Section: 5.31.5 Non-IP Data Delivery (NIDD)
Content: Functions for NIDD may be used to handle Mobile Originated (MO) and Mobile Terminated (MT) communication for unstructured data (also referred to as Non-IP). Such delivery to the AF is accomplished by one of the following two mechanisms: - Delivery using the NIDD API; - Delivery using UPF via a Point-to-Point (PtP) N6 tunnel. NIDD is handled using an Unstructured PDU session to the NEF. The UE may obtain an Unstructured PDU session to the NEF during the PDU Session Establishment procedure. Whether or not the NIDD API shall be invoked for a PDU session is determined by the presence of a "NEF Identity for NIDD" for the DNN/S-NSSAI combination in the subscription. If the subscription includes a "NEF Identity for NIDD" corresponding with the DNN and S-NSSAI information, then the SMF selects that NEF and uses the NIDD API for that PDU session. The NEF exposes the NIDD APIs described in TS 23.502[ Procedures for the 5G System (5GS) ]  [3] on the N33/Nnef reference point. The NEF uses the provisioned policies to map an AF Identifier and UE Identity to a DNN/S-NSSAI combination if the Reliable Data Service (RDS) is not enabled. If RDS is enabled, the NEF determines the association based on RDS port numbers and the provisioned policies that may be used to map AF Identifier and User identity to a DNN. The NEF also supports distribution of Mobile Terminated messages to a group of UEs based on the NIDD API. If an External Group Identifier is included in the MT NIDD request, the NEF uses the UDM to resolve the External Group Identifier to a list of SUPIs and sends the message to each UE in the group with an established PDU Session. The Protocol Configuration Options (PCO) may be used to transfer NIDD parameters to and from the UE (e.g. maximum packet size). The PCO is sent in the 5GSM signalling between UE and SMF. NIDD parameters are sent to and from the NEF via the N29 interface.