The W-APN Operator Identifier is composed of six labels. The last three labels shall be "pub.3gppnetwork.org". The second and third labels together shall uniquely identify the PLMN. The first label distinguishes the domain name as a W-APN.
For each operator, there is a default W-APN Operator Identifier (i.e. domain name). This default W-APN Operator Identifier is derived from the IMSI as follows:
"mnc" and "mcc" serve as invariable identifiers for the following digits.
<MNC> and <MCC> are derived from the components of the IMSI defined in clause 2.2.
Alternatively, the default W-APN Operator Identifier is derived using the MNC and MCC of the VPLMN. See TS 24.234
for more information.
The default W-APN Operator Identifier is used in both non-roaming and roaming situations when attempting to translate a W-APN consisting only of a Network Identifier into the IP address of the PDG in the HPLMN.
In order to guarantee inter-PLMN DNS translation, the <MNC> and <MCC> coding used in the "w-apn.mnc<MNC>.mcc<MCC>.pub.3gppnetwork.org" format of the W-APN OI shall be:
<MNC> = 3 digits
<MCC> = 3 digits
If there are only 2 significant digits in the MNC, one "0" digit shall be inserted at the left side to fill the 3 digits coding of MNC in the W-APN OI.
As an example, the W-APN OI for MCC 345 and MNC 12 is coded in the DNS as:
For situations when the PDG serving the W-APN is located in such network that is not part of the GRX (i.e. the Interoperator IP backbone), the default Operator Identifier described in clause 14.7.2
is not available for use. This restriction originates from the ".3gppnetwork.org" domain, which is only available in GRX DNS for actual use. Thus an alternative format of W-APN Operator Identifier is required for this case.
The Alternative W-APN Operator Identifiers shall be constructed as follows:
"w-apn.<valid operator's REALM>"
<valid operator's REALM> corresponds to REALM names owned by the operator hosting the PDG serving the desired W-APN.
REALM names are required to be unique, and are piggybacked on the administration of the Public Internet DNS namespace. REALM names may also belong to the operator of the VPLMN.
As an example, the W-APN OI for the Operator REALM "notareal.com" is coded in the Public Internet DNS as: