Section: 6.5.1 UE requested PDN connectivity procedure 6.5.1.1 General
Content: The purpose of the UE requested PDN connectivity procedure is for a UE to request the setup of a default EPS bearer to a PDN. The UE requests connectivity to a PDN by sending a PDN CONNECTIVITY REQUEST message to the network. If accepted by the network, this procedure initiates the establishment of a default EPS bearer context. If EMM-REGISTERED without PDN connection is not supported by the UE or the MME, the procedure is used either to establish the first default bearer by including the PDN CONNECTIVITY REQUEST message into the initial attach message, or to establish subsequent default bearers to additional PDNs in order to allow the UE simultaneous access to multiple PDNs by sending the message stand-alone. If EMM-REGISTERED without PDN connection is supported by the UE and the MME, the procedure is used to establish the first or subsequent default bearers to a PDN or additional PDNs by sending the PDN CONNECTIVITY REQUEST message stand-alone. If the UE requests PDN connectivity for emergency bearer services, the MME shall not check for regional restrictions or subscription restrictions when processing the PDN CONNECTIVITY REQUEST message. If there is already a PDN connection for emergency bearer services established, the UE shall not request an additional PDN connection for emergency bearer services. A UE attached for emergency bearer services shall not request a PDN connection to any other PDN. A UE attached for access to RLOS shall not request any additional PDN connection for RLOS nor any PDN connection to any other PDN. The UE may also initiate the UE requested PDN connectivity procedure to add 3GPP access to the PDN connection which is already established over WLAN as specified in the clause 6.2.2 of 3GPP TS 23.161[ Network-Based IP Flow Mobility (NBIFOM); Stage 2 ]  [34]. The UE may also initiate the UE requested PDN connectivity procedure to transfer an existing PDU session in the 5GS to EPS as specified in 3GPP TS 24.501[ Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3 ]  [54]. If the UE supports the device triggering short message as specified in 3GPP TS 23.040[ Technical realization of the Short Message Service (SMS) ]  [57] and supports non-IP PDN type, then upon receiving from ESMS entity as specified in 3GPP TS 24.007[ Mobile radio interface signalling layer 3; General Aspects ]  [12] an indication requesting establishment of a PDN connection for non-IP PDN type using the default APN as specified in 3GPP TS 24.011[ Point-to-Point  (PP) Short Message Service (SMS) support on mobile radio interface ]  [13A], the UE shall initiate the UE requested PDN connectivity procedure in order to request connectivity to a PDN using the default APN and non-IP PDN type.