Abstract:
A method for managing a service flow of a mobile subscriber station (MSS) in a serving base station (BS) for a mobile communication system including the serving BS in communication with the MSS through a wireless access channel, and at least one active BS included in an active BS set of the MSS. Upon receiving a service flow management request from the MSS, the serving BS updates a service flow with the MSS, and transmits the updated service flow to the active BS using a predetermined message. Upon receiving a response message for the updated service flow from the active BS, the serving BS transmits service flow information of each active BS included in the response message to the MSS.

Description:
PRIORITY  
       [0001]     This application claims priority under 35 U.S.C. § 119 to an application entitled “Service Flow Management Method of Mobile Subscriber Station Having Active BS Set in a Mobile Broadband Wireless Access System” filed in the Korean Intellectual Property Office on Mar. 5, 2004 and assigned Serial No. 2004-15207, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a service flow offering method in a mobile communication system, and more particularly, to a method for changing service flow by a mobile subscriber station (MSS) or a base station (BS).  
         [0004]     2. Description of the Related Art  
         [0005]     Referring to FIGS.  1  to  3 , a procedure for changing an existing service flow in an IEEE 802.16e system according to the prior art is described.  
         [0006]     A service flow change procedure, that may include adding or deleting service, is a procedure defined between one MSS and one BS.  FIG. 1  illustrates a Dynamic Service Addition (DSA) procedure for adding a new service flow by an MSS  10 .  
         [0007]     Referring to  FIG. 1 , an MSS  10  transmits a Dynamic Service Addition Request (“DSA-REQ”) message with service parameters for a service flow to a BS  20  to add the corresponding service flow in step  11 . An exemplary format of the “DSA-REQ” message is illustrated in  FIG. 2 .  
         [0008]     Upon receiving the “DSA-REQ” message, the BS  20  transmits a DSx Received (“DSX-RVD”) message to the MSS  10  in step  12 , to inform the MSS  10  that it has received and is processing the “DSA-REQ” message. An exemplary format of the “DSX-RVD” message is illustrated in  FIG. 3 . The “DSX-RVD” message is a message that a BS transmits to an MSS in response to a Dynamic Service Addition (DSA) message, a Dynamic Service Change (DSC) message, and a Dynamic Service Deletion (DSD). After adding the service flow requested by the MSS  10 , the BS  20  transmits the result to the MSS  10  through a Dynamic Service Addition Response (“DSA-RSP”) message in step  13 .  
         [0009]     An exemplary format of the “DSA-RSP” message is illustrated in  FIG. 4 . The “DSA-RSP” message includes a confirmation code (CC) of the “DSA-REQ” message and parameters for the requested new service flow. The parameters are illustrated in  FIG. 5 .  
         [0010]     Unless all of the parameters requested in the “DSA-REQ” message are not satisfied, the “DSA-RSP” message includes failure fields called “Service Flow Error Set.” In step  14 , the MSS  10  transmits a Dynamic Service Addition Acknowledgement (“DSA-ACK”) message to the BS  20  to inform the BS  20  that it has received the “DSA-RSP” message. An exemplary format of the “DSA-ACK” message is illustrated in  FIG. 6 .  
         [0011]      FIG. 7  illustrates a Dynamic Service Change (DSC) procedure for changing an existing service flow, which may be used to change service parameters for an existing service flow.  
         [0012]     Referring to  FIG. 7 , an MSS  30  transmits service flow parameters with new traffic characteristics, or scheduling requirements of a service flow to be changed, to a BS  40  through a Dynamic Service Change Request (“DSC-REQ”) message in step  31 . An exemplary format of the “DSC-REQ” message is illustrated in  FIG. 8 .  
         [0013]     Upon receiving the “DSC-REQ” message, the BS  40  transmits a “DSX-RVD” message to the MSS  30  in step  32 , to inform the MSS  30  that it has received, and is processing the “DSC-REQ” message. After processing changes for the service flow requested in the “DSC-REQ”, the BS  40  transmits a Dynamic Service Change Response (“DSC-RSP”) message with a confirmation code, a Connection ID (CID) to be newly allocated, and a parameter, to the MSS  30  in step  33 . An exemplary format of the “DSC-RSP” message is illustrated in  FIG. 9 .  
         [0014]     Lastly, the MSS  30  transmits a Dynamic Service Change Acknowledgement (“DSC-ACK”) message to the BS  40  to inform the BS  40  that it has received the “DSC-RSP” message. An exemplary format of the DSC-ACK message is illustrated in  FIG. 10 .  
         [0015]      FIG. 11  is a signaling diagram illustrating a Dynamic Service Deletion (DSD) procedure for deleting an existing service flow of an MSS. Referring to  FIG. 11 , an MSS  50  transmits a Dynamic Service Deletion Request (“DSD-REQ”) message with a Service Flow ID to delete, to a BS  60  in step  51 . An exemplary format of the DSD-REQ message is illustrated in  FIG. 12 .  
         [0016]     In response, the BS  60  deletes the corresponding service flow, and transmits a Dynamic Service Deletion Response (“DSD-RSP”) message with a confirmation code and a deleted service flow ID to the MSS  50  in step  52 . An exemplary format of the DSD-RSP message is illustrated in  FIG. 13 .  
         [0017]     As described above, in the existing IEEE 802.16e system, because the MSS accesses only one serving BS (S-BS) service flow is only processed in the S-BS when the MSS changes service flow.  
         [0018]     Recently, an active BS set concept disclosed in Korean patent application No. 2004-15040, filed by the applicant, entitled “Method for Supporting Active BS Set for Improving Handover Performance in a Mobile Broadband Wireless Access System and Signaling Procedure therefor,” has been introduced.  
         [0019]     The active BS set refers to a set of BSs that are not required to perform the remaining procedures except for a ranging process upon handover of an MSS that includes providing the MSS with a wireless access channel for data transmission and reception via an S-BS.  
         [0020]     The ranging process is where an MSS performs timing correction and power correction with a BS. One MSS can have several service flows, and the service flow is a unit flow that is serviced with a specific Quality of Service (QoS) and is identified by a service flow identifier (SFID).  
         [0021]     Accordingly, there is a demand for technology in which all active BSs of an MSS can process a service flow requested by the MSS.  
       SUMMARY OF THE INVENTION  
       [0022]     It is, therefore, an object of the present invention to provide a method for enabling all active BSs of an MSS to process a service flow requested by the MSS.  
         [0023]     It is another object of the present invention to provide a method in which upon an MSS&#39;s processing request for a particular service flow, the MSS can perform only a ranging process and immediately access any active BS included in an active BS set in course of a network re-entry procedure, thereby enabling fast handover.  
         [0024]     It is further another object of the present invention to provide a method in which upon addition or any change of a particular service flow by two or more active BSs, the active BSs efficiently transmit service flow-related parameters to an MSS via an S-BS with duplicate information omitted.  
         [0025]     In accordance with one aspect of the present invention, there is provided a method for managing a service flow of a mobile subscriber station (MSS) in a serving base station (BS) for a mobile communication system including the serving BS in communication with the MSS through a wireless access channel, and at least one active BS included in an active BS set of the MSS. The method includes, upon receiving a service flow management request from the MSS, updating a service flow with the MSS; transmitting the updated service flow to the active BS using a predetermined message; and upon receiving a response message for the updated service flow from the active BS, transmitting service flow information of each active BS included in the response message to the MSS.  
         [0026]     In accordance with another aspect of the present invention, there is provided a method for managing a service flow in a mobile subscriber station (MSS) for a mobile communication system including the MSS in communication with a serving base station (BS) though a wireless access channel, and at least one active BS included in an active BS set of the MSS. The method includes, upon occurrence of a service flow management request, transmitting a predetermined service flow update message to the serving BS; and receiving a response to the service flow update message from the serving BS, and updating a service flow based on the received response.  
