APN

An APN (Access Point Name) is the name a device sends when it asks a mobile network for a data connection. It tells the network which gateway to use and which data network to connect to — the public internet, a private enterprise network, or an operator service such as IMS for voice. In 5G the equivalent is the DNN (Data Network Name).

APN format

3GPP TS 23.003 defines an APN in two parts:

Part	Example	Meaning
Network identifier	internet, ims, iot.example	Chosen by the operator; the part users normally configure
Operator identifier	mnc015.mcc234.gprs	Derived from the MCC/MNC; identifies the operator whose gateway serves the APN

Devices usually send only the network identifier, and the network adds the operator part. The core network uses the full APN to select a gateway — the PDN gateway in LTE, or the session management function in 5G. For roaming subscribers, the APN configuration also determines whether traffic is routed back to the home network or broken out locally in the visited one.

Where APNs come from

• Subscription: the home subscriber database lists the APNs a subscriber may use, usually including a default.
• Device configuration: set manually, pushed by the operator, or carried in the SIM or eSIM profile.
• Special-purpose APNs: ims for VoLTE, MMS APNs, and private APNs for enterprise and IoT fleets.

Common APN failures

Symptom	Likely cause
Registers, but no data	Wrong or unsubscribed APN on the device
ESM cause #27	Missing or unknown APN
ESM cause #29	User authentication or authorization failed, e.g. wrong private APN credentials
ESM cause #33	Requested service option not subscribed

ESM causes are defined in 3GPP TS 24.301. In LTE, a default data bearer is set up as part of attach, so an APN problem can make the attach itself fail with EMM cause #19 “ESM failure” (see attach reject cause).

Why it matters for testing

APN problems are among the most common reasons a profile registers but delivers no data. Tests should confirm the default APN, any private APNs and the IMS APN used for voice. In SimCheck.ai, a profile’s APN is inherited from its group or network unless overridden, and any test can override the APN for that run — see quick tests.