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    Overview of APNs

    In a mobile network, the access point name (APN) is the virtual private network (VPN) that connects the user equipment through the Packet Data Network Gateway (P-GW) to the Packet Data Network (PDN). User equipment can access many APNs, which are domain names and associated parameters, and one is the default APN. APNs are very similar to MPLS VPNs in landline networks.

    In the Long Term Evolution (LTE) architecture for the Evolved Packet Core (EPC), the APN determines the P-GW the user equipment should use. The APN also defines the tunnel connecting the user equipment to a PDN such as the Internet. Each PDN that the user subscribes to has an APN and an associated P-GW, often called a “PDN subscription context.” One context is the default APN, connecting to a PDN such as the Internet unless the user activates another APN. Figure 1 shows the relationship among APNs, P-GWs, and packet networks.

    Figure 1: APNs and the P-GW

    APNs and the P-GW

    APNs are configured by network operators and hold many of the parameters that characterize the user session to the PDN. The APN determines authorization and address allocation methods, several types of timeouts, and various other parameters. It also determines the IP address pools to be used, the charging type (such as offline or online) to be used, and the policy model (for example, if a policy and charging rules function [PCRF] is used for policy control).

    The P-GW can also use various rules to determine which APN the user equipment should use. This is called the APN service selection method. The APN in turn defines the service and the P-GW that the user equipment employs.

    APNs often look like Internet domain names and have two parts:

    • Network identifier—This defines the PDN the user connects to through a P-GW. This part of the APN is mandatory. It can be as simple as internet or have a more complicated structure such as juniper.net.
    • Operator identifier—This defines the operator whose PDN the user connects to through a P-GW. This part of the APN is optional and is often omitted. If present, it consists of the operator’s Mobile Country Code (MCC) and Mobile Network Code (MNC). A more complex APN would be something like internet.mnc012.mcc345.gprs or, more realistically, Web.omnitel.it.

    Published: 2011-11-16