Section: 25.2 Home network domain name
Content: The home network domain name of the OCS 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 domain of the OCS 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. If the home network domain of the OCS is not known (e.g. through an available static address or through its reception from another node), it shall be: - in the form of "ocs.mnc<MNC>.mcc<MCC>.3gppnetwork.org", where "<MNC>" and "<MCC>" fields correspond to the MNC and MCC of the operator's PLMN to which the OCS belongs. Both the "<MNC>" and "<MCC>" fields are 3 digits long. If the MNC of the PLMN is 2 digits, then a zero shall be added at the beginning; and - derived from the subscriber's 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]) 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" domain name; 3. add the label "ocs" to the beginning of the domain name. An example of a home network domain name is: IMSI in use: 234150999999999; Where: MCC = 234; MNC = 15; MSIN = 0999999999; Which gives the home network domain name: ocs.mnc015.mcc234.3gppnetwork.org. NOTE: It is implementation dependent to determine that the length of the MNC is 2 or 3 digits.