A 3GPP Evolved Packet System (EPS) is composed of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN), a Mobility Management Entity (MME), a Serving Gateway (S-GW), a Packet Data Network Gateway (P-GW), a Home Subscriber Server (HSS), a 3GPP Authentication Authorization Accounting (AAA) server, a Policy and Charging Rules Function (PCRF) entity and other supporting nodes. Wherein, the MME is responsible for control plane related works, such as mobility management, processing of signaling on non-access layers and management of the context of the mobility management of subscribers; the S-GW, which is an access gateway device connected to the E-UTRAN, forwards data between the E-UTRAN and the P-GW and is responsible for buffering paging waiting data; the P-GW, which is a border gateway between the 3GPP EPS and a Packet Data Network (PDN), is responsible for the access of the PDN and forwards data between the EPS and the PDN; the PCRF, which is a policy and charging rules function entity, interacts with an IP Application Function (AF) of an operator via an Rx interface to obtain service information, the PCRF is connected to gateway devices (S-GW and P-GW) in the network through S7/S7a/S7c interfaces and is responsible for initiating setup of an IP carrier, ensuring Quality of Service (QoS) of service data and controlling the charging.
FIG. 1 is a block diagram of the architecture of the EPS. The EPS supports and implements interworking with a non-3GPP network via S2a/S2b/S2c interfaces. The P-GW acts as an anchor point between the 3GPP and non-3GPP networks. A non-3GPP system is divided into a trusted non-3GPP IP access and an untrusted non-3GPP IP access. The trusted non-3GPP IP access may directly interface with the P-GW via the S2a interface; while the untrusted non-3GPP IP access has to connect with the P-GW via an evolved Packet Data Gateway (ePDG). The interface between the ePDG and the P-GW is S2b.
In the traditional 3GPP network, the Policy and Charging Enforcement Function (PCEF) exists only in the P-GW, the PCRF can control all the functions as long as it interfaces with the P-GW, and the PCRF exchanges information with the P-GW via the S7 interface, as shown in FIG. 1.
However, after the 3GPP network provides the function of interworking with the non-3GPP network, when the interface between the P-GW and the S-GW is based on the Packet Mobile Internet Protocol (PMIP), the policy enforcement function part in the PCEF, which is called Gateway Control Function (GWCF), such as the binding function of a carrier, also exists in the S-GW. The S-GW exchanges information with the PCRF via the S7c interface (see FIG. 1). When the trusted non-3GPP access system accesses and interworks with the 3GPP system via the S2a interface, the GWCF also resides in the trusted non-3GPP access gateway, as shown in FIG. 1.
There is a plurality of PCRF nodes in a Public Land Mobile Network (PLMN) of the EPS, and all of the PCRF nodes belong to one or more Diameter (PCRF) domains, with all the PCRFs in a Diameter (PCRF) domain being equal. A connection from a UE to a PDN is referred to as an IP Connectivity Access Network (IP-CAN) session. In order to ensure that the Policy and Charging Control (PCC) of one IP-CAN session is determined by only one PCRF, the EPS introduces a logical function entity, namely a Diameter Routing Agent (DRA) network element, into each Diameter (PCRF) domain. When the UE initiates setup of an IP-CAN session, the DRA selects a PCRF for this IP-CAN session.
When a UE is in a non-roaming scenario and the 3GPP core network applies the EPC architecture, typically, three cases exist: the first is that the UE is within the coverage of the 3GPP; the second is that the UE is within the coverage of the trusted non-3GPP, and the third is that the UE is within the coverage of the untrusted non-3GPP.
However, for the three cases in which the UE is in a non-roaming scenario, there is no specific planning in the current EPS for the DRA to select a PCRF. Besides, since the policy enforcement function part exists in many network elements, such as the S-GW and P-GW (GWCF and PCEF), when the S-GW and P-GW both require the DRA to select a PCRF, the PCRFs selected by the DRA for the same IP-CAN session might be inconsistent. Therefore, a problem in the prior art need to be solved urgently: how to associate, through the DRA, all of the PCEF, GWCF and AF related to one IP-CAN session of a UE with the same PCRF, when the UE is in the non-roaming scenario.