Section: 4.3.17.8.3 Delivery mechanism
Content: 4.3.17.8.3.1 General At each PDN connectivity request, the MME decides which delivery mechanism (SCEF based delivery or SGi based delivery) is used for delivering the Non-IP data between RAN and AS. An indication associated with the used APN determines if SCEF based delivery or SGi based delivery shall be used. 4.3.17.8.3.2 SCEF based delivery When the MME decides to use SCEF based delivery mechanism for Non-IP data, a PDN connection is established towards the selected SCEF. Such a PDN Connection is also known as an "SCEF Connection". The APN used for SCEF based delivery is an FQDN, which either resolves to an SCEF hostname or to an SCEF IP address. The SCEF based delivery is applicable only to the Control Plane CIoT EPS Optimisation (see clause 4.10). The support of Non-IP data via the SCEF is further defined in TS 23.682[ Architecture enhancements to facilitate communications with packet data networks and applications ]  [74]. 4.3.17.8.3.3 SGi based delivery 4.3.17.8.3.3.1 General When support of Non-IP data is provided at the SGi interface, different point-to-point tunnelling techniques may be used. Point-to-point tunnelling by UDP/IP encapsulation can be used as described in clause 4.3.17.8.3.3.2 below. Other techniques as described in clause 4.3.17.8.3.3 below may be used. Support for the SGi based delivery of Non-IP data can be used by any UE. That is, it is independent of support for the User Plane CIoT EPS Optimisation and the Control Plane CIoT EPS Optimisation (see clause 4.10). The P-GW decides at PDN connection establishment based on pre-configuration which point-to-point tunnelling technique is used for the SGi based delivery between the P-GW and the AS. NOTE: The pre-configuration can be done in the P-GW per APN or based on other criterion such as SLA between operator and 3rd party application service provider, etc. 4.3.17.8.3.3.2 SGi PtP tunnelling based on UDP/IP SGi PtP tunnelling based on UDP/IP may be used to deliver Non-IP data to AS via SGi. A point-to-point tunnel is used by the P-GW towards the AS. The tunnel parameters (i.e. destination IP address and UDP port) for SGi PtP tunnelling based on UDP/IP are pre-configured on the P-GW. IP address allocation procedures for PDN connections are performed locally (e.g. without involving the UE) by the P-GW based on APN configuration and according to clause 5.3.1. Only single IP address is used (i.e. both IPv4 and IPv6 addresses are not allocated). The P-GW acts as a transparent forwarding node for the payload between the UE and the AS. For uplink Non-IP data, the P-GW forwards the received data to the AS over the SGi PtP tunnel using UDP/IP encapsulation. When the Reliable Data Service is enabled, the P-GW processes the Reliable Data Service Header. The Reliable Data Service Configuration is pre-configured on the P-GW. The Reliable Data Service Configuration is defined in TS 23.682[ Architecture enhancements to facilitate communications with packet data networks and applications ]  [74]. For downlink Non-IP data, the AS sends the data using UDP/IP encapsulation with the IP address of the UE and the 3GPP defined UDP port for "Non-IP" data. The P-GW decapsulates the received data (i.e. removes the UDP/IP headers) and forwards the data to S-GW on the GTP-U tunnel identified by the IP address of the UE (i.e. PDN connection) for delivery to the UE. When the Reliable Data Service is enabled, the P-GW adds the Reliable Data Service Header. The P-GW performs the IP related operations (e.g. allocates IP address for the PDN connection), but the IP address or IP prefix is not provided to the UE (i.e. SLAAC / Router Advertisements are not performed. DHCP or DHCPv6 are not used). In the case of IPv6 the P-GW assigns an Interface Identifier for the PDN connection. The allocated IP address or IPv6 prefix identifies the PDN connection of the UE. The P-GW shall inform the MME of the assigned IPv4 address or IPv6 prefix and Interface Identifier for a PDN Connection of a given UE. However, the UE is not informed about the assigned IPv6 prefix and Interface Identifier. NOTE: It is recommended to use IPv6 for CIoT. IPv4 based addressing is deprecated for machine type communication used over 3GPP accesses, see TS 23.221[ Architectural requirements ]  [27]. 4.3.17.8.3.3.3 Other SGi PtP tunnelling mechanisms SGi PtP tunnelling mechanisms such as PMIPv6/GRE, L2TP, GTP-C/U, etc, may be used to deliver Non-IP data to AS via SGi. The general handling of such delivery mechanisms is as described below. A point-to-point tunnel is established by the P-GW towards the AS. Depending on the type of protocol employed on the SGi PtP tunnel, the SGi PtP tunnel setup may be done at the time of Attach or at the time of first MO datagram being sent by the CIoT UE. The P-GW selects the AS based on the P-GW configuration (e.g. per APN, or per PtP tunnel type etc.). However, IP address allocation procedures for the UE (according to clause 5.3.1) are not performed by the P-GW. NOTE: An AS can be dedicated for handling a specific Non-IP data protocol. The P-GW acts as a transparent forwarding node between the UE and the AS. For uplink Non-IP data, the P-GW forwards the received data to the AS over the established SGi PtP tunnel. For downlink Non-IP data, the AS locates the right SGi PtP tunnel for the UE (using information such as UE identifiers in the Non-IP protocol itself, etc) to forward the data. The AS sends the data to P-GW over the established SGi PtP tunnel. The P-GW in turn sends the data to S-GW on the GTP-U tunnel identified by the associated SGi PtP tunnel for delivery to the UE.