The Access Point Name (APN) in LTE networks is a reference point that acts as a gateway between the mobile network and external Packet Data Networks (PDNs). It determines how a mobile user accesses various data services.
What is an APN in LTE?
- APN Definition: The APN is a name assigned to a PDN that the mobile user can connect to for accessing internet and other services.
- PDN Examples: Examples of PDNs include the public internet, operator-managed service networks (such as IMS for VoIP), and enterprise networks.
Subscription and Default APN.
- APN Subscription: A mobile user subscribes to one or more APNs, with each APN providing access to different services or networks.
- Default APN: There is one default APN for each user, which is used if no specific APN is requested during service access.
- Wildcard APN: In some cases, a wildcard APN may be defined, allowing access to any unsubscribed APNs. However, the default APN must be explicit and cannot be a wildcard APN.
APN Information Distribution.
- HSS, PGW, DNS: The APN information is stored and maintained in the Home Subscriber Server (HSS), Packet Gateway (PGW), and Domain Name Server (DNS).
- APN Labels: The HSS contains a set of APN labels. Each user subscribes to one or more of these APNs, and the labels are stored in the UE (User Equipment) during subscription.
APN and Bearer Management.
- Default Bearer: Typically, a user has one default bearer to an APN. This bearer carries the initial IP address and other parameters necessary for the connection.
- IPv4 and IPv6 Bearers: If “multiple PDN IPv4v6” is provisioned, a user can have two default bearers—one for IPv4 and one for IPv6.
Connecting to an APN.
- Initial Connection: When a UE attaches to the network, it receives the IP address for the default APN if no specific APN is requested.
- Service Access: If the user attempts to access a service without specifying an APN, the default APN is automatically used.
- Wildcard APN Access: If a wildcard APN is defined in the HSS subscription, the UE is allowed to connect to any APN not explicitly subscribed.
Network Elements Involved.
- PGW: The PGW provides access to the specific APN in the PDN, acting as the gateway for data traffic.
- MME: The Mobility Management Entity (MME) manages the signaling for APN connectivity, ensuring proper attachment and bearer setup.
Important Considerations.
- Explicit APN for Default: The default APN must always be explicit and not a wildcard. This ensures the UE connects reliably to a known network.
- Subscription Management: Proper subscription management ensures users connect only to authorized APNs, maintaining security and service quality.
In summary, the LTE APN is a important element in LTE networks, enabling users to access various PDNs seamlessly. It ensures that each user can connect to the necessary services efficiently while maintaining robust network management and security.