Abstract:
A method and system for session modification are provided. The method includes these steps: A home policy and charging rules function (h-PCRF) sends a policy and charging control (PCC) rule providing message to a first policy and charging enforcement function (PCEF) according to a received PCC rule request message, an application layer service message, or an h-PCRF self-trigger event; and the h-PCRF sends a PCC rule providing message to a second PCEF according to a PCC rule response message received from the first PCEF. With this present disclosure, session modification may be implemented when two or more PCEFs are included in the PCC architecture of a system architecture evolution (SAE) system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Application No. PCT/CN2008/072267, filed on Sep. 4, 2008. This application claims the benefit of Chinese Application No. 200710154146.1, filed on Sep. 19, 2007. The disclosure of the above applications is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to communication technologies, and in particular, to an IP connectivity access network (IP-CAN) technology. 
       BACKGROUND OF THE INVENTION 
       [0003]    In a Third Generation Partnership Project (3GPP) system, policy and charging functions are implemented by a policy and charging control (PCC) architecture. 
         [0004]    The PCC architecture mainly enforces policy and charging control. As shown in  FIG. 1 , a PCC architecture in the prior art includes an application function (AF), a policy and charging rules function (PCRF), a subscription profile repository (SPR), a policy and charging enforcement function (PCEF), and an online charging system (OCS) or an offline charging system (OFCS). 
         [0005]    The AF is adapted to provide access points for service applications and is connected to the PCRF through an Rx interface. Dynamic policy control needs to be performed on the network resources used by these service applications. During parameter negotiation on the service plane, the AF transfers relevant service information to the PCRF. If the service information is consistent with the policy rules defined on the PCRF by operators, the PCRF accepts the service parameters. Otherwise, the PCRF refuses the service parameters and may also carry acceptable service parameters in a response message. Then the AF may return these parameters to users. 
         [0006]    The PCRF is adapted to generate policies and charging rules and is connected to the SPR through an Sp interface. As the core of the PCC system, the PCRF provides service data flow based network control rules, including data flow detection, gating, quality of service (QoS) control, and flow-based charging control. The PCRF sends the generated polices and charging rules to the PCEF through a Gx interface and the PCEF charges for service flows accordingly. The PCRF needs to generate policies and charging rules according to the relevant service information obtained from the AF, relevant user subscription data obtained from the SPR, and relevant bearer network information obtained from the PCEF. In addition, the PCRF needs to ensure that these rules are consistent with the user subscription data and to deliver trigger events to the PCEF so that the PCEF may actively request PCC rules from the PCRF when these trigger events occur. 
         [0007]    The PCEF is adapted to: enforce the policies and charging rules generated by the PCRF on the bearer plane, receive trigger events delivered by the PCRF so as to actively request PCC rules from the PCRF when these trigger events occur, detect service data flows according to the traffic filter in the rules sent from the PCRF, control these service data flows according to the polices and charging rules generated by the PCRF, and charge for the service data flows online or offline. In online charging mode, the PCEF is connected to the OCS through a Gy interface and works with the OCS to complete credit management. The OCS includes customized applications for mobile network enhanced logic service control point (CAMEL SCP) and a service data flow based credit control. In offline charging mode, the PCEF is connected to the OFCS through a Gz interface and exchanges relevant charging information with the OFCS. In general, the PCEF is located on a gateway (GW) in a network. 
         [0008]    The SPR is adapted to store PCC-related user subscription data, including service information that can be used by users, QoS information that can be used by user services, charging-related user subscription data, and group types of users. The PCRF reads the information stored in the SPR through the Sp interface and performs policy control and charging based on user subscription data. 
         [0009]    In the PCC architecture, IP-CAN session modification may be initiated by the PCEF. For example, the PCEF may initiate an IP-CAN session modification process when detecting an internal event of IP-CAN session modification caused by an operator&#39;s configuration or when detecting a bearer change during data transmission. IP-CAN session modification may also be initiated by the PCRF. For example, the PCRF may initiate an IP-CAN session modification process when the service information at the application layer on the AF changes, when the user subscription data stored in the SPR changes, or when an internal event occurs. 
         [0010]    To ensure the competitiveness of the 3GPP system in the coming ten or more years, the 3GPP organization internally proposes system architecture evolution (SAE). In an SAE system, a new PPC architecture including multiple S7 or PCEF interface entities is adopted. In this PCC architecture, multiple S7 or PCEF interface entities are connected to the same PCRF at the same time for any IP-CAN session, which is beyond the capabilities of the PCC architecture in the prior art. 
         [0011]    The new PCC architecture includes a roaming PCC architecture and a non-roaming PCC architecture. 
         [0012]      FIG. 2  shows a non-roaming PCC architecture in the prior art. The non-roaming PCC architecture includes an AF in a packet data network (PDN), a home PCRF (h-PCRF), a home OCS (h-OCS), a first PCEF (PCEF a), and a second PCEF, PCEF b. The PCEF b is connected to the PDN, h-PCRF, h-OCS, and PCEF a through an SGi interface, an S7b interface, a Gyb interface, and a client mobility IP/proxy mobility IP (CMIP/PMIP) interface respectively. The PCEF a is connected to the h-PCRF and the PCEF b through an S7a interface and a CMIP/PMIP interface respectively. The h-PCRF is connected to the AF through an RX+ interface. 
         [0013]    As shown in  FIG. 2 , the PCEF in the new PCC architecture is divided into two parts: PCEF a and PCEF b. The PCEF a may be configured on an IP access GW such as a serving GW, a PDN GW, or a core network (CN) entity. The PCEF b may be configured on a PDN GW or a CN entity. The bearer concept is not defined on the CMIP/PMIP interface between the PCEF a and the PCEF b. Thus, the bearer-related functions such as bearer binding are configured on the PCEF a. In addition, the SGi interface between the PCEF b and the PDN is a data transmission interface between the CN and the PDN. Thus, the charging and gating functions are configured on the PCEF b. 
