Section: 17.2.1 Home network realm
Content: The home network realm shall be in the form of an Internet domain name, e.g. operator.com, as specified in IETF RFC 1035 [19] and IETF RFC 1123 [20]. The home network realm consists of one or more labels. Each label shall consist of the alphabetic characters (A-Z and a-z), digits (0-9) and the hyphen (-) in accordance with IETF RFC 1035 [19]. Each label shall begin and end with either an alphabetic character or a digit in accordance with IETF RFC 1123 [20]. The case of alphabetic characters is not significant. The UE shall derive the home network realm from the IMSI as described in the following steps: 1. take the first 5 or 6 digits, depending on whether a 2 or 3 digit MNC is used (see 3GPP TS 31.102[ Characteristics of the Universal Subscriber Identity Module (USIM) application ]  [27], 3GPP TS 51.011[ Specification of the Subscriber Identity Module - Mobile Equipment (SIM-ME) interface ]  [66]) and separate them into MCC and MNC; if the MNC is 2 digits then a zero shall be added at the beginning; 2. use the MCC and MNC derived in step 1 to create the "mnc<MNC>.mcc<MCC>.3gppnetwork.org" network realm; 3. add the label "gan." to the beginning of the network realm. An example of a home network realm is: IMSI in use: 234150999999999; Where: MCC = 234; MNC = 15; MSIN = 0999999999, Which gives the home network realm: gan.mnc015.mcc234.3gppnetwork.org. NOTE: If it is not possible for the UE to identify whether a 2 or 3 digit MNC is used (e.g. SIM is inserted and the length of MNC in the IMSI is not available in the "Administrative data" data file), it is implementation dependent how the UE determines the length of the MNC (2 or 3 digits).