Patent Publication Number: US-2007116004-A1

Title: Method and apparatus for guaranteeing QoS using end-to-end CAC in internet service network

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims priority to and the benefit of Korean Patent Application No. 2005-111792, filed Nov. 22, 2005, the disclosure of which is incorporated herein by reference in its entirety.  
     BACKGROUND  
      1. Field of the Invention  
      The present invention relates to a method and apparatus for guaranteeing quality of service (QoS) using end-to-end call admission control (CAC) in an Internet service network, and more particularly, to a method and apparatus for guaranteeing QoS of Internet service using end-to-end CAC in an IP network having a structure for guaranteeing QoS by resource reservation.  
      2. Discussion of Related Art  
      An existing Internet service is provided in the form of a best effort type service whose quality depends on a network status regardless of quality requirement for corresponding service. However, in a next generation network (NGN), a premium level service which consistently guarantees a quality of each service is suggested.  
      The premium level service requires a certain amount of resources (i.e., guaranteed rate), and in order to guarantee QoS for the resources, the network should perform a call admission control (CAC) procedure which finds resources which can satisfy QoS requirement of each service, reserves the resources, and then admits a service request.  
      However, a conventional QoS guaranteeing method performs a CAC procedure by calculating an available resource in a network domain and comparing it with a requested resource. That is, only network domain CAC is considered, and a bandwidth resource of a subscriber line domain which is an environment in which a user accesses the network is not considered, and thus there is a problem in a service admission control and resource management method for end-to-end QoS. The conventional QoS guaranteeing method will be described in detail with reference to  FIG. 1 .  
       FIG. 1  is a schematic diagram illustrating a range of subscriber domain CAC, network domain CAC, and end-to-end CAC.  
      The CAC is a concept for allowing the network to admit a call or a service only when a resource capable of guaranteeing QoS of each service can be assigned. Many CAC procedures and resource reservation methods for guaranteeing QoS have been suggested.  
      However, as shown in  FIG. 1 , the conventional QoS guaranteeing method considers only a network domain  12  of an access node—a core nodes—an access node but does not consider a subscriber domain  11 . That is, since the CAC procedure is performed only in a domain after the access node but is not performed in the subscriber domain, it is impossible to guarantee QoS only with the CAC which considers only the network domain in the service admission control and resource management method for QoS.  
      That is, in order to guarantee end-to-end QoS, it is necessary to first check whether a network access means of a service user can accommodate a bandwidth demand of a newly requested service or not. However, if a service is admitted since a network resource is enough even though a line bandwidth of a user side is not enough, it is impossible to guarantee QoS. Thus, there is a need for a CAC technique which considers an end-to-end domain  13  between user terminals in order to guarantee end-to-end QoS.  
     SUMMARY OF THE INVENTION  
      The present invention is directed to a method and apparatus for guaranteeing end-to-end QoS for a guaranteed rate service having constant-level bandwidth requirement in a QoS-guaranteeing network by performing subscriber domain CAC based on an available bandwidth of a subscriber line domain and then performing network domain CAC for determining whether a resource of a network domain is available or not, that is, by performing a resource reservation procedure according to a service request and a resource release procedure according to service termination through end-to-end CAC which incorporates both the subscriber domain CAC and the network domain CAC.  
      One aspect of the present invention is to provide a method for guaranteeing end-to-end CAC in an Internet service network, the method comprising: (a) performing a subscriber domain CAC by querying a subscriber DB to determine whether to admit a call based on available bandwidth information of a subscriber when a subscriber terminal requests resource reservation; (b) performing a network domain CAC by querying a resource DB based on a result of the subscriber domain CAC to determine whether a resource required for service can be reserved or not; and (c) updating reserved bandwidth information and available bandwidth information of a subscriber domain in the subscriber DB and resource use information of a network domain in the resource DB when the resource reservation is completed through the steps (a) and (b).  