         [0014]      FIG. 3  shows a structure of a first roaming PCC architecture in the prior art. Different from the non-roaming PCC architecture shown in  FIG. 2 , the roaming PCC architecture further includes a visited PCRF (v-PCRF) and a visited OCS (v-OCS). As shown in  FIG. 3 , the PCEF b is connected to the IP Access Network (such as a PDN), h-PCRF, h-OCS, and PCEF a through an SGi interface, an S7b interface, a Gyb interface, and a CMIP/PMIP interface respectively. The PCEF a is connected to the v-PCRF and PCEF b through an S7a interface and a CMIP/PMIP interface respectively. The h-PCRF is connected to the AF and v-PCRF through an RX+ interface and an S9 interface respectively. 
         [0015]    In the roaming PCC architecture, the PCEF b may be further divided into a PCEF b 1  and a PCEF b 2 . 
         [0016]      FIG. 4  shows a structure of a second roaming PCC architecture in the prior art. Different from the PCEF b in the first roaming PCC architecture shown in  FIG. 3 , the PCEF b in the second roaming PCC architecture further includes first and second PCEF sub-elements (PCEF b 1  and PCEF b 2 ). As shown in  FIG. 4 , the PCEF b 2  is connected to the IP Access Network (such as a PDN), h-PCRF, h-OCS, and PCEF b 1  through an SGi interface, an S7b2 interface, a Gyb2 interface, and a CMIP/PMIP interface respectively. The PCEF a is connected to the v-PCRF and PCEF b 1  through an S7a interface and a CMIP/PMIP interface respectively. The h-PCRF is connected to the AF and v-PCRF through an RX+ interface and an S9 interface respectively. The PCEF b 1  is connected to the PCEF b 2  and PCEF a through CMIP/PMIP interfaces respectively. In actual applications, the PCEF b 1  may be also connected to the v-PCRF through an S7b1 interface. 
         [0017]    The inventor of the present invention discovers that the PCEF in the PCC architecture of the SAE system in the prior art is divided into two parts. That is, the new PCC architecture includes two PCEFs and the PCEF that may perceive a bearer event does not support service data flow based charging. In this case, in online charging mode, it is impossible to ensure that all the PCC rules received by the PCEF that may perceive bearer events pass credit authorization. 
       SUMMARY OF THE INVENTION 
       [0018]    Embodiments of the present invention provide a method and system for session modification to modify a session in a PCC architecture of an SAE system. 
         [0019]    To realize the preceding objective, an embodiment of the present invention provides a method for session modification. The method includes: 
         [0020]    sending, by a home policy and charging rules function, h-PCRF, a first policy and charging control, PCC, rule providing message to a first policy and charging enforcement function, according to a received PCC rule request message, an application layer service message, or an h-PCRF self-trigger event; and 
         [0021]    sending, by the h-PCRF, a second PCC rule providing message to a second PCEF according to a PCC rule response message received from the first PCEF. 
         [0022]    An embodiment of the present invention provides a method for transferring information. The method includes: 
         [0023]    receiving, by a home policy and charging rules function, h-PCRF, a policy and charging control, PCC rule request message from a first policy and charging enforcement function; 
         [0024]    obtaining, by the h-PCRF, information of a trigger event that occurs on the first PCEF and information of affected PCC rules from the received PCC rule request message; and 
         [0025]    sending, by the h-PCRF, a PCC rule providing message to a second PCEF, where the PCC rule providing message comprises the information of the trigger event that occurs on the first PCEF. 
         [0026]    An embodiment of the present invention provides a system for session modification. The system includes a first PCEF, a second PCEF, an AF, an h-OCS, and an h-PCRF, where: 
         [0027]    the second PCEF is connected to the AF, h-PCRF, h-OCS, and first PCEF through an SGi interface, an S7b interface, a Gyb interface, and a CMIP/PMIP interface respectively; 
         [0028]    the first PCEF is connected to the h-PCRF through an S7a interface; 
         [0029]    the h-PCRF is connected to the AF through an RX+ interface; 
         [0030]    the h-PCRF sends a PCC rule providing message to the second PCEF according to a received PCC rule request message, an application layer service message, or a self-trigger message; and 
         [0031]    the h-PCRF sends a PCC rule providing message to the first PCEF according to a PCC rule response message sent from the second PCEF. 
