Section: 14.8 Emergency Realm and Emergency NAI for Emergency Cases
Content: The emergency realm shall be of the form of a home network realm as described in clause 14.2 prefixed with the label "sos." at the beginning of the domain name. An example of a WLAN emergency NAI realm is: IMSI in use: 234150999999999; Where: MCC = 234; MNC = 15; MSIN = 0999999999 Which gives the home network domain name: sos.wlan.mnc015.mcc234.3gppnetwork.org. The NAI for emergency cases shall be of the form as specified in clauses 14.3 and 14.4, with the addition of the emergency realm as described above for PLMNs where the emergency realm is supported. When UE is using I-WLAN as the access network for IMS emergency calls and IMSI is not available, the Emergency NAI shall be an NAI compliant with IETF RFC 4282 [53] consisting of username and realm, either constructed with IMEI or MAC address, as specified in 3GPP TS 33.234[ 3G security; Wireless Local Area Network (WLAN) interworking security ]  [55]. The exact format shall be: imei<IMEI>@sos.wlan.mnc<visitedMNC>.mcc<visitedMCC>.3gppnetwork.org or if IMEI is not available, mac<MAC>@sos.wlan.mnc<visitedMNC>.mcc<visitedMCC>.3gppnetwork.org The realm part of the above NAI consists of the realm built using the PLMN ID (visitedMCC + visitedMNC) of the PLMN selected as a result of the network selection procedure, as specified in clause 5.2.5.4 of the 3GPP TS 24.234[ 3GPP system to Wireless Local Area Network (WLAN) interworking; WLAN User Equipment (WLAN UE) to network protocols; Stage 3 ]  [48]. The MNC and MCC shall be with 3 digits coded. 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 realm of the NAI. For example, if the IMEI is 219551288888888, and the selected PLMN is with MCC 345 and MNC 12, the Emergency NAI then takes the form of imei219551288888888@sos.wlan.mnc012.mcc345.3gppnetwork.org. For example, if the MAC address is 44-45-53-54-00-AB, and the selected PLMN is with MCC 345 and MNC 12, the Emergency NAI then takes the form of mac4445535400AB@sos.wlan.mnc012.mcc345.3gppnetwork.org, where the MAC address is represented in hexadecimal format without separators.