Content for  TS 23.682  Word version:  16.8.0

Functions for NIDD may be used to handle mobile originated (MO) and mobile terminated (MT) communication with UEs, where the data used for the communication is considered unstructured from the EPS standpoint (which we refer to also as Non-IP). The support of Non-IP data is part of the CIoT EPS optimizations. The Non-IP data delivery to SCS/AS is accomplished by one of two mechanisms:

• Delivery using SCEF;
• Delivery using a Point-to-Point (PtP) SGi tunnel.

The delivery using a Point-to-Point (PtP) SGi tunnel is further described in TS 23.401. NIDD via the SCEF is handled using a PDN connection to the SCEF. The UE may obtain a Non-IP PDN connection to the SCEF either during the Attach procedure (see TS 23.401, clause 5.3.2.1) or via UE requested PDN connectivity (see TS 23.401, clause 5.10.2) or via PDP Context Activation Procedure (see TS 23.060, clause 9.2.2.1). An association between the SCS/AS and a PDN Connection to the SCEF needs to be established to enable transfer of non-IP data between the UE and the SCS/AS. When the Reliable Data Service is not enabled, the SCEF determines the association based on provisioned policies that may be used to map an SCS/AS identity and User identity to an APN. When the Reliable Data Service is enabled, the SCEF determines the association based on port numbers and provisioned policies that may be used to map SCS/AS identities and User identity to an APN (see clause 4.5.14.3). NIDD via SCEF uses the User Identity, APN, and the SCS/AS identity to identify which UE a particular T6a/T6b connection belongs to. The User Identity is the user's IMSI. The user's IMSI shall not be used on the interface between SCEF and SCS/AS. In order to perform NIDD configuration or to send or receive NIDD data, the SCS/AS shall use MSISDN or External Identifier to identify the user. In order to facilitate correlation of SCS/AS requests to T6a/T6b connection for a given UE, the HSS provides to the SCEF (see NIDD Configuration procedure in clause 5.13.2) the user's IMSI, and if available, the MSISDN (when NIDD Configuration Request contains an External Identifier) or if available, External Identifier (when NIDD Configuration Request contains an MSISDN). Depending on operator configuration, the SCEF may perform buffering of MO and/or MT Non-IP data. In this release of specification, neither the MME/SGSN nor the IWK-SCEF are expecting to buffer data pertinent to PDN connection to the SCEF. The Protocol Configuration Options (PCO) may be used to transfer parameters between the UE and SCEF (e.g. maximum packet size). The PCO's information shall be passed transparently through the MME/SGSN. As specified in TS 23.401 and TS 23.060, the PCO is sent in the EPS Session Management signalling between UE and MME and in GPRS Session Management signalling between UE and SGSN. The SCEF applies rate control as described in TS 23.401, clause 4.7.7.

To ensure reliable delivery of Non-IP data (NIDD) between UE and SCEF using the Control Plane CIoT EPS Optimization, the following functions may be supported by the 3GPP system:

• Reliable delivery by acknowledgements on a hop-by-hop basis, i.e. the link layer protocol on each interface used for NIDD uses acknowledgments and nodes apply retransmissions if needed to ensure reliable delivery.
• The UE may retransmit UL data that was not acknowledged by the RLC on the AS layer in the UE;
• The MME may retransmit DL data for which it got a non-delivery indication from the eNodeB (see e.g. TS 23.401, clause 5.3.4B.3, step 15);
• The MME indicates to the SCEF the status of the DL data delivery. The SCEF may forward this status to the AS;
• Disabling/enabling of MME retransmission is handled by a subscription parameter 'Acknowledgements of downlink NAS data PDUs'.

The Reliable Data Service may be used by the UE and SCEF or P-GW when using PDN Connection of PDN Type 'Non-IP'. The service provides a mechanism for the SCEF or P-GW to determine if the data was successfully delivered to the UE and for UE to determine if the data was successfully delivered to the SCEF. When a requested acknowledgement is not received, the Reliable Data Service retransmits the packet. The service is enabled or disabled based on APN Configuration per SLA. When the service is enabled, a protocol is used between the end-points of the Non-IP PDN Connection. The protocol uses a packet header to identify if the packet requires no acknowledgement, requires an acknowledgement, or is an acknowledgment and to allow detection and elimination of duplicate PDUs at the receiving endpoint. Reliable Data Service supports both single and multiple applications within the UE. Port Numbers in the header are used to identify the application on the originator and to identify the application on the receiver. The UE, the SCEF and the P-GW may support reservation of the source and the destination port numbers for their use and subsequent release of the reserved port numbers. Reliable Data Service protocol (as defined in TS 24.250) also enables applications to query their peer entities to determine which port numbers are reserved and which are available for use at any given time. During NIDD Configuration, the SCS/AS may indicate which serialization formats it supports for mobile originated and mobile terminated traffic in the Reliable Data Server Configuration. When port numbers are reserved by the UE, the serialization format that will be used by the application may be indicated to the SCEF. When port numbers are reserved by the SCEF, the serialization format that will be used by the application may be indicated to the UE. If the receiver does not support the indicated serialization format, it rejects the port number reservation request and the sender may re-attempt to reserve the port number with a different serialization format. If, during NIDD Configuration, the SCS/AS indicated that it supports multiple serialization formats, the SCEF determines the serialization format that it will indicate to the UE based on local policies and previous negotiations with the UE (e.g. the SCEF may indicate the same serialization format that was indicated by the UE or avoid indicating a serialization format that was previously rejected by the UE). When serialization formats are configured for reserved port numbers, the SCEF stores the serialization formats as part of the Reliable Data Service Configuration and provides the updated Reliable Data Service Configuration to the SCS/AS. The UE indicates its capability of supporting Reliable Data Service in the Protocol Configuration Options (PCO) to the SCEF or P-GW. If SCEF or P-GW supports and accepts Reliable Data Service then it indicates to the UE, in the PCO, that the Reliable Data Service shall be used if enabled in the APN configuration. In order to prevent situations where a Reliable Data Service instance needs to interface to both the user and control plane, the Reliable Data Service may only be used with PDN connections for which the "Control Plane Only" indicator is set or with PDN connections using the Control Plane EPS CIoT Optimization when the MME does not move PDN connections to the user plane. The Control Plane CIoT EPS Optimization is defined in TS 23.401.