         [0032]    In the technical solution of the present invention, when the PCC architecture of the SAE system includes two or more PCEFs, the h-PCRF sends a PCC rule providing message to the second PCEF according to the received PCC rule request message and determines whether to send a PCC rule providing message to the first PCEF according to a PCC rule response message sent from the second PCEF. This ensures that all the PCC rules received by the first PCEF pass credit authorization in online charging mode so that operators may easily perform PCC on service data flows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]      FIG. 1  shows a general PCC architecture in the prior art; 
           [0034]      FIG. 2  shows a non-roaming PCC architecture in the prior art; 
           [0035]      FIG. 3  shows a first roaming PCC architecture in the prior art; 
           [0036]      FIG. 4  shows a second roaming PCC architecture in the prior art; 
           [0037]      FIG. 5   a  is a flowchart showing that a PCEF a initiates an IP-CAN session modification process when an h-PCRF directly delivers a trigger event to the PCEF a in a first embodiment of the present invention; 
           [0038]      FIG. 5   b  is a flowchart showing that a PCEF b initiates an IP-CAN session modification process in the first embodiment of the present invention; 
           [0039]      FIG. 5   c  is a flowchart showing that an h-PCRF initiates an IP-CAN session modification process in the first embodiment of the present invention; 
           [0040]      FIG. 6   a  is a flowchart showing that a PCEF a initiates an IP-CAN session modification process when an h-PCRF delivers a trigger event to the PCEF a through a v-PCRF in a second embodiment of the present invention; 
           [0041]      FIG. 6   b  is a flowchart showing that a PCEF b initiates an IP-CAN session modification process in the second embodiment of the present invention; 
           [0042]      FIG. 6   c  is a flowchart showing that an h-PCRF initiates an IP-CAN session modification process in the second embodiment of the present invention; 
           [0043]      FIG. 7  is a flowchart showing that a PCEF a initiates an IP-CAN session modification process when an h-PCRF delivers a trigger event to the PCEF a through a v-PCRF in a third embodiment of the present invention; 
           [0044]      FIG. 8  is a flowchart showing that a PCEF b 2  initiates an IP-CAN session modification process in the third embodiment of the present invention; and 
           [0045]      FIG. 9  is a flowchart showing that an h-PCRF initiates an IP-CAN session modification process in the third embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0046]    For better understanding of the objective, technical solution and merits of the present invention, the present invention is hereinafter described in detail with reference to accompanying drawings and exemplary embodiments. 
         [0047]    The first embodiment implements IP-CAN session modification and credit re-authorization based on a non-roaming PCC architecture shown in  FIG. 2 . 
         [0048]    In the PCC architecture shown in  FIG. 2 , the PCEF a and PCEF b both receive a trigger event delivered from the h-PCRF. The PCEF a may receive a trigger event in one of the following modes: 
         [0049]    the h-PCRF directly delivers the trigger event to the PCEF a; and 
         [0050]    the h-PCRF delivers the trigger event to the PCEF b, and then the PCEF b sends the bearer-related trigger event information to the PCEF a. 
         [0051]    The h-OCS sends credit re-authorization events to only the PCEF b and no credit re-authorization event is available on the PCEF a. 
         [0052]    Thus, when an event that occurs matches a trigger event, the PCEF a and PCEF b may both initiate an IP-CAN session modification process. When an event that occurs matches a credit re-authorization event, however, only the PCEF b initiates a credit re-authorization process. 
         [0053]    The h-PCRF may send PCC rules to the PCEF a and PCEF b in one of the following modes: 
         [0054]    A. PCC rules to be enforced are pre-configured on the PCEF a and PCEF b respectively. The h-PCRF sends the same PCC rules to the PCEF a and PCEF b. Then the PCEF a and PCEF b obtain their own PCC rules to be enforced from the received PCC rules according to their pre-configured PCC rule information. 
         [0055]    B. The h-PCRF sends the same PCC rules to the PCEF a and PCEF b. The h-PCRF provides instructions for enforcing PCC rules for the PCEF a and PCEF b before or when providing PCC rules for the PCEF a and PCEF b. Then the PCEF a and PCEF b obtain their own PCC rules to be enforced according to the received enforcement instructions. 
         [0056]    C. The h-PCRF generates different PCC rules for the PCEF a and PCEF b according to the functions of the PCEF a and PCEF b and sends corresponding PCC rules to the PCEF a and PCEF b respectively. Then the PCEF a and PCEF b directly enforce the received PCC rules. 
         [0057]    The following describes the IP-CAN session modification process and the credit re-authorization process respectively. 
         [0058]    When the h-PCRF directly delivers trigger events to the PCEF a, the PCEF a may perceive bearer-related events but the PCEF b may not because the bearer concept is not defined on the interface between the PCEF a and the PCEF b. The PCEF b, however, needs to perform credit re-authorization according to the bearer-related event that occurs. Thus, for the IP-CAN session modification process initiated by the PCEF a, the h-PCRF receives a PCC rule request message including the information of the trigger event that occurs and affected PCC rules from the PCEF a, generates new PCC rules, and then delivers the new PCC rules and the obtained information of the trigger event that occurs and affected PCC rules to the PCEF b, while giving an instruction indicating that trigger event information is used to match a credit re-authorization event. To indicate that trigger event information is used to match a credit re-authorization event, the h-PCRF may: 
         [0059]    add a trigger event type that is only used to match a credit re-authorization event when delivering the trigger event to the PCEF b; 
         [0060]    add a mark to the existing trigger event information to identify that the trigger event is used to update the trigger event stored on the PCEF b or match a credit re-authorization event; or 
         [0061]    use other methods. Then the PCEF b matches the received trigger event information for matching a credit re-authorization event from the h-PCRF with the stored credit re-authorization event and determines whether to perform credit re-authorization according to the matching result. If credit re-authorization is required, the PCEF b performs credit re-authorization on all the affected PCC rules received from the h-PCRF. 
         [0062]      FIG. 5   a  is a flowchart showing that a PCEF a initiates an IP-CAN session modification process when an h-PCRF directly delivers a trigger event to the PCEF a in the first embodiment of the present invention. The process includes the following steps: 
         [0063]    Step  5   a   1 : The PCEF a determines that an IP-CAN session modification process needs to be initiated to update PCC rules. 
         [0064]    In this step, the PCEF a may determine whether to initiate an IP-CAN session modification process according to whether an event that matches the trigger event stored on the PCEF a or an internal trigger event occurs. The trigger event includes but is not limited to dedicated bearer setup, modification, and deletion initiated by a UE. 
         [0065]    Step  5   a   2 : The PCEF a sends a PCC rule request message to the h-PCRF. 
