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    Overview of Packet Data Network Gateway Functions

    In a mobile network, a major function of the Packet Data Network Gateway (P-GW) is to allocate IP addresses to the user equipment during default bearer setup. The user equipment can still connect to multiple packet networks through multiple P-GWs, and also to older, non-3GPP-compliant IP networks.

    Note: The MobileNext Broadband Gateway does not support interfaces to non-3GPP IP networks.

    In the Long Term Evolution (LTE) architecture for the Evolved Packet Core (EPC), the P-GW acts as an anchor for user plane mobility. User traffic can be filtered at the P-GW for quality-of-service (QoS) differentiation among multiple packet flows. The P-GW collects charging information and forwards these Charging Data Records (CDRs) for processing.

    Figure 1: Packet Data Network Gateway Functions

    Packet Data Network Gateway Functions

    Note: The MobileNext Broadband Gateway does not initially support inter-S-GW handovers, connectivity to Non-3GPP IP networks, or direct rate enforcement.

    The important interfaces on the P-GW shown in Figure 1 are:

    • EPS Bearer—This is the interface to the user equipment associated with the P-GW. It is a tunnel and used for IP address allocation and other purposes.
    • Rx—Although not a direct P-GW interface, this interface is used for all kinds of unsolicited reporting between the policy and charging rules function (PCRF) and the IP Multimedia Subsystem (IMS) network. The IMS delivers services such as voice over IP (VoIP) to the user equipment. This interface uses the Diameter protocol over Steam Control Transport Protocol (SCTP) and TCP, and passes the PCRF permissions to the service network.
    • SGi—This is the interface to the IMS and other internal and external Packet Data Networks (PDNs), where services are usually rendered. Examples are IMS for voice, Web portals, simple Internet access, and so on. All traffic is in the form of IP packets and flows.
    • S5—This is the interface to the Serving Gateway (S-GW) associated with the P-GW. This interface supports the GPRS tunneling protocol (GTP) for the user plane.

    Published: 2011-11-16