         [0027]     In accordance with further aspects of the present invention, there is provided a method for adding a service flow of a mobile subscriber station (MSS) in a serving base station (BS) for a mobile communication system including the serving BS in communication with the MSS through a wireless access channel, and at least one active BS included in an active BS set of the MSS. The method includes, upon receiving a service flow addition request from the MSS, adding a service flow identifier (ID); transmitting the added service flow ID to the active BS using a predetermined message; and upon receiving a response message with the added service flow ID from the active BS, allocating a new connection ID to the MSS.  
         [0028]     In accordance with still further other aspects of the present invention, there is provided a method for changing a service flow of a mobile subscriber station (MSS) in a serving base station (BS) for a mobile communication system including the serving BS in communication with the MSS through a wireless access channel, and at least one active BS included in an active BS set of the MSS. The method includes, upon receiving a service flow change request from the MSS, changing a service flow identifier (ID); transmitting the changed service flow ID to the active BS using a predetermined message; and upon receiving a response message with the changed service flow ID from the active BS, transmitting information on the changed service flow to the MSS.  
         [0029]     In accordance with yet still further other aspects of the present invention, there is provided a method for deleting a service flow of a mobile subscriber station (MSS) in a serving base station (BS) for a mobile communication system including the serving BS in communication with the MSS through a wireless access channel, and at least one active BS included in an active BS set of the MSS. The method includes, upon receiving a service flow deletion request from the MSS, deleting a service flow identifier (ID); transmitting the deleted service flow ID to the active BS using a predetermined message; and informing the MSS of deletion of a connection ID.  
         [0030]     In accordance with still further aspects of the present invention, there is provided a method for managing a service flow of a mobile subscriber station (MSS) in a serving base station (BS) for a mobile communication system including the serving BS in communication with the MSS through a wireless access channel, and at least one active BS included in an active BS set of the MSS. The method includes upon receiving a service flow management request from the MSS, allocating a connection identifier (ID) to the MSS according to the service flow; and transmitting to the MSS the allocated connection ID and a connection ID allocated to the MSS according to the service flow in the at least one active BS exclusive of the serving BS.  
         [0031]     In accordance with still further other aspects of the present invention, there is provided a method for managing a service flow in a mobile subscriber station (MSS) for a mobile communication system including a serving base station (BS) in communication with the MSS through a wireless access channel, and at least one active BS included in an active BS set of the MSS, with the exception of the serving BS. The method includes, upon occurrence of a service flow management request, transmitting a predetermined service flow update request message to the serving BS; and receiving a response message for the service flow update request message from the serving BS, and updating service flows of active BSs included in the active BS set. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]     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:  
         [0033]      FIG. 1  is a signaling diagram illustrating a dynamic service flow addition method in a mobile broadband wireless access system according to the prior art;  
         [0034]      FIG. 2  is diagram illustrating an example of a format of a DSA-REQ message;  
         [0035]      FIG. 3  is a diagram illustrating an example of a format of a DSX-RVD message;  
         [0036]      FIG. 4  is a diagram illustrating an example of a format of a DSA-RSP message;  
         [0037]      FIG. 5  is a diagram illustrating a format of Confirmation code;  
         [0038]      FIG. 6  is a diagram illustrating an example of a format of a DSA-ACK message;  
         [0039]      FIG. 7  is a signaling diagram illustrating a dynamic service flow change procedure in an IEEE 802.16/802.16e system according to the prior art;  
         [0040]      FIG. 8  is a diagram illustrating an example of a format of a DSC-REQ message;  
         [0041]      FIG. 9  is a diagram illustrating an example of a format of a DSC-RSP message;  
