds to step  705  where it sends a DSD-RSP message. 
         [0069]    In  FIG. 7 , an exemplary operation has been described in which a BS performs a modulo operation and detects a frame where the BS and the MS will simultaneously update their CID lists. However, in order for the BS and the MS to simultaneously update their CID lists, not only the BS but also the MS should perform a modulo operation and detect a frame where it will update its CID list. The MS&#39;s modulo operation is started at the time the MS sends the DSD-REQ message to the BS, and since an operation in which the MS performs a modulo operation and detects a frame where it will update its CID list is similar to the above-described operation in which the BS performs a modulo operation and detects a frame where it will update its CID list, a detailed description thereof will be omitted herein. 
         [0070]      FIG. 8  is a diagram illustrating a BS-initiated DSD procedure in a communication system according to a fourth embodiment of the present invention. 
         [0071]    Referring to  FIG. 8 , if an existing CID is deleted (step  810 ), a BS  801  sends to an MS  803  a DSD-REQ message for requesting the deletion of a service flow for the deleted CID (step  812 ). At the same time, the BS  801  sets a number of a frame where the DSD-REQ message is transmitted, as a start frame number, and then starts a modulo operation (step  814 ). After deleting the CID as a result of the service flow deletion, the MS  803  sends the result to the BS  801  through a DSD-RSP message (step  816 ). At the same time, the MS  803  sets a number of the frame where the DSD-RSP message is transmitted, as a start frame number, and then starts a modulo operation (step  818 ). That is, the BS  801  and the MS  803  perform a modulo operation on every frame with a preset value N and detect a frame number of the frame where a result value of the modulo operation becomes 0. Thereafter, if a length of a frame interval from the start frame number to the detected frame number exceeds a threshold, the BS  801  and the MS  803  simultaneously update their own CID lists at the frame corresponding to the detected frame number (step  820 ). 
         [0072]    However, if the length of the frame interval from the start frame number to the detected frame number is less than or equal to the threshold, the BS  801  and the MS  803  lack the time required for a CID list update and a round robin delay time. Therefore, if the length of the frame interval is less than or equal to the threshold, the BS  801  and the MS  803  re-set the detected frame number as a start frame number, and then perform a modulo operation. Thereafter, as described above, the BS  801  and the MS  803  detect a frame number of the frame where a result value of the modulo operation becomes 0, and simultaneously update their own CID lists at the frame corresponding to the detected frame number. 
         [0073]    If an uplink bandwidth request of the MS  803  occurs after step  820  (step  824 ), the MS  803  and the BS  801  perform relevant operations using their updated CID lists. However, if the uplink bandwidth request of the MS  803  occurs before step  820  (step  822 ), the MS  803  and the BS  801  perform relevant operations using their non-updated CID lists for the CID included in the non-updated CID lists, and perform relevant operations independently of the non-updated CID lists for the CID deleted by the service flow deletion. 
         [0074]      FIG. 9  is a flowchart illustrating a BS-initiated DSD procedure for updating a CID list in a communication system according to the fourth embodiment of the present invention. 
         [0075]    Referring to  FIG. 9 , if an existing CID is deleted, a BS sends to an MS a DSD-REQ message for requesting the deletion of a service flow for the deleted CID in step  901 . In step  903 , the BS sets a number of the current frame, or a frame where the DSD-REQ message is transmitted, as a start frame number. 
         [0076]    In step  905 , the BS determines if a result value obtained by performing a modulo operation on a first frame having the set start frame number with a preset value N is 0, and if the result value obtained by performing a modulo operation on the first frame with the value N is not 0, the BS proceeds to a second frame or the next frame of the first frame (step  913 ), where it performs step  905 . However, if the result value obtained by performing a modulo operation on the second frame with the value N is 0, the BS proceeds to step  907 . 
         [0077]    In step  907 , the BS determines if a length of a frame interval from the first frame to the second frame where the result value obtained by performing the modulo operation is 0, exceeds a threshold, and if the length of the frame interval is less than or equal to the threshold, the BS proceeds to step  915  where it re-sets a number of the second frame as a start frame number. Thereafter, the BS proceeds to step  905  where it performs step  905  for the frame having the re-set start frame number. However, if it is determined in step  907  that the length of the frame interval exceeds the threshold, the BS proceeds to step  909 . 
         [0078]    In step  909 , the BS determines if it has received a DSD-RSP message from the MS, and upon receipt of a DSD-RSP message, the BS proceeds to step  911  where the MS and the BS simultaneously update their CID lists. However, upon failure to receive the DSD-RSP message, the BS proceeds to step  901  where it retransmits the DSD-REQ message. 
         [0079]    In  FIG. 9 , an exemplary operation has been described in which a BS performs a modulo operation and detects a frame where the BS and the MS will simultaneously update their CID lists. However, in order for the BS and the MS to simultaneously update their CID lists, not only the BS but also the MS should perform a modulo operation and detect a frame where it will update its CID list. The MS&#39;s modulo operation is started at the time the MS sends the DSD-RSP message to the BS, and since an operation in which the MS performs a modulo operation and detects a frame where it will update its CID list is similar to the above-described operation in which the BS performs a modulo operation and detects a frame where it will update its CID list, a detailed description thereof will be omitted herein. 
         [0080]    As is apparent from the foregoing description, for CID synchronization between an MS and a BS, the present invention performs a modulo operation on every frame and simultaneously updates CID lists of the MS and the BS according to a detected arbitrary period, thereby making it possible to immediately withdraw the unused CID(s) and allocate it to another service flow. As a result, it is possible to efficiently manage a limited number of CIDs. 
         [0081]    Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.