Section: 9.1.2 Format of APN Operator Identifier
Content: The APN Operator Identifier is composed of three labels. The last label (or domain) shall be "gprs". The first and second labels together shall uniquely identify the GPRS/EPS PLMN. For each operator, there is a default APN Operator Identifier (i.e. domain name). This default APN Operator Identifier is derived from the IMSI as follows: "mnc<MNC>.mcc<MCC>.gprs" where: "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. This default APN Operator Identifier is used for home routed inter-PLMN roaming situations when attempting to translate an APN consisting only of a Network Identifier into the IP address of the GGSN/PGW in the HPLMN. The PLMN may provide DNS translations for other, more human-readable, APN Operator Identifiers in addition to the default Operator Identifier described above. Alternatively, in the roaming case if the GGSN/PGW from the VPLMN is to be selected, the APN Operator Identifier for the UE is constructed from the serving network PLMN ID. In this case, the APN-OI replacement field, if received, shall be ignored. In order to guarantee inter-PLMN DNS translation, the <MNC> and <MCC> coding used in the "mnc<MNC>.mcc<MCC>.gprs" format of the APN OI shall be: - <MNC> = 3 digits - <MCC> = 3 digits - If there are only 2 significant digits in the MNC, one "0" digit is inserted at the left side to fill the 3 digits coding of MNC in the APN OI. As an example, the APN OI for MCC 345 and MNC 12 will be coded in the DNS as "mnc012.mcc345.gprs". The APN-OI replacement is used for selecting the GGSN/PGWfor non-roaming and home routed scenarios. The format of the domain name used in the APN-OI replacement field (as defined in 3GPP TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [3] and 3GPP TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [72]) is the same as the default APN-OI as defined above except that it may be preceded by one or more labels each separated by a dot. It is up to the operators to determine what labels shall precede the "mnc<MNC>.mcc<MCC>.gprs" trailing labels (see clause 5.1.1.1 in TS 29.303[ Domain Name System Procedures; Stage 3 ]  [73] and also clause 13.1 in TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [3]). EXAMPLE 1: province1.mnc012.mcc345.gprs EXAMPLE 2: ggsn-cluster-A.provinceB.mnc012.mcc345.gprs The APN constructed using the APN-OI replacement field is only used for DNS translation. The APN when being sent to other network entities over GTP interfaces shall follow the rules as specified in 3GPP TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [3] and 3GPP TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [72].