         [0042]      FIG. 10  is a diagram illustrating an example of a format of a DSC-ACK message;  
         [0043]      FIG. 11  is a signaling diagram illustrating a dynamic service flow deletion procedure in an IEEE 802.16/802.16e system according to the prior art;  
         [0044]      FIG. 12  is a diagram illustrating an example of a format for a DSD-REQ message;  
         [0045]      FIG. 13  is a diagram illustrating an example of a format of a DSD-RSP message;  
         [0046]      FIG. 14  is a signaling diagram illustrating a dynamic service flow addition procedure in an IEEE 802.16/802.16e system according to an embodiment of the present invention;  
         [0047]      FIG. 15  is a diagram illustrating an example of a format of an I-am-host-of message according to an embodiment of the present invention;  
         [0048]      FIG. 16  is a diagram illustrating an example of a format of an MSS-info-request message according to an embodiment of the present invention;  
         [0049]      FIG. 17  is a diagram illustrating an example of a format of an MSS-info-response message according to an embodiment of the present invention;  
         [0050]      FIG. 18  is a diagram illustrating an example of a format of an MSS-info-confirm message newly defined according to an embodiment of the present invention for service flow management in an active BS set;  
         [0051]      FIG. 19  is a diagram illustrating an example of a format of a DSA-RSP message modified in the present invention for service flow management in an active BS set;  
         [0052]      FIG. 20  is a signaling diagram illustrating a dynamic service flow addition procedure in an IEEE 802.16/802.16e system according to an alternative embodiment of the present invention;  
         [0053]      FIG. 21  is a signaling diagram illustrating a dynamic service flow change procedure in an IEEE 802.16/802.16e system according to a further alternative embodiment of the present invention;  
         [0054]      FIG. 22  is a diagram illustrating an example of a format of a DSC-RSP message modified in an embodiment of the present invention for service flow management in an active BS set;  
         [0055]      FIG. 23  is a signaling diagram illustrating a dynamic service flow change procedure in an IEEE 802.16/802.16e system according to another alternative embodiment of the present invention;  
         [0056]      FIG. 24  is a signaling diagram illustrating a dynamic service flow deletion procedure in an IEEE 802.16/802.16e system according to an embodiment of the present invention;  
         [0057]      FIG. 25  is a flowchart illustrating an operation of an MSS in the procedure of  FIG. 14  according to an embodiment of the present invention; and  
         [0058]      FIGS. 26A and 26B  are flowcharts illustrating an operation of an S-BS in the procedure of  FIG. 14  according to an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0059]     Several preferred embodiments of the present invention will now be described in detail with reference to the annexed drawings. In the drawings, the same or similar elements are denoted by the same reference numerals even though they are depicted in different drawings. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for conciseness.  
         [0060]     The present invention presents a function and procedure for simultaneously changing a service flow in all BSs included in an active BS set of an MSS, and a corresponding message format. The terms “addition,” “change,” and “deletion” of service as used herein refers to an “update” of service. “Active BS set” refers to a set of BSs not required to perform the procedures other than a ranging process for network re-entry and handover of an MSS, including a Serving BS (S-BS).  
         [0061]     The present invention includes a method for managing a service flow with the following procedures: 
        ( 1 ) a dynamic service flow addition procedure for an MSS with two or more active BSs in an IEEE 802.16e system,     ( 2 ) a dynamic service flow change procedure for an MSS with two or more active BSs in an IEEE 802.16e system, and     ( 3 ) a dynamic service flow deletion procedure for an MSS with two or more active BSs in an IEEE 802.16e system.        
 
         [0065]     A service flow management method for an MSS supporting an active BS set according to an embodiment of the present invention will now be described, focusing on the above-listed procedures.  
         [0066]      FIG. 14  is a signaling diagram in which an MSS having an active BS set including three active BSs adds a new service flow. Referring to  FIG. 14 , an MSS  100  with three active BSs  110 ,  120  and  130  transmits a “DSA-REQ” message to an S-BS  110  for addition of a new service flow in step  101 . The conventional message of  FIG. 2 , defined in IEEE 802.16REVd_D 3 - 2004 , may be used for the “DSA-REQ” message.  
