Section: 5.6.3 Transport of NAS messages procedure 5.6.3.1 General
Content: The purpose of the transport of NAS messages procedure is to carry SMS messages in an encapsulated form between the MME and the UE. The procedure may be initiated by the UE or the network and can only be used when the UE is attached for EPS services and non-EPS services or for EPS services and "SMS only", and the UE is in EMM-CONNECTED mode. NOTE 1: If the UE is in EMM-IDLE mode and is using EPS services with control plane CIoT EPS optimization, the UE transports the first SMS message by encapsulating it in the NAS message container IE in the Control Plane Service Request message. NOTE 2: When the UE is using EPS services with control plane CIoT EPS optimization, the network can initiate downlink transport of NAS messages procedure even if the UE does not have any PDN connections established.