         [0066]    In this step, the PCC rule request message carries update information required for the h-PCRF to make PCC decisions, information of a trigger event that occurs, and information of the PCC rules affected by the trigger event. 
         [0067]    Step  5   a   3 : The h-PCRF generates PCC rules. 
         [0068]    When generating PCC rules, the h-PCRF may interact with the AF or the SPR to obtain the required application layer service information or subscription data information. 
         [0069]    Step  5   a   4 : The h-PCRF sends a PCC rule providing message to the PCEF b. 
         [0070]    In this step, the PCC rule providing message may carry the obtained information of the trigger event and affected PCC rules from the PCEF a and an instruction indicating that trigger event information is used to match a credit re-authorization event. 
         [0071]    Step  5   a   5  and step  5   a   6 : In online charging mode, the PCEF b determines whether to initiate a credit re-authorization process according to stored credit re-authorization event information and trigger event information in the PCC rule providing message. 
         [0072]    In this step, the PCEF b matches stored credit re-authorization event information with trigger event information in the PCC rule providing message. If the matching is successful, the PCEF b initiates a credit re-authorization process and performs credit re-authorization on all the affected PCC rules received from the h-PCRF. 
         [0073]    Step  5   a   7 : The PCEF b returns a PCC rule response message to the h-PCRF. The response message may carry the enforcement result information of the PCC rules. In online charging mode, the response message may also carry credit availability information. 
         [0074]    Step  5   a   8 : The h-PCRF sends a PCC rule providing message to the PCEF a according to the PCC rule response message sent from the PCEF b. 
         [0075]    In online charging mode, the PCC rule response message sent from the PCEF b to the h-PCRF may also carry credit availability information. If the credit is available, the h-PCRF sends a PCC rule providing message to the PCEF a, carrying new PCC rules. If the credit is unavailable, the h-PCRF sends a PCC rule providing message to the PCEF a, without carrying the new PCC rules generated for the unavailable credit. 
         [0076]    If the h-PCRF delivers a trigger event to the PCEF b, and then the PCEF b sends the bearer-related trigger event to the PCEF a, the PCEF a may also initiate an IP-CAN session modification process. In this case, after detecting the trigger event, the PCEF a sends the information of the trigger event and the information of the affected PCC rules to the PCEF b; the PCEF b sends the received information to the h-PCRF to request new PCC rules; after receiving the new PCC rules from the h-PCRF, the PCEF b determines whether to initiate a credit re-authorization process according to the information received from the PCEF a and the new PCC rules received from the h-PCRF. 
         [0077]      FIG. 5   b  is a flowchart showing that a PCEF b initiates an IP-CAN session modification process. The process is different from the IP-CAN session modification process shown in  FIG. 5   a . Specific differences are as follows: 
         [0078]    In step  5   b   1 , the PCEF b may determine whether to initiate an IP-CAN session modification process according to whether an event that matches the trigger event stored on the PCEF b or an internal trigger event occurs. 
         [0079]    In step  5   b   2 , the PCC rule request message sent from the PCEF b to the h-PCRF carries the update information required for the h-PCRF to make PCC decisions. 
         [0080]    In step  5   b   4 , the h-PCRF sends a PCC rule providing message to the PCEF b. 
         [0081]      FIG. 5   c  is a flowchart showing that an h-PCRF initiates an IP-CAN session modification process in the first embodiment of the present invention. The process includes the following steps: 
         [0082]    Step  5   c   1 : The AF sends an application layer service providing or modification message to the h-PCRF to trigger the h-PCRF to initiate an IP-CAN session modification process. The h-PCRF may also initiate an IP-CAN session modification process according to an internal trigger event. 
         [0083]    Step  5   c   2 : The h-PCRF returns an application layer service providing or modification acknowledgement message to the AF. 
         [0084]    Step  5   c   3 : The h-PCRF generates PCC rules. 
         [0085]    Step  5   c   4 : The h-PCRF sends a PCC rule providing message to the PCEF b. 
         [0086]    Step  5   c   5  and step  5   c   6 : In online charging mode, the PCEF b determines whether to initiate a credit re-authorization process according to credit re-authorization event information and trigger event information in the PCC rule providing message. 
         [0087]    In this step, according to stored credit re-authorization event information and the PCC rule providing message, the PCEF b needs to request a new credit from the h-OCS for a new charging key. For an unavailable charging key, the PCEF b returns a final report and remaining credits to the h-OCS. Other events meeting credit re-authorization conditions may also trigger the PCEF b to request new credits from the h-OCS. 
         [0088]    Step  5   c   7 : The PCEF b returns a PCC rule response message to the h-PCRF. The response message may carry the enforcement result information of the PCC rules. In online charging mode, the response message may also carry credit availability information. 
         [0089]    Step  5   c   8 : The h-PCRF sends a PCC rule providing message to the PCEF a according to the PCC rule response message sent from the PCEF b. 
         [0090]    In online charging mode, the PCC rule response message sent from the PCEF b to the h-PCRF may also carry credit availability information. If the credit is available, the h-PCRF sends a PCC rule providing message to the PCEF a, carrying new PCC rules. If the credit is unavailable, the h-PCRF sends a PCC rule providing message to the PCEF a, without carrying the new PCC rules generated for the unavailable credit. 
         [0091]    The second embodiment implements IP-CAN session modification and credit re-authorization based on a roaming PCC architecture shown in  FIG. 3 . 
         [0092]    In the PCC architecture shown in  FIG. 3 , the PCEF a and PCEF b both receive the trigger event delivered from the h-PCRF. The PCEF a may receive a trigger event in one of the following modes: 
         [0093]    the h-PCRF directly sends the trigger event to the PCEF a; and 
         [0094]    the h-PCRF sends the trigger event to the PCEF b, and then the PCEF b sends the bearer-related trigger event information to the PCEF a. 
