Section: 19.3.6 Emergency NAI for Limited Service State
Content: This clause describes the format of the UE identification needed to access the 3GPP EPC from both 3GPP and non-3GPP accesses, when UE is performing an emergency attach and IMSI is not available or not authenticated (see clause 19.3.1). For more information, see clauses 4.6.1 and 5.2 of 3GPP TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [68]. The Emergency NAI for Limited Service State shall take the form of an NAI, and shall have the form username@realm as specified in clause 2.1 of IETF RFC 4282 [53]. The exact format shall be: imei<IMEI>@sos.invalid NOTE: The top level domain ".invalid" is a reserved top level domain, as specified in IETF RFC 2606 [64], and is used here due to the fact that this NAI never needs to be resolved for routing (as specified in 3GPP TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [68]). or mac<MAC>@sos.invalid For example, if the IMEI is 219551288888888, the Emergency NAI for Limited Service State then takes the form of imei219551288888888@sos.invalid. For example, if the MAC address is 44-45-53-54-00-AB, the Emergency NAI for Limited Service State then takes the form of mac4445535400AB@sos.invalid, where the MAC address is represented in hexadecimal format without separators.