      Preferably, the method may further include the steps of: obtaining circuit ID information of a subscriber using a dynamic host configuration protocol (DHCP) packet; and recording and managing information about previously-reserved bandwidth and available bandwidth for the subscriber in the subscriber DB based on the obtained circuit ID information.  
      Preferably, the method may further include the steps of: when the subscriber terminal requests resource release, releasing the resource through network setting in response to the resource release request; and updating reserved bandwidth information and available bandwidth information in the subscriber DB and resource use information in the resource DB as the resource is released.  
      Preferably, the method may further comprise: a step of, when resource reservation is requested in a state that a caller and a callee are connected to the same network or different networks, perceiving a status of the callee to transmit a communicable service protocol in response to the caller&#39;s service request; performing a subscriber domain CAC by querying the subscriber DB for each of a caller side and a callee side to determine whether to admit a call based on available bandwidth information of the caller and callee; and performing a network domain CAC by querying the resource DB for each of the caller and callee sides based on the subscriber domain CAC result to determine whether a resource required for service can be reserved.  
      Preferably, the method may further include a step of, when the resource reservation is completed by the subscriber domain CAC and the network domain CAC, updating reserved bandwidth information and available bandwidth information of each of the caller and callee in the subscriber DB and resource use information in the resource DB  
      Preferably, the method may further include the steps of: when resource release is requested in a state that the caller and callee are connected to the same network or different networks, releasing the resource through network setting in response to the resource release request; and updating reserved bandwidth information and available bandwidth information of each of the caller and callee in the subscriber DB and resource use information in the resource DB as the resource is released.  
      Another aspect of the present invention is to provide an apparatus for guaranteeing QoS using end-to-end CAC in an Internet service network, comprising: a service control function for performing subscriber domain CAC which queries a subscriber DB to determine whether to admit a call based on available bandwidth information of a subscriber when resource reservation is requested; and a network control function for performing network domain CAC which queries a resource DB according to the call admission determination result of the service control function to determine whether a resource required for service can be reserved or not, wherein the service control function updates reserved bandwidth information and available bandwidth information of a subscriber in the subscriber DB, and the network control function updates resource use information in the resource DB when the resource reservation is completed.  
      Preferably, the subscriber DB may include fields for subscriber ID information, circuit ID information, IP address information, contracted bandwidth information of a subscriber line, reserved bandwidth information of the scriber line, and available bandwidth information of the subscriber line. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail preferred embodiments thereof with reference to the attached drawings in which:  
       FIG. 1  is a schematic diagram illustrating a range of subscriber domain CAC, network domain CAC, and end-to-end CAC;  
       FIG. 2  is a schematic diagram illustrating an end-to-end CAC procedure when a user requests resource reservation according to an embodiment of the present invention;  
       FIG. 3  is a flowchart illustrating a procedure for obtaining circuit ID information according to the present invention;  
       FIG. 4  shows a subscriber DB having an improved structure according to the present invention;  
       FIG. 5  is a flowchart illustrating an end-to-end CAC procedure when a user requests resource reservation according to the present invention;  
       FIG. 6  is a flowchart illustrating end-to-end CAC when the service reservation is requested in a state that a caller and a callee are connected to the same network;  
       FIG. 7  is a flowchart illustrating an end-to-end CAC procedure when the resource reservation is requested in a state that the caller and callee are connected to different networks;  
       FIG. 8  is a flowchart illustrating an end-to-end resource release procedure when a user requests resource release according to the present invention;  
       FIG. 9  is a flowchart illustrating an end-to-end resource release procedure when the resource release is requested in a state that the caller and the callee are connected to the same network; and  
       FIG. 10  is a flowchart illustrating an end-to-end resource release procedure when the resource release is requested in a state that the caller and the callee are connected to different networks. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      Hereinafter, an exemplary embodiment of the present invention will be described in detail. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various types. Therefore, the present embodiment is provided for complete disclosure of the present invention and to fully inform the scope of the present invention to those ordinarily skilled in the art.  
