Access Point Name

In the GPRS backbone, an Access Point Name (APN) is a reference to a GGSN. To support inter-PLMN roaming, the internal GPRS DNS (Domain Name System) functionality is used to translate the APN into the IP address of the GGSN.

In the EPC network the APN is found in GTP-C signaling when packet contexts are established, but it is no longer found in LTE NAS signaling. This means in turn that for 2.5G and 3G phones the APN is an important parameter to be stored on the (U)SIM card, but for 4G phones the APN does not need to be configured by the end user. This will also resolve the problem where many PDP context setup failures seen currently in the GERAN and UTRAN are due to an unknown or missing APN.

The APN is composed of two parts as follows:

• The APN network identifier; this defines to which external network the GGSN is connected and optionally a requested service by the MS. This part of the APN is mandatory.
• The APN operator identifier; this defines in which PLMN GPRS backbone the GGSN is located. This part of the APN is optional.

The APN operator identifier is placed after the APN network identifier. An APN consisting of both the network identifier and operator identifier corresponds to the DNS name of a GGSN; the APN has, after encoding as defined below, a maximum length of 100 octets.

The encoding of the APN follows the name syntax defined in RFC 2181 [18], RFC 1035 [19], and RFC 1123 [20]. The APN consists of one or more labels. Each label is coded as a one-octet length field followed by that number of octets coded as 8-bit ASCII characters. Following RFC 1035 [19], the labels should consist only of the alphabetic characters (A–Z and a–z), digits (0–9), and the hyphen (-). Following RFC 1123 [20], the labels should begin and end with either an alphabetic character or a digit. The case of alphabetic characters is not significant. The APN is not terminated by a length byte of zero.

Typical APNs are:

• mms.tim.net;
• wap.eplus.net;
• wap.beeline.ru;
• wap.debitel.de;
• web.vodafone.de;
• internet.t-mobile.

The APN of a 3G subscriber is stored in the USIM. In LTE NAS signaling the APN is no longer used, because it is chosen by the intelligent packet routing functions of MME. However, the APN Average Maximum Bit Rate (APN-AMBR) may be signaled to the UE by the MME to control the amount and bandwidth of UL traffic.