         [0095]    The h-OCS sends credit re-authorization events to only the PCEF b and no credit re-authorization event is available on the PCEF a. 
         [0096]    Thus, when an event that occurs matches a trigger event, the PCEF a and PCEF b both may initiate an IP-CAN session modification process. When an event that occurs matches a credit re-authorization event, however, only the PCEF b initiates a credit re-authorization process. 
         [0097]    In this embodiment, the h-PCRF may send PCC rules to the PCEF a and PCEF b in three modes, which is similar to the first embodiment and is not further described. 
         [0098]    The following describes the IP-CAN session modification process and the credit re-authorization process respectively. 
         [0099]    If the h-PCRF sends a trigger event to the PCEF a through a v-PCRF, the PCEF a initiates an IP-CAN session modification process. In this case, the h-PCRF receives a PCC rule request message including the information of the trigger event that occurs and affected PCC rules from the PCEF a through the v-PCRF, generates new PCC rules, and then delivers the new PCC rules and the obtained information of the trigger event that occurs and affected PCC rules to the PCEF b, while giving an instruction indicating that trigger event information is used to match a credit re-authorization event. To indicate that trigger event information is used to match a credit re-authorization event, the h-PCRF may: 
         [0100]    add a trigger event type that is only used to match a credit re-authorization event when delivering the trigger event to the PCEF b; 
         [0101]    add a mark to the existing trigger event information to identify that the trigger event is used to update the trigger event stored on the PCEF b or match a credit re-authorization event; or 
         [0102]    use other methods. 
         [0103]    Then the PCEF b matches the received trigger event information for matching a credit re-authorization event from the h-PCRF with the stored credit re-authorization event and determines whether to perform credit re-authorization according to the matching result. If credit re-authorization is required, the PCEF b performs credit re-authorization on all the affected PCC rules received from the h-PCRF. 
         [0104]      FIG. 6   a  is a flowchart showing that a PCEF a initiates an IP-CAN session modification process when an h-PCRF delivers a trigger event to the PCEF a through a v-PCRF in the second embodiment of the present invention. The process includes the following steps: 
         [0105]    Step  6   a   1 : The PCEF a determines that an IP-CAN session modification process needs to be initiated to update PCC rules. 
         [0106]    In this step, the PCEF a may determine whether to initiate an IP-CAN session modification process according to whether an event that matches the trigger event stored on the PCEF a or an internal trigger event occurs. The trigger event includes but is not limited to dedicated bearer setup, modification, and deletion initiated by a UE. 
         [0107]    Step  6   a   2 : The PCEF a sends a PCC rule request message to the v-PCRF, carrying the update information required for the h-PCRF to make PCC decisions. 
         [0108]    Step  6   a   3 : The v-PCRF forwards the PCC rule request message received from the PCEF a. 
         [0109]    Step  6   a   4 : The h-PCRF generates PCC rules. 
         [0110]    When generating PCC rules, the h-PCRF may interact with the AF or the SPR to obtain the required application layer service information or subscription data information. 
         [0111]    Step  6   a   5 : The h-PCRF sends a PCC rule providing message to the PCEF b. 
         [0112]    In this step, when sending the PCC rule providing message to the PCEF b, the h-PCRF may also provide the received trigger event information and the information of the affected PCC rules from the PCEF a for the PCEF b, while giving an instruction indicating that trigger event information is used to match a credit re-authorization event. 
         [0113]    Step  6   a   6  and step  6   a   7 : In online charging mode, the PCEF b determines whether to initiate a credit re-authorization process according to stored credit re-authorization event information and trigger event information in the PCC rule providing message. 
         [0114]    In this step, the PCEF b matches stored credit re-authorization event information with trigger event information in the PCC rule providing message. If the matching is successful, the PCEF b initiates a credit re-authorization process and performs credit re-authorization on all the affected PCC rules received from the h-PCRF. 
         [0115]    Step  6   a   8 : The PCEF b returns a PCC rule response message to the h-PCRF. The response message may carry the enforcement result information of the PCC rules. In online charging mode, the response message may also carry credit availability information. 
         [0116]    Step  6   a   9 : The h-PCRF sends a PCC rule providing message to the v-PCRF according to the PCC rule response message sent from the PCEF b. 
         [0117]    In online charging mode, the PCC rule response message sent from the PCEF b to the h-PCRF may also carry credit availability information. If the credit is available, the h-PCRF sends a PCC rule providing message to the PCEF a, carrying new PCC rules. If the credit is unavailable, the h-PCRF sends a PCC rule providing message to the PCEF a, without carrying the new PCC rules generated for the unavailable credit. 
         [0118]    Step  6   a   10 : The v-PCRF sends a PCC rule providing message to the PCEF a. 
         [0119]    In this step, the v-PCRF may or may not process the received PCC rule providing message according to local policies. 
         [0120]    If the h-PCRF delivers a trigger event to the PCEF b and then the PCEF b sends the bearer-related trigger event to the PCEF a, the PCEF a may also initiate an IP-CAN session modification process. In this case, after detecting the trigger event, the PCEF a sends the information of the trigger event and the information of the affected PCC rules to the PCEF b; the PCEF b sends the received information to the h-PCRF to request new PCC rules; after receiving the new PCC rules from the h-PCRF, the PCEF b determines whether to initiate a credit re-authorization process according to the information received from the PCEF a and the new PCC rules received from the h-PCRF. 
         [0121]      FIG. 6   b  is a flowchart showing that a PCEF b initiates an IP-CAN session modification process in the second embodiment of the present invention. The process includes the following steps: 
         [0122]    Step  6   b   1 : The PCEF b determines that an IP-CAN session modification process needs to be initiated to update PCC rules. 
         [0123]    In this step, the PCEF b may determine whether to initiate an IP-CAN session modification process according to whether an event that matches the trigger event stored on the PCEF b or an internal trigger event occurs. 
         [0124]    Step  6   b   2 : The PCEF b sends a PCC rule request message to the h-PCRF, carrying the update information required for the h-PCRF to make PCC decisions. 
         [0125]    Step  6   b   3 : The h-PCRF generates PCC rules. 
         [0126]    When generating PCC rules, the h-PCRF may interact with the AF or the SPR to obtain the required application layer service information or subscription data information. 
         [0127]    Step  6   b   4 : The h-PCRF sends a PCC rule providing message to the PCEF b. 
         [0128]    Step  6   b   5  and step  6   b   6 : In online charging mode, the PCEF b determines whether to initiate a credit re-authorization process according to credit re-authorization event information and trigger event information in the PCC rule providing message. 
         [0129]    In this step, according to stored credit re-authorization event information and the PCC rule providing message, the PCEF b needs to request a new credit from the h-OCS for a new charging key. For an unavailable charging key, the PCEF b returns a final report and remaining credits to the h-OCS. Other events meeting credit re-authorization conditions may also trigger the PCEF b to request new credits from the h-OCS. 
         [0130]    Step  6   b   7 : The PCEF b returns a PCC rule response message to the h-PCRF. The response message may carry the enforcement result information of the PCC rules. In online charging mode, the response message may also carry credit availability information. 
         [0131]    Step  6   b   8 : The h-PCRF sends a PCC rule providing message to the v-PCRF according to the PCC rule response message sent from the PCEF b. 
         [0132]    In online charging mode, the PCC rule response message sent from the PCEF b to the h-PCRF may also carry credit availability information. If the credit is available, the h-PCRF sends a PCC rule providing message to the PCEF a, carrying new PCC rules. If the credit is unavailable, the h-PCRF sends a PCC rule providing message to the PCEF a, without carrying the new PCC rules generated for the unavailable credit. 
         [0133]    Step  6   b   9 : The v-PCRF sends a PCC rule providing message to the PCEF a. 
         [0134]    In this step, the v-PCRF may or may not process the received PCC rule providing message according to local policies. 
         [0135]      FIG. 6   c  is a flowchart showing that an h-PCRF initiates an IP-CAN session modification process in the second embodiment of the present invention. The process includes the following steps: 
         [0136]    Step  6   c   1 : The AF sends an application layer service providing or modification message to the h-PCRF to trigger the h-PCRF to initiate an IP-CAN session modification process. The h-PCRF may also initiate an IP-CAN session modification process according to an internal trigger event. 
         [0137]    Step  6   c   2 : The h-PCRF returns an application layer service providing or modification acknowledgement message to the AF. 
         [0138]    Step  6   c   3 : The h-PCRF generates PCC rules. 
         [0139]    Step  6   c   4 : The h-PCRF sends a PCC rule providing message to the PCEF b. 
         [0140]    Step  6   c   5  and step  6   c   6 : In online charging mode, the PCEF b determines whether to initiate a credit re-authorization process according to credit re-authorization event information and trigger event information in the PCC rule providing message. 
         [0141]    In this step, according to stored credit re-authorization event information and the PCC rule providing message, the PCEF b needs to request a new credit from the h-OCS for a new charging key. For an unavailable charging key, the PCEF b returns a final report and remaining credits to the h-OCS. Other events meeting credit re-authorization conditions may also trigger the PCEF b to request new credits from the h-OCS. 
         [0142]    Step  6   c   7 : The PCEF b returns a PCC rule response message to the h-PCRF. The response message may carry the enforcement result information of the PCC rules. In online charging mode, the response message may also carry credit availability information. 
         [0143]    Step  6   c   8 : The h-PCRF sends a PCC rule providing message to the v-PCRF according to the PCC rule response message sent from the PCEF b. 
         [0144]    In online charging mode, the PCC rule response message sent from the PCEF b to the h-PCRF may also carry credit availability information. If the credit is available, the h-PCRF sends a PCC rule providing message to the PCEF a, carrying new PCC rules. If the credit is unavailable, the h-PCRF sends a PCC rule providing message to the PCEF a, without carrying the new PCC rules generated for the unavailable credit. 
         [0145]    Step  6   c   9 : The v-PCRF sends a PCC rule providing message to the PCEF a. 
         [0146]    In this step, the v-PCRF may or may not process the received PCC rule providing message according to local policies. 
         [0147]    The third embodiment implements IP-CAN session modification and credit re-authorization based on a roaming PCC architecture shown in  FIG. 4 . 
         [0148]    As shown in  FIG. 4 , the PCEF a, PCEF b 1 , and PCEF b 2  receive the trigger events delivered from the h-PCRF respectively. The h-PCRF may deliver the trigger events to the PCEF a through the v-PCRF. The h-PCRF may also deliver the trigger events to the PCEF b 2 , and then the PCEF b 2  sends the bearer-related trigger events to the PCEF a through the PCEF b 1 . The h-OCS sends credit re-authorization events only to the PCEF b 2  and no credit re-authorization events are available on the PCEF a and PCEF b 1 . Thus, when an event that occurs matches a trigger event, the PCEF a, PCEF b 1 , and PCEF b 2  may initiate an IP-CAN session modification process respectively. When an event that occurs matches a credit re-authorization event, however, only the PCEF b 2  initiates a credit re-authorization process. 
         [0149]    In this embodiment, the h-PCRF may send PCC rules to the PCEF a, PCEF b 1 , and PCEF b 2  in three modes, which is similar to the first embodiment and is not further described. 