       FIG. 2  is a schematic diagram illustrating an end-to-end CAC procedure when a user requests resource reservation according to an embodiment of the present invention.  
      As shown in  FIG. 2 , the present invention can be applied to a QoS guaranteeing network which includes a user terminal  210  such as a DSL modem or a cable modem, a primary aggregation device  220  such as digital subscriber line access multiplexer (DSLAM) or cable modem termination system (CMTS), a subscriber line  230  for connecting the subscriber terminal  210  to the primary aggregation device  220 , a service control function  240  for performing functions related to a service, a service level agreement (SLA) and a subscriber-related policy, a network control function  250  for controlling network resources, a call agent (CA)  260  for receiving a service request from a user and relaying it for an IP communication service between users, and an IP network  270  having a function for reserving a network resource for a guaranteed rate service which requires a certain bandwidth in advance to thereby guarantee QoS.  
      The service control function  240  preferably includes a policy server  241  for performing a subscriber-related policy function, an authentication server  242  for performing user authentication, a dynamic host configuration protocol (DHCP) server  243  for allocating an IP address, and a subscriber DB  244  for managing subscriber-related information. The network control function  250  preferably includes a CAC server  251  and a resource DB  252  for managing network resources.  
      In the QoS guaranteeing network of  FIG. 2 , in order to guarantee an end-to-end QoS, an end-to-end CAC concept which considers both the subscriber domain CAC and the network domain CAC is introduced. The network domain CAC may be performed by the same method as the convention CAC procedure, but a new CAC procedure for the subscriber domain CAC is needed.  
      That is, a call should be admitted only when a resource can be reserved in order to guarantee the end-to-end QoS. To this end, it is necessary to manage information about a previously-reserved (i.e., allocated) bandwidth and an available bandwidth which can be additionally reserved (i.e., allocated) in a subscriber access line unit.  
      To this end, a bandwidth resource of an end user is managed by the subscriber DB  244  in which a circuit ID for identifying the subscriber line  230  which is a network access means of a user and an IP address of a service user are bound together to be stored. The circuit ID and the subscriber DB will be described later with reference to  FIGS. 3 and 4  and thus are briefly described below.  
      The circuit ID is an identifier unique to the subscriber line  230 , which connects the subscriber terminal  210  such as the DSL modem or the cable modem to the primary aggregation device  220  such as DSLAM or CMTS. In the present invention, the subscriber line is substantially identical to an access line of the user. Preferably, the circuit ID unique to each subscriber line is allocated when the user subscribes to the network operator for the first time.  
      The unique circuit ID information allocated to the subscriber line is obtained when the user first connects an IP terminal to the network  270  to be allocated an IP from the DHCP server  243 . A MAC address of the user terminal and the circuit ID information are transmitted together in the procedure that the user terminal requests allocation of the IP address, and the policy server  241  binds the allocated IP address with the circuit ID to record them in the subscriber DB  244 .  
      The circuit ID and the subscriber ID are bound in the authentication procedure performed by the authentication server  242 , and the bound information is recorded in the subscriber DB  244 . The supplemental information necessary for the present invention can be managed by a separate storage, while the existing subscriber DB is maintained as it is. However, it is assumed that the supplemental information is managed by the subscriber. DB having an improved structure for description convenience.  
      Meanwhile, when CA  260  receives a service request from the service user  210  (S 201 ), the CA  260  finds the other communication party and the requested service standard and requests resource reservation to the network control function  250  (S 202 ). The network control function  250  performs subscriber domain CAC for checking whether the subscriber side has an available bandwidth (S 203  and S 204 ) and then performs network domain CAC for checking whether a resource can be allocated in the network, in order to inform the user of whether to admit a call (S 205  to S 207 ). The procedure briefly described above will be described below in detail.  
      First, when requesting resource reservation to the network control function  250  (S 202 ), the CA  260  transmits an IP address of a caller, an IP address of a callee, and QoS information to the network control function  250 . The network control function  250  performs the subscriber domain CAC (S 203  and S 204 ), which queries to the service control function  240  whether the subscriber side has an available bandwidth based on the information transmitted from the CA  260  and receives a response thereto.  