         [0067]     The MSS  100  and the S-BS  110  know that the MSS  100  has three active BSs. In addition, the MSS  100  knows that the three active BSs include an S-BS  110 , a first active BS (A-BS 1 )  120  and a second active BS (A-BS 2 )  130 . Upon receiving the “DSA-REQ” message, the S-BS  110  transmits the “DSX-RVD” message of  FIG. 3  to the MSS  100  in step  102 , to inform the MSS  100  that it has received, and is processing, the “DSA-REQ” message.  
         [0068]     Thereafter, in step  103 , the S-BS  110  transmits an “I-am-host-of” message to the remaining active BSs of the A-BS 1   120  and the A-BS 2   130 , indicating that it is a host of the MSS  100 ,. An exemplary format of the “I-am-host-of” message is illustrated in  FIG. 15 .  
         [0069]     Referring to  FIG. 15 , the “I-am-host-of” message includes an MSS unique identifier to indicate that the MSS  100  is communicating with the S-BS  110 . Upon receipt of the “I-am-host-of” message from the S-BS  110 , the A-BS 1   120  and the A-BS 2   130  check the MSS unique identifier in the “I-am-host-of” message. Because the A-BS 1   120  and the A-BS 2   130  are active BSs of the MSS  100 , they individually transmit an MSS-info-request message to the S-BS  110  in step  104  to request information on the corresponding MSS  100 .  
         [0070]     An exemplary format of the “MSS-info-request message” is illustrated in  FIG. 16 . Referring to  FIG. 16 , the MSS-info-request message includes one or more MSS unique identifiers.  
         [0071]     Both of steps  103  and  104 , represented by dotted lines in  FIG. 14 , are optional and may be omitted. In this case, an “MSS-info-response” message transmitted in the next step  105  is transmitted without the MSS-info-request message.  
         [0072]     Upon receiving the “MSS-info-request” message, the S-BS  110  transmits an “MSS-info-response” message to the A-BS 1   120  and the A-BS 2   130 , which have transmitted the “MSS-info-request” message, in step  105 .  
         [0073]     An exemplary format of the MSS-info-response message is illustrated in  FIG. 17 . Referring to  FIG. 17 , the “MSS-info-response” message includes a service flow ID (“SFID”) allocated to the current MSS and TLV values of a general DSA-REQ message. PKM, SBC and REG information of the “MSS-info-response” message can be omitted. Herein, PKM information includes authentication-related information of an MSS, SBC information includes capability-related information of an MSS, and REG information includes MSS information such as MAC (Medium Access Control) version and vendor ID the “SFID” ensures the same SFID for each service flow when the MSS  100  is handed over to other active BSs, except the S-BS  110 . The active BSs have the same SFID and different connection IDs (CIDs) for their connections set up to the MSS.  
         [0074]     Upon receiving the “MSS-info-response” message, the A-BS  1   120  and the A-BS 2   130  check the number of network service information elements of the MSS and their corresponding TLV values, included in the MSS-info-response message. The TLV values refer to parameter values including Type, Length and Value. If the checked values are different from the values that the A-BS 1   120  and the A-BS 2   130  have for the MSS, the A-BS 1   120  and the A-BS 2   130  manage a service flow appropriate for the MSS  100 . In particular, where service flow is added as shown in  FIG. 14 , upon detecting an increase in number of network service information elements, the A-BS 1   120  and the A-BS 2   130  add one service flow for the MSS  100  based on the corresponding TLV values, and then transmits the result to the S-BS  110  using an “MSS-info-confirm” message in step  106 .  
         [0075]     An exemplary format of the “MSS-info-confirm message” is illustrated in  FIG. 18 . The “MSS-info-confirm message” is newly defined in the present invention and used to transmit the service flow processing result in the active BSs  120  and  130  to the S-BS  110 . The message may include confirmation codes and TLV values included in DSA-RSP, DSC-RSP and DSD-RSP messages.  