         [0150]    The h-PCRF may also provide different PCC rule enforcement instructions for different PCEFs or provide different PCC rules according to the functions of different PCEFs. Multiple S9 interfaces may be available between the h-PCRF and the v-PCRF and correspond to different PCEFs such as a PCEF a or a PCEF b 1 . In addition, there may be only one S9 interface between the h-PCRF and the v-PCRF. The PCC rule message transmitted on the S9 interface carries the indication provided for the target PCEF. 
         [0151]    The following describes the IP-CAN session modification process and the credit re-authorization process respectively. 
         [0152]    If the h-PCRF sends a trigger event to the PCEF a through the v-PCRF, the PCEF a initiates an IP-CAN session modification process. In this case, the h-PCRF receives a PCC rule request message including the information of the trigger event that occurs and affected PCC rules from the PCEF a through the v-PCRF, generates new PCC rules, and then delivers the new PCC rules and the obtained information of the trigger event that occurs and affected PCC rules to the PCEF b 2 , while giving an instruction indicating that trigger event information is used to match a credit re-authorization event. To indicate that trigger event information is used to match a credit re-authorization event, the h-PCRF may: 
         [0153]    add a trigger event type that is only used to match a credit re-authorization event when delivering the trigger event to the PCEF b 2 ; 
         [0154]    add a mark to the existing trigger event information to identify that the trigger event is used to update the trigger event stored on the PCEF b 2  or match a credit re-authorization event; or 
         [0155]    use other methods. Then the PCEF b 2  matches trigger event information received from the h-PCRF with the stored credit re-authorization event and determines whether to perform credit re-authorization according to the matching result. If credit re-authorization is required, the PCEF b 2  performs credit re-authorization on all the affected PCC rules received from the h-PCRF. 
         [0156]      FIG. 7  is a flowchart showing that a PCEF a initiates an IP-CAN session modification process when an h-PCRF delivers a trigger event to the PCEF a through a v-PCRF in the third embodiment of the present invention. The process includes the following steps: 
         [0157]    Step  701 : The PCEF a determines that an IP-CAN session modification process needs to be initiated to update PCC rules. 
         [0158]    In this step, the PCEF a may determine whether to initiate an IP-CAN session modification process according to whether an event that matches the trigger event stored on the PCEF a or an internal trigger event occurs. The trigger event includes but is not limited to dedicated bearer setup, modification, and deletion initiated by a UE. 
         [0159]    Step  702 : The PCEF a sends a PCC rule request message to the v-PCRF, carrying the update information required for the h-PCRF to make PCC decisions. 
         [0160]    Step  703 : The v-PCRF forwards the received PCC rule request message, carrying the update information sent from the PCEF a or PCEF b 1  and required for the h-PCRF to make PCC decisions. 
         [0161]    Step  704 : The h-PCRF generates PCC rules. 
         [0162]    When generating PCC rules, the h-PCRF may interact with the AF or the SPR to obtain the required application layer service information or subscription data information. 
         [0163]    Step  705 : The h-PCRF sends a PCC rule providing message to the PCEF b 2 . 
         [0164]    In this step, when sending the PCC rule providing message to the PCEF b 2 , the h-PCRF may also provide the received trigger event information and the information of the affected PCC rules from the PCEF a for the PCEF b 2 , while giving an instruction indicating that trigger event information is used to match a credit re-authorization event. 
         [0165]    Step  706  and step  707 : In online charging mode, the PCEF b 2  determines whether to initiate a credit re-authorization process according to stored credit re-authorization event information and trigger event information in the PCC rule providing message. 
         [0166]    In this step, the PCEF b 2  matches stored credit re-authorization event information with trigger event information in the PCC rule providing message. If the matching is successful, the PCEF b 2  initiates a credit re-authorization process and performs credit re-authorization on all the affected PCC rules received from the h-PCRF. 
         [0167]    Step  708 : The PCEF b 2  returns a PCC rule response message to the h-PCRF. The response message may carry the enforcement result information of the PCC rules. In online charging mode, the response message may also carry credit availability information. 
         [0168]    Step  709 : The h-PCRF sends a PCC rule providing message to the v-PCRF according to the PCC rule response message sent from the PCEF b 2 . 
         [0169]    In online charging mode, the PCC rule response message sent from the PCEF b to the h-PCRF may also carry credit availability information. If the credit is available, the h-PCRF sends a PCC rule providing message to the PCEF a, carrying new PCC rules. If the credit is unavailable, the h-PCRF sends a PCC rule providing message to the PCEF a, without carrying the new PCC rules generated for the unavailable credit. 
         [0170]    Step  710 : The v-PCRF sends a PCC rule providing message to the PCEF b 1 . 
         [0171]    In this step, before sending the received PCC rule providing message to the PCEF b 1 , the v-PCRF may or may not process the message according to local policies. 
         [0172]    Step  711 : The v-PCRF sends a PCC rule providing message to the PCEF a. 
         [0173]    In this step, the v-PCRF may or may not process the received PCC rule providing message according to local policies. 
         [0174]    If the h-PCRF delivers a trigger event to the PCEF b 2  and then the PCEF b 2  sends the bearer-related trigger event to the PCEF a through the PCEF b 1 , the PCEF a may also initiate an IP-CAN session modification process. In this case, after detecting the trigger event, the PCEF a sends the information of the trigger event and affected PCC rules to the PCEF b 2  through the PCEF b 1 ; the PCEF b 2  sends the received information to the h-PCRF to request new PCC rules; after receiving the new PCC rules from the h-PCRF, the PCEF b 2  determines whether to initiate a credit re-authorization process according to the information received from the PCEF a and the new PCC rules received from the h-PCRF. 