      Here, in the step S 203  in which the network control function  250  requests the subscriber domain CAC to the service control function  240 , the network control function  250  should send the IP information of the caller and requested bandwidth information of a corresponding service to the service control function  240 , and the service control function  240  determines whether to admit a call by referring to the subscriber DB  244  in response to the subscriber domain CAC query from the network control function  250 . The requested bandwidth of the service is compared to the available bandwidth in the subscriber DB  244 , and the call is admitted when the available bandwidth is greater than the requested bandwidth of the service. A determination result as to whether to admit a call is transmitted to the network control function  250  (S 204 ).  
      Next, the network control function  250  queries the resource DB  252  through the CAC server  251  to check whether a resource of the network side can be reserved or not, and it performs the network domain CAC for reserving the resource when a resource of the network side can be reserved (S 205 ).  
      The network control function  250  transmits a determination result as to whether to admit a call (whether the resource can be reserved) to the CA  260  to thereby inform the user of whether to admit a call (S 206  and S 207 ).  
      In order to guarantee the end-to-end QoS, it is necessary to first check whether the network access means of the service user can accommodate the bandwidth demand of a newly requested service or not. The present invention first performs the subscriber domain CAC based on the available bandwidth of the subscriber domain and then performs the network domain CAC which determines whether the resource of the network domain can be reserved or not. The service is provided to the user when the resource for satisfying the QoS demand can be allocated, thereby guaranteeing the end-to-end QoS as to the guaranteed-rate service.  
      Thus, the resource reservation responsive to the service request is performed through the end-to-end CAC procedure which incorporates both the subscriber domain CAC and the network domain CAC, thereby guaranteeing the end-to-end QoS.  
      Meanwhile, a determination is made as to whether the user terminal can accommodate the bandwidth demand for the service based on the information about the subscriber line  230 , which is the network access means of the user, i.e., the circuit ID information. This determination is used to manage the bandwidth resource of the end user. The method for obtaining the circuit ID will be now described with reference to  FIG. 3 .  
       FIG. 3  is a flowchart illustrating a procedure for obtaining the circuit ID information according to the present invention. In particular,  FIG. 3  shows a method for obtaining the circuit ID information in the authentication and IP allocation procedures.  
      In  FIG. 3 , it is assumed that the circuit ID information is obtained when the IP address allocation is performed and then the subscriber authentication is performed. The method of obtaining and managing the circuit ID information is the same except for an execution order even when the subscriber authentication is performed and then the IP allocation is performed. Typically, the network operator allocates the subscriber ID unique to the subscriber line and manages the information about a physical location and line characteristics of the subscriber line together with the subscriber-related information.  
      In order to implement the present invention, the subscriber number (i.e., subscriber ID) unique to each subscriber line is allocated and is managed together with a contracted speed of each subscriber line. For example, a subscriber number is unique to the subscriber, and so it can be used as the circuit ID as it is.  
      Referring to  FIG. 3 , when the user turns on the user terminal to access the network, the DHCP client, i.e., the user terminal  210  transmits a DHCPDISCOVER message containing the MAC address (S 30 ), and the primary aggregation device  220  adds the circuit ID information to the DHCPDISCOVER message and transmits the DHCPDISCOVER message containing the MAC address and the circuit ID information to the DHCP server  243  (S 31 ).  
      That is, in the conventional network, the user transmits the MAC address to the DHCP server through the DHCP packet to get the IP address, but in the present invention, the circuit ID information is added to the DHCP packet together with the MAC address and then transmitted to the DHCP server  243 .  
      Adding the MAC address and the circuit ID information to the DHCP packet is performed by inserting the circuit ID information into a client identifier which can be defined by an option field of the DHCP message, and this can be applied to the IPv4 and the IPv6.  
      The function for inserting the circuit ID information into the DHCP packet may belong to the user terminal  210  or the primary aggregation device  220 . However, the user terminal  210  does not always access the same subscriber line due to the user mobility. Since the primary aggregation device  220  knows all of the subscriber lines, i.e., physical ports connected to itself and thus can identify the DHCP packet transmitted through each port to insert the circuit ID information into the DHCP packet, it is preferred that the primary aggregation device  220  has the function for adding the circuit ID information to the DHCP packet.  
      Thereafter, the DHCP server  243  selects an appropriate IP address to respond with a DHCPOFFER message (S 32 ), and the user terminal  210  confirms the IP address provided through the DCHPREQUEST (S 33 ). The DHCP server  243  then transmits a DHCPACK message to confirm that allocation of the IP address has been completed (S 34 ).  
      Meanwhile, the policy server  241  receives the allocated IP address and corresponding circuit ID information from the DHCP server  243 , binds them together and temporarily stores them in a memory (S 35  to S 36 ). When the subscriber having the allocated the IP address sends the subscriber ID and the password to the policy server  241  for network authentication (S 37 ), the policy server  241  retrieves the corresponding circuit ID information from the subscriber DB  244  to authenticate the subscriber terminal (S 38 ), binds the circuit ID, the subscriber ID and the IP address together and records them in the subscriber DB  244  (S 39 ).  
      By obtaining the information about the physical subscriber line of the service user through the circuit ID obtaining and binding procedures as described above, i.e., by obtaining the circuit ID information, it is possible to recognize whether the user terminal can accommodate the bandwidth demand for the service, whereby the subscriber domain CAC is ready to be performed.  
      While this embodiment has been described as performing the IP address allocation prior to the authentication, the authentication may be first performed and then the IP address may be allocated to only the authenticated subscribers. In such case, the subscriber ID information is obtained and then the circuit ID information and the IP address information are obtained during the IP address allocation. There is only a difference in a binding order with the circuit ID information. That is, the present invention can be applied to both cases, and the order of performing the authentication and the IP address allocation may depend on a policy of the network operator.  
      The typical subscriber DB includes a subscriber ID field, a password field, an IP address field, and so on. The subscriber DB  244  of the present invention is configured to manage information of pre-reserved bandwidth and available bandwidth that can be further reserved, in a unit of the subscriber line, in order to guarantee the end-to-end QoS. A configuration of the subscriber DB  244  according to the present invention will be described below with reference to  FIG. 4 .  
       FIG. 4  shows the subscriber DB having an improved structure according to the present invention. Fields for the circuit ID and the bandwidth use information of each user may be added to the typical subscriber DB.  
      As shown in  FIG. 4 , the subscriber DB  244  of the present invention includes a subscriber ID field (User_ID)  41 , a password field (PW)  42 , and an IP address field (IP)  44  and further includes a circuit ID field  43 , which is an identifier of the access line, a contracted bandwidth (Cont&#39;d BW) field  45 , a reserved bandwidth (Rsrv&#39;d BW) field  46 , and an available bandwidth (Avail. BW) field  47 , which are newly added.  
      That is, the circuit ID field  43 , which is an identifier of the access line, and fields  45  to  47  for the contracted bandwidth, the reserved bandwidth field  46 , and the available bandwidth, which are bandwidth use specification of a service user using the corresponding subscriber line, are newly added to the subscriber DB  244  to guarantee a QoS. The bandwidth use specification is modified in real time whenever each user newly uses or terminates a service, and thus, the information about the reserved bandwidth and the available bandwidth can be managed in a unit of the user access line, thereby guaranteeing the end-to-end QoS.  
       FIG. 5  is a flowchart illustrating an end-to-end CAC procedure according to the present invention, when the user requests resource reservation. In particular,  FIG. 5  shows the end-to-end CAC procedure when the resource reservation is requested, after the IP allocation and user authentication procedures have been performed and the information about the bandwidth use of each user has been recorded in the subscriber DB  244  based on the circuit ID.  