         [0076]     In  FIG. 14 , an active BS that cannot normally perform service flow addition by step  105  should be deleted from an active BS set of a corresponding MSS. Upon receiving the “MSS-info-confirm” message, the S-BS  110  transmits service flow information, such as SFID and CID added in the active BS to the MSS  100 , using a “DSA-RSP” message in step  107 . In this case, the “DSA-RSP” message includes information on both the A-BS 1   120  and the A-BS 2   130 .  
         [0077]     In a preferred embodiment of the present invention, an exemplary format of the “DSA-RSP message” is modified as shown in  FIG. 19 . Referring to  FIG. 19 , the “DSA-RSP” message includes service flow-related information from all active BSs. As a result, the message size can increase considerably in proportion to the number of active BSs. Where a dedicated channel for transmitting signaling information is not defined, and signaling messages are transmitted using a traffic channel—like the IEEE 802.16 system—if the size of a signaling message, such as the DSA-RSP message increases, it is difficult to transmit or receive messages in a stable manner and within an appropriate delay.  
         [0078]     To solve this problem, the present invention defines a Connection_settings field. The Connection_settings field reduces the size of a Connection_Info field for each active BS that should be transmitted to the MSS  100  in a DSA-RSP message when dynamic service flow addition is performed in the active BS set. This field includes different field values, excluding the same fields as Connection_Info allocated in the S-BS  110 —for example, SFID and Service Class Name—when Connection_Info of the remaining active BSs, except the S-BS  110 , is transmitted to the MSS  100 . In this manner, it is possible to omit or reduce the considerable number of Connection_Info fields in the remaining active BSs.  
         [0079]     Formats of the DSA-RSP/DSC-RSP messages using the Connection_settings field are based on the assumption that in a process of adding the same service flow for the same MSS, even though each active BS separately performs a service flow addition procedure, the Connection_Info should be substantially similar.  
         [0080]     The Connection_settings field is included in the DSA-RSP/DSC-RSP messages when an MSS having two or more active BSs transmits DSA-REQ/DSC-REQ messages, and can also be used when a new active BS is added to the active BS set.  
         [0081]     Finally, upon receiving the “DSA-RSP” message, the MSS  100  transmits a “DSA-ACK” message, like the one of  FIG. 6 , to the S-BS  110  in step  108 , completing MSS&#39;s service flow addition for all active BSs.  
         [0082]      FIG. 20  is a signaling diagram in which an MSS having an active BS set, including three active BSs, adds an existing service flow according to an embodiment of the present invention.  
         [0083]     One difference between the procedures illustrated in  FIGS. 20 and 14  is that the procedure illustrated in  FIG. 20  transmits a processing result of an S-BS  165  by a DSA-REQ message from an MSS  150  to the S-BS  165  in advance of processing results of the remaining active BSs in step  155 . This prevents delays caused when an MSS with two or more active BSs receives a DSA-RSP message in response to its DSA-REQ message, from exceeding the delay caused when an MSS having one S-BS receives a DSA-RSP message in response to its DSA-REQ message. In  FIG. 20 , “DSA-RSP” and “DSA-ACK” messages for the A-BS 1   170  and the A-BS 2   180  may be transmitted individually to the A-BS 1   170  and the A-BS 2   180 .  
         [0084]      FIG. 21  is a signaling diagram for changing an existing service flow according to an embodiment of the present invention when an MSS has a active BS set with three active BSs. The service flow change procedure of  FIG. 21  is similar to the service flow addition procedure of  FIG. 14  except that an MSS  200  transmits a “DSC-REQ” message with new traffic characteristics or scheduling requirements of a service flow to be changed, instead of the DSA-REQ message. And, in the next step, an S-BS  210  transmits processing results therefor in active BSs  210 ,  220  and  230  to the MSS  200  using the DSC-RSP message illustrated in  FIG. 22 .  
         [0085]      FIG. 23  is a signaling diagram for changing an existing service flow according to an alternative embodiment of the present invention. Because the procedure of  FIG. 23  is similar to  FIG. 20 , a detailed description thereof is omitted.  