         [0175]      FIG. 8  is a flowchart showing that a PCEF b 2  initiates an IP-CAN session modification process in the third embodiment of the present invention. The process includes the following steps: 
         [0176]    Step  801 : The PCEF b 2  determines that an IP-CAN session modification process needs to be initiated to update PCC rules. 
         [0177]    In this step, the PCEF b 2  may determine whether to initiate an IP-CAN session modification process according to whether an event that matches the trigger event stored on the PCEF b 2  or an internal trigger event occurs. 
         [0178]    Step  802 : The PCEF b 2  sends a PCC rule request message to the h-PCRF, carrying the update information required for the h-PCRF to make PCC decisions. 
         [0179]    Step  803 : The h-PCRF generates PCC rules. 
         [0180]    When generating PCC rules, the h-PCRF may interact with the AF or the SPR to obtain the required application layer service information or subscription data information. 
         [0181]    Step  804 : The h-PCRF sends a PCC rule providing message to the PCEF b 2 . 
         [0182]    Step  805  and step  806 : In online charging mode, the PCEF b 2  determines whether to initiate a credit re-authorization process according to credit re-authorization event information and trigger event information in the PCC rule providing message. 
         [0183]    In this step, according to stored credit re-authorization event information and the PCC rule providing message, the PCEF b 2  needs to request a new credit from the h-OCS for a new charging key. For an unavailable charging key, the PCEF b 2  returns a final report and remaining credits to the h-OCS. Other events meeting credit re-authorization conditions may also trigger the PCEF b 2  to request new credits from the h-OCS. 
         [0184]    Step  807 : The PCEF b 2  returns a PCC rule response message to the h-PCRF. The response message may carry the enforcement result information of the PCC rules. In online charging mode, the response message may also carry credit availability information. 
         [0185]    Step  808 : The h-PCRF sends a PCC rule providing message to the v-PCRF according to the PCC rule response message sent from the PCEF b 2 . 
         [0186]    In online charging mode, the PCC rule response message sent from the PCEF b to the h-PCRF may also carry credit availability information. If the credit is available, the h-PCRF sends a PCC rule providing message to the PCEF a, carrying new PCC rules. If the credit is unavailable, the h-PCRF sends a PCC rule providing message to the PCEF a, without carrying the new PCC rules generated for the unavailable credit. 
         [0187]    Step  809 : The v-PCRF sends a PCC rule providing message to the PCEF b 1 . 
         [0188]    In this step, before sending the received PCC rule providing message to the PCEF b 1 , the v-PCRF may or may not process the message according to local policies. 
         [0189]    Step  810 : The v-PCRF sends a PCC rule providing message to the PCEF a. 
         [0190]    In this step, the v-PCRF may or may not process the received PCC rule providing message according to local policies. 
         [0191]      FIG. 9  is a flowchart showing that an h-PCRF initiates an IP-CAN session modification process in the third embodiment of the present invention. The process includes the following steps: 
         [0192]    Step  901 : The AF sends an application layer service providing or modification message to the h-PCRF to trigger the h-PCRF to initiate an IP-CAN session modification process. The h-PCRF may also initiate an IP-CAN session modification process according to an internal trigger event. 
         [0193]    Step  902 : The h-PCRF returns an application layer service providing or modification acknowledgement message to the AF. 
         [0194]    Step  903 : The h-PCRF generates PCC rules. 
         [0195]    Step  904 : The h-PCRF sends a PCC rule providing message to the PCEF b 2 . 
         [0196]    Step  905  and step  906 : In online charging mode, the PCEF b 2  determines whether to initiate a credit re-authorization process according to credit re-authorization event information and trigger event information in the PCC rule providing message. 
         [0197]    In this step, according to stored credit re-authorization event information and the PCC rule providing message, the PCEF b 2  needs to request a new credit from the h-OCS for a new charging key. For an unavailable charging key, the PCEF b 2  returns a final report and remaining credits to the h-OCS. Other events meeting credit re-authorization conditions may also trigger the PCEF b 2  to request new credits from the h-OCS. 
         [0198]    Step  907 : The PCEF b 2  returns a PCC rule response message to the h-PCRF. The response message may carry the enforcement result information of the PCC rules. In online charging mode, the response message may also carry credit availability information. 
         [0199]    Step  908 : The h-PCRF sends a PCC rule providing message to the v-PCRF according to the PCC rule response message sent from the PCEF b 2 . 
         [0200]    In online charging mode, the PCC rule response message sent from the PCEF b to the h-PCRF may also carry credit availability information. If the credit is available, the h-PCRF sends a PCC rule providing message to the PCEF a, carrying new PCC rules. If the credit is unavailable, the h-PCRF sends a PCC rule providing message to the PCEF a, without carrying the new PCC rules generated for the unavailable credit. 
         [0201]    Step  909 : The v-PCRF sends a PCC rule providing message to the PCEF b 1 . 
         [0202]    In this step, before sending the received PCC rule providing message to the PCEF b 1 , the v-PCRF may or may not process the message according to local policies. 
         [0203]    Step  910 : The v-PCRF sends a PCC rule providing message to the PCEF a. 
         [0204]    In this step, the v-PCRF may or may not process the received PCC rule providing message according to local policies. 
         [0205]    Although the objective, technical solution, and merits of the present invention have been described in detail with reference to some exemplary embodiments, the invention is not limited to such embodiments. It is apparent that those skilled in the art may make various modifications and variations to the invention without departing from the spirit and scope of the invention. The invention is intended to cover the modifications and variations provided that they fall in the scope of protection defined by the following claims or their equivalents