      First, when an authenticated service user requests a service requiring a certain bandwidth to the CA  260  (S 51 ), the CA  260  requests the network control function  250  to perform CAC (S 52 ).  
      The network control function  250  performs the two-step CAC. In a first CAC step, which is the subscriber domain CAC step, the network control function  250  queries to the service control function  240  whether there is an available bandwidth to accommodate the service (S 53 ), and the service control function  240  determines whether there is an available bandwidth for the requested service and notifies the network control function  250  of the determination result (S 54 ).  
      When it is determined in step S 54  that there is no available bandwidth, the network control function  250  transmits a call rejection message to the CA  260 , and the CA  260  transmits the call rejection message to the service user (S 55 ).  
      When it is determined in step S 54  that there is an available bandwidth, the network control function  250  calculates a path required by the service to perform a second CAC step, which is the network domain CAC step, queries the resource DB  252  to check whether there is an available resource on the path (S 56 ), and determines whether the resource required for the service can be reserved (S 57 ).  
      When it is determined in step S 57  that the resource reservation is possible, the network control function  250  reserves the resource through a network setting process and sends a call admission message to the CA  260  so that the call admission message is delivered to the user (S 58 ).  
      When it is determined in step S 57  that the resource reservation is impossible, i.e., when resource reservation fails, the network control function  250  transmits the call rejection message to the CA  260  so that the call rejection message is delivered to the service user (S 55 ).  
      While the method for guaranteeing QoS of the service required by a user through the end-to-end CAC when a single user terminal connected to the network requests the resource has been described, the method for guaranteeing QoS of a service required by users connected to different networks through the end-to-end CAC will be now described.  
       FIG. 6  is a flowchart illustrating end-to-end CAC when the resource reservation is requested in a state that a caller and a callee access the same network. In  FIG. 6 , a service user_A  610   a  is a caller, a service user_B  610   b  is a callee, and the service user_A  610   a  and user_B  610   b  are managed by different CAs.  
      First, the caller  610   a  requests a service to a CA_A  660   a  (S 601 ), and the CA_A  660   a  perceives a location of the callee and transmits the service request to a called CA_B  660   b  to initiate service negotiation (S 602 ). The CA_B  660   b  perceives a status of the callee  610   b  (S 603  and S 604 ) and transmits a communicable service protocol to the CA_A  660   a  (S 605 ).  
      The CA_A  660   a  determines the bandwidth required for the service based on the negotiated service protocol to request the network control function  650  to perform the CAC (S 606 ), and the network control function  650  queries the subscriber domain CAC to the service control function  640  and receives the response thereto (S 607  and S 608 ).  
      At this time, the service control function  640  should simultaneously perform the subscriber domain CAC for the caller side and the callee side by querying an available bandwidth of the caller side based on the IP address of the caller and querying an available bandwidth of the callee side based on the IP address of the callee.  
      The network control function  650  performs the network domain CAC and performs the resource reservation when the call admission is possible (S 609 ), and notifies the CA_A  660   a  of the call admission result to transmit the call admission message to the caller (S 610  and S 611 ).  
      When the CA_A  660   a  transmits the call admission message to the caller (S 611 ), the service is connected between the two users (S 612 ), and the service control function  640  and the network control function  650  update information in the subscriber DB  644  and the resource DB  652  as the call admission is performed.  
       FIG. 7  is a flowchart illustrating end-to-end CAC when the resource reservation is requested in a state that the caller and the callee are connected to different networks. In  FIG. 7 , a service user A  710   a  is a caller, and a service user B  710   b  is a callee.  
      As shown in  FIG. 7 , when the caller and the callee are connected to different networks, respectively, the service negotiation between a CA_A  760   a  and a CA_B  760   b  is performed through the same process as in  FIG. 6  (S 701  to S 704 ). But, unlike  FIG. 6 , the CA_B  760   b  first requests a network control function  750   b  at the callee side to perform the CAC (S 705 ), and thus the network control function  750   b  at the callee side performs the subscriber domain CAC and the network domain CAC to determine whether to admit the call (S 706  to S 708 ).  
