4.7.2.2 Establishment cause for non-3GPP access

When establishment of an N1 NAS signalling connection over non-3GPP access is initiated, the UE shall:

• determine one or more access identities to be associated with the establishment of the N1 NAS signalling connection as specified in clause 4.5.2 and table 4.5.2.1;
• select the establishment cause for non-3GPP access from the determined one or more access identities and the event which triggered initiation of the N1 NAS signalling connection over non-3GPP access by checking the rules specified in table 4.7.2.2.1; and
• provide the selected establishment cause for non-3GPP access to the lower layers.

While an MMTEL voice call is ongoing:

• any:
• service request procedure; or
• registration procedure;

initiated in 5GMM-IDLE mode is mapped to "MO MMTel voice call" type access attempt.

While an MMTEL video call is ongoing and no MMTEL voice call is ongoing:

• any:
• service request procedure; or
• registration procedure;

initiated in 5GMM-IDLE mode is mapped to "MO MMTel video call" type access attempt.

While an SMSoIP is ongoing, no MMTEL video call is ongoing and no MMTEL voice call is ongoing:

• any:
• service request procedure; or
• registration procedure;

initiated in 5GMM-IDLE mode is mapped to "MO SMS over IP" type access attempt.

If the access attempt matches more than one rule, the establishment cause for non-3GPP access of the lowest rule number shall be used.

Table 4.7.2.2.1: Mapping table for determination of establishment cause for non-3GPP access