         [0086]      FIG. 24  is a signaling diagram for deleting an existing service flow according to an embodiment of the present invention. Referring to  FIG. 24 , an MSS  300  having three active BSs  310 ,  320  and  330  transmits a “DSD-REQ” message to an S-BS  310  to delete an existing service flow in step  310 . The conventional message of  FIG. 12 , defined in IEEE 802.16REVd_D 3 -2004, may be used for the “DSD-REQ” message. The MSS  300  and the S-BS  310  know that the MSS  300  has three active BSs including an S-BS  310 , an A-BS 1   320  and an A-BS 2   330 .  
         [0087]     Upon receiving the “DSD-REQ” message, the S-BS  310  deletes the corresponding service flow and transmits a “DSD-RSP” message, like that of  FIG. 13 , to the MSS  300  in step  302 . Thereafter, in step  303 , the S-BS  310  transmits an “I-am-host-of” message, like that of  FIG. 15 , to the remaining active BSs of the A-BS  1   320  and the A-BS 2   330 . Upon receiving the “I-am-host-of” message from the S-BS  310 , the A-BS 1   320  and the A-BS 2   330  each check an MSS unique identifier in the “I-am-host-of” message, and transmit, in step  304 , an “MSS-info-request” message, like that of  FIG. 16 , to the S-BS  310  to request information on the corresponding MSS  300  as active BSs for the MSS  300 .  
         [0088]     Both steps  303  and  304 , represented by dotted lines in  FIG. 24 , are optional and may be omitted. Upon receiving the “MSS-info-request” message, the S-BS  310  transmits, in step  305 , an “MSS-info-response” message, like that of  FIG. 17 , to the A-BS 1   320  and the A-BS 2   330 . Upon receiving the “MSS-info-response” message, the A-BS 1   320  and the A-BS 2   330  each check the number of network service information elements of the MSS and their TLV values, included in the “MSS-info-response” message, and delete a corresponding service flow of the MSS  300  according to the checking results. Thereafter, in step  306 , the A-BS 1   320  and the A-BS 2   330  each transmit their processing results to the S-BS  310  using an “MSS-info-confirm” message, like that of FIG  18 .  
         [0089]     With reference to  FIGS. 25, 26A  and  26 B, a detailed description will now be made of operations of an MSS and an S-BS in a service flow addition method.  
         [0090]      FIG. 25  is a flowchart illustrating an operation of an MSS in the procedure of  FIG. 14  according to an embodiment of the present invention, and  FIGS. 26A and 26B  are flowcharts illustrating an operation of an S-BS in the procedure of  FIG. 14  according to an embodiment of the present invention. The flowcharts illustrated in  FIGS. 25, 26A  and  26 B include only the parts related to the gist of the present invention.  
         [0091]     Referring to  FIG. 25 , if a service flow addition request is generated in an MSS  100  in step  500 , the MSS  100  transmits a DSA-REQ message to an S-BS  110  in step  501 . The MSS  100  determines, in step  502 , whether the number of active BSs is two or larger. If the number of active BSs is two or larger, the MSS  100  drives a timer Txx in step  503 . If the number of active BSs is one, the MSS  100  drives a timer T 7  in step  504 . The MSS  100  drives a timer T 14  in step  505 , and stores the transmitted DSA-REQ message in preparation for retransmission in step  506 . In step  507 , the MSS  100  sets a DSA-REQ Retries value to a DSx Request Retries value.  
         [0092]     Thereafter, if the timers T 7 /Txx and the timer T 14  expire in steps  520  and  521 , respectively, the MSS  100  determines, in step  522 , whether retransmission is possible. If retransmission is not possible, the MSS  100  ends the Dynamic Service Addition operation in step  523 . However, if retransmission is possible, the MSS  100  stores a DSA-REQ message in step  524 , and drives the timers T 7 /Txx in step  525 .  