      Then, the network control function  750   b  at the callee side transmits a determination result as to whether to admit the call to the CA_B  760   b  at the callee side (S 709 ), and when the call is admitted, the CA_B  706   b  at the callee side notifies the CA_A  760   a  at the caller side of the service negotiation result (S 710 ).  
      Meanwhile, the calling CA_A  760   a  requests a network control function  750   a  at the caller side to perform the CAC based on the negotiated service protocol (S 711 ), and the network control function  750   a  at the caller side performs the subscriber domain CAC and the network domain CAC for the caller side (S 712  to S 714 ) and notifies the CA_A  760   a  at the caller side of the call admission result when the call is admitted (S 715 ). Thus, the call admission message is delivered to the caller (S 716 ), connecting the service between the two users (S 717 ).  
      Similarly to  FIG. 6 , when the service is connected between the caller and the callee, i.e., when the call is admitted according to the end-to-end CAC procedure, the service control function  740   a  and the network control function  750   a  at the caller side reflect it to update the information in the subscriber DB  744   a  and the resource DB  752   a , and the service control function  740   b  and the network control function  750   b  at the callee side also reflect it to update the information in the subscriber DB  744   b  and the resource DB  752   b.    
      While the end-to-end CAC procedure for guaranteeing QoS upon requesting the resource reservation has been described, the present invention can guarantee QoS for subsequently requested service by performing the end-to-end resource releasing procedure to update the information in the subscriber DB and the resource DB. The end-to-end resource releasing procedure will be now described in detail with reference to FIGS.  8  to  10 .  
       FIG. 8  is a flowchart illustrating the end-to-end resource release procedure when the user requests resource release according to the present invention. It is assumed, for convenience of explanation, that the end-to-end resource releasing procedure responsive to the resource release request is performed based on the network configured as in  FIG. 2 .  
      First, when the user terminal  210  requests the service termination to the CA  260  (S 81 ), the CA  260  determines the bandwidth allocated to the service and requests the resource release by notifying the network control function  250  of the service termination (S 82 ).  
      Then, the network control function  250  notifies the service control function  240  of the service termination (S 83 ), and thus, the service control function  240  modifies an allocation specification of the bandwidth in the subscriber DB  244  (S 84 ).  
      The network control function  250  releases the network resource allocated to the corresponding service (S 85 ) and modifies the resource DB  252  (S 86 ).  
      That is, when the user terminal  210  requests the service termination, the resource release procedure according to the service termination is performed to update the subscriber DB  244  and the resource DB  252 . Thus, since the call is admitted only when the resource reservation is possible through the updated subscriber DB  244  and resource DB  252  even though the user requests a new service later, the end-to-end QoS can be guaranteed.  
       FIG. 9  is a flowchart illustrating the end-to-end resource release procedure when the resource release is requested in a state that the caller and the callee are connected to the same network. In  FIG. 9 , a service user A  910   a  is a caller, and a service user B  910   b  is a callee.  
      When the caller A  910   a  transmits a service termination message to a calling CA_A  960   a  (S 901 ), the calling CA_A  960   a  transmits a service termination message to a called CA_B  960   b  (S 902 ). Thus, the service termination message is delivered to a terminal of a callee B  910   b , whereby the callee B terminates the service (S 903  and S 904 ).  
      Next, when the called CA_B  960   b  notifies the calling CA_A  960   a  of the service termination result (S 905 ), the calling CA_A  960   a  confirms the service termination to the caller A  910   a  (S 906 ) and at the same time notifies a network control function  950  of the service termination (S 907 ). The network control function  950  transmits the service termination to a service control function  940  (S 908 ), and the service control function  940  modifies an allocation specification of the bandwidth in a subscriber DB  944 .  
      Meanwhile, the network control function  950  releases the network resource allocated to the corresponding service (S 909 ) and modifies a resource DB  952 .  