         [0093]     Thereafter, the MSS  100  decreases the DSA-REQ Retries value in step  526 . If the MSS  100  receives a DSA-RSP message from the S-BS in step  530 , the MSS  100  stops the timers T 7 /Txx in step  531 , and transmits a DSA-ACK message to the S-BS in step  532 , completing the DSA procedure. If the MSS  100  receives a DSX-RVD message from the S-BS in step  540 , the MSS  100  stops the timer T 14  in step  541 , and waits for a DSA-RSP message.  
         [0094]     Referring to  FIGS. 26A and 26B , if an S-BS  110  receives a DSA-REQ message from an MSS  100  in step  600 , the S-BS  110  transmits a DSX-RVD message to the MSS  100  in step  601 . The S-BS  110  determines, in step  602 , whether service flow addition for the MSS  100  has been completed. If the service flow addition for the MSS  100  has not been completed, the S-BS  110  sets the result in a Confirmation Code (CC) in step  603 . The Confirmation Code represents a processing success (CC=‘0’) of the service flow or a processing failure (CC=‘1’) of the service flow. However, if it is determined, in step  602 , that the service flow addition for the MSS  100  has been completed, the S-BS  110  generates an uplink service flow in step  604 . Herein, the uplink service flow refers to a service flow from the MSS  100  to the S-BS  110 , and pairs with a downlink service flow from the S-BS  110  to the MSS  100 .  
         [0095]     The S-BS  110  determines, in step  605 , whether the number of active BSs for the MSS  100  is two or larger. If the number of active BSs for the MSS  100  is two or larger, the S-BS  110  transmits an I-am-host-of message to the remaining active BSs  120  and  130 , except the S-BS  110  itself, in step  606 . In step  607 , the S-BS  110  receives an MSS-info-request response message for generation of a service flow for the MSS  100  from the active BSs  120  and  130  in step  607 . In step  609 , the S-BS  110  transmits an MSS-info-response message with information on the MSS  100  to the active BSs  120  and  130 .  
         [0096]     In step  610 , the S-BS  110  receives MSS-info-confirm messages from the active BSs  120  and  130 . After step  610 , or if it is determined in step  605  that the number of active BSs is not larger than 2, the S-BS  110  proceeds to step  612 .  
         [0097]     The S-BS  110  generates a DSA-RSP message in step  612 , and transmits the DSA-RSP message to the MSS  100  in step  613 . Thereafter, the S-BS  110  drives a timer T 8  in step  614 .  
         [0098]     The S-BS  110  stores the DSA-RSP message in preparation for retransmission in step  615 , and sets a DSA-REQ Retries value to a DSx Request Retries value in step  616 . Thereafter, if the timer T 8  expires in step  620 , the S-BS  110  determines, in step  621 , whether retransmission is possible. If it is, the S-BS  110  retransmits the stored DSA-RSP message in step  623 , and re-drives the timer T 8  in step  624 . In step  625 , the S-BS  110  decreases a DSA-RSP Retries value and waits for a DSA-ACK message. If the S-BS  110  receives the DSA-ACK message in step  630 , the S-BS  110  stops the timer T 8  in step  631 . Thereafter, the S-BS  110  determines in step  632  whether service flow addition is possible. If service flow addition is possible, the S-BS  110  generates a downlink service flow in step  633 , and completes the service flow addition procedure in step  634 . However, if service flow addition is not possible, the S-BS  110  disables the service flow in step  635 .  
         [0099]     As described above, the present invention proposes a service flow update scheme, that includes addition and deletion of service, between an MSS and a BS in an IEEE 802.16e system in which an active BS set is used. With the use of the new service flow management scheme, an MSS having two or more active BSs can collectively update a service flow for the active BSs. In addition, a Connection_settings field defined in the present invention is used for service flow-related parameters to be transmitted to an MSS due to change of a particular service flow in a plurality of active BSs, thereby preventing transmission of duplicate information and increasing transmission efficiency.  
         [0100]     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.