      In this case, the service control function  940  should simultaneously update the subscriber information of both the caller  910   a  and the callee  910   b  by updating the reserved bandwidth and the available bandwidth of the circuit ID of the caller  910   a  based on his/her IP address and updating the reserved bandwidth and the available bandwidth of the circuit ID of the callee  910   b  based on his/her IP address.  
       FIG. 10  is a flowchart illustrating the end-to-end resource release procedure when the resource release is requested in a state that the caller and the callee are connected to different networks. In  FIG. 10 , a service user A  1010   a  is a caller, and a service user B  1010   b  is a callee.  
      As shown in  FIG. 10 , when the caller  1010   a  and the callee  1010   b  are connected to different networks, the service termination message is transmitted by the same procedure as that of  FIG. 9  (S 101  to S 104 ), and a CA_A  1060   a  at the caller side transmits the service termination message to a network control function  1050   a  at the caller side to induce the resource release (S 110 ), and a CA_B  1060   b  at the callee side transmits the service termination message to a network control function  1050   b  at the callee side to induce the resource release (S 105 ).  
      The process that the network control function  1050   a  and  1050   b  and the service control function  1040   a  and  1040   b  modify the resource DBs  1052   a  and  1052   b  and the subscriber DBs  1044   a  and  1044   b  is the same as that of  FIG. 9  except that each control function updates information of the subscriber managed by the control function.  
      As described above, in order to implement the present invention, it is necessary to modify the primary aggregation device in software so that the circuit ID information is inserted into the DHCP packet in allocating the IP address of the user terminal. In addition, there is a need for a recording medium for managing the bandwidth use specification information based on the circuit ID. These requirements can be satisfied by a simple method, such as the use of a separate recording medium or the modification of an existing DB structure. Thus, it can be appreciated that the present invention can be implemented by upgrading existing equipment in software or improving the subscriber DB structure.  
      In other words, the present invention uses the existing DHCP packet as it is in transmitting circuit ID information and thus the use of a separate device or modification of the existing protocol is not required to implement the present invention. According to the present invention, the end-to-end CAC procedure includes only the subscriber domain CAC and the bandwidth information managing procedure, in addition to the conventional CAC procedure. This makes it possible to keep the conventional network CAC procedure as it is, and thus, the present invention can be easily applied to conventional network systems.  
      Further, according to the present invention, the circuit ID as a unique identifier is used to discriminate the physical access environment of the service user, and the bandwidth use specification of the subscriber domain is managed based on the circuit ID. In this manner, as the subscriber domain CAC which is not considered in the convention CAC method becomes possible, the bandwidth resource of both the subscriber domain and the network domain are searched in advance for the IP communication service having a certain bandwidth demand, and a call is admitted only when the resource reservation is possible, thereby guaranteeing the end-to-end service QoS.  
      Meanwhile, the embodiments of the present invention described above can be provided in the form of a computer program and can be executed by the digital computer through the computer readable recording medium.  
      The computer readable recording medium includes a magnetic storage medium (e.g., ROM, floppy disk, hard disk, etc.), an optical readable medium (e.g., CD ROM, DVD, etc.), and a carrier wave (e.g., transmission via the Internet).  
      As described above, the present invention performs the subscriber domain CAC based on the available bandwidth of each subscriber line domain and then performs the network domain CAC for determining whether the resource is available in the network domain or not, thereby guaranteeing the end-to-end QoS for the service having a certain bandwidth demand in the QoS guaranteeing network.  
      Furthermore, the present invention suggests a method of utilizing the existing DHCP packet as it is in transmitting circuit ID information and a method of managing information about a bandwidth use specification based on a circuit ID through simple modification of an existing subscriber DB structure. Thus, the use of a separate device or modification of the protocol is not required to implement the present invention. According to the present invention, the end-to-end CAC procedure includes only the subscriber domain CAC and the bandwidth information managing procedure, in addition to the conventional CAC procedure. This makes it possible to keep the conventional network CAC procedure and thus the present invention can be easily applied to conventional network systems.  
      While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.